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Scaled-up FT Explorer

#1
For reasons of payload space, I'd like to build an airframe for a budget slow-flying UAV that is essentially the FT Explorer, only scaled up by 1.5 (roughly six foot wingspan, using the polyhedral wing design). I have an ample supply of foamboard, but the wing construction would have to be adapted to the fact that one complete wing can no longer be made from a single sheet of foamboard. Any ideas on how to do this in a simple yet structurally sound way?
 
#2
im stuck at the same problem i made mine 120% to compensate for the thiknes of depron 6mm but i am not shure how to brace the wing so it won't colaps during flight
 

Hai-Lee

Old and Bold RC PILOT
#3
Try a simple change to the standard approach and that is to make a large, (Widest possible from a single sheet of foamboard), span single section for the centre, (over the fuselage), and fit either a spruce or CF spar reinforcement. the polyhedral sections begin from the ends of the flat centre section. By shifting the "wing Joints" outboard reduces the forces acting upon them and makes the wing far more resistant to folding or breaking under high stress loads.

The first polyhedral wing joints should be relatively shallow if the wing segment to be joined is long and the final "Tip wing piece can have a slightly greater angle and much shorter span. Effectively just the wing tip shape. With the wing tips think of changing the planform cut line to introduce washout into the design to give gentler stall characteristics.

Dihedral braces would still be recommended on the 2 inner wing joints or some form of wing detachment mechanism as used in the backpack spitfire. The wing tips could remain permanently connected to the wing outer sections, effectively making the wing a 3 section wing.

Rather than large ailerons with a huge powerful servo you can use trailing edge control surfaces on the 3 inner wing sections with 4 separate servos and the 2 control surfaces on the wing centre section being configured as "Flaperons" and the outer control surfaces as plain ailerons with the possibly of adding crowfoot mixing as well.

Additional measures to improve the rigidity of the structure could be considered. Firstly some wing or fuselage location blocks are recommended to stop the fuselage trying to slide along the wing during maneuvering with heavy loads. Secondly a set of wing struts could be considered fro the fuselage sides out to the centre section wing joints and finally wing leading and trailing edge surface reinforcement to reduce or stop the damage to the wing caused by the increased forces causing the wing hold down rubber bands from cutting through the wing.

If you require any further explanation of my suggested solutions please advise and I will explain further or someone else would.
 

AkimboGlueGuns

Biplane Guy
Mentor
#4
You can try using external wing braces like you find on most light high wing aircraft (a la Cessna 152) right on the polyhedral line. Cheap arrow shafts work great for that, and you can also use them as internal spars.