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Question about Spar Location in Chord

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Tom Kay

Well-Known Member
Joined
Aug 10, 2007
Messages
409
Location
Canada
Hi;

I'd like to talk about the spar location in a Harry Riblett foil. The foil is 35-415, which means that the thickest point is at 35% from the leading edge, and it's a 15% thickness ratio. At least I think that's the case. This is the airfoil that Titan uses for its T-51, although Mr. Riblett mentioned that it tapers to about 12% at the tip.

So, I have 2 questions (and maybe a few sub-questions).

1. Typically, would the best location for the front spar be at 35% from the L.E. ? And by best, I guess I mean producing the strongest, most conventional structure? This seems fairly far back, compared to most wings.

2. The P-51 Mustang has a tapered wing, but the Trailing Edge is tapered more than the Leading Edge. This means that the spar would actually be swept forward a few degrees, if it's important to keep the spar always at 35% of chord. A quick sketch and you'll see that this is true. Or, you can just imagine it with a big TE sweep, but no LE sweep.

So, is there any problem with having the spar swept forward a tad, (I can see a few construction problems where the wings meet in the middle)

OR

is it better to have the spar located a bit behind the 35% location, as we move from root to tip? This would keep the spar straight from tip to tip.

I hope that's not too confusing, the way I've worded it.
Thanks for any input.

Tom.
 
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