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Impossible Turn Testing


FlyingMonkey

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I was flying Saturday and decided to try out the "impossible turn".  It was too bumpy down around my normal 3000ft training altitude for good testing, so I climbed to 4500 feet.  The test procedure went as follows:

 

1) Slow down to about 75 knots at 15° flaps...descend to ~4200ft.

 

2) Get into departure speed attitude:  full power climb at 60kt and 15° flaps

 

3) At 4500ft, pull power to idle and execute turn maneuver.

 

 

I did this three times.  The first time I waited 2 seconds before doing anything (deer in headlights time), the other two runs I maneuvered immediately once I pulled the power.  All three runs were very consistent, with a 180° turn causing a 250-300ft altitude loss.  This is with an aggressive pitch down and immediate roll to a 45° turn.  

 

The only difference with the run where I waited before turning was speed loss; because I started the maneuver in a nose high departure configuration, speed bleeds off very quickly.  When I executed the maneuver immediately, my speed was about 55kt when I got the nose low enough to start a turn, and the speed came up from there to about 60-65kt.  With the delay, speed dropped to about 45-48kt before the speed stabilized and started coming back up.

 

Lessons learned:

 

1) If the engine quits in a climb, GET THE NOSE DOWN, RIGHT NOW.  You only have a few seconds before the speed bleeds down to stall speeds. 

 

2) Given that to really turn back to a runway will require more like a 270° turn back and then another turn back the other way to align with the runway, I think 400' is a bare minimum to get it done, and with less than 500' I'd probably still want to go straight ahead unless the terrain ahead was hostile.

 

3) On a cold day solo in a CT, you might be too CLOSE to the runway to make this turn.  Saturday I was seeing 1200fpm+ climbs, and I was making my 700' AGL turn to crosswind while still over the last few hundred feet of the 5000' runway!  If the engine quit at the crosswind turn, it might be better to make an abbreviated full pattern, going straight to a tight downwind, then making a 180 turn to final to land midway down the runway in the direction you took off from.  I don't know if that close to the runway at 700' AGL you could make all the turns required and get down fast enough to have room left to land behind you, even with full flaps and a big slip.  Especially since that is now likely a downwind landing.

 

4)  Emergency training is fun and educational. 

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There are many scenarios where in a CT you can make the turn but get back with too much altitude and overrun the downwind landing attempt.

 

At home terrain is an issue and my thinking when departing 09 has evolved to: ( assuming engine lost at 600' strait out)

  • lower nose and begin descent on a teardrop initially to the left.
  • 1/2-2/3 way around the teardrop decide to continue or turn back left to land at lower terrain (Crowley Lake)
  • Fly the teardrop descending adequately to make the first 1/2 of the runway and land downwind.
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Another consideration is that you don't always have to get back to the runway.  Just getting back to the airport property with open cut grass areas, taxiways, and possibly an open ramp might be enough to get on the ground safely and a better option than surrounding terrain.  

 

My airport has a lot of open space between runways and taxiways with low cut grass, and there is a golf course across the street.  Depending on where one is when the engine quit, there might be quite a few decent options very close to the airport or on airport property but not on a runway.

 

CT, is your alternate plan to land in in the water of the lake, or is Crowley a dry lake bed?  Do you give any consideration to the BRS system, or is that really a very last option in your planning?  

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CT, is your alternate plan to land in in the water of the lake, or is Crowley a dry lake bed?  Do you give any consideration to the BRS system, or is that really a very last option in your planning?  

 

I've seen quite a number of overloaded planes that couldn't get out of ground effect land on the shore of Crowley.  I can't think of any of them flipped over, I'll probably be the first  :),  Sage, mud, creeks and steers are the hazzards.

 

I have 2 forced landings, both situations kinda ugly but both times I landed and did not go for the 2nd Chanz.  I guess its in my nature to land and not tear up the plane.

 

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In my opinion it is a good idea for most pilots to train on this after they get some experience. I've done it with a fellow pilot at altitude. Here are a couple of observations:

 

*Even at idle, your engine is developing some thrust. There will be different thrust and different drag with a dead engine. One wants to think about this.

 

*When I did it, I, too, got the plane into take-off configuration. I had a fellow pilot aboard who pulled the throttle so I could not specifically anticipate it. Yes, of course one is primed for the event, so that does have one on alert. It seems to me that it helps if one has a departure briefing that one says out loud before take-off (see below).

 

*It is important to think consciously about the wind and if feasible make the turn into the wind. We want to remember that even at a few hundred feet the wind may be different in direction and intensity than we felt at the ground.

 

I lined up over a road as a notional runway and my return attempts yielded altitude losses of 350' and 400' before getting back on line. Mine was at 2500 AGL on a summer day.

 

A possible take-off briefing:

"Any problem on the ground, stay on the ground.

Any problem less than (choose an AGL you are comfortable with) land straight ahead (or nearly so - depends on the specific location)

Any problem over (choose your AGL number) maneuver to best landing site - wind is from the (left, right, ahead)

 

I'm not advocating any of the above, only offering them as points of discussion.

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In my opinion it is a good idea for most pilots to train on this after they get some experience. I've done it with a fellow pilot at altitude. Here are a couple of observations:

 

*Even at idle, your engine is developing some thrust. There will be different thrust and different drag with a dead engine. One wants to think about this.

 

*When I did it, I, too, got the plane into take-off configuration. I had a fellow pilot aboard who pulled the throttle so I could not specifically anticipate it. Yes, of course one is primed for the event, so that does have one on alert. It seems to me that it helps if one has a departure briefing that one says out loud before take-off (see below).

 

*It is important to think consciously about the wind and if feasible make the turn into the wind. We want to remember that even at a few hundred feet the wind may be different in direction and intensity than we felt at the ground.

 

I lined up over a road as a notional runway and my return attempts yielded altitude losses of 350' and 400' before getting back on line. Mine was at 2500 AGL on a summer day.

 

A possible take-off briefing:

"Any problem on the ground, stay on the ground.

Any problem less than (choose an AGL you are comfortable with) land straight ahead (or nearly so - depends on the specific location)

Any problem over (choose your AGL number) maneuver to best landing site - wind is from the (left, right, ahead)

 

I'm not advocating any of the above, only offering them as points of discussion.

A fouth choice I consider is ; deploy BRS.

 

Cheers.

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I'd love to hear some comments on what is the most efficient turn rate with no power.  In other words, do you drop the nose sharply and turn as quickly as possible at best glide speed, or do you keep it all gentle and make a medium bank turn? 

 

Obviously, this is a critical question in making the decision to turn back or not.

 

I read recently that in the Second World War, the RAF taught their pilots that the most efficient engine-out turns were steep ones.

 

Last week I tried this out while flying in the circuit.  I added a few hundred feet to 1300 agl, cut the power,held the nose up until I hit best glide (58-60kts) and then did an aggressive 360 to see how much altitude it cost me while maintaining 60kts.  In both cases it was around 500 ft.  I'm sure an experienced pilot could improve substantially on that, but I'd like to know by how much, and what of turn should be made to minimize altitude loss. (Ikarus C42 with 1 pob, 30 ltrs fuel.) 

 

So the question is, how do you maximise the efficiency of such a turn?

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So I have to ask, has anyone actually pulled the throttle at 500 feet AGL and made it back to the runway and landed successfully?

 

I ask because I have.  Two or three times and it was pretty much a non-event.  Pitch the nose down until you're flying 60 knots, tight turn back with 45 degree bank angle, another tight turn to line up, and you're above the numbers at 200'.  Add flaps and set it down.  Granted, this assumes 1) no traffic  2) no significant wind and 3) 6000 feet of runway.  YMMV.

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I'd love to hear some comments on what is the most efficient turn rate with no power.  In other words, do you drop the nose sharply and turn as quickly as possible at 

 

Last week I tried this out while flying in the circuit.  I added a few hundred feet to 1300 agl, cut the power,held the nose up until I hit best glide (58-60kts) and then did an aggressive 360 to see how much altitude it cost me while maintaining 60kts.  In both cases it was around 500 ft.  I'm sure an experienced pilot could improve substantially on that, but I'd like to know by how much, and what of turn should be made to minimize altitude loss. (Ikarus C42 with 1 pob, 30 ltrs fuel.) 

 

So the question is, how do you maximise the efficiency of such a turn?

 

I think waiting for the speed to decay to best glide is a mistake.  That is just bleeding off energy that you can never get back, while traveling farther away from the intended touchdown.  You can pitch up and use that speed to gain additional altitude, or start your turn immediately and let the speed help you make the turn.  Personally I think using the speed in the turn is better, as you will always lose some energy when translating airspeed to altitude and vice versa.  

 

The more speed you have in the turn, the tighter and faster you can make your turn.  Just turn at 45° or more watching the airspeed, and start easing off the turn or lowering the nose as you get to best glide to avoid an accelerated stall.  But even at 60kt you can easily keep a 45° turn in, though you will be nose low and descending to maintain that speed.

 

Note that using your method you still got a full 360° turn in 500ft, that's pretty good and potentially more than you'd need to make the turn in a real situation.

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I'd love to hear some comments on what is the most efficient turn rate with no power.  In other words, do you drop the nose sharply and turn as quickly as possible at best glide speed, or do you keep it all gentle and make a medium bank turn? 

 

Obviously, this is a critical question in making the decision to turn back or not.

 

I read recently that in the Second World War, the RAF taught their pilots that the most efficient engine-out turns were steep ones.

 

Last week I tried this out while flying in the circuit.  I added a few hundred feet to 1300 agl, cut the power,held the nose up until I hit best glide (58-60kts) and then did an aggressive 360 to see how much altitude it cost me while maintaining 60kts.  In both cases it was around 500 ft.  I'm sure an experienced pilot could improve substantially on that, but I'd like to know by how much, and what of turn should be made to minimize altitude loss. (Ikarus C42 with 1 pob, 30 ltrs fuel.) 

 

So the question is, how do you maximise the efficiency of such a turn?

 

 

You must drop the nose ASAP to obtain best glide. In addition, too aggressive of a turn results in too rapid loss of airspeed and altitude, and since aerodynamic equations are not linear, there are zones where drag is minimal, lift is maximal, and distance traveled is furthest (some others too but irrelevant). For the impossible turn, I believe it's around 30 degrees of bank for the most favorable conditions. Standard rate is too slow and you will run out of altitude before you finish, and steep turns cause you to hemorrhage airspeed (therefore altitude) and greatly increase the risk of spins.

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It surprises me that only one voice has spoken up on the BRS. Why risk either the impossible turn, or worse, an off airport landing into unfriendly terrain? We can practice (and I do!) the impossible turn, engine out landings, etc. all we want, but we cannot simulate your brain going into stupid mode when the s--t hits the fan. IOW, I cannot guarantee that the stress of an engine out situation will not degrade my flying skills enough to cause me to screw the pooch. What I can virtually guarantee is a walk-away-from situation if I pull the red handle. Granted, up to 250AGL, I'm like all those poor slobs without BRS ( :D ) and will make the best of things. Above 250, it's time to give the airplane to the insurance company and live to fly another airplane.

 

Just thought I'd suggest an alternate game plan!

:D Kevin

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"The more speed you have in the turn, the tighter and faster you can make your turn."

 

Andy,

 

This seems counter-intuitive to me. From my way of thinking, the faster you fly, the wider the turn radius will be. IOW, I can turn my CT in a way shorter distance than I could in my Cirrus.

 

What am I missing?

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"The more speed you have in the turn, the tighter and faster you can make your turn."

 

Andy,

 

This seems counter-intuitive to me. From my way of thinking, the faster you fly, the wider the turn radius will be. IOW, I can turn my CT in a way shorter distance than I could in my Cirrus.

 

What am I missing?

 

There are two aspects to a turn, radius and rate.  The radius in this case doesn't matter too much, as in a CT the radius of turn in the impossible turn scenario will not be too much different between 60kt and 80kt.  The RATE of turn (how many degrees per second you can push the nose around the circle) you can sustain with higher speed is greater.  if at 80kt you can keep a 1.8g turn, and at 60kt you can do a 1.5g turn (without stalling) then you are going to make the turn around faster at 80kt.

 

Of course, with a dead engine you are making no thrust and any speed you have decays.  If the engine quits at 80kt, I am going to be able to pull a tighter sustained turn until that speed bleeds off to my "safe" target speed of 60kt than if I wait to make the turn until 60kt, not to mention that as the speed falls I'm traveling farther from my desired landing with no way to recover the energy lost.

 

Now, you could let the nose drop low enough that your speed would stay at 80kt and turn really tight, but that 80kt is above the best L/D ratio of the CT, which is IIRC ~62kt at 15° flaps.  So doing that would make for a quick turn, but you are burning a lot of altitude to do that, and you will likely come out of the turn faster but not have enough glide to get you to the landing zone.

 

I'm not advocating making a turn faster than 60kt; but if the engine quits at 70kt or 80kt, don't wait to make the turn.  Get the nose down and make your turn, just let that extra speed bleed off in the turn and stabilize the turn when you get to ~60kt.  That speed will give you the best distance to glide (at 15° flaps) once you come out of the turn and the best chance to get to your landing zone.

 

Fighter pilots use this all the time, it's what they call an "angles fight".  You don't really care how big your turn is, you care about how many degrees per second you can generate to point your nose on the enemy (or at your landing zone).  The same principle really applies in real dogfights, as airplanes always run out of energy before they run out of maneuvers that the pilots would like to make, so they have to maximize them.   :)

 

This is IMO of course and YMMV, void where prohibited by law.

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It surprises me that only one voice has spoken up on the BRS. Why risk either the impossible turn, or worse, an off airport landing into unfriendly terrain? We can practice (and I do!) the impossible turn, engine out landings, etc. all we want, but we cannot simulate your brain going into stupid mode when the s--t hits the fan. IOW, I cannot guarantee that the stress of an engine out situation will not degrade my flying skills enough to cause me to screw the pooch. What I can virtually guarantee is a walk-away-from situation if I pull the red handle. Granted, up to 250AGL, I'm like all those poor slobs without BRS ( :D ) and will make the best of things. Above 250, it's time to give the airplane to the insurance company and live to fly another airplane.

 

Just thought I'd suggest an alternate game plan!

:D Kevin

 

I agree with you, but it's all about having options.  If you never practice the turn, you have no idea how it might work out, so you have to take that option off the table, leaving only landing straight ahead or the BRS.  But if you have 800' AGL when the engine dies, there is no reason not to make that turn, it's plenty of height.  Even if it doesn't work out, you will know if well before you are outside the BRS deployment envelope, and you still have that option.

 

Imagine a far-fetched scenario.  You are taking off from the Mt. Gonnakillya airport, where the runway departure hangs on the edge of the basin of this giant volcano filled with molten lava.  If your engine quits on takeoff, you can't land straight ahead (remember, lava) and you can't use the BRS (again...lava).  Your ONLY option is to turn back.  

 

Granted that is a silly scenario, but it's not so hard to imagine a scenario where terrain or other circumstances dictate your best option for survival might be knowing how and when to use the impossible turn. 

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" The more speed you have, the tighter you can turn "  is exactly right and here's why.

The stall speed varies with the square root of the " G " force.

If you pull 2 G's,  the square root of "2"  is 1.414 so if your POH says the stall speed is 50 knots,

when pulling 2 G's, the stall speed is now......50X 1.414   which is  70.7 kts for a stall speed.

 

So...for example, if you are flying the pattern at 65 Kts, feeling REALLY safe because you're 15 Kts above your

stall speed and you crank it into a 2 G turn to avoid overshooting the final,  you are now in a steep bank, close to the ground,

and 5 Kts BELOW stall speed. OOPS   DON'T  DO IT !

 

3Gs means your stall speed is 50X 1.732 = 86.6 kts stall speed.

 

So, don't crank it around and pull G's  unless you have airspeed

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You are talking about steeper bank, not tighter turn.  You increase load factor and lose speed.  That's why Morden is not gonna win.  He will try to bank to steeply and loose too much speed while being steep to keep that speed without an engine and hit the ground before he makes it back to the runway.

 

Steeper bank means higher turn rate for the same pitch angle relative to the horizon.  At the same speed, more bank will also give a tighter turn radius as well.  A level turn at 30° bank angle is a 1.2g load, and a level turn at 60° bank angle is a 2g load.  Which one do you think pulls your nose around the horizon faster?  If both turns are made at 80kt, which do you think has a smaller radius?  This is yet another thing that should have been drilled into you in primary training, but apparently was not.  

 

http://en.wikipedia.org/wiki/Load_factor_%28aeronautics%29

 

There is a point beyond which more speed will not generate more turn rate within airframe limits, called "corner speed".  For a CT,  that speed would be where we could generate 4g (airframe limit), which is slightly more than a 75° bank angle in level flight.  We might be able to do that on a brief basis, but I know for a fact that to sustain a 4g level turn would require more power than the 100hp we can generate, by a large margin.

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But if you have 800' AGL when the engine dies, there is no reason not to make that turn, it's plenty of height. Even if it doesn't work out, you will know if well before you are outside the BRS deployment envelope, and you still have that option.

 

 

I'll disagree here.

 

In the case of the "Impossible Turn", the biggest danger is rushing the turn with rudder at low speed. It's so instinctive that even experienced pilots fall victim to it. So, "if it doesn't work out" often means that part way through the turn, the inside wing drops precipitously as the plane enters a spin.

 

At that point, it's unlikely that one could have the presence of mind - and time - to pull the chute.

 

This could likely be the very last thing one saw, with only a few seconds to decide, reach for and pull the chute - which itself takes a finite amount of time to deploy.

 

12969009965_283de39044.jpg

 

Not saying it's "impossible", but I think it's a dangerous assumption to think on an engine failure on climbout one will have the time and mental capacity to sort through things and try them sequentially

 

To avoid repetition, there's a very long thread on this very topic on Pilots of America, where I've weighed in.

 

http://www.pilotsofamerica.com/forum/showthread.php?t=76880

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" The more speed you have, the tighter you can turn "  is exactly right and here's why.

The stall speed varies with the square root of the " G " force.

If you pull 2 G's,  the square root of "2"  is 1.414 so if your POH says the stall speed is 50 knots,

when pulling 2 G's, the stall speed is now......50X 1.414   which is  70.7 kts for a stall speed.

 

So...for example, if you are flying the pattern at 65 Kts, feeling REALLY safe because you're 15 Kts above your

stall speed and you crank it into a 2 G turn to avoid overshooting the final,  you are now in a steep bank, close to the ground,

and 5 Kts BELOW stall speed. OOPS   DON'T  DO IT !

 

3Gs means your stall speed is 50X 1.732 = 86.6 kts stall speed.

 

So, don't crank it around and pull G's  unless you have airspeed

 

Increased bank does not always lead to higher loading and increased stall speed. I have been close to 90° bank while also being close to 0 G's.

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Increased bank does not always lead to higher loading and increased stall speed. I have been close to 90° bank while also being close to 0 G's.

That's why I said "increased bank with the same pitch relative to the horizon." If you are at zero pitch (level), and maintain that pitch, a larger bank angle will increase loading. This will require stick back pressure or nose up trim. Of course if you just let the nose drop, you are just rolling the aircraft, and may or may not be banking appreciably.

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We learned from John Horne I believe that flaps 15 is not best LD.  Just set up a power at idle glide, where you have the field made without flaps then deploy flaps and now you can't make the field.  Its persuasive.

Agreed, but if I'm in a low altitude climb out and the engine quits, I will probably not be messing with flaps much, at least until I'm turned around and can evaluate the need for any config changes.

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