Help with C G
05-18-2004, 01:13 AM
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Help with C G
Heys guys,
I just purchased this used glider as my second plane and I'm doing some "resurrection" work on it and since this is my second plane I'm not a cg expert yet so I was wondering if anyone could help me out to at least estimate were the cg of the airplane is. I fly my Spirit at the slope and because of its wing composition and manufacturer specifications, the cg is not hard to find (right by the main spar); however the wing on this glider is solid (I beleive the right term is sheeted) and I'm not sure where the cg could be. Right now the location of the cg (with battery and everything in of course) is a little past the middle of the wing towards the nose of the plane but then again I could be wrong.
I know that the location of the cg is determined a lot of times by the pilot's preference but since I'm still rated as a novice I could definetely use some help.
Thanks a lot.
I just purchased this used glider as my second plane and I'm doing some "resurrection" work on it and since this is my second plane I'm not a cg expert yet so I was wondering if anyone could help me out to at least estimate were the cg of the airplane is. I fly my Spirit at the slope and because of its wing composition and manufacturer specifications, the cg is not hard to find (right by the main spar); however the wing on this glider is solid (I beleive the right term is sheeted) and I'm not sure where the cg could be. Right now the location of the cg (with battery and everything in of course) is a little past the middle of the wing towards the nose of the plane but then again I could be wrong.
I know that the location of the cg is determined a lot of times by the pilot's preference but since I'm still rated as a novice I could definetely use some help.
Thanks a lot.
05-18-2004, 03:43 PM
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RE: Help with C G
With a swept leading edge, I would be very careful not to get any further forward than Landi's suggestion.
How does it fly at the "somewhere just forward of 50%"? I bet it is a bit "twitchy" and easy to stall. I would think that moving the cg forward by at most 2cm would help. Then test and trim and test...hand launching over grass - the freeflight methods - will tell you if something is drastically wrong at minimum risk.
Suggest that you make a "balance machine" - mine is a pair of 10" long "hurdles" made from 4x3/16 sheet with a 1/4" long length of 1/8 square at right angles on the top edge. Gives me sufficient scope to mark le positions for each of my models to check that cg is ok after repairs, replaced batteries etc...
How does it fly at the "somewhere just forward of 50%"? I bet it is a bit "twitchy" and easy to stall. I would think that moving the cg forward by at most 2cm would help. Then test and trim and test...hand launching over grass - the freeflight methods - will tell you if something is drastically wrong at minimum risk.
Suggest that you make a "balance machine" - mine is a pair of 10" long "hurdles" made from 4x3/16 sheet with a 1/4" long length of 1/8 square at right angles on the top edge. Gives me sufficient scope to mark le positions for each of my models to check that cg is ok after repairs, replaced batteries etc...
05-19-2004, 08:50 AM
#4
RE: Help with C G
No, use two loops of light rope or heavy chord suspended from the ceiling or likewise point, hang the airplane level, then hang a plumb bob from the same point as the chords and lower it to just over your aircraft. The plumb bob points to the CG of your airplane, always.
There is a method for finding the CG of your swept wing, but it is different for single sweep wings than dual sweep wings and I can't remember which is which. There is also a CG calculator out there on the net, If I could just remember Don's last name we would be there.
There is a method for finding the CG of your swept wing, but it is different for single sweep wings than dual sweep wings and I can't remember which is which. There is also a CG calculator out there on the net, If I could just remember Don's last name we would be there.
05-19-2004, 11:35 AM
#5
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RE: Help with C G
Bookmark this site.
Note you must know where you want the c.g. to be... 30% is a good starting point.
http://www.palosrc.com/instructors/cg.htm
Note you must know where you want the c.g. to be... 30% is a good starting point.
http://www.palosrc.com/instructors/cg.htm
05-20-2004, 10:43 PM
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RE: Help with C G
Wow
Thanks for all the help guys. 30% works fine and I think I going to make a bit nose heavy at first because I don't want it to be too responsive. This glider is pretty fast as it is and since it is only my second one I want to have a slow response on the first few flights.
Tall Paul, that's a great link, the rest of you guys should check it out.
Thanks for all the help guys. 30% works fine and I think I going to make a bit nose heavy at first because I don't want it to be too responsive. This glider is pretty fast as it is and since it is only my second one I want to have a slow response on the first few flights.
Tall Paul, that's a great link, the rest of you guys should check it out.
