Question about being unpressurized at higher (Class A) altitudes

"es330td" wrote

To all: This discussion has been very educational. I haven't learned
yet at what altitude a plane gives maximum performance at cruise power
though from these responses it appears that under FL100 is expected
and preferred. I guess I'll leave Class A to the turbine powered
airplanes.

At low altitudes, you can get the engine to produce a lot of power, and go
pretty fast. Unfortunately, you burn a LOT of fuel.

You go up to 7 or 8 thousand feet, and the engine does not produce much
power; perhaps 60 percent, with the throttle wide open. But, since there is
a LOT less drag, (as compared to low altitudes) you can go a lot faster than
60 percent at the lower altitudes.

So, you climb up to 8 thousand feet, and go as fast or faster than you were
going at sea level burning almost twice as much fuel.

There is a trade off between altitude and speed, and each design airplane is
going to have its ideal altitude, to go the fastest, with the least fuel
burn. It all depends on the different types of drag, and how much that
design's drag is reduced, and the power output of the engine.

This is a general overview of the concept that you are trying to grasp, I
hope. Apologies if it is stuff you know already.
--
Jim in NC

Morgans writes:

In airliners, all you have to do is change the cabin altitude pressure
setting, and you can do the same thing, and they do occasionally do this on
(especially on) oceanic red-eyes.

You can only go to 8000 in (most) airliners.

They don't have to go all that high to have a noticeable effect, but it does
make it easy for the flight attendants.

Only if the FAs are wearing oxygen masks.

Matt Barrow writes:

How does the airframe "gain efficiency" at altitude, aside from generating
less drag?

Less drag is a big advantage. The higher an aircraft flies, the more easily
you can move it forward. Ultimately, you end up in outer space, with no air,
and then you don't need any energy at all to keep it moving forward (the
principle behind hypersonic aircraft). This is one reason why the SR-71 is
very efficient in cruise. It's also a reason why jets fly high even though
the engines produce less power at high altitudes--the power required to
maintain a given speed decreases faster than the power provided by the
engines, as altitude increases (within certain limits).

On Sep 13, 10:41 pm, "Matt Barrow"
wrote:
"Andrew Sarangan" wrote in message

ups.com...

The airframe gains efficiency with altitude, but the engine loses
efficiency with altitude.

How does the airframe "gain efficiency" at altitude, aside from generating
less drag?

It gains efficiency because you can move faster for the same engine
power. If you disregard drag, then you might as well disregard the
engine too because thrust = drag at level unaccelerated flight.

Mxsmanic wrote in
:

Matt Barrow writes:

How does the airframe "gain efficiency" at altitude, aside from
generating less drag?

Less drag is a big advantage. The higher an aircraft flies, the more
easily you can move it forward. Ultimately, you end up in outer
space, with no air, and then you don't need any energy at all to keep
it moving forward (the principle behind hypersonic aircraft). This is
one reason why the SR-71 is very efficient in cruise. It's also a
reason why jets fly high even though the engines produce less power at
high altitudes--the power required to maintain a given speed decreases
faster than the power provided by the engines, as altitude increases
(within certain limits).


Wrong again, bozo


Bertie

es330td wrote in news:1189691258.415403.151350@
50g2000hsm.googlegroups.com:

My father has a C182 in which I have been to about 10K ft MSL. I am
currently working on my license and am considering building a Velocity
or Aerocanard, both of which have ceilings up into Class A airspace,
one as high as FL250. (Before anyone cautions me about building one
of these, I know two people with Velocities and a local builder who
has built multiple canard aircraft. I will have lots of support and
will have logged PIC time in one long before mine is built.) While I
know that oxygen is required at altitude, what is the effect of the
lower pressure on pilot and passengers? I am doing this in part for
the purpose of transporting myself and family to visit friends and
relatives and am curious about the effect on my two children,
currently 3 and 5, and whether this will make them less pleasant to
fly with.

TIA


A, your kids will be teenagers at least by the time oyu get the thing done
(ask me how I know this)
B, pax on O2 are usually not happy pax.. It's a pain in the ass, really.
C. You'll probably almost never go up to altitudes where O2 is required for
several reasons unless you're the exception who proves the rule..

Bertie

"Andrew Sarangan" wrote in message
oups.com...
On Sep 13, 10:41 pm, "Matt Barrow"
wrote:
"Andrew Sarangan" wrote in message

ups.com...

The airframe gains efficiency with altitude, but the engine loses
efficiency with altitude.

How does the airframe "gain efficiency" at altitude, aside from
generating
less drag?

It gains efficiency because you can move faster for the same engine
power.

That's not the airframe gainning efficeincy, that's called a reduction in
drag.

If you disregard drag, then you might as well disregard the
engine too because thrust = drag at level unaccelerated flight.

I'll have to dig through my library of physics books to 'splain that one.
:~)

The engine loses the _ability_ to generate power, but that has noting to do
with your T=D formula.

Think: turbocharging.

The airframe is static, so there's no gain or loss in efficiency.

Now, if you have a wing like the F-14, that could be considered as a whole
different story.

On Sep 13, 1:18 pm, Jim Stewart wrote:
John wrote:
I am not at all sure if this is accurate, but Ernie Gann in his book
"Fate is the Hunter" described an episode where he was carrying troops
in the back and they were getting a bit out of hand. He climbed and
the reduced oxygen resulted in a cabin of slumbering souls. Two
caveats: I am not sure . . . but alcohol may have played a role in
the story and . . .

I've read "Fate is the Hunter" several times and I
don't remember that story. If you can think of
another Gann book that it might be in, I'd sure
like to read it.

OK Jim, lemme see. . . I dont think it is in the High and Mighty. . .
so try Gentlemen of Adventure, or Band of Brothers, or In the Company
of Eagles or maybe Hostage to Fortune which is Gann's actual
biography.

Hmmm . . . might be a good excuse to re-read his books. Although I
read the 1986 reprint of Fate is the Hunter had several episodes
editted out that appeared in the original 1961 edition. I do remember
when i re read it last, I was left kinda wondering what happened to
the book.

Take care . . .

John

On Sep 13, 8:48 pm, Andrew Sarangan wrote:

I don't know where you got the information that Velocity has a service
ceiling of 25k. It is not the airframe that determines the service
ceiling as much as the engine choice.- Hide quoted text -

The Velocity won't go that high; according to the specs on their
website the RG Velocities top out about FL200. The Cozy based
Aerocanard will go to FL250, according to http://www.aerocad.com/Performance.htm.
While they could be completely full of it, I don't see too many people
trusting their life and paying over $30K for a homebuilt kit to a
company that lies about its planes' performance numbers.

"es330td" wrote in message
ups.com...

will have logged PIC time in one long before mine is built.) While I
know that oxygen is required at altitude, what is the effect of the
lower pressure on pilot and passengers?

Sinus blockages, intestinal gas and particularly poor dental work (air
behind the fillings, I guess) can be extremely uncomfortable or
excruciating.