aeroncasuperchief wrote: ↑
Wed Nov 21, 2018 8:01 pm
"sideslip" versus "kicking out the crab", the latter is simply a very last-minute application of the former.
If you watch an airliner on approach in a moderate crosswind, the wings are level throughout the whole crab procedure. WHEN the pilot fails to kick out crab at the last moment and correct any follow on effects, you may see a wing low overcorrection into the wind. That wasn't the intended maneuver but a failure to do the maneuver properly. Any airline pilots please correct me if I am wrong !
Any A/C can do the crab technique but the airliners with their huge weight compared to their lifting surface and low hung wing and engines MUST use crab technique most of the time in a crosswind
Crab with a C-150 is counter- productive If you do not make a perfect transition to landing, drift will mess up your landing and track and may set you up for an accident because you are now transitioning to the wing low method at the worst possible time .
OK, I will!
Like I said before, the perception of there being two distinct techniques is mostly a result of people explaining the
same thing two different ways.
The "crab" is always "kicked out". On a high-wing plane it might be "kicked out" some time before touchdown, and the aileron input necessary to control the resulting lateral drift results in the plane approaching the landing surface with a wing down.
On a low-wing plane with underslung engine pods, the crab angle is "kicked out" in the last twenty feet or so. Opposite aileron is still applied in order to keep the upwind wing from lifting, and also to control lateral drift. The wings are kept level or nearly level because the geometry of the plane requires it. On a more massive plane, very late application of the "cross controls" and smaller degree of aileron input into the wind is aided by the plane's mass and relatively high speed, which negates some lateral drift and also allows the aircraft to somewhat tolerate some lateral drift on touchdown, especially on wet runways. Just the way you might not de-crab a skiplane if landing on a slick, icy lake.
The result is the same however: in either scenario the plane touches down with so-called cross controls. The controls are deflected that way for the same reasons. Therefore my attitude is that it's not some entirely different technique, but instead it's the same technique, applied earlier or later as appropriate considering the type of aircraft and the surface condition.
I guess I can agree that a distinction exists in the sense that a plane may or may not be aerodynamically sideslipping immediately prior to the moment of touchdown. But, as photofly
has pointed out, the only thing that counts in crosswinds is what the aircraft and the controls are doing when the aircraft is in contact with the runway.
The reason I disagree with the perception that there are two completely unrelated techniques is that I have seen pilots on light high-wing aircraft decide that they will practice landing "like an airliner". I would rather explain the whole process in common terms, with modifications to the technique as appropriate for the aeroplane type, rather than foster the perception that there is a whole new technique to learn at some future point. It's basically just about using ailerons and rudder together to control track, heading, and side-loading on the gear, in a timely fashion, to a greater or lesser degree depending on the aircraft type.
Here are some comments on various "airliners":
The manual from a popular transport category low-wing twin-jet aeroplane recommends a wing-low touchdown up to about 26 knots of crosswind component, after which it recommends a partially crabbed touchdown in order to avoid further bank angle which may result in wingtip or engine pod strike. This manual states that while zero sideslip landings are possible with the fuselage crabbed as necessary, this isn't recommended on dry runways due to directional control and gear side-loading limitations.
The manual for another popular, similarly-sized transport-category jet with a high
wing recommends a wing-low sideslip touchdown right to the maximum recommended crosswind of 35 knots.
The manual for yet another popular commuter-category jet with a long, highly swept wing and fuselage-mounted engines (therefore pretty stubby landing gear) recommends a wings-level touchdown with lots of downwind rudder just prior to the moment of touchdown. It does however specifically mention the significant amount of simultaneous upwind aileron necessary to keep the wings level and the gear firmly stuck to the runway during this manoeuvre. In fact, even this aircraft will touch down slightly upwind-wheel-first in high crosswinds: This is directly from the manual: As rudder is applied the aircraft will tend to roll in the direction of the rudder input. To counter this, simultaneous input of rudder and opposite aileron is required to keep the wings level. In this wings level condition there will be some sideways drift. A slight, into wind, wing down should control this sideways motion.
I don't see two distinct techniques here, I see a continuum incorporating surface condition, wind intensity, and aircraft design.
I realize I'm simply arguing semantics here. I assure you I land and take off the same way as everyone else on every aircraft I have ever flown. I am simply communicating my opinion that the whole thing might be easier to teach if we stop regarding the art of crosswind runway manoeuvres as two distinct approaches to the same problem. Any technique you discuss for one aircraft type is going to be dangerous to apply on another aircraft type if modifications are not made to the technique.
Sorry for the long post.