Why Do FS9 Jets Fly Under Their Rated Speeds

[flyhigh]

I am a fan of flying commercial jets in FS9, but I have noticed that for the most part the speeds attained by FS9 jets fall way short of their performance limits. For example, an SST has a maximum operating cruising speed of 1350, mph but the FS9 SST will overstress at 450 mph. A Boeing 747-300 has a Max speed (with CF6-80s) of 996km/h. Is there a conversion factor I don't know about. Why am I in such an overspeed situation at such low speed thresholds?

Flyhigh :(

[wdscobie]

flyhigh:

when flying (with some exceptions) aircraft worry only about indicated airspeed -

http://www.aerospaceweb.org/question...ts/q0210.shtml <<--this is the better resouce than below; be sure to follow the 'related topics' link "What is the difference between airspeed, true airspeed..."

http://en.wikipedia.org/wiki/Indicated_airspeed

you need to confirm you have FS set to show indicated airspeed.


groundspeed is also increased/decreased by the direction of the wind (jetstream). in USA aircraft heading east fly routes 'faster' than aircraft going west --- usually because the jetstream is going west to east giving the planes some extra knots of 'free' groundspeed. (this can be 100+ knots at times during the winter resulting in aircraft flying KLAX to KJFK, for example, arriving almost an hour early on the east coast). at the same time aircraft heading west may need to stop enroute for refueling as they are 'slowed' by 100+ headwinds.

if you have been flying smaller prop aircraft in FS, like the cessna, the difference between groundspeed and airspeed are less (in no wind situations) as the pressure difference at a cessna's cruise altitude (5000' or so) is much less than a transport jet at 40000'.

--
edit: additional information
--

[flyhigh]

Thanks D.
That's very helpful and useful, but it doesn't answer why the FS9 jets "overstress" at lower than the real standard cruise speeds that commercial jets typically fly.

Is there a way to increase the speed limits in the aircraft.config so that they reflect the rated parameters of real commercial jets (the military jets seem to do just fine with this). Can I do this without the jet being overstressed where the flight simply stops do to an "overspeed" situation?

Flyhigh

[tgibson]

Hi,

From the web I find that the normal operating speed of a 747-200 is 375 KIAS (knots IAS). The Vne (never exceed speed) is 445 KIAS. Your 996 km/h converts to 537 KIAS. Perhaps the -400 has a higher Vne, I don't know.

You can change the overstress speed by changing either of two lines in the Reference Speeds section of the plane's aircraft.cfg file.

max_indicated_speed=251.000000

and/or

max_mach=0.48

Whichever speed is lower at a given altitude will prevail.

Hope this helps,

[wdscobie]

flyhigh:

you need to confirm you have FS set to show indicated airspeed.

follow this link see a picture of a jetliner at 37000' cruise -

http://www.airliners.net/open.file/0961677/L/

IAS of just of 250kts = M0.78 = groundspeed of over 480kts


here is another link -

http://www.airliners.net/open.file/0437763/L/

at 35000' an IAS 265kts = M0.78 = groundspeed of 501kts and actual airspeed of 458kts.

--

[Kimber]

Max speed can only be obtained above 30,000'!!

[wdscobie]

kimber brings up an important point ... make sure you are conducting an appropriate climb. the following is 'OK' for most jets -

*set engines 92% N1 (will need to make small adjustments during climb)
*hold 250 kts by controlling aircraft pitch to transition altitude (differs by country and airport - USA 10000')
*decrease pitch 'a bit' and accelerate to 290 kts
*increase pitch and adjust as necessary to hold 290 kts until aircraft is a mach 0.74
*adjust pitch to hold M0.74 till cruise altitude reached between 30000' and 39000'.
*now increase mach to cruise setting - now this is different for each aircraft: 727 and 737 classic M.074; for 737NG, A32x, DC9, MD80, and 717 M0.78; 757, 767 about M0.80; for A33x, A34x, 747 and 777 someplace between M0.80 and M0.84.

if you choose cruise altitude below 30000' you will likely be flying at lower than 300kts IAS.

again, these are GENERAL numbers. do some research on the www for specifics for each aircraft type.

--
edit: add below 30000' cuise comment
--

[burner]

There is a reason for the redline on the n1/n2 gauges, use it, no reason to lolygag around at 92% climb power.

[skylab]

>Max speed can only be obtained above 30,000'!!


That's not true in all (real world)aircraft. The highest true airspeed in a stretch 8, for instance, is attained at around FL260. Been there, done that.

[flyhigh]

D.

How do I you need to "confirm you have FS set to show indicated airspeed"?

Flyhigh