Primarily for general aviation discussion, but other aviation topics are also welcome.
#1911803
TopCat wrote:With the crab technique, once you're holding off waiting to land, yawing it straight needs to be timed right, and executed promptly. Too late and you land going sideways; too early, and you're drifting off in the crosswind.

So it's not a violent kick, obviously, but I don't see how it can be gradual without an element of slip being introduced to prevent drifting off.

Feeding in some rudder doesn't change the direction that the aircraft is moving, not at 3,000', not at 6".

OK, if you put in enough rudder and hold it on for long enough the aircraft will eventually start a really inefficient yawing turn, even though the wings are level. Feeding in some rudder to align heading with track at some point during the landing hold off will not instantly send you drifting sideways off the runway.
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By Paul_Sengupta
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#1911866
low&slow wrote:OK, if you put in enough rudder and hold it on for long enough the aircraft will eventually start a really inefficient yawing turn, even though the wings are level. Feeding in some rudder to align heading with track at some point during the landing hold off will not instantly send you drifting sideways off the runway.


Have you ever done it? :D In a good enough crosswind you head off towards the edge of the runway like a scalded cat! At least you do in a PA28 anyway, I guess a 747 is a little different.
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By PeteSpencer
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#1911872
Well I’m not an advocate of ‘wing down ‘ and landing on the into-wind wheel in the arrer.

Have you seen the tiny size of the ‘gear down’ MLG lock?

Nah The Crab and positive rudder application the instant before touchdown has always suited me:

Including the memorable day when we arrived at Le Touquet from Quimper on fumes having experienced much stronger headwinds than forecast to find it was a ‘no ATC’ day, with no-one in the tower . (allegedly)

(I had overlooked this and we had already been weathered in at Quimper for 24 hours)

Lille couldn’t help with the surface winds at Le Touquet and the windsock was virtually horizontal .

After landing I found out that the wind was G30 kt across the runway. :shock:
#1912133
BoeingBoy wrote:I do cringe when I read about there being two methods for crosswind landings. There is only one, and that is to arrive at the point of touchdown with downwind rudder and into wind aileron applied in sufficient amounts to counter any crosswind and land the aircraft aligned with the centre line and with zero drift. What does exist are two ways of arriving at that state.

There is nothing to stop you using offset heading to drift down the centreline for comfort until you're approaching the threshold, but at that point, maybe 100'+ you slowly and smoothly put enough crossed inputs in to keep the wings level and the nose down the centreline.


I don't really agree with your analysis. From the point of view of the aerodynamics, you cannot fly:
  • in an unaccelerating state; and
  • with symmetric power; and
  • with a slip angle (e.g. aligned with the centreline in a crosswind); and
  • with wings level.

Something has to give.

The "wing down" technique gives up wings level, and maintains an upwind wing down slip to touchdown.

Alternatively, you can approach the runway without a slip angle, in other words, crabbed into wind, but to line up the nose wheel with the centreline before touchdown, you must initiate a slip angle by yawing. If the wings are kept level, you will accelerate downwind, since, without the lift vector tilted upwind, the forces on the aircraft are unbalanced, whatever you do with the ailerons. If you commence the slip late enough, that acceleration will not result in much downwind drift velocity by the time you touch down, and the gear will happily absorb it.

I think those are two different techniques: in the former, the touchdown is with a roll angle into wind, in the latter it is wings level.

For the reasons you outline, I prefer to land the Twin Comanche wing down. It's too easy to mis-time the yaw and find myself drifting downwind.
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By MichaelP
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#1912192
I had a DA40 grounded for a couple of weeks because the American instructor had never learned the crab and straighten technique.
He scraped the tiedown ring and the corner off the aileron. The aileron had to be replaced.

I learned in a Cessna 150, which with a high wing and narrow main gear track, is easy to land in a slip.
Many say this is low stress, no side load, but do the geometry!

So I learned the crab and straighten technique as the primary means of crosswind correction as it works on all types with rudder control.
We learned wun wing lo landings as a bit of fun. Can do both.
Cherokees should use the crab and straighten technique, a lot less stress on the gear legs.
Takes a while to accelerate to the crosswind velocity if you straighten too early, and the load is shared if you land wings level.
The into wind gear takes all the stress on a wun wing lo landing, and if the gear is wide this can be a lot of wear and tear.

As an aside, had a Cherokee with terrible nosewheel shimmy... They’d replaced the damper to no effect.
The shimmy was in fact a mainwheel. When jacked this could be rotated left and right on the scissor links. Was this wear and tear due to wun wing lo landings?
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#1912243
Yeah, but there's also a lot more fuselage for the wind to act on.

If we can use the rudder to change the direction the aircraft travels through the air why do we bother to roll to an angle of bank to change direction?

Why don't we just keep the wings level and do what boats/ships do and steer with the rudder?
#1912250
Lol.

Changing effect of the rudder near the stall is something I've been teaching in gliders for over 20 years. You need to be less than 5 knots above the 1G stall speed to make it work (preferably only 1 or 2 knots), where the secondary effect outweighs the primary effect. Any faster and all full rudder gets you is lots of yaw & a little roll. Definitely no immediate flick into a full blown spin.

The question remains, if applying some rudder during the hold off can change the direction in which the aircraft moves through the air why can't we steer the aircraft using just the rudder during the cruise?
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By PeteSpencer
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#1912264
low&slow wrote:
The question remains, if applying some rudder during the hold off can change the direction in which the aircraft moves through the air why can't we steer the aircraft using just the rudder during the cruise?


Of course we can, but the skid induced makes it bloody uncomfortable for any length of time for pax who aren't expecting it.

I use rudder only for a gentle tweak back onto the localiser on an ILS approach. , but this is only a matter of seconds,:wink:
#1912268
Rob P wrote:Because boats aren't known to enter a spin when rudder is applied whilst close to stall speed?

Rob P


If you are tracking forward as in “forward sideslip” (straight on runway heading and G=1), the stall is still very healthy even if your ball goes to the corner :wink: if that it goes sour, you are already raising the falling wing with rudder :thumleft:

It’s stall during turn (heading moves and G>1), especially skid turn config, that is nasty :eye: if that goes sour, you are raising the falling wing with aileron :twisted:

Having said that, while you can sideslip at slow speeds it works better for high rate of descent if you sideslip on faster speeds (at slow speeds near VS one is already dropping like brick :D )
Last edited by Ibra on Sun May 22, 2022 1:44 pm, edited 1 time in total.
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By MichaelP
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#1912287
There’s a certain amount of ignorance about the effective use of controls to fly in the air, and the requirement to abuse the air controls to adapt the aeroplanes’ passage such that the wheels are in line with the runway.

We fly straight in a body of air that is moving across the ground.
If that body of air is not moving in line with the runway then we must skew the aeroplane so that its wheels are moving in the direction of the runway when they come into contact with it.

Ground track and air track are often different.

It’ s the same ignorance some pilots have when it comes to tracking in the air.
Some actually believe they need the rudder in the air to correct for a wind across their direction of flight. No, we fly a heading that corrects for the drift, and we keep the ball in the middle!

Of course it is evident following a takeoff when climbing away, the pilots who have their wings level showing they know how to apply rudder in the climb, and the pilots who don’t who climb wun wing lo using roll to correct for the slipstream and P factors...

The number of times I’ve said “wings level, ball in the middle” on climbout.
Mind the trees!