Touchdown with crab

[Driver 170]

Why is it recommended to use touchdown with crab on slippery runways? And not recommended on dry runways?

Touchdown with crab:

It is recommended to use this method when landing on slippery runways as it reduces drift on touchdown and allows for rapid deployment of the spoilers and autobrake as all main gear have touched down simultaneously. However, rudder and aileron input to de-crab after touchdown must be applied in order to maintain proper directional control.

This method is not recommended on dry runways with strong crosswind conditions as on landing the aircraft will tend to track upwind until the correct de-crab technique is accomplished. This lack of initial directional control is undesirable. Fly the nosewheel onto the runway after the aircraft is tacking the runway centerline.

[Chesty Morgan]

You've pretty much answered your own question with those two quotes.

[Driver 170]

Ah yes of course, but i should of mentioned with zero flying experience what does this mean? Be good to have examples :)

[Intruder]

With zero flying experience, you probably do not understand...

Velocity vector is the primary consideration on touchdown. Whatever it takes with your airplane's roll limitations, land with the velocity vector down the centerline.

[wanabee777]

In crosswinds, B-52's always touchdown in a crab.

[FlightDetent]

Driver 170: These are landings with crab (lateral axis offset from runway centerline, into the wind).

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[Dont Hang Up]

The aircraft will approach crabbed into wind so that the direction of travel is along the direction of runway. This is highly desirable for obvious reasons. However touching down whilst still crabbed on a runway with good grip has the following disadvantages:
a) A sideways stress on the landing gear
b) A tendency of the gear on gaining traction with the ground forcing the aircraft to travel upwind from the centreline.

Consequently the normal technique is to kick-out the crab and align the aircraft with the runway just before touchdown. This alleviates a) and b) but introduces a new disadvantage:
c)Once straight but still airborne the aircraft will begin to drift downwind from the centreline. If the aircraft floats for very long after the kick-straight this may become excessive.

If the runway is slippery then the problems a) and b) are minimised. Therefore the need de-crab and risk introducing problem c) may be removed.

Of course, as many will tell you, some aircraft are designed to touch down crabbed anyway. Others will voice the advantages of the wing down technique as an alternative to crabbing.

[Driver 170]

Thankyou all for helping out and especially - Dont hang up , great explanation;)

[sycamore]

w-777, the B-52 has x-wind landing gear.....

[ehwatezedoing]

In crosswinds, B-52's always touchdown in a crab.
In crosswinds, Turbo Dak never touchdown in a crab :p

[wanabee777]

w-777, the B-52 has x-wind landing gear.....

Quite correct!

[wanabee777]

In crosswinds, Turbo Dak never touchdown in a crab :p

N500MF is one mean look'n Turbo DAK...

http://www.missionaryflights.org/mfi/images/fleet/N500MF.jpg

I've never seen one touch down in a crab. Probably not a good outcome to do so.

[con-pilot]

I never landed a DC-3 in a crab, never even considered trying to do so. Wing into wind low and use differential power. Worked great

[TowerDog]

. I never landed a DC-3 in a crab, never even considered trying to do so. Wing into wind low and use differential power. Worked great

Amen.
Bad things could happen if trying to land a DC-3 in a crab.:ooh:

I miss that plane, good old days.

[Dont Hang Up]

Bad things could happen if trying to land a DC-3 in a crab.

Tailwheel aircraft in general are not tolerant of landing crabbed, or indeed of getting out of shape at any point on the landing roll. Is the DC-3 particularly problematic in this regard?

[ehwatezedoing]

The DC-3 is no more problematic, as you know landing any kind of tailwheel in a crab is asking for trouble. A bit like stepping on one brake right at touch down, let me know how it goes ;)

The Basler can go all the way to 40kts straight crosswind using conpilot technic. Not talking about gust, that's another story!
You have a lot of arrows on your quiver. Wing down, a huge rudder, huge ailerons (when tail is on the ground the "down" aileron act like a spoiler, you can use that as directional control too) And power differential, even reverse. Not too much though or you will blanket the tail.

[TowerDog]

.Tailwheel aircraft in general are not tolerant of landing crabbed, or indeed of getting out of shape at any point on the landing roll. Is the DC-3 particularly problematic in this regard?

The center of gravity is behind the main landing gear, getting any side load on the gear may convince the airplane to swap ends. The cross wind may even help.:sad: