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Project
2 meter custom design and build Electric glider - failed.
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Published
Apr 22 2012 by FaTe
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This project was my latest attempt to build a better FPV platform than a stock model. Unfortunately during it's maiden flight it was found to be highly sensitive to control input with constant adjusting required. I managed to get round a full circuit to land but when coming into a glide slope for landing, slowing down the whole high sensitivity got massively worse, lost air-speed and stalled cracking the wing completely in 2 while 1 piece was still bolted in place - says enough.



I decided to post the project anyway because it's a case of lesson learnt with the design flaws and to be honest is totally surprising it was able to fly a circuit at all.



This glider is pure balsa with carbon fibre re-enforcements, it has a 2 meter wingspan which where designed to come apart into 1 meter pieces for storage. Motor to tail it was 112CM long, the tail was a solid carbon fibre rod 5MM in diameter but it still was pretty flexible this is where my mistake lies. In flight the vibration of the airflow caused a fish tail effect which in turn adjusted the control line lengths (by swaying right it would pull more on the rudder than it should for example). So each correction to bank the opposite way to the roll resulted in the tail flexing and the rudder pulling in the opposite direction so it was full on correcting.



If your building something similar with a not so light model (500 grams +) I'd suggest continuing the fuselage as a whole balsa construction to the tail OR using a 7MM/5MM carbon fibre tube and epoxy the rod inside like a sleeve but this is more weight (I already had to add 245 grams of lead in the nose!) Well here's the build:






fuselage back
The back of the fuselage had a divider separating the tail servos from the main compartment.



fuselage magnet cover
Magnets where used to hold the front panel on the nose in place.



fuselage electronics test setup
Here you can see all the electronics in place and I added a hinge on the nose panel.



fuselage bottom nylon steel nut
The wing was to be held in place using a nylon nut with this steel locking nut in the balsa wood.





glider tail balsa frame
Quite an a-typical tail build with a span of 50CM and a height of 15CM.



solid silver orafilm coating on tail
Now covered using solid silver Orafilm.



panel servos protect wing frame
Most people install servos into the wings on the wing frame meaning later if they need replaced you have to damage the frame. Instead I always put the servos on plywood covers.



wing frame with servos
Mocking up servo placements in the wing.





wing frame work with tounge slot
The basic frame with ribs standing 2 meters tall.



wing support rods 2MM steel
You can see how the wing uses a slot/tongue interlocking system.



wing final fitment join
When the slots overlap they line up the hole for the nylon bolt to pass through pinning the wings together.



2 meter wings balsa frame with tail
All the frame work together.





wing full 2MM balsa top covering
I added 2MM balsa sheeting over the entire wing top which made the wing super solid and didn't actually add that much weight for the benefits gained.



fully sanded wings
All sanded down ready for covering.



wings covered silver orafilm servos installed
Again the same solid silver Orafilm with servo panels installed.



wing top center plate overlap FPV platform
The plan was to mount FPV gear on this plate which overlaps the other wing when together.





carbon fiber tail boom with carbon fiber platted
The tail was pretty flexible so I used carbon fiber strand and platted up and down it before epoxy coating all of it. Evidently after the maiden landing fiasco it still wasn't enough.



tail heavy required 245 gram lead weight nose
When I got to the field and began adding weight to balance COG I ended up adding 245 grams of lead into the nose to balance COG! (Making AUW 1275 grams still light really)



full electric glider set up at flight club
The whole plane in 1 piece for the last time...





wing aileron clean snapped all hinges
So as I said previously when landing and slowing down resulted in a nose dive the damage was not small. Here it just looks like the elevator popped off, thats snapped 3 good grade pin hinges clean off, it was just hanging.



wing snapped completly from center
The true death picture. Notice the wing bolt is still screwed in place... notice the right wing is still in place and the left .. well isn't at all. Totally snapped all the panels.



There is a chance to still use the tail itself (NOT boom) and wings if I make a full box fuselage and use elastic bands to hold the wings (in turn holding them together) so that the steel rods still do their job, however not for a while I'm done with this project for now.

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