All .air file experts - absolute speed limit problem????

[Guest xoio]

Hi there, I'm working on a Trans-Hypersonic Passenger Aircraft. It is based on the Concorde .air file loosely, However, my aircraft accelerates nicely to well over Mach 4 @ 75k - 80k feet, in fact with the winds in favour, I have 'once' seen her hit Mach 5.03 !!!!! superb! (she can reach London UK to New Zealand in UNDER 5 hrs!!!) The engines are nicely tuned, so there is never any over speeding. & the aircraft is lovely & stable at ALL speeds. The problem is ....I seem to hit a 'wall' when my 'GROUND SPEED' reaches 2666kts.(Sometimes a few kts over, but never under.) - Irrespective of what my Mach & Airspeed are...(even when I reached 5.03, the groundspeed was below 2666, thus making the Mach 5+ possible) The airspeed & Mach all fluctuate according to the wind (as you would expect).... but the aircraft seems to suddenly stop accelerating when I reach the above ground speed. Have I discovered a physically programmed speed limit, actually set in stone by the sim? Or am I experiencing a virtual 'wall' set by some parameters in the .air file? If this is so, does anyone know what params to 'tweak' to overcome the problem? (I use 'AirEd' as my air file editor). In the past I'm POSITIVE I've seen aircraft whiz up well past this ground speed, (Mach 7+ - before the fuel quickly ran out :-) ), when messing with engine thrust & drag etc - so it must be possible?.... (Wish I could remember what .air file it was.) Can anyone help? (I've posted this message in the MS 'general' forum as well, to get a wider audience / response.) Kind regards. Al

[Guest xoio]

P.S. I'm trying to achieve a 'groundspeed' of 3128kts (3600mph - 1 mile per sec) or greater.Al

[Guest Ron Freimuth]

I didn't think one could get past Mach 3.2. That's the limit of the 'Mach Tables' in the AIR file. Very likely an MSFS limitation. I don't know about FS9, but previous versions also went crazy above 100,000 ft. Though, I managed to slew to over 200,000 ft once. Also, above FL 600, I don't think the Atmosphere is modeled realistically. FS has a good ISA Standard Atmosphere, but above 60,000 ft (maybe higher) the real temperature starts increasing. That would incrase TAS for a given Mach Number. Ron

[Guest xoio]

Hi,Getting past Mach 3 & 4 is easy...... even Mach 5 has been possible, but it's wierd, a 'wall' is definately reached when a certain groundspeed is reached. (The Mach number & airspeed don't seem to be the problem, (Unless there is a Mach graph that needs altering in the .air file.)I want to achieve a ground speed of at LEAST 3600mph (3128kts) = 1 mile per second.As mentioned already I HAVE seen aircraft blast past this in the past, when messing around with cfg files etc. Now all i want to do is do that again, but controlled & properly.Laz

[MD83 1]

Mach 3.2 is still pretty quick (!) .... :) The aircraft's surface temp will be over 400 degrees Celsius @ Mach 3.2, according to FS temp gauges! :(

[Guest xoio]

I know this :-)At Mach 4.3, the boundary layer temp is over 800 deg C, But i have cryogenic fuel storage *wink*I still want to find out what is stopping the place accelerate beyond 2666kts groundspeed.

[Guest Tom Goodrick]

I will repeat a little of what I said above in your other thread on this topic. Groundspeed means absolutely nothing regarding Mach number. It is only the ratio of your true airspeed to the local speed of sound. The local speed of sound in knots can be calculated from the equation Va = 29.07 * SQRT(459.4+F) where F is the temp in Fahrenheit. As was mentioned above, I doubt very much if FS9 includes a valid atmosphere above 65,000 ft.I designed and evaluated hypersonic vehicles for NASA for several years. At Mach 4 and above, all the ordinary aerodynamics are inapplicable. Air does not flow, it impacts. Airfoils are completely ineffective. Sharp edges on wings and control surfaces get so hot - if they are of normal dimensions - that keeping them from melting is very difficult. Static trim normally goes to about 40 degrees - if, indeed, the vehicle has a static trim. The center of pressure moves so much special means must be incorporated in the design to handle it.It is very unlikely that FS9 can handle these things. I would accept the limit of Mach 3 and stay below 70,000 ft. That transoceanic hypersonic vehicle is intended to go to several hundred thousand feet (at least 300,000 ft). Its flight mechanics are almost the same as a re-entry body's. There are so many control and heat problems with that craft it will not be built until someone invents Miracaluminum, mainly for use in the engines. Then they must learn to make the stuff very cheaply so people can afford to buy tickets.

[Guest xoio]

Tom,I Thankyou for the feedback, :-)However, not to worry, even though I haven't personally worked in the field of aeronautics, I do understand what you are talking about.:-D, Most definately my aircraft is a flight of unrealistic fancy, however my goal here is merely to see if it is possible to push an aircraft in FS2002/4 past the speeds I've mentioned.As i've described, i seem to have hit a 'wall', which is a groundspeed of 2666kts (with a True Airspeed being similar)Depending on the airspeed & direction modelled in ActiveSky @ 75000ft , my Mach is anywhere between M3.95 & M4.8, only once did i achieve M5.03. (This was with a headwind of 220kts.) My IAS in relation to the Mach varies from 550 - 700kts IAS at this altitude.So I fully understand the relation between airspeed & Mach, however it is always the case, ... My craft accelerates nicely until it shows a groundspeed of 2666kts, then stops going any faster!!....All i'm trying to do is discover why :-) & go beyond it. As already said, this is a flight of fancy & a pure bit of fun.Once finished i'll post the aircraft up so that other people can enjoy zipping from London To New Zealand, or wherever, in under 5 hrs. However i want to break the 1 mile per sec velocity, purely for the hell of it.I hope this makes my fun standpoint clear.RegardsAl

[Guest Ron Freimuth]

>I know this :-)>At Mach 4.3, the boundary layer temp is over 800 deg C, >But i have cryogenic fuel storage *wink*>>I still want to find out what is stopping the place accelerate>beyond 2666kts groundspeed. Possibly some integer operation in sim1.sim overflows, or otherwise gets messed up. Get AFSD if you don't have it and check what it displays for thrust and drags. AFSD reads several tables in the AIR file, but also calculates part of the drag and lift from basic physics. So, it will probably show a phoney drag increase at the maximum speed. AFSD might have a problem past Mach 3.2 since it reads 'Mach Drag' from the AIR file and may not know what to do if M > 3.2. We know the newer, float8 tables are extrapolated past the end values at the last value, but I don't think we have run past the ends of the older, integer tables. Extend TBL 401 to Mach 5 or higher. You can edit the higher 'x' entries with Aired to give a smooth curve up to (Mach) 5.0. Just hit 'x' when TBL 401 is up and an edit field for x will appear. However, I doubt this will help; I just mentioned that such tables appear to give the last value when past the last entries. I do know 'variable intake area' needs to be used or Ram Intake Pressure will get very high at high Mach numbers. Fuel Flow and thrust increase greatly, and one can't even trottle back the turbines. I think they have turned into RamJets. "Yeager's Flight Trainer" had an X-15, I could get it to a high altitude and speed by refueling in flight. Eventually it would display 'divide by zero error' and screen dumped back to DOS. At least before FS9, if one managed to get above 100,000 ft the display went screwy. You could make even an orbital vehicle work in X-Plane or Orbiter. Ron

[hervesors 1]

AFSD will not have a problem past Mach 3.2, since it could simply not read any higher value. Mach value is retrieved from FSUIPC offset at &H11C6 (unsigned int16) and converted to Mach by dividing it by 20480..therefore the max Mach value FSUIPC can report is 65535/20480..precisely Mach 3.2..No chance AFSD can be an investigating tool for higher M..I'm not aware of any FLOAT64 mach value FSUIPC will have mapped et this time..May be designers who directly use TOKEN variables can say if values greater than 3.2 are possibleAs regard integer air file tables, AFSD will assign either the first or last table value to any outside range X, but clearly this could not occur for Mach tables since most are formatted with 3.2 as the last valueHerv

[badderjet 181]

>I designed and evaluated hypersonic vehicles for NASA for>several years. At Mach 4 and above, all the ordinary>aerodynamics are inapplicable. Air does not flow, it impacts.>Airfoils are completely ineffective.Very interesting! :-)But what do you mean the air does not 'flow' any more? And why are the airfoils 100% ineffective?Sorry, I am no physics pro. :-)Thanks,Etienne :-wave