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Cross wind landing teqniques

Old 11-06-2010, 10:24 AM
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ntsmith
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Default Cross wind landing teqniques

Perhaps some one could be so kind as to help me get my head round this.
The scenario is a wind of some significant strength coming directly towards me. The aircraft is coming in right to left.
Do I
A/ Give right rudder and correct with left aileron in which case the plane will land with a hefty crab and possibly damage the U/C or
B/ Give right aileron and correct with rudder.
Not sure if A or B is even marginaly correct or should be a mixture with the correction changing at touch down.
Can any body be so kind as to give a walk through of their landing technique (using my scenario just so I can compare easier)
I really look forward to the answers as it is driving me mad and presumably to a certain extent this is going to apply on take off.
Remember the scenario:
The scenario is a wind of some significant strength coming directly towards me. The aircraft is coming in right to left.
Old 11-06-2010, 10:32 AM
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jetmech43
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Default RE: Cross wind landing teqniques

right wing down into the wind opposite rudder
Old 11-06-2010, 10:49 AM
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Default RE: Cross wind landing teqniques

listen to jetmech, he is right on. just keep your speed up.
Old 11-06-2010, 11:42 AM
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Default RE: Cross wind landing teqniques

basic cross wind I learned back when I got my pilot license
Old 11-06-2010, 12:09 PM
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ntsmith
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Default RE: Cross wind landing teqniques

That is opposite to what I was told some where else although that is what I thought is correct. Looking to the fron from the cockpit point of view I was told that you give right rudder (towards the wind direction) which would keep the plane on track and opposite aileron to keep the winds level whereby on landing the rudder is "kicked" to the left to straighten the run and so preventing damage to the U/C.
What you are saying, if I understand is that you are banking the plane into wind and correcting with rudder.
Now I really am confused
Old 11-06-2010, 12:15 PM
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ntsmith
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Default RE: Cross wind landing teqniques

The difference, if I recall is that there are two methods. Crab and sideslip. I usually use the crab method so in my scenario (given in my original post) I would be giving right rudder (crab into wind) and left aileron.
Old 11-06-2010, 02:08 PM
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Default RE: Cross wind landing teqniques

the wing down into the wind opposite rudder, the rudder will keep the nose straight try at some altitude and see what happens
Old 11-06-2010, 02:09 PM
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Default RE: Cross wind landing teqniques

how much rudder?, what ever it takes to keep the nose straight
Old 11-06-2010, 02:14 PM
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Default RE: Cross wind landing teqniques

you where told wrong keep the wing down in this case right wing down into the wind then opposite rudder
Old 11-06-2010, 05:59 PM
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Default RE: Cross wind landing teqniques

This falls into the downwind turn gategory. Just because your nose is pointing out and the plane is crabbing along doesn't mean the plane is flying crooked and needs left or right aileron or left or right rudder. You wouldn't land the plane with crossed controls when the wind is blowing down the strip so why do it when it's a cross wind. (unless you want to bleed off airspeed)

An extreme example would be if you had a right to left groundspeed of 30mph and the wind was blowing in at 30mph the plane would quiet happily "crab" along the strip at a 45deg angle with neutral controls and an airspeed of 42.4mph.

If your holding in rudder then you're forcing the plane to fly crooked which may require you to cross the cross the controls depending on your planes yaw coupling characteristics. Coming in one wing low may work for others but it would be just my luck that if it did decide to drop a wing then the low one would be the first to drop, so I try to keep the wings as level as possible.

Best to get the crab angle sorted on the final turn before leveling the wings, I do this not by looking at the plane as such but referencing it with a background object during the turn. When the plane stops moving as you turn it towards you/the strip then it's pointing in the right direction to fly straight in. If the nose is pointing out or in then so be it.

Straightening the plane before touchdown is pilots option, again depending on your plane and how it's built. A taildragger you probably should straighten it up before touchdown but I'm lazy at times and mostly don't bother.
Old 11-07-2010, 03:25 AM
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Default RE: Cross wind landing teqniques

Hi NTSmith,

To align the model's longitudinal axis with the track of the model one must cross control. Just think of landing on the upwind wheel only, then as the model slows down the downwind wheel touches down and then just a little crab angle is necessary to control drift. I typically end the ground roll with the aileron all the into the wind as the model stops. (The "down" aileron provides drag, and aids in directional control by helping to fight the weathervaning on roll out).

Crab in steady state flight does not require any control surface to be deflected. It's just a heading into the wind to make the model track to the runway. When a little ways out on final, roll the upwind wing down and correct the turn with rudder to line 'er up (right aileron/left rudder for NTS's example) on the strip. It's essentially a slip, a cross control exercise our pattern ships do very well.

The crab to a "kick-out" just at touchdown is a technique used on old jet airliners where a bank angle limit was imposed because of low hanging pod engines. It has little to do with Pattern models until the wind velocity requires the wing to be so low the tip scrapes.
Then the pilot must utilize the "combination wing down plus crab" technique. This is where the model lands with the wing down, cross controlled but still holding a crab (heading into the wind) to counter wind drift, which is removed as the model touches down. It often isn't completely taken out as the model needs to crab a little even on the ground to counter the drift of a strong x-wind.

It takes practice. Trike gear trainers are easier to experiment with (one always feels gutsier), so if one is available go shoot a bunch while trying these various techniques trying to fly it along on the upwind main gear wheel the length of the runway. It's fun and you'll learn a lot.

Hope this helps, you've received mostly good help here from the posters above.

Chris...
Old 11-07-2010, 09:54 AM
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Default RE: Cross wind landing teqniques

That really sounds feasable although I am not sure what you mean when you say "Crab in steady state flight does not require any control surface to be deflected" surely in my example I would have some left aileron to counteract the rudder which is holding track and if I have this right doing a sideslip would be the opposite. That is, right aileron (lower wing lowered into the wind) and rudder to hold track.
I have tried both these on the simulator but because of depth perception problems it isn't as easy as in flying a real model. Not sure how the latest 3d sim by "real flight" would fare there. it may be alot better.
This landing lark is gettingto be quite a busy affair, what with juggling with aileron, rudder and power. Still, all good fun.
I did witness one of our club flyers last year do a very spectacular side slip in to a perfect cross wind landing. Because of the distance away and starting on a turn it looked very impressive.
Practise I guess. practise.
I must also say a huge thank you to the support one receives here. It is very, very useful and very kind of people to take their time to help.
Old 11-07-2010, 05:29 PM
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Default RE: Cross wind landing teqniques

You are quite right about the slip when cross controlling to touchdown, Nigel.

My crab comment was to emphasize the difference between a crab and a slip. When on final, you can fly the model in a crab into the wind with out cross controlling, until say, you cross the end of the runway. The crab is just the heading difference between the track you want to fly and the wind correction you must keep to fly the track. We always do this when flying the sequence, after the turn-around we just turn a little into the wind so the model doesn't keep drifting towards us. We usually don't hold the rudder into the wind the whole time. On final approach we can do the same thing, and then do the cross control, wing down slip at a moment that makes us comfortable. The whole final doesn't need to flown in a slip. But you can if you want to, I suppose.

Hope this helps.

Chris...
Old 11-07-2010, 05:42 PM
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Default RE: Cross wind landing teqniques

Hi ntsmith, I think by "crab" (for want of a better term) we mean the plane is not pointing in the direction that it's tracking across the ground, just as a boat crossing a flowing river will be pointing upstream if it wishes to track straight across. In both cases the boat and plane are flying straight through the air (or water) and don't need to be forced to hold that odd angle as they aren't "sideslipping".

Sideslips are good for getting rid of excess altitude without building up too much speed but the later pattern ships knife edge too good, years ago you could really crank in the rudder and get some wild angles happening and you could hear the air buffeting over the fuselage, now you push in rudder and the thing turns around and starts flying away, you practically have to be in a knife edge.

Given you've asked the question in a pattern orientated forum, needing to cross the controls to counter yaw coupling is something that only needs to be done on a badly setup plane (from a pattern perspective), although perfectable acceptable on a non-aerobatic scale plane/trainer/warbird.

Again I wouldn't recommend the one-wing-low method, it may work fine on full scale stuff but it's a really bad habit, plus flying one wing low requires opposite rudder to keep the same heading otherwise you'll fly in an arc on your landing approach. Another negative is that side gusts tend push the plane down and lulls tend to let it float where with the wings level the plane will tend to automatically weathercock into a side gust and maintain it's ground track. Yeah the tail can wag around a bit but it doesn't worry a well set up ship. Honestly, setting your angle on the final turn really helps.
Old 11-08-2010, 11:37 AM
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Default RE: Cross wind landing teqniques

Hi Nigel,

Some more points to think about with crosswind landings.

With cross wind I do fly with some more airspeed on final, for example 50 km/h (31 mph) instead of 40 km/h (25 mph). Result of this, the crab angle is smaller. (I do have cruise control so I do know the speed which is maintained) Also the plane is much better to control with some more speed in cross wind turbulence.

Also important is to have the right wing incidence. It reduces the sensitivity for cross wind and also the distance between the wingtips and ground surface is more. My Taurus can have a 13 degrees angle before a wingtip touches the ground. The incidence is as it has to be to fly classic pattern. The mid winger will have less tolerance with ground clearance of the tips.

In the Netherlands we learn our wind how to behave, read about “wind gradient”. As result of the wind gradient the (needed) “crab angle” on moment of touch down isn’t as much as people often think, but it depends on ambient circumstances. Try to keep the track an let the model weathercock. The extra airspeed you need also to have left enough airspeed when the vector of crosswind disappears on lower altitude.

To keep the track on final I do not use rudder.

To keep the track on the ground my Taurus does have more pressure on the front wheel as models normally have. The nose leg is "modified".

Cees

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