need advice on the center of gravity
07-19-2008 | 07:54 PM
#1
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From: Hamburg,
NY
need advice on the center of gravity
Hey everyone,
I'm new and bought a trainer at an auction. It's in decent shape, and I have the ST engine running well. It had the servos, but I need to install the rest of the electronics. It looks almost identical to a Sig Kadet LT40. About the same dimensions. I have done research on calculating the center of gravity, and two sites I came across calculated it for you if you put in the info.
This site:http://www.geistware.com/rcmodeling/cg_calc.htm#cg gave me 4.52" from the LE
This site:http://adamone.rchomepage.com/cg_calc.htm gave me 4.99" from the LE. I used 10% for the static margin.
Both figures are more than the 25-35% of the MAC (11.74") recomended by these sites, especially the second one.
Any suggestions would be appreciated, Thanks.
I'm new and bought a trainer at an auction. It's in decent shape, and I have the ST engine running well. It had the servos, but I need to install the rest of the electronics. It looks almost identical to a Sig Kadet LT40. About the same dimensions. I have done research on calculating the center of gravity, and two sites I came across calculated it for you if you put in the info.
This site:http://www.geistware.com/rcmodeling/cg_calc.htm#cg gave me 4.52" from the LE
This site:http://adamone.rchomepage.com/cg_calc.htm gave me 4.99" from the LE. I used 10% for the static margin.
Both figures are more than the 25-35% of the MAC (11.74") recomended by these sites, especially the second one.
Any suggestions would be appreciated, Thanks.
07-19-2008 | 08:38 PM
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From: Tracy,
CA
RE: need advice on the center of gravity
The "25-35% of the MAC" figure is just a starting point for estimating the center of lift for that one surface.
If you go back to those calculators, make a test by increasing the size of the horizontal stabilizer (the tail) to the same as the wing. You'll see the CG has probably shifted completely off the wing to some point behind it, which is where it really would be if you made a plane like that.
I would probably go back to http://adamone.rchomepage.com/cg_calc.htm and make 2 more calcs, one with a 5% margin and the other with a 15% margin. Those measurements would give you the minimum and maximum bounds for the CG of that plane, and I'd probably start somewhere between them, at 4.99" from the LE.
If you go back to those calculators, make a test by increasing the size of the horizontal stabilizer (the tail) to the same as the wing. You'll see the CG has probably shifted completely off the wing to some point behind it, which is where it really would be if you made a plane like that.
I would probably go back to http://adamone.rchomepage.com/cg_calc.htm and make 2 more calcs, one with a 5% margin and the other with a 15% margin. Those measurements would give you the minimum and maximum bounds for the CG of that plane, and I'd probably start somewhere between them, at 4.99" from the LE.
07-19-2008 | 09:15 PM
#3
Senior Member
RE: need advice on the center of gravity
ORIGINAL: wagz
Hey everyone,
I'm new and bought a trainer at an auction. It's in decent shape, and I have the ST engine running well. It had the servos, but I need to install the rest of the electronics. It looks almost identical to a Sig Kadet LT40. About the same dimensions. I have done research on calculating the center of gravity, and two sites I came across calculated it for you if you put in the info.
This site:http://www.geistware.com/rcmodeling/cg_calc.htm#cg gave me 4.52" from the LE
This site:http://adamone.rchomepage.com/cg_calc.htm gave me 4.99" from the LE. I used 10% for the static margin.
Both figures are more than the 25-35% of the MAC (11.74") recomended by these sites, especially the second one.
Any suggestions would be appreciated, Thanks.
Hey everyone,
I'm new and bought a trainer at an auction. It's in decent shape, and I have the ST engine running well. It had the servos, but I need to install the rest of the electronics. It looks almost identical to a Sig Kadet LT40. About the same dimensions. I have done research on calculating the center of gravity, and two sites I came across calculated it for you if you put in the info.
This site:http://www.geistware.com/rcmodeling/cg_calc.htm#cg gave me 4.52" from the LE
This site:http://adamone.rchomepage.com/cg_calc.htm gave me 4.99" from the LE. I used 10% for the static margin.
Both figures are more than the 25-35% of the MAC (11.74") recomended by these sites, especially the second one.
Any suggestions would be appreciated, Thanks.
I've used the geistware ever since discovering it and if you give it a 10% and then a 20% SM, you'll have an excellent CG range to work from.
If you choose to use the forward CG, you'll probably need to have decent elevator throw. If you choose the 10% or rear CG, or a CG close to that far back, you need to be prepared for the elevator throw to WORK WELL.
07-19-2008 | 09:20 PM
#4
Senior Member
RE: need advice on the center of gravity
BTW, those two sites appear to use identical software. It's surprising that they would give different results, since it's obvious they use identical user interface code.
geistware's results have proven to be absolutely reliable over the last 3-4 years of use. If you input correct measurements, you'll get trustworthy CG recommendations.
geistware's results have proven to be absolutely reliable over the last 3-4 years of use. If you input correct measurements, you'll get trustworthy CG recommendations.
