Flying for Fun-2007/12

THERE’S A CERTAIN whimsy in writing
columns because of the strange gap in the
due date and publication date. I am writing
this in mid-August, on a 100° day with
humidity exceeding 50%, yet it will be
distributed for you to read in November. So
although it’s not “beginning to look a lot
like Christmas,” I wish you and yours a
joyful holiday season.
If that’s not weird enough, I’m going to
write about rise-off-water (ROW) flight
with RC models. I will devote a full column
to float-flying even though the water
outdoors north of the Mason-Dixon Line
might be in a solid state right now.
I chose this topic because several
magazine writers have commented on the
increasing number of float-flys that are
being scheduled across the country and the
mushrooming interest in this activity among sport fliers. I thought it
would be appropriate to share my limited knowledge and favorite
tricks with you. I hope this will help when you are converting one of
your models to ROW during the building months.
Consider how many more bodies of water are suitable for RC
flying than there are model flying fields. I guess that also applies to
electrics.
You can measure float-flying’s growth by comparing the large
number of excellent commercial floats that are now available to the
small number available 25 years ago. Back then a few fiberglass
units were available from garage-type suppliers, and they were
expensive. The few commercial units for sale were either extremely
heavy or leaked like a sieve. Now the choices are nearly limitless—
perhaps a chicken-and-egg phenomenon.
As I mentally planned this column I recalled the most definitive
series of articles ever written about float-flying, by the late Chuck
Cunningham for R/C Modeler magazine. A search found the articles
in the February and March 1987 issues.
Flying for Fun D.B. Mathews | [email protected]
A complete RC float-flying primer!
A semiscale Eastbourne published as the “Flying Machine” in the November 1992 Flying
Models magazine. See text for the story.
Left: The Bandito 40 design was published
in the April 2000 R/C Modeler. It has bandsawn
foam floats, Ace landing gear, and a
SuperTigre .40 engine.
Above: Gerald Schajatovic photographed
the Cruiser 60 he built from plans for the
June 2004 MA construction article.
I took the liberty of reproducing several drawings that
accompanied the text. They perfectly illustrate most of the
information anyone would need to mount and set up floats.
Chuck’s work included a considerable amount of information
about constructing one’s own floats from Styrofoam, which I chose
not to write about because most contemporary modelers are likely to
98 MODEL AVIATION
Doesn’t the inset photo make you want to get a set of floats on your favorite model? That was the author’s intent.
Left: Dean Cranston’s Seamaster 40
passes by. These look like they are about
to sink until the power comes up, and
then they pop out of the water and fly
Below: Steve Dockery taxis his Whiz 40
out for what must be its 900th flight at the
Wellington KS float-fly, in June 2007. It is
ancient but still looks good and flies very
well on floats. Duffy photo.
purchase some of the excellent float units. As I mentioned, 25 years
ago one was forced to construct floats from scratch since few were
available commercially.
If you would like to review Chuck’s instructions for constructing
floats, you can contact the AMA library for copies of the articles.
What You Need to Know: If you have looked at the drawings, you
may have noticed that the step (the notch on the bottom of the float)
should be placed roughly 1/2 inch aft (behind) the balance point, or
close to where the wheel axles would be on a conventional-wheeled
tail-dragger.
Additionally, the float length should be approximately 75% of
the fuselage length measured from the back of the propeller to the
rudder hinge line. Width is written on the drawing for various-size
power plants.
An “ancient” saw says that if the model doesn’t sink when placed
in the water, the floats are large enough; if it doesn’t settle roughly
20% from the top of the water, they are too big.
As I’ve written many times through the years, if your land-based
model is adequately powered with a .40 engine, you may need to
substitute a .60 for float-flying. Why? First, floats add considerably
to your model’s overall weight. Second, all that stuff hanging out
there produces a considerable increase in parasitic drag. Also, to
avoid the need for a retrieval boat or a long wait for the wind to
push your model ashore, its engine must sustain a reliable idle.
By the way, these models kick up a considerable amount of
spray, and that will eat up a wooden propeller pronto! Therefore, the
propeller arc should be 4 inches behind the
tips of the floats.
That spray problem also means you must
water-proof the receiver and batteries by
encasing them in a plastic wrap or some
clear bags from the supermarket produce
section. Close them up with the provided tie
wraps. There is really no way to isolate the
servos to keep them dry, so be prepared to
dry them by disassembling if the model
becomes immersed after a crash.
If the engine is submersed, immediately
dry it off as well as you can. Remove the
plug and the fuel line, and spin the engine
awhile with your starter. When the engine is
no longer spitting out water, rehook the fuel
and plug and run it for a tank full. Give the
metal parts a good shot of lubricant and you
should have no damage. I take a hair dryer
to float-flys so I can thoroughly dry the
inside of a model after a day’s flying.
Floats actually improve pitch and roll
stability on a given mode (tail-dragger or
tricycle gear). This fits the old Charles Grant
rule that the more mass there is below a
model’s center of lift, the more stable it will
be. Consider a high-wing aircraft versus a
low-winged aircraft.
However, enlarged vertical fins or
subfins are needed on some airplanes
because that mass hanging down there tends
to require additional area to prevent yaw
(side-to-side) motions. This seems to be
particularly true for full-scale or model Cub
types and some others.
On the opposite hand, turning the model
will usually require more rudder deflection,
but aileron rolls accelerate from the top
down. Sort of neat to watch.
Installing Floats: Most commercial float
kits include adequate installation
instructions, so I’ll just toss in a couple of
my favorite points.
A wide variety of preformed-aluminum
or carbon-fiber landing-gear units is
available at your local hobby shop or by
mail order. Get a pair for simplicity’s sake. I
strongly recommend these instead of the
bent-wire units we used to use.
Steel axles are perfect with these units. I
also prefer to use the nylon nose-gear blocks
(some may need to be sawn into pieces) that
several manufacturers sell to mount the steel
axles to the top of the floats. Quality wheel
collars will retain the brackets to the axles
and allow for some adjustment—that is, if
the floats you are using have hardwood
blocks in the appropriate locations.
These are much stronger and add more
resistance to side-to-side motions than the
nylon gear mounts, which are also sold as
accessories. Through the years the most
common area of failure I’ve observed is
mounting the gear to the floats.
If necessary, epoxy plywood across the
inside fuselage bottom, behind the wing LE
and TE. Don’t skimp on this step; the floats
transmit considerable twisting and sheer
forces to these mounts. I like to use #6 SMS
to secure the landing gear to the fuselage.
I prefer to block up floats on the building
surface until their tops are level. (Use a
spirit level, not your eyeballs, for this.) Then
I use a premarked location on the fuselage to
indicate where the model balanced with
wheels. This is still the balance point on
floats, but it may require you to add weight
to them fore or aft to balance the model after
installation.
Locate the floats relative to the balance
point; measure midline to midline of the
floats, making sure they are pointed straight
ahead; and then mark and drill into the
hardwood blocks for sheet-metal screws to
secure the nose-gear blocks. Floats mounted
toe-in or toe-out can produce wild gyrations
on takeoff and landing.
Most model designs have the fuselage
bottom tapered rearward at the wing TE, so
it is usually necessary to shim the back
landing-gear leg onto the fuselage bottom.
The wing must be set at a slight positive (LE
up) angle or you will end up with a strangelooking
hydroplane.
I used to feel the need for crossbraces
running from float top to float top. That was
apparently needed for flimsy vacuumformed
floats on wire gear, and I no longer
bother.
Steering: This aspect of float-flying exhibits
modelers’ ingenuity. I have observed some
way-out-there setups. I prefer the simple
approach: a piece of tin sheet stock soldered
onto a piece of wire and hung off the rudder.
It looks a bit odd, but you can’t beat it for
easy.
More aesthetically pleasing are the Ernst
and Top Flite units that are hinged to the
back of the floats and driven by either cablein
rod or with a bellcrank in the fuselage,
which is attached to the rudder horn with a
pushrod.
With those the motion is carried through
the fuselage bottom via a torque system to
another series of horns and pushrods. If you
have a waterproof servo, consider mounting
it to the fuselage bottom and run cable-type
rod in nylon sleeves to the water rudders.
The first time I flew a model off water
was in Gunnison, Colorado, with longtime
friend Paul Schlegel and his 4-40 Bipe on
his homemade foam floats. He based them
on ancient FF floats he found in a magazine.
And we did not have a water rudder! This
was in 1984.
We flew our aircraft off a pond and tried
our best to taxi back to shore, but if an
engine died on the water we just waited for
the breeze to drift the model ashore. Who
needed a water rudder or a retrieval boat?
However, I can’t recommend not using a
system for steering the model on the water.
Flying on Floats: It is ideal to start on a
shore that allows you to fly directly into the
wind, to use the drift-ashore thing I
mentioned. You can taxi from anywhere to
get the nose in the wind if need be.
Do not “horse” the model off the water! I
see this much too often, and the result is the
same as on land except exaggerated.
Accelerate until the model gets “on step” on
its own and then gently apply up-elevator to
break out of the water. Torque is torque, and
the same takeoff principles apply as for a
wheeled model.
Landings are identical, except the float
model is much heavier and “draggy,” so
approach speed should be higher and the
approach should be longer. Throttle back
slowly, keep the wings level, stay off the
elevator, and you should see a lovely sliding
sort of landing.
Caption Additions: The Eastbourne (Flying
Machine) was a learning experience for me.
I originally constructed foam floats
following the design of the 1911
prototype. Although the model would get
on step, as you can see in the photo, it was
a chore to get it there and usually required
a judicious application of down-elevator.
In the early years of flying, designers
used a half float with a tail float.
Apparently that worked for the period, but
I found that it took forever to get the
model onto the step. That’s because the
starting position left the nose and wing at
such a steep positive angle that the model
struggled to get into a flying position.
Later I changed to full-length, scratchbuilt
floats, and the Eastbourne flew much
nicer. It had a broken-loose aileron servo
rail at an ACE float-fly years ago, and I
didn’t discover it until later. It turned to
the right fine, but the left turns were
awful.
The Bandito 40 used homemade foam
floats following Chuck Cunningham’s
parameters, and I flew it until it became
so waterlogged that I threw it away. It was
one of my all-time favorites.
The Ace Seamaster kit has been a
favorite of float-flyers for many years. It
is a floatplane as opposed to an airplane
on floats. The factory staff enlarged the
design to 120 size, and it proved to be a
wild airplane.
The crew asked me to look at it later
to see if I could figure out why it flew so
poorly. After roughly an hour of scratching
my head, it dawned on me what might be
wrong.
Ken Willard designed the original 40-
size model, and it used a typical Willard fat,
fully symmetrical airfoil. The enlarged
version used the existing kit ribs and other
parts from my 4-120’s wing.
The design team then attempted to use
the balance point of Ken’s wing on my
semisymmetrical section. His balanced at
25% and mine balanced at 35%. The model
they were flying was viciously nose-heavy!
George Knapple built the Ace Whiz 40
shown more than 16 years ago. He took out
all but 1° of wing incidence, powered it
with a K&B .65, and flew it a lot on wheels.
George crashed the model and gave it to
Steve Dockery, who repaired it and put it on
a pair of Lanier floats using a pair of the
kit’s wide-track, formed-aluminum landing
gear. This setup has been flown—very
well—hundreds of times.
The Cruiser 60 construction article was
published in the June 2004 MA. Gerald
Schajatovic of Chesterland, Ohio, built his
from the magazine plans, powered it with an
O.S. .60 engine, and used Goldberg floats.
Of the 76 designs I’ve had published, the
Cruiser 60 is far and away the best one
never to be kitted.
Enough of this; go put an RC model in
the water, get your socks wet, and fly for
fun. MA