Conflicting Info on CG (Full Version)

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Jim D -> Conflicting Info on CG (3/18/2004 5:33 PM)

Ok, I just checked my plans again for the FF Edge 540 and the CG mark is almost exactly 4.75 inches behind the leading edge of the wing. But in re-reading the Billy Hell review, he states the CG range is given as 5.5-6.75 inches. OK, so what gives?

This bird is for 3D so where do I go with the CG. I do have a hard time getting into harriers now, and the planes suffers from wing rock (moderate) until I get it at a really steep harrier under power. Is this why? Mine is balanced at 4.75 spot on.



DKjens -> RE: Conflicting Info on CG (3/19/2004 4:02 AM)

Jim,
Does your plane fly nose heavy or tail heavy. How much elevator, if any, and which way, is needed when flying inverted? Elevators and harriers are fun, in the way the wings can rock or not. The thing is to keep the velocity down, which means keep the nose up. A wings stall point is dependent on AOA and velocity. First thing is to balance the plane for basically hands off flying upright and inverted, or maybe even a little tail heavy where plane pitches up when slowed down. Then you have a well balanced plane and can work on other problems during elevators and harriers.
DKjens



Jim D -> RE: Conflicting Info on CG (3/19/2004 6:44 AM)

Thanks for the reply DK, and yes I was planning on starting to ease the CG back myself to see what happens. Right now it's pretty close to neutral on the inverted vs upright trim. One of the issues I am having is that I almost have to completly stop the plane and then use throttle to work the tail under it. If it is even flying ever so slow, it just climbs when I touch the elevator.

Part of it is that I am a 3D newbie. But after seeing the conflicting data between Billy Hell's review and what is on the plans, I was also sorta looking for an official clarification from Mike P. or someone at OMP.



AFSalmon -> RE: Conflicting Info on CG (3/19/2004 5:58 PM)

Jim,

4.75 is a conservative starting point as the plane is very stable at this point. I can't imagine having the cg as far back as 6.75 inches but I've seen some pretty extreme things done for the sake of 3D. After all we are the 1%ers. I always tell folks to trim the plane for level flight and then roll inverted. At 3/4 throttle, the plane should still fly level or just very slightly drop the nose. Move your CG back slowly as you get used to this setup and the wing rocking will stop. Wing rocking is a sure sign of nose heaviness.

Mike Pilkenton
Ohio Model Planes



Jim D -> RE: Conflicting Info on CG (3/19/2004 6:41 PM)

Thanks Mike. It's right on 4.75 with empty tank, and I have noticed it acts better as the tank empties. In fact, I doinked it the other night from around 5-6 feet. I got into a nice steep harrier and it really settled in, I was in the groove, I was also out of gas! No harm done but a broken prop.

Again, thanks for a great plane. I will see about moving the engine back a tad and see what I get.



Absolut Yak -> RE: Conflicting Info on CG (3/20/2004 4:07 PM)

Ummmm, if the CG is from the leading edge, I have the CG about 1/8" aft of the plans right now. That puts my CG right at the 6 3/4" mark. Flew it for the first time yesterday and can't complain too much. Hovered really nice, definite nose up inverted, but maybe that is a trim issue at the throttle settings I was loafing around at. Kinda nose high on approach, got a little slow and sproinked it from about two feet. Broke the prop, though. Looks like I have to do some work and get the CG at least to the wing tube. Is that correct? MVVS 2.15, Bisson profile muffler, Zinger 22 X 6 (might change that with this next prop). Imagine that, tail heavy with the big engine up front.

Doug
Orlando



Jim D -> RE: Conflicting Info on CG (3/20/2004 11:59 PM)

quote:

ORIGINAL: djccrn

Ummmm, if the CG is from the leading edge, I have the CG about 1/8" aft of the plans right now. That puts my CG right at the 6 3/4" mark. Flew it for the first time yesterday and can't complain too much. Hovered really nice, definite nose up inverted, but maybe that is a trim issue at the throttle settings I was loafing around at. Kinda nose high on approach, got a little slow and sproinked it from about two feet. Broke the prop, though. Looks like I have to do some work and get the CG at least to the wing tube. Is that correct? MVVS 2.15, Bisson profile muffler, Zinger 22 X 6 (might change that with this next prop). Imagine that, tail heavy with the big engine up front.

Doug
Orlando


Doug, I'm talking about the 40 size Edge, not the 80 incher[:D]



Absolut Yak -> RE: Conflicting Info on CG (3/21/2004 12:56 AM)

Whew! I was worried. I was mentally figuring out how to carve up the fuse to move my rear battery pack. Guess I'll keep flying just like it is until I figure out what I like best.

Doug



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