Future AFM to have IAS?

[EscCtrl]

I've been playing FSX recently with some addon aircraft that have supersonic capabilities, which has made me think recently. I have never played a flight simulator that has modeled IAS limits to the extent FSX has. I was wondering in future versions of Lockon with AFM (which has been mentioned) will overspeeding be modeled?

 

Yes it is annoying in FSX when you overspeed and the game stops and restarts (obviously don't program that bit :D)

 

In case I've worded this badly what I mean is that a plane may have an IAS (indicated airspeed limit) of say 600knots which is slower than mach 1 at sea level (or is for the sake of my case as I don't work in knots) this means if you wanted to fly mach 1 plus, you'd have to fly at a higher altitude with lower air density (less pressure on the aircraft) where the IAS would appear lower even though your actual speed is faster.

 

Whilst this might sound like an overly complex piece of programing that is only going to ruin your flying skills well tough because real pilots have to put up with it and this is after all a simulation.

 

For some background reading for which to structure you're discussion on click here http://www.aerospaceweb.org/question/instruments/q0251.shtml :P

[S77th-GOYA]

Vmax limit is already implemented in LOMAC. It's just that you only get a warning and no damage.

[EscCtrl]

Vmax limit is already implemented in LOMAC. It's just that you only get a warning and no damage.

 

You mean when you fly up real high then afterburn down to sea level and go so fast any inputs have no effect? That's not the same. The link explains well and if anyone has FSX they'll get a better idea.

[GGTharos]

Are you talking about compression?

Supersonic fighters are largely free of the problem compared to aircraft without an all-moving elevator, if I understand the problem correctly.

[EscCtrl]

Are you talking about compression?

Supersonic fighters are largely free of the problem compared to aircraft without an all-moving elevator, if I understand the problem correctly.

 

If by that you mean the ability to turn at speed then no. I'm talking about the fact that a supersonic plane can't always be supersonic e.g. it might be able to do it at altitude where the air is less dense so the aircraft can fly at such an actual speed it is supersonic without going over it's IAS limit. Not to be confused with the fact that sound travels slower at altitude anyway.

 

 

Look at this data for the blackbird for instance:

 

* Maximum IAS, below 7,500 feet: 460 KIAS

* Maximum subsonic airspeed (above 7,500 feet): 500 KEAS

* Maximum supersonic airspeed: 450 KEAS

 

We all no the blackbird can fly much faster than the 400-500knots quoted above in terms of 'actual distance traveled divided by time taken', but the aircraft can't attain this at a low altitude where the air is too dense.

 

IAS is measured using air density (I think in most systems it is the amount of airflow over a wire causing it to cool down and thus reduce resistance - which is measured, which is proportional to density) density is affected by altitude and airspeed (and it can increase close to mach speeds, an inconsistancy explained in that link in the first post)

 

 

 

 

It's hard to explain but if anyone knows what I'm on about would you mind lending a hand in wording this, or directing people to a good link?

[000BIGMAC000]

I think I know what you're trying to get at...I'm just having seconds thoughts about it. First of all the airpseeds used for the sr-71 are in KEAS. So, at say 25K ft 450 KEAS is not much more than mach 1.10

 

I don't think that the blackbird can't go supersonic at low altitude, so much as it doesn't at low altitude because it is extremely fuel inefficient to do so. There are probably other factors for the number ie: maneuvering speed; since the aircraft has almost dry tanks on takeoff and (i assume they don't refuel at 7500 MSL) without the extra weight of fuel the wing loading would be severely reduced...but since I've never flown the plane I can only make an educated guess...

 

Okay, I do however, know of what is called "mach tuck" or Mmo or Vmo (max mach operation speed). This is when an aircraft that CAN produce the thrust required to go faster at any given altitude is limited to a lower airpseed because of structural limitations. ie: The plane is only traveling at 0.85 mach but the air traveling over the wings is actually going .99 mach and the structural design speed of the wing is mach 1. So the aircraft is limited to an KIAS to comply with the design limits of the wing itself. This speed will change as alt. increases/decreases because of pressures associated with different altitudes.

 

Not sure if that is what you are thinking of...hope it helps.

[zaelu]

EscCtrl, you should try IL-2. Try going above 400Mph in a P38 in a shallow dive under 1000m alt (you will se what compression means) or try flying BI-1 above 700KM/h level at 1000m (you will se some flaw in the design perhaps while heading into the ground... fast) or fly a Go-229 at 700+KM/h and try a overG break turn (your wing(s) will fell off) etc etc.

 

One of the best stories was when my squadmate TakeOff was chasing with a BF-109 a Mig-3 in winter Moskova map, near Viazma and apparently in panic the enemy plane started a dive... TakeOff followed him and as the speed was building so was the MiG in the crosshairs and when he was thinking... "almost there" the MiG started to desintegrate in the air, and he said: "What the hell? I didn't started to fire..." :megalol:

[EscCtrl]

By the way what is the difference between KIAS and KEAS?

 

Al lot of this stuff is new to me and I might be all wrong.

 

 

This is from the flight manual of the blackbird (not sure if this is copyright because I got it somewhere that didn't quite say ;) so I'll remove it if the mods so wish)

 

This graph shows the maximum possible mach at a given altitude due to air density. Note there is an artificial restriction to ensure longevity of the airframe and a maximum limit i.e. what the plane actually cannot exceed.

 

 

N.B. The plane can NOT exceed (or even go near to) mach 1 below 15kft

This is different from what you said about it doing mach 1+ at any altitude (000BIGMAC000)

 

 

As for the mach tuck you mentioned I'll have to read into that as it does not sound too familiar. Is that anything to do with the complications of transonic flight where different parts of the aircraft are receiving subsonic or supersonic airflow whilst the collect aircraft is flying near mach 1.0?

[S77th-GOYA]

We all no the blackbird can fly much faster than the 400-500knots quoted above in terms of 'actual distance traveled divided by time taken', but the aircraft can't attain this at a low altitude where the air is too dense.

 

The SR-71 CAN attain that speed at lower altitudes, but it is beyond the structural safety limits of the aircraft. That is already modelled in LOMAC. See my first post. Instead of your canopy melting or parts ripping off, we just get an overspeed warning with no penalty for going beyond structural limits.

[EscCtrl]

The SR-71 CAN attain that speed at lower altitudes, but it is beyond the structural safety limits of the aircraft. That is already modelled in LOMAC. See my first post. Instead of your canopy melting or parts ripping off, we just get an overspeed warning with no penalty for going beyond structural limits.

 

Maybe I was wrong then, it's the fact that, that takes forever to kick in though and it happens at a ridiculous speed. From the statistics of aircraft I've been looking at it suggests they would overspeed far sooner at low altitude though. Also I don't think altitude has any impact in the game, correct me if I'm wrong?

 

 

I'm having trouble finding flight envelope data for the aircraft in the game so it's hard to compare data for the blackbird and try and educatedly guess how the LOMAC aircraft should react. I have a flight manual for the fulcrum to but it's in Russian.

[EscCtrl]

Ok this is from the Russian fulcrum manual. Notice how the aircraft will overspeed sooner at lower altitudes. This is not modelled in the game as I know you have to be doing about 1500/1600kmh in the game to overspeed regardless of altitude. This suggests it will happen at 700kmh at sea level.

 

I can't speak Russian but I'm guessing that's what the graph shows.

 

[GGTharos]

This appears to be showing alpha performance limitations ... that the MiG-29 would overspeed over 700kph is silly, given that the speed of sound at SL is some 1240kph or so.

[EscCtrl]

This appears to be showing alpha performance limitations ... that the MiG-29 would overspeed over 700kph is silly, given that the speed of sound at SL is some 1240kph or so.

 

I see what you're saying and that's what I thought too but it can overspeed at much lower. At higher altitude a faster speed gives a lower IAS reading as the pressure is lower - so a plane that overspeeds at say 700kmh sea level will overspeed at say 1400kmh altitude i.e. above mach 1 (yet the IAS will read 700kmh and the plane will feel the same overspeeding pressure as 700kmh sea level). Hope that makes sense.

 

Well I really don't have that much knowledge of this so will stop digging up apparently inane evidence and do more reading, hope someone who does knows for sure can settle this in the mean time.

[000BIGMAC000]

Is that sr-71 performance chart from sr-71.org ???

[Force_Feedback]

It's about angle of attack limitations by the flight control system. Straight line: 5G 16 degrees angle of attack. Interrupted line: Max. load factor (G) and max. angle of attack.

This has nothing to do with overspeeding, just the control limitations at different speeds.

[S77th-GOYA]

I'm having trouble finding flight envelope data for the aircraft in the game...

 

http://www.ecf.utoronto.ca/~pavacic/lomac/scan0184.JPG

 

Thank SwingKid for the chart. This is for the F-15. Note the configuration of the test aircraft. The "PLACARD" line is what you want.

[000BIGMAC000]

Looks like it is from sr-71.org I find it interesting that the performance envelope is so narrow...well, cheers to Kelly Johnson's team anyway!

[EscCtrl]

Looks like it is from sr-71.org I find it interesting that the performance envelope is so narrow...well, cheers to Kelly Johnson's team anyway!

 

Yeah it is the same data they have. Yeah that's one of the surprising flight characteristics of the aircraft - that it can go so fast yet has very narrow IAS range.

 

 

Thanks for providing the information, but now I'll admit I am confused so I'll keep quiet for awhile :P

 

(and I won't use manuals written in other languages as examples ever again)

[GGTharos]

Don't be discouraged. :)

[192nd_Erdem]

Modern fighter doesn't suffer from the compression much, as GGTharos said. They've got around it with fully moving elevators so I don't think there's much of a problem :)

[EscCtrl]

So how then, do they achieve a maximum speed that isn't so badly affected by the differing pressure at various altitudes? If I read that graph correct for the blackbird than that shows that the SR-71 has a pretty difficult time trying to go as fast as it likes at low speeds and the blackbird is as old as say a tomcat?

 

Or was it that the blackbird was always designed with high speed at high altitude so was not built as strong as a fighter?

 

Thanks, hopefully no one else is as confused as I am then.

[GGTharos]

The BlackBird has very different design parameters than your average interceptor. Keep in mind, this thing's job is to cruise around at M3.2, your average interceptor will only do supersonic *sprints*, but in exchange it has a very wide operating envelope.

[EscCtrl]

The BlackBird has very different design parameters than your average interceptor. Keep in mind, this thing's job is to cruise around at M3.2, your average interceptor will only do supersonic *sprints*, but in exchange it has a very wide operating envelope.

 

Starting to make sense now thanks.

 

Was trying out a hornet addon on FSX (yeah I know these addons, and even FSX aren't that realistic but it's a good comparison between very different aircraft on the same physics engine) and it's definitely better seeing as the game is less likely to restart due to not looking at my g-load readout during a turn and exceeding a limit.

[GGTharos]

In a hornet you should be automatically limited from breaking it anyway ... :D