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Old Jan 26, 2004, 08:33 PM
Registered User
farmington, mn
Joined Sep 2003
871 Posts
why does my manual tell me my wing has a different CG for different motors?

ok my slow stick manual tell me that a 300 size motor the CG on the wing is at 110mm but a 400 size motor my CG should be located at 95mm. why is this? i plan on using a brushless motor with 35 ounces of static thrust should i move the CG even more forward on the wing? i just don't understand how the CG point can change because of a motor
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Old Jan 26, 2004, 08:41 PM
EDF Head
Haldor's Avatar
Stavanger, Norway
Joined Feb 2000
7,999 Posts
Re: why does my manual tell me my wing has a different CG for different motors?

Quote:
Originally posted by jeff262
ok my slow stick manual tell me that a 300 size motor the CG on the wing is at 110mm but a 400 size motor my CG should be located at 95mm. why is this? i plan on using a brushless motor with 35 ounces of static thrust should i move the CG even more forward on the wing? i just don't understand how the CG point can change because of a motor
CG can vary due to wing loading. Difference at extreme ends of the envelope. As the s400 option will be considerably faster a more nose heavy CG will yield a less pitch sensitive model, which is desireable. At very low speeds and very light wing loading you need to increase pitch so a rearward CG is required.

The fullsize F16 supersonic CG is around 45-50% MAC for instance.
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Old Jan 27, 2004, 07:29 AM
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Jacques Flambeau's Avatar
Backwoods Alabama
Joined May 2000
3,861 Posts
That makes good sense. The 400 CG is at 33% and the 300 is at 36%. Just off the top of my head it does not seem that 1 ounce of added motor weight would make that much difference, but it may. The 33-36% values are a reasonable range; what I would do is start with the forward CG and move it back til the elevator felt "twitchy" and then move it forward a bit.

This is an important issue since many SS's are used for AP, which adds several ounces to the design weight. Again, I'd start at 33% and tweak.

--Bill
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