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Retracting Flaps On Touchdown

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Retracting Flaps On Touchdown

Old 3rd Jun 2011, 20:45
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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 ???
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Old 3rd Jun 2011, 21:13
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Why do it if it's not fun?
 
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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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Old 3rd Jun 2011, 21:33
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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 ???
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Old 3rd Jun 2011, 21:50
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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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Old 3rd Jun 2011, 21:52
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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].

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?

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....

Last edited by ifitaintboeing; 4th Jun 2011 at 10:01.
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Old 3rd Jun 2011, 23:38
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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.
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Old 4th Jun 2011, 01:00
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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.
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Old 4th Jun 2011, 02:14
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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 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.
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Old 4th Jun 2011, 02:53
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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.
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Old 4th Jun 2011, 03:19
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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.
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Old 4th Jun 2011, 03:42
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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.



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Old 4th Jun 2011, 07:18
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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.
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Old 4th Jun 2011, 10:52
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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
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Old 4th Jun 2011, 11:02
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Well, I was talking of the good ol' cessnas and pipers with conventional instruments in the cockpit.
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Old 4th Jun 2011, 11:49
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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.
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Old 4th Jun 2011, 19:44
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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....
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Old 4th Jun 2011, 20:23
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On some rough strips it may be a good idea to retract the flaps to prevent stone damage.
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Old 4th Jun 2011, 21:22
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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
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Old 4th Jun 2011, 21:40
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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.

Last edited by Wildpilot; 4th Jun 2011 at 21:51.
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Old 4th Jun 2011, 21:52
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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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