Moving CG around - how does it affect handling? - RC Groups
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Jun 13, 2002, 05:40 PM
Registered User

Moving CG around - how does it affect handling?

A question in general. Let's say you don't take the manufacturer's recommendation of where the CG is and moved it forward, say 1/4"-1/2". What would that do to the flight characteristics?

From searching and reading a few threads, it would make the plane "easier" to fly and from this I'm assuming more stable. Conversely, moving it back would make the plane less stable.

Can some one explain why? I think I have an answer but I'm sure if it's correct.

If I'm not the brazen type (read -> chicken), would it be a good idea to set the CG SLIGHTLY forward of the recommended position during the first flight or a new plane just to see how things go?
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Jun 13, 2002, 07:00 PM
Ascended Master
Sparky Paul's Avatar
The manufacturers c.g. point is usually located so the plane will fly "easily". He does want repeat business, so getting it wrong hurts him, as well as you.
Moving it forward from the recommended point might be OK if your flying skills are modest, and the plane has good performance potential, but generally moving the c.g. forward makes the plane sluggish, more than "easy".
The 3 things I look for is the c.g. at the manufacturers location; no excessive throws on the elevator and ailerons, and no warps.
A plane that fits these parameters will fly OK.
Jul 16, 2002, 06:15 PM
Registered User
zamboni_driver's Avatar
Do most people use the "fingers on wing" method to test their C.G.?? I know there are products out there that help you find C.G. and I'm guessing the more skilled the pilot, the more important this may be. However I have also read that changing the C.G. even slightly can have a severe effect on performance.

So from a novice point of view....where you want the plane to be at its best, because we know the pilot won't be, is the "finger on wing" method still OK to use? I know for example on my plane it "balances" roughly where it is suppose to. But I am always worried that I am making it tougher on myself by not having it properly balanced, and wonder if I should spend the money on something to help out. I would rather put that money into something directly related to the plane if I can like a battery or motor for example...

What do most people do? Just curious.
Jul 16, 2002, 06:29 PM
Registered User
RPatrick's Avatar
I use my fingers on the wing to set the plane to the recommended center of gravity for the first flight.

If I do err, I do it to the nose...

I usually always end up adjusting the C of G on my planes to the rear. To find out if my planes need adjustment, I get up to a safe height, and bring the plane by on a slow pass, nose high, and continue to reduce speed. The plane should be able to lose altitude with its nose up, like it is floating down... If it cannot, I move the C of G back until it can. This works well for me, and allows my belly landings to occur tail hitting first, which is usually very soft and very cool looking.

Jul 16, 2002, 06:46 PM
Ascended Master
Sparky Paul's Avatar
There's no particular to purchase a c.g. machine, unless you're into machinery.
A couple of dowels inserted in a block of wood can do the exact same job just as accurately as any commercial product.
"fingers on the wing" is Ok for sport flying, but more precision doesn't hurt when you're looking for performance.
This isn't a subject to lose sleep over. Set the plane up per the manufacturer's spec and fly it there first.
Then if you encounter a situation that is c.g. related.. sluggish response, or too active response, move the c.g.
I heard yesterday there's one airplane on the market with the suggested c.g. 1 inch ahead of where it should be... makes the plane a poor flier .
Thunder Tiger "Sparky".. (no relation). Their web-site posts the fix, but for those who buy the plane, and don't use the 'net, that's not much help.