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Old 06-17-2006, 07:37 PM   #1
Ryan Davison
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Flying wing Question


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Ok guys Once again I have a question
Get used to it.
Ok I built My own Moth flying wing slope soaring /dynamic soaring glider.
There were Finally South winds here today at 25kmh plus and odd gusts too I cant beleve it after waiting a month an 1/2 for it to come.
Anyway back to the point.
I saw the wind outside thismorning I jumped outta bed grabbed my gear and rocketed to the ski hill.
Maiden flight I set the elevons to neutral trim and gave it a toss. B4 I had time to touch the stick it dove to the ground like a brick
I gave it some up trim and tried again and zoom away it went.
I Had a ball with the thing most of the day today. trying to keep it airborn as long as possible 38 Min was my best.

It flies But I find that It is Way too pitch sensitive.
I can yank back on the elevator and it will pitch up slowly.
But as soon as i very slightly push forward on the stick the nose drops Instantly and it dives for the ground.

Im comming to think this is a cg problem

Is there any formula or some kind of ratio you guys use for balancing thes moth gliders .

The airfoil is swept back very slightly and the cord is about 7 inches.

I havent been able to uncover any usuable balancing info on the net.

Im wondering if the Cg needs to be moved more to the rear or to the front to overcome this problem.

I stuck a rock in the nose to see the affect and it was then very hard to pull the nose up in flight

Also could this possibly be too much throw on the controll surface?

there is bairly and moving of the ailerons at all when i pitch full down the tips move mabey 1/16" of an inch or 1 degree ect down
they move about 1/4" up for positave pitch.

Let me know of any good websites or whatever you do to balance your home made flying machines.
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Old 06-17-2006, 08:10 PM   #2
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CG

Because flying wings have such a short pitch moment, what you are experiencing is right. Pitch sensitivity goes with the territory, and the game is to use it to your advantage, ie, stall recovery is very quick. You can trim it out (CGforward, more up trim) as you found with the rock in the nose, so play with varying noseweight and trim. Roll control is the same: a short roll moment is more sensitive in that axis, ie, short wings roll faster than long ones.

So whether you designed it yourself or not, wings all react to physics.
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Old 06-18-2006, 06:00 AM   #3
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right on

Kool
I better post a pic of my art just to get the guys out of confusion.

I built this glider out of parts I had around from a Vtail glider that was crashed.
I got rid of the rear fuse
Installed a vertical fin and cut elevons out of the solid wing and hinged them on and put micro servos in the wing.

It doesnt look Bad at all for a few hours of getting my fingers stuck together with CA and gorilla glue.
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Old 06-18-2006, 06:11 AM   #4
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Yeah Now that i read again

Im going to Do what you said
I think My balance must be close to dead on as it is because I can keep the glider nose into the wind and it will sit there not going ahead or backwards. Actually It flew backwards too on the slope.
What im getting at Is that it wont tip stall or even show signs of wanting to stall as it is right now.
It will loop and roll like crazy now with ease so that is a positave thing.

My trouble is That I cannot lower the nose at all and try to pick up airspeed. When I try to push the nose just a smidgon down (move the stick a hair) the nose instantly drops about 35 degrees. To fly fast It bobbs up and down like crazy. I hope Im overcontrolling it.
I heared these things are very sensitive to cg "Out of CG by 1/8" can change everything apparently.

Mabey I should Add in even less end point adjustment , Leave the CG alone and just play around with the radio.

Then after playing with the radio alot and no better Ill go back to looking at CG again
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Old 06-18-2006, 06:15 AM   #5
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Better Idea

Hey Heres a Plan

Could one of you guys who has a moth like mine (look at my picture once i post it) That flies perfect Give me some info about it.

What I want to know is What is the cord of the wing (width from LE to TE)
And the Exact measurement from the LE to the CG.
I will take these measurements Put them into a percentage.
and see there that percentage of the cord lines up with the CG on my moth.
I can see if im in the ball park if I do that.

Ok guys In the bottom view pictire you can see 2 black dots on the wing
I have the cg approx half way between the LE and those Dots.

Those Dots were the original Cg dots when it was a V Tail Glider.

What does anybody with experiance think.

This Is my first Elevon attempt at an aircraft.

Perhaps I should Change My username from Ryan Davison to "Types Alot " hahaha
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Old 06-20-2006, 01:45 PM   #6
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hmmm

Nobody out there has any cg info?

I better try google again for info
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Old 06-20-2006, 02:15 PM   #7
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Ryan, flying wings generally fly a little better if the wing has some "reflex".
In other words, the trailing edge of the wing bent upwards slightly.
With your strip ailerons, you could do this by raising both ailerons a bit. Play around with the amount until you get the best flying characteristics.
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Old 06-20-2006, 02:52 PM   #8
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Quote:
Originally Posted by ronm
Ryan, flying wings generally fly a little better if the wing has some "reflex".
In other words, the trailing edge of the wing bent upwards slightly.
With your strip ailerons, you could do this by raising both ailerons a bit. Play around with the amount until you get the best flying characteristics.
Here is a nice article on airfoils.
Scroll down to the part on reflex.
http://www.nurflugel.com/Nurflugel/n_o_d/weird_02.htm
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Old 06-20-2006, 09:09 PM   #9
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Yeah thanks for a reply

Yeah thanks for a reply
Il check that site out asap

When in flight yes my elevons are raised up to fly level

I think the best way to go about it is to fly it over abd over and keep adding weights to the tail untill the twitchy nose thing goes away.

Ill have a look at the link there and see if it helps more

thanks
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Old 06-21-2006, 07:58 PM   #10
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Now you've got it...

Twitchy means unstable; a good thing sometimes, bad other times. Balance the weight in the nose with more up trim on the elevons. I tried to get that across before, sometimes my c omputer writes in Klingon...
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