Reviving a Discussion on Air Speed at Waypoints

[ATAG_Lenny]

There was a discussion last year on the old iL-2 forum about airspeed settings and in-game observations. It didn't really seem to end definitively to me.

It's been nagging me a bit as I build missions and I worried that I was setting an inaccurate or unrealistic waypoint speed that could cause unexpected AI behaviours in-mission. So I asked Artist what precisely the waypoint speed was that the builder set in the FMB. Was it True Air Speed (TAS) which is the actual speed you are going at Sea Level, or Indicated Air Speed (IAS) which is the speed your speedometer says you are going at a given altitude given there are fewer air molecules the higher you go to go through your pitot tube (note the IAS = TAS at sea level), or is it perhaps Calibrated Air Speed (CAS) which adjusts IAS for instrument error and such.

Well it is none of the above. Artist reports that the airspeed you set in the FMB for a waypoint is GROUND SPEED (GS) which is TAS +/- the windspeed vector! GS is used by real mission planners as it enables you to place multiple aircraft over a target (or a point in space) at a given time, some aircraft coming potentially from one direction while others from different directions. Then the sim will figure out given the weather flow conditions on the map, what aircraft have to fly at what speed to achieve that time on target.

What it also means is that that information is available to the AI but not currently to the human pilot. To address this long-standing gap, Artist has already prototyped adding altitude and calculated IAS information to each waypoint in the in-game mini-map. In that way the human pilot will have that information available at any time from briefing to mid-mission.

So the mission builder can use GS to build the mission and the player will get to see the desired waypoint altitude/IAS information to fly the mission. Nice.

Oversimplified:
IAS = TAS minus 7% per 1000m (2% per 1000')
TAS = IAS at 0m
GS = TAS +/- wind vector

Wind in your face of say 20kph then GS = TAS minus 20kph
Wind on your tail of say 20kph then GS = TAS plus 20kph
Wind from any other direction then GS = TAS +/- complicated math but not more or less than a 20kph difference.

Lenny

[FTC_Rostic]

... Artist reports that the airspeed you set in the FMB for a waypoint is GROUND SPEED (GS) which is TAS +/- the windspeed vector! ...

Copy of my original post from Discord server:
In which game version it works like that??
Because in very simple test when path set at 6000m at 300kph in no wind condition AI controlled Bf-109 pass about 84miles (135km) for 20 minutes what is about GAS 405kph and IAS 280-290kph
P.S. Yeah, I know there is no seconds on aircraft clock. But I made screenshots at the moment digital value changed... So, I expect it to be +-2sec time error.

image.jpg

[GANIX]

Before we proceed with any further calculations, please recall that dynamic or impact pressure is the only directly measurable quantity in a single-seat World War II fighter aircraft that relates to its true airspeed (TAS) with respect to the air. Most World War II fighter planes were equipped with a differential or pitot-static tube for this purpose.

To calculate the impact pressure for the true airspeed qc(h,TAS), aerodynamicists use, among other terms, the following equation:

qc = p_o * { [ 0.2 * (CAS/a_o) ² +1} ] ^3.5 -1 } (1)

Where
p_o = standard air pressure at standard sea level in Pascal (Pa)
CAS = calibrated airspeed in metres per second (m/s) (see eq. 4)
a_o = speed of sound at standard sea level in metres per second (m/s)

---

The speed of sound (a) in undisturbed air is a function only of temperature and not altitude as is often mistakenly assumed. It can be computed from the formulae

a_o = (1.4 * 287.053 * T_288.15)^0.5 = 340.294 (2)

Since the dynamic pressure varies with temperature and altitude airspeed indicators are corrected to a single condition based on a Standard Atmosphere model. That single condition is defined as a standard sea level day and corresponds to:

Spoiler: 

Temperature at sea level on a standard day
t_o = 288.15 Kelvin = 15 C^o

Temperature change with altitude on a standard day
L = -6.5 C^o/1000m

Static air pressure at sea level on a standard day
p_o = 1013.25 mbar

Air density at sea level on a standard day
d_o = 1.225 kg/m ³

Speed of sound at sea level on a standard day
a_o = 340.294 m/s (see eq. 2)

---

The Standard Atmosphere is a perfect gas which obeys the equation of state:
p_h = d_h * R_s * T_h

The values measured by the pitot-static tubes are used to calculate static air pressure and impact pressure, using a standardised atmosphere. It is a mathematical model of the atmosphere which is used since 1920s as common reference for temperature and pressure measurements at various altitudes from sea level to approximately 11000 metres above mean sea level.



Aerodynamicists commonly use the following equation to maintain true airspeed (TAS) from dynamic impact pressure qc:

TAS = { 7 * p_h/d_h [ (qc/p_h +1 )^0.2857 -1 ] } ^0.5 (3)

The simplest way to compute true airspeed is using a function of Mach number:

TAS = a_o * Ma * (T_h/T_o) ^0.5 (3a)

Where
q_c = compressible impact pressure
p_h = standard air pressure at flight altitude
d_h = standard air density at flight altitude
a_o = 340.294 m/s (see eq. 2)

---

Calibrated airspeed (CAS) is a virtual 'speed'. The CAS is defined as the airspeed at sea level in the Standard Atmosphere at which the compressible dynamic pressure qc(h,TAS) is the same as the compressible dynamic pressure for TAS at current flight altitude. Aerodynamicists commonly use the following equation to maintain CAS from dynamic impact pressure qc:

CAS = { 7 * p_o/d_o [ (qc/p_o +1 )^0.2857 -1 ] } ^0.5 (4)

Where
q_c = compressible impact pressure
p_o = standard air pressure at mean sea level
d_o = standard air density at mean sea level

---

Equivalent airspeed (EAS) is a virtual 'speed'. The EAS is defined as the airspeed at sea level in the Standard Atmosphere at which the incompressible dynamic pressure q(h,TAS) is the same as the incompressible dynamic pressure for TAS at current flight altitude.Aerodynamicists commonly use the following equation to maintain EAS from dynamic impact pressure qc:

EAS = { 7 * p_h/d_o [ (qc/p_h +1 )^0.2857 -1 ] } ^0.5 (5)

Where
q_c = compressible impact pressure
p_h = standard air pressure at flight altitude

---

The basic definition for EAS is CAS corrected for compressibility effects.

Indicated airspeed (IAS) is the reading displayed on the airspeed indicator dial; like CAS and EAS, it is a virtual ‘speed’. The main advantage of using IAS in the cockpit is that, for a given aircraft configuration, the aircraft will always stall at the same IAS, irrespective of altitude or ambient temperature. This makes the aircraft easier to fly, since the critical speeds defining its operating envelope remain constant across a range of atmospheric conditions. Most Second World War fighter aircraft were equipped with a differential pressure, or pitot-static, system for this purpose. Unlike CAS (see eq. 4) , IAS is defined as the airspeed at sea level in the Standard Atmosphere for which the fictitious but useful incompressible dynamic pressure q (see eq. 6b) is equal to that generated by the TAS at the current flight altitude. Aerodynamicists commonly use the following equations to calculate IAS from the incompressible dynamic pressure q(h,TAS):

IAS = {( 2*q ) / d_o}^0.5 (6)
also,
IAS = (d_h/d_o) ^0.5 * TAS (6a)

Where
q = 3.5 * p_h * { ( 1 + qc / p_h)^0.2857 - 1 } (6b)
IAS = indicated airspeed in metres per second (m/s)
p_o = standard air pressure at sea level
p_h = standard air pressure at flight altitude
d_o = standard air density at sea level
d_h = standard air density at flight altitude

---

You use equation (6b) to convert the compressible Pitot pressure into the equivalent incompressible dynamic pressure. That is precisely the classic IAS/EAS-CAS basis.
The basic definition for IAS is CAS corrected for air compressibility effects.

Groundspeed (GS) is the real-world travel speed over the ground, affected by wind. As its name suggests, this is simply the speed at which an object is moving relative to the ground below. It is a quantity that describes the relationship between speed, distance, and time, and is expressed by this equations:

simplified: speed = distance / time

---

The equation makes it fairly clear that the aircraft is moving independently of this physical reference frame (the ground), and that GS can only describe movement relative to the ground.

Back in the 1930s and 1940s, aviators had to work out Ground Speed (GS) laboriously from Indicated Airspeed (IAS) using tables and charts. To understand this, one first has to know how the speed measured in flight can actually be converted into GS...

Ground Speed (GS) does not affect TAS, CAS or IAS, because these “speeds” describe the aircraft’s motion relative to the surrounding air mass, and the aircraft itself is part of that moving body of air. This may also explain why the term Groundspeed (GS) is used in aerodynamics, rather than Ground Airspeed (GAS).

Now things get confusing because not only can the object be moved through the air, but the air itself can move. The airmass surrounding the aircraft can move along six principal directions. Even so, a relationship between groundspeed (GS) and true airspeed (TAS) can be calculated. In this context, ground speed can also be thought of as a virtual speed, just like CAS and IAS. Back in the 1930s and 1940s, aviators were rarely able to measure the ground speed (GS) directly and must compute the ground speed (GS) from the wind speed (WS) and true airspeed (TAS). Wind speed (WS) is the vector difference between the true airspeed (TAS) and the ground speed (GS). So, the true airspeed (TAS) is also a vector quantity and has both a magnitude and a direction. Ground speed is also a vector quantity so a comparison with the airspeed must be done according to the rules of vector comparisons.

Converted into its equivalent vector representation in Cartesian form it looks like this:

V_gs( ±x_gs, ±y_gs, ±z_gs ) = V_tas( ±x_tas, ±y_tas, ±z_tas ) + V_ws( ±x_ws, ±y_ws, ±z_ws )

---

Without true airspeed, wind direction and wind speed, GS cannot be determined unambiguously. A tailwind makes GS higher than TAS, a headwind makes GS lower than TAS.

References:
Notes On The Standard Atmosphere, (NACA TN No 99, 1922)
Principles Of Ground-Speed Measurement, (NACA Report No. 127, Part III, 1923)
Measuring An Airplane's True Speed In Flight Testing, (NACA TN No. 135, 1923)
Pitot-Static Tubes For Determining The Velocity Of Air, (NACA TM No. 303, 1925)
Standard Atmosphere - Tables And Data, (NACA Report No. 218, 1926)
Procedure For Determining Speed And Climbing Performance Of Airships, (NACA TN No. 564, 1935)
Airspeed Instruments, (NACA Report No. 420, 1941)
Index Of NACA Technical Publications 1915-1949, (NACA, 1950)
Notes On Definitions Of And Nomenclature For "Air Speeds", (A.R.C.1951)
Fundamentals Of Aerodynamics, Sixth Edition (Anderson, ©2017 )

Discussions that are related to speed:

Spoiler: 

IL-2 CloD Route Planner
Kind of speed in FMB
Formula for converting True Air Speed to Indicated Air Speed in CloD, and/or . .
IAS vs TAS vs CAS
Wind Direction

[ATAG_Lenny]

Please… and thank you. I am learning new stuff!

[koko]

I have created my own test script to examine the different speed values in the game in practice, such as ground speed, true airspeed, indicated airspeed, and IAS corrected using the ISA formula. I am attaching a few screenshots taken at very low altitude close to sea level, showing how different speeds affect the values obtained. Based on these, it appears that the game also shows a clear instrument error that changes with both speed and altitude.

The script also suggests that sideslip may increase IAS instrument error, which I think is an interesting additional observation.

I am not publishing the script publicly yet, but if there is someone here with strong knowledge of aerodynamics, flight mechanics, or airspeed calculations who would be willing to review my method and evaluate whether the calculations and implementation are correct, I would be happy to share the script privately for inspection. You can contact me either via forum private message or through Discord.


-koko-

[ATAG_Lenny]

What are your wind flow parameters in these test missions?
Lenny

[koko]

What are your wind flow parameters in these test missions?

The test was done with no wind, with all wind settings set to zero.

-koko-

[ATAG_Lenny]

Artist has strong knowledge of source code and has been looking at it recently re air speed and FMB, hence why I re-raised the subject. If you can share mission/scripts when you are ready, he may be able to look at and see what’s up. That said, I don’t speak for him.
LENNY

[koko]

Artist has strong knowledge of source code and has been looking at it recently re air speed and FMB, hence why I re-raised the subject. If you can share mission/scripts when you are ready, he may be able to look at and see what’s up. That said, I don’t speak for him.

I don’t want to bother Artist with this either, especially right now when he probably already has more than enough on his plate. For me, this is not really a matter of criticism, but more of a small personal area of interest — I simply enjoy using scripts to learn how the game is implemented and how different things behave in it


-koko-

[Artist]

Short version:

A. The speed set in the Full Mission Builder is Ground Speed (GS)

B. What you see on your speedometer in the cockpit is Indicated Airspeed (IAS)

C. In the next patch (5.047) the waypoints of the player in the ingame map will display required IAS and altitude

Details:

A. The speed set in the FMB is Ground Speed (GS)

Only this makes sense, because in the FMB you plan the flights ("start here at this time, be there at that time"), so you must use GS.
It is your responsibilty here to not demand a Tiger Moth to achieve 200 km/h GS against a headwind of 50 km/h while trying to ascend from 1000m to 5000m.
(BTW the FMB activly prevents you from entering 500 km/h GS for a Tiger Moth, replacing it with the model's maximum speed - based on sea level with no wind GS=TAS=CAS=IAS)

IAS/TAS/CAS would make no sense here, because if you change altitude, temperature, wind (direction and/or strength) you'd need to adjust speed in all waypoints.


B. What you see on your speedometer in the cockpit is Indicated Airspeed (IAS)

It takes into account: height, temperature and wind (both strength and direction)


C. In the next patch (5.047) the waypoints of the player in the ingame map will display required IAS and altitude

The IAS and the altitude are given in the dimensions used by the aircraft you are in (km/h or mph, m or ft).
ImgameMap.jpg

If you fly at the given height with the given IAS you should reach the next waypoint (roughly) at the correct time.

***

Thank you, GANIX, for these - I'll post a note there, too.

Discussions that are related to speed:
https://theairtacticalassaultgroup.c...ad.php?t=32559
https://theairtacticalassaultgroup.c...ad.php?t=23718
https://theairtacticalassaultgroup.c...ad.php?t=37830

[FTC_Rostic]

Short version:

A. The speed set in the Full Mission Builder is Ground Speed (GS)

What do you mean by that?

Because according to my tests value entered in FMB has nothing in common with actual aircraft ground speed it is flying in mission. FMB does treat it as like it is GS (by calculating time between waypoints), but in running mission value entered in FMB is the speed that AI tries to achieve as IAS.

[koko]

Thank you Artist for the clarification.

Based on my own tests, however, I still have a small doubt that the situation may not be quite that simple — at least in level flight with zero wind.

I have made a few controlled tests where the waypoint speed in FMB was set to 350 km/h. I will attach two screenshots: one taken essentially at sea level, and another at about 5000 m altitude.

In the sea-level test, TAS and GS match each other very closely, as expected in zero wind and level flight.
However, the game’s own IAS parameter / cockpit indication shows a difference of several km/h compared with the corrected IAS calculated from TAS using ISA formulas.

To me this suggests that there is some kind of IAS instrument error in the game, at least in this test case.

The high-altitude test is even more interesting to me. The leg speed in FMB was still set to 350 km/h, but the aircraft TAS and GS were 448.6 km/h.
Again, TAS and GS match each other very well in zero wind, but the corrected IAS calculated from TAS is very close to the 350 km/h value entered in FMB. The difference is only a few tenths.

So I am not claiming this as final proof, but based on my observations it strongly looks as if, in level flight, the FMB waypoint speed behaves more like a corrected IAS/CAS-type value than a pure ground speed value.

Climb and descent legs seem to be a different matter. In my tests, the speed setting does not seem to have the same direct effect there. The AI appears to try to reach the target altitude using its own internal logic, often with a rather steep climb or descent.

I am attaching the screenshots more as observation material than as a counter-argument. I may of course be interpreting something incorrectly, but based on these readings I do not yet understand how the FMB level-flight speed could be a pure GS value.

-koko-

[Artist]

What do you mean by that?

Because according to my tests value entered in FMB has nothing in common with actual aircraft ground speed it is flying in mission. FMB does treat it as like it is GS (by calculating time between waypoints), but in running mission value entered in FMB is the speed that AI tries to achieve as IAS.

I am not talking about AI (yet). I am talking about FMB value and what the player sees in the cockpit.

When you make an airspawn you see that the GS of the FMB translates correctly into the IAS that you initially see on your speedometer.

[koko]

I think part of the confusion around this topic comes from the fact that two different things are getting mixed together in the discussion.

I also agree that calculating the time / ETA between waypoints must ultimately be based on ground speed, or GS. I also assume that this is probably how the FMB planning logic works.

But the question that, in my opinion, causes the most confusion is really the more general question: “what type of speed does the value entered into the FMB Speed field represent?”

-koko-

[Artist]

“what type of speed does the value entered into the FMB Speed field represent?”

That question is answered: Ground Speed. Period.

1. The timings in FMB are correctly based on that and
2. the players's aircraft has the correct speed and shows the correct IAS on (air)spawn.

E.g. if you configure 300 km/h (Ground Speed) at 9000 m altitude with a headwind of 10 km/h (with 15°C Channel Map's temperature), the speedometer correctly shows 195 km/h IAS when you spawn into the aircraft.
(185 for altitude + 10 for headwind)


***


That said, however, concerning the AI, you and FTC_Rostic are right: The AI does interprete the FMB waypoint's value differrently.

So, the big question here is: Why does the AI accelerate until it has reached the value set as Ground Speed in the FMB as IAS?

Note, the emphasis on accelerate: The AI does spawn with the correct ground speed and IAS (same as the player) and only then hits the gas to reach the ground speed value as IAS.

I have a mission attached to demonstrate this:
FMB-GroundSpeed.zip

• There are two Bf-109E-4 side by side at 9000m altitude, one for the player, one for the AI.
• They are both configured for 300 km/h Ground Speed,
• There's no wind.
• Expected IAS at that altidude is 185 km/h

When you spawn in

• Your speedometer shows the correct 185 km/h
• The AI's is on your right (100m) and initially flies at the same speed (185 IAS, 300 GS)
• If you maintain your 185 km/h IAS, you'll notice that the AI slowly starts to draw ahead, because the AI is accelerating towards 300 km/h IAS

If you want measured proof, do the following:

• Spawn in and immediatle pause game
• Release your position (aircraft) to the AI, so both planes are AI controlled
• Open the ingame map
• The two aircraft are on the lower left corner of the map, scoll there, zoom in
• Take a stopwatch (Smartphone) that allows stops for "rounds"
• The battle area grid is 1000m, you see that at the "start" position the grid line crosses slightly behind the wings.
• Unpause the game and take 'round times' for the 1st, 2nd, 3rd crossing of a grid line
• Calculate the m/s for each 1000m and you will see that
  • the 1st 1000m are close to the correct 83m/s for 300 km/h GS / 185 IAS
  • the 2nd 1000m are already a bit faster than that ...
  • ... and so on, until the AI reaches the 132m/s (GS) for 300km/h IAS (=477.2 km/h GS)

***

I consider this a bug. The value set in the FMB is Ground Speed and the AI should behave accordingly. In fact initially it already does, but then wrongly accelarates. I'm looking into the code on how to stop that.

[Artist]

I found the error in the code ...

When the AI pilot checks its current speed against the speed required by the current waypoint, the original developers forgot that the value in "Speed" in this case is Ground Speed and compared it with the output of the pitot (which gives IAS) without adjusting it to IAS first.

(Professional rant from me: This is a common blunder resulting from not naming variables properly or having the same variable hold different meanings in different circumstances. Ha-hrm!)

[major_setback]

I found the error in the code ...

When the AI pilot checks its current speed against the speed required by the current waypoint, the original developers forgot that the value in "Speed" in this case is Ground Speed and compared it with the output of the pitot (which gives IAS) without adjusting it to IAS first.

(Professional rant from me: This is a common blunder resulting from not naming variables properly or having the same variable hold different meanings in different circumstances. Ha-hrm!)

Is this one of those things that are easily fixed, or one of those things that might appear to be easily fixed, but turn out not to be?
ie: should we make offerings to the gods in hope that they will favour us?

[ATAG_Lenny]

Is this one of those things that are easily fixed, or one of those things that might appear to be easily fixed, but turn out not to be?
ie: should we make offerings to the gods in hope that they will favour us?

Are you referring to Artist? He certainly does seem to have godlike powers.
Lenny

[Artist]

Is this one of those things that are easily fixed, or one of those things that might appear to be easily fixed, but turn out not to be?
ie: should we make offerings to the gods in hope that they will favour us?

The fix itself is/was easy. A simple mistake, a simple correction: turn required GS into IAS and compare with that.

It's more the sideeffects that are keeping me busy now: How to make sure that all the missions out there which based their design on the wrong behaviour will not be affected by the fix? I know the answer, but it is some work.

Are you referring to Artist? He certainly does seem to have godlike powers.

Not all things are what they seem. This one certainly is not.

[FTC_Rostic]

The fix itself is/was easy. A simple mistake, a simple correction: turn required GS into IAS and compare with that.

It's more the sideeffects that are keeping me busy now: How to make sure that all the missions out there which based their design on the wrong behaviour will not be affected by the fix? I know the answer, but it is some work.

Oh, that is one of worst bug types: when you know that is mistake, you know where it is, you know how to fix it, the fix is simple..... but it ruins half of system that was build on top of that bugged but stable and predictable system behavior.

In theory you can make a tool that will know every aircraft IAS units and will scan folders for mission files and alternate existing values to new ones.... but this will patch only official missions published with game. You can release tool for public, but it will not fix missions dynamically generated by scripts...

The better way (from legacy missions support point of view) could be add new parameter to mission file itself. Kind of one line "AIgroupsUseTAS 1" in [MAIN] section. FMB in new game build will patch missions on save, fixing speeds to TAS and adding that line to file. If game loads .mis file without that line, it will autopatch mission on load.

I'm curious if you have better idea?

[GANIX]

At least with the formal release of - Blitz! -, Team Fusion Company surprised virtual flight enthusiasts with a new constant for velocity: <mach = 333.00033300033>.

Those interested can find the constant in the dynamic link library maddox.dll under <public enum VelocityDimensions>.

I hope the Mach number was not meant to be defined as a constant. Mach (Ma) is not speed but a variable ratio comparing an object's true airspeed to the speed of sound. The ratio of the true airspeed of the aircraft to the speed of sound in the air determines the magnitude of many of the compressibility effects... (see: PART I - THEORETICAL INTRODUCTION)

If the constant should be a new standard for Speed of Sound at mean sea level, than it gets really interesting for the TFC developers. Since 100 years Aerodynamicists commonly use the following constant:

Speed of Sound at Standard Mean Sea Level (MSL) = 340.294 m/s (see: PART I - THEORETICAL INTRODUCTION)

" ... Oh, that is one of worst bug types: when you know that is mistake, you know where it is, you know how to fix it, the fix is simple..... but it ruins half of system that was build on top of that bugged but stable and predictable system behavior. ..."

[GANIX]

After the incorporation of Team Fusion Simulations Ltd, 1C and TF signed an agreement granting Team Fusion the exclusive rights to develop the Cliffs of Dover game engine. Unfortunately, TF received an older version rather than the last published one. On the assumption that the 1C-Maddox atmosphere model was inaccurate, Team Fusion introduced an atmosphere that comes very close to what we have known as the International Standard Atmosphere since the 1920s.

The 'Cliffs Of Dover - Blitz' v5.046.0 atmosphere

The following sea-level values for pressure, temperature, and density are assumed for the current ‘Blitz!’ standard atmosphere:

Temperature at sea level on a standard day
T_sl = 288.16 Kelvin

Air density at sea level on a standard day
D_sl = 1.225 [ kg/m³ ] = { 101325 : ( 287.053 * Tsl )}

Static air pressure at sea level on a standard day
P_sl = 101325 [ Pa ] = { 287.053 * 1.225 * Tsl }

Speed of Sound at sea level on a DWT standard day
a_sl = (1.4 * 287.053 * T_288.16)^0.5 = 340.300

---

For mission builders, the v5.046.0 atmosphere temperature profile, given as a quantity in Kelvin, can be used to establish a relationship between pressure, temperature, density, and lapse rate. Assuming the air is modeled as a dry, perfect gas.

When reading the TFC manuals and flashcards, it is important to remember that the collection contains only aircraft you can actually take control of. However, 1C-Maddox also developed more than half a dozen other aircraft, albeit reserved exclusively for AI use. Mission builders should be able to compute accurate speeds for all aircraft, where “all aircraft” includes non-flyable AI aircraft such as the Focke-Wulf Fw 200 C-1.

The required 'real time' values like ambient air temperature, altitude and velocity may be measured/determined/derived by means of FMB script methods (cSharp) provided by 1c-Maddox.

Spoiler: 

To compare the aircraft speed against waypoint values only four Full-Mission-Builder methods are required. Beside a bunch of public "ParameterTypes" Team MADDOX gives us access to:

<(actor as AiAircraft).Pos().z>
reveales the Geometric Altitude given as quantity in meters above mean sea level.

<getParameter(part.ParameterTypes.Z_AmbientAirTemp erature, -1)>
reveales Outer Air Temperatue given in Kelvin above mean sea level.

<getParameter(part.ParameterTypes.Z_VelocityIAS, -1)>
reveales the True Airspeed given as quantity in meters per second,

<getParameter(part.ParameterTypes.Z_Velocity TAS, -1),>
reveales the Groundspeed given as quantity in meters per second,
[/Quote]


For aircraft you take control of, the following additional methods are also available.
[Quote]
<getParameter(part.ParameterTypes.I_VelocityIAS, -1)>
reveales a speed shown on the airspeed indicator as quantity in km/h, mph, or knots

<getParameter(part.ParameterTypes.I_Altitude, -1)>
reveales the height shown on the altimeter as quantity in metres or feet

Team Fusion Company (TFC) “Mission Builders Manual v1.0.4” (page 25) recommends a “one size fits all” approach to speed and climb settings when creating waypoints for missions. I will follow this recommendation by creating a Bf109E-4 and defining two waypoints for level flight using recommended 275kmh speed. The waypoints define the activity task, position, altitude, and speed.

  NORMFLY 80000.00 160500.00 5006.70 275.00
  NORMFLY 262000.00 160500.00 5006.70 275.00

where

		NORMFLY 262000.00 160500.00 6006.60 275.00
		   |         |         |	|      |
		   |         |         |	|    AiAirWayPoint <speed>
		   |         |         |	|
		   |         |         |   AiAirWayPoint <Z> 
		   |         |         |
		   |         |       AiAirWayPoint <Y>
		   |         |
		   |       AiAirWayPoint <X>
		   |
		 AiAirWayPointType <task/activity> <NORMFLY>

---

Each waypoint has four crucial parameters. Setting these properly is the key to a working mission.

The waypoints 'AiAirWayPoint <X>' and 'AiAirWayPoint <Y>' determine the coordinates in the Cartesian world of 'Blitz!'. A waypoint’s 'AiAirWayPoint <Z>' is the height the aircraft will try to reach before flying through the waypoint. If the altitude is unreachable, the aircraft may decide to circle the area whilst trying to climb or dive to it before proceeding to the next waypoint.

The aircraft should attempt to fly through the waypoint at the designated 'AiAirWayPoint <speed>'. This is crucial to properly timing multiple aircraft (flight groups) to meet at the proper time.

Finally, the Action selects the aircraft's (flight group’s) action at the waypoint. 'NORMFLY' means aircraft (flight groups) decide for themselves. If the skies are clear the aircraft (flight group) simply continues on. If enemy opposition is detected, the aircraft (flight group) may decide to engage the enemy or run for home.

Since 1C Entertainment and Team Fusion Company released Cliffs of Dover Blitz, we have been flying in a virtual atmosphere that closely resembles what has been known as the International Standard Atmosphere for nearly 100 years (see: PART I - THEORETICAL INTRODUCTION).

For mission builders, the current v5.046 atmospheric temperature profile, expressed in degrees Kelvin, can therefore be used to establish relationships between pressure, temperature, density, and gravitational acceleration via the hydrostatic equation and the ideal gas law.

Overall, this provides a very good basis for carrying out airspeed tests with relative ease. There is no need to correct for standard mean sea-level conditions, as small speed deviations (±1 km/h) are negligible.

Table (1)
The following speeds were obtained on a standard day in a Bf109E-4, with no wind, 
considering the airplane in steady, level (horizontal) flight:

 |  Z,m |   T,k  |TAS=GS | CAS | IAS | EAS |          80000.00 160500.00 ....... 275.00
 |      |        |       |     |     |     |
 | 6000 | 248.97 |  371  | 274 | 264 | 272 | NORMFLY 262000.00 160500.00 6006.55 275.00
 | 5000 | 255.57 |  352  | 274 | 264 | 273 | NORMFLY 262000.00 160500.00 5006.55 275.00
 | 4000 | 262.15 |  334  | 274 | 264 | 273 | NORMFLY 262000.00 160500.00 4006.55 275.00
 | 3000 | 268.68 |  318  | 274 | 265 | 274 | NORMFLY 262000.00 160500.00 3006.55 275.00
 | 2000 | 275.17 |  302  | 274 | 265 | 274 | NORMFLY 262000.00 160500.00 2006.55 275.00
 | 1000 | 281.64 |  288  | 274 | 265 | 274 | NORMFLY 262000.00 160500.00 1006.55 275.00
 |   52 | 287.81 |  275  | 274 | 265 | 274 | NORMFLY 262000.00 160500.00   58.55 275.00
 |      |        |       |     |     |     |
 |      | Kelvin |  kmh  | kmh | kmh |     |


It appears that the AI pilot-in-command maintains approximately 274 km/h CAS ±1 km/h indefinitely.

Spoiler: 

The following speeds were obtained on a standard day in a Spitfire MkI(100oct), with no wind, 
considering the airplane in steady, level (horizontal) flight:

 |  Z,m |   T,k  |TAS=GS | CAS | IAS | EAS |          80000.00 160500.00 ....... 275.00
 |      |        |       |     |     |     |
 | 6000 | 248.97 |  371  | 274 | 164 | 272 | NORMFLY 262000.00 160500.00 6002.15 275.00
 | 5000 | 255.57 |  352  | 274 | 164 | 273 | NORMFLY 262000.00 160500.00 5002.55 275.00
 | 4000 | 262.15 |  334  | 274 | 164 | 273 | NORMFLY 262000.00 160500.00 4006.55 275.00
 | 3000 | 268.68 |  317  | 274 | 164 | 273 | NORMFLY 262000.00 160500.00 3006.55 275.00
 | 2000 | 275.17 |  301  | 273 | 164 | 273 | NORMFLY 262000.00 160500.00 2006.55 275.00
 | 1000 | 281.64 |  287  | 273 | 163 | 273 | NORMFLY 262000.00 160500.00 1006.55 275.00
 |   52 | 287.81 |  274  | 273 | 164 | 273 | NORMFLY 262000.00 160500.00   54.55 275.00
 |      |        |       |     |     |     |
 |      | Kelvin |  kmh  | kmh | mph |     |

                               1 mph = 1,60934 kmh


It appears that the AI pilot-in-command maintains approximately 274 km/h CAS ±1 km/h indefinitely.

Observations:

The data in Table 1 appear to support the interpretation that the waypoint speed value of 275 is treated as a CAS target. Across the entire altitude range, CAS remains almost constant at approximately 274 km/h, i.e. within about 1 km/h of the specified value. TAS/GS, by contrast, varies significantly with altitude, increasing from 275 km/h near sea level to 371 km/h at 6000 m. This rules out TAS or GS as the controlled speed quantity.
The cockpit IAS also does not match the specified value, remaining around 264–265 km/h. Therefore, the most consistent interpretation is that the AI controls the aircraft to the specified waypoint speed as CAS, while TAS/GS changes with altitude according to atmospheric density. The most notable result is the deviation of the indicated airspeed (IAS). The data do not strongly support the assumption that IAS is computed from a consistently shifted pressure altitude (see: PART I, equation 6).

Table (2)
The following speeds were obtained on a standard day in a Bf109E-4, with no wind, 
considering the airplane in steady, level (horizontal) flight:

 |  Z,m |   T,k  |TAS=GS | CAS | IAS | EAS |          80000.00 160500.00 ....... 480.00
 |      |        |       |     |     |     |
 | 6000 | 248.97 |  589  | 439 | 433 | 431 | NORMFLY 262000.00 160500.00 6002.55 480.00
 | 5000 | 255.57 |  584  | 459 | 451 | 453 | NORMFLY 262000.00 160500.00 5002.55 480.00
 | 4000 | 262.15 |  563  | 465 | 457 | 460 | NORMFLY 262000.00 160500.00 4002.55 480.00
 | 3000 | 268.68 |  544  | 472 | 465 | 469 | NORMFLY 262000.00 160500.00 3002.55 480.00
 | 2000 | 275.17 |  524  | 477 | 471 | 475 | NORMFLY 262000.00 160500.00 2002.55 480.00
 | 1000 | 281.64 |  500  | 478 | 472 | 477 | NORMFLY 262000.00 160500.00 1002.55 480.00
 |   52 | 287.81 |  479  | 478 | 474 | 478 | NORMFLY 262000.00 160500.00   54.25 485.00
 |      |        |       |     |     |     |
 |      | Kelvin |  kmh  | kmh | kmh | kmh |


It appears that the AI pilot-in-command maintains the above speed indefinitely at maximum continuous power.

Observations:

The data in Table 2 appear to support the interpretation that the selected waypoint speed value is significantly higher than the achievable CAS. If the waypoint speed were adjusted to match the CAS values calculated in Table 2, the resulting airspeeds should remain virtually unchanged.
The most notable result is the deviation of the indicated airspeed (IAS). The data do not strongly support the assumption that IAS is computed from a consistently shifted pressure altitude (see: PART I, equation 6).
The deviation is small, not strictly proportional, and changes sign at the highest altitude (see table 2), which points more towards an indication, position, or calibration offset. Thus, the IAS displayed in the cockpit should not be interpreted as being identical to the idealised calculated CAS/IAS value. It appears to include a small yet operationally relevant deviation from the value derived from the standard pitot-static pressure relation.
It should also be noted that the cockpit IAS may be displayed in different units depending on the aircraft type, for example in km/h, mph, or knots. This unit conversion is most likely applied only after the underlying speed quantity has been determined. In other words, the displayed IAS unit does not necessarily indicate which speed quantity is used internally for the waypoint speed command.


Measuring the Different Types of Airspeed in Mission Building

Since most World War II fighter aircraft were equipped with a differential or pitot-static tube, I selected, from the many equations published in numerous historical scientific papers, those which illustrate the relationship between TAS, CAS, and IAS/EAS, on the basis of static pressure and impact pressure. ( Equations and interesting scientific reports are listed in Part I - THEORETICAL INTRODUCTION )

In fact, it takes only 12 lines of C# code (net) to calculate the most important airspeeds:

Spoiler: 

private void CalculateAllOfSpeed() {

        AiAircraft playerPlane = GamePlay.gpPlayer().Place() as AiAircraft;

        /// Altitude Z,m
	ALTz = playerPlane.Pos().z;

        /// Temperature in Kelvin at Altitude Z,m
        Th = playerPlane.getParameter(part.ParameterTypes.Z_AmbientAirTemperature, -1);

        /// True Airspeed TAS = f(qc,ph,Th) = f(q,ph,Th)
        /// in metres per second (m/s)
        tas = playerPlane.getParameter(part.ParameterTypes.Z_VelocityIAS, -1);

        /// Groundspeed GS = f(TAS,h,Th,We,Wn​,Wu)
        /// in metres per second (m/s)
        gs = playerPlane.getParameter(part.ParameterTypes.Z_VelocityTAS, -1);

        /// Airspeed indicated by the airspeed indicator (ASI)
        /// asi = result kilometer per hour (km/h) or miles per hour mph
        asi = playerPlane.getParameter(part.ParameterTypes.I_VelocityIAS, -1);

        /// Static Pressure at Pressure Altitude
	/// in Pascal [Pa] 
	/// where Pascal [Pa] = Newton per square metre [N/m²]
        Ph = 101325 * Math.Pow(1 - 0.0065 * (ALTz / 288.15), 5.25588);

        /// Compressible Dynamic Pressure qc = f(TAS,Ph,Th)
	/// as the inverse function
	/// in Pascal [Pa] at Pressure Altitude
	/// where Pascal [Pa] = Newton per square metre [N/m²]
	qc = Ph * (Math.Pow(1 + Math.Pow(tas, 2) / (7 * 287.053 * Th), 3.5) - 1 );


        /// Calibrated Airspeed CAS = f(qc)
	/// in metres per second (m/s)
        cas = 340.294 * Math.Sqrt(5 * (Math.Pow(qc / 101325 + 1, 0.28571) - 1 ));

        /// Equivalent Airspeed EAS = f(qc,Ph)
	/// in metres per second (m/s)
        eas = Math.Sqrt(7 * (Ph / 1.225) * (Math.Pow(( qc / Ph + 1 ), 0.2857 ) - 1 ));
    }

Note:
I will provide more detailed explanations in this post as soon as possible. Therefore, I would like to provisionally refer to this post as a 'living' post. Naturally I will focus on the 'speed' of Blitz! and, later in third post Desert-Wings. This will happen in separate posts.
Please stay tuned ...

OFF-TOPIC: Patch 5.047.0 is out now.

Post last updated: Jun-04-2026

[Artist]

In theory you can make a tool ... add new parameter to mission file ...

Don't try to teach your grandma how to crack an egg ...
;-))

But you are having the right ideas.

It just takes time to write all the code dealing with it.

[GANIX]

After the incorporation of Team Fusion Simulations Ltd, 1C: Maddox Games and Team Fusion entered into an agreement granting Team Fusion the exclusive rights to continue the development of Cliffs of Dover. While 1C: Maddox Games was responsible for the original game, Team Fusion Simulations went on to expand and refine the Blitz! Edition, ultimately leading to the release of the Desert Wings [Tobruk] add-on in 2020. Of course, with Desert Wings [Tobruk], Team Fusion introduced an atmospheric model that is more reminiscent of a typical North African day than of conditions over the English Channel

The Desert Wings [Tobruk] v 5.047.0 atmosphere

The following sea-level values for pressure, temperature, and density are assumed for a standard 'DWT' day:

Temperature at sea level on a DWT standard day
T_sl = 300.16 Kelvin

Air density at sea level on a DWT standard day
D_sl = 1.176 [ kg/m³ ] = { 101325 : (287.053 * Tsl) }

Static air pressure at sea level on a DWT standard day
P_sl = 101325 [ Pa ] = { 287.053 * 1.176 * Tsl }

Speed of Sound at sea level on a DWT standard day
a_sl = (1.4 * 287.053 * T_300.16)^0.5 = 347.313

---

For mission builders, the v5.047.0 atmosphere temperature profile, given as a quantity in Kelvin, can be used to establish a relationship between pressure, temperature, density, and lapse rate. Assuming the air is modeled as a dry, perfect gas.

Team Fusion Company (TFC) “Mission Builders Manual v1.0.4” (page 25) recommends a “one size fits all” approach to speed and climb settings when creating waypoints for fighter planes. I will follow this recommendation by creating a Bf109E-4 and defining two waypoints for level flight using recommended 275kmh speed.

Table (3)
The following speeds were obtained on a DWT standard day in a Bf109E-4, with no wind, 
considering the airplane in steady, level (horizontal) flight:

 |  Z,m |   T,k  |TAS=GS | CAS | IAS | EAS |         147300.00 236350.00 ....... 275.00
 |      |        |       |     |     |     |
 | 6000 | 259.34 |  379  | 274 | 264 | 272 | NORMFLY 247300.00 236350.00 6006.55 275.00
 | 5000 | 266.22 |  359  | 274 | 264 | 272 | NORMFLY 247300.00 236350.00 5006.55 275.00
 | 4000 | 273.07 |  341  | 274 | 264 | 273 | NORMFLY 247300.00 236350.00 4006.55 275.00
 | 3000 | 279.87 |  324  | 274 | 265 | 274 | NORMFLY 247300.00 236350.00 3006.55 275.00
 | 2000 | 275.17 |  302  | 274 | 265 | 274 | NORMFLY 247300.00 236350.00 2006.55 275.00
 | 1000 | 293.37 |  293  | 274 | 265 | 274 | NORMFLY 247300.00 236350.00 1006.55 275.00
 |   52 | 299.80 |  280  | 274 | 265 | 274 | NORMFLY 247300.00 236350.00   58.55 275.00
 |      |        |       |     |     |     |
 |      | Kelvin |  kmh  | kmh | kmh |     |


It appears that the AI pilot-in-command maintains approximately 274 km/h CAS ±1 km/h indefinitely.
Compared with conditions over the English Channel, TAS varies significantly with altitude as a function of air density.
Due to the reduced air density, the aircraft must fly at a higher TAS in order to maintain the required CAS.

Observations:

The data in Table 3 appear to support the interpretation that the waypoint speed value of 275 is treated as a CAS target. Across the entire altitude range, CAS remains almost constant at approximately 274 km/h, i.e. within about 1 km/h of the specified value. TAS/GS, by contrast, varies significantly with altitude, increasing from 280 km/h near sea level to 379 km/h at 6000 m. This rules out TAS or GS as the controlled speed quantity.
The cockpit IAS also does not match the specified value, remaining around 264–265 km/h. Therefore, the most consistent interpretation is that the AI controls the aircraft to the specified waypoint speed as CAS, while TAS/GS changes with altitude according to atmospheric density. The most notable result is the deviation of the indicated airspeed (IAS). The data do not strongly support the assumption that IAS is computed from a consistently shifted pressure altitude (see: PART I, equation 6).


Note:
I will provide more detailed explanations in this post as soon as possible. Therefore, I would like to provisionally refer to this post as a 'living' post. Naturally I will focus on the 'speed' of Desert Wings [Tobruk].
Please stay tuned ...

Post last updated: Jun-05-2026