Impossible Turn Practice

[Palmpilot]

So why were you using 60 degrees?

I only mentioned 60 degrees because you did.

 

[cherokeeflyboy]

Ed Williams wrote a very interesting paper titled "Dealing with engine failure on
departure and the “impossible turn” decision that I found veryintriguing.
I would be interested in hearing others opinions on what he has to say.
http://williams.best.vwh.net/turnback_seminar_Oct_2008.pdf

In it he says.."There is no performance increase by using bank angles greater than 45 degrees.
Increasing airspeed 10-20 kts above stall adds 100-150’ to descent."

 

[gismo]

I only mentioned 60 degrees because you did.

Oops. I didn't even notice I was replying to you instead of Dan.

 

[gismo]

Ed Williams wrote a very interesting paper titled "Dealing with engine failure on
departure and the “impossible turn” decision that I found veryintriguing.
I would be interested in hearing others opinions on what he has to say.
http://williams.best.vwh.net/turnback_seminar_Oct_2008.pdf

In it he says.."There is no performance increase by using bank angles greater than 45 degrees.

That's consistent with Dr Rogers analysis which shows a minimum in the descent rate during a gliding turn at 45°.

Increasing airspeed 10-20 kts above stall adds 100-150’ to descent."

That also makes sense assuming you're talking about the weight adjusted accelerated stall speed for the 45° banked turn which is 19% higher than the 1 g stall speed for the same airplane at the same weight.

 

[Palmpilot]

Oops. I didn't even notice I was replying to you instead of Dan.

Been there, done that!

 

[Palmpilot]

Ed Williams wrote a very interesting paper titled "Dealing with engine failure on
departure and the “impossible turn” decision that I found veryintriguing.
I would be interested in hearing others opinions on what he has to say.
http://williams.best.vwh.net/turnback_seminar_Oct_2008.pdf

In it he says.."There is no performance increase by using bank angles greater than 45 degrees.
Increasing airspeed 10-20 kts above stall adds 100-150’ to descent."

Thanks for the link. Ed is another one of those highly accomplished physicists.

 

[dmccormack]

That said, I suspect the difference between 45° and what's truly optimal isn't great and since the wind will affect all of that plus the fact that most of us aren't going to hold a target bank angle to within a degree 45 degrees seems like a good target.

So why were you using 60 degrees?

Crank it over and head back! Again, this was in repeated practice at altitude. Best 200 degree turn with least altitude loss was a big push and a big bank -- which my calibrated eye figured was around 60 degrees -- definitely past 45.

Keep in mind this in a Chief -- a draggy airframe with a wide fuselage and light weight.

 

[denverpilot]

Sorry to hijack, but something came to mind that I've always wanted to ask...

Is knife-edge (90 degree bank, zero turn, level flight) flight coordinated or uncoordinated?

It seems to me that "coordination" is a contrived concept in some respects where what you're really saying is that you don't want one wing generating more lift than the other, because in a stall in that configuration, one wing is going to stall before the other.

In an aircraft that can maintain knife-edge flight where lift is being generated by the fuselage and raw engine thrust, "coordination" seems a confusing concept. But only in that scenario where there's zero turn to reference "coordination" off of?

Just thinking about weird things tonight...

So that same aircraft with zero engine thrust and descending rapidly... zero turn, very high descent rate, 90 degree bank... is that coordinated flight or not?

The only reason this came to mind was that the proponents of the "big forward push" brought the "feeling" of that push to mind. If you pushed TOO much while rolling in, let's say to the left, you'd actually begin a right turn. It seems there's a point where pushing too much would be bad if the intent is to turn left, for example. I could see someone who hadn't practiced/tried this, doing that.

Pushing too hard forward as they roll, and actually making a slight turn the wrong direction in the entry, thus killing valuable time and altitude needed to get around the turn-back.

Technique-wise, I could also see someone who'd never done a high roll-rate turn in their spam-can not having a large enough rudder input to counter-act adverse yaw, which during that roll-in would force the nose higher than it needed to be.

The interesting part to me here is -- whether attempting a rapid zero-turn rate roll-in, or allowing the nose to start coming around -- is the most "efficient".

You'd have to be very proficient in your aircraft to nail either one consistently, but I am sure some of the aerobatic competition pilots in the group could choose exactly what they wanted... roll without turn, then pull... or roll and pull simultaneously with nose motion only going to the left (in this example), never up (skidding) or to the right or slipping and forcing the nose toward earth with rudder pressure.

Anyone who's done the confidence maneuver colloquially known as "Dutch Rolls" in a Cessna where you keep the nose on a point on the horizon and roll rapidly from 45 degrees left to 45 degrees right... or who has flown a long-wing aircraft like a glider that has significant adverse yaw will understand the picture I'm trying to paint here with what has to happen with your feet. It's more rudder pressure and foot movement than most low-time Cessna drivers have ever done.

(+1 for getting some time in a glider or taildragger!)

Crank an aileron out at close to full-deflection quickly, the nose is going to go the wrong way, and most pilots aren't practiced enough to countermand that with rudder.

(No offense to the taildragger and glider pilots who probably get it right. I'm trying to reference the average nose-dragger pilot faced with a need to do a hard turn and rapid roll-in.)

Just thoughts... and that pesky "is knife-edge coordinated?" question, just for fun.

 

[dmccormack]

Crank an aileron out at close to full-deflection quickly, the nose is going to go the wrong way, and most pilots aren't practiced enough to countermand that with rudder.

(No offense to the taildragger and glider pilots who probably get it right. I'm trying to reference the average nose-dragger pilot faced with a need to do a hard turn and rapid roll-in.)

Just thoughts... and that pesky "is knife-edge coordinated?" question, just for fun.

Not really -- the application of rudder and aileron should be simultaneous -- not an afterthought.

In some older airplanes, (My Chief, Cubs, Taylorcraft, etc) you actually lead a turn with rudder.

 

[Jaybird180]

In previous paper cited above, it has been identified that >45deg roll is sub-optimal.

 

[denverpilot]

Not really -- the application of rudder and aileron should be simultaneous -- not an afterthought.

In some older airplanes, (My Chief, Cubs, Taylorcraft, etc) you actually lead a turn with rudder.

Yeah, I get that. I just don't think most Cessna drivers would put in *enough* rudder in this scenario of "roll hard while pushing forward".

They'd push it, but not enough. That or they'd push too hard, since they saw this thread, and they'd be skidding.

A rapid roll-rate with high aileron deflection is not something most non-aerobatic pilots do very often. Practice needed. Otherwise it'd be a really sloppy maneuver.

Doing it low-level with an engine that just quit... and not sloughing off a lot of airspeed with bad technique, would be tricky for most low-time non-tailwheel or glider pilots who hadn't flown anything that didn't let you get away with not using your feet.

 

[Palmpilot]

Why push at all? Couldn't you just let the trim take care of lowering the nose? And wouldn't you actually have to add back pressure to prevent airspeed from increasing during the 45 degree bank?

 

[dmccormack]

Why push at all? Couldn't you just let the trim take care of lowering the nose? And wouldn't you actually have to add back pressure to prevent airspeed from increasing during the 45 degree bank?

Trim is at takeoff -- we're pitched up and climbing, engine stops.

An immediate push will be needed to establish Vg ASAP.

 

[COFlyBoy]

Just thoughts... and that pesky "is knife-edge coordinated?" question, just for fun.

I'll bite.

I suggest that the definition of "coordinated flight" is that the logitudinal axis of the aircaft is aligned with the velocity vector of the aircraft (only the yaw component, don't beat me up about pitch). Simple as that. Nothing about gravity, bank, centrifugal/centripetal force or the ball.

So for knife edge, the answer would be no that is not coordinated.

On a side note, I was reading about the HUD in the F-15. It has a little icon on it that shows where the nose is pointing, and another for where your current velocity vector is pointing. Interestingly, that shows both your yaw coordination and the difference between your pitch angle and your actual climb angle. Would be cool to know that in our planes.

 

[mantakos]

... I suggest that the definition of "coordinated flight" is that the logitudinal axis of the aircaft is aligned with the velocity vector of the aircraft (only the yaw component, don't beat me up about pitch)...

Instead of "velocity of the aircraft" I'd say "relative wind", as this eliminates the complication of wind and frame of reference.

If you form a plane (in the geometry sense) that's parallel to the longitudinal and vertical axes, the relative wind vector must be parallel to that plane.

That's a fancy way of saying "the relative wind isn't pushing against one of the sides of the plane (more than the other)".

Nothing about gravity, bank, centrifugal/centripetal force or the ball.

Um, ok, except that all of those are either determining factors or indicators of coordinated flight.
-harry

 

[jsstevens]

I'll bite.

I suggest that the definition of "coordinated flight" is that the logitudinal axis of the aircaft is aligned with the velocity vector of the aircraft (only the yaw component, don't beat me up about pitch). Simple as that. Nothing about gravity, bank, centrifugal/centripetal force or the ball.

So for knife edge, the answer would be no that is not coordinated.

On a side note, I was reading about the HUD in the F-15. It has a little icon on it that shows where the nose is pointing, and another for where your current velocity vector is pointing. Interestingly, that shows both your yaw coordination and the difference between your pitch angle and your actual climb angle. Would be cool to know that in our planes.

Virtually all the modern HUDs on military aircraft have the indicator for where your velocity vector is pointing. Most helpful for landing approach in these nose up, behind the power curve birds.

John

 

[gismo]

Sorry to hijack, but something came to mind that I've always wanted to ask...

Is knife-edge (90 degree bank, zero turn, level flight) flight coordinated or uncoordinated?

It seems to me that "coordination" is a contrived concept in some respects where what you're really saying is that you don't want one wing generating more lift than the other, because in a stall in that configuration, one wing is going to stall before the other.

In an aircraft that can maintain knife-edge flight where lift is being generated by the fuselage and raw engine thrust, "coordination" seems a confusing concept. But only in that scenario where there's zero turn to reference "coordination" off of?

Just thinking about weird things tonight...

So that same aircraft with zero engine thrust and descending rapidly... zero turn, very high descent rate, 90 degree bank... is that coordinated flight or not?

It is possible to fly "coordinated" (i.e. zero sideslip) in a 90 degree bank but this implies that you are accelerating towards the ground at 1g with an appropriate change in yaw (now the effective pitch axis) to keep the nose pointed to where the airplane is going. You can keep this going for several seconds if you start out with a high rate of climb before rolling into the 90° bank but you will eventually be pointed straight down and going fast. Sustained knife edge flight without a change in altitude cannot be coordinated. The difference is very obvious in the airplane.

Also, FWIW you can (and should) be coordinated (again with zero sideslip) when one wing is generating more lift than the other. This opportunity occurs every time you roll into or out of a turn. Unequal lift of the two wings is what makes the plane roll. Using the correct amount of rudder pressure keeps the nose pointed in the right direction.

 

[denverpilot]

Great descriptions. Thanks.

I really wanna go do that 90 degree banked coordinated thing now.

Anyone got an Extra I could borrow?

 

[Capt. Geoffrey Thorpe]

It is possible to fly "coordinated" (i.e. zero sideslip) in a 90 degree bank but this implies that you are accelerating towards the ground at 1g with an appropriate change in yaw (now the effective pitch axis) to keep the nose pointed to where the airplane is going. You can keep this going for several seconds if you start out with a high rate of climb before rolling into the 90° bank but you will eventually be pointed straight down and going fast. Sustained knife edge flight without a change in altitude cannot be coordinated. The difference is very obvious in the airplane.

A wingover is an easy way to end up at 90 degrees ball centered.

 

[Everskyward]

A wingover is an easy way to end up at 90 degrees ball centered.

I think the original question about a 90 degree bank was asking about a sustained 90 degree bank, not a momentary one.

 

[COFlyBoy]

Instead of "velocity of the aircraft" I'd say "relative wind", as this eliminates the complication of wind and frame of reference.

Agreed. We could also call it the velocity vector using the wind as the frame of reference.

Um, ok, except that all of those are either determining factors or indicators of coordinated flight.
-harry

I think the question was what is the definition of coordinated flight. I am saying the definition is only dependent on the angle between 2 vectors (longitudinal axis, and the velocity in the wind frame).

The point the second comment, was that the number of g's you're pulling, your bank angle, and the position of the ball don't define coordinated. In fact there are conditions where those may be doing who knows what, but you are still in coordinated flight.

Good example is any maneuver that is zero g. It could have any bank angle and the ball will be floating.

 

[gismo]

A wingover is an easy way to end up at 90 degrees ball centered.

So's a barrel roll.

 

[nosehair]

Why push at all? Couldn't you just let the trim take care of lowering the nose? And wouldn't you actually have to add back pressure to prevent airspeed from increasing during the 45 degree bank?

Great question,..and demonstrates my point:
While all the theoretical discussions are interesting to some,..the main point is how to fly it.
I noticed several comments in the beginning that said, essentially, "I tried it a couple times and it scares me, so I won't do it, and I think anyone who does is reckless and irresponsible".

The thing is, this maneuver needs consistent repetitious practice, just like making a landing.

We could write a book on the different wing loading vectors, how control inputs change those vectors and how each wind velocity or vector change, an accompanying control input change must simultaneously occur, yada, yada, yada, ...and sometimes we do, but mostly, learning to land is physical practice with a little coaching on where to look, when to pull, etc, etc.

That is all it takes to learn to do this turn-around, ..and then it is just another tool in your box.

And a good excuse to have lot of fun to practice.

 

[bbchien]

Why push at all? Couldn't you just let the trim take care of lowering the nose? And wouldn't you actually have to add back pressure to prevent airspeed from increasing during the 45 degree bank?

The whole purpose of the steep turn maneuver is to teach the crossover between the elevator and the rudder as to pitch control, in the steep turn.

So, no, trim doesn't hack it.

 

[dmccormack]

Great question,..and demonstrates my point:
While all the theoretical discussions are interesting to some,..the main point is how to fly it.
I noticed several comments in the beginning that said, essentially, "I tried it a couple times and it scares me, so I won't do it, and I think anyone who does is reckless and irresponsible".

The thing is, this maneuver needs consistent repetitious practice, just like making a landing.

We could write a book on the different wing loading vectors, how control inputs change those vectors and how each wind velocity or vector change, an accompanying control input change must simultaneously occur, yada, yada, yada, ...and sometimes we do, but mostly, learning to land is physical practice with a little coaching on where to look, when to pull, etc, etc.

That is all it takes to learn to do this turn-around, ..and then it is just another tool in your box.

And a good excuse to have lot of fun to practice.

If you read the thread, you'll see I consistently mentioned my practice and conclusions based on that practice in a particular airplane.

While a quick, steep roll coupled with an aggressive push works in the Chief, it may be excessive in a Bonanza.

 

[Palmpilot]

Trim is at takeoff -- we're pitched up and climbing, engine stops.

An immediate push will be needed to establish Vg ASAP.

I went flying yesterday in a 172N. After climbing to a safe altitude, I set up a full power climb and trimmed to best rate of climb speed (about 73 KIAS). Then I pulled the power to idle, took my hands off the yoke, and watched what happened. The nose came down by itself without intervention from me. The airspeed stayed comfortably within the green arc at all times, there was no stall buffet, and the stall horn did not activate. The only control input I had to make was adding back pressure to keep airspeed from getting too high.

I repeated this while trimmed for best angle of climb speed (about 59), and the above was still true.

I expect that even more back pressure would have been required if I had entered a bank.

So I still don't see why pushing would be required and/or beneficial.

 

[Bobcat1]

I expect that even more back pressure would have been required if I had entered a bank.

So I still don't see why pushing would be required and/or beneficial.

So give the turn a try without pushing and let us know how that goes.

 

[tonycondon]

i was thinking about this thread a lot this weekend as I was having trouble getting my glider to turn the way I wanted it to. Had to keep reminding myself to get the wing loaded up to pull it around the turn. I also had a tendency to skid a bit on entry. Guess I'm just out of practice.

 

[gismo]

i was thinking about this thread a lot this weekend as I was having trouble getting my glider to turn the way I wanted it to. Had to keep reminding myself to get the wing loaded up to pull it around the turn. I also had a tendency to skid a bit on entry. Guess I'm just out of practice.

Maybe married life has made you lazy

 

[Palmpilot]

So give the turn a try without pushing and let us know how that goes.

I will. Have you tried it, and if so, what happened?

 

[dmccormack]

I went flying yesterday in a 172N. After climbing to a safe altitude, I set up a full power climb and trimmed to best rate of climb speed (about 73 KIAS). Then I pulled the power to idle, took my hands off the yoke, and watched what happened. The nose came down by itself without intervention from me. The airspeed stayed comfortably within the green arc at all times, there was no stall buffet, and the stall horn did not activate. The only control input I had to make was adding back pressure to keep airspeed from getting too high.

I repeated this while trimmed for best angle of climb speed (about 59), and the above was still true.

I expect that even more back pressure would have been required if I had entered a bank.

So I still don't see why pushing would be required and/or beneficial.

How far forward (and therefore away form the airport) did you travel after you pulled the power?

How many feet of altitude was lost before you achieved Vg?

 

[Palmpilot]

How far forward (and therefore away form the airport) did you travel after you pulled the power?

I was about twelve miles from the airport.

How many feet of altitude was lost before you achieved Vg?

I don't know, but I doubt that the altitude lost was much different than it would have been if I had immediately established Vg, since the airspeed never got more than about ten knots below it, and the whole process only took a few seconds.

I've been told that when one is doing altitude loss tests, one should wait a few seconds before doing anything anyway, to simulate the time it takes for the pilot to get over the shock of having an engine failure and begin to take action.

 

[Bobcat1]

I will. Have you tried it, and if so, what happened?

It's been so long ago that I can't remember whether I was nudging the stick forward or holding just a little back pressure. What I do remember is that the change in pitch attitude from climb to glide while transitioning in the 180 turn was dramatic, and ya couldn't dawdle while doing it either.

At the time, I was getting it done comfortably in about 300'-400', but I was ready for it and was practicing it as a maneuver. In real life, and the fact that I haven't done something like that in ages, double those numbers and I might almost get it done today (just barely).

You mention that you've been doing this in a 172. Bear in mind that in the real world when you get the engine failure on takeoff, you'll be closer to max gross with people and cargo with the airport surrounded by tall pine trees, high tension wires, and a fuel farm. The 172 won't be acting like it did when you practiced this maneuver alone with half tanks.

I'd have the soft spot straight ahead picked prior to takeoff and have my renter's insurance paid up.

 

[Palmpilot]

It's been so long ago that I can't remember whether I was nudging the stick forward or holding just a little back pressure. What I do remember is that the change in pitch attitude from climb to glide while transitioning in the 180 turn was dramatic, and ya couldn't dawdle while doing it either.

The pitch change in my case was dramatic too, but I didn't have to do anything to bring it about other than trimming for the desired climb speed prior to pulling the throttle, and avoiding pulling on the yoke. The nose started dropping immediately.

You mention that you've been doing this in a 172.

Just to clarify, I haven't been doing it. This was just a single test to see what would happen in straight ahead flight if I didn't push on the yoke.

I haven't tried turnback maneuvers, because my home field is too short for turning back to be a good bet in anything but a string wind, and the obstacle environment off the departure ends of the runway is relatively benign as long as you avoid the high voltage lines.

As for what will happen when I try adding a 45 degree bank to the test, my guess is that I will have to add back pressure, because that's what is required to avoid a buildup of airspeed (and an associated dive) when I turn from downwind to base.