The Highlander

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.

Plans with some english labels are available in the Buschtrottel thread on RC Groups; CLICK HERE

SPECIFICATIONS

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 build
Motor Used: Grayson Hobbies GH2212-10
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 grams each
Landing Gear: .062" music wire
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 as built with 3S 950mAH battery, on 3" wheels: 17-3/8 ounces; Wing loading of 8 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

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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" long).


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 /  plate.

Below: Gluing the tail group in place after verifying that is everything is aligned correctly.





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.


Below is a view of the rudder control rod and horn installation.


I 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 glue.)

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.




Below; 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 melt glue.


Below 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.


Below: Airflow fences were added to the upper wing surface aligned with the flap/aileron junction.


HIGHLANDER 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.

I 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' .
 Laminating film is ironed on the bottom surface for slickness; a bamboo toothpick, flattened on one side, is glued on as a tracking keel strip.


BELOW: 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 glue.


NOTES ON RADIO TRANSMITTER SETUP AND MIXING

Flap deflection while in-flight results in a nose-up movement; without using FLAP > ELEVATOR mixing, this makes the aircraft close to unmanageable!
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.

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Testing 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 sea level.

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 the result.

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 plywood.)



This 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.




By 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 dramatic!


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


1-31-2021 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 inverted flight.

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 the time.)


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