VLD and max altitude

"Chris W" wrote in message
news:2Ze2e.4431$Tn.2869@lakeread06...
I knew there was something wrong with my thinking, that makes perfect
sense, thanks. So I guess the speed I am looking for would be VLP or V
Least Power. Wouldn't that be the speed you are flying when you can't
climb any higher?

"V Least Power" is zero knots. It takes no power at all to stay in one
place (assuming you're on the ground ). It's just like "V Least Drag".

I'm a little confused about what it is you're trying to determine. You
start out asking if you can determine the lowest drag speed by climbing
until you can climb no longer. Todd explained why that won't work. But now
you seem to be looking for *any* speed that can be determined by climbing
until you can climb no longer. It's almost as though what you actually have
is a solution in search of a question.

For what it's worth, when the airplane won't climb any more, you are
necessarily flying at Vy (which is the speed where you have the greatest
*excess* power). You also will happen to be flying at Vx (which is the
speed where you have the greatest excess thrust).

But of course, climbing to the airplane's absolute ceiling doesn't tell you
anything except the absolute ceiling, and the values of Vx and Vy at that
altitude. They both change depending on altitude (Vx gets higher, Vy gets
lower, and they converge at the absolute ceiling). So getting numbers at
the absolute ceiling won't tell you much about them at lower altitudes.

Maybe if you can restate your question to more clearly indicate what it is
you want to know, you might get better help.

Pete

Peter Duniho wrote:

"Chris W" wrote in message
news:2Ze2e.4431$Tn.2869@lakeread06...


I knew there was something wrong with my thinking, that makes perfect
sense, thanks. So I guess the speed I am looking for would be VLP or V
Least Power. Wouldn't that be the speed you are flying when you can't
climb any higher?



"V Least Power" is zero knots. It takes no power at all to stay in one
place (assuming you're on the ground ). It's just like "V Least Drag".


I meant the least power needed to maintain level flight. I'm not what
the correct nomenclature for that would be.

Right after I posted that I realized what I was thinking was wrong.
Because at a high altitude the true air speed would be higher than if
you were close to the ground and flying at the same indicated airspeed
and a higher true air speed requires more power. So the airspeed that
would let you fly with the least amount of power would be different at a
low altitude, or any other altitude for that mater.



I'm a little confused about what it is you're trying to determine. You
start out asking if you can determine the lowest drag speed by climbing
until you can climb no longer. Todd explained why that won't work. But now
you seem to be looking for *any* speed that can be determined by climbing
until you can climb no longer. It's almost as though what you actually have
is a solution in search of a question.


Oh I'm just playing around seeing how high I can get various planes to
fly in FS2004 and it got me to wondering about the speed I should be
flying when at max altitude.

For what it's worth, when the airplane won't climb any more, you are
necessarily flying at Vy (which is the speed where you have the greatest
*excess* power). You also will happen to be flying at Vx (which is the
speed where you have the greatest excess thrust).


If you can't climb any higher, how could you have any excess power?


But of course, climbing to the airplane's absolute ceiling doesn't tell you
anything except the absolute ceiling, and the values of Vx and Vy at that
altitude. They both change depending on altitude (Vx gets higher, Vy gets
lower, and they converge at the absolute ceiling). So getting numbers at
the absolute ceiling won't tell you much about them at lower altitudes.


The more I think about it, that's pretty much what I am realizing.

Maybe if you can restate your question to more clearly indicate what it is
you want to know, you might get better help.


I'm not sure there was specifically something I wanted to know (sort of
thinking out loud) except maybe what speed you should shoot for to get
to the max altitude. If you increase the AOA too much, and go too slow,
you won't reach the highest possible altitude. From what you are saying
I guess Vy is the speed you want to maintain, but as you said that
changes with altitude.

--
Chris W

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"Chris W" wrote in message
newsXj2e.4478$Tn.3559@lakeread06...
[...]
If you can't climb any higher, how could you have any excess power?

The key here is "greatest excess power". At the absolute altitude, your
excess power at Vy is 0. But at any other speed, the airplane actually
requires more power than is available; "excess" power is negative. 0 is
larger than any negative number, thus you are still at the "greatest excess
power".

[...]
I'm not sure there was specifically something I wanted to know (sort of
thinking out loud) except maybe what speed you should shoot for to get to
the max altitude. If you increase the AOA too much, and go too slow, you
won't reach the highest possible altitude. From what you are saying I
guess Vy is the speed you want to maintain, but as you said that changes
with altitude.

You should start at Vy, and gradually reduce your airspeed as you climb. As
a very rough guess, average Vx and Vy at sea level and aim for that at your
final altitude (so, it will help if you have at least a rough guess as to
the absolute ceiling of the airplane in question, so you know how to adjust
your airspeed as you climb). Vx and Vy don't actually change at the same
rate, so the final Vx and Vy that are the same isn't actually their sea
level average. But it's not far.

The question of what airspeed to fly at maximum altitude will be answered
when you reach maximum altitude. There is only one airspeed at maximum
altitude at which you'll stay at maximum altitude. Any other airspeed will
result in a descent.

So, one way you could do this is to start at Vy and climb. When the
airplane stops climbing, reduce your airspeed by a knot or so. If the
airplane starts climbing again, repeat the exercise each time it stops
climbing. Once reducing the airspeed after you've stopped climbing results
in a descent rather than a continuation of your climb, you've hit the
absolute ceiling of the airplane.

Note that all of the above is for real life situations. While I think MSFS
gets more crap for its flight model than it deserves, it's true that some
odd things sometimes happen near the boundary cases. I can't guarantee that
everything will work exactly as it does in real life.

Pete