Asymmetric flaps
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Asymmetric flaps
Having just had some flap repairs it provoked the question as to how violent the effect of asymmetric flaps is.
I appreciate it would depend on the type of aircraft but I would be interested in people’s general comments and views of how likely it would be to successfully recover from a flap becoming detached on final.
I appreciate it would depend on the type of aircraft but I would be interested in people’s general comments and views of how likely it would be to successfully recover from a flap becoming detached on final.
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Recovery would prob depend on how quickly you get the other flap off - too slow on the old lever and a nice barrel roll would ensue I guess. With some types, maybe aileron could overcome the asym effect, but I would think not with big Fowlers.
A
A
Have looked at this quite a few times in flight test of new (light aircraft) prototypes. The reason we've done it has been just this - the need to satisfy ourselves that the handling will be okay if the flap actuator / linkage on one side fails.
Being very generalistic here, the answer is that there is always a degree of handling asymmetry, requiring the pilot to maintain (usually) some aileron to keep the aircraft in balance. However, the force has generally been a few pounds, and the workload whilst it has increased, has not done so exceptionally.
So, should this happen, yes you'll be sweating a bit, but I think that the chances that you won't be able to control the aircraft should be pretty small.
I should say that one of the underlying assumptions of the flight testing we've done has always been that you'd not try and land with asymmetric flaps, but balance them out and land with symmetric flaps. For that reason, we've not taken these asymmetric tests to the stall or landing - the testing risks weren't considered justified.
I'm obviously not giving any detailed information about specific aeroplanes; that's confidential data that I can't share publically, you'd have to ask the individual aircraft manufacturers. But, I've yet to see any type where an average PPL would be unlikely to cope.
G
Being very generalistic here, the answer is that there is always a degree of handling asymmetry, requiring the pilot to maintain (usually) some aileron to keep the aircraft in balance. However, the force has generally been a few pounds, and the workload whilst it has increased, has not done so exceptionally.
So, should this happen, yes you'll be sweating a bit, but I think that the chances that you won't be able to control the aircraft should be pretty small.
I should say that one of the underlying assumptions of the flight testing we've done has always been that you'd not try and land with asymmetric flaps, but balance them out and land with symmetric flaps. For that reason, we've not taken these asymmetric tests to the stall or landing - the testing risks weren't considered justified.
I'm obviously not giving any detailed information about specific aeroplanes; that's confidential data that I can't share publically, you'd have to ask the individual aircraft manufacturers. But, I've yet to see any type where an average PPL would be unlikely to cope.
G
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Isn't it a certification requirement that at all speeds above Vs there must be sufficient aileron authority to keep wings level in the event of a *single stage* assymetric flap condition?
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Genghis the Engineer - thank you for your very informative reply.
It would seem most likely that a flap might detach on the approach and (possibly) towards the late stages when full flap is taken and the load is at its highest.
Is it your general view that were a flap to let go in this configuration (but lets say with rather more height to work with than would actually be the case on late final) the average GA type would have enough authority in the ailerons to prevent the aircraft turning over. I appreciate an early retraction of the flap would be vital but I suspect the loss of a flap would come as such a surprise that the first reaction would be to compensate with aileron whilst working out what had failed.
It would seem most likely that a flap might detach on the approach and (possibly) towards the late stages when full flap is taken and the load is at its highest.
Is it your general view that were a flap to let go in this configuration (but lets say with rather more height to work with than would actually be the case on late final) the average GA type would have enough authority in the ailerons to prevent the aircraft turning over. I appreciate an early retraction of the flap would be vital but I suspect the loss of a flap would come as such a surprise that the first reaction would be to compensate with aileron whilst working out what had failed.
One has to be cautious here, because no two aeroplanes are the same, and I obviously only know about the certification programmes that I've been involved with - which is quite a few, but clearly tiny compared to the number of aircraft types around.
Nonetheless, I would not expect a sudden loss of control, I'd expect asymmetric flap selection to cause a marked but not massive roll rate towards the wing with lower flap deflection, and probably some yaw away from it as well. I would not expect the control forces needed to hold the aircraft level to be massive, but I wouldn't want to be holding them during a landing if it could be avoided, not so much because of the workload, as because of the uncertainty over the stalling characteristics.
As for aileron power, yes I'd be very surprised if there was insufficient aileron power to counteract the effects of asymmetric flaps - just look at it this way, you've got two ailerons (fighting one flap), and they are twice as far (roughly) from the centre of the aircraft as the flaps. So, being incredibly simplistic about this, I'd expect to get about 4 times the roll-power out of both ailerons as I would out of a single asymmetric flap.
G
N.B. So far as certification requirements are concerned, "it depends" there are a lot of different sets of rules depending upon aircraft size and intended use, and a lot of caveats to do with how the flap system is constructed. Add into that different professional opinions amongst the like of I and my colleagues about how each safety requirement should be met - and you get "it depends"! What IO540 has suggested however I'd certainly not regard as surprising or unreasonable if I found it in a test programme.
Nonetheless, I would not expect a sudden loss of control, I'd expect asymmetric flap selection to cause a marked but not massive roll rate towards the wing with lower flap deflection, and probably some yaw away from it as well. I would not expect the control forces needed to hold the aircraft level to be massive, but I wouldn't want to be holding them during a landing if it could be avoided, not so much because of the workload, as because of the uncertainty over the stalling characteristics.
As for aileron power, yes I'd be very surprised if there was insufficient aileron power to counteract the effects of asymmetric flaps - just look at it this way, you've got two ailerons (fighting one flap), and they are twice as far (roughly) from the centre of the aircraft as the flaps. So, being incredibly simplistic about this, I'd expect to get about 4 times the roll-power out of both ailerons as I would out of a single asymmetric flap.
G
N.B. So far as certification requirements are concerned, "it depends" there are a lot of different sets of rules depending upon aircraft size and intended use, and a lot of caveats to do with how the flap system is constructed. Add into that different professional opinions amongst the like of I and my colleagues about how each safety requirement should be met - and you get "it depends"! What IO540 has suggested however I'd certainly not regard as surprising or unreasonable if I found it in a test programme.
Why do it if it's not fun?
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I should say that one of the underlying assumptions of the flight testing we've done has always been that you'd not try and land with asymmetric flaps, but balance them out and land with symmetric flaps
Not all that long ago, I had a flap problem in a PA28, on the approach - the flap lever became jammed. My initial reaction was to perform a go-around and take the problem back into the air, so that's what I did.
Once back at a safe height, I started thinking through the options. It was night, and even with all the cockpit lighting I had available I was unlikely to be able to figure out for certain what the problem was, but I knew that it was neither possible to add more flap nor to retract the flap that I had. I had no indications that there was any asymmetry, but couldn't be certain. The cloud base was too low to be able to get above it and do some stalls, and even if it hadn't been I'm not sure I'd have wanted to do that at night. The only option I had left was to make an approach with whatever flaps I currently had.
It turned out that it was simply the lever which had become jammed - no reason at all why there should have been any asymmetry. But I didn't know that at the time, and even if there had been asymmetry, with the flap lever jammed and it being dark I'd have been stuck with it.
FFF
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It's very easy to dissapear up your own backside with "what if" testing conditions.
In this case, you'd have to have two separate failures, a flap linkage failure, and a jammed lever, to give you asymmetric flaps that you couldn't correct. Both are highly unlikely events (notwithstanding that you experienced one), multiply the two by each other and it becomes absolutely tiny.
There's also a general requirement to make all systems jam-resistant.
G
In this case, you'd have to have two separate failures, a flap linkage failure, and a jammed lever, to give you asymmetric flaps that you couldn't correct. Both are highly unlikely events (notwithstanding that you experienced one), multiply the two by each other and it becomes absolutely tiny.
There's also a general requirement to make all systems jam-resistant.
G
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There was an ILAFFT in Pilot magazine a few years back written by a guy who'd had an asymetric flap deployment on a Bandirante, and couldn't retract them as the whole mechanism jammed up. He managed to land it, somehow, but it sounded pretty scary, as it damn near rolled inverted initially (from what I remember). If I can find the original I may post a synopsis, but it won't be before next week.
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Flaps may be more inboard but they can be very powerful because of their size, especially in the propwash.
It takes just 1mm difference between the flaps, and a plane will be flying well on the p1ss
The first thing to do when rigging is to make sure the flaps are exactly equal. It's no good bending the aileron trim tab first
It takes just 1mm difference between the flaps, and a plane will be flying well on the p1ss
The first thing to do when rigging is to make sure the flaps are exactly equal. It's no good bending the aileron trim tab first
Nonetheless, I would not expect a sudden loss of control, I'd expect asymmetric flap selection to cause a marked but not massive roll rate towards the wing with lower flap deflection, and probably some yaw away from it as well. I would not expect the control forces needed to hold the aircraft level to be massive, but I wouldn't want to be holding them during a landing if it could be avoided, not so much because of the workload, as because of the uncertainty over the stalling characteristics.
Had asymmetric flap on one occasion, flap problems on many others including failure to retract from a full flap position.
The asymmetric flap occured during stall recovery in a C150 (40 degr. flap)
Nose down full power one flap came up.
Didn't take me too long still had my finger on the flap lever, put the other one down again and flew home with full flap extended at appr. 55 mph.
Did roll pretty quick, no idea if full aileron would have stopped it, didn't feel like trying it that time.
Turned out the cable from the flap motor broke.
Also had a window blow out, but I'll save that story for another time...
The asymmetric flap occured during stall recovery in a C150 (40 degr. flap)
Nose down full power one flap came up.
Didn't take me too long still had my finger on the flap lever, put the other one down again and flew home with full flap extended at appr. 55 mph.
Did roll pretty quick, no idea if full aileron would have stopped it, didn't feel like trying it that time.
Turned out the cable from the flap motor broke.
Also had a window blow out, but I'll save that story for another time...
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This happened to a friend of mine in a 150 or 152. The torque tube that connects the flaps broke and he had one up and one down and no movement. Sorry don't remember if it was 40deg or not.
He was able to land normally but I recall him saying it needed pretty much full aileron.
Apparently the bang that it made when it let go was the most frightening part!
He was able to land normally but I recall him saying it needed pretty much full aileron.
Apparently the bang that it made when it let go was the most frightening part!
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My PPL instructor in the early nineties was obsessional about checking the flaps and detents (PA38) before take-off.
Turns out he lost a mate to a major dose of asymmetric flap pretty close to the ground.
Never talked about it much so don't know the details.
But It rubbed of on me: I allus give the Arrer (mechanical flaps) a firm test of the detents during the pre-flight..
Safe (and symmetric) flying
Cusco
Turns out he lost a mate to a major dose of asymmetric flap pretty close to the ground.
Never talked about it much so don't know the details.
But It rubbed of on me: I allus give the Arrer (mechanical flaps) a firm test of the detents during the pre-flight..
Safe (and symmetric) flying
Cusco
