Y con modificaciones de nuevo en los aviones
NOTE ON ENGINE PERFORMANCE!
Here is the deal:
Some of you have noticed that JETS and TURBOPROPS do NOT seem to fly
too well in 9.20 RC-3.
This is actually a problem with EVERY X-PLANE IN THE WORLD EXCEPT
9.20 RC-3, and here is why:
RECIPROCATING engines CAN be turbocharged.
They do this by spinning little turbos as you climb into thinner air
to keep the SAME air pressure going into the engine.
The higher you climb, the faster the little turbos spin to keep the
air coming into the engine at sea-level pressure.
This is why we have a CRITICAL ALTITUDE in Plane-Maker: It is to let
the engine keep SEA-LEVEL power up to some higher altitude, by
spinning the turbos faster-n-faster as you climb into thin air.
Now, JET and TURBOPROP engines do NOT have this ability.
They do NOT have little turbochargers compacting air into them.. they
ALWAYS gobble up ambient air density.
As a result, the JET and TURBOPROP engines do NOT really have a
critical altitude: For a given N1, they will ALWAYS lose power as
they climb.
Now, those that have not yet thought this all the way through will
say: "BUT HOLD ON! I >KNOW< SOME JWTS AND TURBOPROPS HAVE CRITICAL
ALTITUDES ABOVE SEA LEVEL! I SAW IT ON THEIR WEB SITE! THEY SAY THEIR
AIRPLANES FLY AT 50,000 FEET, OR THEIR ENGINES GIVE FULL RATED POWER
TO 30,000 FEET!"
I do not deny that their web sites say this.
But they are only giving HALF the truth.
You see, for the JET or TURBINE engine to put out a CONSTANT power
from sea level up to 50,000 feet, it MUST spin a HIGHER N1 as it
climbs to compensate for the decreasing air density. The thrust or
power will NOT stay constant as you climb unless the N1 is INCREASING
during the climb to make up for the air density loss!!!
So, there is NOT a 'critical altitude' for jet or turbine engines
because their power WILL lapse as you climb.
It is simply the case that many engines might turn only 85% N1 for
takeoff, 100% n1 at hi-altitude cruise, leaving a full 15% N1 in
reserve for hi-alt operations. Now THAT is the type of flat-rating
that jets and turbines do.
So, in X-Plane you should NOT enter a critical altitude for any jet
or turbine engine, because to do so is to pretend that sea-level air
is available to the engine all the way up to altitude.
Well, it ain't.
So, to avoid confusion, and improperly-design acf files in X-Plane, I
REMOVED the jet and turboprop 'critical altitude' variable form the
engines screen in plane-maker, and set the engine model in x-plane to
handle this case properly: lapse the power as you climb, as would
happen in the real engine.
Now, the next question is: If i have (properly and correctly) removed
the turbine critical altitude, how do you make a plane match the
manufacturers specs if it is flat-rated to give a constant power or
thrust up to a high altitude?
Simple.
Enter a the TOTAL TERMODYNAMIC THRUST AVAILABLE FROM THE ENGINE AT
100% AT SEA LEVEL as the engine thrust.
This may well be well OVER the RATED thrust or power of the engine,
but it is what the engine CAN DO (self-destruction aside)
Then, just take off at a lower N1.. JUST AS YOU WOULD DO IN THE REAL
PLANE, to keep the thrust within limits.
Than, as you climb into thin air, ease the throttles forwards to go
up to 100% N1 as the critical altitude approaches, and leave it at
100% N1 above that.
This is what the pilot, or FADEC, of a real plane would do, and this
is what you need to do now.
So, for all under-performing jets, this is probably because the
author erroneously put in a non-zero critical altitude in the acf
file, and that erroneous data is now being ignored. The plane needs
to be corrected by updating the engine thrust to the full thermo
abilities of the engine.. with takeoffs done at reduced N1 to stay
within the rated power.
austin
