CG calculations...HELP!!!!
03-19-2002, 02:38 AM
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CG calculations...HELP!!!!
Greetings
I am building a straight winged foamie out of a $7 glider. I have made the main wing flat and straight but here is the problem; The wing is straight across at the TE and tapers from the root to each tip...Question #1, how does one calculate the proper CG location for this type of wing form. Question #2, the middle 10" of the wing has a fixed 1 1/2" trailing edge, and the rest of the wing has 1 1/2" ailerons. In calculating the CG and wing area does one include the ailerons / trailing edge or not? Any help would be greatly appreciated.
Thanks
Confused in CT
I am building a straight winged foamie out of a $7 glider. I have made the main wing flat and straight but here is the problem; The wing is straight across at the TE and tapers from the root to each tip...Question #1, how does one calculate the proper CG location for this type of wing form. Question #2, the middle 10" of the wing has a fixed 1 1/2" trailing edge, and the rest of the wing has 1 1/2" ailerons. In calculating the CG and wing area does one include the ailerons / trailing edge or not? Any help would be greatly appreciated.
Thanks
Confused in CT
03-19-2002, 03:54 AM
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CG
No bigee.
(You DO include the aileron and trailing edge area for these calculations.)
First, find the average chord:
Add the root and tip chords together, and divide by 2. (example: Root=10 inches chord and Tip=8 inches chord. 10 + 8=18, divided by 2= average chord of 9"
Now find the place on the wing where wing chord matches this number. That position is your Mean Aerodynamic Chord. (MAC) That's where you measure from, in the next step.
Decide where you want to start with the CG, performance-wise. Locating the CG at 25% to 30% MAC is a safe starting place for most planes. (For a 25% MAC CG, in the example above, the math would be .25 X 9=2.25 So the CG would be 2.25 inches back from the leading edge at the MAC.)
Happy CG-ing!
(You DO include the aileron and trailing edge area for these calculations.)
First, find the average chord:
Add the root and tip chords together, and divide by 2. (example: Root=10 inches chord and Tip=8 inches chord. 10 + 8=18, divided by 2= average chord of 9"
Now find the place on the wing where wing chord matches this number. That position is your Mean Aerodynamic Chord. (MAC) That's where you measure from, in the next step.
Decide where you want to start with the CG, performance-wise. Locating the CG at 25% to 30% MAC is a safe starting place for most planes. (For a 25% MAC CG, in the example above, the math would be .25 X 9=2.25 So the CG would be 2.25 inches back from the leading edge at the MAC.)
Happy CG-ing!
03-19-2002, 12:08 PM
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CG calculations...HELP!!!!
Could you confirm your method. If I have a parrallel wing with 10" chord. 10 + 10 = 20. 20\2 =10. This would put the MAC right on the trailing edge. Is this correct? With a swept wing with parrallel chord this would not work.
MAC was explained to me very differently. This applies to any wing planform. From the fuselage C/L determine the mid-span point of each wing panel. At that point determine the mid chord point. Join these two points up with a line across the C/L of the fuselage. Where they cross the fuselage C/L is the MAC. From this point is the CG established. Try that with a swept wing and you will see what happens.
Ed S
MAC was explained to me very differently. This applies to any wing planform. From the fuselage C/L determine the mid-span point of each wing panel. At that point determine the mid chord point. Join these two points up with a line across the C/L of the fuselage. Where they cross the fuselage C/L is the MAC. From this point is the CG established. Try that with a swept wing and you will see what happens.
Ed S
03-19-2002, 02:34 PM
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CG calculations...HELP!!!!
Hi Ed,
You didnt do the last step.
"If I have a parrallel wing with 10" chord. 10 + 10 = 20. 20\2 =10"
10 x .25 = 2.5 in from LE
Of course since it is a straight wing you can skip the adding of root and tip chords and dividing by two. You only need to do that part for swept and taper wings.
Cheers.
James
You didnt do the last step.
"If I have a parrallel wing with 10" chord. 10 + 10 = 20. 20\2 =10"
10 x .25 = 2.5 in from LE
Of course since it is a straight wing you can skip the adding of root and tip chords and dividing by two. You only need to do that part for swept and taper wings.
Cheers.
James
