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Slips

“A crab to crosswind landing is a co- ordinated approach and does not involve any use of cross controls unless you include the use of the pedals to straighten the aircraft and into wind aileron during flare.”
I have crabbed a Pa28, by choice, but doubt I could safely do it in a lighter Jodel tailwheel.

Maoraigh
EGPE, United Kingdom

The distinction crab vs slip in crosswinds is so entangled that any skilled pilot would swap from one vs other and mix the two without even noticing: if wind is smooth 15kts crab works better, if it’s 15kts gust factor slips worked better, if you are landing in 30G40 you need both

Just like power for speed vs power for height, it helps someone learning to land during PPL or first ILS training but it gets out out of fashion when someone start flying in windy days…

Last Edited by Ibra at 27 Sep 21:08
Paris/Essex, France/UK, United Kingdom

I confess I’ve never, ever done a crab to touchdown. I just don’t see the point. Everyone bangs on about stabilised approaches, and here you’re intentionally doing something that requires massive split-second correction at the last moment. Necessary if you’re flying a 747 but I don’t see the point in anything that doesn’t have engines under the wings. I guess the exception would be if you absolutely HAVE to do a crosswind landing beyond what a slip-to-land can handle.

LFMD, France

Yes crab to touchdown during flare should never happen: near ground effect the wind will always decay and rudder becomes effective at slow speeds, it’s hard to run out of rudder authority on the ground during flare, on high wings you have enough wing clearance to bank it while in low wings they are hidden in slow wind inside boundary layer

However, above 100ft agl one may not be able to maintain runway heading with slip and rudder only but it takes plus 25kts to get there…

Max demonstrated wind is 0.2*VS while approach is 1.3*VS is barely 9deg crab, something that can get fully absorbed by sideslip in any certified aircraft (we can talk about lack of rudder authority if one gets near 25 crab which usually means flying more than max demonstrated wind which means gusty and some sideslip is “obligatoire”)

The old Archer Century autopilot used to disconnect at 20deg max WCA or crab angle on VLOC on windy days before I jump to show him how it should be done on ILS with some rudder

Last Edited by Ibra at 27 Sep 21:40
Paris/Essex, France/UK, United Kingdom

johnh wrote:

I was thinking about the “danger” of slip entry. I guess that if you’re already slow, and you do the entry rudder first, then aileron, you COULD set up an incipient spin

Has this ever happened for real? I have never heard about such a thing actually occurring. Stalling and “spinning” in a turn due to way to little speed, yes, but spinning due to a side-slip? never. A side slip is done to get rid off excess energy. Stalling and “spinning” is a result of too little energy.

The elephant is the circulation
ENVA ENOP ENMO, Norway

Has this ever happened for real? I have never heard about such a thing actually occurring.

Me neither. I was just hypothesising about why someone might consider a direct entry to a forward slip to be dangerous. This was the best I could do.

LFMD, France

Asymmetric flying at higher speeds is very benign, it’s happens in MEP all day along, the speed at which one lose control in C172 at max rudder deflection when countered with ailerons on straight & level power off is about VS+1kts on full power climb it’s probably about VS+2kts, maybe more or less depending on flaps, I would not blame that on the slip side of the story, it’s just the old wisdom of “speed is king”

It could happen at higher speeds in SEP with asymmetric flaps at slow speeds but someone has already invented a rule “no flaps in turns”

Last Edited by Ibra at 28 Sep 07:35
Paris/Essex, France/UK, United Kingdom

@Ibra, if I am reading your last post correctly, I couldn’t disagree with you more. The crab is a co-ordinated approach in crosswind landing.
The slip is unco-ordinated and usually used to reduce height or speed.
The “slip?” used for a crosswind landing is unco-ordinated as it maintains the aircraft in line with the centre line using rudder whilst avoiding turning during the descent with into wind aileron and therefore involves touch down on the wheel (usually one wheel on light GA aircraft). On certain aircraft too much into wind aileron due to too strong a crosswind has on many occasions caused the tip of the into wind wing to touch runway markers or lights with a loss of control of the aircraft. This type of incident is of course less likely with high wing aircraft than with lower wing aircraft.
The crab technique takes advantage of the fact that an aircraft turns its nose into wind, naturally during flight. When we fly anywhere we take account of any crosswind and adjust our heading accordingly, don’t we?
It is the same with a crosswind landing using crab technique. Let’s say you have a 40knt crosswind 90° from the left of the runway centre line. And for arguments sake you have calculated your approach speed including Ve at 60kts which gives a Fb of 1. Therefore you need to take a heading of QFU plus 40 on the approach. Wings are level ball is in the centre. The nose is kept on the centre line using power or in a glider speed control. As you descend the wind generally becomes less and will back due to friction of the wind over the ground. You gradually reduce the heading gap to account for this and the nose makes less of an angle with the axis of the runway. As you flare at your normal flaring height you simultaneously kick the aircraft straight with rudder and apply into wind aileron to avoid the wind pushing the wing up and over, you touch down on both wheels along the centre line so you don’t put any strain on the landing gear. Once travelling on the runway you may need small movements on the pedals and a little more into wing aileron as the aircraft slows.
For those that were never taught the crab technique, it is much easier and more instinctive than it sounds and I learnt this technique when I started flying including in Jodels, Robins, Wassmer Baladou, PA 28, Cessna 150 and I still use it in preference to a sideslip in the DA40 and DA42.
But hey each of us have learnt different techniques, and for those of us who have carried out many crosswind landings or needed to lose height and speed quickly for a short field landing without power we have by now decided on our preferred technique.
One thing I would say, is IMO if you have power it is usually better to use it and make a go around rather than continue to make a good landing from a bad approach.

France

I think there is no free lunch either you risk touching with wing tip in slip or risk of runway excursion in crab, you pick whatever you wish or mix for the landing flare, in theory, bellow max demonstrated cross wind both should work, even no technique works: you may not even apply any correction and the aircraft should cope as per certification testing, but above max demonstrated wind, you need the right mix for the day conditions & type geometry

If it’s unstable you go-around but again it won’t solve the limitations of one technique vs the other, I personally, don’t know which one I use, so I have zero preference

Taxi on the ground in windy days has to be on cross-control, so no escape from slipping sooner or later, some aircraft tolerate taxi in neutral up to 40kts, some aircraft ground loop in neutral at 5kts wind

Last Edited by Ibra at 28 Sep 07:47
Paris/Essex, France/UK, United Kingdom

@Ibra I still don’t understand why you feel you risk a runway excursion. When you decrab just before the wheels touch, you are straight along the runway as in a normal landing.
Max demonstrated is just that. The highest crosswind that occurred during testing. It does not mean that an aircraft cannot be landed safely above this crosswind. Although some insurance companies might use this as an excuse to decline a claim should damage occur.
For me all crosswind landings require some degree of thought depending on the aircraft you are flying and your approach speed.

France
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