Retracting Flaps On Touchdown

[TurboJ]

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 ???

[FlyingForFun]

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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[TurboJ]

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

[FlyingForFun]

full flap provides more drag than liftTrue (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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[ifitaintboeing]

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

Flight Training: Short Field Approaches and Landing (http://flighttraining.aopa.org/students/maneuvers/skills/shortapproach.html)

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].

As a UK instructor, having taught at some of the biggest schools, I've never heard of this

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/Section%201%20Subpart%20C%20-%20Amdt%205%20_JAR-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....

[TurboJ]

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.

[99jolegg]

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.

[172_driver]

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.

[doubleu-anker]

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.

[Big Pistons Forever]

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.

[max_continuous]

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.

[Guru8904]

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.

[TurboJ]

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

[Guru8904]

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

[ifitaintboeing]

lovin the CRM

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.

[Pilot DAR]

but only on the single engine, fixed gear fleet, not the multi-engine, retractable gear fleet

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....

[Lou Scannon]

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

[TurboJ]

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

[Wildpilot]

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.

[FlyingForFun]

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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[Pilot DAR]

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

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.

[ifitaintboeing]

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.

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

[FlyingForFun]

For the Cessna 172N (http://www.scribd.com/doc/3801614/C172N-POH), 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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[Wildpilot]

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.

[Big Pistons Forever]

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 ?

[Wildpilot]

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

[trex450]

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.

[Sillert,V.I.]

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.

[scotbill]

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.

[FLCH]

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:

[Wildpilot]

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.

[BEagle]

I remember they would float a long way if you were carrying any excess speed into the flare..

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.

[scotbill]

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/src:www.pprune.org/get/images/buttons/reply_small.gif (http://www.pprune.org/newreply.php?do=newreply&p=6500214&noquote=1)

[bfisk]

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.

[Tinstaafl]

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.

[ProfChrisReed]

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.

[SloppyJoe]

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.

YouTube - ‪Cubdriver: ALASKA - Cubdriver749er.com‬‏

[Merchant Banker]

Aviation Video: Piper PA-38 Tomahawk - Untitled (http://www.flightlevel350.com/aviation_video.php?id=5152)

[Big Pistons Forever]

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.

[good finish]

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

[kenguan]

Guru - using CB's as a switch is not recommended because CBs are not meant to be used as switches. Simply put, switchs are meant to make electrical contacts without arcs. CBs might not be "arc free"...

More on maximum flaps on landing roll - yes max flaps causes more drag than lift, but remember the speed/drag formula thingy, at low speed, the amount of drag caused is low.
Increase speed 2x, drag increases 4x, vice versa.
So for me retract the flaps if you need max braking.

Same principal with large aircraft having spoilers:
- Used in the air they are known as speed brakes.
- Used on ground they are known as lift dumpers, because their main purpose is to destroy the lift & get the weight on the wheels, although the spoilers do contribute to drag to slow down the aircraft, but probably only when the aircraft speed is still high (right after touch down)

[Martin Barnes]

are you serious!

must be the most pointless post ever.

[osmosis]

raising the flaps while the aircraft is still in the air but very close to the ground

I was being ferried to a spraying outfit an hour or so away from base in a very ancient C172. Over our destination looking at the paddock containing our one way strip the pilot remarked to me there wasn't a whole lot of space to get it in. To reassure him I reminded him of the gentle uphill slope and the spray aircraft already on the ground. On short final with full flap his speed was about right but at the full-flare stage he reached down for the handle and literally dumped all flap. The aircraft sat on the ground in no uncertain terms and remained there; I don't remember how much braking he used. It was the first time I had seen such a thing done whilst still airborne and I have to say it worked on this occasion but I would need to be pursuaded to use the same technique myself. Does/has anyone else regularly dumped flap in the flare?

[Guru8904]

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. As I have said in my above post, it is perfectly safe if done at the correct height/speed. I have done it a number of times on 172s and others and been able to achieve the desired results without compromising safety.

[osmosis]

The post above has reminded me that I too have dumped flap in an Arrow on downhill grass. Fading memory apparently.

[Big Pistons Forever]

A C172 flown at the correct airspeed will touch down with very little float and will stop in less distance then it is possible to take off in. If you need to retract the flaps in the flare to get the aircraft on the ground you are approaching too fast. The correct response is to go around. If flying instructors are teaching retracting flaps before the aircraft is firmly on the ground then they are IMO exibiting very poor airmanship.

[Harry Spotter]

Did it many times for fun to show short field distance on Pipers (mainly the "Archers" , with nosewheel) Was quite impressive , if done just before touchdown- mainly to show off and get the first intersection (which was actually meant to be a line up for departure one couldn't be normally used as an exit :-)
Don't do this at home, you need to be really experienced , no low-hour stuff, wouldn't do it now as I don't have too much recency in SEP anymore.

On tailwheel , like a C185 , it was usefull do dump lift and get the tailwheel firm on the ground after a wheellanding (especially in (strong) crosswinds).
same on Piper Super Cubs allthough less noticeable.

This is all true on planes with a flap-handle where you can raise your full flap in a blink of an eye.
Can't see the point in C172 types with electrically operated flaps as the flap travel is too slow to have an effect. (I vaguely remember a nosewheel four-seater cessna with a manual flap handle though , have to get the logbook out for that one)

Finally it was a placard in at least the Beech Sundowner , literally :
"Raise flaps to increase brake effectiveness".
I guess it was after reading this placard I started using it as mentioned above.
Basically flew thousands of hours on SEP without the need to use it !

[Craggenmore]

In the PA28 that I used to teach on we could stop before the PAPI's..!

Touchdown on the stall - dump flap - full aft on the CC and Max braking.

15m or less every time. A real eye opener for the uninitiated as it was for me the first time it I sat through it..!

An easy drill to teach to the more proficient of students.

I kind of miss those days but not the pay :}

[mountain-goat]

was taught it at Denham (EGLD)... along with the pros and cons (frowned upon by some) of retracting a stage of flap as a last resort on final approach on a PFL.... which I read with interest was utilised by the skipper of the BA B777 into Heathrow to make it over the airfield perimeter.



MG :ok:

[kenguan]

Yeah, read that the BA 777 crew retracted flaps, that's why they managed to actually made it "safely" short of the runway.

BUT, as far as I can remember during my PPL training, you NEVER NEVER retract flaps after extending them while on final. You don't want to sink that close to the ground.

What the BA 777 crew did probably was not "per SOP" I think, but it worked. Retracting late stages of flaps reduced drag more than lift.

The USAir that ditched in the Hudson, the crew did something not "per SOP" too - I read that they switched on the APU even though it was not part of the engine out procedure, & that probably helped 'save' the aircraft.

But if you do something that is not part of the SOP & caused something bad to happen, you've had it...
You do everything as per SOP & still something went wrong, that's fine...

[Big Pistons Forever]

Yeah, read that the BA 777 crew retracted flaps, that's why they managed to actually made it "safely" short of the runway.

BUT, as far as I can remember during my PPL training, you NEVER NEVER retract flaps after extending them while on final. You don't want to sink that close to the ground.

What the BA 777 crew did probably was not "per SOP" I think, but it worked. Retracting late stages of flaps reduced drag more than lift.

The USAir that ditched in the Hudson, the crew did something not "per SOP" too - I read that they switched on the APU even though it was not part of the engine out procedure, & that probably helped 'save' the aircraft.

But if you do something that is not part of the SOP & caused something bad to happen, you've had it...
You do everything as per SOP & still something went wrong, that's fine...

Good operating techniques are aircraft specific. There are lots of things that are good operating practices in light singles that would be an extremely bad idea in a heavy jet airliner, and vice versa..........

[Cows getting bigger]

Anyone want to lend an arbitrary low-houred PPL their aircraft to try out some of these techniques?


Thought not. :suspect:

[WestWind1950]

I was never taught it ever, anywhere! And I can't imagine it being good on the gear.

I saw it done by a pilot and thought he was just showing off... I'm surprised at how "commmon" it seems to be. I also noticed people doing it at competition in order to "hit" the first landing sections of runways to get the max. points. Because of a number of bad results (i.e. damaged gear) they then forbid it, which I think is a sensible idea.

[STOLskunkworks]

As many have pointed out in Cessnas (at least the singles I flew) this is the procedure for a proper short field landing.

In many aircraft including turboprops and some Heavy Jets a go around requires raising the flaps one notch. The previously mentioned 777 crew would have been flying a safe speed for one notch less flaps which as you can tell worked out great for them. Less Drag = they made it further.

I have not seen the show to which the original question was referring but can tell you that when operating on contaminated runways bush flying raising the flaps can help prevent nice rock shaped dents in your flaps.
Also in many bush types my memory may be failing me here but I believe the Beaver and Twin Otter come to mind the flaps actually block the rear door. And if you were in the ditch you would be rather unhappy to find that the only door you could get out was blocked by the flaps.

I guess the procedure you use depends on each situation. I also find that in limiting cross winds the less flaps the better.

I personally would be less than happy having to sit through a hairy landing by my colleague if I thought they were not so much as capable of lifting a flap lever during a landing.

Many places worldwide seem to train with the sole objective being how can we fast track this 0 hr wonder to his first Boeing/Bus rating and they skip over the real learning and hand flying stages.

[Sillert,V.I.]

BUT, as far as I can remember during my PPL training, you NEVER NEVER retract flaps after extending them while on final.

Interestingly when I did my PPL many years ago (in a PA-38) I was taught to use flaps to control the rate of descent when doing a glide approach.

If I were ever unfortunate enough to be facing a real forced landing, then in an A/C with manual flaps I'd fly the approach with one hand on the flap lever.

[Pilot DAR]

I was taught to use flaps to control the rate of descent when doing a glide approach.

Hmmm, I would like to gently suggest several reasons why that's not so good:

Poor discipline, sideslipping is the accepted technique for this, not down and up with the flaps, particularly for flapless aircraft!

If you have applied a lot of flap for this technique, and you decide to stretch your glide, you're going to raise some of the flap, and suddenly raise you're stall speed. Very unsafe, if you were already slow, 'cause you were already stretching it in. If you slip and unslip, you're changing drag instantly, but leaving lift undisturbed.

If you get used to this "crutch for proper technique", you'll be buggered flying a plane with no, or electric flaps, particulary after an electrical failure.

There are planes with much more effective flaps than a Tomahawk (C-180, for example). Playing with the flaps up and down during a glide will be more dramatic in one of those types.

And lastly, if you really have to glide one day, you'll want to concentrate on flying with the primary controls, and having a free hand for the required securing of the cockpit. it should not be commited to the flaps.

I'd be surprised to see a flight manual that recommends this procedure....

[Sillert,V.I.]

PilotDAR, some excellent points there. I'd agree that slipping is usually the best way to lose a little excess height on approach, and indeed may be the only option if you are flying a flapless, brakeless taildragger. However, if for whatever reason you need to stretch the glide, slipping the aircraft won't help you and in some types (even some very large ones!), retracting some or even all of the flaps whist maintaining a safe airspeed might just make the difference between clearing the hedge and taking it with you. I think it's always a good idea to know as much as you can about the capabilities of your aircraft and knowing how it will behave if you retract the flaps in the glide at approach speed may give you an additional option that could just be useful someday. As has been said before, this is probably most useful if your type has simple manual flaps & it also helps if (like the PA-38) flap retraction won't cause a significant trim change.

At the time I was doing my own basic training (almost 30 years ago now) I remember my instructors didn't allow low hrs students to slip the aircraft (we were all taught the crab method for Xwind landings) yet seemed quite happy for us to mess around with flap settings in the way I've described. I guess I can see the logic of this - the tomahawk is perhaps not the safest of aircraft for the inexperienced to be flying slowly with crossed controls close to the ground.

[plucka]

As an Ag pilot I always lift the flaps on touchdown or slightly before. Alot of the strips we work off 'going around' is not an option. By lifting the flaps this ensures minimal float, it also gets the tailwheel on the ground and with this locked then using reverse (turbo prop) is an option if required.
The flap switch ( electric flaps) is located on the stick in the trigger position. This makes it easy to get to and doesn't require another hand.
Flying these planes, you are living on the flap switch, flaps for T/o, flaps to turn, flaps to climb, flaps to land. If your flaps stop working it is time to go home.
I don't think dumping the flaps on landing should be considered the norm but it is something worth demonstrating to your students in my opinion.
Especially useful trick in a taildragger in extreme x-winds.

[Intercepted]

Quote:
Originally Posted by kenguan http://images.ibsrv.net/ibsrv/res/src:www.pprune.org/get/images/buttons/viewpost.gif (http://www.pprune.org/flying-instructors-examiners/453498-retracting-flaps-touchdown-3.html#post6543955)
BUT, as far as I can remember during my PPL training, you NEVER NEVER retract flaps after extending them while on final.

Interestingly when I did my PPL many years ago (in a PA-38) I was taught to use flaps to control the rate of descent when doing a glide approach.

If I were ever unfortunate enough to be facing a real forced landing, then in an A/C with manual flaps I'd fly the approach with one hand on the flap lever

I also learned to never retract flaps on final during my PPL training :=. Post-PPL I had some extra lessons with the CFI at the same school and got introduced to the secret of retracting flaps on final :ok:.

[Teddy Robinson]

Fine in theory, until you raise the gear by mistake ... as has been done all too many times by people trying to be slick ... in a word ... don't.
Plan the perormance, if the approach isn't right go around.

Retract flaps appears in the after landing checklist with the aircraft stopped clear of the runway, not as a fuzzy memory item.

[Teddy Robinson]

ESPECIALLY on a Pa38 !!

[trex450]

if you are a mile out on final and realise you have put down more flap than you need what is the problem with raising a notch? You should have plenty of time to ensure that you raise the flap and not the gear and avoid dragging the aircraft in for an excessive period. If you refuse to raise the flap and you engine quits you are not going to make the runway which would be a bit daft.
As for raising the flap just before landing it is never anything I have done but I can see how in capable hands it might have its place, for the average ppl though it has not. I have operated a standard (160hp) 172 in and out of 300m and never found any real difference with raising the flaps in the landing roll (the book procedure for shortfield) and not. They were electric though so they spent most of their time going through the t/o setting and therefore lightening the load on the wheels and defeating the object.
Of course if you did raise the flap prior to landing to shorten the role and got it a bit wrong and ended up with damaged gear/wing spar as a result then the insurance man might not be too sympathetic.

[bingofuel]

Slight thread drift from retracting flap on touchdown but, I remember many years ago doing an FI revalidation with a very experienced examiner, the sort of guy who has forgotten more than I will ever know.
As I briefed the PFL exercise I made the statement once flap was selected, not to raise it again. This invoked the slightly raised eyebrows and the comment,''oh, why?'' and I realised I had dug a hole that I was not going to get out of.
We then had a lengthy discussion about the pros and cons of raising flap and rate of descent etc. The bottom line was, never say never, and the BA 777 at Heathrow proved his point many years later.
Flap is just one flight control to be used as and when appropriate.

[Teddy Robinson]

Trex, first question has to be why was the flap lowered in the first place ?

Second, the object is to have 3 conditions satisfied by 300 aal, cleared to land, runway clear, and aircraft on speed/profile or it's go-around time.

Third, to follow the logic through, then every landing would be from a glide approach, otherwise any loss of power will result in an undershoot.

to follow that logic further, everything is fine until one changes aircraft type, when "habits" rather than training can catch one out. Try this example on the Pa 38 thats been mentioned here ....

"oh I have too much flap" just before base to final turn ... so you retract to flap zero, aircraft accelerates, off comes the power, add an overbank to try and hold the centreline, oops now I'm too low ... raise nose, add power stall warner ... goodnight Vienna.

( I would suggest trying it at a safe atitude first btw)

[Pilot DAR]

There is mention here of what I will refer to as "modulating" the flaps during the approach, rather than applying the flaps in increasing increments, at appropriate phases in the approach.

Personally, were I to see flaps being retracted during the approach, I would hope it was because climb power had been applied for the purpose of aborting the landing. Other than that, I would likely make a negative comment.

It has been said that flaps are a flight control. I disagree. They are a supplementary lift/drag control. Lift is primarily controlled by pitch. The primary pitch control provided in the aircraft is more than capable of controlling the whole range of pitch and lift required for the aircraft. The lift (and drag) may then be supplemented with flaps. However, as you are applying flaps to change the lift characteristics (we presume in the lower speed range), there is no need to further "control" that lift with flaps - the pitch control still works.

This is primarily because the drag change when controlling the plane in pitch with the pitch control is small, and proportionate. The drag change with the use of flaps can be much larger, and is very likely not at all proportionate. If your approach with a bit of flaps extended requires a brief increase in drag, sideslip (type permitted), or play with power and pitch for a moment. Increasing flap extension as a temporary means of glidepath control is poor form. If you need to do that, your approach has already been botched.

The glide ratio for the aircraft is established flaps up (unless otherwise stated). Thus, untill you have the field "made" you're not going to be extending (or extending more) flaps, until you're completely sure you need them. Once you're sure you need them, why would you un-need them!

Increasing flaps is a configuration change in preparation for a later stage of the approach, or landing. It is not to be done and undone during one approach. You would not put the wheels up and down for drag control, so why mess with the flaps? If you have spoilers, that is what they are there for. If your plane does not have spoilers, it has demonstrated ample capacity for a range of approach types, without configuration changes.

I challenge anyone to present a flight manual, or training manual which suggests modulating flaps during approach. If I were checking out a pilot who did this, there would be no further checkout, until this habit was evidently broken.

As for retracting flaps after the wheels are firmly on the ground, yes, it is advisable with caution, under certain circumstances. Retracting flaps as a means of getting the wheels on the ground is, in my opinion, only acceptable in either of two circumstances: You own the aircraft being flown, or the person who does, has directed that this technique be employed (I would be floored to hear of that!). Other than that, there is not a flight manual anywhere which suggests retracting flaps prior to touchdown is acceptable. I think that doing this is simply foolish. For all the chatter I have seen in other threads about the horrors of momentary zero G flight, this is much much less acceptable flying technique.

I have no need to demonstrate this for certification, and I would expect that were I to be caught doing it, I would be disallowed the use of that aircraft again.... I have never done it.

I propose that developing new flight techniques be left to the test pilots, and I doubt you'll see them doing it without a really good reason. If fooling with the flaps was necessary to land the aircraft, it would not get certified.

[Teddy Robinson]

:D:D:D:D Well said that man... seconded.

[osmosis]

I'd be interested to know what our Alaskan/Canadian friends think...

[Pilot DAR]

I'd be interested to know what our Alaskan/Canadian friends think...

I'm sure that as with any group, you'll find a variation of thinking among us.

Many skilled pilots I know in Alaska own their own aircraft, and fly out of runways you'd have to see to believe. I flew an MD500 out of one, and was nervous!

[osmosis]

Pilot DAR, Yes. After seeing the magnificant stol performances typically in modified Cubs posted on pprune and youtube my point was I'd like to see what goes on inside the cockpit. You can see and hear a lot from the outside of course but, in keeping with this thread, methinks the flap lever is used rather more than set and forget.

But if I were these blokes, I wouldn't be posting what I do on pprune lest I upset those precious traditionalists.

[bingofuel]

Pilot DAR
Once you're sure you need them, why would you un-need them!
I am certainly not advocating 'modulating' flaps on approach.
What I was trying to say was that there may be a situation where there is benefit in raising flaps on approach.
Let us consider the PFL, the pilot is now flying a glider, he is manouvering for a field or some suitable landing spot, but he makes an error and selects flap too early increasing his rate of descent and it is clear he can no longer reach the selected area. What the examiner was trying to get me to understand was that in that situation, raising flap to a lesser angle will reduce the drag (albeit with an initial slight sink) but the overall result is a reduction in rate of descent which means you can glide a greater distance.
The learning point was on 'not saying never raise flap' but teach the student to understand what is happening and be aware there may be a situation when it is a viable option, but certainly not to use it as a modulating system as a matter of course.

Hope this clarifies what I was trying to say

[Pilot DAR]

Well....

I am subject to someone with more wisdom than I coming along to correct me, or overlay my thoughts with more detail, and further subject to a qualified flying instructor (which I am not), presenting accepted training techniques, but...

So far in my flying career, I have come to accept that if you are gliding for the purpose of best glide ratio, you want the greatest L/D. If you extend flaps, you upset that ratio. Once upset, you can't just put it back as before, without a loss. The loss is the setting with the loss of lift, and the need to loose altitude to do a power off acceleration, to restore the aircraft to the flaps up best glide speed. I suspect that the net effect of these losses would exceed any benefit resulting from the reduced drag of the flaps being retracted.

Though my only "proof" is the absence of something, I've got to say that if retracting the flaps for any phase of a landing between their first application, and wheels on the ground were necessary, or otherwise a good idea, a flight manual somewhere would say so. Aside from basic techniques, flight manuals generally present all of the information and techniques required to fly the aircraft. If it's not in there, you don't need to do it, and their probably is no beneift to doing it. I agree that there are some handling techniques which go beyond (like lifting one float out of the water on takeoff), which may not be mentioned in a flight manual, which are described in training manuals, but modulating flaps on approach is not one of them. You don't see airliners doing it, and they fly by the same physics we do!

In part, I would imagine that this no mention in training manuals is becasue of the dramatic differences in aircraft handling with flaps from one type to another - you cannot generalize this. I assure you that if you go from full to half flap in a gliding Twin Otter, you will need a lot of altitude under you!

So, certainly, as a part of becoming a proficient pilot at altitude, experiment with flaps settings. At altitude, it's not dangerous, it just has no benefit. I suspect that if you measure performance, you'll see what I mean. But if you really need to glide, use the flaps the way the flight manual says to!

[trex450]

Hi Teddy
Assuming full flap had been selected a bit early then surely you only gain by going back to take off flap as you will be losing the excess drag without compromising stall speed. Your planning on when to select full flap should be such that when you select it it stays down until after landing or a go around is initiated I agree but not every approach is the same. My point on raising flap was not to go from full to zero, just up a stage simultaneously adding a bit of power to cover the sink.
For what it is worth my scenario, not fully explained, was that in which you have accidentally extended more flap than intended. On realising pretty much immediately then little height is lost in getting rid of that extra flap.
I am not suggesting that every landing should be from a glide approach, especially having done a bit of STOL stuff over the years but dragging the aircraft in for longer than necessary in a configuration such that the runway would not be made in the event of an engine failure does not have me feeling comfortable.
As for your example on the PA38, the height should be OK, as I find that I need to tighten the turn I would either add power (as you do for a steep turn but this would be the worst option given altitude) or accept overshooting the centre line and then come back onto it from the other side. It might look a bit scrappy but it would be safe. As you mentioned on an earlier post if in doubt go around and that can be from any point within the circuit, it does not have to be from short final.

[christian archer]

Hi all,

I have only read the first page of this thread because I got bored and so I appologise if I am repeating someone here.

I am an FI in the UK and have to admit that although I had heard this theory, hadn't actually read it in the syllabus. But lets be honest, if flap retraction on short field landings is neccessary for maximum braking efficiency, you sure as hell aren't getting back out of that field again anyway since TO requires a lot more field in SEPs than landing.

Regardless of it being in the syllabus, I will not teach my students to fiddle around with flap levers on the ground roll. If its that short they shouldn't be going there.

[Pilot DAR]

Though I agree that selecting flaps while on the rollout is a less than ideal action, some flight manuals do specify it, in which case is is worthy of consideration, if pilot skill and workload permit.

you sure as hell aren't getting back out of that field again anyway since TO requires a lot more field in SEPs than landing.



There are a number of types (Cessna 182RG, for example) where this is not so much the case. Before I lengthed my home runway from 1700 feet to 2100, getting the 182RG in was never pleasant, but it would always jump out. Similarly the taildragger amphibian I fly here now, uses much more getting in than out.

Generally, for lower powered singles, I would agree with the assumption of you remark though...

[Wildpilot]

Christian archer,

You are kind of missing the point and if you are instructing in the UK I can understand why.

This flap up as soon as you touch down is to aid weight on the wheels and give either improved braking for a short strip or in the wet season in Africa just to stop sliding about so much or flat spotting the tyres on extremely hot tarmac.

You are right not to teach your students something you have not had to do yourself and they should not need unless they go on to fly into these sorts of conditions.

I can't believe this thread has gone on and on, it does work, lots of pilots improve safety in certain situations by doing it and no a ppl or instructor knocking about most countries will not need to know how to do it.

If I had to fly by the manual in my float plane then most days I could not do the job, much like an ag pilot. It is one of many advanced techniques that bush/float/ag pilots use that the average instructor does not generally need.

[ProfChrisReed]

Pilot DAR wrote: So far in my flying career, I have come to accept that if you are gliding for the purpose of best glide ratio, you want the greatest L/D. If you extend flaps, you upset that ratio. Once upset, you can't just put it back as before, without a loss. The loss is the setting with the loss of lift, and the need to loose altitude to do a power off acceleration, to restore the aircraft to the flaps up best glide speed. I suspect that the net effect of these losses would exceed any benefit resulting from the reduced drag of the flaps being retracted. This last sentence does not match the experience of many glider pilots.

One of the reasons why your chosen flap setting for the approach might turn out to be wrong is hitting heavy sink. 10kt down (1,000 fpm) is not unknown in the UK, and in hotter parts of the world even stronger sink might be encountered.

In these circumstances you need to (a) increase speed (to spend as little time as possible in the sink) and (b) improve the glide angle and reduce drag by, inter alia, reducing flap. The short-lived loss of lift on retracting flaps is more than compensated by the improved L/D, assuming you have sufficient height to make these adjustments. Of course, you need to know the effect of raising flaps on your aircraft - if, say, you lose 50 ft and are only 51ft agl then it's hopeless. If you're at 250ft, in most gliders you'll probably improve the situation if your speed is such that reducing flap doesn't put you on the back slope of the drag curve (or worse, cause you to stall, but you shouldn't be approaching that slowly in most instances)..

In a Cessna/Piper XXX the height at which you can benefit is clearly greater, so if you don't know the effect on the aircraft it might be best not to fiddle with the flaps. But if you do know, ideally from practice, it would be foolish to stick with a losing flap setting which will only put you in the hedge.

[SoundBarrier]

This discussion has diverged into two situations :-
1. Retracting Flap at / just before touchdown or during the rollout
2. Fiddling with flap during the approach.


1. Retracting Flap at / just before touchdown or during the rollout
This is mentioned in the POH for some (SEP) aircraft for improved braking. I personally don't do it given the areas in which I fly, but I have done it. C182 with Manual Flap for example.

2. Fiddling with flap during the approach.
In the SEP's in is not in the POH, it is not a very good technique not to mention when you have the well known, tested methods we were all taught in our PPL's that actually work.

I'm not a test pilot - nor do I want to be.

[Pilot DAR]

I certainly agree that there could be aircraft types (sailplanes) for which the "don't fiddle the flaps" theory might not be as appropriate. As I have very little experience in sailplanes, perhaps that is beneficial for them.

It was the Cessna/Piper XXX types which were the subject of my opinion. I'll be doing some flight testing on a single with 60 degrees of flaps available, so I'll do some experimenting in the weeks to come, to gather more objective data.

[ProfChrisReed]

Pilot DAR: I certainly agree that there could be aircraft types (sailplanes) for which the "don't fiddle the flaps" theory might not be as appropriate. As I have very little experience in sailplanes, perhaps that is beneficial for them.

It was the Cessna/Piper XXX types which were the subject of my opinion. I'll be doing some flight testing on a single with 60 degrees of flaps available, so I'll do some experimenting in the weeks to come, to gather more objective data.

I doubt we're actually in disagreement. Don't fiddle with flaps on the approach unless you know what you're doing must be the right approach.

It would interest Cessna/Piper XXX drivers to know whether raising flaps might help them, but even then it should be a case of "don't touch" until they've practiced it safely at height.

[LH2]

But lets be honest, if flap retraction on short field landings is neccessary for maximum braking efficiency, you sure as hell aren't getting back out of that field again anyway since TO requires a lot more field in SEPs than landing.

Are you assuming the same conditions on landing as on take-off? That does not necessarily hold in many different practical scenarios, e.g., dropping payload, wet vs. dry runway, wind / air density changes, etc.

Regardless of it being in the syllabus, I will not teach my students to fiddle around with flap levers on the ground roll.

If it's in the syllabus, it's probably because someone who knows better than you has put it there for a good reason. I'm not sure you're not doing your students a disservice by not following the syllabus without due justification.

If its that short they shouldn't be going there.

If it's contemplated in the POH and they have the necessary skills why not? Of course, unless someone competent teaches them, how could they develop those skills safely? More generally, from the fact that there is a runway, one can assume that other pilots are using it successfully. If your students aren't, it surely follows that you are giving your pupils a lower quality of instruction.

Finally, and as has been mentioned before, another reason for retracting flaps is to avoid rocks punching holes through them, or simply to reduce drag sufficiently to be able to reach the top of very steep runways--both of which are common occurrences in my kind of flying.