Friday Update, February 10, 2012

[Robo.]

Originally Posted by Varrattu

By the way: the BF109E-iL2CoD is fitted with a 1200 PS machine.

True, we've got the Aa version in game.

British document states following numbers (quoted as German sources) - mph at SL:

Bf109 283 (465kph)
Hurricane I 246
Hurricane II 268
Spitfire I 282

Not sure how accurate and helpful they are as no information about engine version / MFP and rpm is provided other than corrected BHP at FT height which is 950 for the 601, 965 for Merlin III and 1075 for Merlin XX.

Sounds about right for A-1 at SL, 1.35ata at 2400 rpm though.

[Talisman]

Originally Posted by Robo.

True, we've got the Aa version in game.

British document states following numbers (quoted as German sources) - mph at SL:

Bf109 283 (465kph)
Hurricane I 246
Hurricane II 268
Spitfire I 282

Not sure how accurate and helpful they are as no information about engine version / MFP and rpm is provided other than corrected BHP at FT height which is 950 for the 601, 965 for Merlin III and 1075 for Merlin XX.

Sounds about right for A-1 at SL, 1.35ata at 2400 rpm though.

Robo,

I am no expert, so please go easy with me as I try to clear the fog in my head over all this, but I assume that the above speeds for the Hurricane and Spitfire would be increased at low level with operation of the emergency boost cut-out with 100 Octane fuel (by approx 30 mph)? Or have I got the wrong end of the stick?

Happy landings,

Talisman

[Richie]

How many Kms slower is a 109 speedometer at sea level than actual true airspeed?

[Varrattu]

Originally Posted by Richie

How many Kms slower is a 109 speedometer at sea level than actual true airspeed?

It depends on ...

True airspeed, or TAS, is a measure of the physical speed of the aircraft in relation to the air around it. Just as differences in wind velocity affect groundspeed, differences in air density affect true airspeed. At the same engine power setting, e.g., 75 percent power, an airplane can move faster through air that is less dense. That’s why higher altitudes can
translate to higher true airspeeds.
Like aircraft groundspeed, TAS cannot be measured directly. Rather, the pilot uses outside air temperature (OAT), pressure altitude, and calibrated airspeed CAS to calculate
this value.

Regards Varrattu

[Insuber]

Originally Posted by Varrattu

It depends on ...

True airspeed, or TAS, is a measure of the physical speed of the aircraft in relation to the air around it. Just as differences in wind velocity affect groundspeed, differences in air density affect true airspeed. At the same engine power setting, e.g., 75 percent power, an airplane can move faster through air that is less dense. That’s why higher altitudes can
translate to higher true airspeeds.
Like aircraft groundspeed, TAS cannot be measured directly. Rather, the pilot uses outside air temperature (OAT), pressure altitude, and calibrated airspeed CAS to calculate
this value.

Regards Varrattu

You are right about actual T/P vs. standard atmosphere influencing the speed of the plane. As you will know however the eventual decrease in resistance due to lower air density affects not only the plane drag, but also the engine performance and the measure of the pitot tube. For the pitot tube, the ASI will indicate a lower speed than TAS for density lower than the standard atmosphere … in practice, the IAS reported by the ASI during tests must always be corrected for non-standard atmospheric conditions.

Cheers.

[Insuber]

To have some (nerd's) fun:

http://www.luizmonteiro.com/Altimetry.aspx#TrueAirspeed

Cheers,
Ins

[klem]

Originally Posted by Richie

How many Kms slower is a 109 speedometer at sea level than actual true airspeed?

On a 'standard day' they should be virtually identical providing the CoD ASI is actually showing the 'Calibrated' airspeed. Calibrated airspeed is the airspeed that an ASI usually shows corrected for errors caused by the position of the sensor or pitot tube but I don't know if position error is modelled in CoD. If you want a headache see:-
http://www.tscm.com/mach-as.pdf

The complexities gather......

Assume its a standard day and the ASI reading = 'calibrated' = True Airspeed at sea level. You'll lose less sleep.

Anyone know what kind of day we have in CoD?