[CloCloZ]

Hope this is the right sub-forum to ask that, my question is of general kind but is applicable to MODS development too.

These days I am performing some speed tests on IL-2 planes, using the Devicelink-based "Autopilot" utility by LesniHU (http://lesnihu.wz.cz/autopilot/autopilot.html), on Crimea map.
Since Autopilot returns just IAS speed and not TAS (AFAIK Devicelink doesn't export TAS speed), I have to convert IAS to TAS for every recorded max speed figure at various altitudes.

There are some tables and conversion formulas around (e.g at http://www.gpforums.co.nz/thread/217754/) and also some tools like Converter Excel Sheet by Lt.Wolf (Converter.rar). (The link is inoperative)

The problem is: "Wonder Woman view" TAS speed gauge (the instrument in the no-cockpit view) is markedly "optimistic" both at SL than at high altitudes.
For example, when flying at 20 (twenty) mt on SL, if I reach 629,25 km/h IAS I can convert it to 630 TAS with the usual formulas, but WW gauge says 648 km/h.
At high alts it's even worse: 455,47 km/h IAS converts to 724 km/h TAS whereas WW gauge says 758 km/h.

I know this isn't a new issue (you can find hints about it on some IL-2 forums), but I have found no info about the reason.


So my questions are:

1) a question to all: do you know how is TAS calculated in IL-2? For sure, Oleg could have exactly calculated it just by computing time and distance related to some ground point, but I suspect they used some conversion from IAS to TAS or vice-versa.
In any case, in no way IAS and TAS at SL (20 mt!) should differ by 18 km/h!
This makes me suspect there is something wrong in IL-2 speed, either in IAS or in TAS.

2) to all, again: are you aware of any other way, WW gauge view apart, to have direct TAS reading from IL-2?

3) a specific question to plane modders: what is your reference when checking speed of new modded planes, to verify if they are plausible? Do you "believe" in WW TAS view or in TAS converted from IAS (and, in this case, using which formula)?


Many thanks.

[danimalhanke]

When talking about TAS and IAS EVERYTHING is related to how many miles/kilometers you are travelling across the ground. (BTW today's lesson is free as I am a Certified Filght Instructor) Standard conversion charts will not be usable when flying because many different factors come into play when determining TAS. Things like density altitude, wind speed and heading etc. You CANNOT simply apply a standardrized conversion with so many variables. It is why pilots carry their trusty flight computer with them whenever they fly. So, if you do not know the density altitude, the wind speed and heading, performance curves for the particular acft you're flying then give up because it will NEVER come out right!!!!! One example: You're flying your 1964 Cessna 172 (which I own) at 91 knots into a head wind of 70 knots at a heading of 0 degrees and your density altitude is 29.92 then your TAS is 21 knots. See what I mean?
If you want more detailed explainations then simply google IAS vs TAS.

Indicated airspeed will differ from true airspeed at air densities other than some reference density. Air density is affected by temperature, moisture content, and altitude. Indicated airspeed is used in aircraft operation as the aircraft stalling speed and structural limiting speeds are dependent on indicated airspeed, irrespective of true airspeed. However, proper navigation via dead reckoning (without constant ground reference) requires the use of true airspeed and wind corrections.

Rules of thumb to estimating your TAS.
http://www.flightsimaviation.com/rule-o ... d_TAS.html

One more to show the futility of what you're attempting to do. At least you're trying! :lol:
http://www.auf.asn.au/groundschool/umodule2.html

[KC Jones]

When talking about TAS and IAS EVERYTHING is related to how many miles/kilometers you are travelling across the ground. (BTW today's lesson is free as I am a Certified Filght Instructor) Standard conversion charts will not be usable when flying because many different factors come into play when determining TAS. Things like density altitude, wind speed and heading etc. You CANNOT simply apply a standardrized conversion with so many variables. It is why pilots carry their trusty flight computer with them whenever they fly. So, if you do not know the density altitude, the wind speed and heading, performance curves for the particular acft you're flying then give up because it will NEVER come out right!!!!! One example: You're flying your 1964 Cessna 172 (which I own) at 91 knots into a head wind of 70 knots at a heading of 0 degrees and your density altitude is 29.92 then your TAS is 21 knots. See what I mean?
If you want more detailed explainations then simply google IAS vs TAS.

Indicated airspeed will differ from true airspeed at air densities other than some reference density. Air density is affected by temperature, moisture content, and altitude. Indicated airspeed is used in aircraft operation as the aircraft stalling speed and structural limiting speeds are dependent on indicated airspeed, irrespective of true airspeed. However, proper navigation via dead reckoning (without constant ground reference) requires the use of true airspeed and wind corrections.

Rules of thumb to estimating your TAS.
http://www.flightsimaviation.com/rule-o ... d_TAS.html

One more to show the futility of what you're attempting to do. At least you're trying! :lol:
http://www.auf.asn.au/groundschool/umodule2.html

Something like this ?

Okay, its an old RAF WWII one, but its still an E6B http://en.wikipedia.org/wiki/E6B

[RAF_Magpie]

I've been saving up to replace my old E6B with one of those fancy electronic jobbies...

Pity is their a bit steep this side of the ditch, what do they go for over in the states?

[P/O W. 'Moggy' Cattermole]

IAS and TAS have never been much of a problem for me, since i'm

1)a moron with little understanding [don't try and explain, I understand enough the principle, but not how it works in practise, and at any rate i'm happy in my ignornce]

2) Never able to achieve any where like the speeds aircraft were meant to be able to fly at anyway, even with 25% fuel, full boost and no ammunition -- a hurricane could top 270mph, or more, but I sure as hell can't do that on IL2, and the lord knows i've tried...

Still, never mind, it's a small price for a fantastic game.

[.041 Safety Wire]

One example: You're flying your 1964 Cessna 172 (which I own) at 91 knots into a head wind of 70 knots at a heading of 0 degrees and your density altitude is 29.92 then your TAS is 21 knots. See what I mean?I totally disagree with this statement, speed through the air is speed thru the air non dependent on tailwinds or headwinds. Me thinks you better take the CFI refresher course.

If your airspeed is only 21 knots how is the aircraft flying, I beleieve that your speed over the ground is 21 knots. Under your way of thinking if you are flying your 1964 Cessna 172 which you own at 91 knots into a 91 knot headwind then your TAS is 0, I ain't buying it.

Indicated airspeed (IAS) is the airspeed read directly from the airspeed indicator on an aircraft, driven by the pitot-static system. IAS is directly related to calibrated airspeed (CAS), but includes instrument errors and position error.

An aircraft's indicated airspeed in knots is typically abbreviated KIAS for "Knots-Indicated Air Speed" (vs. KCAS for calibrated airspeed and KTAS for true airspeed).


[edit] IAS and V speeds
Unless an aircraft is at a sufficient sea level under International Standard Atmosphere conditions (15

[P/O W. 'Moggy' Cattermole]

If your airspeed is only 21 knots how is the aircraft flying, I beleieve that your speed over the ground is 21 knots. Under your way of thinking if you are flying your 1964 Cessna 172 which you own at 91 knots into a 91 knot headwind then your TAS is 0, I ain't buying it

He's right, leastaways i think so. The Fiesler Storch could practically hover in a strong headwind.

If you fly into a 30mph wind, your will travel 30mph slower than if there was no wind. And aircraft could fly at 0mph in a strong wind; it has happened. Indeed, an old british first world war trainer, the Farman Shorthorn, could fly at about 25mph or there abouts. When the wind picked up over Salsbury Plain enough, it flew backwards. One instructor even landed it backwards (and snapped off the tail skid for his efforts).

[.041 Safety Wire]

Thanks Moggy, I couldn't let the above statement pass as a fact of Aerodynamic knowledge. I spent 34 years in and around all types of aircraft so I somewhat know what I am talking about. I don't know where that CFI came up with his info but as I said he needs to take a refresher course, You're right about the Fiesler. I saw Couriers both hover and fly backwards at Oshkosh back in the 80,s Its a pretty neat thing to see. It also a common mistake that aircraft stall at a certain speed which in fact an aircraft can be stalled at any speed under the right circumstances.

So if you fly into a 30mph wind, your true airspeed will be 30mph slower than if there was no wind. And aircraft could fly at 0mph in a strong wind; it has happened. Indeed,

Your airspeed will be your speed through the air your ground speed will be thirty mph slower.

I think you guys are getting confused about airspeed and speed over the ground. An aircraft flys at a certain airspeed regardless of headwind tailwind or crosswind. If an aircraft is flying between two points at 100 miles per hour, 100 miles apart it will take him approx 1 hour to reach this point If he is flying into a 50 mph headwind his airspeed is still 100 but his groundspeed is now 50mph so it will take him 2 hrs to reach his destination. His airspeed does not change.

The definition of airspeed: The forward speed of an object relative to the air through which it is flying; commonly used in reference to canopies, airfoils, or aircraft.

[P/O W. 'Moggy' Cattermole]

ok, sorry. I'll shut up. :oops:

[CloCloZ]

When talking about TAS and IAS EVERYTHING is related to how many miles/kilometers you are travelling across the ground.
....

If you are saying that speed related to ground is related to both IAS and TAS, that's obvious ...
But if TAS is by definition "air distance flown over time" (as stated in one of your links), just TAS is significant about true speed related to ground.
Unless TAS just means "speed related to the air", in which case wind would be important.

Thanks for the info (I already knew the TAS/IAS relation with air density/temperature but is always useful to have clear references), although you didn't asked to any of my questions (but you haven't to do it, if you have no answers to some of them! :wink: ).

Anyway, I could guess that IL-2 computes TAS from speed relative to ground and that IAS is a derivated figure that, at SL on Crimea map, can differ from TAS by almost 20 km/h, that is much more than I expected on a map that likely shouldn't be "extreme" at least about temperature.

My question about what plane modders use as speed reference (TAS from IL-2 WW gauge, I suppose) remains.

[.041 Safety Wire]

(DOD) The speed of an aircraft relative to its surrounding air mass. The unqualified term "airspeed" can mean any one of the following. a. calibrated airspeed--Indicated airspeed corrected for instrument installation error. b. equivalent airspeed--Calibrated airspeed corrected for compressibility error. c. indicated airspeed--The airspeed shown by an airspeed indicator. d. true airspeed--Equivalent airspeed corrected for error due to air density (altitude and temperature).

Do you see anything in the above statement about headwind or tailwind, This is the Department of Defense definition of airspeed.

[.041 Safety Wire]

A small refresher course for you guys. The airspeed of the aircraft is calculated through the difference between ram air pressure which is read by the pitot head and static pressure which is read by the static port. The pitot head is normally mounted outside of the propeller slipstream so it is in undisturbed air. The static port is usually on the side of the aircraft and operates in the boundry layer. The speed that the indicator in the cockpit shows is the IAS or indicated airspeed. The difference after taking into account the density of the outside air and several other factors is the true airspeed.

[.041 Safety Wire]

ok, sorry. I'll shut up. :oops:

And aircraft could fly at 0mph in a strong wind; it has happened. Indeed, an old british first world war trainer, the Farman Shorthorn, could fly at about 25mph or there abouts.

Yes 0 mph groundspeed but never 0mph airspeed. The only types of AC that fly at 0 mph airspeed are VTOLs and helis but even with the helicopter the craft still has airspeed over its wing which is called a rotor blade. One other unique thing about helis is once the craft starts moving forward the advancing blade develops more lift while the retreating blade develops less. So the whole rotor head has to teeter or be articulated or the copter will roll away from the advancing blade.

Again look at the B6 computers in the above photographs. These are used for calculating TAS do you see anything on the computer about headwind or tailwind. No because it does not enter into the equation. It has nothing to do with IAS or TAS.

[Trooper117]

lol.. loving this stuff..
I'm heavily into my navigation phase of my ppl at the moment, so my nav computer is getting some heavy use!..
I often sit and watch these debates about fm's, accuracy in game, and quite often points being made and reinforced by people who don't even fly.. (I love it when people who do actualy fly chip in) often to be shouted down by people who only read books about it!..lol! (the next comments are usualy..'yes, but you can't compare your Cessna to a WWII aircraft'.. they still have to be right!)
Makes for interesting reading as usual.

[P/O W. 'Moggy' Cattermole]

I often sit and watch these debates about fm's, accuracy in game, and quite often points being made and reinforced by people who don't even fly..

Guessing that was aimed at me? Heh, well, give it a few years and the Army Aircorps could be paying me to learn to fly and then.... Well, then i'll be able to legitimately join in! Haha!