lnl1950

I am trying to help a buddy come up with a CG for a plane with no instruction book and with no idea of who the manufacturer is. I ran the dimensions thru the Super Calculator on the Aircraft Proving Grounds Website and came up with a CG but I am not sure it is correct.

The Wing is similar to an EDGE 540, they are slightly tapered (2" from root to tip) the leading edge is straight, I am calling it forward sweep? I attached some pics.

When calculating the MAC, is forward sweep calculated the same as rearward sweep, or is it disregarded? My guess would be that it should be included in the calculation because you are calculating the "Mean Aerodynamic Center" of the flying surfaces.

Can anyone confirm this for me,

Thanks,

Larry

Lnewqban

Your guess is correct.
For proper location of the CG, the MAC location of the semi-wing and the tail must be calculated.
When calculating the MAC for the wing, enter S=0 into the calculator, since the imaginary equivalent straight semi-wing should be located closer to the leading edge.
When calculating the MAC for the tail, enter S=value of sweep back at the tip.
For a leading edge that is actually swept forward (not straight like yours), the value of S should be negative.

Crash Campbell

Hi Larry,

This may help.
http://www.inlandsloperebels.com/Calc/cgcalc.html
Cheers,

Colin

da Rock

I never used the application you mention, but have use the CG locator at geistware. It's documentation shows that it uses the same formulas I used to figure out on paper. All it takes to get a reliable CG is measuring your model and plugging in those measurements.

http://www.geistware.com/rcmodeling/cg_super_calc.htm

I use 5 and 15 for the margins to get a CG range to use for the first flights. Then adjust as the plane tells me to.

lnl1950

Thanks guys, I really appreciate the help,

Larry