Retracting Flaps On Touchdown
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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.
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.
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.
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.
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Sorry to be pedantic ... but.
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)
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)
Last edited by Teddy Robinson; 11th Jul 2011 at 20:54. Reason: in case someone is silly enough to try this in the circuit)
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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.
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.
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I'd be interested to know what our Alaskan/Canadian friends think...
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!
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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.
But if I were these blokes, I wouldn't be posting what I do on pprune lest I upset those precious traditionalists.
Pilot DAR
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
Once you're sure you need them, why would you un-need them!
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
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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!
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!
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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.
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.
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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.
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.
Moderator
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.
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...
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.
Generally, for lower powered singles, I would agree with the assumption of you remark though...
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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.
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.
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Pilot DAR wrote:
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.
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.
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.
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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.
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.
Moderator
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.
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.
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Pilot DAR:
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.
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.
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.
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.
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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.
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.
