Accurate plane performace?

I love FS2004 -- hell of a value for $50. I've recently been
downloading and playing with the slew of fan-designed aircraft. I
love speed, and so I've been gravitating to some of the supersonic
military aircraft -- Mig 29, F-18, F-16, F-15, F-14, SR-71, etc.

However, I've yet to find one such aircraft that performs in speed
and altitude the way that they're supposed to. The F-16, for example,
struggles to break mach 1.2 at 40,000 feet -- this is a plane capable
of Mach 2 at that altitude. The SR-71 can sustain Mach 3.3 for an
hour at 80,000 feet. The SR-71 I downloaded stalls out at around
70,000 feet -- at 60,000 feet, it's struggling along at 200 kts. (The
U-2 stalled out at 55,000 feet -- that got a good laugh from me.) All
of these planes can tear the MSFS world up at low altitudes -- I had
the SR-71 popping Mach 3 at 5,000 feet (which is also unrealistic; the
plane would fly apart at that speed at that altitude). But get them
to their cruise ceiling, and suddenly they perform subsonically.

Am I doing something wrong? Yes, gear is up, flaps are up, spoilers
are not deployed. Is MSFS not that good at rendering supersonic
flight? Or are the makers of these add-on planes not building them
correctly to interface with MSFS 2004? I've even tried going into the
..air file and doubling or tripling the engine thrust... doesn't seem
to help much at the higher altitudes. (Which are not really "high" to
these aircraft.) I'm puzzled. I'd love to fly a SR-71 mission 80,000
feet over Russia, but that's not going to happen at 100 kts.

-R

"Jeffrey Voight" wrote in message
...
I don't know if this is what you're experiencing in the FS, but I'd
check the GPS ground speed before filing a bug report to M$.

Your guess as to what the person posting as "R" is complaining about is
probably right on the money.

For the non-pilot crowd, often the best solution is simply to change the
setting so that true airspeed is displayed rather than indicated. The
option is under the Realism settings. They usually want to see a specific
number on the airspeed indicator, and don't care about the difference
between true and indicated.

Of course, if they are displaying true, they need to remember that the stall
speed will be higher at higher altitudes. They should not be surprised if
one cannot slow down very much from max cruise before stalling, when flying
at 50000 feet (for example).

Pete

"R" wrote in message
...
...
However, I've yet to find one such aircraft that performs in speed
and altitude the way that they're supposed to. The F-16, for example,
struggles to break mach 1.2 at 40,000 feet -- this is a plane capable
of Mach 2 at that altitude. The SR-71 can sustain Mach 3.3 for an
hour at 80,000 feet. The SR-71 I downloaded stalls out at around
70,000 feet -- at 60,000 feet, it's struggling along at 200 kts. (The
U-2 stalled out at 55,000 feet -- that got a good laugh from me.) All
of these planes can tear the MSFS world up at low altitudes -- I had
the SR-71 popping Mach 3 at 5,000 feet (which is also unrealistic; the
plane would fly apart at that speed at that altitude). But get them
to their cruise ceiling, and suddenly they perform subsonically.
...

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. As
you slow down, less air move over the wings - meaning they produce less
lift. To compensate, you have to rise the nose a bit which increase the lift
but this produce more drag, hence slowing the plane further and the cycle
continues - you are heading streight for a stall no matter what kind of
plane you are flying - Cessna or SR-71 - it does not matter the physics is
the same. Of course if the model is wrong it won't work, but you forgot to
say which model we are talking about?? As far as I recall, I manage to get
Kirk Olsson's F-16 over 60000 using this method, and apparently the correct
number is 61500 feet.

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

You can play around and rise the nose to see how much higer you can get, but
you should not expect to maintain the altitude gained this way. Again, from
memory I think it was 65000 I managed to get Kirk Olsson's F-16 to for a few
seconds. I used the flaps just before it stalled to buy another couple of
hundred feets, but using the flaps to maintain altitude is like peeing in
your pants to keep warm - it might help for a few seconds, but then you are
worse of than you where before.

Regards
Lars

"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

Yes, I should probably have made it clearer that I was only refering to
climbing close to the ceiling. Would have saved you a lot of typing.

Regards
Lars

"Lars Møllebjerg" wrote in message
...

By the way, saying that lift is equal to weight is a bit wierd as the lift
is a force generated, while weight isn't a force, but a number calculated
from the mass and gravity. But I guess it's one of those simplification
making it easier for people to understand.

/Lars

"Lars Møllebjerg" wrote in message
...
By the way, saying that lift is equal to weight is a bit wierd as the lift
is a force generated, while weight isn't a force, but a number calculated
from the mass and gravity.

The number you calculate from mass and gravity is a force. Gravity is an
acceleration, and mass is, well...mass is mass. F=ma.

In other words saying that lift is equal to weight makes perfect sense.
They are both forces.

But I guess it's one of those simplification
making it easier for people to understand.

I know you mean well, but frankly you really have not been helpful in the
"understanding" department.

Pete

By the way, saying that lift is equal to weight is a bit wierd as the lift
is a force generated, while weight isn't a force, but a number calculated
from the mass and gravity. But I guess it's one of those simplification
making it easier for people to understand.

The above comment is wrong. First of all weight *is* a force. Then
"saying that lift is equal to weight is a bit wierd" is not wierd but
it is a simplification. This will be true only in straight and level
flight. In a turn or descent/climb, lift will not be equal to weight.

In fact in a steady climb lift is *smaller* than weight! This is
because weight is tilted backward relative to the flight path (weight
always point to the centre of Earth). Therefore it adds a component to
the drag, which must then be balanced by an increase in thrust (the
"excess thrust") but the weight component that must be balanced by the
lift is now less so lift is smaller.


Chris

On Sun, 7 Dec 2003 01:27:39 -0800, "Peter Duniho"
wrote:

"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.

Actually, I wasn't even climbing at that speed. I'd get it to
around 65,000, level off, and see how fast it would fly. 200kts was
about average. Even with "true airspeed" selected, I wasn't coming
near Mach 1 in a plane that should pull Mach 3.3 at 80,000 feet. I
had similar speed issues with most fighter aircraft, as well -- the
F-16 barely chugging along at 400 kts at 50,000 feet. This is a plane
that has enough thrust to climb from takeoff to 20,000 feet at a *90
degree angle*.

With the SR-71, I mostly climb with the autopilot. Granted, I
usually set at the default 1,100 fpm climb rate, but I didn't think
that would be too much of a problem for the fastest (known) plane in
the world, a plane that pulls Mach 3.3 at 80,000 feet. At some point
well before 80,000 feet, the autopilot more or less fails, pulling the
nose up into a stall.

I don't have stalling problems with fighter aircraft, but they don't
go anywhere near their advertised speed capability at high altitude.
Oddly, they come closer to approaching their max speed at low
altitude, which is kind of silly, as a plane flying mach 2 at 500 feet
would promptly break apart or begin to melt.

I did find one interesting speed glitch in the game. With the
air-stress option untoggled, it is possible to get nearly any jet
aircraft out of the sim reality's "envelope" and send it into a
hyperspeed journey. Take any jet aircraft (fighters work well) up to
a high altitude, say, 65,000 feet. Bring the nose to 90 degrees down.
Do some barrel rolls on the way down. At some point, your plane gets
a tremendous speed boost, up to around mach 5. Pull out of it.
Better have your wing leveler on, as, at this speed, the plane bounces
all over the place with turblence. Once you do this, it is impossible
to slow down. Cut the throttle, turn the engines off, it doesn't
matter. You are now God's guided missile. I made a trip from Seattle
to LAX in around 15 minutes this way.

I never owned FS2002. Did supersonic aircraft perform correctly in
that package? I'm tempted to think that most of the 2004 planes are
just 2002 conversions, and that perhaps the two versions handle high
speed dynamics differently. If the developers didn't change anything
before porting to 2004 (or, in the case where I just load 2002 planes,
like the SR-71), the planes may perform incorrectly.

-R

With the SR-71, I mostly climb with the autopilot. Granted, I
usually set at the default 1,100 fpm climb rate, but I didn't think
that would be too much of a problem for the fastest (known) plane in
the world, a plane that pulls Mach 3.3 at 80,000 feet. At some point
well before 80,000 feet, the autopilot more or less fails, pulling the
nose up into a stall.

is that autopilot capable of maintaining a certain IAS during a climb?
if so, i'd try 300 knots or so and see how it goes. if not, try keeping
an eye on the IAS and lowering the 1100 fpm if IAS goes below those 300
knots...