A scratch-built 36" span bush
plane built from Depron foam sheets in 6mm and 3mm thickness
This page was last updated on
February 1st, 2021 - thanks for visiting!
Above: my January 2021
build of the Just Aitcraft HIGHLANDER, a variant based on
Thomas B's plans for the Buschtrottel which were published
in the German 'Modelflug' magazine
My build features a shaped
airfoil KFm3 variant wing, full wing tip plates, Slats on the
wing's leading edge, horizontal stabilizer tip plates, and
airflow fences on the separating line between the flaps and
ailerons. The removable wing has four 5 gram servos to control
the ailerons and flaps. The elevator and rudder are controlled
with 9 gram servos.
Above: this is a view of the
"Viking Highlander" build before the wing's leading edge slats
were added; it sits high on 4" diameter tundra tires.
This is one of the more
recent custom builds of the LSA Highlander sold as a kit by Just
Aircraft; it features wing tip plates, horizontal stabilizer tip
plates, and the airflow fences on the upper wing surface.
Wingspan: 35 5/8"
Wing Chord:8 3/4"
Wing Area: 310 square
inches = 2.15 square feet
Overall length: 31"
6mm White and Black Depron and 3mm black Depron used in this
Motor Used: Grayson
Propellers used: APC Slow
Flyer 9"x3.8", 8"x3.8"
Battery : 3S LiPo 1000mAH,
3S 1300mAH, 3S 950 mAH Nano-Tech
ESC: 18 Amp to 20 Amp
Radio Receiver: 6 channel
Wheels : [Banggood] 4.00
inch @ 32 grams each, or [Hobby King] 3" foam wheels @
13 grams each
Optional: 1/32" 3 ply Birch Aircraft ply skis 2.5" x 8", 16
Landing Gear: .062" music
Flying Weight as built
with 3S 1300mAH battery, on 4" wheels: 19-3/4 ounces; Wing
loading of 9.2 Oz / Sq Ft
Flying Weight with Optional
Under-camber Aileron Wing
with 3S 950mAH battery, on 3" wheels: 15-3/8 ounces; 2.85 Sq Ft,
Wing loading of 5.34 Oz / Sq Ft
Flying Weight as
built with 3S 950mAH battery, on 3" wheels: 17-3/8 ounces;
Wing loading of 8 Oz / Sq Ft
KFm3 Variant Shaped
Airfoil Wing Building
I cut wing, fuselage, and
tail group panels as laid out on Thomas B's plans. From there,
I added internal wing structure as shown below, adding the
black 3mm depron panel which forms the secondary step, and
adding a 1/2" wide 6mm thick strip at 30% of chord to support
the high point of the forward airfoil's curvature. The upper
panel was rolled on a 3.3" O.D. cardboard shipping tube to get
the desired curvature. It was then tape hinged in place to the leading
edge. 6 minute epoxy was applied to the three contact areas,
and the wing was folded closed into the airfoil shape and
weighted down thoroughly with many 1/2 pound lead weights to
keep it in shape while the epoxy set.
Below is an end view of
the wing structure after glueing.
Below is a top view of the wing
structure; full length ailerons / flaperons had been cut and
tape-hinged before the glueing was done.
BELOW is a sheet of the
templates I made and used to complete this build; it is 8.5" x
11"at 300 DPI. If you right click on it, select "save as", and
then print it out, you'll have what I developed & worked with.
No, it's not a fancy cad document, it's a full size scan. I hope
you find this useful.
The wing top surface airflow fence
template matches the curvature of the top surface of my KFm3 wing
build; adjust to fit your build.
Below: wing tip plates now
epoxied in place, leading edge shaped, sanded, heat-formed. I
then ironed on a 3" wide piece of 1.7 mil clear document
laminating film wrapping over the wing's leading
edge; about 2" on top and 1"
on the underside of the shaped leading edge. I also decided to
set up the wing for separate flaps (9" long) and ailerons (7"
Below is a view of the
underside oh the wing, showing the control horns , 5 gram servos,
and linkages. servos were inset into the wing structure where the
aileron servo extension
wires could be routed
internally just behind the wing's high point internal spacer. A
cutout on center allows the wires to be brought out to go to the
radio receiver which mounts inside the fuselage just under the
wing. The two aileron servos' wires were combined into a
single plug, soldered & heat shrink covered. servo wires from
the two flap servos were also combined into a single plug.
I added .080 Carbon Fiber rods
to the leading and trailing edges of the wing where the rubber
bands would hold down the wing; the leading edge piece is 7" long.
These were added before the laminating film was ironed over the
leading edge. I then also ironed on laminatine film in the
trailing edge area from the secondary KF step back, wrapping the
entire area top and bottom to further strengthen this area
of the wing.
I added extra structure
inside the fuselage at the leading and trailing edges of the
fuselage to facilitate adding the wing mounts. 1/32" 3 ply birch
aircraft plywood in then glued to the outsides of the fuselage,
and .1" diameter bamboo dowels are passed through drilled holes.
This allows mounting the removable wing with four #32 rubber
bands. An additional former was also added inside the fuselage
to support the rear end of the battery carrying tray /
Below: Gluing the tail group
in place after verifying that is everything is aligned
The Buschtrottel plans by
Thomas B show two pieces of 1/16" diameter music wire, so I cut
them , then bent the legs of the second piece to join the main
gear legs as shown. I then wrapped these joints with kevlar fly
tying thread and coated the wraps with thin CyA glue. I then cut a
piece of 6mm black Depron to fit the inside of the wire, and glued
it solidly in place with hot melt glue . I then decided in a gear
location; I wanted the landing gear legs directly below the
leading edge of the wing. I then added in another white 6mm Depron
vertical support for the landing gear's front edge location.
Below is a view of the underside
of the fuselage; the 6mm black depron was glued in place, and a
section of velcro was added for the landing gear mounting.The motor
is mounted, waiting to be connected. I chose an APC 9x3.8 slow flyer
propeller for early flights.
BELOW: The elevator has a
section of .080" solod CF rod as the center joiner; this was
installed before bevel cutting and tape-hinging the elevator to the
horizontal stabilizer. The rudder was also bevel-cut and tape hinged
to the vertical stabilizer before the tail group members were
assembled to the rear end of the fuselage.
9 gram servos are used for the
elevator and rudder control, cut into the rear fuselage top deck as
seen in the photo below. control horns are made from 1/32" 3 ply
birch aircraft ply. I prefer to use EZ-connectors on the control
horns. since servo horn holes match .040 music wire, the ends of the
.080 CF control rods are made from that size music wire; the metal
ends are then wrapped in place with kevlar thread, with the wraps
then being coated with thin CyA glue.
is a view of the rudder control rod and horn installation.
did the window & door graphics with hand-cut colored (2.2 mil?)
packaging tape. Since tape doesn't bond very well to bare Depron, I
used 1.7 mil iron-on CP document laminating film to overlay a clear
base surface to which the colored tape could bond solidly. I ironed on
the clear film from the from edges of the nose of the fuselage back to
the wing's leading edge on the upper surface, back on both sides to
about 2" behind the doors, and back on the bottom surface to the
landing gear velcro mount area. (This bottom skin provided a tough
surface to which the ESC could be mounted with a bit of hot melt
I save the backing sheets from other letter-size adhesive laminating
film as a working surface; on one full ~9" x 12" sheet, I covered it
with the blue colored tape with fairly narrow overlaps; this gave me a
solid blue sheet of the blue tape from which to cut the doors &
front window using the templates. Once the window & doors were
applied to the fuselage, I laid out the black tape on another backing
sheet, and cut the narrow strips to create all of the black outlining.
4" wheels are held on the axles
with short sections of wire insulation.
The area for the ESC mounting was first overlaid with laminating film;
then the wiring was completed, and the ESC mounted in place with hot
is the view of the Battery access door, which was bevel-cut in the
side of the fuselage, and tape-hinged; a 3S 1300mAH battery is shown
in it's mounting position.
Airflow fences were added to the upper wing surface aligned with the
with skis mounted.
Below is z\a
closer look at the ski mounting details. To keep them in place with a
slightly nose-up attitude during normal flight, torque rods are used.
Start with !/6" plated brass wheel collars; drill a .040 hole, cut and
bend a piece of .040 music wire to suit you build, and solder the music
wire into the wheel collar using 2% silver solder.
I pulled out a set of lightweight
skis with a fair amount of surface area and mounted them in place of the
tundra tires. Each ski weighs 1/2 ounce less than the tire it replaces.
make lightweight skis from 1/32" 3 ply birch plywood.These
skis are 8" long by 2-1/2" wide; once cut to shape, the nose end is
submerged in boiling water; depth of water is only enough for the area
you want to bend. It doesn't take long for 1/32" birch aircraft ply to
become flexible, so do one ski at a time, testing the flex until it's
pliable enough to curve nicely, then get it out of the water. weight
down the main flat ski body withe a HEAVY weight with the ski's tip
blocked up to the desired height, and let it dry thoroughly.
The lengthwise spine is cut from 1/8" 3 ply poplar 'lite ply' .
film is ironed on the bottom surface for slickness; a bamboo
toothpick, flattened on one side, is glued on as a tracking keel
The slats have been cut and rolled, then heat formed into shape. They
were then covered with laminating film before mounting. I made spacers
for iether end, and also added a support at the front end of the
airflow fences. These slats are permanently installed witth hot melt
NOTES ON RADIO TRANSMITTER SETUP AND
deflection while in-flight results in a nose-up movement; without using
FLAP > ELEVATOR mixing, this makes the aircraft close to
I've now set
my 1/2 flap switch position result in a drop of 15/16". I temporarily
have full down flaps set at 1-3/8". My mixing setting is presently at
-79% on my Airtronics RD8000 transmitter.
Another Wing on the Highlander: Reduced Wing Loading
The air is thinner up here at 10,000
ft. ASL in South Park; it's only 71% of the density of air close to
The wing loading on my KFm3 variant build of the Highlander is at 9.2
ounces per square foot. In order for an aircraft to fly at a slower
airspeed, the wing loading has to be reduced.
My slowest flying conventional layout aircraft are built light, with
single surface under-camber wings.
On my WOODSTOK float plane, I'd designed & flew an under-cambered
single surface flat-built wing with ailerons; that wing was quite
light weight, and performed very well.
So I decided to design a new wing that would mount on the Highlander
fuselage, with more wing area and less weight. The photos below show
This wing is made from DOW Bluecor P/P; span is 39.5", chord including
ailerons is 10.5" for 2.85 square feet of wing area. Wingtip plates
are made from black 3mm thick Depron, covered with 1.7 mil Doculam CP
iron-on laminating film. There is a .080 diameter solid CF rod along
the entire leading edge of the wing. A 17" long piece of the same
material is also inset along the upper trailing edge.
One HXT900 9 gram servo is built in at the center of the wing, with
.040 music wire control rods going out to the EZ-connectors on the
aileron control horns (which are made from 1/32" 3 ply birch aircraft
wing has a span of 39.5", and a total averaged chord of 10.5",
including the 2" wide ailerons, for 2.85 square feet of wing area; and
it's 2 ounces lighter than the KFm3 variant wing.
switching from the 32 gram 4" wheels to a set of 13 gram 3" wheels, I
dropped another 38 grams of weight. Then I installed a 1/2 ounce
lighter 3S 1000mAH battery.
With the wing area increase and the flying weight dropped down to 16
ounces, I've ended up with a wing loading that dropped from 9.2 ounces
per square foot down to 5.6 ounces per square foot... the difference
in slow flight capability in this thin air up here should be fairly
Winds are gusting somewhere in the twenties today- a better building
day than flying day. When I get a chance to get back to test flying,
I'll fine-tune the wing incidence; I already have the wing's trailing
edge raised 6mm, and for this type of airfoil, it may need to have
it's trailing edge raised even more [compared to the Buschtrottel
plans' stock wing incidence for the flat built KFm2 wing.]
Under-Camber Highlander Wing Test Flight
Update: Winds died down during the night, and it warmed up to about 17
F by 10:30 AM, so I headed to my test flight spot- the Helipad.
I pulled out a 3S 950 mAH Nano-Tech battery which is lighter weight
yet ( at 2.55 ounces), bringing the flying weight down to 15-3/8
ounces for a wing loading of 5.34 Oz. per square foot. I'm flying an
APC 8x3.8 Slow Flyer prop right now with this wing.
SEE PHOTO ABOVE: With the 6mm thick Depron shim added under the wing's
trailing edge (to lower the wing incidence relative to the horizontal
stabilizer), this under-cambered wing is happy with the wing
incidence. (The shim structure is tack-glued to the T.E. of this wing
itself, making swaps between the two wings simple & quick.)
It took off nicely, and flew well. Being under-cambered, this wing
wants to fly right-side-up; it's not designed for aerobatics, but
turns well with the ailerons. Mixing aileron into rudder should
optimize the turning capabilities. It flat spins nicely in a tight
gradual downward spiral, loops well, but really isn't meant for
A cool breeze came up; coming in low & slow into this modest
breeze, the aircraft slows down to walking speed or below, and is
still responsive to the control inputs. It was almost slowed down on
forward ground speed to doing a helicopter touchdown- (no flaps needed
on this wing). This under-cambered wing really is capable of very slow
landings, yet still handles higher speed flight well. For windier
conditions & more aerobatic flight, I'll just swap back to the
KFm3 wing. (I may fly the lighter battery & lighter wheels more of
Web sight designed and
maintained by Bruce Stenulson, Fairplay, Colorado. (c) 2021; All