MikeSt
Aug 06, 2002, 11:49 PM
I threw together a little 9" wingspan foamie (made from foam pistol-targets from Le Baron).
Weighs in at a heft 2grams ;)
Specs, Wspan 9"
Mac - 1.7"
Fuse Len - 7"
HStab ~ 22% of wing ( ~3 x ~1)
Vstab ~ 1/3 of Hstab
The nose sticks out .75" ahead of the L.E.
The 1/4 C works out to about .5" from the L.E. , the 1/3C around 5/8" from the L.E. So ~ 1.25" - 1.38" should be the C.G.
The empty frame balances around 3/8" behind the T.E. (2.25") from the L.E... 3" from the nose, around (3 - 1.25 = ) 1.75" too far back.
So initially, I just wound solder around the nose, till the C.G. moved up between the 1/4 - 1/3 point. The little critter glides around pretty nicely ! My plan is to RFFS this thing, or maybe even something smaller.
I was trying to figure out what the formula would be to adjust the C.G. I found one in a full scale a.c. book. It was :
Weight_to_move = (Dist_to_move_C.G. / Dist_between_old_Arm_New_Arm) * Airplane_Weight.
Plugging my numbers in, I get : (using the nose as the ref point)
1.75 " / (3 - .75 = 2.25) * 2gm = 1.5 gm. I hung ~2gm of solder on the nose, but the C.G. didn't move far enough until I made it closer to 3g of solder.
Admittedly these are tiny numbers, and lots of margin for error, but is that the right formula ?
Mike
Weighs in at a heft 2grams ;)
Specs, Wspan 9"
Mac - 1.7"
Fuse Len - 7"
HStab ~ 22% of wing ( ~3 x ~1)
Vstab ~ 1/3 of Hstab
The nose sticks out .75" ahead of the L.E.
The 1/4 C works out to about .5" from the L.E. , the 1/3C around 5/8" from the L.E. So ~ 1.25" - 1.38" should be the C.G.
The empty frame balances around 3/8" behind the T.E. (2.25") from the L.E... 3" from the nose, around (3 - 1.25 = ) 1.75" too far back.
So initially, I just wound solder around the nose, till the C.G. moved up between the 1/4 - 1/3 point. The little critter glides around pretty nicely ! My plan is to RFFS this thing, or maybe even something smaller.
I was trying to figure out what the formula would be to adjust the C.G. I found one in a full scale a.c. book. It was :
Weight_to_move = (Dist_to_move_C.G. / Dist_between_old_Arm_New_Arm) * Airplane_Weight.
Plugging my numbers in, I get : (using the nose as the ref point)
1.75 " / (3 - .75 = 2.25) * 2gm = 1.5 gm. I hung ~2gm of solder on the nose, but the C.G. didn't move far enough until I made it closer to 3g of solder.
Admittedly these are tiny numbers, and lots of margin for error, but is that the right formula ?
Mike