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A Depron Super Cub

#1
I have built many planes but never a Super Cub so I thought it was about time I did!

True scale, 40" Span, nothing special except it should be very light, built in 2 & 3mm Depron.

The fuselage formers.
FuseFormers.JPG
The side panels are in two parts to create the fuselage 'crease' down each side.
Fuselage1.JPG
The micro 3.7g elevator servo is mounted under the tailplane. It will be 'bank and yank' so no rudder.
EleServo.JPG
The small 2805 1500kV motor will drive a scale diameter 7" prop on a 2s LiPo.
1500kV2805.JPG
The motor will be fixed to a small circular ply bulkhead that is mounted inside a Depron tube that itself spans the first and second formers.
MotorTube1.JPG
This arrangement provides a light but rigid fixing that spreads the load widely through the fuselage.
The motor mounted in the tube. The bell runs very close to the tube!
MotorMntd.JPG
A Depron nose block complete the motor installation.
NoseBlock1.JPG
The fuselage is the most complicated part of the structure by comparison the wings are simple!
 
#5
DDSflyer
The motor only draws 7A (50W) at full power and it should fly on a quite a bit less so hopefully cooling will be too much of an issue.
 

xuzme720

Dedicated foam bender
Mentor
#8
Hopefully neither, or if anything slightly nose heavy. Of course, that will be set up later once all the components are installed.
 
#9
The wing are slightly unusual, they have no spar and rely entirely on the strength of the Depron skin and wing bracing.
LandRwings.JPG
The 3.7g aileron servo is built into each wing before the top skin is applied.
RHcomplete.JPG
The tail feather are simple Depron plates with balsa reinforcing at the elevator line. It has no rudder so the fin is in one piece.
TailFeathers.JPG
The undercarriage mounting consists of an plastic sheet 'plate' glued to the side of the fuselage.
UCmounting.JPG
The wing struts are retained by the rear undercarriage leg.
Even the wheels are made of Depron with sheet plastic centres.
DepronTyre.JPG
Each 1.75"x0.8" wheel weighs only 0.1oz (2.8g).
The Depron tail wheel is mounted in the same way.
TailWheel.JPG
For no reason other than I was the paint I had to hand it is black and yellow.
Painted1.JPG
The battery is mounted very close to the CofG and is accessed through a hatch in the wing centre section.
BattRadioESC.JPG
The ESC and radio are housed here as well.

With an 800mAh 2s it weighs just under 8oz giving 100W/lb. The wing loading is 4.5oz/sqft and it has a thrust to weight ratio of nearly 1:1.

As I hoped it has a good short take off even on rough grass. The landing run is almost zero!
[video=vimeo;70798549]https://vimeo.com/70798549[/video]

The front bearing of the motor failed after just a few minutes running. When replacing the motor I took the opportunity to increase the diameter of the motor tube so the bell had a bit more clearance!
MotorOut.JPG

It now flies with a 1500mAh 2s which gives a potential endurance approaching 30 minutes.

I now have a Super Cub!
About its only disadvantage is its light weight which means it really can only be flown in pretty calm conditions!
 

colorex

Rotor Riot!
Mentor
#10
Wow, that's really nice. I have desires to build an Extra with balsa, which of course uses the ribbed wing technique. So much fun!
 

DDSFlyer

Senior Member
#11
That's awesome! Great build, good looking plane, and I love the Super Cub! Got my Horizon one as my first plane and it's still my go to at the field for fun relaxing flying
 

xuzme720

Dedicated foam bender
Mentor
#12
Those wheels and short take-off make this one a proper bush cub! Very nice build and makes me want to do more with foam.
 
#13
In hind sight (its a wonderful thing!) I should not have built it as a 'bank and yank'. It saves weight but with its big wing, modest fin moment and light weight it really needs a rudder for adequate slow speed control. Even with 100% aileron differential it is still rather sluggish turning to right (against the motor torque).
In the video it turns to the left after take off, not that I could do much about it!

It will be one of the winter jobs.
 
#14
After somr thought I decided on a coupled aileron/rudder system using 7lb mono filament fishing line in a 'closed loop'.
From the RH aileron horn the line goes forward to a tiny eye on the wing underside.
RdrCable1.JPG
Along the underside of the wing to the fuselage to another eye and then directly back to the double sided rudder horn.
RdrCable3.JPG
Similar on the other side to the LH aileron.
The rudder has top and bottom 'pin' hinges.
Simple and weighs almost nothing.
It has certainly transformed the Super Cub's handling.
It still really is a 'calm day only' flyer but that did not stop me climbing power off in a thermal with it this week!
.
 
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Foam Addict

Squirrel member
#15
Cool! I love your simplicity with the closed loop system! That cub is a work of art, and with a wingloading that low, well I'm not surprised it can thermal.
 
#16
One advantage of building very light for its size is it reduces the power required to fly so the battery can last a long time.

A few days ago with some very calm weather I thought I would try to find out just how long.
A HK altimeter was on board to record the flight duration but no other modifications.
26Jun14.jpg
53 minutes!
The battery (a rather old 1500mAh 2s) was taken right down to the LVC. I had not realised this until it got low enough to see that the prop was no longer going round! :eek:
The battery took 1250mAh to fully balance recharge. It was a real 'cheapie' so I doubt it ever really had the claimed capacity even when new!
Doing the sums shows that it was taking on average 1.35A.
With a average battery voltage of say 7.4 that means it was using just 10W and that was powering the servos and radio as well.
Not bad for a 40" true scale plane with oversize tundra wheels.
 

Foam Addict

Squirrel member
#17
Very nice, you have completely inspired me Quorneng. I built a DTFB specter clone, and at a 48" span it only takes 36 watts at WOT,
It has a 2 hour duration on a 2200 mah.