Flap retraction on landing

As I understand it, (I have no direct experience with anything that uses spoilers-not even a sailplane) spoilers disrupt the airflow to reduce lift AND they create drag.

Retracting the flaps would reduce lift, but also REDUCE drag.

I think, based on my own experience (applies to C-172s), if you are seeing a big difference by retracting flaps you are touching down to fast to start with. If you're really dealing with a short field landing you should have been on the back side of the power curve before touching down. Pull the power and you are DONE flying.

John
 
RotorAndWing said:
You're the one making the comparison. Why don't you enlighten us? :rolleyes:
Click to expand...

They both are going to dump lift, there are certain instances this would be beneficial, would you agree with that?
 
I thought the purpose of flaps was to increase lift at slower speeds, which is why most POH's call for flaps for short field takeoffs and lower lift off speeds. Spoilers are there to interrupt the flow of air over the top of the wing and disrupt lift.

I am sure someone will be along to straighten me out soon enough.
 
In a 172 or in my CTSW I retract to shorten the transition from flying to driving. When the gust factor exceeds 15kts a number of things can happen in that vulnerable period.
 
Silvaire said:
Not really, any flow over the airfoil is going to create some lift as is evidenced by the wings of a parked airplane rocking in the wind. The amount of lift is also influenced by the AOA up to the critical point where a stall occurs. When the flaps are deployed you have a different airfoil, one that creates greater lift at a slower speed but it's all relevant because you land at that slower speed.

In the OP's original post he specifically asked about Cessna 152/172's which are both tricycle geared aircraft with pretty much identical wing and flap designs driven by an electric motor. By the time you have flared to the stall point, planted the mains and dropped the nose wheel you have put the airfoil into an AOA that will not support enough lift for further flight. You are also in a constant deceleration and the flaps at that point, as designed, are providing aerodynamic drag to help slow the airplane down.

In that specific scenario I see no advantage to raising the flaps early.
Click to expand...

You didn't account for the scenario of a wind straight down the runway with a high gust factor. You could well be done flying until the headwind gust comes along.
jsstevens said:
I think, based on my own experience (applies to C-172s), if you are seeing a big difference by retracting flaps you are touching down to fast to start with. If you're really dealing with a short field landing you should have been on the back side of the power curve before touching down. Pull the power and you are DONE flying.

John
Click to expand...
It's in the POH section on short-field landings in the P models I trained in and the S model I currently have both say to retract flaps after nosewheel touchdown. Keep in mind also, the approach technique recommends a speed 14kts slower at the same gross weight (S model, don't remember P model speed).
 
James331 said:
Derailing the topic of flaps on touch down just to be a smart ass eh :rolleyes:
Click to expand...

Um, you were the one who stated that retracting flaps was similar to deploying spoilers. :dunno:
 
jsstevens said:
Um, you were the one who stated that retracting flaps was similar to deploying spoilers. :dunno:
Click to expand...


Jebus people!

When it comes to killing lift, yeah they both do that :mad2:
 
airguy said:
I do it in the 172, just as soon as the aircraft is down on all 3 and stable the flap switch comes up immediately. My home strip is only 2500' with power lines on both ends, so I've effectively only got about 2000' to play with, making every landing a short-field landing. Airspeed control is key but I still don't want a gust of wind trying to convince the airplane to get light. I don't dump the flaps to enable heavier braking - I dump the flaps to get a little more grip on the tires to make the transition from an airplane to a land vehicle a little quicker.
Click to expand...

I have no issues with the concept of making every landing a short field landing, but if you think 2000' requires it, plus you lose 500' due to power lines, I think slowing down on final will improve your performance a lot more than picking up the flaps on touch down.
 
FastEddieB said:
In general, I would say the a manufacturer's recommended procedures trump broad FAA recommendations in their publications.

To all the pilots saying they retract flaps immediately after landing as a normal procedure, I'm curious if you were taught that way originally or started doing it on your own, either independently or under the tutelage of another instructor.
Click to expand...

Taught that way. Both to avoid prop blast on the wing flaps ( prop picking up possible crap on the runway) and to add weight to the mains on touch down.
 
Prop blast on landing? Are you doing them carrier style ready to Bolter?:dunno: My props don't pick anything up until I add power clear of the runway, cleaned up and ready to taxi.
 
jsstevens said:
I think, based on my own experience (applies to C-172s), if you are seeing a big difference by retracting flaps you are touching down to fast to start with. If you're really dealing with a short field landing you should have been on the back side of the power curve before touching down. Pull the power and you are DONE flying.
Click to expand...

Not done rolling, though. The only way to know whether there is a difference worth worrying about in the braking distance is to fly some experimental landings by a pilot who is otherwise consistent approach speeds, the winds don't vary much during the test runs, and there is some way to measure the stopping distance without a lot of hassle (a camera might come in handy for immediate recording of location landmarks.) Half the landings with flaps left in, half with flaps immediately retracted; maybe alternate the landings.

If the weather were better here I'd be tempted to try it. Could use the practice anyway.
 
Jimmy cooper said:
Taught that way. Both to avoid prop blast on the wing flaps ( prop picking up possible crap on the runway) and to add weight to the mains on touch down.
Click to expand...

Thanks.

I learned to fly back in the late 70's and went on to teach at Burnside Ott at Opa Locka not long after.

I just recall that back then, lifting flaps on rollout was verboten. I don't know if it was because the FAA had placed emphasis on it as a result of retractables having their gear pulled up accidentally, the recommendation in the FAA publications, the wording of the Practical Test Standards, or some combination of the above. It may have just been in the syllabus of my Part 141 school. In any case the training stuck, so I simply never got in the habit of futzing with stuff in the cabin on landing roll, and tried to pass that philosophy on to my students.

I'll go ahead and stipulate that pulling flaps up on the rollout will hardly ever have any adverse effects, and those who do it as habit probably do not need to change.

But other than some very specific cases, I still don't see it as a big help. And I'm unlikely to change my habit after all these years.

So there you have it!
 
Henning said:
I have no issues with the concept of making every landing a short field landing, but if you think 2000' requires it, plus you lose 500' due to power lines, I think slowing down on final will improve your performance a lot more than picking up the flaps on touch down.
Click to expand...

Never said 2000' requires it, you jumped to that conclusion. I said that I dump the flaps when using that runway. The short available length leads me to treat each landing as a short-field approach, which has nothing to do with dumping the flaps. I dump the flaps to keep the wing heavy and enhance wheel grip in those first few seconds after touchdown since the runway is only 25' wide and I don't want to do battle with crosswind gusts and light wheels. The intent is just to shorten the transition from sluggish aircraft through skittish land vehicle to relatively stable land vehicle.

MAKG1 said:
Ground roll is 530 feet at sea level on a standard day with no wind. It can be arbitrarily shorter in the presence of wind.
Click to expand...


Heheh, that's cute, quoting book performance like a good little student.

Home drome is 2700', now throw in a decent load in the airplane (full fuel, I have extended tanks, two butts in the seats) plus a 100-degree summer afternoon, and you'll need to carry a little more speed on short final because the runway is only 25' wide and you've got 5G11 cross component. Now go show me book performance.
 
Last edited:
airguy said:
Never said 2000' requires it, you jumped to that conclusion. I said that I dump the flaps when using that runway. The short available length leads me to treat each landing as a short-field approach, which has nothing to do with dumping the flaps. I dump the flaps to keep the wing heavy and enhance wheel grip in those first few seconds after touchdown since the runway is only 25' wide and I don't want to do battle with crosswind gusts and light wheels. The intent is just to shorten the transition from sluggish aircraft through skittish land vehicle to relatively stable land vehicle.




Heheh, that's cute, quoting book performance like a good little student.

Home drome is 2700', now throw in a decent load in the airplane (full fuel, I have extended tanks, two butts in the seats) plus a 100-degree summer afternoon, and you'll need to carry a little more speed on short final because the runway is only 25' wide and you've got 5 gusting 11 cross component. Now go show me book performance.
Click to expand...

Do you have manual flaps? If so, ok. If you have electric flaps you are are actually lightening the wings at the time you most desire weight on the wheels, while taking away the drag when it does the most. If you stall the plane onto the runway, a 172 will roll to a stop in under 1000' with no brakes applied.
 
airguy said:
Home drome is 2700', now throw in a decent load in the airplane (full fuel, I have extended tanks, two butts in the seats) plus a 100-degree summer afternoon, and you'll need to carry a little more speed on short final because the runway is only 25' wide and you've got 5G11 cross component. Now go show me book performance.
Click to expand...

Home drome is 2400 feet, and 2000 doesn't faze me at all.

I can stop under 1000 feet almost every time with normal, not short field, procedures. Why can't you?

That 530 feet figure should tell you where you need to start worrying about field length, at least at sea level. Twice as long as that is plenty of margin, and every pilot should be capable of meeting that spec. If you need short field procedure at four times book value, you need to fix that.

And you have landing performance tables for that hot day, too. 100 deg at sea level needs 565 feet roll. How did that 35 extra feet (well, 70 with the factor-of-two margin) turn into 1500? I've never even seen 5G11 reported; it's almost understood with "calm" winds. That's not a lot of crosswind and SHOULD account for a whopping extra 3 knots. And the book value is for max gross weight. I hope your two butts in the seats and full tanks don't exceed that.

You're having trouble because you're approaching and perhaps landing too damn fast, not because your flaps need to get raised. Not that this is a rare affliction; quite the contrary. It's just that pilots who operate on 1/2 mile fields need to get that under control.

Honestly, if two King Airs can land in 2400 feet every evening (and even the occasional small jet can as well), we should be able to do just fine in a small airplane approaching at half their speed.
 
Last edited:
Henning said:
So, why don't airliners pick up the flaps on touch down?
Click to expand...

Do the spoilers cancel out the lifting effect of the flaps? If the lifting effect of the flaps is canceled out by the spoilers, does leaving the flaps extended aid in aerodynamic braking due to the extra drag, without detracting from wheel braking?
 
dmspilot said:
Do the spoilers cancel out the lifting effect of the flaps? If the lifting effect of the flaps is canceled out by the spoilers, does leaving the flaps extended aid in aerodynamic braking due to the extra drag, without detracting from wheel braking?
Click to expand...

Correct, now, when you have flaps 30°+ in you are producing no more lift than with 10°, but you have added drag for added aerodynamic braking. With electric flaps, if you are hitting them to retract right away, you are taking away that drag when it is working for you most and you shouldn't be standing an the brakes yet anyway and lengthening your run in that aspect. I'm sure that with a test pilot that reproduced exacting standards that dumping flaps made some difference.

I personally have no problem with the practice, but in reality, I have never seen it be that much of an issue, but then I have a lot of time in twins where I can get into a lot of fields it isn't exactly safe to get out of. Performance wise no worries, but if one fails I die quickly. Even so, I could reasonably safely operate the 310 off 2000' at my normal flying weight.
 
Henning said:
So, why don't airliners pick up the flaps on touch down?
Click to expand...

A 140 knot, 400,000 lbs. airliner is a little different than a 2,500 lbs Cessna. They are too busy deploying thrust reversers and getting the plane slowed down. They'd rather use brakes(which have anti-skid) than have the pilots fumbling around with flap levers.

Their landing figures aren't based off flaps being moved on touchdown. Most of them don't even factor in thrust reversers(in case they don't deploy). For the most part runway length is not a factor for airliners because of the size of airport they fly into.
 
Gucci Pilot said:
A 140 knot, 400,000 lbs. airliner is a little different than a 2,500 lbs Cessna. They are too busy deploying thrust reversers and getting the plane slowed down. They'd rather use brakes(which have anti-skid) than have the pilots fumbling around with flap levers.

Their landing figures aren't based off flaps being moved on touchdown. Most of them don't even factor in thrust reversers(in case they don't deploy). For the most part runway length is not a factor for airliners because of the size of airport they fly into.
Click to expand...

For the most part runway length is even less of an issue for a 172 operating off pavement.;) That's real issue, it is on the bottom of the totem of criticality. It's unnecessary except in extreme cases. Even when everything is a bit ugly, you are better off focusing on control than getting the flaps up to help your braking. Braking isn't likely your best move at high speed when things are ugly, just keep flying the damned plane and it won't come off the runway. It should be an emergency maneuver. If you land at a correct speed and let the nose come down, you are done flying into the air.
 
Last edited:
Henning said:
:D One does slow down quickly.:wink2:
Click to expand...

I have to admit you caught your error pretty fast.

But you gotta be faster than that to get by Fast Eddie!

Seriously, in it's own way it made a case for how easy it is to confuse the gear and the flaps.

Tell me it was intentional and I might almost believe you!
 
Henning said:
For the most part runway length is even less of an issue for a 172 operating off pavement.;) That's real issue, it is on the bottom of the totem of criticality. It's unnecessary except in extreme cases. Even when everything is a bit ugly, you are better off focusing on control than getting the flaps up to help your braking. Braking isn't likely your best move at high speed when things are ugly, just keep flying the damned plane and it won't come off the runway. It should be an emergency maneuver. If you land at a correct speed and let the nose come down, you are done flying into the air.
Click to expand...

Preaching to the choir
 
Gucci Pilot said:
Most of them don't even factor in thrust reversers(in case they don't deploy). For the most part runway length is not a factor for airliners because of the size of airport they fly into.
Click to expand...

Well...except when that land at the wrong field in Branson! :goofy:
 
FastEddieB said:
In general, I try to fly in the same manner as I teach.

And I try to teach to FAA standards.

So, it has become my habit to leave the flaps alone right after landing, and that habit has served me well for the kind of flying I do.

I understand there may be special cases where it's a valid technique.

Alex Wolf is an experienced Cirrus instructor. He recently posted a simulated engine out in a Cirrus to a 2,100' strip:

http://youtu.be/Lew__usHLCE

You can fast forward to about 3:25 for the flaps part.

It looks to me like he raises the flaps just prior to landing, and it seems to work. Not criticizing - in an emergency you do what you need to do and are skilled enough to pull off. Still, it's not a technique I ever recall being taught or teaching.
Click to expand...

I like having my blue knob to pull out for extending the glide. 600 fpm vs 2000 fpm in the video. If I hit my electric flap switch in the flare like he appeared to, it would be 15 sec to reflex position. Aerodynamic braking helps me until under 40 kts, then I slowly lower the nose. I enjoy the challenge of engine out practice.
 
Depending on what I'm in plane and how hard the wind is blowing, I will partially bring the flaps up on touchdown.
For example: In a light sport, with a stall speed of 40kts, full flaps, rolling at 20 kts into a 20 kts headwind means I'm still flying. Raise some flaps to raise the stall speed and now I'm taxiing.
 
Shepherd said:
Depending on what I'm in plane and how hard the wind is blowing, I will partially bring the flaps up on touchdown.
For example: In a light sport, with a stall speed of 40kts, full flaps, rolling at 20 kts into a 20 kts headwind means I'm still flying. Raise some flaps to raise the stall speed and now I'm taxiing.
Click to expand...

Huh?

You land using airspeed, not ground speed. It makes no difference to the aircraft handling whether it's calm or blowing at 20 knots. It does make a difference in the length of the ground roll.

Unless the wind exceeds the stall speed, you'll just touch down slower in the wind.

The one exception is half the gust factor. NOT the total wind. If you did that, you'd be landing on your nose gear in significant wind every time.
 
Henning said:
So, why don't airliners pick up the flaps on touch down?
Click to expand...

Because they do not have propellers to blow crap all over the flaps and possibly damage them. Plus I've been on airliners that do retract them as they taxi in. Possibly habit. To mistake the gear control from the flap control in most aircraft is pretty hard unless your mentally challenged or very new to the airplane type. Pretty absurd subject.
 
Last edited:
Jimmy cooper said:
Because they do not have propellers to blow crap all over the flaps and possibly damage them. Plus I've been on airliners that do retract them as they taxi in. Possibly habit. To mistake the gear control from the flap control in most aircraft is pretty hard unless your mentally challenged or very new to the airplane type. Pretty absurd subject.
Click to expand...
I think the main issue is not people mistaking the flap lever for the gear lever. It's added distraction that is mostly unecessary. That added distraction while fiddling with the flaps can cause you not to focus on other things like maintaining centerline, getting off of the runway when advised, etc.
 
You must log in or register to reply here.
Back
Top