Scratch-built Micro Skyhunter

3mm depron version of the wonderful little twin boom Eachine Micro Skyhunter.
Dimensions are similar to the original but with a slimmer fuselage.
1300mAH 3S battery and FPV gear.
CG best around 35mm.
The final version has a shorter nose, reinforced horizontal stab and rounded wing tips

Build video

Maiden flights

Mods Q&A and FPV

Albatross 2m sloper

Before the Red Sloper came this 2m wingspan sloper. It actually started life as a motor glider but a dodgy ESC connector stopped that project from being fully realised. I'll revisit it soon.

I call this one the Albatross for obvious reasons.

The orange plane is the pusher trainer with a 1.5m polyhedral no-aileron wing adapted from the slim wing. I'll post about that one when we get a nice calm day to do a proper maiden.

The depron I use comes in 1000mm x 700mm sheets so I can make the 2m wing in 2 halves.

I used 3 Skyshark spars all up, 2 joined with a 10mm x 150mm ali tube for the main spar and another spanning the join closer to the leading edge. The spar layout is visible in this shot of the wing on an earlier version of the fuselage.

The wing has full span ailerons operated by TGY 9018MG metal gear micro servos. Total chord is 200mm including the 35mm ailerons. That gives a 10:1 aspect ratio.

I suspect 40 to 45mm ailerons would have been better to give a faster roll rate for some aerobatics but they are fine for smooth cruising.

Airfoil thickness is 23mm, formed by using a 3mm strip of depron over the main spar, giving an 11.5% airfoil.

The tail is just a little scaled up from the Red Sloper but basically the same shape.

Horizonal stab is 460mm wide x 90mm deep tapered to 70mm at the ends plus a 50mm elevator.

Vertical stab is 220mm high x 130mm at the base tapered to 60mm at the top plus a 50mm rudder.

Elevator servo, hidden inside the fuselage, is a TGY 9018MG and rudder servo is HXT 900.

Fuselage is a 1000mm long x 70mm square tube tapered towards both ends for looks, weight saving and aerodynamics.

Weight is 650g without battery and balance weights and 830g flying weight.








The big wing makes for an excellent light wind slope soarer which also works well in strong winds. It's smooth and languid in the air, not so aerobatic, but a delight to cruise along the ridge.

UPDATE: I made the nose removable so I could swap to a motor pod. Just have to pull off the tape around the join and re-tape the motor pod on. The motor glider version is 730g without battery and 925g flying weight.

It took some decalage adjustment to smooth out the tendency to loop up under power. I needed to tilt the wing forward by sticking about 8mm of packing under the rear mounting area. Then it tracked level and glided much better.

Better airfoils using 6mm depron

After the poor performance of my first 2m motor glider and great performance of the slim wing and symmetrical wing I though it was time to investigate airfoils more thoroughly.

My standard building materials are 6mm depron and 7.5mm Skyshark P4X spars while Experimental Airlines and Flite Test use 5mm Dollar Tree foam so I needed to tweak their methods for my designs.

For inspiration I looked at the Bixler 2 wing which glides beautifully, and the widely used Clark Y airfoil.

The key features are ... maximum thickness is around 11.7% of the total chord and positioned 30% back from the leading edge.

My mission was to come up with a technique to replicate these features using my materials.




Wing section construction

My standard wing building method is to cover one side of the 6mm depron with packing tape. I have used PPS and Scotch tapes and prefer the cheaper PPS.

The inside of the bottom trailing edge is tapered to 1" to conform with the top layer for gluing. I found it was better not to sand all the way down to the covering tape but to leave about 2mm thickness at the trailing edge. This allows the aileron to better blend in to the overall airfoil shape.

I make a slight dent line (with the other end of a pencil) along the inside of the leading edge position to give an accurate fold. Don't make the dent too deep or you will have a sharp leading edge.


I made up airfoil sections ranging in chord length (including ailerons) from 6.5" to 9.5", spar placement 20 to 30% back from the leading edge line with 20mm formers glued either side, and zero, half or a full thickness former on top of the spar.


The combinations that most closely matched the Clark Y airfoil were:

A. 7.0" chord (5.5" plus 1.5" aileron) Spar 53mm back with no extra former
B. 8.0" chord (6.5" plus 1.5" aileron) Spar 61mm back with an extra 3mm former layer
C. 9.5" chord (7.5 plus 2" aileron) Spar 76mm back with an extra 6mm former layer

To my eye these sections looked much nicer than my previous builds and much closer to commercially produced RC gliders and planes. Depron will kink rather than bend smoothly over the formers if the curve is too great but it's not a problem with these slimmer sections.

These have become my standard wing chord designs now. I would add larger 2" ailerons for aerobatic models, especially slope soarers. Varying degrees of airfoil section symmetry can be built-in by varying how much you press the wing down flat while gluing up.

A symmetrical section gives better inverted and aerobatic performance while a flat bottomed section gives more lift and better gliding performance.

I used the B section in my next project, the wonderful 2m slope soarer.

Symmetrical Armin wing slope soarer

This symmetrical Armin wing was designed specifically for aerobatic slope soaring. After two frustrating weeks of bad winds I finally got the chance to test it.

1.4m wingspan
20mm thick
140mm (5.5") chord plus 50mm (2") ailerons





Here's the proper maiden flight in 10-15kn NW. The wind was slightly off slope to the left but the glider behaved beautifully, a delight to fly and aerobatics worked nicely. Inverted flight was excellent, rolls and loops worked well too. It's quite a light weight at 480g and needed some ballast from a bigger battery when the wind picked up.

A few days ago in desperation I tossed it off the dune in 30kn and it did fly but exhibited some frightening elevator flutter. That flight was more survival than flying so it didn't count as the maiden.
The large aerobatic elevator with some area forward of the hinge contributed to the flutter, as well as sloppy linkages, short control arms, loose servo mount and a dodgy tape hinge.  The flutter only happened on launch into 30kn so it's not an issue in normal conditions.