Retracting flaps all at once causes loss of lift?

[RyanB]

Ok, so i know during go arounds it is taught that you retract flaps to the lowest degree until you get a positive rate of climb then you retract the rest. By retracting them all at once it causes a loss of lift. Yesterday I was out practicing some sim. engine failures to landing. On one of them I was on base, had the runway made so i put 10 degrees of flaps down which is the first degree in the 152 (10, 20, 30 degrees). So i lowered the first degree to 10 on base then i decided I'm going to try a no flap landing so i retracted that 10 degrees so then I had no flaps in. Right after doing it I thought about, should I have had a positive rate of climb before bringing that 10 degrees flap up? I might have just felt the slightest drop in lift when i did it, because, as i was on base i was obviously descending already and i took away that first notch of flap so it might have put me in a slightly higher rate of descent. Did I do something that was dangerous? should i have had a positive rate before i lifted that 10 flap up? or was it okay being that i had plenty of altitude? Opinions?

 

[FORANE]

Sure does.
Crashes have occurred as a result of removing flaps too fast. I was almost one of them. I made that rookie mistake as a student pilot and sake towards the runway fast. It is really hard to overcome the instinctive pull back on yoke when the ground is coming at you.

 

[dtuuri]

...I was on base ... should I have had a positive rate of climb before bringing that 10 degrees flap up?

On base leg? C'mon.

You should use your elevator and flaps together so as to not wake up any sleeping passengers with a sinking feeling.

dtuuri

 

[RyanB]

I know removing them all at once does cause loss of lift, which is why you don't retract them at once on a go around. But being 1500+ feet in the air when only having 10 flap down then removing the 10 flap while on base. Could that have caused anything significant of does it only have major effects close to the ground, such as a go around?

 

[Jimmy cooper]

I know removing them all at once does cause loss of lift, which is why you don't retract them at once on a go around. But being 1500+ feet in the air when only having 10 flap down then removing the 10 flap while on base. Could that have caused anything significant of does it only have major effects close to the ground, such as a go around?

I don't see how, 10 percent is very little. At 1500 feet of little consequence.

 

[Hank S]

The caution about removing flaps all at once is from the landing flaps that you choose. In a Skyhawk, I normally took them out 10º at a time. On a go around with 30º flaps, get positive rate of climb and raise to 20º, make sure nothing is coming at you [hills, trees, towers, anything you want to climb over], then raise to 10º, give her a little time to climb and raise them the rest of the way.

I don't see how a 152 would be significantly different.

 

[flyingron]

You should read your POH. The go around procedure in many Cessnas is to bring the flaps to 20 degrees while going to full power.

In planes like electric flapped cessnas (or my hydraulic flapped Navion), it's hard to retract them too quickly, the motor just doesn't run that fast. I always laugh when someone is "slowly raising the flaps" in a 172 by moving the handle to 30 waiting until the indicator catches up and then immediately moving it to 20, ... they might has well have just set it at zero.

 

[Timmer]

There are different techniques. I've been taught to not remove the final 10 degrees of flaps until more than 200' above ground or whatever obstacle you're avoiding. Next time you're doing a go-around, pay attention to the drop you'll get with that final set of flaps: you're losing a lot of lift and not much drag.

It's why a general rule is never to retract flaps once you've lowered them during your approach. You were trying something different, so I don't see any issue with that as long as you're aware you just lost lift and you'll need to account for it.

 

[AggieMike88]

The caution about removing flaps all at once is from the landing flaps that you choose. In a Skyhawk, I normally took them out 10º at a time. On a go around with 30º flaps, get positive rate of climb and raise to 20º, make sure nothing is coming at you [hills, trees, towers, anything you want to climb over], then raise to 10º, give her a little time to climb and raise them the rest of the way.

I don't see how a 152 would be significantly different.

I do essentially the same in the C182

 

[RyanB]

Normal go-around procedure we do is, full power flaps to 10 carb heat cold, positive rate of climb flaps up. The thing is, i wasnt doing a go around. What i did was abeam touchdown point on downwind i did carb heat power to 1500 rpm, flaps to 10. As i was turning base, i decided to do a flapless landing so retracted the 10 degree flaps. Didnt notice a big loss of lift more than i was already descending. The thing im wondering is, was this a dangerous thing to do? Should i have not brought up the 10 until i had a positive rate, even though i was descending on base?

 

[Captain]

It would be wholly inappropriate to initiate a climb on descent to remove flaps for whatever reason unless its to go around. Its pretty weird to be raising flaps anyway. In the situation you described just raise them or leave them and try a no flap on the next circuit.

 

[Timmer]

The thing im wondering is, was this a dangerous thing to do? Should i have not brought up the 10 until i had a positive rate, even though i was descending on base?

No, the positive rate thing is a difference of the '> 200 AGL' concept when doing a go-around. It's there to counter the momentary loss of lift when you're trying to climb and haven't built up excess thrust yet.

You were defending in an approach -- I would be careful of retracting flaps when on an approach and less than a few hundred feet AGL just for the same reason but 500-800' AGL on base as long as you were compensating for it with some power, I wouldn't stop my defending to climb just to raise flaps.

OTOH, I wouldn't use base to reconfigure for a different landing just for giggles. Why change your stabilized approach at that point? Just do the no-flaps landing on the next lap.

 

[RyanB]

No, the positive rate thing is a difference of the '> 200 AGL' concept when doing a go-around. It's there to counter the momentary loss of lift when you're trying to climb and haven't built up excess thrust yet.

You were defending in an approach -- I would be careful of retracting flaps when on an approach and less than a few hundred feet AGL just for the same reason but 500-800' AGL on base as long as you were compensating for it with some power, I wouldn't stop my defending to climb just to raise flaps.

OTOH, I wouldn't use base to reconfigure for a different landing just for giggles. Why change your stabilized approach at that point? Just do the no-flaps landing on the next lap.

Good point, thank you, just was curious about this and how all the "flap retraction/loss of lift worked 100%" I didnt think it was a big deal since i was already descending, but next time i will just wait and retry the landing during the next lap around! Always learning, thats for sure!

 

[poadeleted20]

I know removing them all at once does cause loss of lift,

True to an extent, but that extent varies greatly between aircraft.

which is why you don't retract them at once on a go around.

Depends on what you're flying. You retract them all at once in a Grumman AA-1/5 type because the change in coefficient of lift is insignificant. You do not in the high wing Cessna singles because that change is large. What you do in other planes varies depending on their design.

But being 1500+ feet in the air when only having 10 flap down then removing the 10 flap while on base. Could that have caused anything significant of does it only have major effects close to the ground, such as a go around?

Not unless you didn't pitch the plane appropriately to match the change in wing curvature. However, at the speeds one should be flying a 152 on base, it should not be a big deal to do that. Seems to me based on your post that you know how to control your plane, and you did. Worry about something else, and move on.

 

[RyanB]

Thanks for the input Ron, as i have said, every time I go up it is a learning experience.

 

[mikea]

When you have a Cherokee heavy the main worry is that you're ready to immediately lower the nose into the no-flaps attitude. When you have lotsa excess power you aren't gonna sink so much.

Like: my CFI always yelled at me and drilled it into me that it won't climb with full flaps. It certainly will.

I think the wisdom is for youse guys in Cessnas with 40 degrees of flaps.

 

[brcase]

<snip>

Like: my CFI always yelled at me and drilled it into me that it won't climb with full flaps. It certainly will.

The reason your CFI yelled at you was to instill the fact that while most the time it may climb there are times when it won't. Heavy and/or high density altitude it is a lot more important to get the plane configured properly. The big concern is getting the plane behind the Drag curve in such a way that you can't climb. I once watched a 250 Commanche take off but was horsed off the ground in less then 1500 feet. At 5000 feet and at the end of the runway he was still nose high and only 5 feet off the ground in ground effect as he went off the end of the runway and crashed. All walked away.

As to the OP's question. As long has keep you speed up there is no issue retracting flaps, this is true even in the go around situatiation, but it may not be possible to accelerate well with out loosing altitude, So we teach it is better to bring them up slowly to reduce drag and give the plane time to accelerate. While descending for landing this is not much of an issue as long as you maintain your airspeed as you do so, since you are descending already.

As an extreme example that doesn't really apply to most planes my glider has flaps that go from -10 degrees to 90 degrees and are quickly and continuously adjustable. They reduce my 38:1 L/D to 2:1 at 90 degrees. Often once I turn final I simply point the glider to the point just short of where I want to land and add or reduce flaps to maintain my 50kt approach speed. This works as long as I maintain a steep approach. Shallower approaches will require I pitch down as I add flaps to maintain airspeed.

Brian
CFIIG/ASEL

 

[poadeleted20]

As to the OP's question. As long has keep you speed up there is no issue retracting flaps, this is true even in the go around situatiation,

As I said above, that depends on the airplane.

The dramatic change in both wing area and maximum lift coefficient you get with the Cessna 150/152/172/etc means that stall speed changes significantly between zero flap and full flap. That means you could be flying fine with 30-40 flaps in those planes, but complete flap retraction will put you so close to stall speed that you can't maintain altitude and accelerate. The dramatic change in wing curvature you also get with those means you need a significantly greater pitch attitude for the same flight path/angle of attack when flaps are retracted, so even with enough speed, you need to rotate the nose pitch up significantly to maintain the same amount of lift at the same speed. Put those two together, and complete flap retraction at over-the-fence speed could put you in the ground before you get things organized.

OTOH, the Grumman AA-1/5-series planes have almost no change in maximum lift coefficient between full flap and zero flap. As a result, you will not raise stall speed enough to make that a problem if you completely retract the flaps all at once in those planes. The necessary pitch attitude to obtain the same angle of attack does change significantly during flap retraction, but it's not hard to pitch the plane to compensate during retraction. Further, since the flaps on the Grummans contribute a lot of drag but little lift, getting rid of that drag so you can accelerate is very important. The Diamond DA-40 is much the same in these regards. Take a look at the straight, narrow-chord flap design on the Grummans and Diamonds, and compare that to the wide chord, Fowler-type slotted flaps on the Cessnas I mentioned and you'll see the differences which drive these characteristics.

but it may not be possible to accelerate well with out loosing altitude,

Again, that depends on what you're flying.

So we teach it is better to bring them up slowly to reduce drag and give the plane time to accelerate.

In some planes, yes; in others, no. Know your plane, fly your plane.

 

[JeffDG]

There are many things that one shouldn't do close to the ground that are just fine to do at higher altitudes.

I think the admonition against retracting flaps too rapidly is one of them...if the pitch change or lift change surprises you, you have plenty of air below you to recognize and adjust.

As I'm an advocate of finding out how your plane behaves (within the bounds of safety)...perhaps go out, at a suitable altitude, configure the plane for slow-flight, and pull the flaps up. It'll give you a feel for what the plane would do in a takeoff/go-around situation without the danger of an unintended aircraft-terrain interface.

 

[JimNtexas]

In any Cessna with electric flaps, be sure and visually confirm that the flaps are really moving when you raise the flap handle!

Especially if you are doing a go around on a dark night at a country airport! DAMHIK!!!!!!!!!

 

[flyingron]

In any Cessna with electric flaps, be sure and visually confirm that the flaps are really moving when you raise the flap handle!

Especially if you are doing a go around on a dark night at a country airport! DAMHIK!!!!!!!!!

I had the opposite issue. I was flying an old Cessna 150. This has a toggle switch that you have to hold down to extend the flaps (it springs back to the neutral position) but it will latch in the up position to retract the flaps.

Here I am flying on final having run full flaps down. All of a sudden I'm going faster. I can't figure it out. Fortunately it was a long runway. I look over and see the switch is in the locked-up position. Apparently when I removed my finger quickly from it while extending it sprung up past the neutral position and locked up removing my flaps as the approach progressed.

There's a lesson here. If something unexplained happens, abort.

There was a Continental flight coming in to Houston years ago that due to poor cockpit discipline they had neglected to turn up the hydraulics. In the -9 you don't get the gear down if you do that. The first officer was flying and realized there had to be some configuraiton problem as the airplane wasn't slowing down like usual. Unfortunately when relaying this to the captain, the captain just kept saying it was OK and eventually took control and proceeded to execute a nice belly landing.

 

[jtheune]

I know removing them all at once does cause loss of lift, which is why you don't retract them at once on a go around. But being 1500+ feet in the air when only having 10 flap down then removing the 10 flap while on base. Could that have caused anything significant of does it only have major effects close to the ground, such as a go around?

Why are you at 1500+ feet on base?

 

[poadeleted20]

I think the admonition against retracting flaps too rapidly is one of them...if the pitch change or lift change surprises you, you have plenty of air below you to recognize and adjust.

If the pitch change or lift change surprises you, you weren't properly trained. Holding the plane at about 1.2 Vs0 and running the flaps from full up to full down while holding that airspeed is part of every type checkout I give, and should be part of primary training for every fixed wing pilot. There shouldn't be any surprises left about the pitch/lift changes for flap extension/retraction for anyone signed off in any airplane.

 

[denverpilot]

If the pitch change or lift change surprises you, you weren't properly trained. Holding the plane at about 1.2 Vs0 and running the flaps from full up to full down while holding that airspeed is part of every type checkout I give, and should be part of primary training for every fixed wing pilot. There shouldn't be any surprises left about the pitch/lift changes for flap extension/retraction for anyone signed off in any airplane.

That's a very good thing to do. The pitch change necessary in the 182 is fairly dramatic but if you're prepared for it, and have the speed, you can select 0 and pitch (and trim a bunch if you don't have ape arms!) and just keep pulling...

It's a coordination test. Are you as smooth as a small motor running relatively slowly?

 

[kgruber]

In most airplanes, and all spam cans, as long as the airspeed is in the green arc, retracting flaps will increase lift.

One will have to pitch up in most airplanes because of a trim change. The only difference will be less margin between your current airspeed and stall.

The only range of airspeed where flaps add more lift than drag is below the green arc.

 

[poadeleted20]

In most airplanes, and all spam cans, as long as the airspeed is in the green arc, retracting flaps will increase lift.

If that were true, then stall speed would be higher with flaps down than with flaps up. I can't think of an airplane where that is so.

One will have to pitch up in most airplanes because of a trim change.

The main reason you have to pitch up to avoid losing altitude during flap retraction in all non-slatted airplanes is that the trailing edge is moving up, changing the effective incidence angle of the wing, and reducing the angle of attack at the same pitch attitude. The lesser reason for that is with Fowler type flaps, wing area is reduced during retraction. Either way, total lift is reduced nd angle of attack must be increased to maintain the same total lift at the current airspeed.

As for trim, it varies with design. While most light planes have a net pitch moment change requiring more nose-up trim during flap retraction and nose-down during extension, a few go the other way.

The only range of airspeed where flaps add more lift than drag is below the green arc.

...i.e., below flaps-up stall speed, and I would agree with that. Other than that, L/D always goes down with flap extension.

 

[kgruber]

Ron,

Easy enough to prove for yourself. Take your Tiger up and hold altitude at the bottom of the green with a clean wing.

Now deploy a notch of flaps. Let the airplane stabilize at the bottom of the green and report back if you are now climbing or descending.

Without doubt, you will be in a descent.

 

[Timmer]

Won't that be due to higher drag at higher speeds overriding the small amount of increased lift?

 

[poadeleted20]

Easy enough to prove for yourself. Take your Tiger up and hold altitude at the bottom of the green with a clean wing.

Now deploy a notch of flaps. Let the airplane stabilize at the bottom of the green and report back if you are now climbing or descending.

Absent some power, pitch or trim input, if I do that, the airspeed will not stabilize at the bottom of the green arc, i.e., at the same speed it was before I extended the flaps. Not in my Tiger, not in anything. That would require there to be zero pitch moment change between flaps up and flaps down at the same speed, and no plane I know does that. But if the airplane does stabilize after doing that (albeit at a different airspeed), the wing will be developing exactly the same amount of lift as it was before I extended the flaps (minus the weight of the fuel burned in the interim). If it is descending at that point, it will not be due to a lower amount of lift, but rather due to insufficient power to maintain altitude in that configuration at that speed.

For further study on this, I suggest Dr. John S. Denker's excellent "See How It Flies" web site, which is well-written for the less technically inclined and includes a lot of excellent graphics to help understand the materials. For those for who took and still remember some advanced math (preferably but not necessarily including calculus), Prof. Harry Hurt's "Aerodynamics for Naval Aviators" is the most popular text (although the graphics date from the 1950's), and it's available as a free download in ForeFlight's documents section.

And yes, that's the same Harry Hurt known for motorcycle safety research.

 

[kgruber]

Ron,

I understand your wanting to obscurate this discussion with gobbledigook.

But it is VERY simple. I maintain that at green line the clean wing has more lift than with the addition of any flap.

You take exception to that. My test, as outlined in VERY SIMPLE terms above will prove either you or me correct.

I HAVE done it and guarantee the addition of flap will cause more drag than lift and the airplane will descend.

If you don't want to test this, fine. But you are still incorrect in your knowledge.

 

[poadeleted20]

I understand your wanting to obscurate this discussion with gobbledigook.

Then you understand something which does not exist. I merely wish to point out that you made several fallacious statements which directly contradict the laws of aerodynamics.

But it is VERY simple. I maintain that at green line the clean wing has more lift than with the addition of any flap.

I know of no "green line" on the airspeed indicator. However, if you are talking about the bottom of the green arc, then that would depend on how much power you are developing. If the engine is at idle, then the bottom of the green arc is (at least at maximum gross weight) where the clean wing stalls. In that case, the wing is developing near zero lift, while with flap extended, it is still developing lift (unless there is no change in stall speed with flap extension, and I've never seen that in a light plane). That alone shows the falsity of your statement unless you think zero lift is more than some lift.

You take exception to that. My test, as outlined in VERY SIMPLE terms above will prove either you or me correct.

Your test would prove nothing.

I HAVE done it and guarantee the addition of flap will cause more drag than lift and the airplane will descend.

I never said otherwise. But that doesn't change the fact that the following statements you made are false:
"In most airplanes, and all spam cans, as long as the airspeed is in the green arc, retracting flaps will increase lift."
"One will have to pitch up in most airplanes because of a trim change."
"The only range of airspeed where flaps add more lift than drag is below the green arc."
And your test will not prove the truth of any of them.

Please take the time and effort to do some study of basic aerodynamics via either of the sources I suggested. You'll see the flaws in your statements. And it's my guess that it will take days or weeks for you to get through that material, so please take the time to do so before you respond further.

 

[kgruber]

Then you understand something which does not exist. I merely wish to point out that you made several fallacious statements which directly contradict the laws of aerodynamics.
I know of no "green line" on the airspeed indicator. However, if you are talking about the bottom of the green arc, then that would depend on how much power you are developing. If the engine is at idle, then the bottom of the green arc is (at least at maximum gross weight) where the clean wing stalls. In that case, the wing is developing near zero lift, while with flap extended, it is still developing lift (unless there is no change in stall speed with flap extension, and I've never seen that in a light plane). That alone shows the falsity of your statement unless you think zero lift is more than some lift.

Your test would prove nothing.
I never said otherwise. But that doesn't change the fact that the following statements you made are false:
"In most airplanes, and all spam cans, as long as the airspeed is in the green arc, retracting flaps will increase lift."
"One will have to pitch up in most airplanes because of a trim change."
"The only range of airspeed where flaps add more lift than drag is below the green arc."
And your test will not prove the truth of any of them.

Please take the time and effort to do some study of basic aerodynamics via either of the sources I suggested. You'll see the flaws in your statements. And it's my guess that it will take days or weeks for you to get through that material, so please take the time to do so before you respond further.

My GOD!

What are you talking about, engine at idle? The power in this test is whatever it takes to stay level at the bottom of the green. After that, power is constant.

The only thing that changes is flaps.

Your efforts to sweep your errant tracks are astounding.

I am not going to do your research for you. You are afraid to do the test. Simple and to the point.

Let me know when you get a grasp.

 

[kgruber]

I know of no "green line" on the airspeed indicator.

And just where would I have EVER said that?

 

[poadeleted20]

And just where would I have EVER said that?

Right here:

But it is VERY simple. I maintain that at green line the clean wing has more lift than with the addition of any flap.

You clearly don't understand either the language or the laws of aerodynamics, and also clearly have no interest in learning either. Law of Readiness applies -- no point continuing this further.

 

[flyingron]

I'll have to agree with C'Ron on this. The statement that retracting flaps increases lift is nonsense. It decreases drag for for a couple of reasons, but lift also decreases (but not necessarily in proportion).

Further, the test you propose does not measure lift. You seem to not understand simple physics. Holding a constant airspeed and moving the flaps causes a change in both lift and drag. To hold the same speed when lowering the flaps, you need to overcome the drag. Hence you're not maintaining the same angle of attack. Lift changes dramatically with angle of attack.

As we like to say in my business, everything is deeply intertwingled.