Lindberg
Final Approach
Vx climb is for clearing obstacles.
Airspeed, or Altitude After Takeoff?
- Thread starter tobnpr
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Most light single engine airplanes have a steeper glide angle than climb angle. So in the unlikely case of engine failure after takeoff, climbing at Vx puts the airplane in a better position (closer and higher) if the pilot makes the decision (usually ill-advised) to turn back and attempt to land on the runway.
However, this doesn't mean one should climb at Vx after takeoff. The "impossible turn" is actually possible in some situations, though these are the exceptions that prove the opposite rule.
PS: my point is that climbing at Vx after takeoff is a maximum performance maneuver that increases safety risk and stress on the engine. It should not be the normal takeoff procedure, but used only when necessary. Pilots who recommend it as a standard procedure often do so because it puts you in a better position for the impossible turn if the engine fails, but this is a bad idea for multiple reasons already discussed in this thread.
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sarangan
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Andrew, CFI-I
There are times when you have to use Vx and Vy, but unless there is a compelling reason, I focus more on the climb pitch than Vx or Vy. The Skylane I fly climbs at a high pitch angle even at Vy. My preference is to select a pitch angle so that the windshield is not all blue. In my case that works out to be faster than Vy. I believe this is safer in case of a power loss because the pitch transition won't be too dramatic, and I have a better view of the terrain during climb.
Lindberg
Final Approach
No, it puts you lower. Assuming your engine fails at rotation + T in both cases, you will be higher if you climb at Vy than if you climb at Vx. Climbing at Vx puts you closer to the runway and lower than climbing at Vy. I'm not sure that's a better setup for the impossible turn.
That can be true, depending on whether you look at height relative to distance, or height in absolute terms. Suppose the engine fails T seconds after rotation...
Climbing at Vx put you closer to the runway, not as high as Vy but at a steeper angle, in other words higher relative to your distance from the runway, thus easier to glide back.
If you climbed at Vy instead, yes it's true that you would be higher in absolute terms MSL, but you would also be much further away relative to that height. It's a shallower angle, thus harder to glide back.
Midwest_Wings
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Midwest_Wings
So on the airplanes I’ve flown, there’s no pitch up moment upon power reduction. Usually it’s the opposite. So is it mostly psychological factors that lead to stall if there’s an engine failure shortly after takeoff? If Vy is 74, I usually have it trimmed for that speed, or a few knots over, and maintaining a very light back pressure to maintain Vy…
As far as the OP, you typically hold Vx to 100 feet, basically treetop height, then accelerate to Vy, and then to cruise climb at 1000 feet or so. In a lot of GA, the exact climb speeds are not a big deal because we don’t put ourselves in situations where we need maximum performance - but they are training for higher performance work and do make a difference. Try climbing at various speeds and note climb rate or time to climb. Note that these speeds reduce with altitude. At absolute ceiling, Vx=Vy=Vstall
As far as the OP, you typically hold Vx to 100 feet, basically treetop height, then accelerate to Vy, and then to cruise climb at 1000 feet or so. In a lot of GA, the exact climb speeds are not a big deal because we don’t put ourselves in situations where we need maximum performance - but they are training for higher performance work and do make a difference. Try climbing at various speeds and note climb rate or time to climb. Note that these speeds reduce with altitude. At absolute ceiling, Vx=Vy=Vstall
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WDD
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Vintage Snazzy (so my adult children say)
No, the white zone is for loading and unloading passengers only.....
idahoflier
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idahoflier
I'll echo "It depends". That said, if I was operating out of a densely urban area that surrounded the airport I would probably climb out at Vx until I was beyond the ability to put the aircraft down on the airport property, then I would climb at Vy. Otherwise Vy...
Good question. I believe it's a matter of how much and how fast the pitch must change to avoid the stall. At Vx the airplane is close to Vldmax with a steep nose-up pitch. That is a relatively dangerous pitch/speed combination. To glide, you've got to pitch down without losing any airspeed. If the engine suddenly quits, the airspeed may drop faster than the pitch changes, causing a stall. You've got to push hard to pitch the nose down before the airspeed decays. Especially after considering the lag of reaction time.
A picture's worth 1000 words, so here it is. The red arrow is the flight path for Vx, blue for Vy, each shows where you'll be in the same time T after takeoff. Scale depends on the airplane of course, but Vx always gives the steeper angle while Vy always gives greater height above the ground. If you had to glide back (as inadvisable as that is), Vx puts you in a better position.
Lindberg
Final Approach
Is this a real airplane where the Vx rate of climb is 90% the Vy rate of climb? Regardless, the first step of the "impossible" turn is the turn. Less altitude is not going to help you there. And if there's any wind, being close to the runway isn't going to help either.
Clear obstacles at Vx. Climb at Vy.
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I'll take Vy, no doubt. At Vx, you will be at a lower altitude and an airspeed less than best glide. During the turn back to the field you will have to give up altitude to keep above stall speed, which may be a bit of altitude. At Vy you will have more potential energy in altitude and kinetic energy from velocity. This will give you more time....time to consider that impossible turn or other options. Vx climb will limit those options.
brcase
En-Route
Haven't read all the responses yet, but have some seen some good responses so far.
Here is mine...
The CFI is only partially right, the quote should be "energy is your friend" it can be kinetic (airspeed) or potential (altitude).
The problem with the Vx climb is it isn't the most efficient climb and wastes energy, so if you have an power failure (lose the other potential energy source) you will have less energy at at Vx climb than you would have had at a Vy climb.
The other issue is at very low altitudes in a Vx climb you may not have enough time to convert the altitude into airspeed for a flare for landing. The other way to say it is you are climbing at a high pitch altitude and angle, with a power loss you are going slow very quickly unless you pitch down quickly (Zero G pitch over may be required) or you will lose a lot more airspeed and may not be able to get enough airspeed to flare and stop the descent sufficiently to not damage the airplane. There is also a higher risk of not pushing over fast enough and stall/spinning the airplane.
With an experienced CFI you can demonstrate this... try some simulated powered failures from a Vx climb from 100 ft, then 75, 50 and 25 feet. CAUTION: below 50 feet it is very possible you will not be able to or won't pitch over fast enough and just the right amount to flare and land the airplane without damaging it, be prepared to add a lot power and abort the simulation. Be careful not to overpitch and put the plane in a descent you can't recover from. I had a student do this to me once on a normal landing, is my only insurance claim as I could not stop the descent enough to not damage the landing gear.
FYI we have this same issue when ground launching gliders. For the 1st 100 feet we could climb steeper, but it puts us in a nose high position that we could not recover from if we had a launch failure like a rope break or winch failure.
Brian
CFIIG/ASEL
Instructing since 1998 and 6000+ hrs instruction including tailwheel and gliders.
Brad W
Pattern Altitude
I'm still not convinced the diagram actually simplifies anything. You're presupposing that at the arrow head when your engine quits, that you're high enough to make the turn back.
which is a fair-enough assumption and basis
but
What if instead the altitude is something far too low for that, AND the end of the white graph 'paper' represents the tree line or granite or just the airport fence (at whatever height, I don't mean the trees or fence are above your altitude)?
Failure at Vx at least opens a possibility of landing straight ahead onto the runway or overrun...or grass or taxiway, etc.... while Vy puts you into the trees or outside the fence
That points more to what I experienced and concluded (see my earlier post this thread). Had I been on my short home runway at Vy I'd probably be in the marsh or in the trees...or even in the school's playground, etc... but at Vx, I might have a chance for the overrun
That's why it seems to me that more of a hybrid mix approach makes sense... Similar to the ideas in a retract -gear up at positive rate or gear up at no more runway
Vx or near it till the first option of landing straight ahead is no more, transitioning to VY till you have other options, then transition to cruise climb.
with all being conditional on location, condition, weather, etc... And as I think about what Martin wrote earlier, maybe it's not so rigid that it be actual Vx...or Vy because I get that there's clear risks to Vx especially. Depending on conditions maybe you'd want to split the difference....or maybe you skip the Vx segment going straight to the Vy segment initially.... or maybe with a long enough runway and wide open spaces you skip Vy and go pretty much straight to a cruise climb number....
Nope. No assumptions. The purpose of the diagram is to show the difference between angle vs. rate of climb. In most cases, neither gets you high enough to turn back. Unless you have a high performance engine, exceptional glide rate, or stiff headwind.
Good questions and understanding the difference is important to choosing one's climb-out speed.
Salty
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True, but to be fair, if your concern is maximum height to get back to the airport, Vx is going to give you the most advantageous altitude to airport distance ratio.
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In my Navion it's:
Full Power, Vx climb attitude.
Positive rate of climb, gear up.
Clear of obstacles, retract flaps, back to climb power (which is less than firewalled throttle and prop at lower altitudes). Set climb fuelflow, Climb at a moderate angle (faster than Vy unless there's a compelling reason).
As you level off, set cruise power, lean
Full Power, Vx climb attitude.
Positive rate of climb, gear up.
Clear of obstacles, retract flaps, back to climb power (which is less than firewalled throttle and prop at lower altitudes). Set climb fuelflow, Climb at a moderate angle (faster than Vy unless there's a compelling reason).
As you level off, set cruise power, lean
Good point. Vy is the airspeed of maximum excess power, which means it should give the most rapid increase in total energy of the airplane (combination of speed and height).
chemgeek
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I'll join the crowd with Vy until 1000 AGL. Why? Vy gives you the highest rate of climb: more altitude quicker. Vx gives you the best angle of climb: useful for clearing nearby obstacles but slower in gaining absolute altitude. After reaching 1000 AGL I transition to a cruise climb that is kinder to the engine. The faster you get higher, the more options you have in case of a power failure.
Lindberg
Final Approach
Show your work.
Lindberg
Final Approach
There's no "should." We know that it gives you more potential energy because you're higher when climbing at Vy, by definition. And we know it gives you more kinetic energy because you're faster when climbing at Vy, by definition. So climb at Vy.
[Assuming we're choosing between Vx and Vy.]
chemgeek
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I would be concerned that at Vx, you are closer to the stall speed, and that a sudden power failure coupled with a the delay of startle reaction time coupled with a steep turn would lead to excessive loss of altitude and a possible stall/spin compared to the same situation at Vy. In my light single, the difference between these to speeds is 12 mph, or a 10 kt. That's a lot of cushion.
Below 1000 AGL, there is virtually no chance of returning to the airport, regardless of takeoff technique. At lower airspeeds, the steep turn required to make such a maneuver successful enhances the risks of stall or excessive altitude loss. Rather, the role of gaining altitude during the initial takeoff phase is to increase options for an emergency landing, which will, below 1000 AGL, probably involve options within 30 degrees or so of the takeoff heading. Vy gets you higher faster.
In my time flying, I know of several local area incidents where pilots walked away from putting down a plane in the trees or a lake after a power failure of one sort of another. Nobody survives the stall/spin scenarios.
Albany Tom
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I learned at a relatively short and obstructed field, and it was Vx to clear the trees, then Vy to pattern altitude. We always did a briefing, and it included <1000 AGL, limit it to 30 degrees in front. I still fly that way. Vx is only when I need or am practicing short field, Vy otherwise.
At Vy, In addition to having a higher energy to give you a bit more reaction time on a Vy vs Vx engine failure, you also have less of an adjustment to make to pitch to get to the right glide angle. Vx pitch can be pretty steep for higher HP than average trainers, like a PA-28-180 for example. Finally, if you're flying on a gusty day in a field surrounded by trees, the wind is likely to pick up as soon as you get above the trees. I kinda like being at Vy rather than Vx then, too.
One thing you can do, that might help, is do a downwind departure, turning crosswind a couple of hundred feet below pattern altitude. That would put you more or less pointed toward the airport when you get to 1000', and should make a power off landing much more achievable. I don't do that, but it might not be a bad plan if your airport was surrounded by houses in all directions. At some point, though, you're going to end up flying over things that you don't want to land on, at least around here.
At Vy, In addition to having a higher energy to give you a bit more reaction time on a Vy vs Vx engine failure, you also have less of an adjustment to make to pitch to get to the right glide angle. Vx pitch can be pretty steep for higher HP than average trainers, like a PA-28-180 for example. Finally, if you're flying on a gusty day in a field surrounded by trees, the wind is likely to pick up as soon as you get above the trees. I kinda like being at Vy rather than Vx then, too.
One thing you can do, that might help, is do a downwind departure, turning crosswind a couple of hundred feet below pattern altitude. That would put you more or less pointed toward the airport when you get to 1000', and should make a power off landing much more achievable. I don't do that, but it might not be a bad plan if your airport was surrounded by houses in all directions. At some point, though, you're going to end up flying over things that you don't want to land on, at least around here.
I think the back and forth here has done a fine job of making clear that IT DEPENDS, and why you should make the various choices.
My instructor emphasized the instantaneous steps that were required for an engine failure before the obstructions were cleared at our less than 3,000 foot runway, hard 20 foot obstruction one end, 60 foot trees at the other end.
Toward the railroad, turn parallel if possible, and crash into the creek. The other way, pick which two trees to go between, to loose both wings at the same time, if low, or trees most likely to bend a lot if high.
Over my many years at that airport, I saw 2 planes go into the trees, no serious injuries, planes totaled.
The railroad end, 2 crashes by non locals, straight ahead into the railroad bed, every one went to the hospital with life threatening injuries. Both planes caught fire, and were destroyed, some of the occupants were saved because there were friends waiting for them, who drug them out of the flaming wrecks.
I only used VX to get above the obstacles, from short runways, and then VY until safe glide to someplace to land, and thereafter, cruise climb. I agree that speed is your friend as soon as you are above nearby obstacles.
My instructor did not allow take off and landing practice at our field, there were many much safer airports nearby, why add the risk present at home?
PS, We trained to perform engine out at VX while at 3,000 feet or higher, so that mistakes were correctable and safe.
My instructor emphasized the instantaneous steps that were required for an engine failure before the obstructions were cleared at our less than 3,000 foot runway, hard 20 foot obstruction one end, 60 foot trees at the other end.
Toward the railroad, turn parallel if possible, and crash into the creek. The other way, pick which two trees to go between, to loose both wings at the same time, if low, or trees most likely to bend a lot if high.
Over my many years at that airport, I saw 2 planes go into the trees, no serious injuries, planes totaled.
The railroad end, 2 crashes by non locals, straight ahead into the railroad bed, every one went to the hospital with life threatening injuries. Both planes caught fire, and were destroyed, some of the occupants were saved because there were friends waiting for them, who drug them out of the flaming wrecks.
I only used VX to get above the obstacles, from short runways, and then VY until safe glide to someplace to land, and thereafter, cruise climb. I agree that speed is your friend as soon as you are above nearby obstacles.
My instructor did not allow take off and landing practice at our field, there were many much safer airports nearby, why add the risk present at home?
PS, We trained to perform engine out at VX while at 3,000 feet or higher, so that mistakes were correctable and safe.
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FastEddieB
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Fast Eddie B
A nice illustration. Thanks.
And a good discussion. However, virtually everything being said here is covered pretty concisely in the Airplane Flying Handbook. Larry in TN was nice enough to provide a link in the second post to this thread. I’d suggest any new pilot go back and review that if they haven’t already.
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Pinecone
En-Route
Blue Line is not Vmc (Velocity Minimum Control). It is Vyse = Best Rate of Climb Single Engine. It is above Vmc.
But yes, they want to get at or above Vmc and Blue Line as quickly as possible.
Pinecone
En-Route
I am in the it depends camp.
But for return to the airport, Vx can make it more likely in some aircraft. AOPA, IIRC, did an impossible turn video. A Cub has no trouble no matter what you do (within reason). A Bonanza will not make it back because you are to far from the runway to glide back when you reach the minimum altitude to do the turn back.
But for return to the airport, Vx can make it more likely in some aircraft. AOPA, IIRC, did an impossible turn video. A Cub has no trouble no matter what you do (within reason). A Bonanza will not make it back because you are to far from the runway to glide back when you reach the minimum altitude to do the turn back.
WDD
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Vintage Snazzy (so my adult children say)
To be applicable, that chart needs to have the X axis as Time, not Distance. That would show you get to altitude earlier with Vy.
Why Time? The chance of engine failure is dependent on Time running, not distance. It will fail after so many crank revolutions, time before an oil line ruptures, fuel line clogs. In other words, it is dependent on the time it takes for these things to happen. The distance you might or might not have flown has no factor in breaking the engine.
Why Time? The chance of engine failure is dependent on Time running, not distance. It will fail after so many crank revolutions, time before an oil line ruptures, fuel line clogs. In other words, it is dependent on the time it takes for these things to happen. The distance you might or might not have flown has no factor in breaking the engine.
Lindberg
Final Approach
So what is the circumstance where being lower and having less energy when your engine fails is better?
How does this show that climbing at Vx makes success more likely? If the Bonanza climbs at Vx can it make it back, or is it now just too low to do so?
WDD
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Vintage Snazzy (so my adult children say)
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.
Actually, the chart doesn't have to show the X axis as time because it shows both vectors at the same snapshot in time, T seconds after rotation. The fact that Vy is higher shows that you get to altitude earlier. But of course it is also further away since Vy > Vx. Even though Vy is higher the angle, or ratio of height to distance, is greater at Vx.
The angle is important because your glide ratio or Vldmax is also an angle.
Note: I'm not recommending climbing at Vx, just explaining the diagram.
WDD
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Vintage Snazzy (so my adult children say)
Fair point. BTW - I think you’ll always have greater glide distance at V max glide at the Vy altitude vs Vx altitude, even with being further away.
PilotAl
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PilotAl
Speed is Your Friend my Friend, Especially in a Twin! Yes, Altitude is Definitely Important, But if you lose control (stall) what’s the point!
WDD
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Vintage Snazzy (so my adult children say)
Vy is always a higher airspeed than Vx.
Brad W
Pattern Altitude
So as I've been revisiting this thought process lately for obvious reasons....and after watching that AOPA video that pinecone linked to above, now youtube's algorithm is pushing other videos to me in the topic. Currently watching a video from Gold Seal on the topic. One theme I am noticing in many posts here and in a lot of the scenarios folks are painting is that each opinion (and therefore personal rules) seem to be based on a fairly specifically defined 'box' of assumptions.
I guess the thing I keep going back to ever since my engine out experience years ago, is that there are definitely different phases of flight....every takeoff has these different phases...and they change depending on the aircraft being flown and the weather conditions and the location.
I think in that AOPA presention they collectively pointed out a couple very key points
a) Every takeoff will have spans in time that carry significant risk (meaning I think that in every takeoff there might be time windows where there are zero good options no matter which speed you choose)
and 2) the climb gradient vs the glide gradient is key
That I think is why my mind seems to always come back to a more hybrid complex approach as a better solution.... (which admittedly brings more risks with the complexity so maybe better only as a theoretical thought exercise and not as practical)
so depending on the climb gradient of the aircraft, Vx (or something slower than Vy) might make more sense for the very early part of the departure leg. To get you higher up while there is still a chance to land straight ahead within the runway/airport environment...... you're increasing the amount of time spent in the 'zone' where straight ahead back onto the runway is an option
Then, very quickly once that option is becoming no more, it seems to me that this is when you'd want to be transitioned or transitioning to Vy to be gaining as much altitude as possible over a given unit of time so that you are quickly increasing your secondary options. This begins the Vy segment at a higher altitude and in a way shortens the time spent in that altitude window between when you can no longer land straight ahead on the airport and when you are high enough to have a decent glide ring diameter for other off aiport landing options.
And so depending on actual situations....
if there is for example tons of open spaces close to the airport, maybe after a very short initial high angle climb, you can skip the higher rate climb segment and go straight to cruise.
Or, if the open fields and options are just next to the airport with no obstacles at all, then it might make more sense to skip the high angle segment entirely and maybe even skip the high rate segment too.... instead climbing at more of a cruise climb at a higher speed than Vy in order to keep the angle of attack lower, etc...to increase the reaction time, decrease stall risk, etc...
I'd still want to maximize my time window when I can land back onto the same runway straight ahead....but if say at 200 ft AGL you have just as many off airport options as you do at 1,000ft, then why not just consider that more like cruise enroute just as soon as landing straight ahead on airport is no longer an option?
I guess the thing I keep going back to ever since my engine out experience years ago, is that there are definitely different phases of flight....every takeoff has these different phases...and they change depending on the aircraft being flown and the weather conditions and the location.
I think in that AOPA presention they collectively pointed out a couple very key points
a) Every takeoff will have spans in time that carry significant risk (meaning I think that in every takeoff there might be time windows where there are zero good options no matter which speed you choose)
and 2) the climb gradient vs the glide gradient is key
That I think is why my mind seems to always come back to a more hybrid complex approach as a better solution.... (which admittedly brings more risks with the complexity so maybe better only as a theoretical thought exercise and not as practical)
so depending on the climb gradient of the aircraft, Vx (or something slower than Vy) might make more sense for the very early part of the departure leg. To get you higher up while there is still a chance to land straight ahead within the runway/airport environment...... you're increasing the amount of time spent in the 'zone' where straight ahead back onto the runway is an option
Then, very quickly once that option is becoming no more, it seems to me that this is when you'd want to be transitioned or transitioning to Vy to be gaining as much altitude as possible over a given unit of time so that you are quickly increasing your secondary options. This begins the Vy segment at a higher altitude and in a way shortens the time spent in that altitude window between when you can no longer land straight ahead on the airport and when you are high enough to have a decent glide ring diameter for other off aiport landing options.
And so depending on actual situations....
if there is for example tons of open spaces close to the airport, maybe after a very short initial high angle climb, you can skip the higher rate climb segment and go straight to cruise.
Or, if the open fields and options are just next to the airport with no obstacles at all, then it might make more sense to skip the high angle segment entirely and maybe even skip the high rate segment too.... instead climbing at more of a cruise climb at a higher speed than Vy in order to keep the angle of attack lower, etc...to increase the reaction time, decrease stall risk, etc...
I'd still want to maximize my time window when I can land back onto the same runway straight ahead....but if say at 200 ft AGL you have just as many off airport options as you do at 1,000ft, then why not just consider that more like cruise enroute just as soon as landing straight ahead on airport is no longer an option?
MauleSkinner
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And even more relevant is what glide ratio are you going to make good starting at Vx or below?
Midwest_Wings
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Yes, and the math will always show a greater chance of hitting the trees at Vy than at Vx. If you don’t hit the trees, you have a higher chance of returning to a safe landing spot. Maybe that’s what was meant.
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, …
Lindberg
Final Approach
What math is that? Being higher gives you more options.
Palmpilot
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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.