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No More Chinese/Crabs

A better way to land in a crosswind
  [vote for,

Background: There are 2 methods of landing an aircraft in a crosswind.

The first is the crab. The wings are held level and the rudder is used to counter the force of the wind. This puts the aircraft onto the runway in a sideways position and can cause damage to the landing gear and a loss of control on roll-out.

The second, preferred, method is the forward slip. The upwind wing is dropped to maintain a counter to the wind and the rudder is used to maintain a runway heading. The landing causes you to land on the upwind wheel first with the upwind wing barely above the runway. (The Chinese… or, “One Wing Low” method)

I have used the forward slip when flying into KHAF where the runway runs North and South (30 & 12) and the winds are always off the ocean at a brisk clip. On windy days, the upwind wingtip is less than a foot from striking the runway.

The idea of the forward slip is that you are killing lift in one wing. So my idea is to have a trim tab in the cockpit with would retract the upwind wingtip a few inches, killing lift but keeping the aircraft level. The trim tab could shorten the span with a flick of the finger and then the rudder could be used to maintain centerline control. With decreased drag on the upwind wing, the drag on the downwind wing would be greater and there would be a yawing effect to the downwind wing and rudder pressures would also be diminished. No crab and no low wing.

I would think that a decrease of just a few inches of span would be enough. Landing would be straighter and flatter.

Klaatu, Apr 06 2010

Robin DR-400 http://en.wikipedia.org/wiki/Robin_DR400
A docile little aircraft. [8th of 7, Apr 06 2010]


       " retract the upwind wingtip a few inches, "   

       I love it, if only for it's stress effect on aircraft inspectors.
normzone, Apr 06 2010

       Surely to maintain a straight line over the ground, you need to be making an angle to windward through that air? i.e. slipping sideways in the direction the wind is coming from. Obviously the two 'standard' methods you suggest cause the aeroplane to slip sideways through the air, but it is not clear that your plan does.   

       i.e. to prove this idea works, fly straight and level in still air, and then pull the switch. Does the aeroplane crab sideways, and if so, why?
pocmloc, Apr 06 2010

       why not a pair of fins on the top and bottom of the plane at the nose and the tail that can steer the plane slightly in the vertical axis? This would allow for a slight strafe while maintaining the plane's level stance.
WcW, Apr 06 2010

       Other solutions might be:   

       Differential flap deployment - like the elevator trim wheel, but for "unbalancing" the flaps by a small, controlled amount.   

       Spoilers on the upper mainplane might achieve the same thing.   

       At the point all this is happening you're going to be down into the ground effect which makes it all rather more complicated.   

       Or get a Robin (DR-400) or similar with a marked dihedral on the wing tips.
8th of 7, Apr 06 2010

       I'm sure I have seen a '30s photo of a 'plane with castoring main wheels as well as castoring tailwheel, to allow the 'crab' method described first in the idea. I understand it made steering on the ground tricky. So instead of allowing the wheels to castor, how about let the pilot manually set them to the drift angle? Then she or he can fly level, steering slightly into the wind, turn a big steering wheel to crank the landing wheels parallel to the runway and land safely and securely at a wonky angle.
pocmloc, Apr 06 2010

       The gear is typically placed to transmit the force up into the mainspar and thence to the fuselage. Moving it further out would substantially increase the turning moment at the wing root, possibly causing failure.
8th of 7, Apr 06 2010

       I'm not sure I buy the premise. The crab/slip doesn't seek to affect lift on the upwind side, but to course-correct for the deflection caused by a crosswind.   

       Shortening the upwind wing will reduce lift on that side, but I don't think a crosswind will compensate for it.   

       (As for castoring wheels, a number of large U.S. Air Force aircraft can land straight down a runway while the aircraft is actually pointing significantly to one side.)
phoenix, Apr 07 2010

       what amazes me is the endless source of experience present in the HB. I have yet to see a topic that does not have a number of people with the experience to comment....
senatorjam, Apr 07 2010

       Disappointed: thought this was going to be an idea to rid the Thames of eriocheir sinensis.
coprocephalous, Apr 07 2010

       // I have yet to see a topic that does not have a number of people with the experience to comment.... //   

       Just don't ask about incest.
8th of 7, Apr 07 2010

       "What about simply rotating the runway?"
That's what the world needs - a lazy susan airport.

       "Tower, Cessna 757GR reporting midfield downwind on 21...er 22...er 23..."
phoenix, Apr 07 2010

       // rotating the runway //   

       It's called an "Aircraft Carrier".
8th of 7, Apr 07 2010

       So, a large circular pond is excavated in the centre of a major city (e.g. in the main park). A retired navy aircraft carrier is installed in the pond. The carrier always faces into the wind; aircraft benefit from steam catapult takeoff and arrestor hook landing. International air service to the centre of the city. The pond can also be used by ducks and pedalos. The economic benefits of such a project could easily pay for replacement of all the world's navies' carriers with updated models, as every city installs a carrier pond.
pocmloc, Apr 07 2010

       Phoenix: // (As for castoring wheels, a number of large U.S. Air Force aircraft can land straight down a runway while the aircraft is actually pointing significantly to one side.) //   

       And if I remember rightly, the X-31 could actually *fly* that way as well :-)
gtoal, Apr 09 2010

       I really think that a front stabilizer similar to the one on the tail but mounted underneath the nose would be an effective solution. The two working together could trim out the side wind and allow the pilot to land as in a calm. The pilot lines up for the landing, trims out the horizontal drift with a lever that shifts both the rear and front stabilizer a few degrees off center, then lands as normal using the foot pedals to shift the rear stabilizer as normal (from it's new false center position, the front stabilizer would stay put.)
WcW, Apr 09 2010

       I fly Galway-Luton a lot on a turboprop. The preferred landing method in a crosswind (in Galway, that's always) is the crab for some reason. I don't like it - it can visualise the plane tipping as the wheels take control and set it straight. Fix it.
wagster, Apr 09 2010


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