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May 13, 2001, 01:51 PM

f-14 center of gravity verus center of lift

i read something a while back that if a plane had variable swept wings that to make it aerodynamically stable in flight the center of gravity would have to move with the wing sweep. in my thinking i thought that having the center of gravity stay forward of the center of lift would cause it to be more stable in the sweept back wing position. any help would be appreciated. thanks. tony
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May 13, 2001, 04:25 PM
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>.. in my thinking i thought that having the
>center of gravity stay forward of the
>center of lift would cause it to be more
>stable in the sweept back wing position.

Yes but it's possible to have too much of a good thing. "Most" planes fly best with the COG as far back as stability will allow. The further forward the COG the more downforce the tail has to generate (=more drag)... and the wing has to compensate by producing more lift (=more drag again). A rearward COG also helps with manoeuvreability.
May 13, 2001, 06:53 PM
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Doc Watson's Avatar

The 'real' F14 compensates for wing movement by pumping fuel into forward and aft fuel tanks. Models can be designed to fly with a 'fixed' CG position, goto and check out the Chris Golds Tornado which is an electric EDF swing wing model. I think the plans are avalible through Traplet publications.

May 14, 2001, 01:46 AM
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Troy's Avatar
I couldn't find Chris Gold's Tornado on the Wemotec site??
May 14, 2001, 06:05 AM
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GregG's Avatar
Originally posted by Troy:
I couldn't find Chris Gold's Tornado on the Wemotec site??
That's too bad, it used to be there. I also have dreamed about making a swing wing F-14. It seems to me that the CG should move with the wings to get everything in balance. Cwatters explained it the way I think it should be. I also think that if you're up to making a model with such advanced features as Swing Wings, the CG movement to coincide with wing sweep should be now big deal. I'd do a cheap, lookalike styro glider at first to get things worked out. Take it up to a slope and try it with the wings in both configurations. Once you get that to fly reliably and get the CG figured out , then move on to your scale project. Just my opinions on the way I'd try it. Be sure to let us all know how yours works out.
May 14, 2001, 01:48 PM
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francois's Avatar
Doc is absolutely correct, the F-14 pumps fuel aft to deal with the aft CP shift. Also if you ever look at pictures of the F14 in a fully swept configuration at supersonic speeds these little canards pop out of the wing glove box just ahead of the wing pivot. These little areas help move the Cp foward as at transonic and supersonic speeds the Cp moves aft.

Hmnn a swing wing ducted fan....too many projects already :P


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