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help on balance

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Old 11-10-2005, 09:58 PM
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doom
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Default help on balance

How would you balance a plane thats almost round,What percent from where.Pic attached.
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Old 11-10-2005, 10:19 PM
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Default RE: help on balance

I would shoot for about 1/4 back from the leading edge. The closest plane I have ever flown to this is a "pizza box" - 24 inches square. So if the diameter of the circular wing is 24 inches, I would put the CG about 6 inches from the leading edge.
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Old 11-10-2005, 11:28 PM
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Default RE: help on balance

I was thinking maybe 1/3,But this this aint a usual flying machine.May not even fly at all.With the engine behind right now seems pretty tail heavy.
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Old 11-11-2005, 08:52 AM
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Default RE: help on balance

You might make a scaled-down simple model of sheet wood, a glider, and test it to get the CG in the ballpark for your powered model.
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Old 11-11-2005, 05:55 PM
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Default RE: help on balance

I also thoght about balancing it in the middle.Any thoughts on that.
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Old 11-11-2005, 06:21 PM
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Default RE: help on balance

Doom it seems what you have there is an extremely low aspect ratio flying wing. The vast majority of model aircraft configurations are happiest with the CG at somewhere between 25 and 30% MAC. Some exceptions occur with airfoils used for instance deeply undercambered airfoils as used on many old timers fly well with CG's as far back as 50 to 60% and another are flying wings. With these many do well which are of a higher aspect ratio do well with CG at around 12 to 18% and a little up reflex of the airfoil or simply the trailing edge control surface rigged with a few degress of up at neutral.

I would suggest going back with the CG as far as the middle would be catastrofic. The 25% point suggested by DMcQuin would be an absolute rearmost starting point. My best guess would put it somewhere around 18 to 20%. Dsegal suggestion of making a simple balsa sheet chuck glider to test CG's is a marvelous method that is a well tested and effective technique used by many model designers particularly in the case of unusually configured aircraft.

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Old 11-11-2005, 07:11 PM
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Default RE: help on balance

I,ll try a 30%.what do you think about vortex generators on the front to disturb the air and help out at lower speeds.Might help as an air spoiler to simulate an air foil.
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Old 11-11-2005, 07:36 PM
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Default RE: help on balance

Thirty percent is going to be to far back, To acheve any kind of positive pitch stability at all 25 is going to be at the limit of aft CG and more than likely around 20. Vortex generators anywhere are a moot point.

Another potential problem are the vertical surfaces. They appear to at about 50% MAC and would contribut nothing to yaw stability, in other words the airplane really won,t care if its pointing in the right direction or not. A better place for the fins would be back and just outboard of the rear trailing edge cutouts.

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Old 11-11-2005, 07:59 PM
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Default RE: help on balance

Ok 25%.As long as it gets in the air,I might want to take a trash bag with me when I try it.It has a little diehedral also.I flew a jack stafford b24 on one engine and got it back without crashing it,Maybe I'll be able to handle this thing.
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Old 11-11-2005, 10:41 PM
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Default RE: help on balance

Hey Doom ....

You got a lot of good advise here. However I would like to give you a lottle more food for thought. First of all, a slightly nose heavy airplane will fly. It probably won't be as responsive as you would like. But ... I slightly tail heavy airplane can be a hadful at best and is usually more like a total disaster. Having said that, you won't go wrong at even 20%. If I were you, I would probably slid my battery pack foward and get to what was said earlier 18-20%. Worst case situation would be that you don't like the charactistics and move the battery further toward the tail for the second flight. At least you stand a better chance of comming home with the plane in one piece.
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Old 11-11-2005, 11:01 PM
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Default RE: help on balance

From front to tail its 19" thats going to put the balance ruffly at 4" back at 20% 4 3/4 at 25%.
Its 32" wide.Dont know the weight.Yea nose heavy is better than tail heavy.
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Old 11-12-2005, 10:43 AM
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Default RE: help on balance

I'd suggest you follow Mr. Buckners advice, if anything make it nose heavy, especially if you have reflex built in. A good starting point for this type of planform is 12% or MAC.
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