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CG question for semi-wing - 7/10/2002 2:29:40 AM   
wsmalley



Posts: 1041
Joined: 2/16/2002
From: Monterey, TN, USA
Status: offline 		Have an Altech Pilatus Porter,ST.61 with heavy prop extension shaft to get prop out on that long skinny nose. Has 6' ws with 10" chord semi-symmetrical wing. Plans call for CG to be about 1/2" behind LE. Plane flies ok but little elevator authority, made some pretty hard landings. I'm running a Futaba PA1 autopilot and with it on, plane still drops nose in a turn-have to feed in a lot of elevator. My flyin' bud thinks it's way to nose heavy and I agree. He suggests starting at 25% which happen to be right on line with the strut mount points. At that balance point, I stuck 2 oz. of lead in the tail to balance. Any how with a high wing semi, what's a good balance point to start with?

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If I die, and I have the most toys, what do I win?
       Post #: 1

CG location - 7/10/2002 7:38:15 AM   
florida817


 

Posts: 47
Joined: 1/8/2002
From: Pace, FL, USA
Status: offline 		I think your flying buddy is right on the mark. Most conventional planform aircraft balance between 25% and 33% of the Mean Aerodynamic Chord (MAC). If the Porter has a straight wing with a 10" chord and no taper or sweep, a good starting balance point will be 2.5" aft of the LE.

You're seeing all the classic signs of a CG that's too far forward in the flying qualities of the Porter. I feel sure that you'll enjoy flying the airplane a lot more with a CG location that's further aft.

Tom

(in reply to wsmalley)
       Post #: 2

CG question for semi-wing - 7/11/2002 5:45:31 AM   
JERRY RCIA


 

Posts: 63
Joined: 2/27/2002
From: DALLAS, TX
Status: offline 		I start out balancing all of my planes at the 30% mark and adjust from there to suit my taste. I'm currently flying a sport plane which is balanced at 35% and it is very tame but very aerobatic. I will say that, I've never moved the CG forward from 30% point on anything I've tried...................Jerry

(in reply to wsmalley)
       Post #: 3

CG - 7/11/2002 6:37:15 AM   
wsmalley



Posts: 1041
Joined: 2/16/2002
From: Monterey, TN, USA
Status: offline 		O.K. guys, if the weather holds I'll try tomorrow, starting with 25% at 2.5" and go from there. I'm not good enough to fly something with a CG too far to the rear, so I'll start conservatively. I wound up with 2 oz. of lead in the tail to balance on 25% even with the elevator and rudder servos in the tail. I'm sure the large adapter I made to extend the shaft threw the weight forward from the plans, which did not call for such a thing.

_____________________________

If I die, and I have the most toys, what do I win?

(in reply to wsmalley)
       Post #: 4

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