Airspeed, or Altitude After Takeoff?

Lindberg said:
So what is the circumstance where being lower and having less energy when your engine fails is better?
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The circumstance where you’re still over the runway and able to land. Or even where your best option is a large field straight off the end of the runway.
 
Midwest_Wings said:
Yes, and the math will always show a greater chance of hitting the trees at Vy than at Vx.
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Nobody’s saying that Vx is the wrong speed to clear obstacles.
Midwest_Wings said:
A turn back to the runway is fascinating in itself. Do you pitch for best glide? Do you drop a notch of flaps so you can fly slower with a greater rate of turn, what are the winds doing, …
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”Ahead of the wings, into the wind” is going to be better than attempting a turn back until you’re high enough that there’s no need to make those kinds of decisions for most airplanes and pilots.
 
Palmpilot said:
I doubt that adding drag is going to be beneficial in that situation, unless and until you find yourself in the enviable position of being too high once you get turned toward the field.
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I wasn’t thinking drag. Flying slower allows us to turn tighter. I’m not referring to bank angle - I’m referring to the radius of the turn - how many degrees of heading the plane can turn in a given space. The flaps comment was around lowering stall speed and permitting slower flight. Many airplanes have a lower sink rate with some flaps or at high AOA by the way, so you still get as much time, or more.

Maule Skinner, I don’t disagree. Which is why I wrote above that in most GA these speeds don’t matter a whole lot. What matters is that it’s turning out to be a fine day here - and I’m getting the itch to go fly :), which I plan to do from a runway that is 4x longer than the book asks for.
 
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Lindberg said:
Show your work.
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True. The usual problem people have on RTL situations is running off the far end of the runway rather than coming up too short. I can tell you that my first engine failure I ended up nearly doing so.
 
Half Fast said:
The circumstance where you’re still over the runway and able to land. Or even where your best option is a large field straight off the end of the runway.
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I know lots of ways to lose energy without an engine. I know fewer ways to gain it.
 
Lindberg said:
So what is the circumstance where being lower and having less energy when your engine fails is better?
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The one where you would have hit the 50 foot tree at the end of the runway if you had used Vy
 
Silvaire said:
The one where you would have hit the 50 foot tree at the end of the runway if you had used Vy
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Everyone agrees that you should climb at Vx to clear obstacles. I've said that at least twice in this thread.
 
Lindberg said:
It is what I asked, and your example doesn't work because I can always trade too high for lower.
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Baloney.

You asked, “So what is the circumstance where being lower and having less energy when your engine fails is better?”

I gave you such a circumstance.

The fact that you can lose energy matters when you have excess energy. If you have less excess energy to begin with and you’re low over the runway, you’re in a better position to land safely than if you were too high and too fast to get down.

QED
 
Lindberg said:
It is what I asked, and your example doesn't work because I can always trade too high for lower.
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Yeah, that’s why I had to make a 360 over the end of the runway a couple of times in gliders with one student.

I don’t think being in a position to land on the runway longer is a valid reason to climb at Vx, however.
 
MauleSkinner said:
Yeah, that’s why I had to make a 360 over the end of the runway a couple of times in gliders with one student.

I don’t think being in a position to land on the runway longer is a valid reason to climb at Vx, however.
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S turns, 360s, flaps, slips, slow down, etc. I would rather be too high for a no-power landing than too low 100/100 times.
 
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Half Fast said:
Baloney.

You asked, “So what is the circumstance where being lower and having less energy when your engine fails is better?”
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Correct. I said "better." Not "good," or "acceptable," or "ok," or "survivable."

Half Fast said:
I gave you such a circumstance.

The fact that you can lose energy matters when you have excess energy. If you have less excess energy to begin with and you’re low over the runway, you’re in a better position to land safely than if you were too high and too fast to get down.
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You gave me a circumstance where being lower and having less energy is ok, maybe even just as good, but not better. If I can convert condition A into condition B, but not vice versa, how can condition B be better?

Ok, maybe if you're on fire and need to be on the ground, whenever, soonest.
 
Lindberg said:
S turns, 360s, flaps, slips, slow down, etc. I would rather be too high for a no-power landing than too low 100/100 times.
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My boss wasn’t happy when the wingtip was close to the fence posts in the 45+ degree bank.
 
For the old timers ,i thought we answered that question,when we discussed zoom takeoffs.
 
Midwest_Wings said:
I wasn’t thinking drag. Flying slower allows us to turn tighter. I’m not referring to bank angle - I’m referring to the radius of the turn - how many degrees of heading the plane can turn in a given space. The flaps comment was around lowering stall speed and permitting slower flight. Many airplanes have a lower sink rate with some flaps or at high AOA by the way, so you still get as much time, or more.
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A few years ago, an instructor had me try 10 degrees of flaps in a 182 in a power-off 180-degree turn from the downwind, and it did improve the results.
 
flyingron said:
True. The usual problem people have on RTL situations is running off the far end of the runway rather than coming up too short. I can tell you that my first engine failure I ended up nearly doing so.
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My instructor pointed out that the speed by the time you run off the end would likely be slow enough that it could be better than the alternatives (depending on how bad the alternatives were, of course).
 
Lindberg said:
S turns, 360s, flaps, slips, slow down, etc. I would rather be too high for a no-power landing than too low 100/100 times.
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For many GA aircraft, the glide angle may exceed the climb angle (depending on wind, DA, etc.). In that circumstance, additional altitude gained by using Vy increases the risk that you will be too far from the runway to make it back.
 
WDD said:
I can't think of how that can be. At any X time interval between take off and engine failure that you can pick, the math will always show you at a higher altitude at Vy vs Vx, and thus have a higher chance of a better outcome / impossible turn, etc.
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But you are also further from the runway.

And the point where you can make it back is based on altitude, not time from take off.

You set a hard number that says, below this, you land straight ahead. Above this, depending on wind and such, you MAY be able to turn back.

For gliders, you do this for a rope break. Normally 200 AGL.
 
Agree that the point where you can return is based on altitude. And Vy will always get you higher sooner. So yes, taking climb per minute into consideration your point of return is time dependent - as that determines your altitude.

Yes, you are higher and farther out with Vy. The extra altitude more than compensates for any extra distance from the runway. You have a better chance of covering the distance back to the runway with Vy vs Vx.
 
WDD said:
The extra altitude more than compensates for any extra distance from the runway.
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That is not a given in all aircraft. You are assuming the turn back and then straight glide averages a shallower path than the climb.
 
MauleSkinner said:
Not even a given under all conditions for any aircraft.
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Can someone please pick an airplane and tell us at what time T after takeoff, and under what wind conditions, that airplane will be able to make a u-turn and safety land on the runway only if it climbs at Vx?
 
Lindberg said:
Can someone please pick an airplane and tell us at what time T after takeoff, and under what wind conditions, that airplane will be able to make a u-turn and safety land on the runway only if it climbs at Vx?
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I appreciate that sentiment of getting to specifics.
In my case though, I think of Vx NOT so much in terms of the "u-turn"...but instead in terms of the straight ahead landing....just for that very low altitude portion of the departure leg when no matter the climb rate you aren't going to be high enough to glide to any of the options outside the airport boundary.

Again, yeah I get it....granted this introduces more risk because of the high AOA and need for no delay push over

But just as an exaggerated thought experiment...
1) If I can be at TPA by the time I'm at the runway's mid point and at that point my engine shuts down cold, I can see three obvious options
a) slip to a landing straight ahead​
b) circle back downwind to land on the same runway same direction​
c) I might be high enough to glide lots of other places both on and off the airport​
(I'm thinking a little Cub or a Champ or any of those STOL competition aircraft you see at Sun n Fun, etc...)

2) On the other hand.... climbing at what might seem like a cruise speed, very low climb rate...I'm at half TPA well outside the airport fence. Now what are my options, 500 ft AGL out over anything but open spaces? That glide ring is pretty small....
(I'm currently thinking of the climb rate I experienced in multi training in that old tired Apache 150, climb gradient nearly flat even with two engines turning, with one...yeah that was eye opening)
 
This page has a bunch of interesting info on the topic: https://www.nar-associates.com/technical-flying/technical-flying.html#Turnback

In particular, check out the study by David Rogers from the US Naval Academy: https://www.nar-associates.com/technical-flying/impossible/impossible_wide_screen.pdf
It starts with a critique of Eckalbar's Bonanza society letter, which assumes (among several other things) a climb-out at Vy.
Rogers says:
As the analysis below shows, the velocity for maximum climb angle is a better choice for the initial climb segment ...

Rogers explains and computes in more detail, including discussion of Vx vs Vy, on pages 8-9.
 
Brad W said:
I appreciate that sentiment of getting to specifics.
In my case though, I think of Vx NOT so much in terms of the "u-turn"...but instead in terms of the straight ahead landing....just for that very low altitude portion of the departure leg when no matter the climb rate you aren't going to be high enough to glide to any of the options outside the airport boundary.

Again, yeah I get it....granted this introduces more risk because of the high AOA and need for no delay push over

But just as an exaggerated thought experiment...
1) If I can be at TPA by the time I'm at the runway's mid point and at that point my engine shuts down cold, I can see three obvious options
a) slip to a landing straight ahead​
b) circle back downwind to land on the same runway same direction​
c) I might be high enough to glide lots of other places both on and off the airport​
(I'm thinking a little Cub or a Champ or any of those STOL competition aircraft you see at Sun n Fun, etc...)

2) On the other hand.... climbing at what might seem like a cruise speed, very low climb rate...I'm at half TPA well outside the airport fence. Now what are my options, 500 ft AGL out over anything but open spaces? That glide ring is pretty small....
(I'm currently thinking of the climb rate I experienced in multi training in that old tired Apache 150, climb gradient nearly flat even with two engines turning, with one...yeah that was eye opening)
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Your climb rate comment had me recall getting stuck in ground effect in a tired 150M because I rotated a bit too early. Vx vs Vy is all good ... but that day as I approached the end of the runway I learned that sometimes it has to be Vy lol.
 
MRC01 said:
This page has a bunch of interesting info on the topic: https://www.nar-associates.com/technical-flying/technical-flying.html#Turnback

In particular, check out the study by David Rogers from the US Naval Academy: https://www.nar-associates.com/technical-flying/impossible/impossible_wide_screen.pdf
It starts with a critique of Eckalbar's Bonanza society letter, which assumes (among several other things) a climb-out at Vy.
Rogers says:
As the analysis below shows, the velocity for maximum climb angle is a better choice for the initial climb segment ...

Rogers explains and computes in more detail, including discussion of Vx vs Vy, on pages 8-9.
Click to expand...
I read the first page. It seems to assume the timing of engine failure based on altitude. That assumption introduces survivor bias in favor of Vx because between Vx and Vy, at any given altitude, the plane climbing at Vx will be closer to the runway. I'll have to read the Rogers study later.
 
MRC01 said:
This page has a bunch of interesting info on the topic: https://www.nar-associates.com/technical-flying/technical-flying.html#Turnback

In particular, check out the study by David Rogers from the US Naval Academy: https://www.nar-associates.com/technical-flying/impossible/impossible_wide_screen.pdf
It starts with a critique of Eckalbar's Bonanza society letter, which assumes (among several other things) a climb-out at Vy.
Rogers says:
As the analysis below shows, the velocity for maximum climb angle is a better choice for the initial climb segment ...

Rogers explains and computes in more detail, including discussion of Vx vs Vy, on pages 8-9.
Click to expand...
thanks... a lot of links there, will make for some good "light" reading as soon as I get a chance!
 
Lindberg said:
I read the first page. It seems to assume the timing of engine failure based on altitude. That assumption introduces survivor bias in favor of Vx because between Vx and Vy, at any given altitude, the plane climbing at Vx will be closer to the runway. I'll have to read the Rogers study later.
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That's a good point. He's aware of it too and specifically mentions this near the bottom of page 8.
 
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