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Balancing a biplane

Hi;

I've tried to do a little research on blancing a biplane, but even so, it seems two trains of thought emerge:

1) Viewed from the top, consider the combined outline of both wings as a single wing, and calculate the center of lift as you would for that single wing. It seems to me this method would disregard the leading edge of the lower wing and the trailing edge of the upper wing, meaning you could move either at will and not affect the center of lift. That doesn't sound right to me, unless the overlap renders that part of the wing less effective? Maybe this is more of a rule-of-thumb method?

2) Calculate the center of lift for each wing individually, then locate a midpoint between the two, skewed toward the larger wing based on the areas of the two.

Number two sounds like the preferred method to me. Any thoughts on this, or does anyone have a better idea?

The model, in case you're wondering, is something like a 14" Pitts S1-B. I'm just setting it up for unpowered gliding at this point, so the main wing incidence is 0-0, and I have a degree or two negative on the horizontal.

Thanks, Dan.

Reply to
BÿkrDan
Loading thread data ...

On 4/22/2004 2:43 PM Ted shuffled out of his cave and grunted these great (and sometimes not so great) words of knowledge:

I can not find the URL for the site, but someone may be able to explain this better.

Basically, it involved taking a piece of string and making a "figure 8" between the top and bottom wings. Where the lines crossed was the "CG". What I am no longer sure about is if there was details/adjustments for varying chords on the wings. Hopefully, someone will see this and be able to provide better details.

Reply to
Ted Campanelli

Here's the criss-cross method for finding the Mean Aerodynamic Chord of one wing:

Once you find the MAC, then you can place the CG between

25% to 33% of the MAC, project that back to the fuselage, and come up with a good starting point for flight tests.

The rules for finding the CG of a biplane can be found on the AMA web site. See the link at the bottom of the page above.

Marty

Reply to
Martin X. Moleski, SJ

Thanks for the links, guys.

So, it looks like the consensus is "consider the outline of both wings as a single wing and balance it as such".

Will do. Dan.

Reply to
BÿkrDan

I read that you measure the distance from the top wing LE to the bottom wing TE. Subtract 25% from that and you will have the balance point .

Reply to
RCFlyerNYC

That would work fine if both wings are rectangular in planform.

You need to do a little more work if the wings are oddly shaped.

Marty

Reply to
Martin X. Moleski, SJ

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