center of gravity/balance????
03-10-2003 | 04:55 AM
#1
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From: Hemet,Ca
center of gravity/balance????
Im just getting into flying and picked up a few old planes and radios on a good deal. One is a custom built glider with no plans how do i find the center of gravity and balance the plane. ive flown it a few times and it struggles to stoy in the air. pretty sure its tail heavy.
03-10-2003 | 03:16 PM
#2
My Feedback: (1)
center of gravity/balance????
Get yourself a piece 1x6 board about a foot long then get two quarter inch dowels ten inchs long. Now drill a hole in the 1x6 near one end and glue one of the dowel sticks in and drill a series of holes srtarting about two inchs from the first one and make these every inch untill you get them about twelve inchs apart. The second stick will not be glued and adjust in the different holes for differant fuselage widths. Cap the sticks with some glued on felt or some rubber vacuum caps.
With the sticks set pretty close to the width of the fuselage set your glider wing on the sticks and adjust it fore and aft untill it will set on those two sticks level. This is your actual center of gravity. If this point is more than a quarter of the way back from the front of the wing then you are correct and the CG is to far back. We want to shoot for CG at '25% of the mean aerodynamic chord' all that fancy phrase means is "a quarter of the way back from the front (leading edge) on the average width (chord) of the wing. Now since most gliders are double tapered or near it we are just going to set that CG at 25% right at the wingroot to make things easy.
when you have the ship on the sticks at the 25% point then you may have to move the battery forward or even servos forward and as a last resort add lead to the nose compartment all the way forward.
John
With the sticks set pretty close to the width of the fuselage set your glider wing on the sticks and adjust it fore and aft untill it will set on those two sticks level. This is your actual center of gravity. If this point is more than a quarter of the way back from the front of the wing then you are correct and the CG is to far back. We want to shoot for CG at '25% of the mean aerodynamic chord' all that fancy phrase means is "a quarter of the way back from the front (leading edge) on the average width (chord) of the wing. Now since most gliders are double tapered or near it we are just going to set that CG at 25% right at the wingroot to make things easy.
when you have the ship on the sticks at the 25% point then you may have to move the battery forward or even servos forward and as a last resort add lead to the nose compartment all the way forward.
John
03-10-2003 | 04:33 PM
#4
My Feedback: (1)
center of gravity/balance????
Mike, of course 25 to 30% is a normal range for most conventional aircraft but under the circumstances starting at the farthest aft position of controlability, is I feel a mistake. Since we are dealing with an unknown glider and a newbie here combined with the difficulty of trying to explain MAC on an unknown plan form then I just suggested a safe initial figure that will work for the gentleman.
But then agine I suspect you knew that and are just baiting me to get me to explain myself.
John
But then agine I suspect you knew that and are just baiting me to get me to explain myself.
John
