Rib spacing
06-20-2004, 07:39 PM
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Rib spacing
I'm making a sailplane and i was wondering what a good distance would be for the spaces between ribs on the airfoil? Also how many spars should I have connecting the ribs?
06-20-2004, 08:33 PM
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RE: Rib spacing
It all depends on how much sheeting you have or if you're going to use lots of turbulator spars as non load bearing covering support.
In any event for something this performance oriented I don't like to use more than a 2 inch spacing max. It helps to hold the trailing edge shape more accuratley and thus maintain the shape of the airfoil to a higher degree of accuracy.
In any event for something this performance oriented I don't like to use more than a 2 inch spacing max. It helps to hold the trailing edge shape more accuratley and thus maintain the shape of the airfoil to a higher degree of accuracy.
06-21-2004, 02:02 PM
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RE: Rib spacing
As Bruce has hinted, some more detail would help.
Things to think about in making these decisions are -
[ul][*] Span [*] All up weight[*] Wing section (rib shape)[*] Lauch method
[/ul]
All of these have an impact on the forces within the wing and hence the size, shape and composition of the spars.
Most of the wings I build have effectively only one spar. But its shape is essentially the front 1/3 of the wing.
Take a look at www.charlesriverrc.org and Mark Drela's design for Allegro (the built up wing versions) to see what I mean. The way he builds his main spar and the "D" box leading edge is straight from freeflight gliders (where I come from...).
By tying the leading edge, and main spar into a "tube" you are making one very large, very strong spar.
I would not space ribs more than 75mm on a large wing. Bruce is right coming down to 50mm for greater "accuracy". The problem of sagging behind the main spar can be solved by extending the sheeting further back. It is all compromise at that point.
Things to think about in making these decisions are -
[ul][*] Span [*] All up weight[*] Wing section (rib shape)[*] Lauch method
[/ul]
All of these have an impact on the forces within the wing and hence the size, shape and composition of the spars.
Most of the wings I build have effectively only one spar. But its shape is essentially the front 1/3 of the wing.
Take a look at www.charlesriverrc.org and Mark Drela's design for Allegro (the built up wing versions) to see what I mean. The way he builds his main spar and the "D" box leading edge is straight from freeflight gliders (where I come from...).
By tying the leading edge, and main spar into a "tube" you are making one very large, very strong spar.
I would not space ribs more than 75mm on a large wing. Bruce is right coming down to 50mm for greater "accuracy". The problem of sagging behind the main spar can be solved by extending the sheeting further back. It is all compromise at that point.
