Airspeed, or Altitude After Takeoff?

T

tobnpr

Pre-takeoff checklist
Joined
Aug 29, 2022
Messages
127
Location
Lakeland, FL
Display Name
Display name:
tobnpr
As a low-time student, I spend a lot of time studying what to do- and not to do, during critical phases of flight.
After reading of several recent suspected or confirmed engine-out mishaps after takeoff I'm curious as to opinions on whether most of you do a typical (not short field, no obstructions to consider) takeoff at Vx, Vy, or something in between.

CFI told me "altitude is your friend" and had me typically climbing at Vx to gain altitude as quickly as possible in the event of an engine-out right after takeoff.
BUT... as I try to wrap my head around energy management, I question it.

Yes, I have more altitude at any given point than if I were at Vy- but I also have slower airspeed, and a greater angle of attack.
By the time I would process, and react to an engine out- I'd have lost more precious airspeed than I otherwise would have, more energy, and would need to pitch down more aggressively for best glide speed.

Where am I wrong in thinking that I'd be better off with lower altitude- but more kinetic energy?
 
tobnpr said:
CFI told me "altitude is your friend" and had me typically climbing at Vx to gain altitude as quickly as possible in the event of an engine-out right after takeoff.
BUT... as I try to wrap my head around energy management, I question it.
Click to expand...
You are right to question it because it isn’t wise.

Climbing at Vx is something to do in specific situations where you need to climb at a steeper angle for terrain or other obstacles.

But to do it as a regular practice is asking for trouble for a couple of reasons.

One, if you are climbing with a high angle at Vx you are much closer to your stall speed. If the engine does quit on you in such a situation you have less reaction time to get the nose down before you stall/spin. Any extra altitude you gained climbing at Vx doesn’t help if you spin it in.

The other issue is that as you move into higher performance airplanes you will find heat management is a factor. Climbing in a high performance airplane at Vx usually results in less airflow over the cylinders and consequently higher CHTs. In warmer environments, you can actually damage your cylinders by climbing at Vx all the way to pattern altitude.
 
tobnpr said:
CFI told me "altitude is your friend" and had me typically climbing at Vx to gain altitude as quickly as possible in the event of an engine-out right after takeoff.
Click to expand...
Altitude may be your friend, but climbing at Vx doesn’t gain altitude as quickly as possible. That’s Vy.

Vx would have you at a given altitude closer to the airport, but unless you have a definite need for best angle, I don’t think there’s a good reason to use it.

just as a point of reference, I had an engine failure at Vx and about 75 feet AGL on a go around. getting the nose down with no delay was critical to the outcome, and that occurred simply because of good, repetitive training.
 
Last edited:
whats that term (though mostly applies to twins ) - airspeed is life, altitude is life insurance.
 
Practical application of a Vx is to clear an obstacle. Realistically, that obstacle, in an airport environment and lined up with runway heading, is not likely to be hundreds of feet. For short-field takeoffs and landings during training, that obstacle was simulated to be at 50 ft AGL. So a Vx climb becomes a Vy climb very soon after takeoff.

I can say that other than for training or practice I’ve never needed to climb at Vx. That’s because my plane’s performance is adequately paired with the airport runway lengths that I use. A short field is only short relative to the plane’s capability, pilots being equal :)

All my takeoffs are Vy.
 
It's more an altitude AND airspeed issue. You are constantly changing the mix depending on what you need.

but the critical thing is climbing away from the runway as soon as you can and getting to altitude, where you have options when the engine quits.

If you are doing a short field takeoff, you’ll want to break ground & when the obstacle clearance is assured, push over & get some more speed. Same for soft field.

but the critical thing is climbing away from the runway as soon as you can and getting to altitude, where you have options when the engine quits.

Btw, you’ll likely see some twins skim the runway building speed rather than gaining altitude. That’s because twin pilots are playing a different game. They want to get past minimum controllable single engine speed (blue line) as quickly as possible. They are looking to bank options, too.
 
Furthermore… Airplanes basically don’t know how high they are. They ALL know how fast they are, and NONE will give an exception of even one knot slower than stall speed allowance. And for some reason, we in GA don’t know what our real angle of attack is, for current conditions…

So…

It’s my belief airspeed is more important. The law of conservation of energy gives us the same time aloft for any given energy state, whether that consist of kinetic or potential energy.
 
I had a partial engine failure (not a cold failure but power dropped significantly) a couple hundred feet up after takeoff once, in a C172. Probably climbing Vy. Very long 8,000 ft runway, landed straight ahead
But that event shook me because had I been at my home airport with it's 3,000 ft runway I'd probably have been in the trees or the marsh
....and I thought a lot about that even on a very long runway, if that happens during a very shallow angled faster airspeed climbout, I might be out of runway by the time I'm high enough for options
so my mind leans more to the idea of Vx for a short time to gain altitude over the runway, then speed to VY to gain altitude more quickly.

I think about it as sort of a conflict.... pros and cons to each approach.
and it's about balancing risk
on one hand you might think that the odds of an engine problem increase with an increase in minutes spent with the engine running....so since Vy gets you to altitude in the fewest minutes.... that seems like a good idea
BUT if you're out of runway or clear options by the time that altitude happens the altitude may not be all that helpful.
 
Skip Miller said:
Negative. Blue line (marked on the airspeed indicator) is the minimum speed a twin can be controlled with one engine out and the other engine at full tilt boogie power.

-Skip
Click to expand...
No. Redline is Vmc- minimum controllable airspeed with operating engine at full power and one engine failed, not feathered. Below this you will roll over unless you quickly pull the good engine back. Blue line is Vyse- speed for best climb (or slowest descent) with one engine inop, feathered, good engine max power and banked appropriately into the good engine. This speed is your best chance to climb out if you have an engine failure. (Note that climb may not be possible in all situations even if you are at blue line but would still be slowest rate of descent)
 
Best to think of how to stack he deck in your favor in case of engine out on climb out. Every runway and plane is different. As mentioned twins favor airspeed over altitude so that’s why they may fly level after gear up until reaching blue line. For short runways, Vx may keep you closer to the runway environment but at a cost of less time to react. Other places you may be better off starting crosswind turn sooner to put you closer to another runway or favorable off field terrain. It’s good that you’re thinking of these things. But don’t think Barack and white this airspeed or that. Think if my engine dies at 400-600’ where do I want the airplane to be positioned for the best possible outcome and where do I want to be pointed. This will change with every airport and every takeoff. Do this as a pre takeoff brief so it’s fresh in your mind every time. If it’s an unfamiliar airport check out surrounding terrain on the way in, or look at google earth etc to get a sense of best place to go. May even mean taking off with slight 3-5kt tailwind as there is a large field off that end vs into the wind where there’s nothing but water or houses. Every situation is different.
 
I think the risk of a takeoff stall is more than the risk of an engine out. As others have said reserve Vx for specific situations.
 
Thinking about it and trying to fully wrap your head around it is a very healthy practice. Because in aviation the answer is "it depends".

Altitude and airspeed are both very good things, but they are tradeoffs. Add one, you decrease the other. And low level stalls also worry me more than engine failures. But there is a lot to learn and CFI will often simplify things with rules of thumb to keep it from becoming overwhelming too soon. Often the nuance is learned later in the program, but the nuance is important. I dislike it when someone says "always".

In a single, I usually climb at Vy to about 800AGL and then lower the nose for cruise climb to keep the engine temps happy. Vx is for when I don't want to hit something. In the twin, there are even more things to think about.

But I think it's very good you are looking for a deeper understanding of this. Energy management is a crucial skill.
 
Greg Bockelman said:
No. He meant blue line. Minimum safe single engine speed.
Click to expand...
What he actually said was:
rhkennerly said:
They want to get past minimum controllable single engine speed (blue line) as quickly as possible.
Click to expand...

Perhaps in your twin the lines are colored differently than mine. In mine, the minimum controllable single engine speed is indicated by a red line.

Tokirbymd said:
Redline is Vmc- minimum controllable airspeed with operating engine at full power and one engine failed, not feathered. Below this you will roll over unless you quickly pull the good engine back. Blue line is Vyse- speed for best climb (or slowest descent) with one engine inop, feathered, good engine max power and banked appropriately into the good engine. This speed is your best chance to climb out if you have an engine failure. (Note that climb may not be possible in all situations even if you are at blue line but would still be slowest rate of descent)
Click to expand...
:yeahthat:
 
As a student, read and perform according to the ACS. After that, worry more about such things.
 
MauleSkinner said:
Yeah, best not to think about safety until After the checkride. :rolleyes:
Click to expand...
My read of the ACS is that it incorporates safety.
It also specifies what speed to climb out at for what scenarios. There is no better reference for Vx Vy blah blah blah at the student pilot stage.
 
4RNB said:
My read of the ACS is that it incorporates safety.
It also specifies what speed to climb out at for what scenarios. There is no better reference for Vx Vy blah blah blah at the student pilot stage.
Click to expand...
so whats wrong with this discussion
and for the record, the ACS is NOT a reference for Vx Vy blah blah blah. It is the testing standard for Vx Vy blah blah blah.
 
Chrisgoesflying said:
Vy until about 1,000 ft AGL. Then something that gives me a shallower climb with higher airspeed for cooling, visibility and getting to destination faster purposes.
Click to expand...
I do the same. The FAA mentions that running rich of peak power helps cool the engine, which is true. Yet airspeed / airflow cools the engine more effectively. Pitching down to climb at a shallower angle and higher speed is good practice whenever terrain & airspace permit.

Full power climb at Vx is hard on the engine and closer to critical AoA making recovery more difficult in case of emergency. Use it only when necessary to clear an obstacle than you cannot go around. That's after asking yourself why you are putting yourself in a situation where you must do a maximum performance climb at Vx to clear an obstacle you cannot go around.
 
Been a long time since I flew something with a blue line.

Got close. Right idea, wrong term.
 
I'm aiming for a compromise between airspeed and altitude. When departing from long runways and/or flat terrain, there is really no need for a Vx climb, ever. I can somewhat see the rationale behind Vy, though personally I transition (slowly) to my cruise climb speed pretty quickly. In the Bonanza, my flight director will ask for wings level and 7 deg pitch up on take-off; in most cases (for me) that is safe guidance to start a safe climb away from terra firma while slowly accelerating. Once I reach 500 feet AGL I typically accelerate to 120 KIAS, which still gives me a good rate of climb while providing better forward visibility, better forward speed, and better engine cooling than Vy.

Special circumstances require other techniques, like high density altitude take-offs or very heavy take-off weight.

See this article from the late John Deakin on Vx and Vy, and why much of what we've been taught about those speeds for take-off should be thrown out the window.

- Martin
 
I would always use Vy unless there was some reason to do something else- usually that would be a short field takeoff using Vx until clearing an obstacle then going back to Vy.
 
tobnpr said:
CFI told me "altitude is your friend" and had me typically climbing at Vx to gain altitude as quickly as possible in the event of an engine-out right after takeoff.
Click to expand...
You or your CFI got this exactly backwards. You gain attitude fastest at Vy. That's the definition of Vy: the speed at which you gain altitude the fastest.
 
MauleSkinner said:
so whats wrong with this discussion
and for the record, the ACS is NOT a reference for Vx Vy blah blah blah. It is the testing standard for Vx Vy blah blah blah.
Click to expand...

Seems like Lindberg above adequately describes what is wrong.
Other: https://www.boldmethod.com/blog/2014/03/vx-vs-vy/

This student pilot is trying to "wrap" ones head around new material, a worthy endeavor. The student pilot is being told to do things a certain way, for a certain reason.
I assume the goal of a student pilot is to pass the tests. The ACS has the test standards. If a CFI has one trying to do normal takeoffs contrary to what they should be, using the ACS as an uncompromising standard, one gets to fly in a manner that will pass the test. And have proof to argue with the CFI. Also, if the POA internet response teams answer insufficiently for understanding, well source material is right there in the ACS.

Energy management, impossible turns, and other mental self pleasure activities run up billable hours whilst flight training.
 
Martin Pauly said:
I'm aiming for a compromise between airspeed and altitude. When departing from long runways and/or flat terrain, there is really no need for a Vx climb, ever. I can somewhat see the rationale behind Vy, though personally I transition (slowly) to my cruise climb speed pretty quickly. In the Bonanza, my flight director will ask for wings level and 7 deg pitch up on take-off; in most cases (for me) that is safe guidance to start a safe climb away from terra firma while slowly accelerating. Once I reach 500 feet AGL I typically accelerate to 120 KIAS, which still gives me a good rate of climb while providing better forward visibility, better forward speed, and better engine cooling than Vy.

Special circumstances require other techniques, like high density altitude take-offs or very heavy take-off weight.

See this article from the late John Deakin on Vx and Vy, and why much of what we've been taught about those speeds for take-off should be thrown out the window.

- Martin
Click to expand...
I've started adapting this kind of takeoff. Thanks for sharing, great stuff.

More good stuff on Gami site.
 
It’s hard for a new student to understand Vy vs Vx. I know I had a hard time wrapping my head around it back then.

Vy = Fastest way to gain altitude in terms of time.
Vx = Fastest way to gain altitude in terms of distance.

If the exact same airplanes take off at the same moment and climb for 1 minute, the one flying Vy will be at a higher altitude after that minute.

If the exact same airplanes take off at the same moment and fly one mile away from the airport, the one flying at Vx will be at a higher altitude at that one mile mark, albeit it’ll get there slower.
 
4RNB said:
Seems like Lindberg above adequately describes what is wrong.
Other: https://www.boldmethod.com/blog/2014/03/vx-vs-vy/
Click to expand...
so you start out by directing AWAY from the ACS. Good.
4RNB said:
This student pilot is trying to "wrap" ones head around new material, a worthy endeavor. The student pilot is being told to do things a certain way, for a certain reason.
Click to expand...
And, as you noted below, the instructor may be (and in this case, is) wrong.
4RNB said:
I assume the goal of a student pilot is to pass the tests.
Click to expand...
I assume the goal of the student is to learn to fly safely, but either one of us could be making a faulty assumption.
4RNB said:
The ACS has the test standards. If a CFI has one trying to do normal takeoffs contrary to what they should be, using the ACS as an uncompromising standard, one gets to fly in a manner that will pass the test. And have proof to argue with the CFI. Also, if the POA internet response teams answer insufficiently for understanding, well source material is right there in the ACS.
Click to expand...
correct for purposes of the checkride, but there are ACS criteria that run counter to safety. I don’t have the familiarity with the Private Pilot ACS to provide examples there, but flying per the ATP ACS has killed at least one airliner full of people.
4RNB said:
Energy management, impossible turns, and other mental self pleasure activities run up billable hours whilst flight training.
Click to expand...
Which is why a lot of these discussions SHOULD take place here.
 
Chrisgoesflying said:
It’s hard for a new student to understand Vy vs Vx. I know I had a hard time wrapping my head around it back then.
Click to expand...
True, though it's a simple concept, people think differently.

Chrisgoesflying said:
Vy = Fastest way to gain altitude in terms of time.
Vx = Fastest way to gain altitude in terms of distance.
Click to expand...
True, and alternately:
Vy = best rate of climb
Vx = best angle of climb

Alternately:
Rate of climb is determined by excess power. Vy is the airspeed having maximum excess power, thus maximum rate of climb.
Angle of climb is determined by excess thrust. Vx is the airspeed having maximum excess thrust, thus maximum angle of climb.

At sea level, Vx is always slower than Vy. As you gain altitude, Vx gets faster and Vy gets slower (as indicated airspeed) until they meet at the airplane's ceiling. So at high DA, one must adjust the POH values: increase Vx and decrease Vy.
 
Appreciate all the feedback, and the many "it depends" replies are certainly logical.
Class D, and usually with the prevailing winds the runway used is 7,000 ft long. Huge grass infield between the two runways which are 60 degrees apart.
Half a mile from the end of the runway is an expressway with miles of dense residential development on the other side.

There's about 4,000 feet of clear infield to the left of that runway- so no "impossible" turn would be needed to get to the runway- grass infield might not be ideal, but it's about as good as it gets aside from another runway.

Needing little more than 10-15% of the runway to get airborne, I'm around 400-500 ft AGL at the end of the runway. Engine out shortly after takeoff, adequate runway to set it back down. With enough altitude and airspeed, could possibly make the turn wide enough to use the other runway. I can see scenarios where more altitude would be a plus, others where it would actually be detrimental. Since we can never know if/when/where, I don't see how a Vx climb here could be seen as advantageous as a rule (?).
 
You must log in or register to reply here.
Back
Top