locating CG
 

Can anyone help me figure out how to calculate the CG for a forward swept wing aircraft?

I am speaking about a wing similar to an X-29 but with no tail. I think maybe the standard formula for CG may work for this type of wing, am I correct?

thanks

Brad

RE: locating CG
 

Is the wing a constant taper and sweep or is it made up of different sections?

RE: locating CG
 

You need to find the MAC or Mean Aerodynamic Chord of the wing just like you would for any other straight or swept wing. The MAC calculations or online calculators will work fine regardless of sweep direction. Once you have the MAC you can do the CG and neutral point calculations as per "normal".

RE: locating CG
 

Brad:
Bruce is right on the MAC, but a tailess aircraft MUST have the CG very far forward. I'm building a Simitar tailess aircraft at this moment and the CG is 15% MAC instead of the usual 30%.
Frank

RE: locating CG
 

Oops, I just saw the X29 bit.

Yep, use the MAC calculator to find the MAC and then you're looking at 15 to 18% CG.

Also with a swept back wing you washout the tips to give you the stability you require. As a side benifit it tends to reduce tip stalls when turning at lower airspeeds or in high G turns. A swept forward wing isn't going to be so tidy. For the tips you'll want regular lifting sections but for the root you'll be wanting a strongly reflexed type of airfoil to generate the proper lift progression. You may even have to build some washIN into the tips.

This is why you don't see many strongly swept forward X29 style flying wings.

RE: locating CG
 

rc = Root Chord
t = Taper Ratio = (Tip Chord ÷ Root Chord)
MAC = rc x 2/3 x (( 1 + t + t2 ) ÷ ( 1 + t ))
say the root chord is 11" and the tip chord is 6"
t = 6 ÷ 11 = .5455
Now plug t into the formula to find the MAC. Note that the wingspan and sweep do not matter. No matter what the span or how much the wing is swept, the MAC will always be the same length.
MAC = 11 x 2/3 x (( 1 + .5455 + .54552 ) ÷ ( 1 + .5455 ))
MAC = 22/3 x ( 1.8431 ÷ 1.5455 )
MAC = 7.3333 x ( 1.8431 ÷ 1.5455)

MAC = 7.3333 x 1.19254

MAC = 8.7453"

RE: locating CG
 

Gary, what you've shown is not the MAC but rather just the average chord. When we designate a MAC it implies not only the average chord length but also the LOCATION of that effective chord. And in the case of a wing with a 1/4 chord line that has sweep in it the sweep and span are very important to finding the location of the effective chord. This whole location and length answer is what the MAC is.