False behavior in high Levels
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CAS is TAS at a specific pressure, temperature, and humidity, I think 1013 hPa, 20°C, and “dry” air.
Almost correct. International Standard Atmosphere (ISA) conditions are at 15° C. (can be found here)
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Almost correct. International Standard Atmosphere (ISA) conditions are at 15° C. (can be found here)
Indeed ! Thanks for the precision.
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Almost correct. International Standard Atmosphere (ISA) conditions are at 15° C. (can be found here)
… Almost correct. International Standard Atmosphere (ISA) conditions are at 15° C , 1013.25 hPa … at sea level
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Thanks for the fast Answers! -
I never thought of switching to TAS or GS. I knew the difference between the Speed-Types but didnt think of them in relation to my Problem. You solved it very precisely. Thanks -
This post is deleted! -
so whoa whoa whoa whoa
whoa
what? i didn’t know anything about this. how do you switch to TAS? i’ve never seen anything about this in all the MFDs i’ve switched to. you’re telling me you’re actually faster at high altitudes? i’ve always stuck to angels ~20 because i thought it was the most efficient cruising altitude (as a median between cruising speed and fuel use) am i totally wrong about this?
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20.000 ft is pretty low. Not efficient in consumption and not at all tactical wise.
For a AG striker, I cruise around 26.000 ft. And for a Air to Air, around 35.000 ft.
Don’t bother with TAS in medium / high level. The only moment you should work in TAS is for low level coordinated attack like popup, TOSS, etc… Fly with mach. -
flying fuel efficient is an art. it only starts with these simple things. if you can fight fuel efficient you get into it.
select ‘5’ - CRUS in the DED and your optimum speed and altitude is displayed.
it depends on your weapons loadout / drag.
for an empty jet it is much higher. a packed jet would indeed be cruising best around 22 - 24 thousand feet.the airspeed readout is selected on the right console (the HUD panel - TAS true air speed /CAS calibrated air speed /GND ground speed switch)
won’t make you faster though. -
@Cik:
so whoa whoa whoa whoa
whoa
what? i didn’t know anything about this. how do you switch to TAS? i’ve never seen anything about this in all the MFDs i’ve switched to. you’re telling me you’re actually faster at high altitudes? i’ve always stuck to angels ~20 because i thought it was the most efficient cruising altitude (as a median between cruising speed and fuel use) am i totally wrong about this?
Yes. At higher alt for same TAS you have to set higher RPM but the specific fuel consumption (SFC) is decreasing up to 30-39k feet depending on your loadout. Just check your speed and fuel flow rate and calculate the nm/lbs SFC. The CAS is good because shows the amount of lift and drag forces on airframe, but your TAS and Mach numer indicates your real airspeed. In short if you wish the same turn rate at 1k or 30k on a certain speed you have to reach the same CAS. Only problem that on 1k feet the CAS and TAS are literally the same but on 30k feet the CAS and your thurst is much smaller. This is why happened 95% of air combat below 25k feet in RL since 1953.
These are one of the most basic things in aviation without this is impossible to fly well and AC or do air combat…
Check the performance envelope curves as well as the CAS-TAS relation.
https://info.publicintelligence.net/HAF-F16-Supplement.pdf
http://www.hochwarth.com/misc/AviationCalculator.html -
yes. i just didn’t know TAS existed. fighting at high altitudes seemed nigh-impossible when i’ve tried it, because turning is so sluggish and your fuel consumption (and thus, i assume raw thrust output) are so low. you bleed speed in even small turns like nothing. this is why i burn up to angels 30~ or whatever for BVR engagements but otherwise stay lowish. i like to be able to actually manage a decent turn if i have to. i’ll have to look at your stuff though, thanks for the info.
so is there a “optimal altitude” for cruising to mission then? if it’s true that CAS only really matters for maneuvers, and TAS is your “real” airspeed that determines how fast you are going overland, is there a specific altitude that allows you to cover lots of ground while still staying at the 30000~ fuel output of about 3000 (as opposed to angels 15 at like 10000~)
and i assume when you say “specific fuel consumption” you mean efficiency of engine output as in TAS attainable per unit of fuel consumption per second?
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There are many types of specific fuel consumption. Engine manufacturers for comparison give thrust/(weight of fueal*h) value which provide info about how much fuel is required to produce X thurst for one hour. Of couse this kind of SFC is depending on many variables.
This is the engine data of MiG-25. Yes, the SFC is decresing with incresing speed but this does not mean that total FC is smaller because thrust is also increasing with speed. Thrust x SFC = total fuel consumption
http://www.leteckemotory.cz/motory/r-15/R-15 was a very special engine here is AL-31.
http://www.leteckemotory.cz/motory/al-31/You can see how depend the thrust and SFC on alt.
There is no optimal altitude generally it depends what is your priorty. If you fly at high you can save lots of fuel but eng. range of heavy SAMs also increasing until a certain alt because it is worth to climb higher the missile to fly with smaller drag. If you fly lower you can reach faster the more dense air where the BVR missile looses very quickly energy and your manoverability is also increasing. The tyical combat cruising alt is the last 20-30 year was 15-25k feet except for TFR capable low level attackers.
During ODS after first week of campaign the med alt. flying was typcal because the heavy SAMs were mostly destroyed, the risk of facing with few survivors of SA-2/3/5/6/etc was smaller then facing the AAA/MANPAD/SHORAD which are pop up threast and can be anywhere, and in that time MAWS against IR missiles were not available.
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alright, thanks for the lecture molni. it was helpful. sorry if i’m asking too many questions, how do you toggle CAS/TAS/mach readouts? is the mach readout a seperate thing? i’m not sure if i’m stupid not to have seen it. is it somewhere in the MFDs?
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@Cik:
alright, thanks for the lecture molni. it was helpful. sorry if i’m asking too many questions, how do you toggle CAS/TAS/mach readouts? is the mach readout a seperate thing? i’m not sure if i’m stupid not to have seen it. is it somewhere in the MFDs?
For selecting CAS/TAS/GS; already answered a few post above here:
@Cik
the airspeed readout is selected on the right console (the HUD panel - TAS true air speed /CAS calibrated air speed /GND ground speed switch)
won’t make you faster though.Also check the BMS manual in de Docs folder on your hard drive. Page 53, section 1.2.5.3 HUD panel.
The mach number can be found on your center pedestal mach meter , see same manual page 39 section 1.2.3.9 Machmeter.
It can also be read on your HUD low left. See same manual page 98 section 1.5.1 HUD Settings -
@Cik:
alright, thanks for the lecture molni. it was helpful. sorry if i’m asking too many questions, how do you toggle CAS/TAS/mach readouts? is the mach readout a seperate thing? i’m not sure if i’m stupid not to have seen it. is it somewhere in the MFDs?
Ctrl+Shift+v as I can remember the three position swich in on the righ panel next to the joystick from left to radar alt swich. Mach number is always displayed on HUD except the dogfight override mode.
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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.