skysfallin

My Feedback: (10)

I know this has been discussed here before but I cant find it. Can someone tell me how CG affects a knife edge as far as how the plane will couple towards the gear or canopy. I have a new Sbach 50 cc that couples slightly towards the gear and I thought I read here that CG will affect how the plane willl couple that way. Thanks in advance.

ThumbSkull

My Feedback: (57)

It varies with different airframes as to whether CG and how much it will affect KE coupling.
I would set the CG rather based on upright and inverted trim being the same for elevator.
You want the CG where it will be neutral upright or inverted. If it noses down inverted, move the CG back a little.

One thing that will affect coupling is flap trim.
Get the CG where you want it for the above, then work on trimming the flap up or down to affect coupling.

skysfallin

My Feedback: (10)

So if its coupling toward the gear set both aeilerons toward the gear. If im understanding you correctly.

ThumbSkull

My Feedback: (57)

Yes. Other things that affect coupling are too much down thrust.
3D airplanes need the down thrust at zero degrees to the mid line.
You can also switch to lighter wheels.

gene737

A heading change towards the canopy in KE usually means a slight nose heavy CG. For example the elevator is trimmed slightly up to counteract the nose heavy condition and when the plane is rolled into KE, this uptrim causes a heading change towards the canopy. If tailheavy, the slight down trim works to change heading toward the gear. Good luck, chasing this problem can be a bugger.

Dave45

since cg is largely a matter of personal taste, I prefer to set the cg to fit my flying style ( hair of down required inverted) and mix out the coupling.

skysfallin

My Feedback: (10)

I also like a hair of down in inverted flight just enough to give you a feel of the airplane. I was playing with knife edges all weekend on this plane and the coulpling is so slight Im not going to try and change it with CG adjustment. It's flying too good in all other characteristics, but thanks for the input.

littlephoenix

i usually leave the CG where the book says, and am able to snap any knife edge, not really sure what you guys mean by coupling,,,

Jezmo

Set the CG for best upright and inverted flight then mix out any coupling with the radio.