Accurate plane performace?

"Lars Møllebjerg" wrote in message
...
I can't say much about the max speed at different altitudes, but I did
notice one point where you are probably not maintaining the correct climb
method.
You should NEVER EVER allow the SR-71 to slow down to 200 doing a climb.

This part might be true. Not having flown either the real or simulated
SR-71, I don't know. The rest of the post leaves a lot to be desired.

[...] If you at full power start loosing speed in a climb, lower the nose
immidiatly to build up speed. Run it as close to the max speed at the
current altitude as you can to get maximum lift.

This is very wrong advice.

There are a few interesting airspeeds one can use for climbs. Two in
particular have special names, "Vx" and "Vy". "Vx" is the airspeed at which
the airplane will gain the most altitude over a given distance; it is the
steepest climb angle. "Vy" is the airspeed at which the airplane will gain
the most altitude over a given time; it produces the largest vertical speed.
These airspeeds are what one should choose for "best" climb performance;
which one to choose depends on whether you want a steeper angle or a faster
rate of ascent.

Vx is always slower than Vy, and both are WELL below normal cruise speed,
never mind "max speed at the current altitude". As far as "to get maximum
lift" goes, that is also incorrect. In unaccelerated flight (e.g. a steady
state climb), lift is equal to weight. Always. There's no minimum or
maximum...lift is simply always the same as weight. The "Vx" and "Vy"
airspeeds correspond to the airspeeds at which the airplane has the most
excess thrust and the most excess power, respectively. Lift keeps an
airplane in the air. Excess power is what makes an airplane climb.

A more general airspeed is known as the "cruise climb" airspeed. This is
going to be somewhat higher than Vy, but still will be nowhere near the
maximum airspeed for a given altitude, except for normally aspirated piston
engine airplanes near their ceiling.

When you are flying at
maximum speed and the plane no longer is able to climb 100 feet per minute
(I think that's the number, but I'm not too sure - might be 300 or another
random number) you have reached the planes maximum altitude

Actually, what you're referring to is called "service ceiling" and in the US
that's established at the altitude at which the climb is 100 feet per
minute. An airplanes "absolute ceiling" is the altitude at which the
airplane simply will not climb any higher. As it happens, the "Vx" and "Vy"
airspeeds are equal at this altitude (and converge all the way from their
sea level values to their single absolute ceiling value).

(and this is the
configuration where you should compare it to the real world aircraft to
see
how well the model is done).

Well, it's certainly one data point one ought to be looking at. However, a
simulation model that gets the service ceiling correct may or may not get
any of the rest of the simulation details correct.

Your general advice -- one cannot simply climb at a higher rate by blindly
raising the nose -- is well-intentioned and the basic idea is correct.
However, you took things too far by ignoring the fact that the best climb
performance does still occur in the lower region of the airplane's airspeed
range, and the nose will in fact be pitched relatively high.

Claiming that one should climb at the maximum airspeed possible for a given
altitude is just plain wrong, and in fact that advice will NEVER work. The
maximum airspeed possible for a given altitude (assuming no descent) is in
straight and level, *zero* vertical speed flight. If you are climbing, you
can *always* go a little faster by lowering the nose and not climbing.

Pete