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Airfoil alignment

If you need help on creating or dealing with a plan in dxf or other formats, then this is the place to ask.
pdewaegep
Posts: 6
Joined: 06 Oct 2020, 01:15
Location: Colombia

Airfoil alignment

Post by pdewaegep »

Maybe a stupid question, but it's running through my head! On a trapezoidal wing, the root profile is thicker than that of the wing tip. The question, you align them along the median line (the upper plane will go down, the lower plane up), or align them on the upper part of the profile (thus increasing the angle of the lower plane). To have better sustenance, my logic leads me to think that the second solution is the best.
Thanks in advance for your replies.
Patrick

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Peter Balcombe
Posts: 1178
Joined: 18 Mar 2015, 10:13
Location: Clevedon, North Somerset, U.K.

Re: Airfoil alignment

Post by Peter Balcombe »

Patrick,
Unless the wing airfoil section (% thickness) changes along the span from root to tip then for a totally rectangular planform (plan view) wing, then the tip thickness will be the same as at the root - same airfoil % thickness & same chord length, so same physical thickness.
With a glider wing in particular, the wing chord usually tends to be smaller at the tip than at the root, so the same percentage thickness gives you a thinner physical tip thickness.
If the airfoil section % thickness reduces then that will also lead to a correspondingly smaller tip physical thickness.

I think that if a wing has zero wing dihedral angle, then a line drawn between the root & tip mid-depth at the maximum thicknesses point, should be level.
However, as most wings have some dihedral angle, this line will be at the dihedral angle (say 2 - 3 degrees)

It is common on a model plan for the designer to show how much the underside of the wingtip should be above the underside of the wing root to achieve the required dihedral angle (taking everything above into account).

Hope this helps,
Peter

pdewaegep
Posts: 6
Joined: 06 Oct 2020, 01:15
Location: Colombia

Re: Airfoil alignment

Post by pdewaegep »

Peter, thanks for your response.

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