PPRuNe Forums - View Single Post - consequences of exceeding the X-wind limit
Old 16th May 2003 | 22:54
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Genghis the Engineer
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Not really, although rudder power is clearly a player. Here are a few real world examples - they all exist but for the purpose I'll elect not to name them.

#1 - large span, low wing, moderate lateral and directional stability and moderate rudder power. Crosswind limit is basically set by the need to avoid touching the wingtip on the ground, so the main players are lateral stability and geometry.

#2 - high wing, high rudder power, high directional stability, high lateral stability. We set the limit at about 15kn on that aircraft, although the controls made a 25kn X-wind flyable BUT the sideforces in sideslip were so high that we felt that no normal pilot could reasonably be expected to function in that environment. So, the big player there was directional stability.

#3 - high wing, roll control design that gave very little adverse yaw, moderate lateral and directional stability, very little rudder power (because in normal flight it wasn't needed). So in that case the crosswind limit, which was fairly low, was clearly determined by rudder power.

#4 - biplane, linked roll and yaw controls so no independent rudder control. The aircraft was deliberately landed crabbed right onto the deck (an interesting experience) but the undercarriage was specifically strengthened to take the loads as the aircraft touched down skewed then was pulled straight by it's inertia. So in that case the crosswind limit was determined by maingear strength.

G

N.B. If you've really got a 50m wide runway, land on the diagonal and thus reduce the crosswind component.
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