Model Aero Polaris XL- 2012/05

www.ModelAviation.com May 2012 Model Aviation 61
Eric Henderson
[email protected] REVIEW Model Aero Polaris XL
My previous experience with
building Depron “slab-type”
foamies for 3-D flying and
general bashing around the sky gave
me a degree of building confidence,
so I was looking forward to putting
together a Model Aero Polaris XL.
The Polaris XL was conceived by
designer Steve Shumate and is a park
flyer adaptation of Laddie Mikulasko’s
beautiful North Star seaplane. It has
a floating hull that is also the fuselage
and a delta-wing configuration, but
uses ailerons and a conventional midtail
elevator.
The Polaris XL is a sheet-foam kit.
Most of the parts are made from lasercut
Depron foam sheeting. The sheet
patterns were well-designed and it was
easy to pop out the numerous small
and large shapes.
The box was originally opened at
the 2011 Electric Nall eWeek event,
held at the Triple Tree Aerodome
in Woodruff, South Carolina. The
instructions were on a CD, but the
super-helpful Joe Nall staff took the
CD and printed the building directions
for me.
If I have one criticism of this kit, it is
the instructions. Using the correct ones
was not easy. There are many parts, and
even if a picture is worth a thousand
words, a photo of lots of “white
sheeting” does not lead to clarity.
There were no identity tags on the
Depron parts either, so be advised to
take your time before you glue. The
construction of the Polaris line is well
covered in online hobby-discussion
sites such as RCGroups.com.
A lesser issue is that the laser-cutting
process causes the edge of the Depron
parts to be slightly concave. You have
to accurately—albeit lightly—sand all
of the edges to a smooth 90° before
gluing. This is not a big deal, but when
you are making a water-tight hull
chamber for a flying boat, accurate and
continuous-edge gluing is important.
Three free evenings allowed me to
complete the bulk of the assembly.
Three weeks after the Joe Nall eWeek,
I was back in Maryland and the Polaris
XL was completed in another evening
of wiring and gluing.
There is nothing difficult to do in
the building of a Polaris XL. I estimate
The Polaris XL is a flying boat that takes on the look
of a modern Eurofighter jet from certain angles.
The popular
Polaris gets
supersized
Photos by the author
62 Model Aviation May 2012 www.ModelAviation.com
Specifications
Model type: Electric-powered amphibian
Skill level: Intermediate builder;
intermediate pilot
Wingspan: 38.5 inches
Wing area: 606 square inches
Weight: 28 to 34 ounces
Length: 53 inches
Flying weight: 28 to 34 ounces
Power system: 270- to 340-watt electric
Battery: Three-cell 2200 mAh LiPo
Radio required: Four-channel required
Construction: 6mm Depron foam
Price: $79.95; $94.95 w/decal set
TEST-MODEL DETAI LS
Motor: Spin Max 2810-9
ESC: Spin Max 40-amp ESC
Battery: Nano-Tech 2200 mAh three-cell
LiPo 25C discharge rate
Propeller: APC 8 x 6
Radio system: Spektrum DX8 transmitter,
Spektrum AR6115 receiver,
four Hitec HS-55 servos
Ready-to-fly
weight: 26.5 ounces
Flight duration: 8-10 minutes
PLUSES
• Lightweight construction
• Capable of impressive aerobatics
• Good water-handling characteristics
• Colorful decals that stay in place
• Pushrod exit design
• Options to purchase with recommended
equipment
MINUSES
• A better breakdown of steps needed in the
instructions
• Servos sealed in
• Parts identification lacks clarity
• No hinging tape included
AT A GLANCE....
The box structure is built from many
flat parts of 6mm Depron sheeting.
that it would take roughly three days
to build—if the builder stayed in one
place! The solid design means you will
not have to change anything to have
a successful flying boat. I probably
logged more miles with this review
than with any review that I have done,
but the Polaris XL traveled well!
What follows are some comments on
the actual building, some tips, and why
I chose to make a few changes.
The ailerons and elevators are hinged
with Blenderm tape, which was not
supplied. This tape turned out to be
hard to find. I tried several waterresistant
“pharmacy” substitutes, but
they all peeled up by the end of the
next day.
A visit to my local hobby store
(Hobby Works) was rewarded with a
Du-Bro product called Electric Flyer
Hinge Tape. When I looked inside the
roll of tape it said—you guessed it—
Blenderm.
This tape does the job of foam-board
hinging and handled all of the water
tests well. When you apply Blenderm
tape, avoid stretching it. Unroll a length
and wait a few seconds for it to relax
before applying it to the Depron.
One major change I made was the
orientation of the rudder and aileron
servos. The kit has the servos inverted
and the horns and pushrods exiting
under the wing. Because I wanted to
keep all wire and wood out of the water
and any grass stubble (the Polaris XL is
a watercraft, but it can also take off on
grass), the servos were placed upright
and the horns placed on the top of the
wing. I raised the rudder horn out of the
water to line up above the wing.
This servo change solves a concern
I had about serviceability and
maintainability of the servos. It is easier
to access the servos with a sharp knife.
All you will have to cut into is the top
deck. The spin-off benefit was that
the bottom hull chambers could be
completely and permanently sealed.
I went to the trouble of doing this
because this airplane is so much fun
to fly that you will want it to last and
be easy to fix in the event of a servo
failure.
The ESC and heat sink were
mounted through the side of the
fuselage instead of the recommended
hatch position. This allowed cooling for
the ESC, but avoided the tugging and
pulling on the delicate Depron hatch.
The firewall/engine mount plate
and fin/engine pod plate are shown as
painted black. If you don’t have any
paint, you can use magic marker. Once
colored, the wooden parts, including
the horns, should be sealed with thin
CA to waterproof them.
The fin is in two parts. The bottom
section is made from four laminates
of Depron foam board. The top half
of the fin is a single sheet. There is a
keyway to keep the top fin section
straight, but it still seemed particularly
vulnerable to hangar rash. I glued two
1/2-inch strips of Depron on either side
of the top fin to give it more support.
The push wires were modified to
include adjustment Zs. This adjustment
is unnecessary for elevator and rudder
setting. You can get a close setting
with a pair of pliers and then adjust
the electronic subtrim to get a good
neutral for the elevator and the rudder.
You cannot do this with the ailerons,
because the ailerons go up and down in
www.ModelAviation.com May 2012 Model Aviation 63
Left: The Polaris XL airframe shown here
is ready to fly. It will be easier to see
after self-adhesive decals are applied.
Right: The Polaris XL is available
with or without decals. This
shows the model with decals.
The Polaris XL is at home on
the water. This larger model
in the Polaris line sits high
and will leave the water very
quickly.
opposite directions at the ends of the
servo arm.
The instructions are in a file so you
can modify them to personalize and
match your needs and construction
sequencing.
The Polaris XL is moderately priced
at $79.95 and full details can be found
on Model Aero’s website. The airplane
can be bought as a basic model by the
pilot who already has many of the
electronics, or with the recommended
equipment needed to complete the
model.
The review model came with an
ESC, decals, the Spin Max 2810-9
(1400 Kv) motor, and APC 8 x 6
propeller, but no servos.
Flight Report: Model Aero states,
“The Polaris XL is a 133% version
of the standard-size Polaris, and
the larger size enhances the flight
characteristics that made the original
such a popular airplane. The wing
loading is even lighter and the gentle
flight performance will amaze you, yet
the XL is capable of some impressive
aerobatics and a surprising turn of
speed!”
The Polaris XL is a flying boat, so
the first test was to see how it floated.
The opportunity to fly at Joe Nall had
passed by, so I used a local RC boating
pond.
The water handling was great. The
airplane sets high in the water and
responds well to the rudder at low
speeds. At high speed, the hull comes
up on the step and the rudder is
less effective. This is not a problem,
because by this time the boat is
becoming an airplane.
I performed several taxi tests at
different speeds and there was no
sign of any tipping or porpoise action.
The square hull created a wide wake
and then the whole front lifted out
of the water and only the rear section
behind the step made contact. This
was a boating-only pond, so I only
tested a few hops, but it was clear that
the airplane would leave the water in
about 10 to 15 feet at full power.
After drying the hull on the outside
and checking for any water inside
(none was found), the local flying
field was my next port of call. It was
a lovely, sunny day and the grass was
dry. I was not sure if it would be
possible to take off without wheels
and was ready to do some hand
launching.
My fears were unfounded. The
Polaris XL effortlessly slid forward
on the grass and was airborne in less
than 10 feet. A few beeps of downtrim
were required and then it was
basically hands off. The first flight was
for the camera. It was pleasing to feel
how smooth and well the Polaris XL
tracked near the ground. The overall
look in the air is more that of a jet
fighter than a flying boat.
A simple landing on the grass let me
put in a fresh three-cell 2200 mAh LiPo
and then it was time to wring it out!
Takeoff was predictable and I made
a steep climb as soon as the grass was
gone. Initial aerobatics were done
at altitude. After roughly a minute,
I found myself flying at 20 feet and
doing slow rolls and loops from level
flight.
Flying inverted was a pleasant
surprise. The flat-section wing did not
seem to care which way it flew. Only
a slight amount of down-elevator was
needed. An outside loop was as easy
to do as an inside loop.
I performed the initial flights on
low rates, then mid rates, and finally
everything I had. As long as you use
exponential (approximately +26% in
JR terms), the Polaris XL is smooth
around stick center.
A knife-edge attempt showed that
rudder will also roll the airframe.
Some counter aileron was mixed with
the rudder, which allowed some flat
turns. The Polaris XL’s star feature
is the delta-wing behavior. You can
slow this airplane down to a crawl
by feeding in the power at the same
time as the elevator. The nose will
stay pointed up at a steep angle, also
known as a high-alpha angle of attack!
The wings will wobble a bit, as do
all deltas at this angle of attack, but
there is no real stall. The Polaris XL
mushes and loses height slowly. This
feature lets you do some amazing
landing approaches. You can bring the
airplane to a stop before it flops onto
the ground.
I give this airplane two thumbs up
in the flying department, and have
every confidence that on land or
water, it will be a blast to fly.
—Eric Henderson
[email protected]