pilot dood

I took measurements of wings for ref to accurately locate CG.. upper wing is fwd of lower wing 4" cord is 6 5/16 " lower wing span is
36 " upper wing span is @ or about 39 7/8"
Will this help at all ??

Thanx again all !!

Bob [email protected]

Dorsal

My Feedback: (17)

http://adamone.rchomepage.com/cg_calc.htm

crasherboy

Do you have the aug 08 issue of Model Aviation. ? If you do there is a drawing on pg. 103 that shows how to set your cg for a biplane.If you don't have this copy ,let me know and I will photocopy and post it for you.Let me know. I will describe the drawing for you. first ,you draw an imaginary line from the center of the leading edge of both upper and lower wings.Go back 25% MAC on both wings.
Draw an imaginary line between these two points next go 50% between the on this imaginary line. This should be close to what would fly right. If the wings are swept back you would have to consider this to,but on a waco I don't think the are.

pilot dood

Thanx crasherboy, but no I dont have a copy of that issue, and your steps w/ the imaginary lines totally way lost me lol
This wing config is NOT at all swept.
I would really like to fly this bipe before i clean up my big P-51 and my very over powered spit.
Thanx for your efforts

Bob

BMatthews

Bob, use the CG calculator linked in your other thread or from the links in the sticky thread about calculators. For the wing chord dimension use the most forward leading edge (upper wing in your case) and the most rearward trailing edge (lower wing in your case) as the overall wing chord. Most Waco's used constant chord wings so the root and tip chord will be the same. For the wing's half span fudge the span such that the chord times half span is the proper area for the two wings added together. You'll have to fudge the sizes to deal with rounded tips a little but you can ignore the center section cutaway safely. Do all this and the CG calculator will give you a number that should be safe for first flight use.

crasherboy

I could not seem to find any way of imbedding the drawing that I mentioned,but I have uploaded it to my profile. Click on my usser name in the box to the left and should come up as my picture.

Dorsal

My Feedback: (17)

There are instructions elsewhere about this, but things are a lot easier on the WACO because both wings are shaped the same. Just use the average distance from the LE of the tail to the LE's of the wings. In other words, if one wing is 4 inches ahead of the other, and the most forward wing is, say, 25 inches from its LE to the LE of the horizontal stabilizer, you would input (25 minus 2 inch = 3) inches from LE to LE. (Or you could use the distance to the least forward wing and add 2 inch in my example.)
Then input the length of the wing as the TOTAL of both wings. For that, if the top wing is 60 inches (30 inches half-span) and the bottom wing is 58 inches (29 inches half-span) then you would input (30 + 29 = 59 inches Half-Span). This little trick will get the proper answer for you. The other way to do it would be to use the average half-span, but tell the program you have double the chord of a single wing. Either way, you need to tell the program enough to calculate the total wing area that includes both wings.
Using these methods, you could calculate CG for a Fokker Tri-plane also.
Just remember the program will give you the distance to the CG from the imaginary "average" Leading Edge, so remember to add or subtract the input distance (2 inch in my example) when you are marking your CG. It wouldn't help for me to measure my WACO because it's 1/5 scale and does have a 60" top wing. sorry.

Hope that helps.

"The AC location for biplanes with positive stagger (top wing ahead of the bottom wing), is found according to the drawing below.
[link=http://adamone.rchomepage.com/index5.htm]http://adamone.rchomepage.com/index5.htm about 3/4 down[/link]
For conventional designs (with main wing and horizontal stab) the CG location range is usually between 28% and 33% from the leading edge of the main wing's MAC, which means between about 5% and 15% ahead of the aircraft's Neutral Point NP."