18 MODEL AVIATION
by Gary Fuller
DURING THE FIRST part of the Cold War, the P2V Neptune
was the US Navy’s primary long-range, land-based, antisubmarine
patrol aircraft. Designed in 1944 as a replacement for the PV-1
Ventura and the PV-2 Harpoon, the Neptune’s versatility ensured
that it would remain in service for a long time. Its last use in
combat was by the Argentineans against the British during the fight
over the Falkland Islands.
The Neptune is still being used, to fight forest fires in the
United States. With the installation of a mad boom on the tail, the
addition of a pair of jet engines, and many other minor
modifications, the later versions of the Neptune bore little
resemblance to the early production P2Vs.
I have always had a soft spot in my heart for historical airplanes
that are seldom modeled. The Neptune’s straightforward lines
ensure a good-flying model, yet the mad boom, radomes, jet
engines, and various other components give it considerable
character that would make it unique at the flying field.
I didn’t want an all-out competition-quality Scale model, so to
simplify it I used an easy-to-build box type of fuselage that is not
much different from what most trainer-type aircraft have. The
engine nacelles are also the box type, with the bottom left open so
you don’t have to mess with any finicky landing-gear doors. The
nacelles are glued to the wing with some glass cloth for
reinforcement.
The inboard section of the wing is fully sheeted and the
outboard section of the wing uses typical D-tube construction. The
jet engines and wingtip fuel tanks are balsa blocks carved and
sanded to shape. The wing is mounted to the fuselage with a joiner
tube so the model can be disassembled for transport to and from
the flying field.
I wanted to make the Neptune as large as possible yet
economical to build and fly, so I decided to build it with an 80-inch
wingspan. Power was to be a pair of O.S. .25 engines, but I was
bitten by the electric bug during the time I was building the model.
While researching motors for a future project, I realized that I
could easily mount electric power plants to my Neptune with no
major rework. I was in the process of covering the airplane when I
decided to make the change to electric power!
RC version of US Navy patrol
aircraft can be powered with
engines or motors
On right fuselage side you can see 1/4 balsa triangle stock,
forward fuselage doubler, formers F2 and F3, and nose-wheel
mounting plate installed.
Forward fuselage after joining the sides. This is a good time to
mount nose gear. Nose-wheel mount has been reinforced with 1/4
balsa triangle stock.
Upper fuselage sheeting is being installed. Author used Ambroid
glue here so the glue joint will be easier to sand when shaping
top of sheeting. Many T-pins hold sheeting in place as glue dries.
Carpenter’s square and sharpened brass tube are used to cut
slot for 1/4 plywood dihedral brace. One of R3 ribs has been
glued to spars using R3 angle guide; other R3 rib is being glued
to spar using 1/8 scrap wood to set distance between them.
I used a pair of MaxCim MaxN32-13Y motors direct drive
spinning APC 10 x 5E propellers. The motor controllers are MaxCim
Maxμ35D-21. I used 2000 mAh Kokam Li-Poly batteries wired 3S2P,
for a total of 11.1 volts and 4000 mAh for each motor. That easily gave
me a flight time exceeding 10 minutes with the motors throttled back
and more than adequate power to take off from a grass field.
The retractable gear is the standard size, and normal modeling
techniques are used to build the Neptune. If you have never built a
model from plans, this should not be too difficult—especially if you
have a few kits under your belt.
Since this is not really a beginner’s airplane, I won’t go into much
detail in the construction notes. I did not take any great pains to keep
the weight down on my Neptune, I did not use contest-grade balsa, nor
did I cut lightening holes in any of the sheet balsa. However, I am quite
sure that if you used contest-grade wood and other weight-saving
techniques, you could shave some weight from your Neptune.
CONSTRUCTION
I started my model by cutting all the parts and assembling them like
a kit. If you have never built from plans, I recommend the following.
To accurately cut the small parts from wood, cut the parts from the
plans and then lightly spray the backside of a paper cutout with contact
glue. When it has dried for approximately 10 minutes, to a light tack,
place the paper shape for the part on the wood, and then cut the wood
using a band saw or a jigsaw. Remove the paper after you have cut the
part.
To cut more than one of the same part, do the same thing as in the
preceding and then lightly spray both sides of some scrap paper with
contact glue. Sandwich this paper between as many sheets of wood as
necessary for the number of parts required. Cut the stack of wood
with a band saw or jigsaw. Once the stack is cut, separate each piece
and remove the paper.
If you have never done this, try it on scrap wood and paper first. I
have found that some brands of contact glue won’t work because
they are too tacky. I use carpet and headliner glue that comes in a
spray can and is available in auto-part stores. A good alternative is
Elmer’s school glue stick; it works as well without the mess.
Fuselage: The fuselage sides are too long and wide to cut from a
single sheet of balsa, so you will need to splice some sheets together.
I like to have the vertical splice where the wing doubler will
reinforce the joint. Be careful with the sides until the doublers are
installed. I like to lay the fuselage sides next to each other top to top
as I glue on the various parts; that way I won’t make two left or two
right sides.
Start the fuselage by gluing the 1/4 balsa triangle stock to the sides
as shown on the plans. Glue the doublers for the wing and forward
fuselage to the fuselage sides. Glue formers F2 through F5 to one
fuselage side, and then glue the nose-wheel mounting plate to F2 and
the side to which F2 is glued.
Glue the 1/4 x 3/8 balsa side stiffeners in place as shown on the
plans. Once the adhesive has dried, join the fuselage sides. I did this
by standing the side with the formers up on its bottom and then
placing the other side in place. Once I was satisfied with the fit of the
other side, I glued it to the formers.
I joined the forward end of the fuselage by weighting the fuselage
to the table and then using some clamps to draw the ends together until
former F1 would fit. I checked the alignment of the fuselage and
Photos by the author
20 MODEL AVIATION
Make both ends of wing-joiner tube same height above table so
wing will be square to fuselage from the top.
spars and the LE flush with the outermost R1C rib.
You will need to cut the R1C ribs for the 1/4 plywood dihedral
brace, I did this by using a 1/4-inch-outside-diameter brass tube that
was sharpened at one end. I used the tube to cut holes in the R1C ribs
at the dihedral brace’s location, using a carpenter square as a guide.
After the holes were cut, I used a file to finish the slot in the ribs
for the dihedral brace. Glue the dihedral brace to the ribs and the spar
after you are satisfied with the fit.
Carefully pull the wing-joiner socket tube from the wing and rough
it up with 80-grit sandpaper. Reinsert the socket tube in the wing and
glue it to the ribs. Glue some scrap balsa between the socket tube and
the 3/8 x 1/4 spars. Sheet the top of the inboard section with 3/32 balsa.
Once the glue for the sheeting has dried, remove the inboard
portion of the wing and set it aside.
Start the outboard section of the wing by pinning the lower
outboard 3/8 x 1/4 spruce spar to the plans. Glue the R2 and R4 through
R10 ribs to the spar. Position the R1 and R3 ribs on the spar, but do
not glue them in place yet. Place the upper 3/8 x 1/4 spruce spar on the
ribs and glue it to the R2 and R4 through R10 ribs. Also glue the 3/8
balsa LE to these ribs.
Using the R1 rib angle guide, glue rib R1 to the upper and lower
spar and the LE edge. Using the R3 rib angle guide, adhere one R3 rib
to the spars and LE. Use scrap 1/8 balsa as a spacer between the R3
ribs, and glue the other R3 rib to the spars and LE. Glue the 1/4 balsa
TE to ribs R5 through R10.
Sand the spars and the LE flush with R1, and then, using the same
method you used for the inboard section of the wing, cut the slot for
the 1/4 plywood dihedral brace in ribs R1 and R2. Sheet the top of the
outer wing with 3/32 balsa, as shown on the plans.
When the sheeting is dry, remove the outer section from the
building board and fit it to the inboard section of the wing. Once you
are satisfied with the fit, glue the outer wing section to the inboard
section. I used a wood block to prop up the wingtip while the glue
dried.
Sheet the bottom of the wing with 3/32 balsa. The inboard section
and the outboard section are done separately, and the part that is not
being sheeted is blocked up to prevent the wing from warping.
I tried to sheet as much of the bottom of the wing without cutting
off the building tabs as I could. I did that by gluing the edge of the LE
sheeting to only the 3/8 balsa LE first. After the glue dried, I wet the
sheeting to make it easier to bend, applied glue to the ribs, and then
placed the wing back on the worktable right-side up and weighted it
until the sheeting dried.
Once the wing is sheeted, glue the 1/4 balsa TE in place, and then
sand the LE and TE to match the airfoil. Drill a hole for the 3/8-inchdiameter
antirotation pin, and glue the antirotation pin in place. Drill
and tap the hole for the 1/4 x 20 nylon wing-mounting bolt.
Repeat this whole process for the other wing. Build the ailerons.
Final Assembly: Go back and align and install the wing-joiner tube
Type: RC Sport Scale
Wingspan: 80 inches
Wing area: 622 square inches
Flying weight: 10 pounds
Wing loading: 37 ounces/square foot
Length: 73.25 inches
Power: Two .25 glow engines or two
MaxCim MaxN32-13Y direct-drive
motors
Fuel tank: Two 6-ounce Sullivan slant
tanks (glow)
Battery: 11.1-volt 4000 mAh Li-Poly
(for electric version)
Radio system: Five channels
Construction: Balsa and plywood
Covering/finish: MonoKote,
LustreKote paint
adjusted until it was straight, and then I glued F1 in place. I joined the
aft end of the fuselage in the same manner.
Glue the 1/4 balsa triangle to the nose-gear mount as shown on the
plans. Mount the nose gear to its mounting plate with 4-40 screws and
blind nuts. Glue the 1/8 plywood hatch mounting plate in place as
shown on the plans. Install the 1/8-inch cockpit floor.
Sheet the top and bottom of the fuselage with 3/16 balsa, glued on
so that the wood grain is crosswise to the fuselage sides. Set the
fuselage aside.
Wing: Pin the 3/8 x 1/4 lower inboard spruce spar to your worktable.
Glue an end cap of 3/32 balsa scrap on the outboard end of the wingjoiner
socket tubes. Glue the 1/4 plywood doublers to R1B. After the
glue has dried on the cap, slide the R1 ribs and R1B rib into place on
the wing-joiner tube socket; don’t glue the ribs to the joiner socket
yet.
Space the ribs on the tube, place them on the lower inboard spruce
spar, and glue them to the spar. Glue the ribs R1C to the spar, and
make sure the ribs are perpendicular to the spar vertically and
longitudinally. Insert the forward 1/4 square spruce spars and the
upper 3/8 x 1/4 spruce spar, and glue the ribs to the spars.
Glue the 3/8 balsa LE to this part of the wing. Sand the inboard
June 2005 21
Clothespins hold TE to 12-inch steel rule to keep them aligned to
each other while nacelles are being fitted to wing.
Aluminum angle bracket is used to hold engine nacelles in
alignment to each other while nacelles are glued to wing.
Engine nacelles are built in same manner as fuselage. For
simplicity’s sake there are no gear doors. Bottoms of nacelles
are left open.
socket in the fuselage. Flip the fuselage upside down on the worktable
and secure it so it won’t move. Glue one of the 1/8 plywood joiner
doublers inside one side of the fuselage.
Rough up the outside of the joiner tube socket with some
sandpaper, and insert the socket into the fuselage. Slip the other 1/8
plywood joiner doubler onto the socket as you insert it into the
fuselage, but don’t glue the socket or the doubler to the fuselage yet.
Insert the joiner tube into the socket so it is centered in the
fuselage and an equal length of the tube extends out of the fuselage on
either side. Measure the ends of the joiner tube to the worktable. Sand
the hole in the fuselage that does not have the plywood doubler on it
so that both ends of the joiner are an equal height above the work
surface. Use a carpenter’s square to square the joiner tube to the
fuselage sides also by sanding the hole without the doubler.
When you are satisfied that the joiner tube is square to the fuselage
side, block the joiner tube so that it cannot move, and then doublecheck
to make sure the joiner tubes’ ends are an equal height above
the work surface. Glue the plywood doubler and the joiner tube socket
to the fuselage side. Glue the other end of the joiner socket to the
other side of the fuselage.
The wing-joiner tube I bought was too long for the wings, so I
ended up cutting approximately 6 inches from it. I set this short piece
aside; it will be used to align the wings to each other as the nacelles
are mounted.
Slide the wings on the wing-joiner tube so that they fit snugly up
against the fuselage sides. Adjust the wing so that it is at 0°. Place the
1/8 plywood doubler on the antirotation pin and carefully adhere the
doubler to the fuselage side, being careful not to get any glue on the
antirotation pin. Use the same technique to glue the 1/8 plywood wingmount
bolt doubler to the fuselage side.
The engine nacelles are identical to each other except for the
landing-gear mounts. The nacelles are built like the fuselage, so I
won’t go into detail about the method used to construct them. Just
make sure that you build a left and a right one.
The method I used to align and mount the nacelles to the wings
should work if you plan to use electric or glow power. Because I
decided to go electric after my Neptune was nearly completed, I will
describe the method using glow engines.
You will need a roughly 3-foot section of aluminum angle, which
you can get in most hardware stores. It is used to hold the engines in
alignment with each other when you mount the nacelles to the wings.
Cut off approximately a 6-inch piece of the aluminum angle.
Mount both wings to the short scrap piece of the wing-joiner tube.
Slide the wings together as close as you can without letting the
antirotation pins interfere with each other. Clamp the 6-inch angle to
both wings’ TEs to keep the TEs aligned to each other.
On the finished model, the centerlines of the nacelles are 85/16
inches from the sides of the fuselage. Because the fuselage will
interfere with this method of mounting the nacelles, you will need to
compensate for the absence of the fuselage.
Measure the gap between the root ribs of the left and right wing,
and then add that amount to the 165/8-inch measurement. If the gap
is 2 inches, the total will be 185/8 inches. On your aluminum angle
drill two holes on center 185/8 inches apart. The diameter of the
holes will need to fit the prop shaft of the engines or motors you
plan to use.
Mount the engines to the nacelles, and then, using the prop shaft
of each engine, bolt the engines to the aluminum angle in the holes
you drilled. At this point the engines are aligned to each other. This is
important. The nacelles don’t really need to be aligned to each other,
but the engine thrustlines do.
Place the wing in the wing saddle of the nacelles, and adjust the
wing in the saddles so that the inside side of the nacelles are
approximately 69/16 inches from the edge of the wing root. Do not
adjust the gap between the wings. If you measured accurately, both
nacelles should be that length from the root rib.
Measure the distance from the wing LE to the aluminum angle at
the dihedral break on both wings. Adjust this distance so that the
measurement is the same on both wings. Check the engine
upthrust/downthrust line in relationship to the wing’s incidence with
an incidence meter, and sand the nacelles’ saddles so that the
thrustline is 0°.
The P2V Neptune’s completed framework is ready for covering. This model features extremely clean workmanship!
Full-Size Plans Available—see page 183
Once you are satisfied with all of these
measurements, tack-glue the nacelles to the
wings. Flip the wings over so you can glue
the nacelles to the wing with epoxy and glass
cloth on the inside of the nacelles. Carefully
unbolt the engines from the aluminum angle
and then separate the wings from each other.
Install the wings to the fuselage, and
mount the horizontal stabilizer so it is at 0°
incidence to the wing. Mount the vertical
stabilizer.
It is time to start all the little details such
as the dummy jet engines, the wingtip tanks,
the radomes, and the canopy. I made my
canopy and the forward observer’s canopy on
the nose from clear plastic, but you can carve
and sand a balsa block to shape if you want.
To supply some cooling air for the
batteries, I vacuum-formed the big radome
on the bottom of the fuselage from plastic.
On the front of the radome I cut some holes,
and on the bottom of the fuselage I cut holes
where the radome mounts. This allows the
radome to act like a big air scoop to cool the
batteries. I cut holes on the back end of the
fuselage hatch to allow the air to escape.
Radio Installation: This is fairly
straightforward. I used some flat wing servos
for the ailerons, and these needed to be
installed before I covered the wing. Before I
decided to switch to electric power, each
engine was to have had a separate throttle
servo that I planned to mount behind the
main landing gear in the nacelles.
I mounted the elevator, rudder, and retract
servos in the fuselage. An important thing
here is to make sure you have clear access to
the wing-mounting bolts in the fuselage.
Otherwise, mount the radio gear as you see
fit. After test-flying I found that aileron
differential is recommended along with some
rudder mixed into the ailerons.
Since this was my first electric-powered
twin, I decided to use one motor controller
and a separate battery pack for each motor,
and a servo “Y” harness to connect the motor
controllers to the receiver. I also used a
separate battery to power the receiver and
servos.
The fuel tanks need special attention
because the main landing gear will fold up
next to the tanks, and it is a tight fit. You will
need narrow tires and narrow fuel tanks, for
which I planned to use Sullivan 6-ounce slant
oval fuel tanks.
I also planned something different to
mount the fuel tanks. After the model was
finished and the nacelles were fuel-proofed, I
simply RTVed (room-temperature
vulcanized) the tanks to the inside of the
nacelles. Rough up the side of the fuel tank
with 80-grit sandpaper if you try this.
I mounted the ESCs for the motors using
Velcro in the place where I was going to
mount the fuel tanks. Using more Velcro, I
mounted the retract air tank to the inside top
of the fuselage just behind the cockpit.
Finishing: I covered my model with
MonoKote in the color scheme that US Navy
patrol squadrons used in the 1960s. If you
want a more visible scheme, you could try
one with a red tail that the naval reserve
squadrons used or use the colors that are on
some of the forest-fire-fighting versions.
Some Neptunes were used to launch drones
and missiles and had highly visible
appearances. There is much information
about this airplane on the Internet.
I sanded the dummy jet engines and tip
tanks smooth and filled the grain, and then I
painted them with LustreKote. All of the
markings are trim MonoKote.
For those who plan to use glow engines, I
will describe the method I have used on my
previous glow-powered, twin-engine models
to set up the power plants. Before you fly
your airplane, make sure both engines are
properly adjusted on the ground so that they
are reliable. I don’t bother to get them
synchronized to each other; I try to get them
to run dependably.
I set each engine independently for a
reliable idle with a smooth transition to high
speed. I set the high-speed needle by
pinching the fuel line and noting a slight rise
in the rpm without the engine dying. I point
the model’s nose straight up and straight
down to see if the engine sags or dies. I also
do this with the engine at idle.
Once I have both engines running reliably
one at a time, I run both at the same time and
check each engine using the same methods. I
do all of this at home so I don’t feel pressured
to fly the model. This also gives me a chance
to make sure nothing shakes loose.
I’m right-handed, so I start the left
engine first on my twins. This makes it
easier to stay out of the way of the left
engine while I start the right engine.
Flying: I balanced my Neptune 27/8 inches
behind the wing’s LE. After test-flying, I
feel that this is probably the farthest aft I
recommend to balance the model for good,
smooth flying.
I had to wait what seemed like forever
for the weather to cooperate—it was either
too windy or raining—but I was finally able
to sneak out early in the morning and testfly
my Neptune before the wind picked up.
After I assembled it at the field, I did a
range check of the radio with the motors
running.
I taxied the model to the end of the
runway and pointed it into the wind. I
advanced the throttles, and after roughly 150
feet I started to ease in some up-elevator. I
was pleasantly surprised when the airplane
gently rotated and started to climb out at a
nice, realistic climb rate.
It seemed to be flying well, so I flipped
the landing-gear switch, only to be
dismayed to see just the nose wheel and the
left main wheel retract. I flipped the gear
switch to the down position, and the nose
wheel came down and the left main wheel
stayed up!
I wasn’t going to let this ruin my test
flight, so I continued by climbing the model
to altitude to check the trims. My Neptune
required only some up-trim with the throttles
pulled back to a realistic cruise speed.
After cruising around for a few minutes,
I throttled down to check the stall
characteristics. My Neptune slowed better
than I expected, but it had a sharp stall. If
you build one, keep the airspeed up on the
landing approach. I did a few low passes
down the runway and then I tried a few
practice approaches.
When I finally decided to land the
Neptune, I was able to put it down gently,
but the nose gear collapsed and it skidded
down the runway on the radome and left
dummy jet engine. I was surprised that the
nacelle and the radome held up (I thought
they were going to be destroyed), but my
Neptune ended up with only some paint
scraped off the radome and the left jet
engine.
After learning that the landing-gear air
valve had a small leak, I locked the gear
down and did one more flight that day with
no problems. My model ended up weighing
just less than 10 pounds ready to fly, which
was slightly heavier than I wanted, but the
motors provide more than enough power for
flight.
The Neptune’s glide is a tad steep, but I
suppose two propellers windmilling creates
quite a bit of drag. Carry some power on the
landing approach, and as the Neptune gets
near the ground, slowly reduce power and
bleed the airspeed off with the elevator.
With practice you should be able to grease it
in on the mains and roll out a short distance
before the nose wheel comes down.
Final Thoughts: This has been one of the
most enjoyable models I have built in
awhile. It went together much better than I
expected, the flight characteristics are better
than I expected, and it looks great in the air.
The last-minute conversion to electric
power was a good move, and it has
convinced me that this is the way to go on
my future airplanes. MA
Gary Fuller
7076 E. Heather Dr.
Claremore OK 74019
[email protected]
Edition: Model Aviation - 2005/06
Page Numbers: 18,19,20,21,22,24,26
Edition: Model Aviation - 2005/06
Page Numbers: 18,19,20,21,22,24,26
18 MODEL AVIATION
by Gary Fuller
DURING THE FIRST part of the Cold War, the P2V Neptune
was the US Navy’s primary long-range, land-based, antisubmarine
patrol aircraft. Designed in 1944 as a replacement for the PV-1
Ventura and the PV-2 Harpoon, the Neptune’s versatility ensured
that it would remain in service for a long time. Its last use in
combat was by the Argentineans against the British during the fight
over the Falkland Islands.
The Neptune is still being used, to fight forest fires in the
United States. With the installation of a mad boom on the tail, the
addition of a pair of jet engines, and many other minor
modifications, the later versions of the Neptune bore little
resemblance to the early production P2Vs.
I have always had a soft spot in my heart for historical airplanes
that are seldom modeled. The Neptune’s straightforward lines
ensure a good-flying model, yet the mad boom, radomes, jet
engines, and various other components give it considerable
character that would make it unique at the flying field.
I didn’t want an all-out competition-quality Scale model, so to
simplify it I used an easy-to-build box type of fuselage that is not
much different from what most trainer-type aircraft have. The
engine nacelles are also the box type, with the bottom left open so
you don’t have to mess with any finicky landing-gear doors. The
nacelles are glued to the wing with some glass cloth for
reinforcement.
The inboard section of the wing is fully sheeted and the
outboard section of the wing uses typical D-tube construction. The
jet engines and wingtip fuel tanks are balsa blocks carved and
sanded to shape. The wing is mounted to the fuselage with a joiner
tube so the model can be disassembled for transport to and from
the flying field.
I wanted to make the Neptune as large as possible yet
economical to build and fly, so I decided to build it with an 80-inch
wingspan. Power was to be a pair of O.S. .25 engines, but I was
bitten by the electric bug during the time I was building the model.
While researching motors for a future project, I realized that I
could easily mount electric power plants to my Neptune with no
major rework. I was in the process of covering the airplane when I
decided to make the change to electric power!
RC version of US Navy patrol
aircraft can be powered with
engines or motors
On right fuselage side you can see 1/4 balsa triangle stock,
forward fuselage doubler, formers F2 and F3, and nose-wheel
mounting plate installed.
Forward fuselage after joining the sides. This is a good time to
mount nose gear. Nose-wheel mount has been reinforced with 1/4
balsa triangle stock.
Upper fuselage sheeting is being installed. Author used Ambroid
glue here so the glue joint will be easier to sand when shaping
top of sheeting. Many T-pins hold sheeting in place as glue dries.
Carpenter’s square and sharpened brass tube are used to cut
slot for 1/4 plywood dihedral brace. One of R3 ribs has been
glued to spars using R3 angle guide; other R3 rib is being glued
to spar using 1/8 scrap wood to set distance between them.
I used a pair of MaxCim MaxN32-13Y motors direct drive
spinning APC 10 x 5E propellers. The motor controllers are MaxCim
Maxμ35D-21. I used 2000 mAh Kokam Li-Poly batteries wired 3S2P,
for a total of 11.1 volts and 4000 mAh for each motor. That easily gave
me a flight time exceeding 10 minutes with the motors throttled back
and more than adequate power to take off from a grass field.
The retractable gear is the standard size, and normal modeling
techniques are used to build the Neptune. If you have never built a
model from plans, this should not be too difficult—especially if you
have a few kits under your belt.
Since this is not really a beginner’s airplane, I won’t go into much
detail in the construction notes. I did not take any great pains to keep
the weight down on my Neptune, I did not use contest-grade balsa, nor
did I cut lightening holes in any of the sheet balsa. However, I am quite
sure that if you used contest-grade wood and other weight-saving
techniques, you could shave some weight from your Neptune.
CONSTRUCTION
I started my model by cutting all the parts and assembling them like
a kit. If you have never built from plans, I recommend the following.
To accurately cut the small parts from wood, cut the parts from the
plans and then lightly spray the backside of a paper cutout with contact
glue. When it has dried for approximately 10 minutes, to a light tack,
place the paper shape for the part on the wood, and then cut the wood
using a band saw or a jigsaw. Remove the paper after you have cut the
part.
To cut more than one of the same part, do the same thing as in the
preceding and then lightly spray both sides of some scrap paper with
contact glue. Sandwich this paper between as many sheets of wood as
necessary for the number of parts required. Cut the stack of wood
with a band saw or jigsaw. Once the stack is cut, separate each piece
and remove the paper.
If you have never done this, try it on scrap wood and paper first. I
have found that some brands of contact glue won’t work because
they are too tacky. I use carpet and headliner glue that comes in a
spray can and is available in auto-part stores. A good alternative is
Elmer’s school glue stick; it works as well without the mess.
Fuselage: The fuselage sides are too long and wide to cut from a
single sheet of balsa, so you will need to splice some sheets together.
I like to have the vertical splice where the wing doubler will
reinforce the joint. Be careful with the sides until the doublers are
installed. I like to lay the fuselage sides next to each other top to top
as I glue on the various parts; that way I won’t make two left or two
right sides.
Start the fuselage by gluing the 1/4 balsa triangle stock to the sides
as shown on the plans. Glue the doublers for the wing and forward
fuselage to the fuselage sides. Glue formers F2 through F5 to one
fuselage side, and then glue the nose-wheel mounting plate to F2 and
the side to which F2 is glued.
Glue the 1/4 x 3/8 balsa side stiffeners in place as shown on the
plans. Once the adhesive has dried, join the fuselage sides. I did this
by standing the side with the formers up on its bottom and then
placing the other side in place. Once I was satisfied with the fit of the
other side, I glued it to the formers.
I joined the forward end of the fuselage by weighting the fuselage
to the table and then using some clamps to draw the ends together until
former F1 would fit. I checked the alignment of the fuselage and
Photos by the author
20 MODEL AVIATION
Make both ends of wing-joiner tube same height above table so
wing will be square to fuselage from the top.
spars and the LE flush with the outermost R1C rib.
You will need to cut the R1C ribs for the 1/4 plywood dihedral
brace, I did this by using a 1/4-inch-outside-diameter brass tube that
was sharpened at one end. I used the tube to cut holes in the R1C ribs
at the dihedral brace’s location, using a carpenter square as a guide.
After the holes were cut, I used a file to finish the slot in the ribs
for the dihedral brace. Glue the dihedral brace to the ribs and the spar
after you are satisfied with the fit.
Carefully pull the wing-joiner socket tube from the wing and rough
it up with 80-grit sandpaper. Reinsert the socket tube in the wing and
glue it to the ribs. Glue some scrap balsa between the socket tube and
the 3/8 x 1/4 spars. Sheet the top of the inboard section with 3/32 balsa.
Once the glue for the sheeting has dried, remove the inboard
portion of the wing and set it aside.
Start the outboard section of the wing by pinning the lower
outboard 3/8 x 1/4 spruce spar to the plans. Glue the R2 and R4 through
R10 ribs to the spar. Position the R1 and R3 ribs on the spar, but do
not glue them in place yet. Place the upper 3/8 x 1/4 spruce spar on the
ribs and glue it to the R2 and R4 through R10 ribs. Also glue the 3/8
balsa LE to these ribs.
Using the R1 rib angle guide, glue rib R1 to the upper and lower
spar and the LE edge. Using the R3 rib angle guide, adhere one R3 rib
to the spars and LE. Use scrap 1/8 balsa as a spacer between the R3
ribs, and glue the other R3 rib to the spars and LE. Glue the 1/4 balsa
TE to ribs R5 through R10.
Sand the spars and the LE flush with R1, and then, using the same
method you used for the inboard section of the wing, cut the slot for
the 1/4 plywood dihedral brace in ribs R1 and R2. Sheet the top of the
outer wing with 3/32 balsa, as shown on the plans.
When the sheeting is dry, remove the outer section from the
building board and fit it to the inboard section of the wing. Once you
are satisfied with the fit, glue the outer wing section to the inboard
section. I used a wood block to prop up the wingtip while the glue
dried.
Sheet the bottom of the wing with 3/32 balsa. The inboard section
and the outboard section are done separately, and the part that is not
being sheeted is blocked up to prevent the wing from warping.
I tried to sheet as much of the bottom of the wing without cutting
off the building tabs as I could. I did that by gluing the edge of the LE
sheeting to only the 3/8 balsa LE first. After the glue dried, I wet the
sheeting to make it easier to bend, applied glue to the ribs, and then
placed the wing back on the worktable right-side up and weighted it
until the sheeting dried.
Once the wing is sheeted, glue the 1/4 balsa TE in place, and then
sand the LE and TE to match the airfoil. Drill a hole for the 3/8-inchdiameter
antirotation pin, and glue the antirotation pin in place. Drill
and tap the hole for the 1/4 x 20 nylon wing-mounting bolt.
Repeat this whole process for the other wing. Build the ailerons.
Final Assembly: Go back and align and install the wing-joiner tube
Type: RC Sport Scale
Wingspan: 80 inches
Wing area: 622 square inches
Flying weight: 10 pounds
Wing loading: 37 ounces/square foot
Length: 73.25 inches
Power: Two .25 glow engines or two
MaxCim MaxN32-13Y direct-drive
motors
Fuel tank: Two 6-ounce Sullivan slant
tanks (glow)
Battery: 11.1-volt 4000 mAh Li-Poly
(for electric version)
Radio system: Five channels
Construction: Balsa and plywood
Covering/finish: MonoKote,
LustreKote paint
adjusted until it was straight, and then I glued F1 in place. I joined the
aft end of the fuselage in the same manner.
Glue the 1/4 balsa triangle to the nose-gear mount as shown on the
plans. Mount the nose gear to its mounting plate with 4-40 screws and
blind nuts. Glue the 1/8 plywood hatch mounting plate in place as
shown on the plans. Install the 1/8-inch cockpit floor.
Sheet the top and bottom of the fuselage with 3/16 balsa, glued on
so that the wood grain is crosswise to the fuselage sides. Set the
fuselage aside.
Wing: Pin the 3/8 x 1/4 lower inboard spruce spar to your worktable.
Glue an end cap of 3/32 balsa scrap on the outboard end of the wingjoiner
socket tubes. Glue the 1/4 plywood doublers to R1B. After the
glue has dried on the cap, slide the R1 ribs and R1B rib into place on
the wing-joiner tube socket; don’t glue the ribs to the joiner socket
yet.
Space the ribs on the tube, place them on the lower inboard spruce
spar, and glue them to the spar. Glue the ribs R1C to the spar, and
make sure the ribs are perpendicular to the spar vertically and
longitudinally. Insert the forward 1/4 square spruce spars and the
upper 3/8 x 1/4 spruce spar, and glue the ribs to the spars.
Glue the 3/8 balsa LE to this part of the wing. Sand the inboard
June 2005 21
Clothespins hold TE to 12-inch steel rule to keep them aligned to
each other while nacelles are being fitted to wing.
Aluminum angle bracket is used to hold engine nacelles in
alignment to each other while nacelles are glued to wing.
Engine nacelles are built in same manner as fuselage. For
simplicity’s sake there are no gear doors. Bottoms of nacelles
are left open.
socket in the fuselage. Flip the fuselage upside down on the worktable
and secure it so it won’t move. Glue one of the 1/8 plywood joiner
doublers inside one side of the fuselage.
Rough up the outside of the joiner tube socket with some
sandpaper, and insert the socket into the fuselage. Slip the other 1/8
plywood joiner doubler onto the socket as you insert it into the
fuselage, but don’t glue the socket or the doubler to the fuselage yet.
Insert the joiner tube into the socket so it is centered in the
fuselage and an equal length of the tube extends out of the fuselage on
either side. Measure the ends of the joiner tube to the worktable. Sand
the hole in the fuselage that does not have the plywood doubler on it
so that both ends of the joiner are an equal height above the work
surface. Use a carpenter’s square to square the joiner tube to the
fuselage sides also by sanding the hole without the doubler.
When you are satisfied that the joiner tube is square to the fuselage
side, block the joiner tube so that it cannot move, and then doublecheck
to make sure the joiner tubes’ ends are an equal height above
the work surface. Glue the plywood doubler and the joiner tube socket
to the fuselage side. Glue the other end of the joiner socket to the
other side of the fuselage.
The wing-joiner tube I bought was too long for the wings, so I
ended up cutting approximately 6 inches from it. I set this short piece
aside; it will be used to align the wings to each other as the nacelles
are mounted.
Slide the wings on the wing-joiner tube so that they fit snugly up
against the fuselage sides. Adjust the wing so that it is at 0°. Place the
1/8 plywood doubler on the antirotation pin and carefully adhere the
doubler to the fuselage side, being careful not to get any glue on the
antirotation pin. Use the same technique to glue the 1/8 plywood wingmount
bolt doubler to the fuselage side.
The engine nacelles are identical to each other except for the
landing-gear mounts. The nacelles are built like the fuselage, so I
won’t go into detail about the method used to construct them. Just
make sure that you build a left and a right one.
The method I used to align and mount the nacelles to the wings
should work if you plan to use electric or glow power. Because I
decided to go electric after my Neptune was nearly completed, I will
describe the method using glow engines.
You will need a roughly 3-foot section of aluminum angle, which
you can get in most hardware stores. It is used to hold the engines in
alignment with each other when you mount the nacelles to the wings.
Cut off approximately a 6-inch piece of the aluminum angle.
Mount both wings to the short scrap piece of the wing-joiner tube.
Slide the wings together as close as you can without letting the
antirotation pins interfere with each other. Clamp the 6-inch angle to
both wings’ TEs to keep the TEs aligned to each other.
On the finished model, the centerlines of the nacelles are 85/16
inches from the sides of the fuselage. Because the fuselage will
interfere with this method of mounting the nacelles, you will need to
compensate for the absence of the fuselage.
Measure the gap between the root ribs of the left and right wing,
and then add that amount to the 165/8-inch measurement. If the gap
is 2 inches, the total will be 185/8 inches. On your aluminum angle
drill two holes on center 185/8 inches apart. The diameter of the
holes will need to fit the prop shaft of the engines or motors you
plan to use.
Mount the engines to the nacelles, and then, using the prop shaft
of each engine, bolt the engines to the aluminum angle in the holes
you drilled. At this point the engines are aligned to each other. This is
important. The nacelles don’t really need to be aligned to each other,
but the engine thrustlines do.
Place the wing in the wing saddle of the nacelles, and adjust the
wing in the saddles so that the inside side of the nacelles are
approximately 69/16 inches from the edge of the wing root. Do not
adjust the gap between the wings. If you measured accurately, both
nacelles should be that length from the root rib.
Measure the distance from the wing LE to the aluminum angle at
the dihedral break on both wings. Adjust this distance so that the
measurement is the same on both wings. Check the engine
upthrust/downthrust line in relationship to the wing’s incidence with
an incidence meter, and sand the nacelles’ saddles so that the
thrustline is 0°.
The P2V Neptune’s completed framework is ready for covering. This model features extremely clean workmanship!
Full-Size Plans Available—see page 183
Once you are satisfied with all of these
measurements, tack-glue the nacelles to the
wings. Flip the wings over so you can glue
the nacelles to the wing with epoxy and glass
cloth on the inside of the nacelles. Carefully
unbolt the engines from the aluminum angle
and then separate the wings from each other.
Install the wings to the fuselage, and
mount the horizontal stabilizer so it is at 0°
incidence to the wing. Mount the vertical
stabilizer.
It is time to start all the little details such
as the dummy jet engines, the wingtip tanks,
the radomes, and the canopy. I made my
canopy and the forward observer’s canopy on
the nose from clear plastic, but you can carve
and sand a balsa block to shape if you want.
To supply some cooling air for the
batteries, I vacuum-formed the big radome
on the bottom of the fuselage from plastic.
On the front of the radome I cut some holes,
and on the bottom of the fuselage I cut holes
where the radome mounts. This allows the
radome to act like a big air scoop to cool the
batteries. I cut holes on the back end of the
fuselage hatch to allow the air to escape.
Radio Installation: This is fairly
straightforward. I used some flat wing servos
for the ailerons, and these needed to be
installed before I covered the wing. Before I
decided to switch to electric power, each
engine was to have had a separate throttle
servo that I planned to mount behind the
main landing gear in the nacelles.
I mounted the elevator, rudder, and retract
servos in the fuselage. An important thing
here is to make sure you have clear access to
the wing-mounting bolts in the fuselage.
Otherwise, mount the radio gear as you see
fit. After test-flying I found that aileron
differential is recommended along with some
rudder mixed into the ailerons.
Since this was my first electric-powered
twin, I decided to use one motor controller
and a separate battery pack for each motor,
and a servo “Y” harness to connect the motor
controllers to the receiver. I also used a
separate battery to power the receiver and
servos.
The fuel tanks need special attention
because the main landing gear will fold up
next to the tanks, and it is a tight fit. You will
need narrow tires and narrow fuel tanks, for
which I planned to use Sullivan 6-ounce slant
oval fuel tanks.
I also planned something different to
mount the fuel tanks. After the model was
finished and the nacelles were fuel-proofed, I
simply RTVed (room-temperature
vulcanized) the tanks to the inside of the
nacelles. Rough up the side of the fuel tank
with 80-grit sandpaper if you try this.
I mounted the ESCs for the motors using
Velcro in the place where I was going to
mount the fuel tanks. Using more Velcro, I
mounted the retract air tank to the inside top
of the fuselage just behind the cockpit.
Finishing: I covered my model with
MonoKote in the color scheme that US Navy
patrol squadrons used in the 1960s. If you
want a more visible scheme, you could try
one with a red tail that the naval reserve
squadrons used or use the colors that are on
some of the forest-fire-fighting versions.
Some Neptunes were used to launch drones
and missiles and had highly visible
appearances. There is much information
about this airplane on the Internet.
I sanded the dummy jet engines and tip
tanks smooth and filled the grain, and then I
painted them with LustreKote. All of the
markings are trim MonoKote.
For those who plan to use glow engines, I
will describe the method I have used on my
previous glow-powered, twin-engine models
to set up the power plants. Before you fly
your airplane, make sure both engines are
properly adjusted on the ground so that they
are reliable. I don’t bother to get them
synchronized to each other; I try to get them
to run dependably.
I set each engine independently for a
reliable idle with a smooth transition to high
speed. I set the high-speed needle by
pinching the fuel line and noting a slight rise
in the rpm without the engine dying. I point
the model’s nose straight up and straight
down to see if the engine sags or dies. I also
do this with the engine at idle.
Once I have both engines running reliably
one at a time, I run both at the same time and
check each engine using the same methods. I
do all of this at home so I don’t feel pressured
to fly the model. This also gives me a chance
to make sure nothing shakes loose.
I’m right-handed, so I start the left
engine first on my twins. This makes it
easier to stay out of the way of the left
engine while I start the right engine.
Flying: I balanced my Neptune 27/8 inches
behind the wing’s LE. After test-flying, I
feel that this is probably the farthest aft I
recommend to balance the model for good,
smooth flying.
I had to wait what seemed like forever
for the weather to cooperate—it was either
too windy or raining—but I was finally able
to sneak out early in the morning and testfly
my Neptune before the wind picked up.
After I assembled it at the field, I did a
range check of the radio with the motors
running.
I taxied the model to the end of the
runway and pointed it into the wind. I
advanced the throttles, and after roughly 150
feet I started to ease in some up-elevator. I
was pleasantly surprised when the airplane
gently rotated and started to climb out at a
nice, realistic climb rate.
It seemed to be flying well, so I flipped
the landing-gear switch, only to be
dismayed to see just the nose wheel and the
left main wheel retract. I flipped the gear
switch to the down position, and the nose
wheel came down and the left main wheel
stayed up!
I wasn’t going to let this ruin my test
flight, so I continued by climbing the model
to altitude to check the trims. My Neptune
required only some up-trim with the throttles
pulled back to a realistic cruise speed.
After cruising around for a few minutes,
I throttled down to check the stall
characteristics. My Neptune slowed better
than I expected, but it had a sharp stall. If
you build one, keep the airspeed up on the
landing approach. I did a few low passes
down the runway and then I tried a few
practice approaches.
When I finally decided to land the
Neptune, I was able to put it down gently,
but the nose gear collapsed and it skidded
down the runway on the radome and left
dummy jet engine. I was surprised that the
nacelle and the radome held up (I thought
they were going to be destroyed), but my
Neptune ended up with only some paint
scraped off the radome and the left jet
engine.
After learning that the landing-gear air
valve had a small leak, I locked the gear
down and did one more flight that day with
no problems. My model ended up weighing
just less than 10 pounds ready to fly, which
was slightly heavier than I wanted, but the
motors provide more than enough power for
flight.
The Neptune’s glide is a tad steep, but I
suppose two propellers windmilling creates
quite a bit of drag. Carry some power on the
landing approach, and as the Neptune gets
near the ground, slowly reduce power and
bleed the airspeed off with the elevator.
With practice you should be able to grease it
in on the mains and roll out a short distance
before the nose wheel comes down.
Final Thoughts: This has been one of the
most enjoyable models I have built in
awhile. It went together much better than I
expected, the flight characteristics are better
than I expected, and it looks great in the air.
The last-minute conversion to electric
power was a good move, and it has
convinced me that this is the way to go on
my future airplanes. MA
Gary Fuller
7076 E. Heather Dr.
Claremore OK 74019
[email protected]
Edition: Model Aviation - 2005/06
Page Numbers: 18,19,20,21,22,24,26
18 MODEL AVIATION
by Gary Fuller
DURING THE FIRST part of the Cold War, the P2V Neptune
was the US Navy’s primary long-range, land-based, antisubmarine
patrol aircraft. Designed in 1944 as a replacement for the PV-1
Ventura and the PV-2 Harpoon, the Neptune’s versatility ensured
that it would remain in service for a long time. Its last use in
combat was by the Argentineans against the British during the fight
over the Falkland Islands.
The Neptune is still being used, to fight forest fires in the
United States. With the installation of a mad boom on the tail, the
addition of a pair of jet engines, and many other minor
modifications, the later versions of the Neptune bore little
resemblance to the early production P2Vs.
I have always had a soft spot in my heart for historical airplanes
that are seldom modeled. The Neptune’s straightforward lines
ensure a good-flying model, yet the mad boom, radomes, jet
engines, and various other components give it considerable
character that would make it unique at the flying field.
I didn’t want an all-out competition-quality Scale model, so to
simplify it I used an easy-to-build box type of fuselage that is not
much different from what most trainer-type aircraft have. The
engine nacelles are also the box type, with the bottom left open so
you don’t have to mess with any finicky landing-gear doors. The
nacelles are glued to the wing with some glass cloth for
reinforcement.
The inboard section of the wing is fully sheeted and the
outboard section of the wing uses typical D-tube construction. The
jet engines and wingtip fuel tanks are balsa blocks carved and
sanded to shape. The wing is mounted to the fuselage with a joiner
tube so the model can be disassembled for transport to and from
the flying field.
I wanted to make the Neptune as large as possible yet
economical to build and fly, so I decided to build it with an 80-inch
wingspan. Power was to be a pair of O.S. .25 engines, but I was
bitten by the electric bug during the time I was building the model.
While researching motors for a future project, I realized that I
could easily mount electric power plants to my Neptune with no
major rework. I was in the process of covering the airplane when I
decided to make the change to electric power!
RC version of US Navy patrol
aircraft can be powered with
engines or motors
On right fuselage side you can see 1/4 balsa triangle stock,
forward fuselage doubler, formers F2 and F3, and nose-wheel
mounting plate installed.
Forward fuselage after joining the sides. This is a good time to
mount nose gear. Nose-wheel mount has been reinforced with 1/4
balsa triangle stock.
Upper fuselage sheeting is being installed. Author used Ambroid
glue here so the glue joint will be easier to sand when shaping
top of sheeting. Many T-pins hold sheeting in place as glue dries.
Carpenter’s square and sharpened brass tube are used to cut
slot for 1/4 plywood dihedral brace. One of R3 ribs has been
glued to spars using R3 angle guide; other R3 rib is being glued
to spar using 1/8 scrap wood to set distance between them.
I used a pair of MaxCim MaxN32-13Y motors direct drive
spinning APC 10 x 5E propellers. The motor controllers are MaxCim
Maxμ35D-21. I used 2000 mAh Kokam Li-Poly batteries wired 3S2P,
for a total of 11.1 volts and 4000 mAh for each motor. That easily gave
me a flight time exceeding 10 minutes with the motors throttled back
and more than adequate power to take off from a grass field.
The retractable gear is the standard size, and normal modeling
techniques are used to build the Neptune. If you have never built a
model from plans, this should not be too difficult—especially if you
have a few kits under your belt.
Since this is not really a beginner’s airplane, I won’t go into much
detail in the construction notes. I did not take any great pains to keep
the weight down on my Neptune, I did not use contest-grade balsa, nor
did I cut lightening holes in any of the sheet balsa. However, I am quite
sure that if you used contest-grade wood and other weight-saving
techniques, you could shave some weight from your Neptune.
CONSTRUCTION
I started my model by cutting all the parts and assembling them like
a kit. If you have never built from plans, I recommend the following.
To accurately cut the small parts from wood, cut the parts from the
plans and then lightly spray the backside of a paper cutout with contact
glue. When it has dried for approximately 10 minutes, to a light tack,
place the paper shape for the part on the wood, and then cut the wood
using a band saw or a jigsaw. Remove the paper after you have cut the
part.
To cut more than one of the same part, do the same thing as in the
preceding and then lightly spray both sides of some scrap paper with
contact glue. Sandwich this paper between as many sheets of wood as
necessary for the number of parts required. Cut the stack of wood
with a band saw or jigsaw. Once the stack is cut, separate each piece
and remove the paper.
If you have never done this, try it on scrap wood and paper first. I
have found that some brands of contact glue won’t work because
they are too tacky. I use carpet and headliner glue that comes in a
spray can and is available in auto-part stores. A good alternative is
Elmer’s school glue stick; it works as well without the mess.
Fuselage: The fuselage sides are too long and wide to cut from a
single sheet of balsa, so you will need to splice some sheets together.
I like to have the vertical splice where the wing doubler will
reinforce the joint. Be careful with the sides until the doublers are
installed. I like to lay the fuselage sides next to each other top to top
as I glue on the various parts; that way I won’t make two left or two
right sides.
Start the fuselage by gluing the 1/4 balsa triangle stock to the sides
as shown on the plans. Glue the doublers for the wing and forward
fuselage to the fuselage sides. Glue formers F2 through F5 to one
fuselage side, and then glue the nose-wheel mounting plate to F2 and
the side to which F2 is glued.
Glue the 1/4 x 3/8 balsa side stiffeners in place as shown on the
plans. Once the adhesive has dried, join the fuselage sides. I did this
by standing the side with the formers up on its bottom and then
placing the other side in place. Once I was satisfied with the fit of the
other side, I glued it to the formers.
I joined the forward end of the fuselage by weighting the fuselage
to the table and then using some clamps to draw the ends together until
former F1 would fit. I checked the alignment of the fuselage and
Photos by the author
20 MODEL AVIATION
Make both ends of wing-joiner tube same height above table so
wing will be square to fuselage from the top.
spars and the LE flush with the outermost R1C rib.
You will need to cut the R1C ribs for the 1/4 plywood dihedral
brace, I did this by using a 1/4-inch-outside-diameter brass tube that
was sharpened at one end. I used the tube to cut holes in the R1C ribs
at the dihedral brace’s location, using a carpenter square as a guide.
After the holes were cut, I used a file to finish the slot in the ribs
for the dihedral brace. Glue the dihedral brace to the ribs and the spar
after you are satisfied with the fit.
Carefully pull the wing-joiner socket tube from the wing and rough
it up with 80-grit sandpaper. Reinsert the socket tube in the wing and
glue it to the ribs. Glue some scrap balsa between the socket tube and
the 3/8 x 1/4 spars. Sheet the top of the inboard section with 3/32 balsa.
Once the glue for the sheeting has dried, remove the inboard
portion of the wing and set it aside.
Start the outboard section of the wing by pinning the lower
outboard 3/8 x 1/4 spruce spar to the plans. Glue the R2 and R4 through
R10 ribs to the spar. Position the R1 and R3 ribs on the spar, but do
not glue them in place yet. Place the upper 3/8 x 1/4 spruce spar on the
ribs and glue it to the R2 and R4 through R10 ribs. Also glue the 3/8
balsa LE to these ribs.
Using the R1 rib angle guide, glue rib R1 to the upper and lower
spar and the LE edge. Using the R3 rib angle guide, adhere one R3 rib
to the spars and LE. Use scrap 1/8 balsa as a spacer between the R3
ribs, and glue the other R3 rib to the spars and LE. Glue the 1/4 balsa
TE to ribs R5 through R10.
Sand the spars and the LE flush with R1, and then, using the same
method you used for the inboard section of the wing, cut the slot for
the 1/4 plywood dihedral brace in ribs R1 and R2. Sheet the top of the
outer wing with 3/32 balsa, as shown on the plans.
When the sheeting is dry, remove the outer section from the
building board and fit it to the inboard section of the wing. Once you
are satisfied with the fit, glue the outer wing section to the inboard
section. I used a wood block to prop up the wingtip while the glue
dried.
Sheet the bottom of the wing with 3/32 balsa. The inboard section
and the outboard section are done separately, and the part that is not
being sheeted is blocked up to prevent the wing from warping.
I tried to sheet as much of the bottom of the wing without cutting
off the building tabs as I could. I did that by gluing the edge of the LE
sheeting to only the 3/8 balsa LE first. After the glue dried, I wet the
sheeting to make it easier to bend, applied glue to the ribs, and then
placed the wing back on the worktable right-side up and weighted it
until the sheeting dried.
Once the wing is sheeted, glue the 1/4 balsa TE in place, and then
sand the LE and TE to match the airfoil. Drill a hole for the 3/8-inchdiameter
antirotation pin, and glue the antirotation pin in place. Drill
and tap the hole for the 1/4 x 20 nylon wing-mounting bolt.
Repeat this whole process for the other wing. Build the ailerons.
Final Assembly: Go back and align and install the wing-joiner tube
Type: RC Sport Scale
Wingspan: 80 inches
Wing area: 622 square inches
Flying weight: 10 pounds
Wing loading: 37 ounces/square foot
Length: 73.25 inches
Power: Two .25 glow engines or two
MaxCim MaxN32-13Y direct-drive
motors
Fuel tank: Two 6-ounce Sullivan slant
tanks (glow)
Battery: 11.1-volt 4000 mAh Li-Poly
(for electric version)
Radio system: Five channels
Construction: Balsa and plywood
Covering/finish: MonoKote,
LustreKote paint
adjusted until it was straight, and then I glued F1 in place. I joined the
aft end of the fuselage in the same manner.
Glue the 1/4 balsa triangle to the nose-gear mount as shown on the
plans. Mount the nose gear to its mounting plate with 4-40 screws and
blind nuts. Glue the 1/8 plywood hatch mounting plate in place as
shown on the plans. Install the 1/8-inch cockpit floor.
Sheet the top and bottom of the fuselage with 3/16 balsa, glued on
so that the wood grain is crosswise to the fuselage sides. Set the
fuselage aside.
Wing: Pin the 3/8 x 1/4 lower inboard spruce spar to your worktable.
Glue an end cap of 3/32 balsa scrap on the outboard end of the wingjoiner
socket tubes. Glue the 1/4 plywood doublers to R1B. After the
glue has dried on the cap, slide the R1 ribs and R1B rib into place on
the wing-joiner tube socket; don’t glue the ribs to the joiner socket
yet.
Space the ribs on the tube, place them on the lower inboard spruce
spar, and glue them to the spar. Glue the ribs R1C to the spar, and
make sure the ribs are perpendicular to the spar vertically and
longitudinally. Insert the forward 1/4 square spruce spars and the
upper 3/8 x 1/4 spruce spar, and glue the ribs to the spars.
Glue the 3/8 balsa LE to this part of the wing. Sand the inboard
June 2005 21
Clothespins hold TE to 12-inch steel rule to keep them aligned to
each other while nacelles are being fitted to wing.
Aluminum angle bracket is used to hold engine nacelles in
alignment to each other while nacelles are glued to wing.
Engine nacelles are built in same manner as fuselage. For
simplicity’s sake there are no gear doors. Bottoms of nacelles
are left open.
socket in the fuselage. Flip the fuselage upside down on the worktable
and secure it so it won’t move. Glue one of the 1/8 plywood joiner
doublers inside one side of the fuselage.
Rough up the outside of the joiner tube socket with some
sandpaper, and insert the socket into the fuselage. Slip the other 1/8
plywood joiner doubler onto the socket as you insert it into the
fuselage, but don’t glue the socket or the doubler to the fuselage yet.
Insert the joiner tube into the socket so it is centered in the
fuselage and an equal length of the tube extends out of the fuselage on
either side. Measure the ends of the joiner tube to the worktable. Sand
the hole in the fuselage that does not have the plywood doubler on it
so that both ends of the joiner are an equal height above the work
surface. Use a carpenter’s square to square the joiner tube to the
fuselage sides also by sanding the hole without the doubler.
When you are satisfied that the joiner tube is square to the fuselage
side, block the joiner tube so that it cannot move, and then doublecheck
to make sure the joiner tubes’ ends are an equal height above
the work surface. Glue the plywood doubler and the joiner tube socket
to the fuselage side. Glue the other end of the joiner socket to the
other side of the fuselage.
The wing-joiner tube I bought was too long for the wings, so I
ended up cutting approximately 6 inches from it. I set this short piece
aside; it will be used to align the wings to each other as the nacelles
are mounted.
Slide the wings on the wing-joiner tube so that they fit snugly up
against the fuselage sides. Adjust the wing so that it is at 0°. Place the
1/8 plywood doubler on the antirotation pin and carefully adhere the
doubler to the fuselage side, being careful not to get any glue on the
antirotation pin. Use the same technique to glue the 1/8 plywood wingmount
bolt doubler to the fuselage side.
The engine nacelles are identical to each other except for the
landing-gear mounts. The nacelles are built like the fuselage, so I
won’t go into detail about the method used to construct them. Just
make sure that you build a left and a right one.
The method I used to align and mount the nacelles to the wings
should work if you plan to use electric or glow power. Because I
decided to go electric after my Neptune was nearly completed, I will
describe the method using glow engines.
You will need a roughly 3-foot section of aluminum angle, which
you can get in most hardware stores. It is used to hold the engines in
alignment with each other when you mount the nacelles to the wings.
Cut off approximately a 6-inch piece of the aluminum angle.
Mount both wings to the short scrap piece of the wing-joiner tube.
Slide the wings together as close as you can without letting the
antirotation pins interfere with each other. Clamp the 6-inch angle to
both wings’ TEs to keep the TEs aligned to each other.
On the finished model, the centerlines of the nacelles are 85/16
inches from the sides of the fuselage. Because the fuselage will
interfere with this method of mounting the nacelles, you will need to
compensate for the absence of the fuselage.
Measure the gap between the root ribs of the left and right wing,
and then add that amount to the 165/8-inch measurement. If the gap
is 2 inches, the total will be 185/8 inches. On your aluminum angle
drill two holes on center 185/8 inches apart. The diameter of the
holes will need to fit the prop shaft of the engines or motors you
plan to use.
Mount the engines to the nacelles, and then, using the prop shaft
of each engine, bolt the engines to the aluminum angle in the holes
you drilled. At this point the engines are aligned to each other. This is
important. The nacelles don’t really need to be aligned to each other,
but the engine thrustlines do.
Place the wing in the wing saddle of the nacelles, and adjust the
wing in the saddles so that the inside side of the nacelles are
approximately 69/16 inches from the edge of the wing root. Do not
adjust the gap between the wings. If you measured accurately, both
nacelles should be that length from the root rib.
Measure the distance from the wing LE to the aluminum angle at
the dihedral break on both wings. Adjust this distance so that the
measurement is the same on both wings. Check the engine
upthrust/downthrust line in relationship to the wing’s incidence with
an incidence meter, and sand the nacelles’ saddles so that the
thrustline is 0°.
The P2V Neptune’s completed framework is ready for covering. This model features extremely clean workmanship!
Full-Size Plans Available—see page 183
Once you are satisfied with all of these
measurements, tack-glue the nacelles to the
wings. Flip the wings over so you can glue
the nacelles to the wing with epoxy and glass
cloth on the inside of the nacelles. Carefully
unbolt the engines from the aluminum angle
and then separate the wings from each other.
Install the wings to the fuselage, and
mount the horizontal stabilizer so it is at 0°
incidence to the wing. Mount the vertical
stabilizer.
It is time to start all the little details such
as the dummy jet engines, the wingtip tanks,
the radomes, and the canopy. I made my
canopy and the forward observer’s canopy on
the nose from clear plastic, but you can carve
and sand a balsa block to shape if you want.
To supply some cooling air for the
batteries, I vacuum-formed the big radome
on the bottom of the fuselage from plastic.
On the front of the radome I cut some holes,
and on the bottom of the fuselage I cut holes
where the radome mounts. This allows the
radome to act like a big air scoop to cool the
batteries. I cut holes on the back end of the
fuselage hatch to allow the air to escape.
Radio Installation: This is fairly
straightforward. I used some flat wing servos
for the ailerons, and these needed to be
installed before I covered the wing. Before I
decided to switch to electric power, each
engine was to have had a separate throttle
servo that I planned to mount behind the
main landing gear in the nacelles.
I mounted the elevator, rudder, and retract
servos in the fuselage. An important thing
here is to make sure you have clear access to
the wing-mounting bolts in the fuselage.
Otherwise, mount the radio gear as you see
fit. After test-flying I found that aileron
differential is recommended along with some
rudder mixed into the ailerons.
Since this was my first electric-powered
twin, I decided to use one motor controller
and a separate battery pack for each motor,
and a servo “Y” harness to connect the motor
controllers to the receiver. I also used a
separate battery to power the receiver and
servos.
The fuel tanks need special attention
because the main landing gear will fold up
next to the tanks, and it is a tight fit. You will
need narrow tires and narrow fuel tanks, for
which I planned to use Sullivan 6-ounce slant
oval fuel tanks.
I also planned something different to
mount the fuel tanks. After the model was
finished and the nacelles were fuel-proofed, I
simply RTVed (room-temperature
vulcanized) the tanks to the inside of the
nacelles. Rough up the side of the fuel tank
with 80-grit sandpaper if you try this.
I mounted the ESCs for the motors using
Velcro in the place where I was going to
mount the fuel tanks. Using more Velcro, I
mounted the retract air tank to the inside top
of the fuselage just behind the cockpit.
Finishing: I covered my model with
MonoKote in the color scheme that US Navy
patrol squadrons used in the 1960s. If you
want a more visible scheme, you could try
one with a red tail that the naval reserve
squadrons used or use the colors that are on
some of the forest-fire-fighting versions.
Some Neptunes were used to launch drones
and missiles and had highly visible
appearances. There is much information
about this airplane on the Internet.
I sanded the dummy jet engines and tip
tanks smooth and filled the grain, and then I
painted them with LustreKote. All of the
markings are trim MonoKote.
For those who plan to use glow engines, I
will describe the method I have used on my
previous glow-powered, twin-engine models
to set up the power plants. Before you fly
your airplane, make sure both engines are
properly adjusted on the ground so that they
are reliable. I don’t bother to get them
synchronized to each other; I try to get them
to run dependably.
I set each engine independently for a
reliable idle with a smooth transition to high
speed. I set the high-speed needle by
pinching the fuel line and noting a slight rise
in the rpm without the engine dying. I point
the model’s nose straight up and straight
down to see if the engine sags or dies. I also
do this with the engine at idle.
Once I have both engines running reliably
one at a time, I run both at the same time and
check each engine using the same methods. I
do all of this at home so I don’t feel pressured
to fly the model. This also gives me a chance
to make sure nothing shakes loose.
I’m right-handed, so I start the left
engine first on my twins. This makes it
easier to stay out of the way of the left
engine while I start the right engine.
Flying: I balanced my Neptune 27/8 inches
behind the wing’s LE. After test-flying, I
feel that this is probably the farthest aft I
recommend to balance the model for good,
smooth flying.
I had to wait what seemed like forever
for the weather to cooperate—it was either
too windy or raining—but I was finally able
to sneak out early in the morning and testfly
my Neptune before the wind picked up.
After I assembled it at the field, I did a
range check of the radio with the motors
running.
I taxied the model to the end of the
runway and pointed it into the wind. I
advanced the throttles, and after roughly 150
feet I started to ease in some up-elevator. I
was pleasantly surprised when the airplane
gently rotated and started to climb out at a
nice, realistic climb rate.
It seemed to be flying well, so I flipped
the landing-gear switch, only to be
dismayed to see just the nose wheel and the
left main wheel retract. I flipped the gear
switch to the down position, and the nose
wheel came down and the left main wheel
stayed up!
I wasn’t going to let this ruin my test
flight, so I continued by climbing the model
to altitude to check the trims. My Neptune
required only some up-trim with the throttles
pulled back to a realistic cruise speed.
After cruising around for a few minutes,
I throttled down to check the stall
characteristics. My Neptune slowed better
than I expected, but it had a sharp stall. If
you build one, keep the airspeed up on the
landing approach. I did a few low passes
down the runway and then I tried a few
practice approaches.
When I finally decided to land the
Neptune, I was able to put it down gently,
but the nose gear collapsed and it skidded
down the runway on the radome and left
dummy jet engine. I was surprised that the
nacelle and the radome held up (I thought
they were going to be destroyed), but my
Neptune ended up with only some paint
scraped off the radome and the left jet
engine.
After learning that the landing-gear air
valve had a small leak, I locked the gear
down and did one more flight that day with
no problems. My model ended up weighing
just less than 10 pounds ready to fly, which
was slightly heavier than I wanted, but the
motors provide more than enough power for
flight.
The Neptune’s glide is a tad steep, but I
suppose two propellers windmilling creates
quite a bit of drag. Carry some power on the
landing approach, and as the Neptune gets
near the ground, slowly reduce power and
bleed the airspeed off with the elevator.
With practice you should be able to grease it
in on the mains and roll out a short distance
before the nose wheel comes down.
Final Thoughts: This has been one of the
most enjoyable models I have built in
awhile. It went together much better than I
expected, the flight characteristics are better
than I expected, and it looks great in the air.
The last-minute conversion to electric
power was a good move, and it has
convinced me that this is the way to go on
my future airplanes. MA
Gary Fuller
7076 E. Heather Dr.
Claremore OK 74019
[email protected]
Edition: Model Aviation - 2005/06
Page Numbers: 18,19,20,21,22,24,26
18 MODEL AVIATION
by Gary Fuller
DURING THE FIRST part of the Cold War, the P2V Neptune
was the US Navy’s primary long-range, land-based, antisubmarine
patrol aircraft. Designed in 1944 as a replacement for the PV-1
Ventura and the PV-2 Harpoon, the Neptune’s versatility ensured
that it would remain in service for a long time. Its last use in
combat was by the Argentineans against the British during the fight
over the Falkland Islands.
The Neptune is still being used, to fight forest fires in the
United States. With the installation of a mad boom on the tail, the
addition of a pair of jet engines, and many other minor
modifications, the later versions of the Neptune bore little
resemblance to the early production P2Vs.
I have always had a soft spot in my heart for historical airplanes
that are seldom modeled. The Neptune’s straightforward lines
ensure a good-flying model, yet the mad boom, radomes, jet
engines, and various other components give it considerable
character that would make it unique at the flying field.
I didn’t want an all-out competition-quality Scale model, so to
simplify it I used an easy-to-build box type of fuselage that is not
much different from what most trainer-type aircraft have. The
engine nacelles are also the box type, with the bottom left open so
you don’t have to mess with any finicky landing-gear doors. The
nacelles are glued to the wing with some glass cloth for
reinforcement.
The inboard section of the wing is fully sheeted and the
outboard section of the wing uses typical D-tube construction. The
jet engines and wingtip fuel tanks are balsa blocks carved and
sanded to shape. The wing is mounted to the fuselage with a joiner
tube so the model can be disassembled for transport to and from
the flying field.
I wanted to make the Neptune as large as possible yet
economical to build and fly, so I decided to build it with an 80-inch
wingspan. Power was to be a pair of O.S. .25 engines, but I was
bitten by the electric bug during the time I was building the model.
While researching motors for a future project, I realized that I
could easily mount electric power plants to my Neptune with no
major rework. I was in the process of covering the airplane when I
decided to make the change to electric power!
RC version of US Navy patrol
aircraft can be powered with
engines or motors
On right fuselage side you can see 1/4 balsa triangle stock,
forward fuselage doubler, formers F2 and F3, and nose-wheel
mounting plate installed.
Forward fuselage after joining the sides. This is a good time to
mount nose gear. Nose-wheel mount has been reinforced with 1/4
balsa triangle stock.
Upper fuselage sheeting is being installed. Author used Ambroid
glue here so the glue joint will be easier to sand when shaping
top of sheeting. Many T-pins hold sheeting in place as glue dries.
Carpenter’s square and sharpened brass tube are used to cut
slot for 1/4 plywood dihedral brace. One of R3 ribs has been
glued to spars using R3 angle guide; other R3 rib is being glued
to spar using 1/8 scrap wood to set distance between them.
I used a pair of MaxCim MaxN32-13Y motors direct drive
spinning APC 10 x 5E propellers. The motor controllers are MaxCim
Maxμ35D-21. I used 2000 mAh Kokam Li-Poly batteries wired 3S2P,
for a total of 11.1 volts and 4000 mAh for each motor. That easily gave
me a flight time exceeding 10 minutes with the motors throttled back
and more than adequate power to take off from a grass field.
The retractable gear is the standard size, and normal modeling
techniques are used to build the Neptune. If you have never built a
model from plans, this should not be too difficult—especially if you
have a few kits under your belt.
Since this is not really a beginner’s airplane, I won’t go into much
detail in the construction notes. I did not take any great pains to keep
the weight down on my Neptune, I did not use contest-grade balsa, nor
did I cut lightening holes in any of the sheet balsa. However, I am quite
sure that if you used contest-grade wood and other weight-saving
techniques, you could shave some weight from your Neptune.
CONSTRUCTION
I started my model by cutting all the parts and assembling them like
a kit. If you have never built from plans, I recommend the following.
To accurately cut the small parts from wood, cut the parts from the
plans and then lightly spray the backside of a paper cutout with contact
glue. When it has dried for approximately 10 minutes, to a light tack,
place the paper shape for the part on the wood, and then cut the wood
using a band saw or a jigsaw. Remove the paper after you have cut the
part.
To cut more than one of the same part, do the same thing as in the
preceding and then lightly spray both sides of some scrap paper with
contact glue. Sandwich this paper between as many sheets of wood as
necessary for the number of parts required. Cut the stack of wood
with a band saw or jigsaw. Once the stack is cut, separate each piece
and remove the paper.
If you have never done this, try it on scrap wood and paper first. I
have found that some brands of contact glue won’t work because
they are too tacky. I use carpet and headliner glue that comes in a
spray can and is available in auto-part stores. A good alternative is
Elmer’s school glue stick; it works as well without the mess.
Fuselage: The fuselage sides are too long and wide to cut from a
single sheet of balsa, so you will need to splice some sheets together.
I like to have the vertical splice where the wing doubler will
reinforce the joint. Be careful with the sides until the doublers are
installed. I like to lay the fuselage sides next to each other top to top
as I glue on the various parts; that way I won’t make two left or two
right sides.
Start the fuselage by gluing the 1/4 balsa triangle stock to the sides
as shown on the plans. Glue the doublers for the wing and forward
fuselage to the fuselage sides. Glue formers F2 through F5 to one
fuselage side, and then glue the nose-wheel mounting plate to F2 and
the side to which F2 is glued.
Glue the 1/4 x 3/8 balsa side stiffeners in place as shown on the
plans. Once the adhesive has dried, join the fuselage sides. I did this
by standing the side with the formers up on its bottom and then
placing the other side in place. Once I was satisfied with the fit of the
other side, I glued it to the formers.
I joined the forward end of the fuselage by weighting the fuselage
to the table and then using some clamps to draw the ends together until
former F1 would fit. I checked the alignment of the fuselage and
Photos by the author
20 MODEL AVIATION
Make both ends of wing-joiner tube same height above table so
wing will be square to fuselage from the top.
spars and the LE flush with the outermost R1C rib.
You will need to cut the R1C ribs for the 1/4 plywood dihedral
brace, I did this by using a 1/4-inch-outside-diameter brass tube that
was sharpened at one end. I used the tube to cut holes in the R1C ribs
at the dihedral brace’s location, using a carpenter square as a guide.
After the holes were cut, I used a file to finish the slot in the ribs
for the dihedral brace. Glue the dihedral brace to the ribs and the spar
after you are satisfied with the fit.
Carefully pull the wing-joiner socket tube from the wing and rough
it up with 80-grit sandpaper. Reinsert the socket tube in the wing and
glue it to the ribs. Glue some scrap balsa between the socket tube and
the 3/8 x 1/4 spars. Sheet the top of the inboard section with 3/32 balsa.
Once the glue for the sheeting has dried, remove the inboard
portion of the wing and set it aside.
Start the outboard section of the wing by pinning the lower
outboard 3/8 x 1/4 spruce spar to the plans. Glue the R2 and R4 through
R10 ribs to the spar. Position the R1 and R3 ribs on the spar, but do
not glue them in place yet. Place the upper 3/8 x 1/4 spruce spar on the
ribs and glue it to the R2 and R4 through R10 ribs. Also glue the 3/8
balsa LE to these ribs.
Using the R1 rib angle guide, glue rib R1 to the upper and lower
spar and the LE edge. Using the R3 rib angle guide, adhere one R3 rib
to the spars and LE. Use scrap 1/8 balsa as a spacer between the R3
ribs, and glue the other R3 rib to the spars and LE. Glue the 1/4 balsa
TE to ribs R5 through R10.
Sand the spars and the LE flush with R1, and then, using the same
method you used for the inboard section of the wing, cut the slot for
the 1/4 plywood dihedral brace in ribs R1 and R2. Sheet the top of the
outer wing with 3/32 balsa, as shown on the plans.
When the sheeting is dry, remove the outer section from the
building board and fit it to the inboard section of the wing. Once you
are satisfied with the fit, glue the outer wing section to the inboard
section. I used a wood block to prop up the wingtip while the glue
dried.
Sheet the bottom of the wing with 3/32 balsa. The inboard section
and the outboard section are done separately, and the part that is not
being sheeted is blocked up to prevent the wing from warping.
I tried to sheet as much of the bottom of the wing without cutting
off the building tabs as I could. I did that by gluing the edge of the LE
sheeting to only the 3/8 balsa LE first. After the glue dried, I wet the
sheeting to make it easier to bend, applied glue to the ribs, and then
placed the wing back on the worktable right-side up and weighted it
until the sheeting dried.
Once the wing is sheeted, glue the 1/4 balsa TE in place, and then
sand the LE and TE to match the airfoil. Drill a hole for the 3/8-inchdiameter
antirotation pin, and glue the antirotation pin in place. Drill
and tap the hole for the 1/4 x 20 nylon wing-mounting bolt.
Repeat this whole process for the other wing. Build the ailerons.
Final Assembly: Go back and align and install the wing-joiner tube
Type: RC Sport Scale
Wingspan: 80 inches
Wing area: 622 square inches
Flying weight: 10 pounds
Wing loading: 37 ounces/square foot
Length: 73.25 inches
Power: Two .25 glow engines or two
MaxCim MaxN32-13Y direct-drive
motors
Fuel tank: Two 6-ounce Sullivan slant
tanks (glow)
Battery: 11.1-volt 4000 mAh Li-Poly
(for electric version)
Radio system: Five channels
Construction: Balsa and plywood
Covering/finish: MonoKote,
LustreKote paint
adjusted until it was straight, and then I glued F1 in place. I joined the
aft end of the fuselage in the same manner.
Glue the 1/4 balsa triangle to the nose-gear mount as shown on the
plans. Mount the nose gear to its mounting plate with 4-40 screws and
blind nuts. Glue the 1/8 plywood hatch mounting plate in place as
shown on the plans. Install the 1/8-inch cockpit floor.
Sheet the top and bottom of the fuselage with 3/16 balsa, glued on
so that the wood grain is crosswise to the fuselage sides. Set the
fuselage aside.
Wing: Pin the 3/8 x 1/4 lower inboard spruce spar to your worktable.
Glue an end cap of 3/32 balsa scrap on the outboard end of the wingjoiner
socket tubes. Glue the 1/4 plywood doublers to R1B. After the
glue has dried on the cap, slide the R1 ribs and R1B rib into place on
the wing-joiner tube socket; don’t glue the ribs to the joiner socket
yet.
Space the ribs on the tube, place them on the lower inboard spruce
spar, and glue them to the spar. Glue the ribs R1C to the spar, and
make sure the ribs are perpendicular to the spar vertically and
longitudinally. Insert the forward 1/4 square spruce spars and the
upper 3/8 x 1/4 spruce spar, and glue the ribs to the spars.
Glue the 3/8 balsa LE to this part of the wing. Sand the inboard
June 2005 21
Clothespins hold TE to 12-inch steel rule to keep them aligned to
each other while nacelles are being fitted to wing.
Aluminum angle bracket is used to hold engine nacelles in
alignment to each other while nacelles are glued to wing.
Engine nacelles are built in same manner as fuselage. For
simplicity’s sake there are no gear doors. Bottoms of nacelles
are left open.
socket in the fuselage. Flip the fuselage upside down on the worktable
and secure it so it won’t move. Glue one of the 1/8 plywood joiner
doublers inside one side of the fuselage.
Rough up the outside of the joiner tube socket with some
sandpaper, and insert the socket into the fuselage. Slip the other 1/8
plywood joiner doubler onto the socket as you insert it into the
fuselage, but don’t glue the socket or the doubler to the fuselage yet.
Insert the joiner tube into the socket so it is centered in the
fuselage and an equal length of the tube extends out of the fuselage on
either side. Measure the ends of the joiner tube to the worktable. Sand
the hole in the fuselage that does not have the plywood doubler on it
so that both ends of the joiner are an equal height above the work
surface. Use a carpenter’s square to square the joiner tube to the
fuselage sides also by sanding the hole without the doubler.
When you are satisfied that the joiner tube is square to the fuselage
side, block the joiner tube so that it cannot move, and then doublecheck
to make sure the joiner tubes’ ends are an equal height above
the work surface. Glue the plywood doubler and the joiner tube socket
to the fuselage side. Glue the other end of the joiner socket to the
other side of the fuselage.
The wing-joiner tube I bought was too long for the wings, so I
ended up cutting approximately 6 inches from it. I set this short piece
aside; it will be used to align the wings to each other as the nacelles
are mounted.
Slide the wings on the wing-joiner tube so that they fit snugly up
against the fuselage sides. Adjust the wing so that it is at 0°. Place the
1/8 plywood doubler on the antirotation pin and carefully adhere the
doubler to the fuselage side, being careful not to get any glue on the
antirotation pin. Use the same technique to glue the 1/8 plywood wingmount
bolt doubler to the fuselage side.
The engine nacelles are identical to each other except for the
landing-gear mounts. The nacelles are built like the fuselage, so I
won’t go into detail about the method used to construct them. Just
make sure that you build a left and a right one.
The method I used to align and mount the nacelles to the wings
should work if you plan to use electric or glow power. Because I
decided to go electric after my Neptune was nearly completed, I will
describe the method using glow engines.
You will need a roughly 3-foot section of aluminum angle, which
you can get in most hardware stores. It is used to hold the engines in
alignment with each other when you mount the nacelles to the wings.
Cut off approximately a 6-inch piece of the aluminum angle.
Mount both wings to the short scrap piece of the wing-joiner tube.
Slide the wings together as close as you can without letting the
antirotation pins interfere with each other. Clamp the 6-inch angle to
both wings’ TEs to keep the TEs aligned to each other.
On the finished model, the centerlines of the nacelles are 85/16
inches from the sides of the fuselage. Because the fuselage will
interfere with this method of mounting the nacelles, you will need to
compensate for the absence of the fuselage.
Measure the gap between the root ribs of the left and right wing,
and then add that amount to the 165/8-inch measurement. If the gap
is 2 inches, the total will be 185/8 inches. On your aluminum angle
drill two holes on center 185/8 inches apart. The diameter of the
holes will need to fit the prop shaft of the engines or motors you
plan to use.
Mount the engines to the nacelles, and then, using the prop shaft
of each engine, bolt the engines to the aluminum angle in the holes
you drilled. At this point the engines are aligned to each other. This is
important. The nacelles don’t really need to be aligned to each other,
but the engine thrustlines do.
Place the wing in the wing saddle of the nacelles, and adjust the
wing in the saddles so that the inside side of the nacelles are
approximately 69/16 inches from the edge of the wing root. Do not
adjust the gap between the wings. If you measured accurately, both
nacelles should be that length from the root rib.
Measure the distance from the wing LE to the aluminum angle at
the dihedral break on both wings. Adjust this distance so that the
measurement is the same on both wings. Check the engine
upthrust/downthrust line in relationship to the wing’s incidence with
an incidence meter, and sand the nacelles’ saddles so that the
thrustline is 0°.
The P2V Neptune’s completed framework is ready for covering. This model features extremely clean workmanship!
Full-Size Plans Available—see page 183
Once you are satisfied with all of these
measurements, tack-glue the nacelles to the
wings. Flip the wings over so you can glue
the nacelles to the wing with epoxy and glass
cloth on the inside of the nacelles. Carefully
unbolt the engines from the aluminum angle
and then separate the wings from each other.
Install the wings to the fuselage, and
mount the horizontal stabilizer so it is at 0°
incidence to the wing. Mount the vertical
stabilizer.
It is time to start all the little details such
as the dummy jet engines, the wingtip tanks,
the radomes, and the canopy. I made my
canopy and the forward observer’s canopy on
the nose from clear plastic, but you can carve
and sand a balsa block to shape if you want.
To supply some cooling air for the
batteries, I vacuum-formed the big radome
on the bottom of the fuselage from plastic.
On the front of the radome I cut some holes,
and on the bottom of the fuselage I cut holes
where the radome mounts. This allows the
radome to act like a big air scoop to cool the
batteries. I cut holes on the back end of the
fuselage hatch to allow the air to escape.
Radio Installation: This is fairly
straightforward. I used some flat wing servos
for the ailerons, and these needed to be
installed before I covered the wing. Before I
decided to switch to electric power, each
engine was to have had a separate throttle
servo that I planned to mount behind the
main landing gear in the nacelles.
I mounted the elevator, rudder, and retract
servos in the fuselage. An important thing
here is to make sure you have clear access to
the wing-mounting bolts in the fuselage.
Otherwise, mount the radio gear as you see
fit. After test-flying I found that aileron
differential is recommended along with some
rudder mixed into the ailerons.
Since this was my first electric-powered
twin, I decided to use one motor controller
and a separate battery pack for each motor,
and a servo “Y” harness to connect the motor
controllers to the receiver. I also used a
separate battery to power the receiver and
servos.
The fuel tanks need special attention
because the main landing gear will fold up
next to the tanks, and it is a tight fit. You will
need narrow tires and narrow fuel tanks, for
which I planned to use Sullivan 6-ounce slant
oval fuel tanks.
I also planned something different to
mount the fuel tanks. After the model was
finished and the nacelles were fuel-proofed, I
simply RTVed (room-temperature
vulcanized) the tanks to the inside of the
nacelles. Rough up the side of the fuel tank
with 80-grit sandpaper if you try this.
I mounted the ESCs for the motors using
Velcro in the place where I was going to
mount the fuel tanks. Using more Velcro, I
mounted the retract air tank to the inside top
of the fuselage just behind the cockpit.
Finishing: I covered my model with
MonoKote in the color scheme that US Navy
patrol squadrons used in the 1960s. If you
want a more visible scheme, you could try
one with a red tail that the naval reserve
squadrons used or use the colors that are on
some of the forest-fire-fighting versions.
Some Neptunes were used to launch drones
and missiles and had highly visible
appearances. There is much information
about this airplane on the Internet.
I sanded the dummy jet engines and tip
tanks smooth and filled the grain, and then I
painted them with LustreKote. All of the
markings are trim MonoKote.
For those who plan to use glow engines, I
will describe the method I have used on my
previous glow-powered, twin-engine models
to set up the power plants. Before you fly
your airplane, make sure both engines are
properly adjusted on the ground so that they
are reliable. I don’t bother to get them
synchronized to each other; I try to get them
to run dependably.
I set each engine independently for a
reliable idle with a smooth transition to high
speed. I set the high-speed needle by
pinching the fuel line and noting a slight rise
in the rpm without the engine dying. I point
the model’s nose straight up and straight
down to see if the engine sags or dies. I also
do this with the engine at idle.
Once I have both engines running reliably
one at a time, I run both at the same time and
check each engine using the same methods. I
do all of this at home so I don’t feel pressured
to fly the model. This also gives me a chance
to make sure nothing shakes loose.
I’m right-handed, so I start the left
engine first on my twins. This makes it
easier to stay out of the way of the left
engine while I start the right engine.
Flying: I balanced my Neptune 27/8 inches
behind the wing’s LE. After test-flying, I
feel that this is probably the farthest aft I
recommend to balance the model for good,
smooth flying.
I had to wait what seemed like forever
for the weather to cooperate—it was either
too windy or raining—but I was finally able
to sneak out early in the morning and testfly
my Neptune before the wind picked up.
After I assembled it at the field, I did a
range check of the radio with the motors
running.
I taxied the model to the end of the
runway and pointed it into the wind. I
advanced the throttles, and after roughly 150
feet I started to ease in some up-elevator. I
was pleasantly surprised when the airplane
gently rotated and started to climb out at a
nice, realistic climb rate.
It seemed to be flying well, so I flipped
the landing-gear switch, only to be
dismayed to see just the nose wheel and the
left main wheel retract. I flipped the gear
switch to the down position, and the nose
wheel came down and the left main wheel
stayed up!
I wasn’t going to let this ruin my test
flight, so I continued by climbing the model
to altitude to check the trims. My Neptune
required only some up-trim with the throttles
pulled back to a realistic cruise speed.
After cruising around for a few minutes,
I throttled down to check the stall
characteristics. My Neptune slowed better
than I expected, but it had a sharp stall. If
you build one, keep the airspeed up on the
landing approach. I did a few low passes
down the runway and then I tried a few
practice approaches.
When I finally decided to land the
Neptune, I was able to put it down gently,
but the nose gear collapsed and it skidded
down the runway on the radome and left
dummy jet engine. I was surprised that the
nacelle and the radome held up (I thought
they were going to be destroyed), but my
Neptune ended up with only some paint
scraped off the radome and the left jet
engine.
After learning that the landing-gear air
valve had a small leak, I locked the gear
down and did one more flight that day with
no problems. My model ended up weighing
just less than 10 pounds ready to fly, which
was slightly heavier than I wanted, but the
motors provide more than enough power for
flight.
The Neptune’s glide is a tad steep, but I
suppose two propellers windmilling creates
quite a bit of drag. Carry some power on the
landing approach, and as the Neptune gets
near the ground, slowly reduce power and
bleed the airspeed off with the elevator.
With practice you should be able to grease it
in on the mains and roll out a short distance
before the nose wheel comes down.
Final Thoughts: This has been one of the
most enjoyable models I have built in
awhile. It went together much better than I
expected, the flight characteristics are better
than I expected, and it looks great in the air.
The last-minute conversion to electric
power was a good move, and it has
convinced me that this is the way to go on
my future airplanes. MA
Gary Fuller
7076 E. Heather Dr.
Claremore OK 74019
[email protected]
Edition: Model Aviation - 2005/06
Page Numbers: 18,19,20,21,22,24,26
18 MODEL AVIATION
by Gary Fuller
DURING THE FIRST part of the Cold War, the P2V Neptune
was the US Navy’s primary long-range, land-based, antisubmarine
patrol aircraft. Designed in 1944 as a replacement for the PV-1
Ventura and the PV-2 Harpoon, the Neptune’s versatility ensured
that it would remain in service for a long time. Its last use in
combat was by the Argentineans against the British during the fight
over the Falkland Islands.
The Neptune is still being used, to fight forest fires in the
United States. With the installation of a mad boom on the tail, the
addition of a pair of jet engines, and many other minor
modifications, the later versions of the Neptune bore little
resemblance to the early production P2Vs.
I have always had a soft spot in my heart for historical airplanes
that are seldom modeled. The Neptune’s straightforward lines
ensure a good-flying model, yet the mad boom, radomes, jet
engines, and various other components give it considerable
character that would make it unique at the flying field.
I didn’t want an all-out competition-quality Scale model, so to
simplify it I used an easy-to-build box type of fuselage that is not
much different from what most trainer-type aircraft have. The
engine nacelles are also the box type, with the bottom left open so
you don’t have to mess with any finicky landing-gear doors. The
nacelles are glued to the wing with some glass cloth for
reinforcement.
The inboard section of the wing is fully sheeted and the
outboard section of the wing uses typical D-tube construction. The
jet engines and wingtip fuel tanks are balsa blocks carved and
sanded to shape. The wing is mounted to the fuselage with a joiner
tube so the model can be disassembled for transport to and from
the flying field.
I wanted to make the Neptune as large as possible yet
economical to build and fly, so I decided to build it with an 80-inch
wingspan. Power was to be a pair of O.S. .25 engines, but I was
bitten by the electric bug during the time I was building the model.
While researching motors for a future project, I realized that I
could easily mount electric power plants to my Neptune with no
major rework. I was in the process of covering the airplane when I
decided to make the change to electric power!
RC version of US Navy patrol
aircraft can be powered with
engines or motors
On right fuselage side you can see 1/4 balsa triangle stock,
forward fuselage doubler, formers F2 and F3, and nose-wheel
mounting plate installed.
Forward fuselage after joining the sides. This is a good time to
mount nose gear. Nose-wheel mount has been reinforced with 1/4
balsa triangle stock.
Upper fuselage sheeting is being installed. Author used Ambroid
glue here so the glue joint will be easier to sand when shaping
top of sheeting. Many T-pins hold sheeting in place as glue dries.
Carpenter’s square and sharpened brass tube are used to cut
slot for 1/4 plywood dihedral brace. One of R3 ribs has been
glued to spars using R3 angle guide; other R3 rib is being glued
to spar using 1/8 scrap wood to set distance between them.
I used a pair of MaxCim MaxN32-13Y motors direct drive
spinning APC 10 x 5E propellers. The motor controllers are MaxCim
Maxμ35D-21. I used 2000 mAh Kokam Li-Poly batteries wired 3S2P,
for a total of 11.1 volts and 4000 mAh for each motor. That easily gave
me a flight time exceeding 10 minutes with the motors throttled back
and more than adequate power to take off from a grass field.
The retractable gear is the standard size, and normal modeling
techniques are used to build the Neptune. If you have never built a
model from plans, this should not be too difficult—especially if you
have a few kits under your belt.
Since this is not really a beginner’s airplane, I won’t go into much
detail in the construction notes. I did not take any great pains to keep
the weight down on my Neptune, I did not use contest-grade balsa, nor
did I cut lightening holes in any of the sheet balsa. However, I am quite
sure that if you used contest-grade wood and other weight-saving
techniques, you could shave some weight from your Neptune.
CONSTRUCTION
I started my model by cutting all the parts and assembling them like
a kit. If you have never built from plans, I recommend the following.
To accurately cut the small parts from wood, cut the parts from the
plans and then lightly spray the backside of a paper cutout with contact
glue. When it has dried for approximately 10 minutes, to a light tack,
place the paper shape for the part on the wood, and then cut the wood
using a band saw or a jigsaw. Remove the paper after you have cut the
part.
To cut more than one of the same part, do the same thing as in the
preceding and then lightly spray both sides of some scrap paper with
contact glue. Sandwich this paper between as many sheets of wood as
necessary for the number of parts required. Cut the stack of wood
with a band saw or jigsaw. Once the stack is cut, separate each piece
and remove the paper.
If you have never done this, try it on scrap wood and paper first. I
have found that some brands of contact glue won’t work because
they are too tacky. I use carpet and headliner glue that comes in a
spray can and is available in auto-part stores. A good alternative is
Elmer’s school glue stick; it works as well without the mess.
Fuselage: The fuselage sides are too long and wide to cut from a
single sheet of balsa, so you will need to splice some sheets together.
I like to have the vertical splice where the wing doubler will
reinforce the joint. Be careful with the sides until the doublers are
installed. I like to lay the fuselage sides next to each other top to top
as I glue on the various parts; that way I won’t make two left or two
right sides.
Start the fuselage by gluing the 1/4 balsa triangle stock to the sides
as shown on the plans. Glue the doublers for the wing and forward
fuselage to the fuselage sides. Glue formers F2 through F5 to one
fuselage side, and then glue the nose-wheel mounting plate to F2 and
the side to which F2 is glued.
Glue the 1/4 x 3/8 balsa side stiffeners in place as shown on the
plans. Once the adhesive has dried, join the fuselage sides. I did this
by standing the side with the formers up on its bottom and then
placing the other side in place. Once I was satisfied with the fit of the
other side, I glued it to the formers.
I joined the forward end of the fuselage by weighting the fuselage
to the table and then using some clamps to draw the ends together until
former F1 would fit. I checked the alignment of the fuselage and
Photos by the author
20 MODEL AVIATION
Make both ends of wing-joiner tube same height above table so
wing will be square to fuselage from the top.
spars and the LE flush with the outermost R1C rib.
You will need to cut the R1C ribs for the 1/4 plywood dihedral
brace, I did this by using a 1/4-inch-outside-diameter brass tube that
was sharpened at one end. I used the tube to cut holes in the R1C ribs
at the dihedral brace’s location, using a carpenter square as a guide.
After the holes were cut, I used a file to finish the slot in the ribs
for the dihedral brace. Glue the dihedral brace to the ribs and the spar
after you are satisfied with the fit.
Carefully pull the wing-joiner socket tube from the wing and rough
it up with 80-grit sandpaper. Reinsert the socket tube in the wing and
glue it to the ribs. Glue some scrap balsa between the socket tube and
the 3/8 x 1/4 spars. Sheet the top of the inboard section with 3/32 balsa.
Once the glue for the sheeting has dried, remove the inboard
portion of the wing and set it aside.
Start the outboard section of the wing by pinning the lower
outboard 3/8 x 1/4 spruce spar to the plans. Glue the R2 and R4 through
R10 ribs to the spar. Position the R1 and R3 ribs on the spar, but do
not glue them in place yet. Place the upper 3/8 x 1/4 spruce spar on the
ribs and glue it to the R2 and R4 through R10 ribs. Also glue the 3/8
balsa LE to these ribs.
Using the R1 rib angle guide, glue rib R1 to the upper and lower
spar and the LE edge. Using the R3 rib angle guide, adhere one R3 rib
to the spars and LE. Use scrap 1/8 balsa as a spacer between the R3
ribs, and glue the other R3 rib to the spars and LE. Glue the 1/4 balsa
TE to ribs R5 through R10.
Sand the spars and the LE flush with R1, and then, using the same
method you used for the inboard section of the wing, cut the slot for
the 1/4 plywood dihedral brace in ribs R1 and R2. Sheet the top of the
outer wing with 3/32 balsa, as shown on the plans.
When the sheeting is dry, remove the outer section from the
building board and fit it to the inboard section of the wing. Once you
are satisfied with the fit, glue the outer wing section to the inboard
section. I used a wood block to prop up the wingtip while the glue
dried.
Sheet the bottom of the wing with 3/32 balsa. The inboard section
and the outboard section are done separately, and the part that is not
being sheeted is blocked up to prevent the wing from warping.
I tried to sheet as much of the bottom of the wing without cutting
off the building tabs as I could. I did that by gluing the edge of the LE
sheeting to only the 3/8 balsa LE first. After the glue dried, I wet the
sheeting to make it easier to bend, applied glue to the ribs, and then
placed the wing back on the worktable right-side up and weighted it
until the sheeting dried.
Once the wing is sheeted, glue the 1/4 balsa TE in place, and then
sand the LE and TE to match the airfoil. Drill a hole for the 3/8-inchdiameter
antirotation pin, and glue the antirotation pin in place. Drill
and tap the hole for the 1/4 x 20 nylon wing-mounting bolt.
Repeat this whole process for the other wing. Build the ailerons.
Final Assembly: Go back and align and install the wing-joiner tube
Type: RC Sport Scale
Wingspan: 80 inches
Wing area: 622 square inches
Flying weight: 10 pounds
Wing loading: 37 ounces/square foot
Length: 73.25 inches
Power: Two .25 glow engines or two
MaxCim MaxN32-13Y direct-drive
motors
Fuel tank: Two 6-ounce Sullivan slant
tanks (glow)
Battery: 11.1-volt 4000 mAh Li-Poly
(for electric version)
Radio system: Five channels
Construction: Balsa and plywood
Covering/finish: MonoKote,
LustreKote paint
adjusted until it was straight, and then I glued F1 in place. I joined the
aft end of the fuselage in the same manner.
Glue the 1/4 balsa triangle to the nose-gear mount as shown on the
plans. Mount the nose gear to its mounting plate with 4-40 screws and
blind nuts. Glue the 1/8 plywood hatch mounting plate in place as
shown on the plans. Install the 1/8-inch cockpit floor.
Sheet the top and bottom of the fuselage with 3/16 balsa, glued on
so that the wood grain is crosswise to the fuselage sides. Set the
fuselage aside.
Wing: Pin the 3/8 x 1/4 lower inboard spruce spar to your worktable.
Glue an end cap of 3/32 balsa scrap on the outboard end of the wingjoiner
socket tubes. Glue the 1/4 plywood doublers to R1B. After the
glue has dried on the cap, slide the R1 ribs and R1B rib into place on
the wing-joiner tube socket; don’t glue the ribs to the joiner socket
yet.
Space the ribs on the tube, place them on the lower inboard spruce
spar, and glue them to the spar. Glue the ribs R1C to the spar, and
make sure the ribs are perpendicular to the spar vertically and
longitudinally. Insert the forward 1/4 square spruce spars and the
upper 3/8 x 1/4 spruce spar, and glue the ribs to the spars.
Glue the 3/8 balsa LE to this part of the wing. Sand the inboard
June 2005 21
Clothespins hold TE to 12-inch steel rule to keep them aligned to
each other while nacelles are being fitted to wing.
Aluminum angle bracket is used to hold engine nacelles in
alignment to each other while nacelles are glued to wing.
Engine nacelles are built in same manner as fuselage. For
simplicity’s sake there are no gear doors. Bottoms of nacelles
are left open.
socket in the fuselage. Flip the fuselage upside down on the worktable
and secure it so it won’t move. Glue one of the 1/8 plywood joiner
doublers inside one side of the fuselage.
Rough up the outside of the joiner tube socket with some
sandpaper, and insert the socket into the fuselage. Slip the other 1/8
plywood joiner doubler onto the socket as you insert it into the
fuselage, but don’t glue the socket or the doubler to the fuselage yet.
Insert the joiner tube into the socket so it is centered in the
fuselage and an equal length of the tube extends out of the fuselage on
either side. Measure the ends of the joiner tube to the worktable. Sand
the hole in the fuselage that does not have the plywood doubler on it
so that both ends of the joiner are an equal height above the work
surface. Use a carpenter’s square to square the joiner tube to the
fuselage sides also by sanding the hole without the doubler.
When you are satisfied that the joiner tube is square to the fuselage
side, block the joiner tube so that it cannot move, and then doublecheck
to make sure the joiner tubes’ ends are an equal height above
the work surface. Glue the plywood doubler and the joiner tube socket
to the fuselage side. Glue the other end of the joiner socket to the
other side of the fuselage.
The wing-joiner tube I bought was too long for the wings, so I
ended up cutting approximately 6 inches from it. I set this short piece
aside; it will be used to align the wings to each other as the nacelles
are mounted.
Slide the wings on the wing-joiner tube so that they fit snugly up
against the fuselage sides. Adjust the wing so that it is at 0°. Place the
1/8 plywood doubler on the antirotation pin and carefully adhere the
doubler to the fuselage side, being careful not to get any glue on the
antirotation pin. Use the same technique to glue the 1/8 plywood wingmount
bolt doubler to the fuselage side.
The engine nacelles are identical to each other except for the
landing-gear mounts. The nacelles are built like the fuselage, so I
won’t go into detail about the method used to construct them. Just
make sure that you build a left and a right one.
The method I used to align and mount the nacelles to the wings
should work if you plan to use electric or glow power. Because I
decided to go electric after my Neptune was nearly completed, I will
describe the method using glow engines.
You will need a roughly 3-foot section of aluminum angle, which
you can get in most hardware stores. It is used to hold the engines in
alignment with each other when you mount the nacelles to the wings.
Cut off approximately a 6-inch piece of the aluminum angle.
Mount both wings to the short scrap piece of the wing-joiner tube.
Slide the wings together as close as you can without letting the
antirotation pins interfere with each other. Clamp the 6-inch angle to
both wings’ TEs to keep the TEs aligned to each other.
On the finished model, the centerlines of the nacelles are 85/16
inches from the sides of the fuselage. Because the fuselage will
interfere with this method of mounting the nacelles, you will need to
compensate for the absence of the fuselage.
Measure the gap between the root ribs of the left and right wing,
and then add that amount to the 165/8-inch measurement. If the gap
is 2 inches, the total will be 185/8 inches. On your aluminum angle
drill two holes on center 185/8 inches apart. The diameter of the
holes will need to fit the prop shaft of the engines or motors you
plan to use.
Mount the engines to the nacelles, and then, using the prop shaft
of each engine, bolt the engines to the aluminum angle in the holes
you drilled. At this point the engines are aligned to each other. This is
important. The nacelles don’t really need to be aligned to each other,
but the engine thrustlines do.
Place the wing in the wing saddle of the nacelles, and adjust the
wing in the saddles so that the inside side of the nacelles are
approximately 69/16 inches from the edge of the wing root. Do not
adjust the gap between the wings. If you measured accurately, both
nacelles should be that length from the root rib.
Measure the distance from the wing LE to the aluminum angle at
the dihedral break on both wings. Adjust this distance so that the
measurement is the same on both wings. Check the engine
upthrust/downthrust line in relationship to the wing’s incidence with
an incidence meter, and sand the nacelles’ saddles so that the
thrustline is 0°.
The P2V Neptune’s completed framework is ready for covering. This model features extremely clean workmanship!
Full-Size Plans Available—see page 183
Once you are satisfied with all of these
measurements, tack-glue the nacelles to the
wings. Flip the wings over so you can glue
the nacelles to the wing with epoxy and glass
cloth on the inside of the nacelles. Carefully
unbolt the engines from the aluminum angle
and then separate the wings from each other.
Install the wings to the fuselage, and
mount the horizontal stabilizer so it is at 0°
incidence to the wing. Mount the vertical
stabilizer.
It is time to start all the little details such
as the dummy jet engines, the wingtip tanks,
the radomes, and the canopy. I made my
canopy and the forward observer’s canopy on
the nose from clear plastic, but you can carve
and sand a balsa block to shape if you want.
To supply some cooling air for the
batteries, I vacuum-formed the big radome
on the bottom of the fuselage from plastic.
On the front of the radome I cut some holes,
and on the bottom of the fuselage I cut holes
where the radome mounts. This allows the
radome to act like a big air scoop to cool the
batteries. I cut holes on the back end of the
fuselage hatch to allow the air to escape.
Radio Installation: This is fairly
straightforward. I used some flat wing servos
for the ailerons, and these needed to be
installed before I covered the wing. Before I
decided to switch to electric power, each
engine was to have had a separate throttle
servo that I planned to mount behind the
main landing gear in the nacelles.
I mounted the elevator, rudder, and retract
servos in the fuselage. An important thing
here is to make sure you have clear access to
the wing-mounting bolts in the fuselage.
Otherwise, mount the radio gear as you see
fit. After test-flying I found that aileron
differential is recommended along with some
rudder mixed into the ailerons.
Since this was my first electric-powered
twin, I decided to use one motor controller
and a separate battery pack for each motor,
and a servo “Y” harness to connect the motor
controllers to the receiver. I also used a
separate battery to power the receiver and
servos.
The fuel tanks need special attention
because the main landing gear will fold up
next to the tanks, and it is a tight fit. You will
need narrow tires and narrow fuel tanks, for
which I planned to use Sullivan 6-ounce slant
oval fuel tanks.
I also planned something different to
mount the fuel tanks. After the model was
finished and the nacelles were fuel-proofed, I
simply RTVed (room-temperature
vulcanized) the tanks to the inside of the
nacelles. Rough up the side of the fuel tank
with 80-grit sandpaper if you try this.
I mounted the ESCs for the motors using
Velcro in the place where I was going to
mount the fuel tanks. Using more Velcro, I
mounted the retract air tank to the inside top
of the fuselage just behind the cockpit.
Finishing: I covered my model with
MonoKote in the color scheme that US Navy
patrol squadrons used in the 1960s. If you
want a more visible scheme, you could try
one with a red tail that the naval reserve
squadrons used or use the colors that are on
some of the forest-fire-fighting versions.
Some Neptunes were used to launch drones
and missiles and had highly visible
appearances. There is much information
about this airplane on the Internet.
I sanded the dummy jet engines and tip
tanks smooth and filled the grain, and then I
painted them with LustreKote. All of the
markings are trim MonoKote.
For those who plan to use glow engines, I
will describe the method I have used on my
previous glow-powered, twin-engine models
to set up the power plants. Before you fly
your airplane, make sure both engines are
properly adjusted on the ground so that they
are reliable. I don’t bother to get them
synchronized to each other; I try to get them
to run dependably.
I set each engine independently for a
reliable idle with a smooth transition to high
speed. I set the high-speed needle by
pinching the fuel line and noting a slight rise
in the rpm without the engine dying. I point
the model’s nose straight up and straight
down to see if the engine sags or dies. I also
do this with the engine at idle.
Once I have both engines running reliably
one at a time, I run both at the same time and
check each engine using the same methods. I
do all of this at home so I don’t feel pressured
to fly the model. This also gives me a chance
to make sure nothing shakes loose.
I’m right-handed, so I start the left
engine first on my twins. This makes it
easier to stay out of the way of the left
engine while I start the right engine.
Flying: I balanced my Neptune 27/8 inches
behind the wing’s LE. After test-flying, I
feel that this is probably the farthest aft I
recommend to balance the model for good,
smooth flying.
I had to wait what seemed like forever
for the weather to cooperate—it was either
too windy or raining—but I was finally able
to sneak out early in the morning and testfly
my Neptune before the wind picked up.
After I assembled it at the field, I did a
range check of the radio with the motors
running.
I taxied the model to the end of the
runway and pointed it into the wind. I
advanced the throttles, and after roughly 150
feet I started to ease in some up-elevator. I
was pleasantly surprised when the airplane
gently rotated and started to climb out at a
nice, realistic climb rate.
It seemed to be flying well, so I flipped
the landing-gear switch, only to be
dismayed to see just the nose wheel and the
left main wheel retract. I flipped the gear
switch to the down position, and the nose
wheel came down and the left main wheel
stayed up!
I wasn’t going to let this ruin my test
flight, so I continued by climbing the model
to altitude to check the trims. My Neptune
required only some up-trim with the throttles
pulled back to a realistic cruise speed.
After cruising around for a few minutes,
I throttled down to check the stall
characteristics. My Neptune slowed better
than I expected, but it had a sharp stall. If
you build one, keep the airspeed up on the
landing approach. I did a few low passes
down the runway and then I tried a few
practice approaches.
When I finally decided to land the
Neptune, I was able to put it down gently,
but the nose gear collapsed and it skidded
down the runway on the radome and left
dummy jet engine. I was surprised that the
nacelle and the radome held up (I thought
they were going to be destroyed), but my
Neptune ended up with only some paint
scraped off the radome and the left jet
engine.
After learning that the landing-gear air
valve had a small leak, I locked the gear
down and did one more flight that day with
no problems. My model ended up weighing
just less than 10 pounds ready to fly, which
was slightly heavier than I wanted, but the
motors provide more than enough power for
flight.
The Neptune’s glide is a tad steep, but I
suppose two propellers windmilling creates
quite a bit of drag. Carry some power on the
landing approach, and as the Neptune gets
near the ground, slowly reduce power and
bleed the airspeed off with the elevator.
With practice you should be able to grease it
in on the mains and roll out a short distance
before the nose wheel comes down.
Final Thoughts: This has been one of the
most enjoyable models I have built in
awhile. It went together much better than I
expected, the flight characteristics are better
than I expected, and it looks great in the air.
The last-minute conversion to electric
power was a good move, and it has
convinced me that this is the way to go on
my future airplanes. MA
Gary Fuller
7076 E. Heather Dr.
Claremore OK 74019
[email protected]
Edition: Model Aviation - 2005/06
Page Numbers: 18,19,20,21,22,24,26
18 MODEL AVIATION
by Gary Fuller
DURING THE FIRST part of the Cold War, the P2V Neptune
was the US Navy’s primary long-range, land-based, antisubmarine
patrol aircraft. Designed in 1944 as a replacement for the PV-1
Ventura and the PV-2 Harpoon, the Neptune’s versatility ensured
that it would remain in service for a long time. Its last use in
combat was by the Argentineans against the British during the fight
over the Falkland Islands.
The Neptune is still being used, to fight forest fires in the
United States. With the installation of a mad boom on the tail, the
addition of a pair of jet engines, and many other minor
modifications, the later versions of the Neptune bore little
resemblance to the early production P2Vs.
I have always had a soft spot in my heart for historical airplanes
that are seldom modeled. The Neptune’s straightforward lines
ensure a good-flying model, yet the mad boom, radomes, jet
engines, and various other components give it considerable
character that would make it unique at the flying field.
I didn’t want an all-out competition-quality Scale model, so to
simplify it I used an easy-to-build box type of fuselage that is not
much different from what most trainer-type aircraft have. The
engine nacelles are also the box type, with the bottom left open so
you don’t have to mess with any finicky landing-gear doors. The
nacelles are glued to the wing with some glass cloth for
reinforcement.
The inboard section of the wing is fully sheeted and the
outboard section of the wing uses typical D-tube construction. The
jet engines and wingtip fuel tanks are balsa blocks carved and
sanded to shape. The wing is mounted to the fuselage with a joiner
tube so the model can be disassembled for transport to and from
the flying field.
I wanted to make the Neptune as large as possible yet
economical to build and fly, so I decided to build it with an 80-inch
wingspan. Power was to be a pair of O.S. .25 engines, but I was
bitten by the electric bug during the time I was building the model.
While researching motors for a future project, I realized that I
could easily mount electric power plants to my Neptune with no
major rework. I was in the process of covering the airplane when I
decided to make the change to electric power!
RC version of US Navy patrol
aircraft can be powered with
engines or motors
On right fuselage side you can see 1/4 balsa triangle stock,
forward fuselage doubler, formers F2 and F3, and nose-wheel
mounting plate installed.
Forward fuselage after joining the sides. This is a good time to
mount nose gear. Nose-wheel mount has been reinforced with 1/4
balsa triangle stock.
Upper fuselage sheeting is being installed. Author used Ambroid
glue here so the glue joint will be easier to sand when shaping
top of sheeting. Many T-pins hold sheeting in place as glue dries.
Carpenter’s square and sharpened brass tube are used to cut
slot for 1/4 plywood dihedral brace. One of R3 ribs has been
glued to spars using R3 angle guide; other R3 rib is being glued
to spar using 1/8 scrap wood to set distance between them.
I used a pair of MaxCim MaxN32-13Y motors direct drive
spinning APC 10 x 5E propellers. The motor controllers are MaxCim
Maxμ35D-21. I used 2000 mAh Kokam Li-Poly batteries wired 3S2P,
for a total of 11.1 volts and 4000 mAh for each motor. That easily gave
me a flight time exceeding 10 minutes with the motors throttled back
and more than adequate power to take off from a grass field.
The retractable gear is the standard size, and normal modeling
techniques are used to build the Neptune. If you have never built a
model from plans, this should not be too difficult—especially if you
have a few kits under your belt.
Since this is not really a beginner’s airplane, I won’t go into much
detail in the construction notes. I did not take any great pains to keep
the weight down on my Neptune, I did not use contest-grade balsa, nor
did I cut lightening holes in any of the sheet balsa. However, I am quite
sure that if you used contest-grade wood and other weight-saving
techniques, you could shave some weight from your Neptune.
CONSTRUCTION
I started my model by cutting all the parts and assembling them like
a kit. If you have never built from plans, I recommend the following.
To accurately cut the small parts from wood, cut the parts from the
plans and then lightly spray the backside of a paper cutout with contact
glue. When it has dried for approximately 10 minutes, to a light tack,
place the paper shape for the part on the wood, and then cut the wood
using a band saw or a jigsaw. Remove the paper after you have cut the
part.
To cut more than one of the same part, do the same thing as in the
preceding and then lightly spray both sides of some scrap paper with
contact glue. Sandwich this paper between as many sheets of wood as
necessary for the number of parts required. Cut the stack of wood
with a band saw or jigsaw. Once the stack is cut, separate each piece
and remove the paper.
If you have never done this, try it on scrap wood and paper first. I
have found that some brands of contact glue won’t work because
they are too tacky. I use carpet and headliner glue that comes in a
spray can and is available in auto-part stores. A good alternative is
Elmer’s school glue stick; it works as well without the mess.
Fuselage: The fuselage sides are too long and wide to cut from a
single sheet of balsa, so you will need to splice some sheets together.
I like to have the vertical splice where the wing doubler will
reinforce the joint. Be careful with the sides until the doublers are
installed. I like to lay the fuselage sides next to each other top to top
as I glue on the various parts; that way I won’t make two left or two
right sides.
Start the fuselage by gluing the 1/4 balsa triangle stock to the sides
as shown on the plans. Glue the doublers for the wing and forward
fuselage to the fuselage sides. Glue formers F2 through F5 to one
fuselage side, and then glue the nose-wheel mounting plate to F2 and
the side to which F2 is glued.
Glue the 1/4 x 3/8 balsa side stiffeners in place as shown on the
plans. Once the adhesive has dried, join the fuselage sides. I did this
by standing the side with the formers up on its bottom and then
placing the other side in place. Once I was satisfied with the fit of the
other side, I glued it to the formers.
I joined the forward end of the fuselage by weighting the fuselage
to the table and then using some clamps to draw the ends together until
former F1 would fit. I checked the alignment of the fuselage and
Photos by the author
20 MODEL AVIATION
Make both ends of wing-joiner tube same height above table so
wing will be square to fuselage from the top.
spars and the LE flush with the outermost R1C rib.
You will need to cut the R1C ribs for the 1/4 plywood dihedral
brace, I did this by using a 1/4-inch-outside-diameter brass tube that
was sharpened at one end. I used the tube to cut holes in the R1C ribs
at the dihedral brace’s location, using a carpenter square as a guide.
After the holes were cut, I used a file to finish the slot in the ribs
for the dihedral brace. Glue the dihedral brace to the ribs and the spar
after you are satisfied with the fit.
Carefully pull the wing-joiner socket tube from the wing and rough
it up with 80-grit sandpaper. Reinsert the socket tube in the wing and
glue it to the ribs. Glue some scrap balsa between the socket tube and
the 3/8 x 1/4 spars. Sheet the top of the inboard section with 3/32 balsa.
Once the glue for the sheeting has dried, remove the inboard
portion of the wing and set it aside.
Start the outboard section of the wing by pinning the lower
outboard 3/8 x 1/4 spruce spar to the plans. Glue the R2 and R4 through
R10 ribs to the spar. Position the R1 and R3 ribs on the spar, but do
not glue them in place yet. Place the upper 3/8 x 1/4 spruce spar on the
ribs and glue it to the R2 and R4 through R10 ribs. Also glue the 3/8
balsa LE to these ribs.
Using the R1 rib angle guide, glue rib R1 to the upper and lower
spar and the LE edge. Using the R3 rib angle guide, adhere one R3 rib
to the spars and LE. Use scrap 1/8 balsa as a spacer between the R3
ribs, and glue the other R3 rib to the spars and LE. Glue the 1/4 balsa
TE to ribs R5 through R10.
Sand the spars and the LE flush with R1, and then, using the same
method you used for the inboard section of the wing, cut the slot for
the 1/4 plywood dihedral brace in ribs R1 and R2. Sheet the top of the
outer wing with 3/32 balsa, as shown on the plans.
When the sheeting is dry, remove the outer section from the
building board and fit it to the inboard section of the wing. Once you
are satisfied with the fit, glue the outer wing section to the inboard
section. I used a wood block to prop up the wingtip while the glue
dried.
Sheet the bottom of the wing with 3/32 balsa. The inboard section
and the outboard section are done separately, and the part that is not
being sheeted is blocked up to prevent the wing from warping.
I tried to sheet as much of the bottom of the wing without cutting
off the building tabs as I could. I did that by gluing the edge of the LE
sheeting to only the 3/8 balsa LE first. After the glue dried, I wet the
sheeting to make it easier to bend, applied glue to the ribs, and then
placed the wing back on the worktable right-side up and weighted it
until the sheeting dried.
Once the wing is sheeted, glue the 1/4 balsa TE in place, and then
sand the LE and TE to match the airfoil. Drill a hole for the 3/8-inchdiameter
antirotation pin, and glue the antirotation pin in place. Drill
and tap the hole for the 1/4 x 20 nylon wing-mounting bolt.
Repeat this whole process for the other wing. Build the ailerons.
Final Assembly: Go back and align and install the wing-joiner tube
Type: RC Sport Scale
Wingspan: 80 inches
Wing area: 622 square inches
Flying weight: 10 pounds
Wing loading: 37 ounces/square foot
Length: 73.25 inches
Power: Two .25 glow engines or two
MaxCim MaxN32-13Y direct-drive
motors
Fuel tank: Two 6-ounce Sullivan slant
tanks (glow)
Battery: 11.1-volt 4000 mAh Li-Poly
(for electric version)
Radio system: Five channels
Construction: Balsa and plywood
Covering/finish: MonoKote,
LustreKote paint
adjusted until it was straight, and then I glued F1 in place. I joined the
aft end of the fuselage in the same manner.
Glue the 1/4 balsa triangle to the nose-gear mount as shown on the
plans. Mount the nose gear to its mounting plate with 4-40 screws and
blind nuts. Glue the 1/8 plywood hatch mounting plate in place as
shown on the plans. Install the 1/8-inch cockpit floor.
Sheet the top and bottom of the fuselage with 3/16 balsa, glued on
so that the wood grain is crosswise to the fuselage sides. Set the
fuselage aside.
Wing: Pin the 3/8 x 1/4 lower inboard spruce spar to your worktable.
Glue an end cap of 3/32 balsa scrap on the outboard end of the wingjoiner
socket tubes. Glue the 1/4 plywood doublers to R1B. After the
glue has dried on the cap, slide the R1 ribs and R1B rib into place on
the wing-joiner tube socket; don’t glue the ribs to the joiner socket
yet.
Space the ribs on the tube, place them on the lower inboard spruce
spar, and glue them to the spar. Glue the ribs R1C to the spar, and
make sure the ribs are perpendicular to the spar vertically and
longitudinally. Insert the forward 1/4 square spruce spars and the
upper 3/8 x 1/4 spruce spar, and glue the ribs to the spars.
Glue the 3/8 balsa LE to this part of the wing. Sand the inboard
June 2005 21
Clothespins hold TE to 12-inch steel rule to keep them aligned to
each other while nacelles are being fitted to wing.
Aluminum angle bracket is used to hold engine nacelles in
alignment to each other while nacelles are glued to wing.
Engine nacelles are built in same manner as fuselage. For
simplicity’s sake there are no gear doors. Bottoms of nacelles
are left open.
socket in the fuselage. Flip the fuselage upside down on the worktable
and secure it so it won’t move. Glue one of the 1/8 plywood joiner
doublers inside one side of the fuselage.
Rough up the outside of the joiner tube socket with some
sandpaper, and insert the socket into the fuselage. Slip the other 1/8
plywood joiner doubler onto the socket as you insert it into the
fuselage, but don’t glue the socket or the doubler to the fuselage yet.
Insert the joiner tube into the socket so it is centered in the
fuselage and an equal length of the tube extends out of the fuselage on
either side. Measure the ends of the joiner tube to the worktable. Sand
the hole in the fuselage that does not have the plywood doubler on it
so that both ends of the joiner are an equal height above the work
surface. Use a carpenter’s square to square the joiner tube to the
fuselage sides also by sanding the hole without the doubler.
When you are satisfied that the joiner tube is square to the fuselage
side, block the joiner tube so that it cannot move, and then doublecheck
to make sure the joiner tubes’ ends are an equal height above
the work surface. Glue the plywood doubler and the joiner tube socket
to the fuselage side. Glue the other end of the joiner socket to the
other side of the fuselage.
The wing-joiner tube I bought was too long for the wings, so I
ended up cutting approximately 6 inches from it. I set this short piece
aside; it will be used to align the wings to each other as the nacelles
are mounted.
Slide the wings on the wing-joiner tube so that they fit snugly up
against the fuselage sides. Adjust the wing so that it is at 0°. Place the
1/8 plywood doubler on the antirotation pin and carefully adhere the
doubler to the fuselage side, being careful not to get any glue on the
antirotation pin. Use the same technique to glue the 1/8 plywood wingmount
bolt doubler to the fuselage side.
The engine nacelles are identical to each other except for the
landing-gear mounts. The nacelles are built like the fuselage, so I
won’t go into detail about the method used to construct them. Just
make sure that you build a left and a right one.
The method I used to align and mount the nacelles to the wings
should work if you plan to use electric or glow power. Because I
decided to go electric after my Neptune was nearly completed, I will
describe the method using glow engines.
You will need a roughly 3-foot section of aluminum angle, which
you can get in most hardware stores. It is used to hold the engines in
alignment with each other when you mount the nacelles to the wings.
Cut off approximately a 6-inch piece of the aluminum angle.
Mount both wings to the short scrap piece of the wing-joiner tube.
Slide the wings together as close as you can without letting the
antirotation pins interfere with each other. Clamp the 6-inch angle to
both wings’ TEs to keep the TEs aligned to each other.
On the finished model, the centerlines of the nacelles are 85/16
inches from the sides of the fuselage. Because the fuselage will
interfere with this method of mounting the nacelles, you will need to
compensate for the absence of the fuselage.
Measure the gap between the root ribs of the left and right wing,
and then add that amount to the 165/8-inch measurement. If the gap
is 2 inches, the total will be 185/8 inches. On your aluminum angle
drill two holes on center 185/8 inches apart. The diameter of the
holes will need to fit the prop shaft of the engines or motors you
plan to use.
Mount the engines to the nacelles, and then, using the prop shaft
of each engine, bolt the engines to the aluminum angle in the holes
you drilled. At this point the engines are aligned to each other. This is
important. The nacelles don’t really need to be aligned to each other,
but the engine thrustlines do.
Place the wing in the wing saddle of the nacelles, and adjust the
wing in the saddles so that the inside side of the nacelles are
approximately 69/16 inches from the edge of the wing root. Do not
adjust the gap between the wings. If you measured accurately, both
nacelles should be that length from the root rib.
Measure the distance from the wing LE to the aluminum angle at
the dihedral break on both wings. Adjust this distance so that the
measurement is the same on both wings. Check the engine
upthrust/downthrust line in relationship to the wing’s incidence with
an incidence meter, and sand the nacelles’ saddles so that the
thrustline is 0°.
The P2V Neptune’s completed framework is ready for covering. This model features extremely clean workmanship!
Full-Size Plans Available—see page 183
Once you are satisfied with all of these
measurements, tack-glue the nacelles to the
wings. Flip the wings over so you can glue
the nacelles to the wing with epoxy and glass
cloth on the inside of the nacelles. Carefully
unbolt the engines from the aluminum angle
and then separate the wings from each other.
Install the wings to the fuselage, and
mount the horizontal stabilizer so it is at 0°
incidence to the wing. Mount the vertical
stabilizer.
It is time to start all the little details such
as the dummy jet engines, the wingtip tanks,
the radomes, and the canopy. I made my
canopy and the forward observer’s canopy on
the nose from clear plastic, but you can carve
and sand a balsa block to shape if you want.
To supply some cooling air for the
batteries, I vacuum-formed the big radome
on the bottom of the fuselage from plastic.
On the front of the radome I cut some holes,
and on the bottom of the fuselage I cut holes
where the radome mounts. This allows the
radome to act like a big air scoop to cool the
batteries. I cut holes on the back end of the
fuselage hatch to allow the air to escape.
Radio Installation: This is fairly
straightforward. I used some flat wing servos
for the ailerons, and these needed to be
installed before I covered the wing. Before I
decided to switch to electric power, each
engine was to have had a separate throttle
servo that I planned to mount behind the
main landing gear in the nacelles.
I mounted the elevator, rudder, and retract
servos in the fuselage. An important thing
here is to make sure you have clear access to
the wing-mounting bolts in the fuselage.
Otherwise, mount the radio gear as you see
fit. After test-flying I found that aileron
differential is recommended along with some
rudder mixed into the ailerons.
Since this was my first electric-powered
twin, I decided to use one motor controller
and a separate battery pack for each motor,
and a servo “Y” harness to connect the motor
controllers to the receiver. I also used a
separate battery to power the receiver and
servos.
The fuel tanks need special attention
because the main landing gear will fold up
next to the tanks, and it is a tight fit. You will
need narrow tires and narrow fuel tanks, for
which I planned to use Sullivan 6-ounce slant
oval fuel tanks.
I also planned something different to
mount the fuel tanks. After the model was
finished and the nacelles were fuel-proofed, I
simply RTVed (room-temperature
vulcanized) the tanks to the inside of the
nacelles. Rough up the side of the fuel tank
with 80-grit sandpaper if you try this.
I mounted the ESCs for the motors using
Velcro in the place where I was going to
mount the fuel tanks. Using more Velcro, I
mounted the retract air tank to the inside top
of the fuselage just behind the cockpit.
Finishing: I covered my model with
MonoKote in the color scheme that US Navy
patrol squadrons used in the 1960s. If you
want a more visible scheme, you could try
one with a red tail that the naval reserve
squadrons used or use the colors that are on
some of the forest-fire-fighting versions.
Some Neptunes were used to launch drones
and missiles and had highly visible
appearances. There is much information
about this airplane on the Internet.
I sanded the dummy jet engines and tip
tanks smooth and filled the grain, and then I
painted them with LustreKote. All of the
markings are trim MonoKote.
For those who plan to use glow engines, I
will describe the method I have used on my
previous glow-powered, twin-engine models
to set up the power plants. Before you fly
your airplane, make sure both engines are
properly adjusted on the ground so that they
are reliable. I don’t bother to get them
synchronized to each other; I try to get them
to run dependably.
I set each engine independently for a
reliable idle with a smooth transition to high
speed. I set the high-speed needle by
pinching the fuel line and noting a slight rise
in the rpm without the engine dying. I point
the model’s nose straight up and straight
down to see if the engine sags or dies. I also
do this with the engine at idle.
Once I have both engines running reliably
one at a time, I run both at the same time and
check each engine using the same methods. I
do all of this at home so I don’t feel pressured
to fly the model. This also gives me a chance
to make sure nothing shakes loose.
I’m right-handed, so I start the left
engine first on my twins. This makes it
easier to stay out of the way of the left
engine while I start the right engine.
Flying: I balanced my Neptune 27/8 inches
behind the wing’s LE. After test-flying, I
feel that this is probably the farthest aft I
recommend to balance the model for good,
smooth flying.
I had to wait what seemed like forever
for the weather to cooperate—it was either
too windy or raining—but I was finally able
to sneak out early in the morning and testfly
my Neptune before the wind picked up.
After I assembled it at the field, I did a
range check of the radio with the motors
running.
I taxied the model to the end of the
runway and pointed it into the wind. I
advanced the throttles, and after roughly 150
feet I started to ease in some up-elevator. I
was pleasantly surprised when the airplane
gently rotated and started to climb out at a
nice, realistic climb rate.
It seemed to be flying well, so I flipped
the landing-gear switch, only to be
dismayed to see just the nose wheel and the
left main wheel retract. I flipped the gear
switch to the down position, and the nose
wheel came down and the left main wheel
stayed up!
I wasn’t going to let this ruin my test
flight, so I continued by climbing the model
to altitude to check the trims. My Neptune
required only some up-trim with the throttles
pulled back to a realistic cruise speed.
After cruising around for a few minutes,
I throttled down to check the stall
characteristics. My Neptune slowed better
than I expected, but it had a sharp stall. If
you build one, keep the airspeed up on the
landing approach. I did a few low passes
down the runway and then I tried a few
practice approaches.
When I finally decided to land the
Neptune, I was able to put it down gently,
but the nose gear collapsed and it skidded
down the runway on the radome and left
dummy jet engine. I was surprised that the
nacelle and the radome held up (I thought
they were going to be destroyed), but my
Neptune ended up with only some paint
scraped off the radome and the left jet
engine.
After learning that the landing-gear air
valve had a small leak, I locked the gear
down and did one more flight that day with
no problems. My model ended up weighing
just less than 10 pounds ready to fly, which
was slightly heavier than I wanted, but the
motors provide more than enough power for
flight.
The Neptune’s glide is a tad steep, but I
suppose two propellers windmilling creates
quite a bit of drag. Carry some power on the
landing approach, and as the Neptune gets
near the ground, slowly reduce power and
bleed the airspeed off with the elevator.
With practice you should be able to grease it
in on the mains and roll out a short distance
before the nose wheel comes down.
Final Thoughts: This has been one of the
most enjoyable models I have built in
awhile. It went together much better than I
expected, the flight characteristics are better
than I expected, and it looks great in the air.
The last-minute conversion to electric
power was a good move, and it has
convinced me that this is the way to go on
my future airplanes. MA
Gary Fuller
7076 E. Heather Dr.
Claremore OK 74019
[email protected]
Edition: Model Aviation - 2005/06
Page Numbers: 18,19,20,21,22,24,26
18 MODEL AVIATION
by Gary Fuller
DURING THE FIRST part of the Cold War, the P2V Neptune
was the US Navy’s primary long-range, land-based, antisubmarine
patrol aircraft. Designed in 1944 as a replacement for the PV-1
Ventura and the PV-2 Harpoon, the Neptune’s versatility ensured
that it would remain in service for a long time. Its last use in
combat was by the Argentineans against the British during the fight
over the Falkland Islands.
The Neptune is still being used, to fight forest fires in the
United States. With the installation of a mad boom on the tail, the
addition of a pair of jet engines, and many other minor
modifications, the later versions of the Neptune bore little
resemblance to the early production P2Vs.
I have always had a soft spot in my heart for historical airplanes
that are seldom modeled. The Neptune’s straightforward lines
ensure a good-flying model, yet the mad boom, radomes, jet
engines, and various other components give it considerable
character that would make it unique at the flying field.
I didn’t want an all-out competition-quality Scale model, so to
simplify it I used an easy-to-build box type of fuselage that is not
much different from what most trainer-type aircraft have. The
engine nacelles are also the box type, with the bottom left open so
you don’t have to mess with any finicky landing-gear doors. The
nacelles are glued to the wing with some glass cloth for
reinforcement.
The inboard section of the wing is fully sheeted and the
outboard section of the wing uses typical D-tube construction. The
jet engines and wingtip fuel tanks are balsa blocks carved and
sanded to shape. The wing is mounted to the fuselage with a joiner
tube so the model can be disassembled for transport to and from
the flying field.
I wanted to make the Neptune as large as possible yet
economical to build and fly, so I decided to build it with an 80-inch
wingspan. Power was to be a pair of O.S. .25 engines, but I was
bitten by the electric bug during the time I was building the model.
While researching motors for a future project, I realized that I
could easily mount electric power plants to my Neptune with no
major rework. I was in the process of covering the airplane when I
decided to make the change to electric power!
RC version of US Navy patrol
aircraft can be powered with
engines or motors
On right fuselage side you can see 1/4 balsa triangle stock,
forward fuselage doubler, formers F2 and F3, and nose-wheel
mounting plate installed.
Forward fuselage after joining the sides. This is a good time to
mount nose gear. Nose-wheel mount has been reinforced with 1/4
balsa triangle stock.
Upper fuselage sheeting is being installed. Author used Ambroid
glue here so the glue joint will be easier to sand when shaping
top of sheeting. Many T-pins hold sheeting in place as glue dries.
Carpenter’s square and sharpened brass tube are used to cut
slot for 1/4 plywood dihedral brace. One of R3 ribs has been
glued to spars using R3 angle guide; other R3 rib is being glued
to spar using 1/8 scrap wood to set distance between them.
I used a pair of MaxCim MaxN32-13Y motors direct drive
spinning APC 10 x 5E propellers. The motor controllers are MaxCim
Maxμ35D-21. I used 2000 mAh Kokam Li-Poly batteries wired 3S2P,
for a total of 11.1 volts and 4000 mAh for each motor. That easily gave
me a flight time exceeding 10 minutes with the motors throttled back
and more than adequate power to take off from a grass field.
The retractable gear is the standard size, and normal modeling
techniques are used to build the Neptune. If you have never built a
model from plans, this should not be too difficult—especially if you
have a few kits under your belt.
Since this is not really a beginner’s airplane, I won’t go into much
detail in the construction notes. I did not take any great pains to keep
the weight down on my Neptune, I did not use contest-grade balsa, nor
did I cut lightening holes in any of the sheet balsa. However, I am quite
sure that if you used contest-grade wood and other weight-saving
techniques, you could shave some weight from your Neptune.
CONSTRUCTION
I started my model by cutting all the parts and assembling them like
a kit. If you have never built from plans, I recommend the following.
To accurately cut the small parts from wood, cut the parts from the
plans and then lightly spray the backside of a paper cutout with contact
glue. When it has dried for approximately 10 minutes, to a light tack,
place the paper shape for the part on the wood, and then cut the wood
using a band saw or a jigsaw. Remove the paper after you have cut the
part.
To cut more than one of the same part, do the same thing as in the
preceding and then lightly spray both sides of some scrap paper with
contact glue. Sandwich this paper between as many sheets of wood as
necessary for the number of parts required. Cut the stack of wood
with a band saw or jigsaw. Once the stack is cut, separate each piece
and remove the paper.
If you have never done this, try it on scrap wood and paper first. I
have found that some brands of contact glue won’t work because
they are too tacky. I use carpet and headliner glue that comes in a
spray can and is available in auto-part stores. A good alternative is
Elmer’s school glue stick; it works as well without the mess.
Fuselage: The fuselage sides are too long and wide to cut from a
single sheet of balsa, so you will need to splice some sheets together.
I like to have the vertical splice where the wing doubler will
reinforce the joint. Be careful with the sides until the doublers are
installed. I like to lay the fuselage sides next to each other top to top
as I glue on the various parts; that way I won’t make two left or two
right sides.
Start the fuselage by gluing the 1/4 balsa triangle stock to the sides
as shown on the plans. Glue the doublers for the wing and forward
fuselage to the fuselage sides. Glue formers F2 through F5 to one
fuselage side, and then glue the nose-wheel mounting plate to F2 and
the side to which F2 is glued.
Glue the 1/4 x 3/8 balsa side stiffeners in place as shown on the
plans. Once the adhesive has dried, join the fuselage sides. I did this
by standing the side with the formers up on its bottom and then
placing the other side in place. Once I was satisfied with the fit of the
other side, I glued it to the formers.
I joined the forward end of the fuselage by weighting the fuselage
to the table and then using some clamps to draw the ends together until
former F1 would fit. I checked the alignment of the fuselage and
Photos by the author
20 MODEL AVIATION
Make both ends of wing-joiner tube same height above table so
wing will be square to fuselage from the top.
spars and the LE flush with the outermost R1C rib.
You will need to cut the R1C ribs for the 1/4 plywood dihedral
brace, I did this by using a 1/4-inch-outside-diameter brass tube that
was sharpened at one end. I used the tube to cut holes in the R1C ribs
at the dihedral brace’s location, using a carpenter square as a guide.
After the holes were cut, I used a file to finish the slot in the ribs
for the dihedral brace. Glue the dihedral brace to the ribs and the spar
after you are satisfied with the fit.
Carefully pull the wing-joiner socket tube from the wing and rough
it up with 80-grit sandpaper. Reinsert the socket tube in the wing and
glue it to the ribs. Glue some scrap balsa between the socket tube and
the 3/8 x 1/4 spars. Sheet the top of the inboard section with 3/32 balsa.
Once the glue for the sheeting has dried, remove the inboard
portion of the wing and set it aside.
Start the outboard section of the wing by pinning the lower
outboard 3/8 x 1/4 spruce spar to the plans. Glue the R2 and R4 through
R10 ribs to the spar. Position the R1 and R3 ribs on the spar, but do
not glue them in place yet. Place the upper 3/8 x 1/4 spruce spar on the
ribs and glue it to the R2 and R4 through R10 ribs. Also glue the 3/8
balsa LE to these ribs.
Using the R1 rib angle guide, glue rib R1 to the upper and lower
spar and the LE edge. Using the R3 rib angle guide, adhere one R3 rib
to the spars and LE. Use scrap 1/8 balsa as a spacer between the R3
ribs, and glue the other R3 rib to the spars and LE. Glue the 1/4 balsa
TE to ribs R5 through R10.
Sand the spars and the LE flush with R1, and then, using the same
method you used for the inboard section of the wing, cut the slot for
the 1/4 plywood dihedral brace in ribs R1 and R2. Sheet the top of the
outer wing with 3/32 balsa, as shown on the plans.
When the sheeting is dry, remove the outer section from the
building board and fit it to the inboard section of the wing. Once you
are satisfied with the fit, glue the outer wing section to the inboard
section. I used a wood block to prop up the wingtip while the glue
dried.
Sheet the bottom of the wing with 3/32 balsa. The inboard section
and the outboard section are done separately, and the part that is not
being sheeted is blocked up to prevent the wing from warping.
I tried to sheet as much of the bottom of the wing without cutting
off the building tabs as I could. I did that by gluing the edge of the LE
sheeting to only the 3/8 balsa LE first. After the glue dried, I wet the
sheeting to make it easier to bend, applied glue to the ribs, and then
placed the wing back on the worktable right-side up and weighted it
until the sheeting dried.
Once the wing is sheeted, glue the 1/4 balsa TE in place, and then
sand the LE and TE to match the airfoil. Drill a hole for the 3/8-inchdiameter
antirotation pin, and glue the antirotation pin in place. Drill
and tap the hole for the 1/4 x 20 nylon wing-mounting bolt.
Repeat this whole process for the other wing. Build the ailerons.
Final Assembly: Go back and align and install the wing-joiner tube
Type: RC Sport Scale
Wingspan: 80 inches
Wing area: 622 square inches
Flying weight: 10 pounds
Wing loading: 37 ounces/square foot
Length: 73.25 inches
Power: Two .25 glow engines or two
MaxCim MaxN32-13Y direct-drive
motors
Fuel tank: Two 6-ounce Sullivan slant
tanks (glow)
Battery: 11.1-volt 4000 mAh Li-Poly
(for electric version)
Radio system: Five channels
Construction: Balsa and plywood
Covering/finish: MonoKote,
LustreKote paint
adjusted until it was straight, and then I glued F1 in place. I joined the
aft end of the fuselage in the same manner.
Glue the 1/4 balsa triangle to the nose-gear mount as shown on the
plans. Mount the nose gear to its mounting plate with 4-40 screws and
blind nuts. Glue the 1/8 plywood hatch mounting plate in place as
shown on the plans. Install the 1/8-inch cockpit floor.
Sheet the top and bottom of the fuselage with 3/16 balsa, glued on
so that the wood grain is crosswise to the fuselage sides. Set the
fuselage aside.
Wing: Pin the 3/8 x 1/4 lower inboard spruce spar to your worktable.
Glue an end cap of 3/32 balsa scrap on the outboard end of the wingjoiner
socket tubes. Glue the 1/4 plywood doublers to R1B. After the
glue has dried on the cap, slide the R1 ribs and R1B rib into place on
the wing-joiner tube socket; don’t glue the ribs to the joiner socket
yet.
Space the ribs on the tube, place them on the lower inboard spruce
spar, and glue them to the spar. Glue the ribs R1C to the spar, and
make sure the ribs are perpendicular to the spar vertically and
longitudinally. Insert the forward 1/4 square spruce spars and the
upper 3/8 x 1/4 spruce spar, and glue the ribs to the spars.
Glue the 3/8 balsa LE to this part of the wing. Sand the inboard
June 2005 21
Clothespins hold TE to 12-inch steel rule to keep them aligned to
each other while nacelles are being fitted to wing.
Aluminum angle bracket is used to hold engine nacelles in
alignment to each other while nacelles are glued to wing.
Engine nacelles are built in same manner as fuselage. For
simplicity’s sake there are no gear doors. Bottoms of nacelles
are left open.
socket in the fuselage. Flip the fuselage upside down on the worktable
and secure it so it won’t move. Glue one of the 1/8 plywood joiner
doublers inside one side of the fuselage.
Rough up the outside of the joiner tube socket with some
sandpaper, and insert the socket into the fuselage. Slip the other 1/8
plywood joiner doubler onto the socket as you insert it into the
fuselage, but don’t glue the socket or the doubler to the fuselage yet.
Insert the joiner tube into the socket so it is centered in the
fuselage and an equal length of the tube extends out of the fuselage on
either side. Measure the ends of the joiner tube to the worktable. Sand
the hole in the fuselage that does not have the plywood doubler on it
so that both ends of the joiner are an equal height above the work
surface. Use a carpenter’s square to square the joiner tube to the
fuselage sides also by sanding the hole without the doubler.
When you are satisfied that the joiner tube is square to the fuselage
side, block the joiner tube so that it cannot move, and then doublecheck
to make sure the joiner tubes’ ends are an equal height above
the work surface. Glue the plywood doubler and the joiner tube socket
to the fuselage side. Glue the other end of the joiner socket to the
other side of the fuselage.
The wing-joiner tube I bought was too long for the wings, so I
ended up cutting approximately 6 inches from it. I set this short piece
aside; it will be used to align the wings to each other as the nacelles
are mounted.
Slide the wings on the wing-joiner tube so that they fit snugly up
against the fuselage sides. Adjust the wing so that it is at 0°. Place the
1/8 plywood doubler on the antirotation pin and carefully adhere the
doubler to the fuselage side, being careful not to get any glue on the
antirotation pin. Use the same technique to glue the 1/8 plywood wingmount
bolt doubler to the fuselage side.
The engine nacelles are identical to each other except for the
landing-gear mounts. The nacelles are built like the fuselage, so I
won’t go into detail about the method used to construct them. Just
make sure that you build a left and a right one.
The method I used to align and mount the nacelles to the wings
should work if you plan to use electric or glow power. Because I
decided to go electric after my Neptune was nearly completed, I will
describe the method using glow engines.
You will need a roughly 3-foot section of aluminum angle, which
you can get in most hardware stores. It is used to hold the engines in
alignment with each other when you mount the nacelles to the wings.
Cut off approximately a 6-inch piece of the aluminum angle.
Mount both wings to the short scrap piece of the wing-joiner tube.
Slide the wings together as close as you can without letting the
antirotation pins interfere with each other. Clamp the 6-inch angle to
both wings’ TEs to keep the TEs aligned to each other.
On the finished model, the centerlines of the nacelles are 85/16
inches from the sides of the fuselage. Because the fuselage will
interfere with this method of mounting the nacelles, you will need to
compensate for the absence of the fuselage.
Measure the gap between the root ribs of the left and right wing,
and then add that amount to the 165/8-inch measurement. If the gap
is 2 inches, the total will be 185/8 inches. On your aluminum angle
drill two holes on center 185/8 inches apart. The diameter of the
holes will need to fit the prop shaft of the engines or motors you
plan to use.
Mount the engines to the nacelles, and then, using the prop shaft
of each engine, bolt the engines to the aluminum angle in the holes
you drilled. At this point the engines are aligned to each other. This is
important. The nacelles don’t really need to be aligned to each other,
but the engine thrustlines do.
Place the wing in the wing saddle of the nacelles, and adjust the
wing in the saddles so that the inside side of the nacelles are
approximately 69/16 inches from the edge of the wing root. Do not
adjust the gap between the wings. If you measured accurately, both
nacelles should be that length from the root rib.
Measure the distance from the wing LE to the aluminum angle at
the dihedral break on both wings. Adjust this distance so that the
measurement is the same on both wings. Check the engine
upthrust/downthrust line in relationship to the wing’s incidence with
an incidence meter, and sand the nacelles’ saddles so that the
thrustline is 0°.
The P2V Neptune’s completed framework is ready for covering. This model features extremely clean workmanship!
Full-Size Plans Available—see page 183
Once you are satisfied with all of these
measurements, tack-glue the nacelles to the
wings. Flip the wings over so you can glue
the nacelles to the wing with epoxy and glass
cloth on the inside of the nacelles. Carefully
unbolt the engines from the aluminum angle
and then separate the wings from each other.
Install the wings to the fuselage, and
mount the horizontal stabilizer so it is at 0°
incidence to the wing. Mount the vertical
stabilizer.
It is time to start all the little details such
as the dummy jet engines, the wingtip tanks,
the radomes, and the canopy. I made my
canopy and the forward observer’s canopy on
the nose from clear plastic, but you can carve
and sand a balsa block to shape if you want.
To supply some cooling air for the
batteries, I vacuum-formed the big radome
on the bottom of the fuselage from plastic.
On the front of the radome I cut some holes,
and on the bottom of the fuselage I cut holes
where the radome mounts. This allows the
radome to act like a big air scoop to cool the
batteries. I cut holes on the back end of the
fuselage hatch to allow the air to escape.
Radio Installation: This is fairly
straightforward. I used some flat wing servos
for the ailerons, and these needed to be
installed before I covered the wing. Before I
decided to switch to electric power, each
engine was to have had a separate throttle
servo that I planned to mount behind the
main landing gear in the nacelles.
I mounted the elevator, rudder, and retract
servos in the fuselage. An important thing
here is to make sure you have clear access to
the wing-mounting bolts in the fuselage.
Otherwise, mount the radio gear as you see
fit. After test-flying I found that aileron
differential is recommended along with some
rudder mixed into the ailerons.
Since this was my first electric-powered
twin, I decided to use one motor controller
and a separate battery pack for each motor,
and a servo “Y” harness to connect the motor
controllers to the receiver. I also used a
separate battery to power the receiver and
servos.
The fuel tanks need special attention
because the main landing gear will fold up
next to the tanks, and it is a tight fit. You will
need narrow tires and narrow fuel tanks, for
which I planned to use Sullivan 6-ounce slant
oval fuel tanks.
I also planned something different to
mount the fuel tanks. After the model was
finished and the nacelles were fuel-proofed, I
simply RTVed (room-temperature
vulcanized) the tanks to the inside of the
nacelles. Rough up the side of the fuel tank
with 80-grit sandpaper if you try this.
I mounted the ESCs for the motors using
Velcro in the place where I was going to
mount the fuel tanks. Using more Velcro, I
mounted the retract air tank to the inside top
of the fuselage just behind the cockpit.
Finishing: I covered my model with
MonoKote in the color scheme that US Navy
patrol squadrons used in the 1960s. If you
want a more visible scheme, you could try
one with a red tail that the naval reserve
squadrons used or use the colors that are on
some of the forest-fire-fighting versions.
Some Neptunes were used to launch drones
and missiles and had highly visible
appearances. There is much information
about this airplane on the Internet.
I sanded the dummy jet engines and tip
tanks smooth and filled the grain, and then I
painted them with LustreKote. All of the
markings are trim MonoKote.
For those who plan to use glow engines, I
will describe the method I have used on my
previous glow-powered, twin-engine models
to set up the power plants. Before you fly
your airplane, make sure both engines are
properly adjusted on the ground so that they
are reliable. I don’t bother to get them
synchronized to each other; I try to get them
to run dependably.
I set each engine independently for a
reliable idle with a smooth transition to high
speed. I set the high-speed needle by
pinching the fuel line and noting a slight rise
in the rpm without the engine dying. I point
the model’s nose straight up and straight
down to see if the engine sags or dies. I also
do this with the engine at idle.
Once I have both engines running reliably
one at a time, I run both at the same time and
check each engine using the same methods. I
do all of this at home so I don’t feel pressured
to fly the model. This also gives me a chance
to make sure nothing shakes loose.
I’m right-handed, so I start the left
engine first on my twins. This makes it
easier to stay out of the way of the left
engine while I start the right engine.
Flying: I balanced my Neptune 27/8 inches
behind the wing’s LE. After test-flying, I
feel that this is probably the farthest aft I
recommend to balance the model for good,
smooth flying.
I had to wait what seemed like forever
for the weather to cooperate—it was either
too windy or raining—but I was finally able
to sneak out early in the morning and testfly
my Neptune before the wind picked up.
After I assembled it at the field, I did a
range check of the radio with the motors
running.
I taxied the model to the end of the
runway and pointed it into the wind. I
advanced the throttles, and after roughly 150
feet I started to ease in some up-elevator. I
was pleasantly surprised when the airplane
gently rotated and started to climb out at a
nice, realistic climb rate.
It seemed to be flying well, so I flipped
the landing-gear switch, only to be
dismayed to see just the nose wheel and the
left main wheel retract. I flipped the gear
switch to the down position, and the nose
wheel came down and the left main wheel
stayed up!
I wasn’t going to let this ruin my test
flight, so I continued by climbing the model
to altitude to check the trims. My Neptune
required only some up-trim with the throttles
pulled back to a realistic cruise speed.
After cruising around for a few minutes,
I throttled down to check the stall
characteristics. My Neptune slowed better
than I expected, but it had a sharp stall. If
you build one, keep the airspeed up on the
landing approach. I did a few low passes
down the runway and then I tried a few
practice approaches.
When I finally decided to land the
Neptune, I was able to put it down gently,
but the nose gear collapsed and it skidded
down the runway on the radome and left
dummy jet engine. I was surprised that the
nacelle and the radome held up (I thought
they were going to be destroyed), but my
Neptune ended up with only some paint
scraped off the radome and the left jet
engine.
After learning that the landing-gear air
valve had a small leak, I locked the gear
down and did one more flight that day with
no problems. My model ended up weighing
just less than 10 pounds ready to fly, which
was slightly heavier than I wanted, but the
motors provide more than enough power for
flight.
The Neptune’s glide is a tad steep, but I
suppose two propellers windmilling creates
quite a bit of drag. Carry some power on the
landing approach, and as the Neptune gets
near the ground, slowly reduce power and
bleed the airspeed off with the elevator.
With practice you should be able to grease it
in on the mains and roll out a short distance
before the nose wheel comes down.
Final Thoughts: This has been one of the
most enjoyable models I have built in
awhile. It went together much better than I
expected, the flight characteristics are better
than I expected, and it looks great in the air.
The last-minute conversion to electric
power was a good move, and it has
convinced me that this is the way to go on
my future airplanes. MA
Gary Fuller
7076 E. Heather Dr.
Claremore OK 74019
[email protected]