'Dumping' the flaps

Us Musketeer Sport Sundowner Sierra drivers have a huge bumper sticker sized placard "raise flaps to increase brake effectiveness". Makes a huge difference - like speed brakes on a jet. I'll see if I can find a video of my donut struts compressing when dumping the flaps, I'll post it.

First landing after buying this thing I forgot about that placard and made a nice bald spot. I now routinely dump the manual flaps as soon as I get the mains on. Amazing how short I can stop a Sierra, imo. About 700 feet best I can figger when light. Kinda fun practicing bush landings in the thing.

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Clip4 said:
The proximity of the gear and flap switches have nothing to do with it.
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Have you ever went to flare and also pushed the yoke the wrong way?

I still don’t get this, seems like a PIO type of thing.
 
SR22 POH says to retract the flaps on short field landing for maximum braking.
And it makes a huge difference; it also makes a big difference if holding the nose up and doing aerodynamic braking.

Tim
 
Juliet Hotel said:
I've always had a hard time believing getting the flaps up in order to get more weight on the wheels is really going to make all that much difference in a plane that weighs less than 3k soaking wet. Put another way, if that's what you have to do in order to land a particular runway safely, you're landing on the wrong runway IMO. Of course I also don't like landing on any runway that requires the brakes to actually work.
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I like this answer a lot. In the first place, since starting speed is the same whether the flaps are dumped up or left down, the main difference is the amount of weight on the wheels. More weight just means more brake energy is being used, i.e., more heat is being dissipated. So, the stopping distance is "theoretically" the same as long as the brake energy "limit" is not exceeded. You don't see airliners dumping flaps, heck, they add even more drag through spoilers. (Of course, I'm no engineer, my favorite people, btw, so I'm going from experience and a little bit of knowledge of aircraft braking theory).

In the second place, all that monkey motion, arms flapping about reaching for stuff while not looking and thinking enough about it, can do the wrong thing with disastrous results. But, boy, it sure makes you feel important!

Third, in a tricycle, too much forward movement of the yoke (not yolk, you know who you are) puts strain on the fragile (all nose gear are "fragile") nose wheel(s) and less weight on the wheels that count. Go into "wheelbarrow mode", and the brakes, er, wheels are off the ground altogether.

Speed is the enemy, not weight, imo.
 
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Nope. Just as retracting flaps drops the tail on a taildragger, so it loads the mains of a nosedragger. I have a hard time believing anyone would argue that. Furthermore, with flaps retracted the trike pilot can pull back on the yoke without fear of balooning into the air. Trike guys can fly high performance landings exceptionally well and a big part is retracting the flaps.
 
dtuuri said:
I like this answer a lot. In the first place, since starting speed is the same whether the flaps are dumped up or left down, the main difference is the amount of weight on the wheels. More weight just means more brake energy is being used, i.e., more heat is being dissipated. So, the stopping distance is "theoretically" the same as long as the brake energy "limit" is not exceeded. You don't see airliners dumping flaps, heck, they add even more drag through spoilers. (Of course, I'm no engineer, my favorite people, btw, so I'm going from experience and a little bit of knowledge of aircraft braking theory).

In the second place, all that monkey motion, arms flapping about reaching for stuff while not looking and thinking enough about it, can do the wrong thing with disastrous results. But, boy, it sure makes you feel important!

Third, in a tricycle, too much forward movement of the yoke (not yolk, you know who you are) puts strain on the fragile (all nose gear are "fragile") nose wheel(s) and less weight on the wheels that count. Go into "wheelbarrow mode", and the brakes, er, wheels are off the ground altogether.

Speed is the enemy, not weight, imo.
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Wrong on many fronts.
Airliners use spoilers not for drag but to dump lift. With the lift largely removed by the spoilers, flaps become significantly more drag than lift so raising them would be detrimental to braking.

On a tricycle plane, raising the flaps can allow significant aerodynamic braking. In a low wing aircraft, ground effect allows the plane to fly a few feet off the ground significantly lower than stall speed. Raising the flaps allows the pilot to raise the nose and perform aerodynamic braking without fear of the plane flying in ground effect and landing on the nose wheel.

Also, raising the flaps reduces the chance of flat spotting your tires by putting weight on the wheels. This also increases directional control in a crosswind.

Tim

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Heh, heh, I out-thought myself.:oops: But not by too much, I bet.

Stewartb said:
Nope. Just as retracting flaps drops the tail on a taildragger, so it loads the mains of a nosedragger.
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You're right, it adds weight to the mains and that's where I had a brain phart. In other comparisons in the back of my mind, like in the same model planes in the same configuration except for weight, what I said was true. In this case, not. Because the configuration is different—the lower flap setting is the cause of the "weight" gain, which makes use of more brake energy available. Kudos to you.;)

That said, the "gain" isn't all profit because you lose aerodynamic drag, assuming both aircraft hold the nosewheel just barely touching the ground in the same attitude and the landing was full stall. So, I bet you could measure the difference with a 50' tape.

tspear said:
Wrong on many fronts.
Airliners use spoilers not for drag but to dump lift. With the lift largely removed by the spoilers, flaps become significantly more drag than lift so raising them would be detrimental to braking.
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Touche! See above.

tspear said:
Raising the flaps allows the pilot to raise the nose and perform aerodynamic braking without fear of the plane flying in ground effect and landing on the nose wheel.
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Try that in a Citation and you'll never slow below 60 KIAS. Dumping flaps trades drag deceleration for more effective braking deceleration. You may benefit, but not worth the effort, imo.

tspear said:
Also, raising the flaps reduces the chance of flat spotting your tires by putting weight on the wheels. This also increases directional control in a crosswind.
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Good technique reduces flat spots best. Except "possibly" on glare ice with a strong crosswind, more rudder increases directional control best, imo.
 
James331 said:
I never got the grabbing the gear by mistake OWT.

Maybe it’s the planes Ive flown, but I don’t see how you could confuse the two and grab the gear instead of the flaps, especially in manual flap planes.
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You probably haven’t flown too many pre-1984 Beech Barons/Bos.

The phenomenon of grabbing the wrong lever in Beech planes was a problem enough that it was the subject of its own NTSB study.
 
I made it a habit to retract flaps right after every landing in a 172. I then pull back on the yoke and the plane slows really quickly. Also if there is any cross wind it makes the plane less likely to drift because if it. A win win


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Dan Thomas said:
I know of at least two instances, one in the flight school where I worked and another at a nearby flight school. Ours was a CPL undergoing flight proficiency assessment, and in the rollout he grabbed the gear handle and raised it. The examiner whacked it down real quick before the gear went up. The other flight school wasn't so lucky; in their twin the student raised the gear instead of the flaps, and got what was demanded. Expensive.

It's not an OWT thing. It happens. You gotta be paying attention. LOTS of attention. With manual gear handles it's less likely, but some retracts have manual gear handles, too.
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Then the plane that the gear raised while on the ground had a maintenance problem. It will only happen if the squat switch is not working, or if the wheels leave the surface again after landing. The squat switch deactivates the gear system when it has weight on it. (And yeah, I am not going to raise the handle while on the ground to check the squat switch)

All planes I have flown the flap switch does not have to be pulled out to raise or lower the flaps. All retractable gear planes I have flown requires the gear handle to be pulled out a little before it can be raised or lowered. So when I raise the flap handle I just put one finger under the little flap shaped handle and raise it.

I fly for a living (when I have a medical) and I have tens of thousands of landings, mostly on non paved surfaces, and I just don't mistake the flap handle for the gear handle. The shape of the handles and locations tell me which one it is. But yes I agree, a low time pilot or the pilot that does not fly often should leave the flap handle alone.
 
Zeldman said:
All planes I have flown the flap switch does not have to be pulled out to raise or lower the flaps. All retractable gear planes I have flown requires the gear handle to be pulled out a little before it can be raised or lowered. So when I raise the flap handle I just put one finger under the little flap shaped handle and raise it.
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Ditto.

Furthermore, my CFI instilled in me to use my pinky finger to raise the flaps on rollout. I've not flown a plane yet where my pinky finger can overcome the gear handle detent. Not saying they don't exist, but apparently I don't have access to one if they do exist.
 
It sounds like most of these posts are describing landings made with excessive speed. Except for gusts, there should be no ballooning of floating after touchdown with the stick full aft.
Maybe I am just too accustomed to STOL landings with little to no energy left at touchdown and very little ground roll.
High speed landings give me the willies.
 
IK04 said:
It sounds like most of these posts are describing landings made with excessive speed. Except for gusts, there should be no ballooning of floating after touchdown with the stick full aft.
Maybe I am just too accustomed to STOL landings with little to no energy left at touchdown and very little ground roll.
High speed landings give me the willies.
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Has to do with more than excessive speed, in a cross wind or some float ops being able to quickly zero the faps has benefits, or being able to work them.
 
jordane93 said:
Unless you’re regularly flying into a short field, I don’t see a reason to touch anything until you’ve cleared the runway. Focus on your roll out and exiting the runway.
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Agreed. Pilots seem to have a strong psychological need to do something right after landing. There’s rarely any need to, and FAA guidance suggests not messing around in the cockpit until stopped clear of the runway.

Back to the OP, I would say that in general, any configuration changes during the landing process is a bad idea. Accident stats show that landing is challenging enough that there’s no need to add distractions. And in this case, except in very edge cases, there’s previous little to be gained by it. In fact, giving up aerodynamic drag while landing seems counterproductive.
 
If anyone cares about FAA guidance on the matter:

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I understand the advantage of retracting flaps on touchdown to increase braking but haven't yet been in a situation tight enough to need it. So, except for touch and goes (where there is enough room not to need it for a normal landing, rollout, reconfiguration for takeoff, and takeoff) I wait.
 
IK04 said:
It sounds like most of these posts are describing landings made with excessive speed. Except for gusts, there should be no ballooning of floating after touchdown with the stick full aft.
Maybe I am just too accustomed to STOL landings with little to no energy left at touchdown and very little ground roll.
High speed landings give me the willies.
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Your avatar shows a Skywagon. So you have Skywagon time? Hard to believe anyone with Skywagon experience doesn’t understand dumping flaps. Let alone a Cub. My last Cub flight had me landing in 20G28 winds from 40* off heading to a strip next to mountains lined with 75’ trees and houses. My stall speed is 18mph. It was a rodeo getting it on the ground and the moment I did I dumped flaps. I couldn’t taxi otherwise. My normal Skywagon strip is plenty long at 1100’ but only 15’ wide. The wind blows there. To land in 30mph winds, buck the wind rolling over the trees, and hit the strip isn’t usually difficult but controlling the plane on the ground isn’t forgiving. Yep, you guessed it. I dump flaps when the wind’s blowing. Every pilot I know that flies actual STOL strips does.
 
Zeldman said:
Then the plane that the gear raised while on the ground had a maintenance problem. It will only happen if the squat switch is not working, or if the wheels leave the surface again after landing. The squat switch deactivates the gear system when it has weight on it. (And yeah, I am not going to raise the handle while on the ground to check the squat switch)
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The airplane was an R182, and the squat switch on those is on the nosegear, which does not even begin to compress after landing if the landing is done nicely and the nose is held up for drag. The squat switch was still closed and the pump began to run. And I was the chief of maintenance there, and that airplane had no issues. The squat switch location is a weakness of the design; can't put it on a main oleo because there ain't any main oleos.
 
dtuuri said:
. You don't see airliners dumping flaps, heck, they add even more drag through spoilers. (Of course, I'm no engineer, my favorite people, btw, so I'm going from experience and a little bit of knowledge of aircraft braking theory).
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Airliners have reverse thrust that offers massive braking capability. They don't need to fool with retracting flaps. WE don't have reverse thrust to play with.

And those spoilers are powerful drag devices, not just for dumping lift as another poster suggested. Some of the Hawker bizjets use only those spoilers for braking; they have no reverse thrust machinery. A friend who flew them told me that the spoilers would throw you up against the shoulder harness.
 
Stewartb said:
My last Cub flight had me landing in 20G28 winds from 40* off heading to a strip next to mountains lined with 75’ trees and houses. My stall speed is 18mph. It was a rodeo getting it on the ground and the moment I did I dumped flaps.
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What kind of Cub? I used to tow rags in a 180hp Supercub that had extended wings. I've put it down on runways with 21kt direct 90 degree crosswinds. Never touched the flaps, held centerline fine, taxied fine. Shrug.
 
I call BS.

My Cub is exp. Back Country Rev 2. Slats, 112” split flaps, 39’wingspan. I had a round tipped PA-12 with -18 flaps prior. I know the limitations of a stock wing Cub, too.
 
You can call whatever you want. I know what I did. The plane had extended wings with droop tips, 180hp engine with an oversize climb prop (typical banner plane mods). I called unicom to ask if they were using 6 or 24. Guy said winds are 150@21 so runway choice is yours. I used 24 because the downwind worked for where I was coming from. I wasn't sure I'd have enough rudder for it but I figured no harm in taking a stab at it and seeing if she held the centerline on approach. Held the centerline with rudder travel to spare so went ahead and landed. Rolled out on the centerline, got it slow and put the tail down, the turned off and taxied in. The FBO guy was already outside when I rolled up. Said when he heard 'supercub downwind for 24' he put his coat on because he thought we was going to see an accident.
 
Juliet Hotel said:
Rolled out on the centerline, got it slow and put the tail down...
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"Put the tail down?" Uh, I think this disqualifies you from this argument. Anybody who can't ride a bucking bronco down through the trees and three point it (while rolling their own cigarette) can't take advantage of the marginal extra braking action due to flap retraction. As the flaps come up, the tail drops, so I'm told, so the wings produce even less negative lift to assist with braking action. Wheel landings increase landing distance, imo, because landing speed is it's #1 enemy.
 
Does not apply to the cub (but who knows with all the crazy wing mods these days), if you have a Robertson stol, or another droop aileron system, zeroing the flaps is more pronounced lift wise
 
I'd never remove the flaps in the flare. Only once the wheels were on the ground (and even then unless you have serious braking issues it's not going to matter much).
I once was flying a Cessna 150 that had one of those "hold down to lower, lift up to raise" flap controls. I'm coming into land and have gotten the flaps down to full extension. As I'm rounding out I realize I'm going "faster". Fortunately, it's a fairly long runway. I look down and the flaps are retracted and the flap lever is in the RAISE position. After playing with it on the ground a bit I find it is possible that if you yank your finger off just right from the depressed position the lever will bounce up into the RAISE detent and retract them all.

I do have a friend with an older 172 that really manipulates the MANUAL (couldn't do it with electric flaps or the slow hydraulic navion flaps). He starts his take-off run with them retracted, pulls it to ten, rotates, and then takes them out when he gets a few knots more speed (ten degrees get you off the ground faster in the 172, but hurts your climb to 50'). He probably dumps them on wheel touch down too, but I've never seen him have to get into a field that tight.

I found out the hard way that the Navion will do an incredibly short ground roll with the flaps down, but it won't climb worth crap (if they'd just come up quicker, I might be able to use that).
 
dtuuri said:
"Put the tail down?" Uh, I think this disqualifies you from this argument. Anybody who can't ride a bucking bronco down through the trees and three point it (while rolling their own cigarette) can't take advantage of the marginal extra braking action due to flap retraction. As the flaps come up, the tail drops, so I'm told, so the wings produce even less negative lift to assist with braking action. Wheel landings increase landing distance, imo, because landing speed is it's #1 enemy.
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When you don’t agree or understand you get offensive. If that’s supposed to reinforce your position? Epic fail. It’s fine that you don’t understand. What’s odd is that you think your perspective establishes a baseline for right or wrong. Maybe you should get some advanced STOL training in a taildragger in real STOL conditions. Then we could discuss these things again.
 
flyingron said:
I found out the hard way that the Navion will do an incredibly short ground roll with the flaps down, but it won't climb worth crap (if they'd just come up quicker, I might be able to use that).
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That seems to be true for all North American designed aircraft. Also very true for the B-25 and T-6.
 
Stewartb said:
When you don’t agree or understand you get offensive. If that’s supposed to reinforce your position? Epic fail. It’s fine that you don’t understand. What’s odd is that you think your perspective establishes a baseline for right or wrong. Maybe you should get some advanced STOL training in a taildragger in real STOL conditions. Then we could discuss these things again.
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Lighten, it was meant to be humorous. I can't see anything serious about dumping flaps in the middle of landing or for that matter on takeoff. Once I was checking out somebody in a Cherokee who hadn't flown in a while, so I asked him to do a short field takeoff. I thought he didn't hear me right because he didn't use any flap. But right at liftoff he reaches down and yanked the flap handle straight up and zoomed back on the stick. "Geezus," I said, "What do you do, drive a truck?" Guess what? He did! I'm in favor of smoothness, not herky jerkiness. The latter strikes me as plain silly.
 
dtuuri said:
But right at liftoff he reaches down and yanked the flap handle straight up and zoomed back on the stick. "Geezus," I said, "What do you do, drive a truck?" Guess what? He did! I'm in favor of smoothness, not herky jerkiness. The latter strikes me as plain silly.
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FWIW, that is actually the published short field technique for the 1948 Cessna 170.
 
dtuuri said:
Wheel landings increase landing distance, imo, because landing speed is it's #1 enemy.
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Not if a wheel landing is done properly. We're not talking of touching down with the tailwheel three feet in the air; it only need to be a few inches off, which means that the touchdown speed is very little more than three-point touchdown speed, and on touchdown the tail is then raised to reduce the lift and the brakes and elevator are modulated for max traction and braking. I've landed a 185 in 250' on grass doing that. Lots of experienced bush guys do it. Some even use a bit of power to maintain elevator effectiveness and get the tail so high that there's no lift at all and lots of traction, more traction and brake effectiveness than there is in added thrust. That sort of thing is only for the very experienced. Very.

Tail-high wheel landings are for strong crosswinds. Get things done one at a time to help maintain control. Upwind wheel, downwind wheel, tailwheel when rudder effectiveness is decaying.
 
Fearless Tower said:
FWIW, that is actually the published short field technique for the 1948 Cessna 170.
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Works with old 172s as well. One doesn't have to be rough or jerky about it. The airplane will accelerate better without the flaps extended, getting to liftoff speed in less distance.
 
Stewartb said:
In a Cessna the wing will fly a lot slower with 40* flaps than when clean. That’s the point of retracting them. Flight over.

BTW, with enough horsepower up front a Cessna will perform it’s shortest takeoffs using 40* flaps.
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I did some practice 40 deg flap landing today as my CFI told me my DPE likes them. I usually do 20deg in the 182. What a difference. 40 you gotta really flog it on final for instrument approach glide slope. Flare very different beast
 
Fearless Tower said:
FWIW, that is actually the published short field technique for the 1948 Cessna 170.
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Well, if someone wants to use that procedure in a Cherokee, the least they can do is warn the CFI. Jeepers.

Btw, a POH for a 1957 230 hp C-182 with manual flaps does NOT mention that technique, nor dumping flaps for short field landings. The distance required is about 1200' (zero wind, average weight) over a 50' obstacle. Of that, 500' (approximately) is for ground roll. So, using normal published technique and a thumb rule for minimum landing distance (able to make a full stall within the first third of the runway), the safe distance for attempting a landing with a 50' obstacle is 1800'. Not many private pilots are going to try that, so that makes sucking up the flaps all the more needless in normal operations.

As to Shepherd's comment, "You don't dump the flaps to slow down, you dump the flaps to stop flying," I'd say it's exactly reversed—you should stop flying first so there's no need to dump flaps at all.
 
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dtuuri said:
As to Shepherd's comment, "You don't dump the flaps to slow down, you dump the flaps to stop flying," I'd say it's exactly reversed—you should stop flying first so there's no need to dump flaps at all.
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You dump the flaps to reduce the lift that's still there. Flaps increase lift at lower speeds. Just because we're on the ground doesn't mean that the lift is all gone.
 
Dan Thomas said:
You dump the flaps to reduce the lift that's still there. Flaps increase lift at lower speeds. Just because we're on the ground doesn't mean that the lift is all gone.
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Yep. If I would have been thinking more quickly when as a low-timer I was caught by a quartering tailwind (because not paying attention to the right things), I could have saved a prop strike and engine tear down (and a wing tip).
 
It depends on the airplane, but at some point, adding more flaps does not increase the lift, but just increases the drag. The C172's with 40 degrees of flaps come to mind.

Flaps? I dunno, if I don't have 6,000 feet of runway available to me in the Arrow, I will divert to an airport with arresting wires.
 
A 172 only needs power to bring 40* flaps to life. Fly a 210hp XP sometime. It's the same wing as the big brothers in the 100 series and they do great at 40*.
 
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