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Thread: Formula for converting True Air Speed to Indicated Air Speed in CloD, and/or . . .

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    Formula for converting True Air Speed to Indicated Air Speed in CloD, and/or . . .

    So in our current campaign server, we are bringing AI aircraft and they are supposed to match speed with/fly along with breather pilots.

    So it's all been going well except I noticed that at high altitudes the aircraft that by ALL INDICATIONS were set to go the same speed as the player's aircraft, were in fact going much, much faster.

    So you can guess the cause of the problem I figured out: When you get an aircraft's current velocity via actor.Vwld() (and thing use the distance formula to convert that into current sped) that is of course, true airspeed. How fast they are moving through space, according to Clod.

    BUT . . . when you set an airwaypoint for an AI aircraft to follow in-game--or as part of a .mis file--the airspeed you enter there is, apparently and sensibly, indicated airspeed.

    So . . . do we know the exact formula CloD is using to convert from true air speed back to the indicated airspeed as shown on the aircraft's dials?

    Or, is there some reliable way to read off the current indicated airspeed for each aircraft, so we can go based on that? When I say "reliable" I mean, something that will work for EVERY aircraft in game, not some hinky thing were you'll have to treat spitfires different from 109s different JU88s different from Beaufighters etc.

    Any thoughts?

    I tried using parameters like this, but none seemed to give me what I really needed. Like the .Z_VelocityTAS and .Z_VelocityIAS values were both the same, when I would expect them to differ by maybe 30% at 6000m altitude.

    Code:
           if (targetAircraft != null) tas = (double)targetAircraft.getParameter(part.ParameterTypes.Z_VelocityTAS, -1);
            if (targetAircraft != null) ias = (double)targetAircraft.getParameter(part.ParameterTypes.Z_VelocityIAS, -1);
            if (targetAircraft != null) mach = (double)targetAircraft.getParameter(part.ParameterTypes.Z_VelocityMach, -1);
    I also tried I_VelocityIAS similarly to above and I don't think I received anything at all there.

    Any thoughts or ideas?

    Can we just use standard TAS/IAS conversion formulas (which . . . sounds super complicated)? Or is there a TAS/IAS converter built into the CLoD code somewhere?

    FWIW I'm using a very simple TAS->IAS approximation formula for now, something like add X% for every 1000m meter altitude gained. It sort of works but it's not the best.
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    Re: Formula for converting True Air Speed to Indicated Air Speed in CloD, and/or . .

    Just use IAS for all calculations?

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    Re: Formula for converting True Air Speed to Indicated Air Speed in CloD, and/or . .

    As anyone who is familiar with or flys vintage aircraft knows, the gauges in the cockpit display indicated airspeed... but the accuracy of the needle is actually off... due to "position error", i.e. the positioning of the pitot, (the pressure gauge which reads speed) on a typical WWII aircraft wing typically means the turbulence in the airflow created by the wing and/or prop causes errors in the pitot reading. To get 'calibrated' airspeed, the pitot would need to be in a turbulence free position... not practical on a combat aircraft.

    The game cannot model all the position error values for all aircraft... simply not possible... many WWII aircraft position error values are not known.

    So the game's gauges model exact IAS for all aircraft without position error... i.e. the player is seeing 'calibrated IAS airspeed'.

    This is good for the mission builders... otherwise they would be going nuts converting airspeed with all the position error values.

    But still, when creating a mission, a Mission Builder has to look up typical cruise/climb speeds for the aircraft type in the mission, (usually given in uncalibrated IAS) then convert to calibrated IAS, (taking into account altitude) and enter that value in the Mission Builder when creating waypoints.

    Probably what we need to do in the game manuals is provide a table of converted indicated airspeed for all the aircraft at various altitudes at both climb or cruise speed.

    So the mission builder can then know what the maximum IAS he should set at a given altitude in cruise/climb and make sure he doesn't enter a IAS value which is higher than what is possible for the aircraft and thus cause problems for the player to keep up with the AI aircraft, as well as problems for the AI trying to match an impossible speed.

    Hopefully we will have time to do this, but can't promise 100% it will be done for release.

    In the meantime, Mission builders recommended course of action is to acquire the recommended cruise/climb speeds from the aircraft manuals, (which although I have all these manuals, I can't post them, because they are copyright and I can't distribute without permission) as well as a conversion utility, (many of which can be found on the internet as for example: https://aerotoolbox.net/airspeed-conversions/ ) and do the work.

    Otherwise the option is just to set the IAS speed and climb rates of the AI aircraft at a low value...


    EDIT RECOMMENDATIONS:


    My 'one size fits all' recommended settings for speeds/climbs when setting speeds and creating waypoints in missions:


    At Altitudes between 0-4000 meters set Speed for waypoints at:


    275 kmh for fighters, Biplane fighters 250 kmh

    220 kmh for bombers


    At altitudes between 0-4000 meters, set Altitude Change time/distance at:


    For 1000 meters increase in altitude, set 2 minutes between waypoints for fighters (equivalent 8.35 ms climb)

    For 1000 meters increase in altitude set 4 minute between waypoints for bombers (equivalent 4.175 ms climb)


    At Altitudes over 4000 meters set Speed for waypoints at:


    250 kmh for fighters, Biplane fighters 225 kmh

    200 kmh for bombers


    At altitudes over 4000 meters, set Climb/Altitude Change at:


    For 1000 meters increase in altitude, set 4 minute waypoints for fighters (equivalent 4.175 ms climb)

    For 1000 meters increase in altitude set 8 minute waypoints for bombers (equivalent 2.0875 ms climb)


    These settings should allow the players to keep up with the AI as well as allowing the AI to climb normally with achievable performance. Speeds in level flight should allow accurate bombing.



    Quote Originally Posted by TWC_Flug View Post
    So in our current campaign server, we are bringing AI aircraft and they are supposed to match speed with/fly along with breather pilots.

    So it's all been going well except I noticed that at high altitudes the aircraft that by ALL INDICATIONS were set to go the same speed as the player's aircraft, were in fact going much, much faster.

    So you can guess the cause of the problem I figured out: When you get an aircraft's current velocity via actor.Vwld() (and thing use the distance formula to convert that into current sped) that is of course, true airspeed. How fast they are moving through space, according to Clod.

    BUT . . . when you set an airwaypoint for an AI aircraft to follow in-game--or as part of a .mis file--the airspeed you enter there is, apparently and sensibly, indicated airspeed.

    So . . . do we know the exact formula CloD is using to convert from true air speed back to the indicated airspeed as shown on the aircraft's dials?

    Or, is there some reliable way to read off the current indicated airspeed for each aircraft, so we can go based on that? When I say "reliable" I mean, something that will work for EVERY aircraft in game, not some hinky thing were you'll have to treat spitfires different from 109s different JU88s different from Beaufighters etc.

    Any thoughts?

    I tried using parameters like this, but none seemed to give me what I really needed. Like the .Z_VelocityTAS and .Z_VelocityIAS values were both the same, when I would expect them to differ by maybe 30% at 6000m altitude.

    Code:
           if (targetAircraft != null) tas = (double)targetAircraft.getParameter(part.ParameterTypes.Z_VelocityTAS, -1);
            if (targetAircraft != null) ias = (double)targetAircraft.getParameter(part.ParameterTypes.Z_VelocityIAS, -1);
            if (targetAircraft != null) mach = (double)targetAircraft.getParameter(part.ParameterTypes.Z_VelocityMach, -1);
    I also tried I_VelocityIAS similarly to above and I don't think I received anything at all there.

    Any thoughts or ideas?

    Can we just use standard TAS/IAS conversion formulas (which . . . sounds super complicated)? Or is there a TAS/IAS converter built into the CLoD code somewhere?

    FWIW I'm using a very simple TAS->IAS approximation formula for now, something like add X% for every 1000m meter altitude gained. It sort of works but it's not the best.
    Last edited by RAF74_Buzzsaw; Feb-22-2020 at 17:20.

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    Re: Formula for converting True Air Speed to Indicated Air Speed in CloD, and/or . .

    Quote Originally Posted by RAF74_Buzzsaw View Post
    ... then convert to IAS, (taking into account altitude) ...
    ... and external temperature? Or is it not modeled?
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    Re: Formula for converting True Air Speed to Indicated Air Speed in CloD, and/or . .

    Removed. Reply not applicable to mission building.
    Last edited by Baffin; Feb-21-2020 at 13:17.
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    Re: Formula for converting True Air Speed to Indicated Air Speed in CloD, and/or . .

    Yes it is modeled in the game... that is another factor you have to consider.

    Quote Originally Posted by ATAG_Noofy View Post
    ... and external temperature? Or is it not modeled?

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    Re: Formula for converting True Air Speed to Indicated Air Speed in CloD, and/or . .

    Have edited my recommended speeds/altitude change for AI aircraft in FMB... see above.

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    Re: Formula for converting True Air Speed to Indicated Air Speed in CloD, and/or . .

    Quote Originally Posted by RAF74_Buzzsaw View Post
    As anyone who is familiar with or flys vintage aircraft knows, the gauges in the cockpit display indicated airs
    Thanks, Buzzsaw - that was an incredibly helpful post.
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    Re: Formula for converting True Air Speed to Indicated Air Speed in CloD, and/or . .

    "Formula for converting True Air Speed to Indicated Air Speed in CloD"

    I hope that this title is a joke!

    True airspeed is the RELATIVE speed to the airmass in which the aircraft is flying. I don't know any "reliable" scientific document discussing a formula for converting TAS to IAS.

    ~V~

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    Re: Formula for converting True Air Speed to Indicated Air Speed in CloD, and/or . .

    Quote Originally Posted by varrattu View Post
    "Formula for converting True Air Speed to Indicated Air Speed in CloD"

    I hope that this title is a joke!

    True airspeed is the RELATIVE speed to the airmass in which the aircraft is flying. I don't know any "reliable" scientific document discussing a formula for converting TAS to IAS.

    ~V~
    Usually the Airspeed Indicators have an inbuilt converter (see picture below).

    You would turn the knob (1) until the external temperature matches your altitude (2).
    This would also turn the white quadrant at the bottom left of the dial. The speed in the black part of the dial is the IAS (or indicated airspeed), and the speed in the white quadrant is the corresponding TAS (or true airspeed).

    In this example (2) the external temp is -10 C and the altitude is 9500 ft.
    In (3) you read the IAS = 175 M.P.H. and the TAS = 202 M.P.H.

    2020-02-23_203908.jpg
    Last edited by ATAG_Noofy; Feb-23-2020 at 14:04.
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    Formula for converting True Air Speed to Indicated Air Speed

    Deleted by GANIX.
    Last edited by GANIX; Apr-12-2023 at 05:40.

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    Re: Formula for converting True Air Speed to Indicated Air Speed in CloD, and/or . .

    To find TAS you add 3% to IAS for every 500 meters of indicated altitude. This approximation is precise within a few percentage points (at our altitudes in the sim).

    TAS = IAS x ( 1 + (0.03 x indicated altitude/500) )

    Example: you fly at 5000m and your IAS is 300km/h, so your TAS = 300 x (1 + 0.03 x 5000/500) = 300 x 1.3 = 390 km/h

    Therefore

    IAS = TAS / ( 1 + (0.03 x indicated altitude/500) )

    I use this in the sim and can confirm that you can hit any fuel storage from 5000m using this formula
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    Re: Formula for converting True Air Speed to Indicated Air Speed in CloD, and/or . .

    Quote Originally Posted by ATAG_Noofy View Post

    I use this in the sim and can confirm that you can hit any fuel storage from 5000m using this formula
    Oh no! Not again!
    I'm still gonna spend all night long repairing our facilities
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    Re: Formula for converting True Air Speed to Indicated Air Speed in CloD, and/or . .

    Quote Originally Posted by Sleepy_Fly View Post
    Oh no! Not again!
    I'm still gonna spend all night long repairing our facilities
    Relax, the server is down tonight…
    Besides, at 5% fuel supply, it will take you more than one all night long to repair…
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    Re: Formula for converting True Air Speed to Indicated Air Speed in CloD, and/or . .

    Quote Originally Posted by ATAG_Noofy View Post
    Example: you fly at 5000m and your IAS is 300km/h, so your TAS = 300 x (1 + 0.03 x 5000/500) = 300 x 1.3 = 390 km/h
    But my Blenheim fly in feet's and MPH...

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    Re: Formula for converting True Air Speed to Indicated Air Speed in CloD, and/or . .

    Quote Originally Posted by 1lokos View Post
    But my Blenheim fly in feet's and MPH...
    The rule of thumb then is to add ~1.5-2% per 1000ft… (1.66% works fine with me)

    If you fly at 16000 ft with a IAS of 180 mph, then your approx. TAS = 180 x (1 + 16 x 1.66%) = 180 x 1.266 = 228 mph
    Last edited by ATAG_Noofy; Oct-18-2022 at 02:14.
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    Re: Formula for converting True Air Speed to Indicated Air Speed in CloD, and/or . .

    Deleted by GANIX.
    Last edited by GANIX; Apr-12-2023 at 05:39.

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