EFATO
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(Note to the reader - this was originally posted in a different thread which was subsequently deleted by the OP. The mods were kind enough to retrieve it from the bit bucket and post it here, since it has some relevance here too. I later tweaked it a bit to better fit in here. The original context was a post where the author believed that with a bank angle of 45 degrees, the load factor automagically increases to 1.41, and thus the stall speed automagically by 20%.)
In a stable turn (non accelerating, non descending etc) the theory says that the load factor in a 45 degree turn is 1.4. But in the engine off scenario you are by definition not in a stable turn. You will be losing altitude for sure, and possibly bleeding speed as well, intended or not. Furthermore, the load vector angle is getting more and more horizontal, and this only increases when you go beyond the 45 degrees.
The result of that is that you can increase and decrease your load factor (by pulling more or less on the stick) a significant amount, but you will only increase or decrease the vertical component of lift by a tiny amount. With an increased load factor comes a higher stall speed, higher induced drag, but also a tighter turning radius. So pulling to the stall gives you the tightest turn, but also the least amount of time to "get it right". (And pull to the stall when the speed is too high/bank angle is too low will cause the aircraft to climb and thus bleed speed even more quickly.)
Making matters worse, without a lot of aerobatics experience (and the subsequent "feel" for the aircraft near the stall), without a G meter and with your head mostly outside the cockpit (which is a very good idea in those circumstances, don't get me wrong) how are you going to judge the load on your aircraft exactly? So how sure are you that your stall speed is indeed 61 knots? It probably could have been anywhere between 50 and 75.
I have not read that Rogers document intimately, but here's what I would do: Throw the aircraft in a 45-60 degree bank and then pull until the stall warner. Then play the stall warner and bank angle against each other so that I know I'm at the maximum turning rate while inevitably bleeding off the airspeed and the altitude. (In fact bleeding the altitude off in a controlled manner is the way to keep the airspeed up.)
But hey, I've got a lot of experience doing 75-degree banked turns (stable, thus 4G) at a mere 80 knots (sometimes even slower), with the stall warner blaring continuously, and playing the buffet. So playing bank angle against the stall buffet is not all that unusual for me.
Anyway, kudos for actually trying this, learning what your aircraft is capable of and how you actually achieve that performance. You now know you can do it from 500' up. If the EFATO ever happens for real, stick to what you've learned so far. Don't try it below 500' because some anonymous bloke on the internet told you it could possibly be done if you altered your technique. Land straight ahead.
In a stable turn (non accelerating, non descending etc) the theory says that the load factor in a 45 degree turn is 1.4. But in the engine off scenario you are by definition not in a stable turn. You will be losing altitude for sure, and possibly bleeding speed as well, intended or not. Furthermore, the load vector angle is getting more and more horizontal, and this only increases when you go beyond the 45 degrees.
The result of that is that you can increase and decrease your load factor (by pulling more or less on the stick) a significant amount, but you will only increase or decrease the vertical component of lift by a tiny amount. With an increased load factor comes a higher stall speed, higher induced drag, but also a tighter turning radius. So pulling to the stall gives you the tightest turn, but also the least amount of time to "get it right". (And pull to the stall when the speed is too high/bank angle is too low will cause the aircraft to climb and thus bleed speed even more quickly.)
Making matters worse, without a lot of aerobatics experience (and the subsequent "feel" for the aircraft near the stall), without a G meter and with your head mostly outside the cockpit (which is a very good idea in those circumstances, don't get me wrong) how are you going to judge the load on your aircraft exactly? So how sure are you that your stall speed is indeed 61 knots? It probably could have been anywhere between 50 and 75.
I have not read that Rogers document intimately, but here's what I would do: Throw the aircraft in a 45-60 degree bank and then pull until the stall warner. Then play the stall warner and bank angle against each other so that I know I'm at the maximum turning rate while inevitably bleeding off the airspeed and the altitude. (In fact bleeding the altitude off in a controlled manner is the way to keep the airspeed up.)
But hey, I've got a lot of experience doing 75-degree banked turns (stable, thus 4G) at a mere 80 knots (sometimes even slower), with the stall warner blaring continuously, and playing the buffet. So playing bank angle against the stall buffet is not all that unusual for me.
Anyway, kudos for actually trying this, learning what your aircraft is capable of and how you actually achieve that performance. You now know you can do it from 500' up. If the EFATO ever happens for real, stick to what you've learned so far. Don't try it below 500' because some anonymous bloke on the internet told you it could possibly be done if you altered your technique. Land straight ahead.
Last edited by BackPacker; 14th Jan 2012 at 14:22.
Famous maybe, detailed fairly, correct debateable. I've spent quite a lot of time picking that paper apart - it's a good starting point, but no more than that. To be honest, as somebody who analyses a lot of aeronautical research papers I'd say it's pretty shallow and there's a lot more work that can be done.
Much the same that the author does to start with - he is quite clear that it's a simplified model leading to a first approximation solution to the problem. He considers one speed margin above the stall, two bank angles and a single aeroplane only - and he hasn't validated his results with any flight test results.
I think if you asked David Rogers, he'd probably agree on all these points. What he did was a very good first stab at a mathematical solution to the problem and demonstrated that the maths, and the historical evidence are broadly consistent - to whit, turnbacks can be possible.
However, it's a real shame in my opinion that 18 years later, that good start by Dr Rogers hasn't been actively followed up and published. Given time, I'd like to have a go at it myself, and may yet do so.
G
I think if you asked David Rogers, he'd probably agree on all these points. What he did was a very good first stab at a mathematical solution to the problem and demonstrated that the maths, and the historical evidence are broadly consistent - to whit, turnbacks can be possible.
However, it's a real shame in my opinion that 18 years later, that good start by Dr Rogers hasn't been actively followed up and published. Given time, I'd like to have a go at it myself, and may yet do so.
G
That makes sense. I think the key learnings from the maths are that a 45 degree bank is optimal for height loss per unit angle turned, and that there is no optimum speed -- it should be as low as possible. It then becomes a question of practicality and pilot skill.
When I did some simple flight tests at altitude in a Mooney 201 (probably 15 years ago), I remember some insights:
* with a decent aural stall warner, flying the aircraft at the edge of the stall-warner onset is fairly easy -- relax pressure if you hear it
* while the height loss in the turn is fairly low (as Rogers predicts), you come out of the turn at low speed and at high rate of descent -- that requires you to accelerate to make a normal landing, which takes time and height
* in the analysis of where you end up, a lot depends on the difference between climb gradient and glide ratio -- in a powerful aircraft, it's much easier to get back to the airfield, while in a poorer performer (or at higher weights, density altitude), you'll end up beyond the upwind threshold.
When I did some simple flight tests at altitude in a Mooney 201 (probably 15 years ago), I remember some insights:
* with a decent aural stall warner, flying the aircraft at the edge of the stall-warner onset is fairly easy -- relax pressure if you hear it
* while the height loss in the turn is fairly low (as Rogers predicts), you come out of the turn at low speed and at high rate of descent -- that requires you to accelerate to make a normal landing, which takes time and height
* in the analysis of where you end up, a lot depends on the difference between climb gradient and glide ratio -- in a powerful aircraft, it's much easier to get back to the airfield, while in a poorer performer (or at higher weights, density altitude), you'll end up beyond the upwind threshold.
I don't read that from the paper - he shows that 45 degrees is better than 35 degrees, but doesn't really explore different speeds, or any other bank angles - so it hasn't got as far as a general case.
Your conclusions from your own testing however Bookworm, are pretty much the same as my conclusions in a PA28-161 and a Thruster TST about half a dozen years ago.
G
Your conclusions from your own testing however Bookworm, are pretty much the same as my conclusions in a PA28-161 and a Thruster TST about half a dozen years ago.
G
I don't read that from the paper - he shows that 45 degrees is better than 35 degrees, but doesn't really explore different speeds, or any other bank angles - so it hasn't got as far as a general case.
Of course one could argue that the true optimum comes from a non-steady state turn, but I don't think you'd do much better.
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The other massive factor is how much runway you have left when you get airborne - it effectively offsets the glide path 'under' the climb path. For that reason alone I don't think you can come up with a single height for a turnback, even on one aircraft. There's a minimum to make the turn sure, but after that it's a question of circumstances.
Oh, I think he does. At the end of the section "the optimum bank angle" he shows that the rate of height loss per unit angle turned (in the steady state case) is proportional to 1/sin(2*bank), which is minimised at 45 degrees. The only reason he shows 35 degrees is because it's Eckalbar's recommendation.
Of course one could argue that the true optimum comes from a non-steady state turn, but I don't think you'd do much better.
Of course one could argue that the true optimum comes from a non-steady state turn, but I don't think you'd do much better.
I think that I may feel the need to go and have a play!
G
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I am grateful for the replies here. I have a PPL although not flown since I got the licence in June 2010...long story...but hope to restart this year.....
In a strong cross wind, one would have to turn into wind if attempting a return to runway.....thing is, will turning into wind reduce the lost of height in any way (quicker airflow over the wings, providing vital lift)?
Maybe I should know the answer to this but I have been out of the aviation loop recently....apologies in advance....
In a strong cross wind, one would have to turn into wind if attempting a return to runway.....thing is, will turning into wind reduce the lost of height in any way (quicker airflow over the wings, providing vital lift)?
Maybe I should know the answer to this but I have been out of the aviation loop recently....apologies in advance....
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dkatwa, as soon as your wheels have left the ground, you're flying inside a block of (moving) air. Inside this block, it really doesn't matter which way you turn. Aerodynamically speaking it's all the same.
The turn into the wind is not to add airflow to the wings or something like that, but simply so that when you come out of the turn, you are still very close to the runway, instead of blown away for miles.
The turn into the wind is not to add airflow to the wings or something like that, but simply so that when you come out of the turn, you are still very close to the runway, instead of blown away for miles.
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I am grateful for the replies here. I have a PPL although not flown since I got the licence in June 2010...long story...but hope to restart this year.....
In a strong cross wind, one would have to turn into wind if attempting a return to runway.....thing is, will turning into wind reduce the lost of height in any way (quicker airflow over the wings, providing vital lift)?
Maybe I should know the answer to this but I have been out of the aviation loop recently....apologies in advance....
In a strong cross wind, one would have to turn into wind if attempting a return to runway.....thing is, will turning into wind reduce the lost of height in any way (quicker airflow over the wings, providing vital lift)?
Maybe I should know the answer to this but I have been out of the aviation loop recently....apologies in advance....
The wind (assuming it is constant) has no effect on the flight dynamics - none!
However, if you draw the basic turn back with no wind (about 270 degrees of turn - 180 back, 45 to track towards the airport, 45 to align with the runway) and then redraw it off setting each position a bit more downwind to reflect the cumulative displacement from the cross wind, you will see the final 45 degrees and then the turn back on course will be substantially reduced. So less turning time and less distance travelled means less height lost.
As an instructor I am hard over on this one. Unless you fly virtually every day and practice this manoever often, a situation that I would argue will never apply, to virtually everyone reading this forum, Then I think one should never attempt a turn back below 1000 feet AGL.
What should be is that every pilot is good enough to a immediately assess the the nature of the emergency, because remember you may only have a partial engine failure (see Gengis post for what a can of worms that can be), then immediately execute a steep low altitude turn at just above stall speed.
What IS however is an accident record where many turnbacks end in fatal crashes. Survivable crashes are ones where you hit the ground wings level in a level flight or nose up attitude. The killer crashes are low altitude stall spins or hitting the ground in a very nose low attitude, precisely what will happen if you screw up the turn back.
I think it is also important to point out that the most important action after an EFATO is to immediately lower the nose to the glide attitude.
An EFATO with the aircraft nose at the Vy attitude will loose airspeed very quickly unless the nose is lowered as soon as the engine fails. I personally know of a fatal accident where the aircraft stalled right after the EFATO because the pilot froze and did not lower the nose in time.
So I teach Vy climb to 1000 AGL as altitude is your friend so you want to get to an altitude where you have options as quickly as possible, and in the event of an engine failure below 1000, it is nose down to the glide and only turning enough to avoid major obstacles.
I also insist that before every takeoff the student reviews the actions for an engine failure during the takeoff and after takeoff including touching the relevant controls. The EFATO portion starts with him/her physically moving the control wheel firmly forward. After doing this brief 30 or 40 times the actions become automatic and that I think is what will save your bacon if you are unfortunate enough to have an EFATO, not some hero pilot split arse low level steep turn.....
Finally one area where the flight school IMO do not place enough emphasis is for an engine failure on the takeoff roll is to immediately fully close the throttle. Again I have personal knowledge of an accident where an airplane was destroyed and the occupants injured because the pilot failed to accomplish this simple action when the engine died on the takeoff roll.
What should be is that every pilot is good enough to a immediately assess the the nature of the emergency, because remember you may only have a partial engine failure (see Gengis post for what a can of worms that can be), then immediately execute a steep low altitude turn at just above stall speed.
What IS however is an accident record where many turnbacks end in fatal crashes. Survivable crashes are ones where you hit the ground wings level in a level flight or nose up attitude. The killer crashes are low altitude stall spins or hitting the ground in a very nose low attitude, precisely what will happen if you screw up the turn back.
I think it is also important to point out that the most important action after an EFATO is to immediately lower the nose to the glide attitude.
An EFATO with the aircraft nose at the Vy attitude will loose airspeed very quickly unless the nose is lowered as soon as the engine fails. I personally know of a fatal accident where the aircraft stalled right after the EFATO because the pilot froze and did not lower the nose in time.
So I teach Vy climb to 1000 AGL as altitude is your friend so you want to get to an altitude where you have options as quickly as possible, and in the event of an engine failure below 1000, it is nose down to the glide and only turning enough to avoid major obstacles.
I also insist that before every takeoff the student reviews the actions for an engine failure during the takeoff and after takeoff including touching the relevant controls. The EFATO portion starts with him/her physically moving the control wheel firmly forward. After doing this brief 30 or 40 times the actions become automatic and that I think is what will save your bacon if you are unfortunate enough to have an EFATO, not some hero pilot split arse low level steep turn.....
Finally one area where the flight school IMO do not place enough emphasis is for an engine failure on the takeoff roll is to immediately fully close the throttle. Again I have personal knowledge of an accident where an airplane was destroyed and the occupants injured because the pilot failed to accomplish this simple action when the engine died on the takeoff roll.
As an instructor ....
... the student reviews .... including touching the relevant controls. The EFATO portion starts with him/her physically moving the control wheel firmly forward. ..... for an engine failure on the takeoff roll is to immediately fully close the throttle.
... the student reviews .... including touching the relevant controls. The EFATO portion starts with him/her physically moving the control wheel firmly forward. ..... for an engine failure on the takeoff roll is to immediately fully close the throttle.
I think you've described two things there that I have seldom, possibly never, seen briefed. It took about 10 seconds of reading your post to decide that you've just shared something really really valuable that will now be a permanent fixture in my flying and teaching.
Thank you very much. G
one should never attempt a turn back below 1000 feet AGL
Far from feeling qualified to argue, I would humbly ask for a bit of clarification: would the 1000' minimum equally apply to slower planes and to the faster? 't Would seem to me that a slower plane - i.e. with lower stall speeds - could try it from less altitude? AIUI, the 1000' was for the average Cessna or PA28, but perhaps a microlight or LSA could make do with less?
I have never flown a AULA/LSA/Microlight so I am not qualified to offer advice as to what would be the best course of action for the EFATO emergency in this class of aircraft
Last edited by Big Pistons Forever; 15th Jan 2012 at 18:38.
You know BPA, I like to think that I can fly, and I'm starting to get the hang of teaching those aspects of flying that I'm qualified to teach.
I think you've described two things there that I have seldom, possibly never, seen briefed. It took about 10 seconds of reading your post to decide that you've just shared something really really valuable that will now be a permanent fixture in my flying and teaching.
Thank you very much.
G
I think you've described two things there that I have seldom, possibly never, seen briefed. It took about 10 seconds of reading your post to decide that you've just shared something really really valuable that will now be a permanent fixture in my flying and teaching.
Thank you very much. G
Another point I alluded to but IMO bears emphasizing is that altitude = options. I see a lot of pilots make very shallow climbs immediately after takeoff. This prolongs the exposure to the low altitude EFATO environment and so for that reason the profile I teach, and always fly myself, is Vy to 1000 feet AGL.
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would the 1000' minimum equally apply to slower planes and to the faster?
But the emergency is not over once you've made the turn. You were climbing out at some angle at Vy from the threshold, now you're still as far away from the threshold as you were when you started the turn, but you lost a few hundred feet and you have no engine power. Is your glide angle sufficient to reach the threshold?
I have seen a Pitts Special climbing away after departure at an angle of 45 degrees. Now the Pitts is reputedly not a good glider, but it should be able to glide at significantly less than 45 degrees nose down. On the other hand, our DA40 with the 135 HP Thielert was normally just able to clear the trees at the far end of a (long) runway, if fully loaded, and would never be able to glide back to the field after a straight out departure. Even if you climbed to 10.000' and then turned, you would not be able to make the runway. (Despite the sailplane heritage, the DA40 still only has a glide angle of 1 in 8, and that's about equal to its climb angle.)
And another factor is how much runway you still have available ahead of you, when you rotate during the take-off. If that is significant then that bit of runway may still be reachable from the glide, whereas your original rotation point may not be reachable.
(And to put a bit of perspective to the debate, and how dependent it is on airplane capabilities and circumstances: In gliding we fly a full (although tight) circuit when the winch cable breaks at 300' or above. Yes, you read that correctly. A full circuit, with four 90 degree turns, to a normal landing in the normal landing area next to the take-off area, from 300 feet. But a winch launch cable break happens by definition *above* the airfield, not beyond the threshold, and any reasonably modern glider will easily beat a 1:30 glide angle.)
Last edited by BackPacker; 15th Jan 2012 at 19:32.
It was a nil wind day, I had given the engine a thorough runup and there was nothing suspicious detected. We had just taken off and at about 100' the engine coughed. At 250' it coughed again, and then one of the magneto's failed. The engine cowling started vibrating quite badly so I smoothly reduced power and the shaking stopped at about 75% throttle. Even on one mag and partial throttle the plane was still climbing so I chose to return to the field instead of landing ahead. Had the engine quit at any time during the reversal turn I was well within gliding distance of a runway (thank goodness I was in a 172M and not the Arrow) and in the end I circled and put her down on a crossing runway.
I realize I didn't exactly do things by the book, so please, follow the advice of the vastly more experienced pilots and instructors lurking around rather than me.
I realize I didn't exactly do things by the book, so please, follow the advice of the vastly more experienced pilots and instructors lurking around rather than me.
It was a nil wind day, I had given the engine a thorough runup and there was nothing suspicious detected. We had just taken off and at about 100' the engine coughed. At 250' it coughed again, and then one of the magneto's failed. The engine cowling started vibrating quite badly so I smoothly reduced power and the shaking stopped at about 75% throttle. Even on one mag and partial throttle the plane was still climbing so I chose to return to the field instead of landing ahead. Had the engine quit at any time during the reversal turn I was well within gliding distance of a runway (thank goodness I was in a 172M and not the Arrow) and in the end I circled and put her down on a crossing runway.
I realize I didn't exactly do things by the book, so please, follow the advice of the vastly more experienced pilots and instructors lurking around rather than me.
I realize I didn't exactly do things by the book, so please, follow the advice of the vastly more experienced pilots and instructors lurking around rather than me.
Your decision to immediately return to the field and to do so in such away as to maximize your chance of landing back on the runway in case the engine suffered any further loss of power, strikes me as exactly "doing it by the book".
All the heated arguments of exactly what bank angle to use for a turn back and lengthy dissertations on changes in AOA, accelerating vs non accelerating turns, variations in the vertical component of lift etc etc, obscure the fact that what happened to you is a lot more common than the sudden complete engine failure at low altitude and that every partial engine failure will have different consequences and so ultimately making sure you fly the aircraft first and then picking a conservative course of action that will give you options should the situation deteriorate further is the best one can do....but I guess that is not as sexy as discussing hero pilot moves......
As an aside one thing that never seems to get talked about in flight training is knowing the minimum power setting to maintain level flight. In the average Cessna it is around 1900 RPM. In the event of a partial engine failure this is a good number to know. If the power winds back but you are still getting a solid
1900 RPM you will stay in the air, at least for now. Less than that and you had better be planning your forced approach.