What are the differences between battens and ribs?

  • $\begingroup$ Look carefully at the top image especially and you can see a subtle splaying of the battens, possibly to account for spanwise flow, or perhaps it's necessary to support a flexible curved training edge, like a battened boat sail. $\endgroup$ – John K Aug 24 '20 at 13:41

A flexible airfoil's battens have the same purpose on a sailboat, windsurfer, hang glider, iceboat, landsailer, 17th century windmill, or anything else. The mast or spar adds stiffness to one dimension (transverse to airflow), the battens to the other (parallel to airflow).

On a rigid airfoil covered by fabric or film, ribs have the same purpose. (Some recent sailboats have such rigid airfoils instead of flexible sails, too.)

The main difference between ribs and battens is that battens usually stiffen only the aft part of the foil. On something that sails on both port and starboard tack, that lets the front part of the foil flex appropriately. (If you found a hang glider that dared to fly inverted, the same would apply.) On a hang glider that doesn't fly inverted, leaving the front part unbattened avoids stress risers and, at any rate, it's only the aft part that would be prone to fluttering like a flag and contributing no lift, were it not stiffened.

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    $\begingroup$ Ummm... I don't think this answers the question... and regarding battens, they can either be full chord or partial, and they are flexible and conform to both tacks on a sailboat and would in a wing too. A rib is a different thing , at least in my mind: ribs are rigid, and can not change their profile. $\endgroup$ – Jpe61 Aug 25 '20 at 14:04
  • $\begingroup$ Ah, I'd overlooked that you meant a swept leading edge. Thank you. I've deleted my previous comments. $\endgroup$ – Camille Goudeseune Aug 25 '20 at 16:45
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    $\begingroup$ Given timestamps it may be you answered the first version of the question, so my critique may be at fault. Anyway it should be noted that a batten can run the full length of chord, ad it will conform to it's designed profile regardless of the side the airflow comes from. In sail "flipping" them may require a yank on the sheet if the winds are light. Full length battens are by no means a rarity. Batten profile can be designed in such a way, that it will help the sail assume an optimal profile, even better than in a partially battened sail, or wing, this being Aviation Stack Exchange :) $\endgroup$ – Jpe61 Aug 25 '20 at 16:59

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