Reduced Flap setting in Gusty x-Wind Conditions

[jumbojohn]

I thought that I know why we landed with less than full flap in gusty x-wind conditions, then I read this months "Air Brained" in Pilot Magazine and now I'm not so sure? Any offers?

[essouira]

I don't have the article but I'm fascinated ! can you give us a brief idea of what it said ?

[bookworm]

An approach in turbulent air with a gusty crosswind may make the use of partial flaps preferable. The reasons for this are than with less than full flap the aircraft will require less of a change of pitch to establish the correct landing attitude.

I agree with the assertion that partial flaps can be preferable, but I don't think that's a good reason. I'm not even sure that it's true -- it looks to me as if in general it requires a smaller change in AOA to provide the same change in speed with full flap. It's all very well claiming, as it does elsewhere in the answer, that the touchdown should be made in a "level flight attitude", but if you touchdown while still at flying speed, it's going to get interesting in many aircraft.

My understanding was always that some aircraft had better aileron authority with only partial flap.

[Kermit 180]

Pitching the nose up requires greater elevator control input with flaps deployed, compare flaring with and without flap and see the differences for yourself.

I thought the reason for deploying partial flap as opposed to full flap was for stability, especially on a high wing aircraft where the full wing surface is exposed to the relative airflow (from the front and side in the case of a crosswind). With full flap the majority of the lift envelope is around the mid area of the wing, making the aircraft less stable than it would be if the envelope was evenly spread across the whole wing plan. I do not agree entirely with this concept for low wing aircraft, where the wing on the downwind side is sheltered by the fuselage. Also using less than full flap will aid penetration through gusting winds and wind shear by using a higher approach speed. Also I would not endorse landing flat. I have never had any problem with landing any aircraft in a crosswind with the nose wheel clear off the ground or tail down in a three point attitude.

Kermie

[FormationFlyer]

Hi folks,

Interesting this...

I use full flap for the most part...however...if conditions get *extreme* I will use a flapless approach and use a higher airspeed.

Why? Because higher airspeed means more control. In gusty conditions you add half the gust factor anyway...

As for ' if you touchdown while still at flying speed, it's going to get interesting in many aircraft. '.

Whats the reasoning behind this statement?

If you insist on stalling it in the flare YOU ARE ASKING FOR AN ACCIDENT. Why? Because you have nothing left to control the aircraft with - all the controls are fairly ineffective, use of aileron could lead to tip stall and digging a tip in. In X/Wind & Gusty conditions you dont want to hold a flare off....you want the wheels on the ground fairly pronto to give you better directional control (nosewheel a/c at least).

I will also add that the crab & kick straight technique is also a good way to cause undercarriage stresses during cross-winds - especially more extreme crosswinds...Personally I use a combination technique - thus landing wings level with no additional control movements to make when the controls are at their most ineffective.

Hope this helps,
FF

[bookworm]

As for ' if you touchdown while still at flying speed, it's going to get interesting in many aircraft. '.

FF asked Whats the reasoning behind this statement? If you insist on stalling it in the flare YOU ARE ASKING FOR AN ACCIDENT.

A good point FF, and I wasn't suggesting stalling it in the flare. But the assertion that you should touch down in "level flight attitude" in the original text doesn't make a lot of sense. Level flight at what speed? If, as I suspect, it is proposing touching down on all three wheels at the same time, then that attitude may not correspond to a speed that is conducive to staying down.

Kermit 180

An interesting point about stability but wouldn't it work the other way round? On a high wing, the lateral stability comes from the interference of the airflow with the fuselage when the aircraft slips. If the lift is coming predominantly from close to the fuselage, the effect would be more pronounced rather than less. The reverse would be the case on a low wing.

[Numptoid]

A reduced flap setting is appropriate for crosswind or 'gusty' conditions for the following reasons:

1. Ensuring adequate control over the aircraft, sure. And a positive touchdown on a sensible part of the runway (ie, not at the other threshold) is appropriate. Techniques for tricycle / tailwheel / monowheel differ - always refer to FM/POH for guidance.

2. Stability. The lateral stability of the aircraft is REDUCED with flaps lowered due to the change in spanwise lift distribution (more lift near the CG) - hence less or no flap is a consideration.

3. The stalling angle of attack (critical angle) generally decreases for conventional (subsonic) aerofoils as flap is lowered (although coef. lift increases). Thus you have reduced protection from the dreaded 'vertical gust.'

It is important to appreciate that a crosswind and 'gusts' (or windshear) are separate issues although often occur together to make life interesting. When using reduced or no flap it is important that we can still comply with FM/POH data for LDR. This may not be possible if excessive increments to Vref/Vat are applied indiscriminately 'for mother.'

Hope this helps.

[FormationFlyer]

Bookworm.

Indeed. I personally discourage a 'level flight attitude' (or 3 point nosewheel landing)!. When I say wings level I mean precisely that...touch down on two main wheels at the same time. I naturally assumed everyone would protect the nosewheel and would therefore be in the 'normal' landing attitude - (sorry if I confused anyone) - as opposed to a wing down one wheel first landing which must be used when the airplane is no longer capable of slipping enough wings level to maintain straight flight down the centreline.

Oh and a word on wing down technique...it doesnt encessarily mean the wing is 'down'. As I just said unless the X-Wind becomes extreme the a/c actually remains wings level - even though you have aileron applied.

This has been a *really* interesting thread. Cheers folks!

Hope this helps,
FF

[bookworm]

Numptoid

3. The stalling angle of attack (critical angle) generally decreases for conventional (subsonic) aerofoils as flap is lowered (although coef. lift increases). Thus you have reduced protection from the dreaded 'vertical gust.'

Not sure I follow this. At a particular lift coefficient, what would seem to matter is the difference between the AOA required in that configuration and the stalling AOA. From the plots I've found in Abbott and von Doenhoff, it looks as if there's slightly more margin with flap than without. Certainly the stalling AOA decreases, but the AOA for approach speed is lower still.

FF

Oh and a word on wing down technique...it doesnt encessarily mean the wing is 'down'. As I just said unless the X-Wind becomes extreme the a/c actually remains wings level - even though you have aileron applied.

Now you are confusing me. :) How can you have aileron (and presumably opposite rudder to stop it turning) applied with the wings level?

[Cardinal]

Something that can be taken from the airline world is the possibility of a tail strike. Without flaps the nose will be higher to generate the same lift coefficient. Obviously a normal approach in most trainers doesnt create a problem in this regard, but if it's botched it gets interesting. The wind was howling yesterday, and I recommended a no flap landing to my student. Used to teaching landings with a normal flap setting, when my student flared a little high I didn't react because I'd "rode out" arrivals like this one before. The airplane came down hard on the mains and whacked the taliskid hard as well. I didn't make the connection, so we went up and tried it again, with the same loud result. I know, stupid move on my part, but something to consider.

[Ivan Ivanovich]

Another reason we use less flap for a gusty approach is for the reduced drag. Should a drop in wind occur the aircraft will lose lift. Power will be required to limit the sink. If max flap - and therefore max drag - is used then it will take longer for the aircraft to respond and recover. Just what you don't want on short finals.

[STATLER]

Alot of people seem to advocate the reduced flap settings in gusty conditions but i am not convinced.

1)correct me if i am wrong but arn't the landing performance graphs in the pilots operating hand book devised on the whole using full flap.

2) what if the strip is field length limiting for the aircraft type,to get in you must use full flap.

[FormationFlyer]

Statler: 1. Yes. 2. your call.

You must remember that there are many circumstances where it is not wise to make an approach. For instance a *short* but soft ground strip - two opposing techinques are required, the short field app and the soft field app - the two cannot really be combined and therefore if you find yourself field length limited in this situation then you gotta make the call...but avoiding the situation would be a good move.

If you go into a short strip you use a short field technique...this technique involves you coming in on the approach with LESS margin above the stall. A severe gust could *stall* your aircraft. Not good. Therefore you then apply margins (0.5*gust) - remember that this increase in airspeed is also NOT covered in the performance charts - therefore you must allow suitable factors. I think somewhere there is a pink AIC that details sensible ones - something like a 10% increase in speed requires a 10% (or is 20%?) increase in landing distance. However, by doing so you may find yourself without enough runway - so just dont go. There is *no* situation that requires a planned landing at a runway that is too short.

So...golden rule is take ALL conditions into account. If you insist in perform a short field landing to get into your short runway in gusty conditions you could well be endangering your aircraft, your life and the lives of others near your approach path...not worth the risk.

Hope this helps,
FF

[Tinstaafl]

Related topic here (http://www.pprune.org/forums/showthread.php?threadid=45065)

[bluskis]

Tinstaafl I followed your link.

Beardy had an explanation which confirms my findings that an approach in gusty conditions is much more comfortable with reduced or no flap.

My thinking was that the effect of a gust was unlikely to be equal on both wings, hence the unequal increase in lift is more pronounced, causing a stronger roll, with flap than without.

The caution against making a flapless approach into too shorter a strip is of paramount importance.

[Turbine]

Decreased flap is only ever required when the crosswind (or any wind for that matter!) is accompanied by an associated turbulence for the following three main reasons.

1. The maximum load factor for most aircraft decreases with flap…

For example, a PA38 has a maximum load factor that decreases from 4.4 to 2.0g with the application of full flap. If you are on a turbulent approach, regardless of the crosswind component, common sense suggests that you should fly the aircraft in a configuration in a way that allows the maximum load to be safely applied upon it.

Prolonged strong gusts on the aircraft with full flap can possibly cause structural damage – even if that damage is only contained entirely to the flap system itself.

2. Reduced Angle of Attack

The reduced AoA with reduced flap in anticipation of a relative gust of wind from under the wing causing a stall is certainly a consideration, albeit not a major one. The main consideration once again is a preventative measure against overstressing the aircraft. (Increased AoA as a consequence of change in RAF = Increased Load Factor… and when flap is down on the aircraft, it will tolerate a lesser LF).

3. Increased Controllability

Additional speed on the approach is simply to assist with the control of the aeroplane in turbulence. With reduced flap the approach speed is normally increased as a product of 1.3V(new)s.

You could perhaps argue that by coming in faster you are subjecting yourself to the crosswind for a longer period of time? The advantages far outweigh this disadvantage assuming the correct technique is applied.


Note that the deceased flap is only ever a possible consideration in turbulence. A strong calm wind in itself is absolutely no justification for reduced flap unless it’s a general consideration (i.e. collision, damage, rough strip, flap failure etc…)

As for stalling onto the runway in a crosswind! You’re altering the flying characteristics of the aeroplane fairly dramatically in awkward conditions and will result in a degree of uncontrollability. If you do this out of ground affect it can make for a very unpleasant ‘arrival’ indeed.

I worked at one school that stated flap was always required, and when available, on a landing “to ensure high drag and high RoD in the flare so as to minimise the effect of the crosswind”. I always debated this philosophy since I was a firm believer of applying a technique that fit the conditions – and using the Ops manual as an eduacted guide.

The above technique suggests that by coming in fast you subject yourself to the crosswind for a longer period of time – NOT that this is a problem for most aircraft, BUT will one-day cause concern if you use the technique indiscriminately.

I know of one situation in Central Australia where a company actually had an STC approved for the operation of an aircraft into a gravel strip without flap even though the POH implicitly implied that under the circumstances it wasn’t permitted. After much red tape, revised TOLD, laising with the manufacturer and flight testing it was approved.


There was a recent article written on crosswind technique in an Aussie Aviation mag as well, jumbojohn. The author is a newly christened Commercial Pilot and I personally think that she doesn’t have the instructional skill, technical knowledge, commercial exposure or experience to write on any operational subject with any authority.

The author was writing about a well-known and very well regarded Sydney flying school and their teaching techniques. I don’t think she came close to articulating the Instructor’s message. Although the article was in the interest of safety I would argue that it could have quite possibly had the opposite effect. This mag has some serious issues to address if they want a serious readership and need to revaluate their expertise and maybe even their duty of care before they continue with such widely read dribble.


Fly in compliance with your Flight Manual, Approved Pilot’s Operating Handbook (POH) or company SOPs (or Part B). Don’t apply a technique that hasn’t been tried, tested and approved by an approved mechanism.

[Send Clowns]

If you put flap down then stability with respect to a crosswind gust is reduced for one additional reason not yet mentioned. A gust from an angle to one side will lift one wing because it will hit the whole of that wing, but the other wing will be shielded by the fuselage an only encounter the gust at the tip section. If flap is used it increases the lift on the inboard section of te wing only. Therefore the imbalance in lift will be greater, as this is the area not producing additional lift on the down-going wing.

Turbine is correct in that in a steady crossswind full flap is a better technique, for thereason he gave. The critical period is the time between kicking off drift and touching down. At this time you will start to drift sideways, so you want to minimise the time spent in this condition.

[slim_slag]

The critical period is the time between kicking off drift and touching down. At this time you will start to drift sideways, so you want to minimise the time spent in this condition.

Isn't this avoided by side slipping instead of crabbing?

[Turbine]

To those that made mention of it (including the author of the article I mentioned above :mad: )…

If you establish yourself nice and early on in the approach in the slipped condition, then you won’t have to worry with applying any crosswind technique on the landing. Can’t say that I entirely agree.

First. Why on Earth would you sideslip the aircraft on the approach and then ‘into’ the flare rather than instead crabbing the aircraft and applying the proper crosswind condition?

Crabbing minimises the drag on the aircraft on the approach. What happens if you get an engine failure and find yourself with the controls all crossed up? What happens, given the turbulent and gusty conditions, if you require additional power but you are already using extra thrust to compensate for the additional drag of a slip? Applying crossed controls to the aircraft in turbulent conditions can also apply a significant stress on the aircraft since it essentially twists the aircraft like a tin can. Light aircraft should be flown (and landed) in a way that minimises the stress on the aircraft.

Some aircraft, like most of the Cessna series, don’t like prolonged slips as well. If you set yourself up in a slip on a 172 on very early final you could well starve the engine of fuel in a slipped condition!


Many believe that if they slip down the approach then you won’t have to apply a crosswind technique. This is incorrect. As you flare and the speed of the aircraft decreases, the aircraft will drift (and yaw) with wind as the amount of control you applied becomes less than what is required to keep straight.

The only advantage of slipping is you don’t have to think about what aileron and what rudder is required. This concern can be entirely eliminated with proper and competent instruction. It’s hardly an ‘advantage’.


Aileron arrests unwanted drift and rudder keeps the aircraft straight. Simple.

[slim_slag]

Turbine

First. Why on Earth would you sideslip the aircraft on the approach and then ‘into’ the flare rather than instead crabbing the aircraft and applying the proper crosswind condition?

We were not taking about the approach, but seeing as you asked.....
I would crab down final and start slipping on short final. Better for the passengers and better technique. I believe in teaching students to slip all the way, so they get to see the effects of aileron and rudder.

What happens if you get an engine failure and find yourself with the controls all crossed up?
Best glide, landing spot, memorised checklist. Controls would be 'uncrossed' rather early in that process, probably automatically.

What happens, given the turbulent and gusty conditions, if you require additional power but you are already using extra thrust to compensate for the additional drag of a slip?

I have plenty of extra power available in the pattern. I don't get that far from the runway, usually I am power idle from abeam the numbers. You may do differently of course, and standard teaching is to power the plane in. Even if you go power to 1800 abeam the numbers and keep that all the way - not that I would - you still have plenty of power. Besides, it takes zero time to go from uncoordinated flight to coordinated flight, it's not an issue.

Even so, it doesn't matter, you are on the same glideslope whether crabbing or slipping, and in both cases if your engine quits you will either land on the runway or not.

Applying crossed controls to the aircraft in turbulent conditions can also apply a significant stress on the aircraft since it essentially twists the aircraft like a tin can. Light aircraft should be flown (and landed) in a way that minimises the stress on the aircraft.

Airframes are incredibly overengineered and certified to handle stresses far higher than you will encounter in a side slip.

I agree with landing stresses being minimised, the gear should be looked after especially well, that's the weakest point.

Some aircraft, like most of the Cessna series, don’t like prolonged slips as well. If you set yourself up in a slip on a 172 on very early final you could well starve the engine of fuel in a slipped condition!.

If you arrive at your destination with that little fuel you are negligent. Probably an old wives tail anyway, and I said you should crab on early final. Slipping is for landing.

Many believe that if they slip down the approach then you won’t have to apply a crosswind technique. This is incorrect.

The slip is the crosswind technique.

As you flare and the speed of the aircraft decreases, the aircraft will drift (and yaw) with wind as the amount of control you applied becomes less than what is required to keep straight.

Indeed, you dynamically change your control input according to the conditions, its called flying. In practice, by rollout, you will have full aileron control input towards the wind - well you know what I mean :D

The only advantage of slipping is you don’t have to think about what aileron and what rudder is required.

Do you mean "The only disadvantage of slipping is you have to think about what aileron and what rudder is required." ????

This concern can be entirely eliminated with proper and competent instruction.

Yep.


Aileron arrests unwanted drift and rudder keeps the aircraft straight. Simple.

Indeed it is. That's why it's the proper configuration to be in during the flare. You gotta think about your landing gear, they tend to collapse if you apply nasty side forces to them, or more likely your tyres might just part company. You don't need either. If the tyres stay attached, they are going to be pushing you off the runway towards the upwind side, which is also the direction you are pointing, and you are at risk of ending up in the dirt. It's a very very bad idea to crab when landing, crosswind or not.

Gusts just need a bit more aquired skill. More fun too!!!

Anyway, to the thread, nothing wrong with using less flap when its gusty. The reasons you gave seem sound, and it seems to work better in practice too I'd say.

[slim_slag]

FormationFlyer

Oh and a word on wing down technique...it doesnt encessarily mean the wing is 'down'. As I just said unless the X-Wind becomes extreme the a/c actually remains wings level - even though you have aileron applied.

What you are describing is a 'boat turn', keeping the wings level and using rudder to 'turn' the plane. This will work for a bit, but eventually the relative wind from the side will turn the plane and you will end up in a sort of crab. If you don't get it right you will stress the gear. It doesn't matter if the crosswind is strong or not, you should always apply the same principles to landing. It's far far far better to land on the upwind wheel with wing down.

The only planes this doesn't work with are jets with engines strapped under their wings. They have to land using a rudder/aileron technique with wings level, but it's a last second maneuver and not needed for GA planes.

cheers

[Turbine]

If you arrive at your destination with that little fuel you are negligent. Probably an old wives tail anyway, and I said you should crab on early final. Slipping is for landing.

The majority of Cessna flight manuals prohibit the slip for in excess of 30 seconds due to the likelihood of starving the engine of fuel. No wives tale. It is possible regardless of the quantity.

I think you may have possibly misunderstood me in reference to the slip v's crab...

The slip technique is a good instructional technique but shouldn't be used as a rule in the course of general flying for the reasons I mentioned.

Something I stupidly failed to mention above was that a slip in turbulence imposes a significant rolling 'g' on the wing... another excellent reason never to slip in turbulent conditions - (on topic now) especially with flap. Simply put, when slipping it takes a lesser force to overstress the aircraft in conditions where continous forces are imposed!

When doing Engineering, our first lesson was to apply a design that would cater for the improper handling of the pilot rather than conditions. Do you really think that the twisting moment applied to an aircraft (in a slip) over the course of a few thousand hours is a good thing? Aircraft are certainly over-engineered but that's to cater for pilots who fly an aeroplane in a manner akin to what you're endorsing.

...it takes zero time to go from uncoordinated flight to coordinated flight, it's not an issue.

Once you uncross controls, say from short final after an engine failure or in the missed approach from ground effect, you continue to develop drag in the process of and then post the action for a few seconds afterwards depending on the design of the aerofoils - and thus my further reasoning for crabbing. It will rob you rob you of excess thrust and it will rob you of controllability.


The only planes this doesn't work with are jets with engines strapped under their wings. They have to land using a rudder/aileron technique with wings level, but it's a last second manoeuvre and not needed for GA planes.

The technique for heavy jets involves holding a crab and then simply kicking it straight. The undercarriage is engineered for this abuse. The aircraft is so heavy and has so much forward inertia that the effect of wind can be considered negligible. This technique does not work on light aircraft in anything more than a knot or two of wind due to their light weight.

This technique is a product of company policy. Many airlines still use the slip on the landing but will never ever use it on the approach. I have a Boeing recommendation here - will post a URL shortly for those interested.

[slim_slag]

Turbine

Sorry if I misunderstood. You appear to imply that side-slipping to landing is a big no-no in a crosswind, bumpy or not.

I don't think slipping an airplane is misflying it, and I will buy you beer all night if you can find me a trainer which has been slipped 'over the course of a few thousand hours'. How long am I advocating you sideslip on an approach? 30 seconds max perhaps? That's a lot of approaches. The wing spars would be knacked well before you get to your thousands of hours in the slip.

I think landing using a technique which applies a significant side force on the wheels is bad practice and will cause a lot more damage/death/injuries than engine failures on short final. I am only advocating slipping on short final and in the flare - if there is a cross wind. It is the only way to land a plane in a crosswind.

I think it's useful to teach slipping all the way down because primary students rarely get to see many crosswinds, and it's educational for them to see how it all works. They are only on final for a minute or so, so not long, maybe they see 20 minutes of crosswinds in their whole training.

Sure, don't put flaps in when it's bumpy, I have no problem with that. I think you provide excellent theoretical reasons why it is bad. Practical experience will agree with you.

Many airlines still use the slip on the landing but will never ever use it on the approach.

So they agree with me then. Slipping all the way down pisses off the customers, not good with swept wings, and turbines don't like it - so I have been told. Not all jets have problems with low slung engines, only some. Those new 737 motors seem to be almost on the floor when they are at the gate! Most jets will side slip on short final and land on one wheel in a strong cross wind - because it's the correct thing to do!! The ones with clearance issues will crab and land as you suggest with side forces that have been engineered for. It's a neccessary evil but better than leaving an engine in the tarmac. Please note I am not a jet pilot so this is what my friends who are tell me.

I always have fuel on 'both' in a Cessna. When configured as such, there is no problem with slipping and fuel flow/starvation, and the pilots manual would agree. The only time I have heard about problems with serious slipping in a Cessna and fuel problems is when water in the tank is dislodged. Fluid still gets to the engine, the problem is water doesn't burn.

Cheers

[Turbine]

slim_slag. I won't reply ;)

As for the crosswind landing in a heavy, check out http://www.aviationpics.com/app/app.htm

[jumbojohn]

Hi All,

Just got online for the first time in a while and am very please with all the replies to my question, I thank you all.

Glad it was not a "stupid question"!

[FormationFlyer]

Slim_Slag:

Um...I think we are talking about the same technique arent we? - using a combination technique.

I also teach students to slip earlier in the approach for the same reason - to give the student time - they just arent skilled enough to set it up at 50' on their first attempts - they just never apply enough rudder! However, I myself convert to slip over the threshold (i.e. 30-50') which stabilises the aircraft in good time prior to touchdown.

As for 'boat turn' lost me there. Are you talking about the wings level bit? If so then do see what you mean - if you apply the slip early you do end up juggling it if you hold it too long - as for the students - this juggling provides them with the time to learn how to fly the aircraft with the controls in a different 'neutral' datum.

Maybe I lost the plot somewhere here - if you think Im teaching/explaining something wrong please explain - im always open to advice - I am happy for such a discussion either here or in private e-mail.

Turbine:
Different techniques for different aircraft....yes sideslips have issues but side loadings on light a/c landing gear can be considerable if technique is incorrect.

I prefer to advocate using appropriate technique for the conditions...But as I said above - the control input required is the *same* at the point of touchdown regardless of technique. It has to be - both techniques aim to put the aircraft in the same situation for landing...(unless you get extreme and *need* to land wing down, upwind wheel first).

Now as an instructor I see a LOT of PPLs/Military pilots/CPLs/ATPLs from a wide background with a with varied depth of experience, landing in a wide variety of crosswinds. I have to say 90% of them have problems with crosswind landings - pretty much always trying the crab technique from start to finish - yeah great if you can do it - but different wind conditions/strengths incl gusty/turbulent conditions make this extremely difficult. I personally do not claim to be a whizz at this technique - and Ive seen a few 1000+ hour pilots have problems here as well..

The main problems are (in order of frequency):-

1. Failure to apply enough rudder
2. Failuer to time the kick properly
3. Failure to apply opposite aileron

Night x-wind (with or without gusts) causes all sorts of problems from failing to kick the a/c round to disappearing sideways (both into/outof wind!) across the runway - at night it is incredibly difficult to kick straight milliseconds before touchdown.

The combination technique removes many of these problems and makes 100% of landings *safe* and stressed within the aircraft operating limits (not design limits). It also makes it possible to *fly* the aircraft to the ground (night landing technique). Indeed this also becomes important when using less flap for the landing during a gusty crosswind at night...

Regards,
FF

[Send Clowns]

Slim_Slag

I was not advocating landing sideways, in fact the point I was making was that a short time in the flare does not allow time for significant drift to develop, given aircraft inertia. However at the flare the pilot must remove the crab, to land straight. This will tend to lift the upwind wing, just at the time when it should be dropped a little to compensate for the wind in a sideslip in the flare if the crosswind is strong. Therefore some into-wind aileron is required. This is the technique taught by the best flying school I ever encountered, the joint services Elimentary flying Training, JEFTS. I was taught the full side-slip approach in my PPL but even by the end of that I was being taught it was better to crab for askilled pilot in all crosswind conditions.

Therefore in gusty conditions, at the point of flare, suddenly in ground effect you have to judge the exact rudder to not only keep the wing from lifting but to drop it the right amount. If you get it wrong, you will start to drift. However if you spend very little time in the flare there is no time for drift to develop, and the problem is removed. Hence the second reason for my advocacy of flapless landing in gusty crosswind.

[bookworm]

I think there's a lot more confusion over terminology than anything else. Here's my take on it:

In the wing-down technique, the aircraft is held in a sideslip using upwind aileron and downwind rudder until touchdown. It touches down on the upwind wheel first.

In the crab-and-kick technique, the aircraft remains wings level, and downwind rudder is applied to kick off the crab angle just before touchdown. Upwind aileron needs to be applied to keep the wings level during the flat turn. It touches down wings level.

They appear to be testably different states in which the aircraft touches the runway.

I'd be interested to know

a) what technique Turbine is actually advocating as "applying the proper crosswind condition"?

b) how (if) Formation Flyer manages to fly the wing-down technique with the wings level? (or did I misunderstand)

[slim_slag]

Turbine

I won't reply.

I accept :) Nice pictures, though I am sure some are fake.

Send Clowns & FormationFlyer

I am sure we are all talking about the same thing, i.e. crab down final then change configuration for landing so you do not land sideways.

I think that at the point of landing in a crosswind, the upwind wheel has to touch first and on its own, and the airplane nose has to be pointing down the centreline. How do we get there?

However at the flare the pilot must remove the crab,

I think this is too late and introduces all the complications you describe. Far better to configure for the side slip a few seconds out, so you can line up, start drift correction, and be ready for changes in the relative wind.

The changes in your control input to account for gusts and less effective control surfaces as you slow down, are an acquired skill. You are not going to get the student to learn this straightaway, but when they are mastered, he will be landing in the best possible configuration.

When I say wings level I mean precisely that...touch down on two main wheels at the same time.

With wings level and nose straight down the centreline, you are not "banking into the crosswind", so you must now be moving with the air mass. With a 10 kt 90 degree crosswind component, the air is moving at around 17 feet per second. Not only does this translate to a nasty sideways force on the tyres, but if you stay in the flare one extra second (easy to do if it's gusty) you now have missed the centreline by 17ft. Two seconds 34ft - how wide is a runway??? I am sure you can make corrections, but they will be far bigger and more prone to error than if you are sideslipping and configured to land on the upwind wheel 15 seconds out. Think of those poor tyres :D

Interesting thread! Thanks,

[Send Clowns]

I've only ever once had a problem touching off the crab in the flare (that was an airfield where I experienced windshear on another occasion, and this time I just sank at the flare so did not have time, skipped a little but nothing serious), all it takes is a little practice and solid basic handling skills - rudder/aileron co-ordination. In light crosswind there is then often not time then for any drift to develop. As I said, in more severe crosswind drop the into-wind wing a little to prevent the drift, but unless that is perfectly-executed some drift will develop, so minimise the time in such a state by taking off crab late and touching down soon after.

[slim_slag]

SendClowns

Why do you have two techniques for light or severe crosswind? At what xwind component do you decide to switch? Do you have numbers in your head for all the types you fly? What if it is gusty?

If you have a steady crosswind you should not get drift developing in the sideslip. In your 'crab and kick' (same mechanics as my boat turn) technique, if you get it wrong and you get a gust, then what do you do? You turn aileron into the wind so you stay above the centreline, then you have to add opposite rudder to keep nose pointing ahead. So you sideslip!!! Why not just sideslip from the beginning?

How about this one. All landings should be sideslip landings. If xwind component=zero, sideslip=zero. As xwind component increases, so does your side slip - if xwind is close to zero, then you might not even know you are sideslipping.

If you do it correct, severity of crosswind (if its steady) will not impact on the potential for drift. You can nail a perfect crosswind landing of any strength up to max rudder. In fact the only time you ever want to 'crab and kick' is when the xwind is above max rudder authority, but you need to be good! IMO.

You only have to learn one landing technique which works beautifully for all wind conditions (up to maximum available rudder authority). Life is so much more pleasant when there are fewer things to worry about :)

All in my opinion, of course:D

[Send Clowns]

It isn't really two techniques at all. The dropping of the wing is simply more of the same: as you kick straight you have to keep that wing down. If you are looking out of the aircraft at this point and feeling and seeing how it is flying, rather than flying by numbers then there is no need to change technique. If you see that you are drifting off the centre line either way, drop the wing to pull the aircraft straight. With a little practice there is no need to think about it, just watch the outside world and react to it. However well judged this technique rarely allows any drift to develop at all. This really is just flying the aircraft all the way to the ground, as all instructors teach.

I agree that if a gust blows in I end up sideslipping through the touchdown. But I am only in this inelegant mode of flight during the transition between flying and rollout, not for a protracted period.

In answer to "why not sideslip from the beginning?" - because I was taught the crab technique, and taught by the best instructors in the business running a highly-standardised course (EFT in the RN). No commercial instructors or IRI since have had any criticism of my technique. It is also the technique used on airliners I believe, as their brief flare does not allow drift to develop, and I hope to move on to fly these soon!

However I could equally say to you "why sideslip from the beginning?". There is no need to, and it is an inelegant, unbalanced form of flight with reduced control authority and stability and more chance of a spin if you should misjudge in gusty conditions and stall.

Crosswind does not necessarily impart sideslip after kicking straight. The aircraft has considerable momentum, so this takes time to develop. Judging the point at which you are about to sink out of the flare into the touchdown it is a simple process to straighten the aircraft in most crosswind conditions with no wing low. As I said before I have only had a problem once, and that was on an airfield where I have noticed peculiar drops in the wind.

All in my limited experience and IMHO of course :D

[slim_slag]

Send Clowns

because I was taught the crab technique, and taught by the best instructors in the business running a highly-standardised course (EFT in the RN).

Ha!! We are doing the "my primary instructor was better than yours, huh" :D :D :D

OK. In about 30 minutes I'm off flying in a Pitts with a guy who has > 5000 hours in aero planes. I am thinking he is planning to move all the blood from my right leg to my left arm, via my head, probably incorporating a slip or two to make sure he gets to all my blood :D :D :D . I might also bump into his buddy, who has >10000 hours in same planes.

They also instruct primary students, and are the best instructors I have ever met! So I shall ask them what they think, and report back!

(Actually I already know what they will say, haha)

Slipping is hardly inelegant! It's great fun, no risk of stalling if you keep your angle of attack in mind - no different to coordinated flight really. It's a very useful technique. Skidding is what kills people in the pattern, and people skid because they don't have the balls or ability to bank a plane. They are scared of banks and uncoordinated flight close to the ground, or even up in the air! This is a common feature of these low time guys being pumped out of the 'airline pilot' sausage mill schools. :D but I guess you don't want people who might decide to explore the limits when flying their 737.

[FormationFlyer]

Send clowns - Im with you I think there is only 1 technique - the difference is in when the controls are applied.

Slim_slag - you got me thinking now...I *know* I land wings level, two wheels down together - even though I am using crossed controls...I cant for the life of me all of a sudden think of the explaination to 'precise' control movements...

The briefing (& airbourne) advice is keep the wings level with aileron & on the runway heading with rudder.

....now...Im flying saturday - so Ill get in early and I think Ill go do this (pray for a x-wind!) so I can report back *precisely* what I do do in the last 30-50'.

I will say that when I touch down wings level on two main wheels first there is *no* sideways component...

Im now confused with how this whole thing works again now!!!!!!!

A *very* interesting thread!

FF

[Turbine]

The final leg of a circuit is no different to any other part of the circuit! You simply point the aircraft into wind as required to keep straight. I think it’s really strange that anybody would rather apply continued uncoordinated flight than simply crabbing the aircraft down final...

All the sensible aerodynamic considerations I previously mentioned aside, the slip is simply uncomfortable – and WILL NOT necessarily remove the requirement to apply (or reapply) a different technique during the landing…

What happens when you set the slip up for a 10-knot crosswind from the right at 150 feet and then it turns into a 20-knot crosswind from the left on the runway? It is really sensible to fly a sideslipping approach expecting certain conditions when they actually don’t exist?

slim_slag. A Pitts is a little different to most modern lighties. The Pitts really has to be slipped down final for visibility. It’s an entirely different kind of flying.

bookworm said:

…what technique Turbine is actually advocating as "applying the proper crosswind technique"?

Bookworm, the correct handling technique, as I know it, is a response to the aircraft’s normal behaviour…

1. Crab aircraft down the approach
2. Normal flare and landing
3. Apply rudder to keep the aircraft straight
4. Certainly anticipate the drift in advance, but apply aileron only as necessary to keep the aircraft from drifting
5. Use rudder as necessary (and only if required) to keep the nose straight
6. Touchdown windward wheel first, then ‘other’ main, then nosewheel
7. Aileron progressively into wind as aircraft slows down

(i.e. Aileron to arrest drift and rudder to keep straight).

You will find that every landing is a crosswind approach & landing to a certain extent since you can always expect at least a little wind! The above technique can be applied all the time…


I don’t like the term ’kick the aircraft into wind’. The term kick suggests that it is a violent response to keep the aircraft straight. The amount of rudder required should be applied as necessary.

If you do ‘kick the aircraft straight’, you will find that you can get a noticeable roll ‘out of the wind’ (due to windward wingtip moving faster), which makes the application of effective rudder difficult.

[slim_slag]

What's going on here Turbine. You are starting to agree with me! :)

I was using the Pitts purely because this very high time and very experienced instructor, who teaches to side-slip late on final in a crosswind, was out flying it today and I asked him what he thinks. It was meant to be a harmless and gentle rib on Send Clowns who said he went to the finest school, when there are plenty of 'finest schools' in the world. You are right, forward visibility is not too good.

FF

I will say that when I touch down wings level on two main wheels first there is *no* sideways component...

If you are in a crosswind, I bet you there is, but it may not be noticeable if it is slight.

[Turbine]

slag,

What's going on here Turbine. You are starting to agree with me!
Could it be possible that we were agreeing all along? :confused:

[Send Clowns]

Slim_Slag

My point was more the extreme standardisation of military EFT, as well as its excellent reputation (undeniable). Central Flying School ensures that all instructors teach exactly the same techniques, and teach in the same way (down to the same colours on the whiteboards for the same items in the briefing!). Therefore what I was taught is the same taught to all military pilots (and it wasn't my primary instruction - I had an FAA PPL long before that, taught wing down at first, then was taught to crab by my PPL instructor).

Agree that the slip is useful - for adjusting a glide, for some taildraggers etc., and that you can avoid the stall. It is hardly elegant though - unless flying aerobatics the aircraft should be balanced! And people do stall on approach, mostly in gusty conditions, and this can be disasterous in a serious sideslip. In co-ordinated flight it is merely embarrassing, or at worst damaging to the undercarriage.

I am happy to slip an aircraft in, and perfectly capable of doing so safely. However if I want to fly a "textbook" circuit in a tricycle-geared aircraft (no taildragger time, so cannot comment on Pitts) with which I am familiar I will crab even into the flare, until the aircraft tells me it wants to settle. Then I use co-ordinated rudder and aileron to fly it straight, exactly as Turbine describes.

In reply to your reply to FF I will refer you back to my comments that if the timing is judged correctly there is no time for drift to develop!

[slim_slag]

Send Clowns,

I am confident you have had some of the best training out there, but there are other good places too who teach differently. At the end of the day it's aerodynamics which count. I think we all agree you should crab down final, but given two competing practices at roundout/flare (crab and kick vs sideslip), one has to be 'better'. I think we tend to agree(ish), and as they say 'any landing you walk away from is a good one'.

In reply to your reply to FF I will refer you back to my comments that if the timing is judged correctly there is no time for drift to develop!

And I will still be happy to bet on the fact that there is a sideways force on the tyres in a 'crab and kick' crosswind landing. As the point of betting is making more money than you lose, I think I would quickly be well in the money, especially if crosswinds are gusty.

Now I'm not saying that in a gusty crosswind you will always do a perfect no sideforce landing if you slip it in. But - if you were to bet on the 'crab and kicker', and I was to bet on the 'side-slipper', and we put strain-gauges on the gear, it wouldn't take long for me to have all your money in my sweaty palms. Yep, I'd put money on that.

regards

[Send Clowns]

I disagree. I rarely have any discernable drift, because as stated I look out of the aircraft, and fly it for a straight landing through to touchdown (however I crab but do not kick, for the reason Turbine said - then this technique would not work). If this requires that one wheel touch first, then so be it. However I do not set out with that intention, and do not see in any way why I should do so, or why to do so would help.

In the gusty winds you are suggesing you cannot put on perfect slip, so you are as likely as I to land with some side load. More so if you really are as prescriptive about your final approach as you seem to be here, which I doubt. Look outside and fly straight : a technique I personally honed on hovering helicopters, but one that most experienced pilots develop. Being prescriptive about the required movements will not get consistent good landings.

[slim_slag]

Send Clowns, let's call it a day! Good luck.

[Send Clowns]

Safe landings :D

[slim_slag]

:D :D :D