Flap retraction/extension during turn
 

Hello everybody,

I spoke with a lot of coleagues about this issue and oppinions are contradictional. However the precentage of pilots who are against this to be done are eldery guys by my experience so it might be connected to the aerodinamic and operational theories and rules of old days. That is my best guess.
Let ussee your oppinions about this.

Regards

Velez2

Depends on whether you have flap asymmetry protection or not IMHO. If you do, like most proper (ie big) airplanes, then no biggie. If you don't, and it is convenient to do it when wings level, sure. I wouldn't make a big fuzz about it though. Unless the POH says you can't do it, then I'd say it's a matter of personal choice!

Well that is my approximately my oppinion also. However recently I read about a accident (military though) with F84G which has been known to have a protection against simetry (torque shaft or other mechanical interconection between flaps) but newertheless it had had asimetry in extension and crashed. Link failed apperantly.
That kinda changed my oppinion in the direction of do not do it.

Thanks for reply

In ag aircraft, applying flaps while turning and taking them back out as one rolls out of the turn is a common practice. With steep turns at 100' every 30 seconds, all day long, it's little more than added stall margin.

its not a fuss, routine checks have to be done for safety reasons but dont worry about it in the slightest, as the second poster said, a matter of choice

Oh stop it now, C'mon !!!! do you know SNS3Guppy's experiences:\


did you check your OpsSpecs for that A320 dimensions, and performance specifications, which is very completely different, of course, from that A321 that you're on....:rolleyes:

Animus I do not understand?

Nah, he is still looking for that 747 that made him "veer" off 35 degrees with no "slope" in his wings, in 3 seconds over Estonia.

do you have the OpsSpecs for the A320,...if so do they answer A320 performance question...? or at least have you looked at the TERPS Criteria for the A320...don't you know that all operational information is for a type is listed in the TERPS under Far 25

and just too add SNS3Guppy is, amongst other things, an expert Ag pilot...so perhaps you could learn a little here from folks like him, no?

I dont know if you mean that by helpfull advice or nasty criticism

I'm telling u 2 look at ur terps or opsspecs... helpful yo you get ansur :cool:

ax ur job to give u the terps under prt 25..what does it say about the 321:)?

Bad practice to raise flaps in the turn. Reason is, you have very high lift devices deployed. raising them in the turn is a no no on a heavy or high performance jet. If you do raise them you are reducing this extra lift when you need it most. The loss of lift can be very sudden and could happen at the wrong time, if you hit a bumpy patch for example. The stall speed is being increased, (therefore the safety margin decreased), at the very time you dont want it the Vs increased.

I also have done my time in ag flying may years ago. As far as assisting the turn was concerned never used flaps as a rule. I always flew clean and fast but had the flaps as a backup if I thought I needed them, although not very often in my 10 years at it. That technique gave me the extra margin of speed. Speed is my friend.

The one exception was the DHC2 Beaver, on ag work.. It needed the flaps applied in a turn, every turn! IMHO

Just my 2 cents worth.

Your general statement is inaccurate.

I've been raising and lowering flaps in turns for 12 years in heavy 747s (all varieties), and haven't had one stall or fall out of the sky yet. Performance margins are more than adequate in all normal flight conditions -- maybe that's why the 747 FCOM and Flight Handbook say it's allowed...

I agree with 'Intruder', providing you have the speed and are accelerating what's the problem? Modern glass cockpits even show min speed per flap setting. I have been taking flaps up (and down) during turns all my life and cannot see any justification for concern. Just fly the aeroplane, or airplane as you lot call it.

The issue of flap operation during a turn specifically relates to flap retraction which usually means an immediate turn after take-off is the worst case of a climb, low speed and low level.

The problem is that flap retraction starts well below the speed for full manoeuvre protection. For example a 737 taking off with Flap 5, entering a turn at 400' would normally start to move to flap 1 at V2+15 (say 170kts) and accelerating, which means that full manoeuvre isn't available until another 20-30kts. With extension the minimum clean speed would 210kts.

Hence, the 737 FCTM recommends for an immediate turn after takeoff, to select just climb thrust and not to accelerate and retract until the turn is completed.

How flaps are used, or how an airplane is configured, really depends on which aircraft, what operation, and what maneuvering is being done, as well as how much flap is to be used.

In the B747, we have minimum flap retraction speeds on takeoff, for example, and limit ourselves to a 15 degree bank angle until 10 knots over those speeds. If given a turn during the clean-up portion of a departure, I will accelerate to 10 knots over the bug speed for a given flap setting, before bringing up the flaps, in order to use the full bank angle in the turn. With flaps retracted, I'm limited to a 15 degree bank until I accelerate a little more, and then I can use the full bank.

We don't do a lot of wild maneuvering in the 747, obviously. In the case of the ag airplane previously mentioned, indeed many modern ag aircraft, flap use is a regular thing. Many ag operators will use flap in a turn and take it back out as one rolls out of the turn, especially when "heavy." The flap switch on a number of ag airplanes is on the throttle, so the flaps can be thumbed in or out while maneuvering. The flaps increase stall margin and reduce turn radius by allowing one to pull a little more through the turn. Larger turn radius and higher speeds equate to more time spent turning and less doing work, and one usually tries to minimize time spent in the turns, and maximize time spent applying chemical in the field.

Likewise, I've done a lot of low level work in the mountains doing firefighting, and flap application is very important, there. One large four-engine airplane I flew doing fire work required 1/2 flaps on the drop, and this made a 50 knot difference in the stall speed...very important in mountain gusty conditions.

Retracting flaps in a turn is not unsafe, but should be done sensibly. The notion that one should never retract flaps in a turn is nonsensical; a turn has no bearing on flap retraction. The speed and energy one has at the time, and one's relationship to angle of attack and minimum speeds, of course, is very relevant. If one is too slow to retract flaps in the turn, then one is too slow; either speed up or wait. If one has adequate energy, margin, and speed, then by all means, put them up or down in the turn.

Flap assymetry is flap assymetry, whether in the turn or not.

The airplane doesn't know if it's in a turn. The airplane doesn't know it's altitude. The airplane knows nothing...flaps retracted in a turn, flaps retracted at 5' of altitude...the airplane doesn't know or care where or when. The airplane can't think...and is perfectly happy two seconds from impact if you fly it into the side of a cliff. The determining factor, then, is you. Raising the flaps is perfectly safe in a turn, if you do it properly. Raising the flaps at 5' above the ground is perfectly safe, if done properly.

Policies exist in various aircraft, either given by the manufacturer or by the operator, regarding aircraft configuration, flap retraction, etc, and these generally dictate how the airplane will be operated. This doesn't mean that raising the flaps in a turn is unsafe; it does mean that an operator who improperly raises them in a turn, perhaps while too slow or at too steep a bank angle for a given angle of attack and airspeed, may be doing something unsafe.

Now...there's a difference in the way a B747 is configured with flaps, and an Air Tractor AT-802 is configured with flaps, as well as a difference in the airfoils, flap retraction times and methods, complexities, flap type, etc. With the initial applications of flap in the 747, for example, not only are the trailing edge flaps configured, and not only do they extend aft and down to increase the wing area, but two types of leading edge devices are deployed to increase wing camber and change the angle of attack. The 747 is a swept wing airplane with a very large wing and a very heavy weight capability. It's mission is different, and it's maneuvering tends to be a lot more benign than say, a Thrush S2R or Dromader M18T. Never the less, the same basic principles apply.

If one is too slow, then raising flaps may be a bad idea. Sometimes raising flaps can be used to good effect. On many occasions over the years in light airplanes, I've raised flaps as I touch down, or just before touchdown, in a light airplane on a rough surface. It's always a standard practice in ag airplanes, for me, too. Retracting flaps helps positively set the airplane down and keep it down. Standard for me in the 802 or Dromader, for example, is to put the airplane on the mains, pin the mains with some forward stick, then retract the flaps while holding the tail off, lower the tail to the surface, and pull reverse. Others whom I know tend to go right to reverse with the tail in the air. I don't do that. But retracting flaps ensures that an airplane which was just barely flying with full flaps, is no longer going anywhere, and it sticks to the ground...no more lift. It also allows the tail to come down more quickly, which allows braking and or reverse to be more effective, and safer. Retraction of flaps is a useful short-field technique on soft and rough fields...and in the real world of short-field work, short fields are often rough fields...where props toss rocks into flaps, and where power plants and props can suck up rocks, sand, and gravel, and be damaged.

Likewise, in a light airplane such as the 802 (light being a relative term; at 16,000 lbs, it's a heavy single-engine light airplane, but it's also performance-limited at that weight, which means it's also got a reduced maneuvering margin), I commonly retract flaps just after takeoff...often while still in ground effect, though sometimes I'll carry flaps during the climb-out, too (a little flap seems to help). Very often in the M18 Dromader, I'll have takeoff flaps retracted by the time I reach the end of the runway, and will initiate my turn on course from ground effect, at a low level, while doing the flap retraction. Again, it's a matter of being sensible. One knows, even as a student pilot in a Cessna 150, that simply retracting flaps and doing nothing might lead to a descent back to the ground, a stall, a wider turn, etc...all depending on what one's doing at the time. This is no different in a Cessna 150 than it is in a Boeing 747...despite the obvious disparity in complexity and operation. Operate sensibly, and you can most certainly apply and retract flaps in a turn.

Something that hasn't been addressed is maneuvering while applying flaps. Loading the structure and the airplane can have an effect on the wing and flaps, and any time flaps are applied, a load is applied to all the attach points as well as the wing itself. Rolling into a turn or out of a turn with aileron applied and other turn devices (ala 747) can place a different load on the wing and it's associated components than if one applies the flaps in level flight. This is largely inconsequential, however, if one operates the airplane inside the known and published flight envelope, respecting the speeds, weights, bank angles, etc, that apply to a given airplane.

SNS3Guppy

A good and informative post indeed.

As far as ag aircraft go, the guys that did apply flap in turns, had flap motors burning out at a a high rate, on S2R operations, IIRC. That was the last thing I needed on a remote operation, downtime for a burnt out flap motor. I flew the S2R, both Iron and turbine but never felt the need to use flap in a turn however. Can't comment on the Air tractor as I never operated it. There weren't a lot of them around when I last strapped an ag aircraft to my backside.

Maybe I should have amended my original post on this thread, to "high performance, high wing loaded aircraft". That would have not made it necessary for us to bring in the B747 so eagerly. I too flew the B747 classic and it was the easiest and most "forgiving" of the heavy aircraft I have operated.

In answer to the original post on this thread I say this. Think long and hard before raising flaps/high lift devises whilest in the turn. Dont let raising flaps in a turn become a reflex action. I still won't raise the flaps in a turn when I am PIC, or let it be done.

I don't know what or where you fly, but nobody I know tries to retract flaps in "an immediate turn after take-off." In fact, the general rule in airline operations is NO turn until above 400' AGL!

Further, flap retraction after takeoff is done on a briefed schedule DURING ACCELERATION. If the pilot adheres to the flap retraction schedule, adequate stall and gust margin is available to 40+ deg of bank, even though the normal turn is at 25 deg bank and max allowed is 30 deg. There is nothing unsafe about retracting flaps in a turn, as long as the design parameters are met.

this is correct, I certainly would not retract just after take off causing confusion and risks, I think its 450 for the a321

Again, of it's own accord, the action of raising flaps in a turn is of no consequence. If one raises the flaps when too slow or at too high an angle of attack in level flight, one may stall or descend. If one does the same in a turn, one can expect the same result. The turn, then, is irrelevant. Operation of the airplane with respect to it's own limitations is the issue. Not the turn.

One can certainly bring the flaps up immediately after takeoff and while in a turn departing the runway. I've been doing it for years. Put it in context, however, and you'll find that this isn't standard practice in many types of operations. Bringing the flaps up immediately after takeoff, or bringing them up in a turn is perfectly acceptable if done properly and in context.

Whether one is in a heavy aircraft, a high performance aircraft, or not, one need have no concern about raising flaps in a turn, if one does so sensibly and properly. If one doesn't exercise sense or safety, then whether one is in a turn or not is irrelevant.

Intruder,
I referenced the 737, that's what I fly. Where is irrelevant, we use near standard Boeing procedures.
An immediate turn after takeoff is generally defined as normally a turn at 400'. Abnormally is another question. I presume we are talking about normal ops here.
As I wrote.
What type are you referring to? For the 737 it isn't a gust margin or a stall margin, it is a margin to stick shaker and "adequate" is not 40º+, it is 15º + 15º overshoot. "Full" is defined as 25º + 15º overshoot.
For the 737, "full" manoeuvre capability is only "guaranteed" for takeoff flap and V2+15 or the flap setting and the associated flap manoeuvring speed. That means that between V2+15 (flap 5) and say 190kts (flap 1) it may be assumed to be less than "full" manoeuvring capability. The word "guaranteed" is only used in association with the "flap manoeuvre speed" and not the EFIS speed tape "minimum manoeuvre speed" amber band. The amber band is calculated differently. However, Boeing does say that the amber band and the flap manoeuvring speeds are independent means of assuring "full" manoeuvring capability. Which is a slight contradiction to what is written elsewhere. You decide what is safe. For me I will continue follow the Boeing recommended practice for an immediate turn which is unambiguous.

Slightly off topic, but I just have to comment on one thing
Although not airline operations, we normally do 25 degrees of bank as low as 50' in the Kingair B200, out of some airports that have scheduled commercial service. I suspect they (the airline) do the same, since they regularly avoid hitting the hard stuff!

May I just make the point that to comply with Schedule A performance (if that is your a/c performance category) the MIN flap retraction height is 400'. Otherwise, I think SNS3 Guppy has said it all.

By the way, can we all just ignore 'bumpyflight' - the posts are not worth commenting on.

In the 744 the amber band, which is normally well below the flap maneuvering speed, gives a 1.3G stall margin, which is defined as
Since stick shaker is also above stall speed (flying with intermittent stick shaker is the recommended technique for terrain avoidance), it is exceedingly clear that there is adequate stall margin for flap retraction according to the normal schedule, while turning and accelerating after takeoff.

We're starting to get some crossed wires. Just to clarify - I don't think anyone is advocating cleaning up immediately after takeoff - at least not in a 737.

An immediate turn is okay, if specified. Normally it's 400'. (Or 450' in bumpyflight's world. . . http://images.ibsrv.net/ibsrv/res/sr...lies/yeees.gif)

Some SIDs include immediate turns and some have speed restrictions that require us to fly part of the SID at speeds that may require Flaps > 0.

A flap retraction is not recommended on a G/A including a course reversal. (I wonder if there's a certain heading max/min change or radius they have in mind?)

My FCTM is happily buried in a hotel thousands of miles away, so feel free to correct/quote away.

Cheers

The 737 FCOM i have available (20.05.2010) states

"Any speed between V2 + 15 and V2 + 25 knots results in approximately the same takeoff profile, it provides a safe margin above stall for a 30° bank with a 15° bank overshoot. Crosscheck indicated airspeed for proper initial climb speed."

Which equates to a margin sufficient for up to 45° of bank. However there is a bank angle limitation that states max bank angle after take off is 30°, unless your speed is below V2+15 where it is limited to 15°, but still with a margin of 15° of overshoot.

The same applies to cleaning up, a safe bank angle of 30° with an overshoot of 15° is assured once you're above V2+15.

Denti,

I should have stated that I am flying the Classic and that I'm referring to the FCTM of 2008. Ours states 25+15 for full manoeuvring capability.

Anyway, the key point as far as I am concerned is that when you retract flaps on take off using the normal procedure, you will be below the flap manoeuvring speed for the newly selected flap. Whether this is considered unsafe or not is another debate. But that fact is that you are below that speed and as such margins are reduced. This I suspect is the single key issue that must be considered when retracting flaps in a turn after takeoff which is why I associated the immediate turn procedure with this thread.

As I previously stated some of the advice in our FCTM is contradictory and it sounds like this has been cleared up in later versions. Therefore some of this is open to interpretation, but "overshoot" is circumstantially defined as "inadvertent overshoot" (to quote our FCTM). Therefore, unless there is specific guidance that applies the situation in question (such as the written Immediate Turn After Takeoff procedure) and the fact VNAV will command 30º, my view is that 25+15 means that I'll limit my bank angle to 25 (plus minus a degree of human error) and allow 15 for such an inadvertent overshoot. That doesn't mean anything else would be officially or otherwise unsafe, but after gathering all the information and working on a risk/benefit basis that is my choice until our manuals are updated.