Cruise speed in aircraft.txt

[Guest]

Should the cruise speed in aircraft.txt be in mph or knots?What is the formula for converting from one to the other?Thanks

[Guest Stamatis]

It should be in knots and you should enter the cruise TAS (True Air Speed), not the IAS (Indicated Air Speed).Conversion:1 sm = 0.86897 nm1 nm = 1.15078 smStamatis

[Guest]

Stamatis,for AI aircrafts this is not really correct. The AI aircraft will set the speed at the A/T according to the cruise speed entry in the aircraft.cfg.This means that the AI aircraft will try to cruise at 440 knots IAS if the cruising speed is set to 440 TAS. Of course 440 KIAS at FL 330 would result in a super sonic flight if the aircraft would have enough power.But this also means that the aircraft will fly at full power at all time (trying to reach the set speed).If you set the cruising speed to let's say 260 knots, then the AI aircraft will cruise at 260 KIAS at FL330 which results in a more realistic speed. (But on a lower FL it would be rather slow)To me it's a bug from FS2002.Or I'm getting something completely wrong ;-)Cheers!Frank

[Guest]

>Stamatis, >>for AI aircrafts this is not really correct. The AI aircraft >will set the speed at the A/T according to the cruise speed >entry in the aircraft.cfg. From every report I've read, along with my own testing, the only purpose for the entry to begin with is to calculate the amount of time the flight will take. FS uses the info in the .air file during the actual flight in its internal calculations.

[Guest]

I think this is very important! To calculate the right arrival times (and cell positions during flight), the cruise speed entry in aircraft.txt needs to correspond with the speed that FS2k2 actually *flies* the AI aircraft.But setting the cruise_speed in the (Reference Speeds) section of the aircraft.cfg doesn't change anything. Only static_thrust and/or drag scalars will let the aircraft fly slower or faster.Amazingly, FS2k2 never updates (when commented out) the cruise_speed when I make changes to the *.air file, but it does with the stall speeds when changing lift coefficients. This is off topic now, but does anyone know from which section of the air file FS does calculate the cruise speed???ckfly

[Guest]

ckfly,please do test that. I'm pretty sure that I am right.Set the cruising_speed entry in the aircraft.cfg (NOT the aircraft.txt of TTools) of a particular aircraft to an extreme value, say 200 knots or less.Then fire up FS2002 and watch that particular aircraft during cruise (I usually use AIMAP). You'll notice that it flies the aircraft slower than before!I say it'll cruise at 200 KIAS (and not as the entry comment suggests at 200 KTAS).Although I'm pretty sure about it I'll also try again.Clear Skies!Frank

[Guest Stamatis]

Frank,You are mixing up and confusing two different things:1) The speed an AI aircraft actually flies at.2) The cruise speed used by the SDK or Ttools to calculate the ETA of the aircraftfor 1) above, the speed used depends on the thrust/drag/weight relationship in the air file and aircraft.cfg file. Btw, it is not the Cruise Speed entry in the aircraft.cfg file. I have tested that myself.For 2) above, the speed used for the calculation is the cruise speed entry in the aircraft.txt file (or aircraft.dat file for the SDK)I hope the above clarifies this very often misundesrsood topic.Of the two speeds above, the most relevant is 2). Why? Because an AI aircraft never flies the entire leg, unless you are constantly within 80 nm of it all the time, rarely the case unless you are specifically following that flight.Outside of the 80 nm radius around you nothing flies as far as AI traffic is concerned. Nothing! No flight whatsoever. Thus, when the program constantly calculates which aircraft should appear at which location within this 80 nm radius, it uses the cruise speed specified in 2) above, not the actual cruise speed of the flight model.Stamatis

[Guest Stamatis]

"To calculate the right arrival times (and cell positions during flight), the cruise speed entry in aircraft.txt needs to correspond with the speed that FS2k2 actually *flies* the AI aircraft."No, it is not so. I have explained why in message no.6 of this thread.Stamatis

[Guest]

I hope we will come to a final conclusion that will enable us to set the speed in both entries to a *as-real-as-it-gets* value. :)Frank, you are right. The cruise_speed (TAS) setting in aircraft.cfg is used by the AI code as some kind of speed guidance. In AI Tactical Display you can see this clearly. AI tries to reach the given speed - by using the throttle (and thus using the aircraft characteristics as defined in the air file). But it will be used as *desired IAS*! Yes, this is a bug which causes the AI aircraft flying way too fast.Stamatis, you are right, too. The speed entry in TTool's aircraft.txt is used by the compiler to calculate the time and position the aircraft materializes in the cell your aircraft currently is situated. It's not *flown* outside the 80 nm zone. But once it's there, it will give full throttle.So, my suggestion is - to set the TTools speed in aircraft.txt to the real cruise speed in KTAS.- to reduce the (confusing) speed entry in aircraft.cfg to an AI guiding value (IAS) typical at jet altitudes, that will produce the same cruise speed. That's what I wanted to express with '...needs to correspond...'.ckfly

[Guest]

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[Guest Stamatis]

"ckfly","The cruise_speed (TAS) setting in aircraft.cfg is used by the AI code as some kind of speed guidance."My experience sofar does not agree with the above.All I can say is that when I changed that entry in the aircraft.cfg file for the default B737-400 and B747-400, I noticed absolutely no chnage in the cruise speed of my AI Traffic B737's and B747s.Only when I changed the egine power output and/or the drag did I observe significant changes in AI Traffic aircraft cruise speeds.I do not doubt for even one minute that what you write is what you observe, but I am very intrigued as to why we have so differing observations...I guess AI Traffic will remain "mysterious" for quite some time :-)Stamatis

[Guest]

Hi all,as promised I tried it one more time and here's the result:The picture shows two times the AIMap screen of the same situation, same location, same time, same flights etc. etc. except for one difference:In the left picture the cruise_speed was set to 440 in the airaft.cfg of the default B737-400, on the right picture it was set to only 200 knots.The result is obvious: On the left side of the picture the speed set on the A/T of the AI aircraft FL220 reads 372 knots. This results in a TAS of 542 knots - way too much.On the right side of the picture the speed set on the A/T of the AI aircraft FL220 reads 198 knots. This results in a TAS of 295 knots - too slow.So it is obvious that the 'artifical' pilot sets the A/T SPD to the value set in the aicraft.cfg. The pilot will do this at every FL. Of course the same IAS will result in a higher TAS the higher the aircraft flies. That means it is impossible to set the cruise speed in means of TAS.But it is possible to set it to a value, so that a B737 would not cruise at over 500 KTAS at 'normal' flight levels.Of course you can achieve the same by reducing the power of the aircraft, but then you might encounter too long t/o rolls for smaller air fields.One question might still arise: Why is the speed on the left side not 440 knots as it was set in the aircraft.cfg? Well, simply because the aircraft is not strong enough to do so. Here the aerodynamics and the engine thrust limit the cruise speed.Hope I could make myself understood ;-)Clear Skies!Frank

[Guest]

Stamatis, >My experience sofar does not agree with the above. A few hours ago, this was my opinion, too! :) See my first message in this thread.>I do not doubt for even one minute that what you write is >what you observe, but I am very intrigued as to why we have >so differing observations... OK, take a look at the attached picture from AI Tactical Display.I would even say that you can compare the cruise_speed in aircraft.cfg with some kind of "AI autopilot" speed setting. It's the same as when you set your autopilot when flying a non-AI plane. 'Des IAS' will even be set to 250 IAS when under 10.000 feet, and to 165 IAS when on final approach.Please, can anyone confirm this!ckfly

[Guest]

Frank,you were a few minutes faster than me. :) But it looks as we would agree. Thanks for posting your discovery!I'm going to change all cruise_speed settings on all AI aircraft to a more reasonable value. And reducing the static_thrust (as found by Stamatis), too.Great, I really like this kind of forum discussion! :)ckfly

[Guest Stamatis]

Very interesting observations.The only difference I can think of between my method of checking on cruise speed and your/Frank's is that I am using Peter Dowson's TrafficLook.exe, the utility which is included in FSUIPC and not AIMap.Can our difference in reaching the same conclusion be due to differences in displaying the correct AI Traffic aircraft cruise speeds between the two programs? I wonder.Can someone who has both check whether both programs display the same AI Traffic airspeed?Stamatis