Retracting Flaps On Touchdown
 

I've been currently watching some of the documentaries on the Discovery channels about Flying in Alaska.

One of the new pilots was been given a check ride and the guy in the right hand seat, not sure if he was an instructor, insisted that the pilot immediately retract the flaps on touchdown. There was no reason given for doing this.

As a UK instructor, having taught at some of the biggest schools, I've never heard of this; never taught or been taught to do this. For a start, full flap will provide aerodynamic braking and reduce the landing distance, messing with flap is fraught with danger as it could be mistaken for something else like the gear, fully retracting the flaps on touchdown provides no flap for the go around scenerio and it's also not in the POH.

Although the pilots are landing off airports e.g. On any 600m space of land, rubble, streams, dirt track, dusty road, apart from not wanting to damage flap by loose debris, I can't see any benefit from retracting the flaps immediately on touchdown.

Has anyone experience of this or know of a logical explanation ???

I have heard of it before. The supposed benefit is less lift, therefore more weight on wheels, therefore more effective wheel braking.

Any discussions I've heard on the subject have always ended with the negatives (which you've listed) outweighing the positives quite comprehensively. However, I didn't see the program, and I have no experience of off-airport operations or whether that might be a factor in this particular case. Thinking through the situation, I wonder if less lift gives less chance of being launched back up into the air when hitting a bump... but then in a good landing this shouldn't be possible anyway, so I'm not doing a good job of convincing myself.

FFF
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Thanks FFF. I did consider your suggestion but then discounted it on the grounds that full flap provides more drag than lift ???

True (for most types), if you're talking about retracting only the last stage of flap, as you would on the initial actions in a go-around scenario (once again, for most types... there will be someone who will point out the exception if I don't qualify it).

But I think the idea here is that you retract all the flap after landing, including the first 20 degrees or so, which (on most types) will give you lots of lift.

FFF
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Article in AOPA Flight Training a while back about this very subject:

Flight Training: Short Field Approaches and Landing

A quick check of the C152, C172, PA28 and Cirrus POH shows that this is recommended procedure for Short Field Landings [see section 4, Normal Procedures].

Well it's in the syllabus....and the skills test. Where did you say you taught? :confused:

PPL Syllabus: Exercise 13.9

PERFORMANCE (MINIMUM LANDING DISTANCE) APPLICATION

See Standards Document 10 (A) Appendix 4 for the exercise number...

http://www.caa.co.uk/docs/175/Sectio...R-FCL%201_.pdf

See Appendix 2 to JAR-FCL 1.135 and FCL684: Contents of the Skill Test for the issue of a PPL (A), section 4b. See also Standards Document 19 (A).

ifitaint...

Edited to add Cessna 152 and Cirrus aircraft....

Well you learn something new every day.....such is aviation.

......I'll have to check the POH again, but if its only a recommended procedure then its hardly critical to start faffing with flaps during the landing roll.

I'd be interested to know the difference in landing distance between the two techniques??

It was also never part of my standardisation or even in the company training manual to teach flap retraction on touchdown. Personally, I think there is more benefit of drag flap during the landing roll out unless it drastically reduces your landing distance.

We were trained to do it in the case of short field landings for the reason mentioned above, that it provides greater brake effectiveness (as well as full aft elevator) - but only on the single engine, fixed gear fleet, not the multi-engine, retractable gear fleet.

I was taught (both in Europe and US) to slam the flaps up after T/D to reduce landing distance. Then we had a solo student accidently raising gear instead of flaps during roll-out, combined with back pressure on the yoke the squat switch did not prevent the gear from coming up :hmm: Did the school learn a lesson? I don't know, they introduced a new challenge "confirm flaps" from student, to be responded "affirm" from instructor before allowed to raise the flaps. All this still taking place during landing roll-out... Do I like the whole thing with raising flaps, NO! Does it make a difference? IMO, Yes... especielly on the BE76 its very easy to lock the wheels if braking too hard. If you get the flaps up, you can stamp them through the floor and braking is very efficient. On the other hand, I don't know any normal airfield where it would ever be necessary to do so. If you are just on speed, on spot you should be able to stop with plenty of room.

What I really don't like is that some students develope a habit of always raising the flaps during rollout after ANY landing. Training is just as much about habits as it is about skill, so if it wasn't for our SOP I wouldn't teach raising the flaps while still at high speed during landing phase.

I am pleased to see it is written in the syllabus!!

Raising the flaps on touchdown gives you more weight on wheels. This is very useful for max braking or during a max or gusty xwind, Where you want the aircraft to remain on the ground and stay there. (Never attempt or instigate a t/o without sufficient flap for the aircraft to fly, in the distance available)

I have seen Ag pilots use this technique in xwinds and/or on extremely narrow strips.

It has the same effect, without the braking effect of raising the spoilers/air-brakes on larger, higher performance aircraft on touch down.

In my view this should only be attempted where the aircraft is fitted with manual flaps. I.E., a flap lever.

A perfectly acceptable and very effective technique in fixed gear singles operated from real world short strips, and is particularly important in Cessna's. As was mentioned in an earlier post bringing the flaps up significantly reduces lift and thus transfers the weight to the wheels which greatly aids braking and steering. If you don't believe me land your Cessna with flaps 40 and then immediately get on the brakes, the wheels will immediately lock up and start skidding, however if the flaps are raised very heavy braking can be used without skidding the tyres. I do not think it is unreasonable to ask the pilot to manipulate the flap switch during roll out in fixed gear aircraft. It is a different story with retractables, however. For those aircraft I teach that the flaps are not touched until the aircraft is clear of the runway.

Currently on a UK FI course and can confirm the following:

For inexperienced "Bloggs" the emphasis is to fly the landing attitude, carry out appropriate landing and thereafter control the aircraft on the ground to vacate the runway in a safe manner...flaps to be raised during afters checks.

This of course assumes training being carried out to a runway with some distance to spare in case of landing balloon/float/power on (some of which I get wrong even now) and that "landing" matters more than performance.

For experienced "Bloggs" it's get the speed correct, round-out correctly and touch asap, control the aircraft, flaps up, pitch to put weight on mains, and brake... and if in doubt GO AROUND!

Get the impression my instructor knows what they are on about, but they'd be the first to say some else knows better.

I was taught this and have practiced it a number of times and it works fine. Yes, the problem of accidentally raising the landing gear instead can also be looked into doing the following:
In case of electrically operated flaps, after you have lowered the flaps for landing, pull out the circuit beaker for flaps and raise the flap lever to up. Just after landing, push the C/B in and the flaps would go up without any risk of touching the L/G lever.
Call me crazy but I was demonstrated yet another procedure to facilitate an early touch down and minimize the landing distance while making a short field landing.
Just after flair, real close to the ground, raise the flaps; the moment the aircraft touches down, go for the brakes and you would achieve the minimum distance landing. I know the procedure is not written in any POH and sounds dangerous but believe me, it has always worked very well with me. I am not recommemnding it to anybody, just highlighting the various possibilities you can try if you like. Before you try somethimng like this, know your aircraft well as well as your own performance limitations.

Thanks for all the posts - I have been so enlightened.

ifitaintboeing - lovin the CRM - I take it there are no gaps in your vast amount of knowledge and experience.

Guru - A bit concerned about pulling CBs that are not in the manuals - with so many electronic flight displays about on light aircraft, pulling CBs for flaps may also affect the computers the flaps talk to ??

TJ

Well, I was talking of the good ol' cessnas and pipers with conventional instruments in the cockpit.

CRM? Crew Resource Management or Cockpit Resource Managment. You are neither my crew nor my cockpit ;-) You have asked a question in order to be educated, and I have offered you several sources of official information where you can find the answer.

TurboJ, we all have gaps in our knowledge and experience; learning is a significant part of developing as an instructor. I did not criticise you personally - I was merely expressing concern that the 'biggest' schools in the UK were not adhering to the UK syllabus and aircraft POH, not at your lack of knowledge. Although, as instructors, we must take some responsibility for being aware of the contents of the POH of the aircraft which we operate.

Well.... back in the early 80's I did my multi ride in a C 310R. After touchdown, I raised the flaps (it was a relatively short runway). The examiner told me I should not have done that, and docked me a few points off the ride. I explained that this was a specified procedure in the flight manual for the 310R, so it was okay to do. He conceded that it was specified on the flight manual, but was still not a good idea, for the obvious reasons. I have to agree with the human factors, and risk vs benefit aspects of making control selections during the ground roll.

I have to agree that obtaining the maximum stopping performance from your aircraft, after touchdown might include rasing the flaps. However, I doubt that most operations involve runway dimensions which demand this. Those who need to do this, probably already know they do!

A few years ago I picked up an MD500 helicopter from a base in Alaska, which I had been told also had a runway. As I walked to the helicopter, I asked another local pilot where the runway was. "this is it" was the reply. It was a hole in the trees so small, I'd think twice before crashing into it! I've been flying STOL equipped Cessnas for 25 years, and I would not have considered landing in there. It was okay for getting the helicopter out, I did not have to vertical out. Some operations are just different in Alaska!

There are many things which can be done in aircraft, which probably should not be done, without a really good reason, as the risks far outweigh any benefit. For general operations, this would be one of them....

On some rough strips it may be a good idea to retract the flaps to prevent stone damage.

Pilot Dar - very interesting post - thanks

With regards to your last paragraph it could be the reason why some UK flight schools don't teach short field take offs and landings

TJ

Used this method pretty much all the time on either tailwind or very cross winded strips sometimes bringing up the flap in a gentle smooth action whilst about to touch down to put her right on at the start to ensure you had maximum braking area. Also on extremely hot tarmac the C206 was very very easy to flat spot so we were taught as soon as you touched down flaps fully retracted to weight the wheels for braking not skimming the tyres.

I think the earlier post was right about the negatives but like most real world flying as opposed to training often this was a safer than the POH method considering the strips and conditions etc. like most advanced skills its knowing when and how to use them and when not to.

Wet season often meant sliding the entire length of the strip in mud and water using blasts of power from the throttle and rudder to keep her straight as the brakes just made you lock up and push huge furrows in the strip, flaps were always retracted as soon as we touched down to ensure she would not fly again.

I would also like to add this operation was in fixed gear singles.

Interesting thread... I'm another one who's embarassed to admit that I had never realised that so many light aircraft specify this in their POH. Of the 4 types ifitaint listed, I have, in the past, flown 3 regularly, and should have known about their procedures.

One point which hasn't been raised yet, though, is that most of these types need a lot more runway for take-off than they do for landing. The chances of ever needing to land in the absolute minimum distance are pretty much zero, because if you need to land in such a short distance, the chances are you won't be taking off again! Now, if we were talking about types with longer landing runs than take-off runs, it would be more critical.....

FFF
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This is indeed the case for nearly all the planes flown by those who frequent here. There are, however, a few aircraft types (PA-18, Husky) for example, which when light get off a short runway and out very well if you work at it. I would venture to say these are aircraft which could sometimes need more runway to land and stop than to clear the hedge.

For the few times I have quickly retracted flaps after touchdown, it was generally to minimize the transition time from wing bourne to weight on wheels for control and braking, or simply control, when you're on skis.

I don't suggest pilots make a habit of this, unless their operations warrant it.

FFF, without wishing to offend and in the politest manner possible, might I suggest you take a look at the C152/172 POH next time you go to fly one. Apart from Cessna only quoting short field take-off and landing performance, you may be surprised to see that the distances are very similar for TODR and LDR.

ifitaint

For the Cessna 172N, at sea level, 20 degrees, maximum take-off weight, TORR = 835', LRR = 530' - a difference of 305', or, to put it another way, the TORR is over 50% greater than the LRR.

The difference between TODR and LDR is not quite as great, "only" 255'. But these differences get markedly bigger at higher altitutes. I will grant you that the differences are smaller on grass runways... but I think I've justified my ealier post!

FFF
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As anyone who has done a bit of bush work will know, the published toff and landing distances are generally nothing like the real toff and landing distances.
That is not to say I or anyone else should not use them, but often in bush operations rightly or wrongly operations are based on what the aircraft will do rather than what the POH says it can do.

Please don't get side tracked into the use or non use of the POH but it is a fact.

And don't be to hard on yourself for not knowing everything in the POH not many pilots do.

A related issue is what is the definition of short field ? The common answer seems to be along the line of what is the definition of pornography......" I know it when I see it ! "

Given the lack of any official definition I tell my students to treat any field that is shorter than double the POH takeoff/landing chart distance as a short field.

I am curious what other instructors take is on this question ?

If I'm scared on finals and before the takeoff roll its short.:ok:

Wether or not it is a good idea to retract flaps immediately after touch down (I understand the idea is simply to reduce lift, increase the weight on the wheels and enable maximum braking) the reality is that if you are going into somewhere that is short enough to warrant raising the flaps then it is only worth doing so with manual flaps. Electric flaps do not come up quickly enough (in my experience) and the extra thought that goes into finding the flap lever distracts from the extra concentration needed to pull off such a landing.

I'd agree with this. I found the technique particularly useful when flying tapered wing PA-28's. I remember they would float a long way if you were carrying any excess speed into the flare & there was always a temptation to put them on the tarmac too soon on shortish runways, in which event quickly retracting the flaps was a certain way to get some weight onto the wheels.

For what it's worth, this was standard practice on DC3s - particularly in strong winds or crosswinds which are endemic in the north of Scotland.,Think of it as the first form of lift dump. X winds are much more demanding in tail draggers and the technique makes sure that the aircraft is going to stick on the ground.

Had a fella that was taught to retract the flaps on a 172, that was all well, until he was sitting in the left seat of a Bonanza, that didn't turn so well for him.

All I remember was clang, clang, clang and him yelling "What happened?"

Doh ....... :eek:

Trex450

I have to disagree, I have used this method on the C206 thousands of times into less than perfect strips and all of the C206 in the fleet had electric flaps.

So learn to fly at the correct approach speed! 63KIAS does not mean 70!

The only logical reason for raising the flaps after a full-stop landing is to avoid stones and gravel damaging them.

The only logical reason for raising the flaps after a full-stop landing is to avoid stones and gravel damaging them.

Maybe from your perspective and your aeroplane.
However, as I have written above, it was a perfectly common part of commercial aviation - although I should have added that it was done by the non-handling pilot. With modern aircraft, lift dump has obviated the need for the technique but I have used it very successfully on aircraft such as the Chipmunk in gusty Xwinds.
http://images.ibsrv.net/ibsrv/res/sr...eply_small.gif

On slippery, icy runways, raising the flaps can help you maintain directional control. Dumping lift to give more weight on the wheels and thus improved friction.

I used to do it regularly when I was flying in Shetland. Strong & gale force winds, sometimes on icy surfaces, meant that the last thing I wanted once on the ground was a wing producing lots of lift.

This is standard practice in most flapped gliders, in this case because aileron authority is reduced with flaps down, but increases in negative flap. Helps to avoid ground looping.

Not relevant to short-winged aircraft, but another example of type-specific differences.

As this was started referring to something in Alaska you should check out some of this guys clips as most people who have never seen some of the places these guys land in Canada and Alaska do not fully understand what short field can mean.

Another point which is germane to this discussion is that raising the flaps while the aircraft is still in the air but very close to the ground is a last ditch option for a forced approach where the speed has been allowed to build excessively and the aircraft is stuck in a nose down attitude in ground effect using up precious field length. The sudden loss of lift will cause the aircraft to plop down and allow the nose to be raised before ground contract.

Needless to say this should never be done during a regular non emergency landing.

Use the flaps up technique on the chipmunk for all landings
Is most useful when windy as it helps to keep the thing on the ground