SPAD e-cobra maiden

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Monhty
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SPAD e-cobra maiden

Post by Monhty »

Hi

today I maidened my coroplast version of Liddle's Cobra using a 5S (2S+3S) with a Turnigy 3536-1100 and a 8x4

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"Fuselaje" is 8 mm pine. Wing is 2 mm coroplast in top surface and 4 mm coro in bottom. Also 4 mm is used in stabilisator and fins which are made of a single piece of coro in U shape

Wing incidence is 1º

Motor and horizontal stabilisator 0º. Motor is level with the wing

Aileron reflex aprox 2 mm.

CG at 23% del MAC

On full throttle goes vertical so some down thrust should work to keep it level

On idle also is tail heavy: so seems CG is too aft

Tryed the 30º diving and goes up wildly as I release the sticks: this would indicate the CG is too forward

Questions:

- should CG be moved forward o after?
- should I put some more reflex?

Thanks in advance,
Last edited by Monhty on Sun Jan 17, 2010 1:11 pm, edited 2 times in total.
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David Drowns
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Re: SPAD e-cobra maiden

Post by David Drowns »

Hey Monhty.

I'm not going to be of any help here but I am curious how your weight came out. When I copied the Mako out of coro it came out real heavy at 4 1/2 lbs. To much for this one to compete. Maybe it was the 3/16 ply I used.

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Monhty
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Re: SPAD e-cobra maiden

Post by Monhty »

Hi,

nice one!!

mine is a bit heavy as I made it from whatever scrap I had around

Now weights 1450 gram (around 50 oz) RTF but the next version can be down to 45 oz without much problem
Last edited by Monhty on Sun Jan 17, 2010 2:28 pm, edited 1 time in total.
Monhty
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Re: SPAD e-cobra maiden

Post by Monhty »

This morning managed to deal with the excess weight

Image

Now must solve the strong spin tendency to the left.

Maybe some motor thrust to the right will do... :mrgreen:
Last edited by Monhty on Sun Jan 17, 2010 1:10 pm, edited 1 time in total.
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Dane McGee
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Re: SPAD e-cobra maiden

Post by Dane McGee »

.............ouch! Better luck on the next one :mrgreen:
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David Drowns
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Re: SPAD e-cobra maiden

Post by David Drowns »

Oohhh......Too bad. I bet that one had to hurt...

OK now since that one is done maybe I can help a little. I wouldn't worry about adding incidence so much. Just build symmetrical (key with coro) with SSC some lift is good. The up and down thing with power settings after reading it again I can help you on. Trim for level flight full throttle, cut power to half, if it drops then crank both ailerons up and retry. if the CG is out you'll notice it by being really snappy in the loop if it's back to far. (maybe someone else could help here since my flying wing experience is low.) Keep trying it. you'll get it right. Then build backups for those unfortunate but likely incidents shown in the last pic and they won't hurt so much....it's coro! :D
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Re: SPAD e-cobra maiden

Post by gsjames »

I found that when my prototype i.c. Cobra hit the ground, the screw eye ripped through the coro stab. We've thought of several possible things to address this problem, one would be to put fiberglass skewers in the flutes ahead and behind the screw eye to distribute the load. The other is to get rid of the screw eye all together and drill two 1/2"-3/4" holes through the coro stab such that the inner edge of each hole is tangent to the side of the motor stick. I will then put cup hooks on the motor stick to serve as a rubber band anchor. I will still put a skewer through the coro flute ahead of the holes to prevent tear out. I think that this method will allow me to slide the motor stick forward and aft to get the balance just right. I'll work on one over the next week and let you know how it goes.
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Re: SPAD e-cobra maiden

Post by jj »

A plane with a CG too far forward flies poorly but a plane with a CG too far back flies once.

Better too far forward at first while testing out a design. If it takes lots of up to land and lands fast, or if it takes a lot of down to fly inverted then your CG is probably too far forward. Try moving it back 1/8" at a time. CG is more critical on flying wings so you don't want to make a big change. I prefer to use the inverted flight method for powered planes and only use the dive recovery method for gliders, but you can use the inverted flight technique for gliders too.
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Monhty
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Re: SPAD e-cobra maiden

Post by Monhty »

Thanks for all your advice

Cg location is really critical. 1/8" adjustments are a must!

Mk2 is in the production line right now

Monhty
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