The impossible turn made possible---simulated engine failure from 600' with turnback

[Palmpilot]

Re: The impossible turn made possible---simulated engine failure from 600' with turnb

Emphasis added:

The "600 feet below" part of that sentence still doesn't make any sense to me.

 

[coloradobluesky]

Re: The impossible turn made possible---simulated engine failure from 600' with turnb

I did it at 500' and tried it at 400'. I BARELY made it at 400'. Id say, in my airplane, flying like that, I wouldnt try it below 500' unless no other good option. Might make it at 400, might. Both times I landed near the end to end middle of the runway.

 

[MAKG1]

Re: The impossible turn made possible---simulated engine failure from 600' with turnb

How can there be homes, cars, and businesses 600 feet below him when he is at 3000 feet AGL?

The homes, cars, and businesses are 2400 feet tall?

It's just poorly worded, nothing more.

 

[austinglasair]

Re: The impossible turn made possible---simulated engine failure from 600' with turnb

I completed the impossible turn last week on Monday (28 Sep) with my student from 500 MSL (about 450 AGL here). I kept the aircraft coordinated and performed a bank just beyond a standard rate turn while pitching for and maintaining best glide.

The aircraft was a Cessna 172P. My options to land straight ahead included buildings. To my left and right also included buildings. Bad options.

I made the approach end of the opposite facing runway with about a 8 knot tailwind.

The landing was followed by a silent meltdown and needing to do some laundry.

 

[OkieAviator]

Re: The impossible turn made possible---simulated engine failure from 600' with turnb

This comes up time and time again because the "impossible" turn is a misnomer.

Should be re-labeled the 'ill advised turn'.

So just where would be the "right" place to experiment with this?

The most risk adverse place to practice anything that involves being close to the ground is at an uncontrolled airport with a long/wide runway that isn't surrounded by houses or buildings.

For these types of activities I use KCSM which is uncontrolled on the weekends. The runway being almost 13,500 ft long you're off in the first 1000 and on turn around you're still over the runway. If for whatever reason you have to put it down off field then there are plenty of open areas to do so.

 

[Sundancer]

Re: The impossible turn made possible---simulated engine failure from 600' with turnb

It's a pretty much useless exercise at altitude - the visual clues are dramatic down low, and influencing. Not much to learn at 3,000 AGL, beyond noting the altitude loss. After that, low value.

I did a lot of practice in a 180HP 172, working down from 1,000 AGL to 600 AGL. I noticed I had my head IN the cockpit more than usual, glancing at the AS and TC more than usual. If the airport environment is the flattest, less obstructed place around, then the goal isn't necessarily to make it to the runway - just touch down level at a reasonable rate of descent - taxiway, grass, wherever; then all the insurance company, tell them where their plane is.

I got no issue with your experiments, or the location - one person's risk tolerance isn't the same as another's. I sure wouldn't question your "judgment". If it's a maneuver you intend to use if the conditions call for it, then definitely practice it - we practice everything else, and it's certainly bogus to say "never turn back" - but it would be kinda flaky if your first time to do it was after a real failure.

 

[steingar]

Re: The impossible turn made possible---simulated engine failure from 600' with turnb

Some planes are waaaaaaaay better than others at that maneuver. Yeah, I'd probably try it in a 172 given the right set of conditions AND nothing better in front of me, but I've also known a VERY experienced instructor who "knew" how to do this die in a Mooney trying.

If I got into a situation like this (very possible) I think I'd leave the gear up until the last possible second, more likely just belly it in. I don't think the insurance company cares where the belly is all scratched up. I bet I could do it too, Mooney glides fairly well clean.

 

[igorek82]

Re: The impossible turn made possible---simulated engine failure from 600' with turnb

Inspired by the OP I did some testing today in 172SP with 2nd set of eyes/pilot and video as proof. This was done at a safe altitude, wind light and variable, from simulated take-off climb at Vy (74 KIAS) following by 4 seconds of "oh ****" moment, dropped the nose to achieve Vbg, waited 4 more seconds, 45-degree bank coordinated turn of 180 degrees, all 4 attempts resulted in 250-300 ft loss of altitude. I am aware that the required turn is in fact more than 180 degrees, but we can extrapolate. I am tempted to try this for real, with a capable CFI next to me of course!

CoopAir,

do you have the videos from 500 and 400 ft AGL? How did it go ?

 

[beestforwardspeed]

Re: The impossible turn made possible---simulated engine failure from 600' with turnb

Inspired by the OP I did some testing today in 172SP with 2nd set of eyes/pilot and video as proof. This was done at a safe altitude, wind light and variable, from simulated take-off climb at Vy (74 KIAS) following by 4 seconds of "oh ****" moment, dropped the nose to achieve Vbg, waited 4 more seconds, 45-degree bank coordinated turn of 180 degrees, all 4 attempts resulted in 250-300 ft loss of altitude. I am aware that the required turn is in fact more than 180 degrees, but we can extrapolate. I am tempted to try this for real, with a capable CFI next to me of course!

CoopAir,

do you have the videos from 500 and 400 ft AGL? How did it go ?

You must have read my mind, as just hours ago I did this exercise from 500 AGL. I shot the video in full HD, so make sure to select 1080p and watch it full screen!

https://www.youtube.com/watch?v=L-8yBoOtP0Y&feature=youtu.be

This is the absolute lowest that I would do it. I didn't feel comfortable at all trying it from 400 AGL.

Furthermore, I will now make 500 AGL my hard limit for a turn back if I ever face this situation in real life.

 

[Palmpilot]

Re: The impossible turn made possible---simulated engine failure from 600' with turnb

By the way, I've said this before, but altitude at time of engine failure is not the only criterion for determining whether the maneuver has a chance of succeeding. There also needs to be a strategy for determining whether climb angle vs. glide angle is sufficient.

 

[igorek82]

Re: The impossible turn made possible---simulated engine failure from 600' with turnb

You must have read my mind, as just hours ago I did this exercise from 500 AGL. I shot the video in full HD, so make sure to select 1080p and watch it full screen!

https://www.youtube.com/watch?v=L-8yBoOtP0Y&feature=youtu.be

This is the absolute lowest that I would do it. I didn't feel comfortable at all trying it from 400 AGL.

Furthermore, I will now make 500 AGL my hard limit for a turn back if I ever face this situation in real life.

Great video, thanks! It looks like the obstructions at the departure end of the runway, such as trees, etc, if any, should increase the 500 AGL hard limit...

 

[beestforwardspeed]

Re: The impossible turn made possible---simulated engine failure from 600' with turnb

By the way. I've said this before, but altitude at time of engine failure is not the only criterion for determining whether the maneuver has a chance of succeeding. There also needs to be a strategy for determining whether climb angle vs. glide angle is sufficient.

Absolutely! Even though I failed to mention it, doesn't mean I failed to neglect it.

Density altitude, weight, runway length, wind direction/speed, all affect the minimum safe turnback altitude.

The 500' number is for sea level density altitude, 250 lbs under gross, 3500' or greater runway, and making turn into a light wind.

If at gross weight on a hot day on a shorter runway, I'd bump it up to perhaps 700'. Its just that the 500' is a good base to work with.

 

[nauga]

Re: The impossible turn made possible---simulated engine failure from 600' with turnb

A mathematical analysis has shown that 45° is the bank angle that results in the least altitude loss.

Note that Rogers clearly states that this is for a *steady state* turn, where you're already at a stabilized speed and decent angle/rate. There has been a lot of other research that shows 45 deg may *not* be optimal if you are accelerating (ha!) or decelerating, as in bleeding airspeed in the turn, and that you *may* lose less altitude this way. Rogers' derivation is perfectly valid with the assumptions he states clearly, but they don't hold for every turnback situation. Know your airplane, know your performance, know your procedures, know when to say no.

Nauga,
whose cows are not all spherical

 

[igorek82]

Re: The impossible turn made possible---simulated engine failure from 600' with turnb

... There has been a lot of other research that shows 45 deg may *not* be optimal if you are accelerating (ha!) or decelerating...

Nauga,
whose cows are not all spherical

I recall reading somewhere (i'll post the source if i find it) that 45 deg is not optimal, but "safest" angle of the bank for the impossible turn...

 

[Kritchlow]

Re: The impossible turn made possible---simulated engine failure from 600' with turnb

I would think winds would be a huge part of the equation. Big headwind on takeoff increases chances dramatically I would think.

 

[yah00]

Re: The impossible turn made possible---simulated engine failure from 600' with turnb

I tried this in the same plane (172sp g1000) last night and I was losing just over 220feet of altitude during the 180 degree power off turn. There are just SO many factors I don't think I would try it unless it was my only option.

Sent from my Nexus 5 using Tapatalk

 

[Captain]

Re: The impossible turn made possible---simulated engine failure from 600' with turnb

I thought fer sure someone would have brought it up by now but since I've not seen it I'll burst y'alls bubble....

These 'simulations' neglect to include one massive component. All these attempt ls to reproduce an engine failure neglect one key aspect of the engine failure....the engine failure!

An engine at idle produces some thrust and even less drag. Hold a birthday cake with lit candles behind any prop on the ramp with an engine at idle to see my point.

If you cage an engine at 500' you won't have any of that idle thrust and a whole bunch of drag that will make your aircraft descend much faster. I'd raise that 'hard floor' guys and gals...

 

[Kritchlow]

Re: The impossible turn made possible---simulated engine failure from 600' with turnb

I thought fer sure someone would have brought it up by now but since I've not seen it I'll burst y'alls bubble....

These 'simulations' neglect to include one massive component. All these attempt ls to reproduce an engine failure neglect one key aspect of the engine failure....the engine failure!

An engine at idle produces some thrust and even less drag. Hold a birthday cake with lit candles behind any prop on the ramp with an engine at idle to see my point.

If you cage an engine at 500' you won't have any of that idle thrust and a whole bunch of drag that will make your aircraft descend much faster. I'd raise that 'hard floor' guys and gals...

Thrust??? I figured it would be drag. It takes wind to windmill the prop. My (many years ago) multi training consisted of power on the dead engine to simulate a feathered prop. Good for flying, but made landings interesting when pulling good engine to idol.

 

[Kritchlow]

Re: The impossible turn made possible---simulated engine failure from 600' with turnb

I do understand what you're saying, but I'm still betting the prop is spinning faster than idol when simulated.

It's been many years, so I could be wrong.

 

[Captain]

Re: The impossible turn made possible---simulated engine failure from 600' with turnb

I do understand what you're saying, but I'm still betting the prop is spinning faster than idol when simulated.

It's been many years, so I could be wrong.

To be sure it is. But that idle gas energy is going somewhere and that somewhere is reduced drag.

 

[Palmpilot]

Re: The impossible turn made possible---simulated engine failure from 600' with turnb

If at gross weight on a hot day on a shorter runway, I'd bump it up to perhaps 700'. Its just that the 500' is a good base to work with.

Do you have a method for determining whether the climb angle is equal to or greater than the glide angle, given the wind and density altitude conditions? The reason this matters is that if it isn't, then the extra altitude hurts rather than helps, because it increases the chances of being be too far away to glide to the runway.

 

[denverpilot]

Re: The impossible turn made possible---simulated engine failure from 600' with turnb

Folks also need to go re-do these tests at max gross. Might find it to be interesting.

 

[Kritchlow]

Re: The impossible turn made possible---simulated engine failure from 600' with turnb

To be sure it is. But that idle gas energy is going somewhere and that somewhere is reduced drag.

I get that, but I don't put a lot faith in the theory. If I take my foot off the gas pedal going downhill, I really don't think the engine is pulling the car downhill.
Clearly, for several reasons, not the perfect analogy, but reasonable premise.

 

[Palmpilot]

Re: The impossible turn made possible---simulated engine failure from 600' with turnb

I get that, but I don't put a lot faith in the theory. If I take my foot off the gas pedal going downhill, I really don't think the engine is pulling the car downhill.
Clearly, for several reasons, not the perfect analogy, but reasonable premise.

It's not pulling the car downhill, but it should be providing less resistance to coasting downhill than would occur with the engine turned off.

Conservation of energy is a VERY well-tested principle.

 

[Kritchlow]

Re: The impossible turn made possible---simulated engine failure from 600' with turnb

It's not pulling the car downhill, but it should be providing less resistance to coasting downhill than would occur with the engine turned off.

Conservation of energy is a VERY well-tested principle.

Again, I do understand your point. I just think the majority of the prop rpm is from drag. I realize there is a certain speed (not glide speed) there would be zero drag. That would be like a zero thrust setting. But, and I'm not smart enough to figure it out, I would guess the windmilling increase above that speed is a huge drag. Not 100%, but I'll but it's a disproportionate amount higher percentage wise.

 

[MAKG1]

Re: The impossible turn made possible---simulated engine failure from 600' with turnb

Thrust??? I figured it would be drag. It takes wind to windmill the prop. My (many years ago) multi training consisted of power on the dead engine to simulate a feathered prop. Good for flying, but made landings interesting when pulling good engine to idol.

It is rather clearly so. Idle RPM in a 172 is around 650 RPM on the ground. In the air, it's 1200 or more. Air is spinning the prop, not vice-versa. With a CS prop, pulling it coarse at idle is an effect you can clearly feel, but it makes little change in fuel flow.

Conservation of energy is true enough, but it's small potatoes. You can estimate it with fuel flow.

Effects of density altitude, weight, and lack of wind are much more significant.

 

[Captain]

Re: The impossible turn made possible---simulated engine failure from 600' with turnb

We're talking about managing the energy of a plane at minimum altitude to complete a course reversal. By definition there is no excess energy. People on this very thread are calling out hard floors based on engine idle simulations.

Now, with that said...how can you discount the energy required to spin the prop at 600 rpm? How would you quantify that energy? My human frame has enough energy to spin that prop at say 20 rpm....for MAYBE 1 minute.

I think that idle power is more energy than ya think. Just turning the engine over is a lot of resistance. And two flat paddles in the wind are going to make a ton of drag making the plane drop faster. Not small potatoes imo. Enough to make a few hundred foot adjustment to the hard floor anyway...

 

[Stewartb]

Re: The impossible turn made possible---simulated engine failure from 600' with turnb

Every strip has different conditions and requires different considerations. Engine out at 600' at Lake Hood? Land straight ahead and you're in the drink. Your chances of survival are very small.You'll die within sight of folks walking their dogs on the coastal trail. Options? There's an international airport a half mile to the west. Streets. Open meadows. Hood strip. What I do and where I choose to go depends on the day, the weather, the load, and the nature of the emergency. But, if I never train for engine out turns I limit my options by limiting my skills. That is unacceptable to me.

 

[MAKG1]

Re: The impossible turn made possible---simulated engine failure from 600' with turnb

We're talking about managing the energy of a plane at minimum altitude to complete a course reversal. By definition there is no excess energy. People on this very thread are calling out hard floors based on engine idle simulations.

Now, with that said...how can you discount the energy required to spin the prop at 600 rpm? How would you quantify that energy? My human frame has enough energy to spin that prop at say 20 rpm....for MAYBE 1 minute.

I think that idle power is more energy than ya think. Just turning the engine over is a lot of resistance. And two flat paddles in the wind are going to make a ton of drag making the plane drop faster. Not small potatoes imo. Enough to make a few hundred foot adjustment to the hard floor anyway...

Most of that resistance is elastic and you get it back elsewhere in the cycle. You should try spinning an engine by hand with no spark plugs or rockers.

You quantify energy with fuel flow.

 

[Everskyward]

Re: The impossible turn made possible---simulated engine failure from 600' with turnb

I don't think the above analogies with cars is very good because cars don't have props. Anyone who has a multiengine rating has been taught that the reason you feather the prop on the failed engine is because a windmilling prop acts like a flat disk as far as drag is concerned. That may not be exactly what happens scientifically, but that is how pilots are taught to think about it. The airflow through the prop is turning the engine and everything attached to it at that point, which causes drag. Therefore, demonstrations at idle will not be accurate.

Early on, I was taught not to try the turnback. Although I have about 4,000 hours in singles I never considered it. But people can decide what they want about this. About a month ago I was a passenger in a single and the pilot self-briefed "no turnbacks below 800". That was the first time I had heard anyone say anything like that. I thought it was interesting but I wasn't concerned. It was his airplane and I was just a passenger.

 

[Palmpilot]

Re: The impossible turn made possible---simulated engine failure from 600' with turnb

Every strip has different conditions and requires different considerations. Engine out at 600' at Lake Hood? Land straight ahead and you're in the drink. Your chances of survival are very small.You'll die within sight of folks walking their dogs on the coastal trail. Options? There's an international airport a half mile to the west. Streets. Open meadows. Hood strip. What I do and where I choose to go depends on the day, the weather, the load, and the nature of the emergency. But, if I never train for engine out turns I limit my options by limiting my skills. That is unacceptable to me.

Makes sense.

By the way, if I recall correctly, Professor Rogers, who wrote the turnback analysis I linked earlier, got interested in the subject because operations at his home airport often involved takeoffs over the ocean.

 

[exncsurfer]

Re: The impossible turn made possible---simulated engine failure from 600' with turnb

Every strip has different conditions and requires different considerations. Engine out at 600' at Lake Hood? Land straight ahead and you're in the drink. Your chances of survival are very small.You'll die within sight of folks walking their dogs on the coastal trail. Options? There's an international airport a half mile to the west. Streets. Open meadows. Hood strip. What I do and where I choose to go depends on the day, the weather, the load, and the nature of the emergency. But, if I never train for engine out turns I limit my options by limiting my skills. That is unacceptable to me.

Why the certain doom on ditching there? Water temp? Or, ditching in general?

 

[Stewartb]

Re: The impossible turn made possible---simulated engine failure from 600' with turnb

Water temperature. Life expectancy in Cook Inlet is said to be <10 minutes.

https://www.youtube.com/watch?v=yxdnuMciGjs

 

[CharlieTango]

Re: The impossible turn made possible---simulated engine failure from 600' with turnb

Several have mentioned the effects of density altitude being a big consideration.

I don't get it, what changes with a departure engine failure at a high DA? I can see a partial failure, but assuming we are talking complete failure where is the DA consideration?

I get it that at high DA you could argue less altitude might be gained before failure but the purpose of this drill is to establish and AGL number where you would consider turning back.

Someone else used 180 degree turn to establish altitude needed but 180 won't get you back on the runway you departed, a tear drop or a left 90 followed by a right 270?

 

[Palmpilot]

Re: The impossible turn made possible---simulated engine failure from 600' with turnb

Several have mentioned the effects of density altitude being a big consideration.

I don't get it, what changes with a departure engine failure at a high DA? I can see a partial failure, but assuming we are talking complete failure where is the DA consideration?

I get it that at high DA you could argue less altitude might be gained before failure but the purpose of this drill is to establish and AGL number where you would consider turning back.

Someone else used 180 degree turn to establish altitude needed but 180 won't get you back on the runway you departed, a tear drop or a left 90 followed by a right 270?

I'm no aeronautical engineer, but I assume the reduction in climb performance at high altitudes would reduce the climb angle. If so, that would increase the likelihood of the glide being steeper than the climb was, which would reduce the chances of making it back to the airport.

 

[bflynn]

Re: The impossible turn made possible---simulated engine failure from 600' with turnb

I don't get it, what changes with a departure engine failure at a high DA? I can see a partial failure, but assuming we are talking complete failure where is the DA consideration?

High DA = lower glide performance. Lower performance in general, the air is thinner. Stall speed doesn't change, but attitude of the airplane at stall does...to keep it flying you have to point it a little further down and you'll lose more altitude in the turn.

 

[frfly172]

Re: The impossible turn made possible---simulated engine failure from 600' with turnb

Thanks for posting the video,leaving yourself open to all the experts and nay Sayers.

 

[CharlieTango]

Re: The impossible turn made possible---simulated engine failure from 600' with turnb

Fair enough but a slightly different argument. Again the result of the test should be a safe altitude to consider turning back, so you are getting into the weeds a bit.

Is it true in this context?

Density altitude, weight, runway length, wind direction/speed, all affect the minimum safe turnback altitude...

 

[FastEddieB]

Re: The impossible turn made possible---simulated engine failure from 600' with turnb

High DA = lower glide performance.

Are you sure?

Perhaps at some very high altitude, but most GA glide performance charts look something like this:

If your assertion was correct, that should be a curved line, correct? I don't ever recall seeing one with other than a straight line.

In any case, altitude should not affect glide distance or glide angle, as long as the correct speed is used. And the same applies to aircraft weight.

Stipulated the above may not be correct on the edge of space, but that's not what the discussion is about.

 

[Captain]

Re: The impossible turn made possible---simulated engine failure from 600' with turnb

High DA affects the wings performance regardless of the operation of the engine.

Yes, you'll take longer to attain a specific AGL altitude but you'll also lose that altitude quicker after the failure. Stall speed remains the same...sort of. While indicated 1G stall speed is the same your TAS will be faster. And you won't be at 1G trying to whip the plane around in a course reversal.

So, DA absolutely is a factor in this maneuver. Any "hard floor" established would need to be raised to compensate for a higher DA.