DaveD
Well-Known Member
The discussion over on on the Tail Boom Attachment thread has got me thinking about the relative merits of two spar wings.
My original thinking was that you could get more torsional stiffness for less weight with a two spar wing (but I haven't done the calcs yet to check, so I could well be wrong!) Surprisingly I couldn't find much discussion of the two vs one spar pros and cons on this site. If anyone wants to chip in their opinion I’d love to hear it. For what it’s worth, here are my thoughts:
The torsion box formed by a two spar wing encloses a larger area than the leading edge “D” cell in a single spar wing, this should give the two spar wing an advantage in greater polar moment of inertia for less weight.
A single spar and D cell will have its shear centre further forward – good for flutter/divergence. The rear spar of a two spar wing needs to be less stiff than the front spar for the same reason.
The rear spar of a two spar wing is more convenient for mounting control surfaces
For “wet wings” the fuel weight is further forward in a D cell but a two spar wing gives more storage volume (and room in the leading edge for control runs, wiring etc.)
The carrythrough structure for a single spar takes up less space in the cabin
And a few questions…
Are single spar wings generally lighter?
I guess they are quicker/easier to construct?
I’m thinking aspect ratio would make a big difference to which arrangement is optimal.
Anyone want to add to the list?
My original thinking was that you could get more torsional stiffness for less weight with a two spar wing (but I haven't done the calcs yet to check, so I could well be wrong!) Surprisingly I couldn't find much discussion of the two vs one spar pros and cons on this site. If anyone wants to chip in their opinion I’d love to hear it. For what it’s worth, here are my thoughts:
The torsion box formed by a two spar wing encloses a larger area than the leading edge “D” cell in a single spar wing, this should give the two spar wing an advantage in greater polar moment of inertia for less weight.
A single spar and D cell will have its shear centre further forward – good for flutter/divergence. The rear spar of a two spar wing needs to be less stiff than the front spar for the same reason.
The rear spar of a two spar wing is more convenient for mounting control surfaces
For “wet wings” the fuel weight is further forward in a D cell but a two spar wing gives more storage volume (and room in the leading edge for control runs, wiring etc.)
The carrythrough structure for a single spar takes up less space in the cabin
And a few questions…
Are single spar wings generally lighter?
I guess they are quicker/easier to construct?
I’m thinking aspect ratio would make a big difference to which arrangement is optimal.
Anyone want to add to the list?
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