Scratch-built depron piper cub

2 years 7 months ago #1059 by Alex
Over the winter I have not been able to fly much so I have been building a simple plane mostly from depron. It is based loosely on some plans I found freely available online for a Piper Cub (see pdf attached)
I heard that the biggest problem with depron planes is the tendancy for the tail and body to twist undesirably so I decided to use a simple wooden frame to give it some rigidity. I also used some 3mm sheet acryllic for the motor mount section because it easily allowed me to get the angles right and I happen to have lots of it lying around. We will see whether this works in the long run, its a bit experimental.

There is also a simple wooden wingspar which should provide some strength and rigidity to the wing and give a nice strong connection to the frame of the fuselage.
I have shown a photo of the wing next to the wing of my Bix3 for comparison. I decided to use an undercambered airfoil for the wing because I ideally want a slow flying plane with plenty of lift as I am still essentially a beginner flyer. I have some concerns over how the shape has turned out but I guess will just have to fly it and see its characteristics.

Wingspan is 130cm
wing width is approx 25cm
weight (with all components inc battery servos etc piled on the scales) is approx 900g so far.

There are still plenty o of adjustments I need to make to even things out and install all the electronics but as its probably going to be a while until we get good flying weather for beginners there's probably no rush.

If anyone has any comments or suggestions I'd be very keen to hear them, this is the first plane ive built so there are probably loads of things that I have overlooked. Thanks :)
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2 years 7 months ago #1060 by flierman1945
I think you have made a good job for a almost scratch build, especially the body section. Not sure about the firewall material. It may be better to install a ply firewall rather than the plastic one you mention. One way to make a strong firewall is to sandwitch 3 layers, use 1/8 th ply each side of a 3/16 hard balsa sheet. This will give good strength, a rigid motor mount and will absorbe some motor vibrations.
The wing with an under camber will give huge amounts of lift and with a weight of around 900gms, the wingspan and chord will generate posibly more lift. Fairly large Ailerons might be needed, not sure what size you have them at present. I wonder how you moulded the depron wing profile?.
When I used to build Deprom models, I mostly used flat plate wings, but they are really next to useless. I tried various ways to make a profile Depron wing and ended up using loads of masking tape planted on the underside of the contour required, this stopped the Depron snapping as I tried to form it. around the nose section. I could only manage a fully and a semi symetrical wing section. They worked much better than my flat plate mwings.
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2 years 7 months ago #1061 by Carl
Replied by Carl on topic Scratch-built depron piper cub
Hi Alex,
It looks like you have done a really good job of your first scatch build. I have never built with depron but was wondering if you have any dihedral in the wing, I know it adds to complexity and a little weight but it will add a level of stability. It also enables you to use the rudder for roll control if the ailerons prove ineffective. It may be a bit late as the wings look more or less complete. You could always make a second set of wings if you get bored!
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2 years 7 months ago #1062 by Alex
Replied by Alex on topic Scratch-built depron piper cub
Thanks for the comments.
I think I will try and reinforce the firewall with some ply to make it more rigid.
For the wing profile I followed the Armin wing process and I moulded the undercamber with a crude process using a broomstick handle. Just after performing the main fold of the wing and applying glue to the inside surfaces I placed the wing on the floor on top of a broom handle about 2/3 of the way from the front then weighed down both sides with a whole pile of books and left it for a day a and a half. Its certainly curved although maybe not quite the right shape.

I havent yet cut the ailerons into the wing - ill be sure to make them nice and large.

I did try to build some dihedral into the wingspar but I dont think it really shows through after covering with depron. I was wary about having a join in the middle of the wingspar so made it a 3 piece spar with the wing tips tilted up by 3 degrees at about 30cms from the ends. Unfortunately it seems the depron just wants to sit completely flat, oh well if i end up damaging the wing ill rebuild it in a different way.

Ill need to sort out some landing gear next, i might try to find some nice big tundra tyres fro that backcountry look :)
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