Emir wrote:
I do the same – crab all the way and just prior to touchdown wing into wind and opposite rudder.
How prior to is prior to? My technique is to decrab when passing the threshold.
I do it later. Just before starting the flare. That said, with tge short runways we have at most GA airfields in Europe, often the flare starts immediately after crossing the threshold.
The PC-12 has higher crosswind demonstrated crosswind with reduced flap, and higher with no flap. Whether this is related to the stick shaker/pusher might be a factor?
Actually flap improves roll control and available angle of bank at slow speed, but reduces lateral stability. The curve of Cl/AoA is sharper with TE flaps, and therefore the airplane may be more prone to wing drop/stalling with less warning symptoms.
I de-crab, flare and put in some aileron basically simultaneously like most here. In my experience slipping all the way down will most of the time need correcting rudder and aileron again anyway just before touchdown because of decreasing X-wind, so might as well just do it once.
gallois wrote:
I also feel ga pilots should try both side slip and crab. There is a reason why CAT crabs rather than side slips.
For passengers crabbing is definitely the better experience. For swept wings, I’m not sure if slipping is a good idea at all. But for GA aircraft? I don’t understand why anyone would prefer crabbing.
Anyway, as WWW points out, ENVA is notorious when the wind is from SE. Severe turbulence (gust) and direction vary wildly. I once was in a KLM from Amsterdam. He had two tries before he managed to land (with lots of cheering and clapping when he finally did 
) The only CAT who has “got it” is SAS. What they do when possible, is to fly visual. They start the final for 09 much farther north, thus the final is flown at approximately 15-30 degree angle I would guess vs the runway. Over the threshold they turn heading 09 and land a second or two later.
It has also happened that GA pilots simple didn’t manage to land. That typically ends in using the N-S taxiway (an old runway closed 50? years ago). The tower then say “no traffic the next X minutes, land as convenient” or something like that. The NW – SE runway was closed some 20 years ago, which was seriously stupid for GA.
The problem with very light aircraft (ULs) is that they are very light. Low wing loading and low touch down speed. The Alphatrainer has a 18 knot cross wind limit according to the POH. The problem is touch down. The Alphatrainer touches down at 25-30 knots max. What happens just before touch down is you are simply blown off the runway and ends up scaringly close to the edge. There’s no speed or aileron authority left to fully compensate. Exactly how this is supposed to be done with 18 knots cross wind in a normal fashion without using most of the width of the runway is beyond me. A much better way then is to use the “SAS-method”, or simply touch down at an angle, using the runway width in a controlled way. Only the “SAS-method” will work at a narrow runway (not yet tried that on any narrow runway though).
Anyway, “effective crosswind”. Is this somewhere along what you mean? Let’s say the cross wind is 10 kts. Your landing speed is 100 kts. Then, for each 100 m along the runway, you are without compensating, blown 10 meter off. The “effective crosswind” is 1:10 or 0.1 At 25 kts landing speed this become 0.4. For each 100m along the runway, you are blown off 40 m. The faster you go, the less “effect” the crosswind has ?
RobertL18C wrote:
Actually flap improves roll control and available angle of bank at slow speed, but reduces lateral stability. The curve of Cl/AoA is sharper with TE flaps, and therefore the airplane may be more prone to wing drop/stalling with less warning symptoms.
Would you or anyone have some good theory sources on the topic of flaps in varying crosswind and/or gusting wind conditions? Had a landing yesterday that I had to abort post flare and make a go around because I got totally destabilized due to varying crosswind with full flaps. On second attempt I again used full flaps and expecting the wind better with a shallower higher power setting approach it worked out better. But I still wonder what the best option is in these conditions theoretically speaking. I prefer full flaps nearly anytime I can use them.
Oh and I too crab and decrab in the flare with wing into the wind.
@Airborne_Again I don’t understand your questions..
Each aircraft is different. Each aircraft ( or many)have a demonstrated crosswind landing figure. Each aircraft has a recommended speed over the threshold or on final, with or without flaps. That speed like all speeds can be calculated as a Facteur de Base for that phase of flight eg a ULM might fly final at 60kts which equals a Fb of 1. You use this 1 to calculate what the wind speed Vw and its angle to the aircrafts track is going to do to the aircraft.
I was trying not to get too pedagogique about this but if Vw = 40knts and Fb = 1 then the maximum Ve (the effect the wind will have on the aircraft) is 40kts.
It doesn’t matter whether you are using it to go from point A.top point B or.whether you are in the hold or landing the maximum effect of that wind is 40kts. At 120 kts the Ve will be 20kts.Of course if you are going into a hold or planning a longer flight or landing and take you might also want to know the angle of Vw to your track and use sin or cos or in the UK the 1/6th rule or whatever to quickly calculate where you should point the nose. But the maximum and I stress maximum will always be Vw x Fb.
What we as pilots are trying to do is to steer the aircraft in the most stable and efficient way possible (not counting for side slipping to lose altitude quickly) from point A to point B or from turning onto final until the roll out on the centre line. All winds will have an effect Ve on you being able to do that but if you are landing at 120kts over the threshold and the wind is 40kts you know that the maximum effect the wind is having on the aircraft is 20kts and you can correct for this. It is very rare to have a full 90° crosswind at such a level but you can prepare for it in the planning stage and decide whether to go or not.
As the aircraft slows or the slower the aircraft the Ve will be higher so of course you have to make allowances for that and I have explained the method I use, ie adding more into wind aileron as the aircraft slows on the runway. The reverse is true on take off gradually reducing the into wind aileron deflection so as to remain on the centre line.
Some aircraft types need less precision than others in the amount of aileron deflection. You do need to know the characteristics of the aircraft you are flying.
I hope I have answered your questions.
@Silvaire I mentioned insurance companies in regard to them finding reasons not to pay out. The demonstrated crosswind figure found in many POHs is just that “demonstrated”. It is neither a limit or a regulation. However, if you have an accident on take off or landing your aircraft and the crosswind is shown to be above this limit, do you think the insurance company will just pay up for all the damage. You have not broken any regulation but I don’t have the same faith in insurance companies as you do.
@LeSving I haven’t done the calculations but if your landing speed is 100knts you have an Fb of around 0.6. If you have a full crosswind of 18kts you have a Ve = 18 × 0.6 = 11kts. Having turned final and making no correction for the wind you will go off track by around 134 metres between turning final passing the threshold. I wouldn’t trust my maths on this I am doing the calculation in my head and these days I tend to fly by feeling nowadays and the twins I flew had avionics which saved the need for calculations except in the planning stage.
Touching down is as I described de crab and into wind aileron during the flare and as you slow add more into wind aileron. You might even reach the limit of aileron as you slow and then you would need to add more rudder to keep you on the runway centre line. Some POHs might even recommend a touch of differential braking. Touching down at 25kts – 30kts should not be a problem with higher crosswinds than 18knts even without full aileron deflection.
I would guess that full aileron into wind deflection would only come about with a full crosswind of around 40kts.
The bigger problem being the wing lifting or weather vaning into the wind, especially in a taildragger.
NB I of course wouldn’t trust my calculations without some testing with an instructor who knows the aircraft well.
It may be just me but I tend not to fly any aircraft solo until I have spent time with someone who knows the type well.
Unbelievable, are you all crabbers?
hazek wrote:
Would you or anyone have some good theory sources on the topic of flaps in varying crosswind
That’s probably where “effective crosswind” comes in, don’t know. But a rule of thumb is the more crosswind, the less flaps. Don’t know of any good theory source, but flaps for landing (a GA aircraft at least) is used to decrease landing speed and increase descent rate (or more precise, the descent angle). That’s not a problem in a crosswind. The speed (across the ground) already is small, and the descent angle is steep. And the lesser airspeed when flaring with flaps is more of a disadvantage than an advantage at high crosswind speeds.
@hazek I don’t know of any book either.
I always thought it was taught at PPL.
Whether to use flaps or not does not have a definitive answer except if its gusting or above Vfe both of which might damage the aircraft.
Personally the maximum flap I would use for a strong crosswind landing would be stage 1 or take off flap. But this might be a personal thing as I find full flaps in anything above 20kts seems to feel as if the aircraft is floating on the wind rather like walking on slippery ground in high winds. I feel as if an invisible hand is trying to move the aircraft up or down left or right.
Many of these decisions can be taken in the planning stage.
As an slightly off topic to try to further demonstrate the importance of Ve.
On my annual MEIR tests I often used to go to Ouessant or Alderney. Part of the test was a few planning briefings and questions before the flight. Eg we will go to Ouessant LFEC where we will do a RNP approach followed by visual circuits. At some stage we will do OEI flight including a possible landing OEI. My planning had to include TEM (threat and error management). So if there were to be crosswinds this would form part of TEM and whether or not to use flaps. Both Ouessant and Alderney have quite short runways for a DA42. Both Ouessant and Alderney have cliff faces just before the threshold when approaching from a certain direction.
Anyway one particular test the destination was Ouessant with a 40kt G50kt headwind right on the axe of the runway. French PPL training for a head wind on landing includes the following calculation Ve = Vw minus 10 divided by 2 plus the difference between between the wind speed and the gust. In this case its 10kts (40G50). What is or are the threats and how should they be managed?
The problem is that it would be impossible IMO to write a book to cover all eventualities which is why the PPL is said to be a licence to learn.
MichaLSA wrote:
Fernando wrote: I got curious to hear what are your personal crosswind limits?My crosswind limit is now 35, as I know from experience that rudder authority of my daily aircraft only lasts up to that – above only skidding landings are possible.
I yet have to find my personal limit. And then – what is a personal limit worth in the case that your airport of destination closes, and a weather alternate without strong sidewind does not exist (or is not within reach)? I had that, and learned from it that 42 knots cross is too much for me to manage a good landing. It’s not the approach, that is doable (crabbing of course and looking at the runway through the side window), it’s the amount of skidding after landing. And it’s really to be done right because the landing gear might collapse. Touchdown has to be settled intentionally, letting the aircraft drop upon cutting off throttle. In my case, from a very broad runway (36 meters) I still used up about half of the width and was just about going around when it finally stopped skidding. Maybe I could have touched down somewhat diagonally. 10 degrees off runway track might have also helped.
gallois wrote:
It is the effect the wind has on the aircraft.
I did sidewind landings in a Cessna 172 just recently, still around 30 knots, but it behaves a lot different after touchdown. The wind can easily lift the wing that’s pointing into the wind. But it doesn’t skid. A low-wing aircraft sits better on the ground, but it’s prone to ground effect so that it skids.
I think the best touchdown technique for any aircraft involves defining exactly the point in time when the aircraft should stop flying. That is typically to hold it with increasing gas and nose up attitude until cutting off the throttle so that the airflow and lift is very suddenly well below that what is needed to fly.
