False behavior in high Levels
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Altitude isn’t matter only for fuel management. I fly .8 in normal conditions > CAS 350~.8 Mach in combat level ~ 20k plus .9 Mach> CAS400 in combat or above enemy territory, calculate the drag also thats why the CJ-s only fly with 2x120-2x9-2x370-and 2x-4x GBU ~ Drag Index < 150 ~ 2x120-2x9-2x370-and 6x CBU Drag Index above <300
And Awacs and Tower always give CAS readouts. -
@Cik:
, and TAS is your “real” airspeed that determines how fast you are going overland
TAS is your real airspeed. Overland speed is the GS ( ground speed )
GS = TAS +/- head wind component
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Okay I have to refresh my memory.
IAS is nice to have because you know the pressure difference of the outside (the pitot gets rammed into the airmasses) to the local alt pressure : Important for the +~- behavior of your Wingsurfaces
CAS is nice to have because the pitot instrument gets errors depending on the position mounted on the plane (for example on the side of an object it becomes the airwave of it) : Important for the exact behavior of Wingsurfaceshere comes my question: Lets say I put my flaps out - or I do not fly 1g - CAS would become different on the same IAS - on the other hand - CAS is for static errors, so it would stay the same? but which one would be the important one for Stalls?
Lets say I have a damn high AOA, the pitot would become less air rammed into it because not being mounted for that angle - but the wingsurface would hit the airmass with even a bigger area?
Every time I try to inform myself I get more confused…continuing
EAS/TAS needs CAS + dynamic values like air density and temperature on the specific altitude : important for preplan navigation
GS is TAS - wind/attitude : important for navigation -
The Pitot is placed to give the same CAS no matter the angle of attack. Its the aircraft manufacturer’s job to place it wisely.
Definition time :
Dynamic pressure is the difference between basic air pressure at the aircraft location, and the air pressure at an “arrest point” in the aircraft (ie : a spot where the air is effectively stopped on the airframe, and not deviated). Thats the value measured by a Pitot probe.TAS is the speed of the aircraft in the mass of air surrouding it.
CAS is the TAS you would have in a pressure of 1013 mb, temperature 15°C, for the exact same dynamic pressure.
IAS is CAS with the error (called static error) induced by Pitot probe position in the airframe (its hard to get an arrest point and another point where pressure is equal to basic air pressure at the aircraft location).
Ground speed is the horizontal speed of the aircraft by respect to the ground.
Mach number is your TAS divided by the speed of sound (which depends only on the temperature, and stay between 570 & 650 kts)
About static errors in Pitot : modern airplanes have an anemobarometric central computer, which computes values from the altimeter, anemometer, and temperature probes. They have an idea of the static errors in these values based on wind tunnels. They then compute CAS, TAS, angle of attack (which you can know too, cant remember how), vertical speed, Mach number… from these basic pressure informations.
I dont know how F16 speeds indications are computed, but I think it has both “basic” instruments (analog instruments) and an anemobarometric computer. Plus the inertial computer can help too.
tl, dr : dont worry about static error, both in Falcon or RL F16.
Use CAS for aircraft performance (turn rates, stall departures). GND speed for navigation. Mach to have an idea of your TAS and thus your ground speed. Dont display TAS on HUD, it doesnt have much interest.
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The Reason is, that the Air-Resistant falls in high Alt. - and he does that in x^2. So, if theres a much lower Resistance than at 20.000ft you would not need more Fuel for holding the Speed.
That’s right, but not the full truth. The engine loses thrust at higher altitude, but usually, this is compensated to at least some degree by the lower air resistance.
All together, higher altitudes are more energy saving than lower altitudes. However, once you reach the point where you have to build up a large AOA (-> induced drag) for creating enough lift and your engine runs out of air to be compressed, it gets worse again. So, there is an optimum cruise speed and altitude.
Otherwise, if only the rule of reduced drag in higher altitudes would apply, we could all fly to space- cause when there’s no air, there is no drag eitherThe rest of the magic is explained by that TAS/CAS/GS stuff.
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High altitude -> less air density -> less Lift force -> more engine thrust required (high speed -> lift increase). It’s simple.
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Hi FBMS Community,
i have a Question about the behavior of the AC in high Flightlevels.
All of you know the Problem with the Speed-Declaration if you fly higher. If I fly at 30.000ft, I need much more Engine-Power than at 20.000ft for holding my Speed. Sometimes I need the Afterburner for staying at 350kn.
Thats not realistic! If you gonna fly at 30.000ft you dont need 110% Power to hold your Cruise-Speed of 350kn. Thats the Statements of the Pilot and my Teacher.
Best regards Guys!
Salute
Korbi has anyone pointed out the flaw in your thinking here.
110% is not power its engine revolutions, all engines produce more power with denser air. Air through the engine is the key here. (Mass/Weight/Density)
So the higher you fly the less power produced for the same engine revolutions, weather it be turbine or piston. And so also the less fuel used. Fuel-Air mixture and engine max rotation are monitored (along with many other inputs) and controlled by the either mechanical/electrical management systems of which your in pit throttle is only one of the control factors.
Looks like most also missed it.
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High altitude -> less air density -> less Lift force -> more engine thrust required (high speed -> lift increase). It’s simple.
Sorry yakovpo. you forget about drag. Aircraft fly at high altitude because they need less thrust, this is where the best cruise efficiency is depending on air craft type and configuration.