Impossible Turn Tested at Altitude

SixPapaCharlie

SixPapaCharlie

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So yesterday I got a chance to fly.
After reading the impossible turn thread, I decided to try it.

4200 feet aligned with 17
Wind was direct down the runway around 8 kts

1/2 flaps, slow to ~Vr, full throttle, pitch to Vy

4500 feet, cut the throttle (alt. didn't matter just needed a starting reference)

I inserted a 3 to 4 second delay to simulate confusion

First instinct was to pitch to best glide 86 kts but that didn't feel right. I was going down to fast. I didn't want that much nose down pitch so I flattened up a bit to around 70 kts while banking to the left

by 600 foot loss I had gone about 135 degrees and was in the vicinity of the airfield where I could have made an off field landing

a little over 800 feet gone and I hit the 180

So I am essentially down wind, I need to turn left to get back to the runway and then turn tight to be lined up with it again.

I lost nearly 1500 feet total to do that.

I bet I can practice it more and change pitches, banks, and flap settings and get that to a lower number but as I sit here I have essentially given myself a ~1800 AGL min for the full turn or ~1000 to turn back to the general area of the field if it has a lot of surrounding flat areas.

I am going to do this more and see what I can consistently get.
I would have expected the number to be a lot lower.
Maybe it will be after some practice.

If you have tried this, what were your results?
 
I've done it at 600'. I was already on crosswind so I made a 270 turn to the right. Straight out I've done 800'. I wouldn't want to do either one under real stress. The 800' I could have easily landed on the taxiway if I felt uncomfortable about making the runway.
 
48dodge said:
I've done it at 600'. I was already on crosswind so I made a 270 turn to the right. Straight out I've done 800'. I wouldn't want to do either one under real stress. The 800' I could have easily landed on the taxiway if I felt uncomfortable about making the runway.
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Excellent.
What are you flying?
 
I regularly practice simulated engine outs on takeoff in the experimental gyroplane I fly.
I am careful to let the tower know what I am fixing to do.
I worked up to it incrementally and at 100 feet AGL and 60kts I can make the impossible turn making a downwind landing on the runway I just departed from.
I can also land straight ahead in 200 feet including roll out from 100 feet AGL and 60kts.
At 400 feet AGL in an actual engine out I had time to call the tower and receive clearance before touch down.I made a 260 degree turn to the cross wind runway.I was past the end of the runway and the oil pressure gage dropped to zero.
This maneuverability is one of the very few advantages a gyroplane has over a fixed wing aircraft.
 
3-4 seconds is a lot longer than it will take when it happens, if you react at all. The turn is best made right above stall speed. For that method, I would be uncomfortable starting it below 400' in most planes that are in the 7-9:1 glide ratio as most of our SEL GA planes are, a DA-20 I bet I could do a lot better.

Yeah, actually a CFI and I experimented with this, as well where the break even altitude was for stopping the prop to extend glide. It's kinda fun when you have a former Navy test pilot and Douglas' chief aerodynamics guy for a flight instructor. :D

We played with various "impossible turn" scenarios and methods in a Citabria in the course of aerobatic instruction.

The only method I found that I could reproduce a <250' loss result was was to immediately pull for 3gs to transfer any excess speed I had into ballistic energy with a slight bank downwind and just as my ballistic energy ran out stomp upwind rudder following it with the yoke and outside aileron while unloading the wing and putting the nose down to follow the ballistic trajectory as I gain flying energy back. As I start to accelerate towards best glide I start easing back so I settle into it. * If you trim the plane to climb at Vy, it will also seek to stabilize glide at that speed, so this is a lot simpler than it sounds, it's kind of automatic really. *

It takes some practice to get a consistent result.
 
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I tried this recently at altitude. I had a cfi on board. Basically after the confusion you must go right into a 45* bank and get to that target airspeed. In my cherokee I dropped about 800ft doing it not under stress. So I would give myself more practice and add a few hundred feet so I'm back to the 1000 agl I'll turn back...but I likely still wouldn't do it! To risky to me. But I know it can be done.
 
Wouldn't you actually want best sink rate instead of best glide speed?
Maybe that's why you felt Vg to be wrong.

Best glide gives you the most distance for altitude (less altitude loss per unit of distance), as opposed to less altitude loss per unit of time.
In the "impossible turn" you are not trying to reach farther, you are trying to stay aloft as long as possible to complete the turn. Actually going farther from the airport might be counter productive.
 
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Johann said:
In the "impossible turn" you are not trying to reach farther, you are trying to stay aloft as long as possible to complete the turn.
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No, you are trying to get through the turn as efficiently as possible. First of all, best sink speed is less aerodynamically efficient than best glide. Secondly, these best sink and best glide speeds don't apply here because of the steep bank angle. A 45 degree bank is about the most efficient bank angle. You would need to test the most efficient airspeed at this 45 degree bank angle. It won't be either your straight-and-level best sink or best glide speed.
 
Henning said:
3-4 seconds is a lot longer than it will take when it happens, if you react at all. The turn is best made right above stall speed. For that method, I would be uncomfortable starting it below 400' in most planes that are in the 7-9:1 glide ratio as most of our SEL GA planes are, a DA-20 I bet I could do a lot better.

Yeah, actually a CFI and I experimented with this, as well where the break even altitude was for stopping the prop to extend glide. It's kinda fun when you have a former Navy test pilot and Douglas' chief aerodynamics guy for a flight instructor. :D

We played with various "impossible turn" scenarios and methods in a Citabria in the course of aerobatic instruction.

The only method I found that I could reproduce a <250' loss result was was to immediately pull for 3gs to transfer any excess speed I had into ballistic energy with a slight bank downwind and just as my ballistic energy ran out stomp upwind rudder following it with the yoke and outside aileron while unloading the wing and putting the nose down to follow the ballistic trajectory as I gain flying energy back. As I start to accelerate towards best glide I start easing back so I settle into it. * If you trim the plane to climb at Vy, it will also seek to stabilize glide at that speed, so this is a lot simpler than it sounds, it's kind of automatic really. *

It takes some practice to get a consistent result.
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So in a Citabria, on a normal takeoff with 2 aboard you can pull 3Gs?

I don't think any if the citabrias I instructed in or flew had that kinda power.
 
James331 said:
So in a Citabria, on a normal takeoff with 2 aboard you can pull 3Gs?

I don't think any if the citabrias I instructed in or flew had that kinda power.
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Yes, it's just a snap back though, just 'whack' yank full back and release. The key is to get the feel for the speed of the yank. From Vy you have just enough excess energy and it's time to start unloading the wing to keep it from stalling and spinning. It's got nothing to do with power, it's about managing the energy left when the power turns off, and that is a factor of weight, speed, and gravity.
 
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RoscoeT said:
No, you are trying to get through the turn as efficiently as possible. First of all, best sink speed is less aerodynamically efficient than best glide. Secondly, these best sink and best glide speeds don't apply here because of the steep bank angle. A 45 degree bank is about the most efficient bank angle. You would need to test the most efficient airspeed at this 45 degree bank angle. It won't be either your straight-and-level best sink or best glide speed.
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Makes sense. I guess I'll try this next time I'm bored in the plane.
 
Henning said:
Yes, it's just a snap back though, just 'whack' yank full back and release. The key is to get the feel for the speed of the yank. From Vy you have just enough excess energy and it's time to start unloading the wing to keep it from stalling and spinning. It's got nothing to do with power, it's about managing the energy left when the power turns off, and that is a factor of weight, speed, and gravity.
Click to expand...

Yeah I get that, but I don't think I've ever flown one that had enough energy that it would pull +3Gs in that stage if flight.
 
SixPapaCharlie said:
1/2 flaps, slow to ~Vr, full throttle, pitch to Vy

4500 feet, cut the throttle (alt. didn't matter just needed a starting reference)

I inserted a 3 to 4 second delay to simulate confusion

First instinct was to pitch to best glide 86 kts but that didn't feel right. I was going down to fast. I didn't want that much nose down pitch so I flattened up a bit to around 70 kts while banking to the left
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What kind of plane?
What was Vy?
Also, after you cut the throttle, at any time did you push forward on the yoke or stick, or did you let the airplane nose down on its own?
 
James331 said:
Yeah I get that, but I don't think I've ever flown one that had enough energy that it would pull +3Gs in that stage if flight.
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You have to yank fast and immediately and you have barely enough. If you pull too slow or hesitate you won't make it, and without it you start using more than 250' of altitude. If you can only pull 2 for example you will use 400'. It really takes a lot of practice to get the feel down just right for a smooth ballistic arc through the 'stall zone'. That's why it's not a realistic method to use, we more did it out of an exercise in intellectual curiosity and some fun figuring it out. Jack had a great way of teaching. He taught me that Newtonian physics is why airplanes fly by flying over a barometer and calculating the weight of the airplane.:D
 
I use 600' in my CTSW. At Mammoth you will likely have high terrain to the left and right so routeing my turn is a big consideration. Abeam the numbers when downwind on 27 you are 200' AGL but 800' above the runway.

600' for 27 and 750 for 09, downhill vs uphill, and some falling terrain vs all rising terrain.
 
Jim Logajan said:
What kind of plane?
What was Vy?
Also, after you cut the throttle, at any time did you push forward on the yoke or stick, or did you let the airplane nose down on its own?
Click to expand...


TB9
80
I pushed
 
Henning said:
Yes, it's just a snap back though, just 'whack' yank full back and release. The key is to get the feel for the speed of the yank. From Vy you have just enough excess energy and it's time to start unloading the wing to keep it from stalling and spinning. It's got nothing to do with power, it's about managing the energy left when the power turns off, and that is a factor of weight, speed, and gravity.
Click to expand...
:needpics:
 
Forget the delay- that's for the "typical" response of the untrained pilot. You are removing yourself from that statistic by training and practicing on a regular basis, much like at least 3 landings in the last 90 days.
IMMEDIATELY roll into a 45° bank and hold just above a stall - by feel - that's why you practice.
You will be amazed how quick you can turn around.
 
James331 said:
Yeah I get that, but I don't think I've ever flown one that had enough energy that it would pull +3Gs in that stage if flight.
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What's the stall speed and Vy for a Citabria? It's easy to estimate g available. 3g stall speed at a given gross weight is ~170% of 1g stall speed at that weight - it's possible in some airplanes but I don't know the Citabria. I would not be pulling 3 g's following an engine failure unless I had way more than enough airspeed pad.

I did know a Douglas test pilot who died teaching turnbacks in a Super-D a few years ago. Not the one Henning is referring to, though.

Energy-sucking fast-pulls are generally not a good way to turn around. There have been many papers published on the optimum way to do it, including how techniques change with weight, winds, speed, and configuration. I can put you in touch with some of the authors if you'd like. ;)

Nauga,
who sees one of them every day. :rolleyes:
 
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nosehair said:
Forget the delay- that's for the "typical" response of the untrained pilot. You are removing yourself from that statistic by training and practicing on a regular basis, much like at least 3 landings in the last 90 days.
IMMEDIATELY roll into a 45° bank and hold just above a stall - by feel - that's why you practice.
You will be amazed how quick you can turn around.
Click to expand...

I would think there would be a delay for me to at least decide what my course of action is. (I know I should have that ahead of time but I am going with worst case here)
 
The more important part of this is flying the testing yourself.

The more you test and practice this, the quicker and more consistent your reaction will be should you ever need to do this in real life.

The fact that Henning can do this in one plane in 250' is irrelevant. What matters is how long it takes me to do it in the plane I happen to have by backside strapped to when the fan quits.
 
Keep in mind you'll be landing downwind. It's entirely possible depending on wind, runway length, and aircraft that you will turn around and not even be able to land before you blow by the end of the runway in the opposite direction you took off.
 
The problem with practicing the impossible turn is there are just to many variables to accurately predict a successful outcome in a generic description of the turn.
Some of the variables are.

Aircraft type.
Aircraft Weight
Aircraft Speed
Aircraft Altitude
Airport elevation
Runway length.
Wind
Bank Angle



While I think it is useful to practice, It will really help you understand what you and the airplane can and can't do. You just can't make a general statement about where it is possible or impossible.

Another factor that I think plays into a lot of stall spin accidents is that we don't maneuver under 500 feet AGL very much and doing so can produce some illusions of speed. I have personally experienced this illusion, it was just like the leans when flying IMC except with the elevator, Any time I took my attention away from the airspeed indicator I would immediately start slowing down.
I have heard another pilot describe it as the elevator being stuck, he could see that he was to slow but had to push very hard to get the elevator to move. Of course afterward there was nothing wrong with the elevator. The subconscious can be very powerful.

So while practicing at altitude can be useful to learn your aircraft, it wont' really prepare you for doing it for real. And in the unlikely event you need to do one for real, be sure you have practiced it under similar conditions, check your airspeed a lot, and look for the signs of a stall and be prepared to recover at the 1st hint of a stall.

Brian
CFIIG/ASEL
 
WoooPigSooie said:
I see. Sorry, I'm a low hour guy just trying to glean anything I can around here...do you take off from short field or is that just a preference you have, or is it typical for your a/c?
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Oh Ok sorry.
No I fly a weird French plane that just has 2 flap settings
one for "takeoff" and one for "Landing"
 
brcase said:
The problem with practicing the impossible turn is there are just to many variables to accurately predict a successful outcome in a generic description of the turn.
Some of the variables are.

Aircraft type.
Aircraft Weight
Aircraft Speed
Aircraft Altitude
Airport elevation
Runway length.
Wind
Bank Angle



While I think it is useful to practice, It will really help you understand what you and the airplane can and can't do. You just can't make a general statement about where it is possible or impossible.

Another factor that I think plays into a lot of stall spin accidents is that we don't maneuver under 500 feet AGL very much and doing so can produce some illusions of speed. I have personally experienced this illusion, it was just like the leans when flying IMC except with the elevator, Any time I took my attention away from the airspeed indicator I would immediately start slowing down.
I have heard another pilot describe it as the elevator being stuck, he could see that he was to slow but had to push very hard to get the elevator to move. Of course afterward there was nothing wrong with the elevator. The subconscious can be very powerful.

So while practicing at altitude can be useful to learn your aircraft, it wont' really prepare you for doing it for real. And in the unlikely event you need to do one for real, be sure you have practiced it under similar conditions, check your airspeed a lot, and look for the signs of a stall and be prepared to recover at the 1st hint of a stall.

Brian
CFIIG/ASEL
Click to expand...

None of us learned to judge proximity to stall by sight. We also didn't (or shouldn't) have learned it by staring at the ASI. We should have learned it by feel in the controls and other kinesthetic cues.

I recall once on takeoff, the plane was 3/4 down the runway, full of people and skipped at Vr and settled back down full weight on the wheels. I was committed to the takeoff and finally got her off the wheels. Next up was the obstacle (trees and a fence) at the DE of Rwy36. We made it aloft, crossed US-50 felt the turbulence of a heated highway and slowly made it over the next set of trees. We were probably 75' AGL and I was on the stall horn the entire time and I was only subconsciously aware of it...I was FTFA and asking for every bit of performance she had.

Later, I told my CFI about this and he asked, "Why did they give you that plane, it's a dog?" I began to consider other flying options and eventually bought a share of my current airplane.

Point is that it was feel that allowed me to get to the edge of the stall. I'm likely not as sensitive on feeling the airplane as I was then. This was shortly after my checkride.
 
I do an engine out EVERY landing. Pull the power abeam the numbers and glide on in. Excellent practice and fun to try and nail the numbers (points off for slipping or needing throttle). YMMV

Oh, and I can to a turnaround and land on takeoff from about 500' (depends on the wind). Again YMMV.
 
JeffDG said:
The more important part of this is flying the testing yourself.

The more you test and practice this, the quicker and more consistent your reaction will be should you ever need to do this in real life.

The fact that Henning can do this in one plane in 250' is irrelevant. What matters is how long it takes me to do it in the plane I happen to have by backside strapped to when the fan quits.
Click to expand...

Do not misunderstand me, I do not suggest this, and do not endorse any radical turn at low level unless the only other option is sure death, like big rocks, or a refinery.

What we were doing was comparing ballistic vs aerodynamic advantage. The ballistic advantage won; in a highly controlled setting. Once again let me make it clear, I do not think this is a viable technique and the chances of it being fatal under stress are exceedingly high, you have to do it just right to see the advantage as well as survive it from a low level. It went wrong many times in the process of working it out. Even surviving it did not mean I could beat the aerodynamic model, again, timing and pull have to be very precise or you lose advantage.

In a "I am sooo ****ed" situation where turning back at low level was the only option that had a hint of survival, I would chose it though, because going in spinning has less forward, and total, energy into the crash than the failed aerodynamic model.

I prefer to rather avoid putting myself into that position, and it is a rare runway that provides no better option.

BTW, 3G appeared to be both the optimum and maximum pull we could achieve for translating speed into ballistic energy.
 
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nosehair said:
Forget the delay...
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Personally I think that's very poor advice.

I've seen too many deer in too many headlights.

I feel many who think they are immune to the delay to the point of forgetting it simply are not, when the chips are down.

But if you're comfortable forgetting it, be my guest!
 
FastEddieB said:
Personally I think that's very poor advice.

I've seen too many deer in too many headlights.

I feel many who think they are immune to the delay to the point of forgetting it simply are not, when the chips are down.

But if you're comfortable forgetting it, be my guest!
Click to expand...

It really depends on the person, typical stress reaction is about .5 seconds. If it is an immediately fatal situation, then some interesting reaction modifiers kick in. One is time dilation, the passage of time in relation to speed of thought slows dramatically and you just do what needs to be done, instantly and calmly, the the reaction times can get down around a 1/10 of a second, possibly faster, it's a hard effect to measure. The effect other people get is to disassociate and freeze, as they have stepped out and are now watching everything on a movie. AF447 is an example of this and shows that the state can last several minutes. It was not until 12,000' that the PF said aloud, "This is really happening, isn't it", it was at that moment of realization, and not since the stall horn had gone off as he lowered the nose and pulled it back up again that his right hand moved. In that case, the reaction time is infinite in an immediate emergency because death comes first.
 
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Post 34 talks of the rare runway. I am watching more housing pop up near my based airport, wherein it once was farmland. It would be nice if airports would own in perpetuity the parcels of land 1/4 - 3/4 mile on the extended centerline.
 
FastEddieB said:
Personally I think that's very poor advice.

I've seen too many deer in too many headlights.

I feel many who think they are immune to the delay to the point of forgetting it simply are not, when the chips are down.

But if you're comfortable forgetting it, be my guest!
Click to expand...

Deer in the headlights comes from not being prepared, that is, cocked and ready for an engine failure at this critical point. I live in the training world and have taught the turn around as an option, when it is appropriate. Of course, it requires the right conditions for it to work. Lots of practice will help you make the right decision when it happens.

When you practice an engine out at altitude, do you delay 3 or 4 seconds before you apply back pressure to hold the nose up? Do you allow the nose to dive as it wa tsunami to? Probably not, because you have practiced. Your CFI prepared you and you automatically hold back pressure and trim while looking for a field.

While landing, do you delay elevator and rudder pressures ?
No, because you have practiced enough to have instant control response without
thinking.
So it is with any maneuver, especially emergency drills.
 
Jaybird180 said:
Post 34 talks of the rare runway. I am watching more housing pop up near my based airport, wherein it once was farmland. It would be nice if airports would own in perpetuity the parcels of land 1/4 - 3/4 mile on the extended centerline.
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I'll take houses and a neighborhood, that is not necessarily lethal, plenty of energy absorbing options around if you look, better odds than the turn.
 
Henning said:
I'll take houses and a neighborhood, that is not necessarily lethal, plenty of energy absorbing options around if you look, better odds than the turn.
Click to expand...

Ask the dead pilot that crashed into the house in Chicago.
 
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