Engine failure turn back.

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BJC

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My airpark is at an airport with several long runways to choose from, and ample straight ahead or near straight ahead landing possibilities for almost every one of those runways. M
Our runways form a T, with the top runway about 2,500 feet and the vertical (N-S) 3,700 feet. There is a “turn left” option on both 36 and 18 that is much better than the trees. There also is an “angle right into the water” option on 36. No good options on 9 that the airplane would survive.


BJC
 

trimtab

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I don't think enough is made of the unusual and potentially startling severity of the maneuvers required to make a turn back successful below the absolute minimum plus about 30%. The descriptors of "windshield full of dirt and no horizon" are very real, as is "controls to the stops" to execute the turn.

The idea that someone who has not practiced it or even been exposed to it can claim a high chance of success on the first try for reelz is just short of absurd. Most people who actually practice it for the first time will immediately realize that as well. The odds improve a lot with practice.
 

Hephaestus

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Practiced - I know my personal numbers; but no... Straight ahead in my windscreen are my only options. The conditions / requirements for success are not going to be seen on a typical day even less likely under stress/duress.

My primary instructor way back in the 80s made it clear, as soon as the engine quit, insurance took ownership. 0 feelings for the aircraft - it's sacrificial, only goal is don't auger in taking out bystanders.

Even cirrus training - loose engine - under 2000' - CAPS deployment. But it's also a terrible glider.
 

tallank

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The hard stuff of physics and math:

View attachment 109694

Look at that increase in load factor and stall speeds between 45° and 60°. The average pilot, and most of us are average pilots, believe it or not, will get into serious trouble at 60 degrees. BJC practices this stuff and knows his airplane thoroughly just from doing aerobatics and accelerated stalls in it. Most of us never tackle that stuff. Add in the overwhelming temptations to hold the nose up to stretch the glide, and to skid that turn to tighten the radius, and you have the classic killer stall-spin crash.
 

tallank

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To achieve the best distance you need to be at best glider or slightly faster. Holding the nose up will only decrease the distance you can make. Also, you can not land / flair at VX. I sure hope you are not flying the pattern at VX because you will die. I climbing at VX and you lose an engine you will instantly be in a stall. Lost a friend who was teaching climbing at VX and practice engine failure. He was an ex Top Gun instructor.
 

speedracer

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I personally know four canard drivers (I'm one) who have made the "impossible turn" from around 200' AGL. That's only possible because canard aircraft don't stall/ spin in a conventual sense, they just don't. You can do 45-60 degree banks with the stick held to the aft stop, power on or off with no worries about a departure. I read about one guy who did it three times in the same day. The second two times he thought he had fixed the problem. As the day wore on the wind picked up and the third time he ran off the end of the runway and pranged his airplane. Keep in mind you can't just do a 180 or you won't end up over the runway. It has to be a "teardrop" 180. In my case it was a prop failure. When I completed the teardrop 180 and was over the runway I knew I was going to land (too) long. I raised the nose rear, touched down and put the nose bumper on the pavement. That left an 850' skid mark of rubber, steel and fiberglass on the runway. I stopped 45' short of the end. The best bragging right was that the skid mark was never more than 12" from the center line.
 

atypicalguy

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NO! You need to be at best glide speed or slightly faster. Near stall you are on the back side of the curve and losing more altitude and getting less distance.
Opinion is great, but that's not what the PhD ATP who actually did the research found. Just above stall, with the horn sounding, and 45 deg is best.
 

BJC

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Opinion is great, but that's not what the PhD ATP who actually did the research found.
The paper discussed factors to complete a 180 degree turn, on instruments, with restrictions on the maximum bank angle (reasonable for instrument flight), followed by no turning (banking) below 100 AGL.

It did not definitively explore all options for a visual return to land on the runway.


BJC
 

Dan Thomas

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To achieve the best distance you need to be at best glider or slightly faster. Holding the nose up will only decrease the distance you can make. Also, you can not land / flair at VX. I sure hope you are not flying the pattern at VX because you will die. I climbing at VX and you lose an engine you will instantly be in a stall. Lost a friend who was teaching climbing at VX and practice engine failure. He was an ex Top Gun instructor.
How much flying time do you have?
 

PredragVasic

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In sailplanes we do these as part of training at 200’. However, we also have 15 meter wings and glide ratios north of 35:1. Lol
Pitch for best glide and always turn into the cross wind so as not to make the impossible turn any larger. Better yet, forget about the aircraft and save your butt by landing ahead.
I flew sailplanes some 35 years ago (Blaník L13). On a winch launch, things happen extremely quickly. When cable snaps, we had three specific procedures. If altitude is 0 - 50m, land straight ahead. If it snaps at 50 - 100m, make a teardrop turn and land back on the runway, downwind. If the altitude is above 100m, fly a tight pattern and land normally.

(sorry for responding to this after the discussion has veered elsewhere; I just saw it)
 

atypicalguy

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The paper discussed factors to complete a 180 degree turn, on instruments, with restrictions on the maximum bank angle (reasonable for instrument flight), followed by no turning (banking) below 100 AGL.

It did not definitively explore all options for a visual return to land on the runway.


BJC
Yes that is true. My understanding of the 45 recommendation is more of a math thing. This paper presents it well: http://www.campbells.org/BIG_FILES/airplaneImpossibleTurn.pdf

I am curious to know what others think about this math, but my understanding from this paper is that 45 is actually better than higher angles in terms of preservation of altitude. 60 degrees will get you through the turn faster, but you will be closer to the ground afterward, despite having spent less time turning, because your induced drag is higher during the turn at 60 degrees and you have to drop the nose further to maintain a higher speed through the turn than you do at 45, so your form drag is higher also.

Specifically (cut and paste from article - please see attached pdf also):

The Optimum Bank Angle Following the development in Jett3, we consider a simple energy analysis of the optimum conditions for a steady gliding turn to a new heading. In a gliding turn the aircraft trades the potential energy embodied in altitude to overcome drag and maintain velocity above the stall velocity of the aircraft. A larger bank angle in the gliding turn requires a higher rate Figure 1. Teardrop flight path. of descent to maintain steady conditions. Consequently, minimum time in the gliding turn to a new heading yields the optimum turn conditions.

From Fig. (2) we have Lcos φ = 1 2 ρV 2SCL cos φ = W (1) and Fc = Lsin φ = V 2 R W g (2) Thus, combining Eqs. (1) and (2) yields the radius of the turn, i.e. R = V 2 g tanφ (3) Figure 2. Forces in the yz plane acting on an aircraft in a steady state gliding turn. Minimizing the radius of the turn keeps the aircraft close to the end of the runway and thus results in a decreased glide distance after completion of the turn.

The time required to turn thorough a given angle, Ψ, is t = Ψ Ψ˙ (4) and in a steady state turn Ψ =˙ dΨ dt = V R = Ψ t (5) The rate at which the aircraft expends the potential energy available from altitude must equal the energy required to overcome drag. Thus, W dh dt = DV (6) Integrating for steady state conditions yields W h t = DV (7) or h = DV t W (8)

Introducing Eqs. (3) and (5) yields h = D W V 2 Ψ g tan φ (9) In a gliding turn with bank angle φ D W = CD CL cos φ (10) Recalling that V 2 = 2W ρSCL cos φ (11) Eq. (9) is written as h = CD C2 L 4W ρSg 1 cos φ sin φ Ψ (12) The steady state conditions for minimum loss of altitude in a gliding turn to a new heading are obtained by differentiating Eq. (12). The result is dh dΨ = CD C2 L 2W ρSg 1 sin 2φ (13) where we have used sin 2φ = 2 sin φ cos φ to simplify the result. Examining this result shows that for a parabolic drag polar, CD = CD0 + kC2 L, the first term CD C2 L = CD0 C2 L + k (14) is a minimum at CLmax. Thus, the optimum speed for minimum loss of altitude in a gliding turn to a new heading occurs for CLmax, i.e., at the stall velocity. Neglecting the small density change with altitude, the second term, 4W/ρSg sin 2φ, is a minimum for sin 2φ = 1 or φ = 45◦, i.e., the optimum bank angle during a gliding turn to a new heading is 45◦.
 

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Vigilant1

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The references to "stall velocity" in the article may indicate a problem. Despite the widespread/common use of the term "stall speed," it is a misnomer. Aerodynamically, there is no such thing as a speed at which a wing stalls. There is only a "critical AoA."
If we don't demand 1 g level flight, then the published stall speed is not relevant.
The analysis in the paper appears to be based on maintaining an airspeed above "stall velocity." I'd like to understand how that works a little better.
 
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kent Ashton

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I personally know four canard drivers (I'm one) who have made the "impossible turn" from around 200' AGL.
I tested it a while back in my Cozy. At 300 AGL, chopping the power, it was doable but of course I was ready for it, had 5500' of runway and some idle power thrust. 400' AGL would be a lot better and 500' AGL would be pretty EZ. Yep, it's nice to be flying a "stall-proof" airplane.
 

Dan Thomas

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it was doable but of course I was ready for it, had 5500' of runway and some idle power thrust.
That is key. Knowing what will happen, and roughly when, is a far cry from the actual event. Like all pilots, I received training in forced landings, but I knew they were going to happen and they never happened over some impossible terrain like the city, the water, or the jagged piles of big, sharp rocks we call mountains here. As an instructor I pulled the power on my share of students, too, sometimes right after takeoff.

I've had two actual engine failures, and it's not nearly the same thing as the instructor or examiner playing with your mind. It's the real thing, and you could die if you don't get it right. Maybe even if you do get it right.
 

Dan Thomas

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I flew sailplanes some 35 years ago (Blaník L13). On a winch launch, things happen extremely quickly. When cable snaps, we had three specific procedures. If altitude is 0 - 50m, land straight ahead. If it snaps at 50 - 100m, make a teardrop turn and land back on the runway, downwind. If the altitude is above 100m, fly a tight pattern and land normally.

(sorry for responding to this after the discussion has veered elsewhere; I just saw it)
I was an instructor in powered aircraft. We sometimes pulled the power right after takeoff, even at Vx. The nose will automatically drop some, the pilot lowers it further. In a 172, Vx is about 9 knots above stall. A 2000-pound airplane doesn't screech to a sudden halt when the engine quits; there is time to lower the nose and establish glide.
 

Kyle Boatright

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I tested it a while back in my Cozy. At 300 AGL, chopping the power, it was doable but of course I was ready for it, had 5500' of runway and some idle power thrust. 400' AGL would be a lot better and 500' AGL would be pretty EZ. Yep, it's nice to be flying a "stall-proof" airplane.
I have done the exact same test in my RV-6. Exact same results - 300' was adequate if I was prepared. Reaction time and the like make more altitude desirable in the real world. The mitigating factor is you *don't* have to land back on the runway. In a true engine failure, it is still a "win" if you put it down on a nice flat space on the airfield - there's a lot of area that isn't technically the runway.
 

Marc Zeitlin

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The references to "stall velocity" in the article may indicate a problem. Despite the widespread/common use of the term "stall speed," it is a misnomer. Aerodynamically, there is no such thing as a speed at which a wing stalls. There is only a "critical AoA."
If we don't demand 1 g level flight, then the published stall speed is not relevant.
The analysis in the paper appears to be based on maintaining an airspeed above "stall velocity." I'd like to understand how that works a little better.
If you read the article, he's very clear that he's assuming a stall speed in the turn of Vs/cos(bank angle), as the math demands. He's NOT assuming a constant stall speed.
 

F3A-1

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We can put the math to any given scenario. The pilot has to evaluate what strait ahead will result in vs a partial, to complete turn back.
I have done it twice. Once in a Smith Mini Plane in daylight with nothing but Oak trees ahead. It was an instant choice to dump the nose and turn. It worked out fine.
The other time was at night in a Stinson108-3. Once again it was an instant choice to rapidly unload the wing and do a steep turn. I was able to use a closed runway with about a 250 degree turn. I could have rolled out and at least landed on the airport vs the boondocks if I could not make a runway or taxiway. Made it with a good margin, and turned final at about 30' and 70 mph. Depth perception at night is a major factor. It stinks! I made it that time too. I might not again, and I know it.
No textbook can tell a pilot to always do anything, only a pilot can make those choices, and they must do that quickly.
 

Vigilant1

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If you read the article, he's very clear that he's assuming a stall speed in the turn of Vs/cos(bank angle), as the math demands. He's NOT assuming a constant stall speed.
Yes, I did see that. The formula is fine for adjusting Vs to non-zero bank angles. But, even at zero degree bank angle the wing still doesn't necessarily stall at Vs if we push the stick forward so that we are not at 1G. The same applies in a bank.
Still, I am not recommending unloading to zero G (and accelerating toward terrra firma at 32 fps^2) as the best technique for making the "impossible turn" with minimal altitude loss.

The paper is an interesting think piece. The simplifying assumptions (instant decision, instant roll to desired bank angle, etc) help keep the length of the paper reasonable, but clearly anyone considering this as a blueprint for action will need to do a lot of work in developing their own technique and "window."
 
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