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LAdamson

Flight characteristics of faster jets.

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Hi.I have been playing around with a few military jets in FSX and i havent been able to reach top speed in them at all. I do a quick climb up to the service ceiling and engage the afterburner but i rarely get up to the speed it is supposed to go (maby just 700-900 KIAS in a mach 2 aircraft).Lately i tried the SR-71 (Alpha) which climbs and accellerate ok for a while, but at one point it claims "overspeed" (around 800 KIAS) and as the speed go higher the viewpoint is "thrown forward" as if you would hit the airbreak and your speed and altitude drops.When this happens the "overspeed" indicator doesnt to away and sticks till i drop down to 300 KIAS, if i go even lower i get a stall warning and the plane drops, so it cannot be near the overspeed limit on the plane.Anyone else seen this? I have seen this in more than one jet and i dont think all airplanes are bugged. I have also tried to make my own aircraft with insane values, as well as try to modify the airplanes but it still wont work.Thanks in advance.

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Indicated Air Speed is unreliable above about 28,000ft. IAS declines with altitude. Use mach meter only. Fly below the aircraft service ceiling as that is above its optimal altitude.Sounds like what you are encountering is some excellent realism.Allcott

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I would use the mach meter, unfortunately it isnt working in the planes i use (Freeware SR-71 and F16).Apart from that, i know that IAS will slow down (guess it is indicated by airflow/pressure that drop) as you go higher. However, if now the real speed is 1000's of knots, why do i still get a stall warning?Another question: How high is the SR-71 supposed to go? I have flown it at 200K feet (maby needs adjustments), feel like i'll bump into ISS soon.

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I believe that FSX doesn't deal with the data of the faster jets like it should be. I believe that these are no really designed for FSX either.I did have the same problem when i tried implementing a F1 car into a racing sim called GTR which uses sportscars. The revs on these cars go up to 7.000 rpm. The ones on F1 cars go up to 19.000 rpm and more. On the rev graphac, the F1 rev graphic went through the roof. Another side effect was that i could not reach 19.000 rpm as if there was a rev limiter used which was set to around 8.000 rpm. It simply wasn't possible to rev the F1 car up to 19.000 rpm because the program (GTR) didn't respond well to this "weird" data.I guess a bit of the same thing happens in FSX...?

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Yeah, you've stumbled onto something I've fought with for years with FS, the jet engine modeling and high speed drag issues. FSX doesn't make any improvements over FS9 in this area, but neither is it any worse.Basically designers have to tune the flight dynamics for low or high altitude flight, and modify the engine output and drag accordingly. If you set up the mach drag table for perfect high altitude high mach flight, you essentially end up making your plane capable of those mach numbers or true airspeed at low altitude at the same time, resulting in something that feels far too overpowered or aerodynamically efficient. Set it up for low level flight and you deprive it of its true high altitude chops.It doesn't handle induced or parasite drag at high speeds very well. Try pushing an F-18 faster than mach 1.2 at sea level in real life. It's a no go, the thrust can't overcome the exponentially higher drag from that dense air. It can however top mach 1.5 easily at FL360 or higher, despite the falloff in engine performance.In reality, a plane stalls at the same indicated airspeed (the value that really matters to airfoils) regardless of altitude, and it hits "the wall" at the end of its flight envelope at the same indicated speed, again regardless of altitude. If Vne is 800 knots indicated, its the same whether it's at sea level or the edge of the atmosphere. FS interprets drag based more on true airspeed though it seems. A few designers have managed to find a good balance though, Pilots' SR71 and Alphasim's Eurofighter come to mind.Part of the problem you may be having is that around FL550, stall speed and Vne for the average high performance jet start to converge. The concorde for example operated in a very narrow speed window during climbs and descents.Also, when modifying thrust values, you basically have to knock 1/3 off any real world value to get the proper amount in FS. The sim interprets 20000 lbs of thrust as more like 35000. Sort of explains the default A321's 6000 fpm climbs. ;)Another area that can be helpful for tweaking is the inlet diameter, but make small changes only or you end up with some pretty odd results. When tuning drag curves I suggest saving a flight where the aircraft in question has minimal fuel, or preferably 0% with "unlimited fuel" turned on, to guarantee you are indeed seeing the maximum attainable speeds at lowest possible weight.And don't even get me started on FS's idea of what the average afterburner adds to performance. You're far better off modifying your throttle output curve in FSUIPC than using Shift-F4. FS seems to think AB = Saturn V rocket. It's the first thing I disable on every jet, not to mention that the majority of aircraft designers seem to think an AB always shoots a 30 foot long flame (Iris excluded). That particular effect only occurs under very specific pressure, temperature, and humidity, and only in stage 5 burner which isn't used all that often outside of a dogfight. The Habu is pretty much the only plane out there that can guarantee such a display. :)All that said, I still prefer it to X-Plane's flight models in the "feel" department. Austin's interpretation is no doubt much more realistic and he deserves mad props for the effort, but it just couldn't ever really sway me for some reason. Guess it was too good and I like tinkering too much. Hehe.Cheers.

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>All that said, I still prefer it to X-Plane's flight models in>the "feel" department. Austin's interpretation is no doubt>much more realistic and he deserves mad props for the effort,Glad this is an FSX forum! :-hah Personally, I think that FSX excells in the "feel of flight" department, more than any sim to date! That along with higher resolution textures is what keeps my interest so high with FSX. L.Adamson --- FSX, FS9, X-Plane 8.50 with global scenery (as well as prior versions, and many demo versions before that)edit: I slightly mis-read, and my mind left the "it to" out. First interpretation was: I still prefer X-Plane flight models in the "feel" department. But I see it isn't so! :)

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