AI actual cruise speed and cruise speed given in config file

I downloaded and installed today a Boeing 777-300 plus the Emirates texture that interested me for AI at a new scenery project. I noted the details for inclusion in the ai and found to my surprise that the cruise speed was given as 330 knots, which was so far below my expectations that I checked it out. The actual real life cruise speed is specified as 562 mph. This plane was loaded onto flight sim in 2005, which is why I haven't questioned the poster, but does anyone else know why this should be so? I presume an ai plane does fly at the cruise speed given? Is there any reason why is shouldn't be corrected to 488 knots (the equivalent of 562 mph)? Tom where are you?

AI planes fly at the speed given in the flightplan, regardless of any aircraft.cfg [Reference Speeds] entries - which are in KTAS and that varies with altitude of course, assuming that this is where you saw the 330 knots figure. These figures are for reference only however, they have no bearing on how fast the plane will actually fly at all, and AI aircraft cruise speed is controlled directly by the AI flightplan.

I don't know for sure, but I'm guessing that the value given is IAS. 330 kt is a very reasonable cruise speed in Indicated Air Speed (what the gauge displays, not the same thing as True Air Speed or Ground Speed).

 

Nadlzfw

Yes, as Tiger1962 says Reference Speeds don't have any bearing on how an aircraft flies. They are KIAS at MLW.

 

However, other related software might use them, for instance the PF3 ATC system add-on uses the "flaps up stall speed" as a basis of the speed it asks you to reduce to when on approach.

 

John

Hi,

 

It appears there is some confusion about these things, let me put in my 2 cents.

 

First, there are two lines in the Reference Speeds section:

 

cruise_speed=477

max_indicated_speed=340.000000

 

The first is True airspeed, and the second is obviously indicated.

 

That said, the cruise_speed value in the Reference Speeds section appears to have little to do with cruise performance of AI aircraft, as far as I can tell. The cruise_speed value instead appears to be used by the flight planner to determine flight times, etc.

 

Next, the Speed values in the Aircraft.txt file of Traffic (flightplan) files are used by the flightplan compiler to determine the predicted speed of the plane during its flight which allows the compiler to predict which sector it will be in to create a sector map (i.e. FS scans these sector maps to determine which AI aircraft it should place into that sector when you load at an airport). They have no effect on the actual cruise speed of the AI aircraft.

 

The relative thrust and drag values in the aircraft.cfg file (modified by the drag scalars in any Flight Tuning section and things like wing_area, etc.) mostly determine the cruise speed of the AI aircraft. I have not checked if the max_indicated_airspeed value does provide a speed limit for AI aircraft, it might.

 

One other line in the Reference Speeds section:

 

flaps_up_stall_speed=142.0

 

does have an effect - the AI aircraft try to rotate at around this speed on takeoff. Whether they actually lift off depends on things like wing_area, etc.

 

Hope this helps,

Tom, Traffic Tool (yes, I still use that old programme, so I can see all the info written out!) only asks for three inputs, the number you give the aircraft, the "name" of the aircraft so it cen be found in FS9, and the cruise speed, so I just upped it to 450 which is close to that of a 737 etc. I think maybe the original designer made a small error when he made cruise speed and max indicated speed the same 330. Anyway, it works.

The first is True airspeed, and the second is obviously indicated.

That intrigues me, because a DC-7 aircraft.cfg by "FSAviator", I presume, that I got from your web site specifically states it as being KIAS:

[Reference Speeds] ;all KIAS and MLW - Pitot error not known so IAS set=CAS

 

But as it is only a reference speed, you could probably put anything you like in without any effect.

 

John

I never knew the flaps_up_stall_speed= affected the rotate, I always thought it was default_vertical_speed=

I have had aircraft almost lift off like a helicopter when I wanted them to fly out nice and steady, also the cruise_lift_scaler affected the rotate as well.

 

Surprising what you learn on some of these threads.

Hi,

 

Yes I know that FSAviator thinks that, but how could the cruise speed be indicated and 477 kts when the max_indicated speed is 340 kts? Doesn't make sense.

Yes I know that FSAviator thinks that, but how could the cruise speed be indicated and 477 kts when the max_indicated speed is 340 kts? Doesn't make sense.

I won't argue at all, Tom - but I had been led to believe FSA's knowledge was beyond criticism.

 

Best regards,

 

John

Hi,

 

No one's perfect. :)