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Will a spar cause lift, or drop?


Old 12-12-2018, 06:38 AM
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Default Will a spar cause lift, or drop?

I was planning to put the spar under the wing but I was wonder if the spar will generate any lift, or drop.
I know that my wing is flat and it is not an airfoil.
Will putting the 1/4" rod on the top of the wing generate any lift?
It seams like the air flowing over the top of the wing may produce a little vacuum behind the rod and lift.
Also, if I put the spar under the wing will it cause the plane to drop?
Would it be better to have the spar on the top or bottom of the wing?

Will a spar above generate lift and will a spar below cause the plane to drop?

Last edited by johnnymax; 12-12-2018 at 09:19 AM.
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Old 12-18-2018, 12:37 PM
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Either way it'll cause more drag than lift. More on the bottom than on top. On a flat plate like this the air over the top becomes highly turbulent at very small angles of attack. So unless the spar is fairly thick and sticks up out of the worst of the rolling turbulence it'll be masked in the turbulence off the sharp leading edge. At least that's my gut feeling on it. And if the scale you show is accurate in proportion that size of spar won't be large enough to stick up out of the turbulent flow at low speeds and higher angles of attack.

I assume that it's a very light and slow flying model. So likely you would not really notice much either way. Or at least it would simply trim out with a click or two of elevator trim.
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Old 12-20-2018, 08:28 AM
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If we are talking about a flat plate, sheet of balsa or foam kind of wing it probably won't matter that much. On a thicker wing a proportionally much smaller trip is sometimes used as a turbulator to trip the airflow and keep it attached to the upper surface of the wing at high angles of attack. At the proportions that you are drawing it might actually act as a spoiler. I forget the name of the wing style but there is one that thicker leading edge for fair in the spar but the bottom surface ends at the spar. I have also seem small U-control planes where the wing was split spanwise and the front half and back half were glued to the front and back half of the spar making for a very thin wing. A lot depends on the application. what are you building?

Edit: After responding here I saw you post about a sign board airplane. In that case I would put the spar on the bottom, primarily for aesthetic reasons..

Last edited by mgnostic; 12-20-2018 at 08:33 AM.
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