Impossible Turn Testing

[IrishAl]

It's been a really useful thread for me - thanks to everyone.

 

Here's what I've learned from this thread regarding the impossible turn.

 

1. The most efficient/best bank angle to use is 45 degrees.

2. The most efficient airspeed for a turn is Vs, not VL/Dmax.

3. Take special consideration when it's windy before committing.

4. Practice, and learn what you and your plane can do.

6. Have established parameters in place.

 

 

Just one question, can anyone confirm that most efficient turn speed is Vs?

[IrishAl]

Footnote: I also learned that there's a lack of clarity among pilots as to the best course of action to take, with widely differing advice being offered.  The amount of caution expressed underlines for me just how dangerous this situation is.

[FlyingMonkey]

 

Just one question, can anyone confirm that most efficient turn speed is Vs?

 

It's probably actually just above Vs...you can't fly at Vs, after all.

 

I would stick with 60kt...it's a good number for a CT because it's close enough to best L/D to be efficient, but far enough away from stall to be much more safe.  You might be able to haul the nose around at just above stall speed, but the margin of error is very slim and the consequences of failure are extremely high.  I'll take an airplane that remains controllable but doesn't quite make my landing spot over one that I have to fight off the stall/spin throughout the entire turn any day.

[FastEddieB]

Hey, you know what, I'm derping . Long forgot that weight has nothing to do with L/D!

 

I assumed you had just had a minor derp.

 

It happens. Even to me sometimes!

 

It's refreshing to just get a quick mea culpa and not an entrenchment - as in he who shall not be named!

 

For lurkers and newbies and as a refresher, glide ratio is determined by airfoil shape. It gets more complicated when that airfoil is attached to a fuselage, but the resultant conglomeration will have one set glide ratio, unaffected by weight.

 

Weight does, however, definitely affect the speed at which that glide ratio will be achieved. Heavier=Faster. Lighter=Slower.

 

It's counter-intuitive, but say you have two identical CT's - but one is made of styrofoam and one of lead. Let's say 9:1 is the glide ratio. Launch them each from a mile up, and if flown at the optimum speed, each will come to rest 9 miles out - assuming no wind, of course.

 

But...

 

...I'm making up speeds here, but the styrofoam one would be gently wafting down at 10k, taking forever to get to that 9 mile point. But the lead one would be making like a lawn dart at 200k, but will still hit the ground 9 miles from launch.

 

Anyway, dwell on that thought experiment for a while, and maybe you'll avoid a future derp! 

[FastEddieB]

Hey Eddie, you just gave me a GREAT idea...400' AGL Split-S to return to the field when engine out!  (KIDDING KIDDING KIDDING!!!)  

 

You do know, of course, that the Split-S maneuver crossed my mind!

 

But in my experience, that Split-S would consume FAR more altitude than would be available from roughly pattern altitude.

 

Anyway, I think the Hammerhead, while still insane, would at least have a chance of working - not that I'd ever dream of trying it. Outside of a simulator perhaps!

[ABQ CTLS]

Impossible turn: I started out with practice at altitude. Then I moved to the airport environment at 500', then 400', then 300'. When I put it to idle, I hold the nose up until 40kts IAS. If I'm climbing at Vx, this occurs quickly. I briskly push to a G-load of 1.2 to 1.5 (I have the G-meter displayed). I bank at 45 to 60°  and speed builds to the low 60's. At 300' it's tight but doable; 400' is no problem. The one suggestion I have that I haven't seen here is to practice at the actual altitude where you think you would be making this turn. Altitude practice is certainly safer but if you ever think you'll do something like this (rather than straight ahead or activate the BRS) then practice at the altitude you'll use. At least you've got an engine to use if you botch the turn.

[IrishAl]

Agreed - any useful practice must be in a 'real world' scenario in order to execute it with confidence when you're required to.  

 

I've one further thought on this subject that might be helpful.  The most dangerous situation in which to encounter a low level engine out is in a full-flap climb out - after a go around, for example.  

 

Losing power in a full-flap climb is like slamming on the brakes - you've already got a low airspeed, your 'airbrakes' are deployed and you're pointing upwards.   If you don't get the nose down instantly, the altitude needed to recover becomes very large very quickly.  

 

My instructor demonstrated this to me and I was astonished at the difference even one second of delay made in the subsequent loss of altitude.   Throwing the nose forward contradicts natural instinct when you're fifty feet off the ground and trying to climb, but if your engine quits in this situation, doing so will make a big difference to the outcome. 

 

Sorry if I'm stating the obvious, but it's a 'pothole' I was not aware of until it was pointed out to me.

[FastEddieB]

Impossible turn: I started out with practice at altitude. Then I moved to the airport environment at 500', then 400', then 300'...I At least you've got an engine to use if you botch the turn.

1) You have apparently refined a skill that I never have. To the extent that an added skill set is a good thing and could come in handy some day, congratulations.

 

2) I've avoided that training for reasons I think I've already articulated in this thread - my game plan at those altitudes does not include a return to the airport, so I see no point in trying for a maneuver I really do not wish to attempt "in anger"!

 

3) The last part about "botching the turn" got my attention. The way I see the turn being "botched" generally would be subconsciously rushing the turn with rudder. The result of a turn "botched" in that way is most often a stall/spin, which from 400' or even 300' would leave no time for a recovery, even if "you've got an engine". I guess there are other ways to "botch" a turn of up to 60° bank close to the ground, but most often it's the stall/spin that is most prevalent in the accident reports.

 

Again, not criticizing your choice to practice that maneuver.

 

Carry on!

[Ed Cesnalis]

1) You have apparently refined a skill that I never have. To the extent that an added skill set is a good thing and could come in handy some day, congratulations.

 

2) I've avoided that training for reasons I think I've already articulated in this thread - my game plan at those altitudes does not include a return to the airport, so I see no point in trying for a maneuver I really do not wish to attempt "in anger"!

 

3) The last part about "botching the turn" got my attention. The way I see the turn being "botched" generally would be subconsciously rushing the turn with rudder. The result of a turn "botched" in that way is most often a stall/spin, which from 400' or even 300' would leave no time for a recovery, even if "you've got an engine". I guess there are other ways to "botch" a turn of up to 60° bank close to the ground, but most often it's the stall/spin that is most prevalent in the accident reports.

 

Again, not criticizing your choice to practice that maneuver.

 

Carry on!

 

Perhaps a good reason to turn right vs left?

[FastEddieB]

Food for thought:

http://www.aopa.org/AOPA-Live.aspx?watch=lyOHVoMjr2oVEH1Ipz6TLpnTSBQ8LWRR

One caveat - I'm surprised they did not mention that it appeared they performed the maneuver at idle thrust. A failed engine, especially a windmilling one, would adversely affect the performance she got.

[FastEddieB]

Perhaps a good reason to turn right vs left?

Reasoning?

[Ed Cesnalis]

Reasoning?

 

I believe that my CT will easily spin to the left, to the right, not so easy.

[IrishAl]

I believe that my CT will easily spin to the left, to the right, not so easy.

 

Even with no power?

[Jim Meade]

I've done a dozen or more dead stick landings in my CTSW, most recently, I cut the engine at 50' above the runway while landing to see if the nose would pitch down dramatically. I was somewhat surprised that it did not. I was already probably in the high 40's low 50's with 30° flaps, probably about my typical setup at that height to land. I land slower, of course, but that is neither here nor there.

My experience on the dead stick landings, which I did in a typical pattern usually shutting off abeam the numbers on downwind, is the prop stops pretty quickly at that speed, which is typically less than 80 kias and which I routinely quickly take to 62 kias because I may go to flaps 30 on base or final, depending on the situation. One does indeed have to put the nose down somewhat more than normal, but not drastically so.

As far as which way to turn, what I do is always know the wind and if I were to execute this maneuver I would turn into the wind if possible. No explanation needed. FWIW, it's what we were taught and how we execute in glider training. Note that this assumes landing back on the runway. If there is a parallel runway or a good taxiway that is clear, one would consider turning to line up with that feature.

As far as spinning, if the prop is stopped and perhaps at idle, I'm not sure why a plane would spin better to the left or right as the engine and prop rotation will have little effect on the maneuver.

As far as a full flap departure, about the only time many of us would contemplate that is if we are executing a go-around after an aborted full-flap approach. I often do a full flap approach. If a deer suddenly sprang out of the woods and stopped on the runway, my response may have to be very quick. If the deer is right in front of you the best course of action may be to hit it head on. I always taught my daugherts in driving "never go in the ditch to avoid an animal". One had to put that advice into action, which she did to good effect. If there is time to avoid the obstacle by climbing, one would put in full power, pitch appropriately about the same time and take the flaps out one step at a time to 15° where it could stay until past the danger point. The most dangerous action would be the impulse to pitch up to steeply too soon. It's better to fly at the object and build airspeed, then pitch up to just clear.

We might want to keep in mind that the necessity for a return in takeoff and climb out may occur in different conditions and each instance probably is unique.

[Ed Cesnalis]

All things being equal ( no adverse wind,  agreeable terrain )  the right turn recommendation is a reply to Eddie's concern about training, presumably at idle.

 

In the real deal I would avoid the mistake of using excess rudder.  I would instead error on the side of a too steep bank and no back pressure.

 

Practicing button hook approaches ( no base leg ) is a great way to see how tightly you can maneuver on approach.  I tend to make this 180 too tight and then have to make 2 more turns to step over to the runway.

[FastEddieB]

 

In the real deal I would avoid the mistake of using excess rudder.

I'd hope so.

 

But don't you think the majority of pilots who spun and died might have also thought that they knew better than to skid a turn?

[IrishAl]

Food for thought:

 

http://www.aopa.org/AOPA-Live.aspx?watch=lyOHVoMjr2oVEH1Ipz6TLpnTSBQ8LWRR

 

One caveat - I'm surprised they did not mention that it appeared they performed the maneuver at idle thrust. A failed engine, espeviall a windmilling one, would adversely affect the performance she got.

Interesting video - thanks.

 

It surprises me often just how 'safety obsessed' society has become in a few short decades.  I think we are becoming so risk-averse that it actually inhibits the learning of parameters and of skill and of good judgement. 

 

The video shows that at 500' the turn is entirely possible (in benign conditions and with practice), and that number includes a  50% safety margin as well as a full five second reaction time.  The instructor is clearly surprised by the results.  Yet he concludes by saying he's still sticking to his original advice of no turnback below 1000' - despite the evidence he's just produced.  

It's as though he's expecting a pat on the back for being such a 'sensible guy'. 

 

Laying down arbitrary markers that are totally inaccurate (because they're a country mile on the safe side of the real line)  and that bow to 'safety at all costs' may actually cause a pilot at 800 feet to face landing in a forest of trees instead of making a pretty sure turn back to the field.  

[Ed Cesnalis]

I'd hope so.

 

But don't you think the majority of pilots who spun and died might have also thought that they knew better than to skid a turn?

 

No I don't.  More than 90% of pilots that I hear comment on the subject use the phrase 'remain coordinated' to avoid spinning.  I don't think most pilots that put it that way know the skid is the spin entry not the slip.

 

I also hear pilots say they avoid slips so they can remain coordinated and avoid spin entry.

 

I've been told myself to limit banks to 30* and my response was 'no thanks'

 

This is a CT forum and it is worth noting that a CT rolls quickly and steeply banked turns are more natural than in many other designs, a big part of the impossible turn is awareness of the terrain and other obstacles and experience maneuvering near terrain as in ridge soaring skills.

 

Some of us began in part 103 ops and are even self taught.  Some in this group are used to 300' patterns for separation, dead stick practice and skills that come with very light aircraft.  My CT does'n't fly like a Cessna but can be flown like one.  It doesn't fly like an ultra light but it can be flown like one.  A background in lighter planes and soaring brings a skill set that is more at home training for and executing a return to the field.

 

Experience flying with 2-stroke engines tends to advance these skills as well.  If you used to fly 2-strokes you likely have some real world practice. 

[FastEddieB]

Interesting video - thanks.

 

It surprises me often just how 'safety obsessed' society has become in a few short decades. 

 

For perspective, when I trained for my Private in 1975 and a couple years later for my CFI, the emphasis even back then was to NOT attempt a return to the airport until approximately pattern altitude.

 

As an instructor, I had to be careful teaching too far outside the book

 

"I know the FAA frowns on turns back to the airport, and has published pamphlets and Advisory Circulars to that effect, but we're going to practice it anyway - what do they know?"

 

One could imagine a scenario where a student died trying to return to an airport, and an instructor found himself in civil court with his students testifying how they had taught them how to do it, in spite of FAA recommendations to the contrary.

 

It's not that I lived in fear of such things. I just tried to stay within the guidelines and recommendations that were being emphasized.

 

Upside is I never to my knowledge had a student later die in a return to an airport. And I never got sued - for anything - with 4,500 hours of dual given.

[IrishAl]

I'd hope so.

 

But don't you think the majority of pilots who spun and died might have also thought that they knew better than to skid a turn?

 

It would seem to me that most skid/stall/spin accidents occur for two reasons.

 

Many happen 'out of the blue' - inattention, lack of awareness, followed by a mistake and then over-correction.   

 

The others occur because of an unexpected event, such as an engine out close to the ground, which is our topic. The pilot is on high alert and everything has his full attention, but he panics, gives it too much rudder and spins.

 

And it seems you're right Eddie, many these pilots felt confident of their ability - until they were stretched and they had nothing to fall back on - in other words, no training in the particular situation.

 

In emergencies, your training kicks in (I think you once called it the 'law of primacy-?) but if you have not trained for the situation, you'll make lots of mistakes when it happens for the first time.

 

I simply can't understand what seems like a 'blanket ban' on turnbacks below 1000', or on practising for them.

 

   Post 108 (Eddie) : 1) You have apparently refined a skill that I never have. 

                                 2) I've avoided that training 

 

Surely logic demands that flying with no power close to the ground be 'trained to death' rather than ignored, and what better way than practising the turnback?  The instructor (in the video) gives the impression that he has rarely if ever carried out the manoeuver with a student, never mind close to the ground.

 

I'd guess that most impossible turn fatalities occur because the pilot has had no training for it and he fluffs it when he has to do it for the very first time - without an engine to fall back on.

[S3flyer]

 

 

I've done a dozen or more dead stick landings in my CTSW, most recently, I cut the engine at 50' above the runway while landing to see if the nose would pitch down dramatically. I was somewhat surprised that it did not. I was already probably in the high 40's low 50's with 30° flaps, probably about my typical setup at that height to land. I land slower, of course, but that is neither here nor there.

Jim -- was there an appreciable difference in glide ratio when doing dead stick versus idle?

[Jim Meade]

What do we know about how "stall spin" accidents start? Is it the plane is flying at 70 kias, makes an uncoordinated maneuver and enters a spin? Or is it the plane is flying at 35 knots trying to stretch an approach, stalls and gets uncoordinated in the recovery and drops a wing? That latter would be called a stall spin just as the former would.

One of the reasons I did my engine out at 50' was to see how much shorter my touchdown was. I found it was not a lot shorter. Of course, different planes are different. If you stopped the engines on a King Air 90 at 50 feet you are in for a sudden drop (even worse if you went into beta ).

What I'm getting at is our aiming point on a runway and whether we choose one that lets us lose an engine on final and not have to accept landing short.

I've had my share of landing a glider and bringing it over the threshhold in ground effect. That may happen because one wants to avoid a long retrieve on the runway but one forgets the headwind on final. Ufda! Wanting to hold the nose up and knowing you need to push it down and then seeking that sweet ground effect spot to compensate for earlier poor decision making.

If one sees the touchdown spot moving ahead in the windshield, some have the tendency to pitch up. Bad idea. But, is that what brings on the stall that then turns into a wing drop (it doesn't have to be a 3 turn spin to be a stall spin).?

We in this discussion may be making unwarranted assumptions about what the NTSB means when it reports "stall spin". My point is that flying too slowly may well lead to a "stall spin" that is really just a stall where a wing dropped as opposed to some radical uncoordinated spin entry.

[Jim Meade]

Jim -- was there an appreciable difference in glide ratio when doing dead stick versus idle?

That's a good question and one I'm going to have to think about a little.

[FlyingMonkey]

1) You have apparently refined a skill that I never have. To the extent that an added skill set is a good thing and could come in handy some day, congratulations.

 

2) I've avoided that training for reasons I think I've already articulated in this thread - my game plan at those altitudes does not include a return to the airport, so I see no point in trying for a maneuver I really do not wish to attempt "in anger"!

 

3) The last part about "botching the turn" got my attention. The way I see the turn being "botched" generally would be subconsciously rushing the turn with rudder. The result of a turn "botched" in that way is most often a stall/spin, which from 400' or even 300' would leave no time for a recovery, even if "you've got an engine". I guess there are other ways to "botch" a turn of up to 60° bank close to the ground, but most often it's the stall/spin that is most prevalent in the accident reports.

 

Again, not criticizing your choice to practice that maneuver.

 

Carry on!

 

Here's a thought...what if you consciously planted your feet on the floor, off the pedals, at the beginning of the maneuver?  Then as you turn you will likely only be either coordinated or uncoordinated in the direction of a slip due to adverse yaw.  There is no danger of "rushing the turn"  with inside skidding rudder inputs because your feet are off the pedals.  It might slow down your turn around due to potential slipping lack of coordination, but takes the skidding stall/spin danger out of the equation.

 

Of course once you are aligned with your landing zone you'd reengage your feet for the landing segment.

 

Just a thought, feel free to point out the doom associated with this idea.   

[FastEddieB]

Between now and Monday I'd be available to go play a bit!