Autopilots, Crosswinds and Air Masses

Is it valid to say that if you fly in a strong "crosswind" at altitude and there's a constant change in windspeed/direction that the autopilot/roll servo will constantly have to correct the flightpath?

Technically yes but only if you are flying a Rate 10 turn in the middle of a tornado

The heading adjustment for any normal wind direction change enroute is utterly negligible and is orders of magnitude below (in servo motor activity) normal roll activity keeping the wings level.

I doubt that the servos have temperature sensors

I think these are just old dumb servos, like the early King KS ones i.e. motor+gearbox, clutch, and probably no electronics. The AP computer certainly gets no feedback on anything from the servo (the wiring shows no such connections).

What you are describing would be turbulence. Have you flown through extensive turbulence where the autopilot dropped out regularly because it was hitting its limits? Outside of turbulence, there is hardly anything that would put a lot of stress on servos.

Is it valid to say that if you fly in a strong "crosswind" at altitude and there's a constant change in windspeed/direction that the autopilot/roll servo will constantly have to correct the flightpath?

Yes, correct.

Will this make the motor in the roll servo get hot eventually and could that be the reason for the A/P to disconnect if the the servo is not perfect?

I doubt that the servos have temperature sensors, but the electronics inside your AP control box will be protected against over-current and maybe overtemperature which might cause the disengagement. On the other hand, the task you describe should be well inside the design limits of any autopilot and not cause disengagement, so I suspect a fault somewhere!

10 - too fast 9 - unstable, flared too high 8 - perfect 7 - good - maybe out of crosswind limits - manufacturer's test? 6 - no idea 5 - no idea 4 - shouldn't hold a licence 3 - ditto (Hong Kong, Kai Tak, I saw a Thai A340 ground both winglets in one landing there!) 2 - shouldn't hold a licence 1 - looked really good until he flared too high and drifted downwind

Some of those approaches were in wind-shear situtations where the pilots would be carrying 10-20 kt extra (notice nose-down approaches and touch-downs). Good to carry that speed on finals, not so good in the flare.

I think the most important thing is to have a stable approach. Airlines insist on a stable approach by 1,000 or 1,500 ft, or go-around. 200 ft works OK for me in a light aircraft than I'm familiar with. It's an old saying, but it's hard to do a good landing from a bad approach.

My 2c...

But I do not agree that the PA28 is a risky plane to land. It lands almost by itself and I never even came close to losing control, no matter how strong the xwind was. But that's just my opinion.

I don't think the PA28 is a risky plane to land, but it has a record of loss of control on landing. I used to own a Cherokee 140 and later an Arrow 200, so I have no bias against it.

I witnessed one incident myself when a Cherokee 140 landed in a crab and the pilot tried to straighten it out but ended up off the runway and in a drainage ditch.

Sorry for confusing you with the OP on different thread.

Nope, I land an A340 exactly the same way as I land an A36, B747, L-1011, or Cessna 120: crabbed approach, flare crabbed, squeeze drift off with rudder just before touchdown.

Sometime it works, sometime it dosen't ;-)

A couple days ago I trained a 150 hrs pilot in crosswind operations in a PA-28. The wind was directly across the runway at around max demonstrated crosswind component (17 KT in a PA-28). The pilot maintained centreline nicely on final using the wing-low method (his choice), but during flare he drifted a little close to the runway edge because he was uneasy about maintaining sufficient aileron so close to the ground (a common problem for low-timers trained in tricycle airplanes). After each of the first two landings, he lost directional control and I had to take over. The main reason he lost control was that when he put the nosewheel down, it was pointing away from the wind because of his rudder correction and he was not prepared for that. This is a well known challenge when landing any PA-28 or PA-32 in a strong crosswind, and probably one of the reasons that runway-loss-of-control appears regularly in the reports with these otherwise benign types.

I use the crab method myself and consider it the "standard" method for cross wind landing, for reasons mentioned in other posts. I see three cases for the crab method: 1) teaching cross wind landings for students; a good way to demonstrate the crossed-control input required to point the nose in the direction of travel; 2) checking on short final whether the cross wind component seems to exceed the capabilities of the airplane (useful but not quite reliable because of wind gradient); and 3) sometimes it is easier when landing tailwheel and other types that need to be lined up exactly in the landing direction.

The crab method can actually allow landings in a stronger crosswind because of the airplane's yawing inertia when kicking out the crab just before touch-down. Good timing is required for that, as someone else wrote also.

Nope, I land an A340 exactly the same way as I land an A36, B747, L-1011, or Cessna 120: crabbed approach, flare crabbed, squeeze drift off with rudder just before touchdown.

That's how I land the TB20.

As I said in my (rather long) post, the yaw inertia (of the considerable yaw which takes place in the last few feet of altitude loss) works in your favour and often very little rudder is required before all 3 wheels are on the ground.