True Air Speed?

[LeeHarvey]

Is the air speed as indicated by the instruments in the cockpit, and that of the HUD panel, the true air speed of the plane? I ask because all of the references I have found for the Spitfire Mk.IX say that the level flight max true air speed of the plane was 403-404 mph @ 20-21,000 ft. In game, I can't even get it to 300 mph at that altitude as indicated by my instruments.

 

[busdriver]

The airspeed indicator shows "indicated" airspeed, not true airspeed. The iterations you progress through are Indicated>>>Calibrated>>>Equivalent>>>True. In USAF pilot training this was referred to as the ICE-T problem.

[Talon_]

The panel and hud is indicated airspeed.

[-=PHX=-SuperEtendard]

Yep, they show both indicated air speed. You will need to do the conversion to TAS.

If you were flying in an autumn map, the true air speed would be roughly 400 mph (394)

Edited August 6, 2018 by -=PHX=-SuperEtendard

[LeeHarvey]

Yes I was flying the Stalingrad Autumn map.

 

I have found a really good collection of reference documents, Spitfire Mk IX Performance Testing. According to these reports, the performance of the Mk.IX in the game is actually more similar (it's almost spot on) to the Merlin 61 Spitfire LF.Mk.IX than the Merlin 66.  

Edited August 6, 2018 by LeeHarvey

[303_Bies]

I have checked.

According documents you have shown:

Spitfire LF Mk. IX(e), Merlin 66, +18.0 lb/sq.in. boost

 

Speed at sea level:

Documents: 336 m.p.h. = 541 km/h

IL2:BoBP                          = 542 km/h (about 545 with clipped wings)

 

Climb at sea level:

Documents: (+18.0 lb/sq.in. boost) 4620 ft/min = 23,5 m/s

IL2:BoBP (  +12.0 lb/sq.in. boost  )                        = 21,5 m/s

 

Looks like it matches perfectly the Spitfire LF Mk. IX(e) with Merlin 66.

BTW. Do you really think the devs which are doing so detailed research would make such a huge and simple mistake?

Edited August 7, 2018 by bies

[CrazyDuck]

At 20.000 ft the following roughly holds: TAS = IAS + 36%.

 

400 mph = 300 mph + 36 %, so I guess you are doing just fine.

 

Remember that this correction isn't linear with altitude, but squared. For the simmers rule of thumb estimation, this table is more than enough:

 

[Bremspropeller]

CD - just out of curiosity - does this table state at which IAS this conversion is made?

The step CAS => EAS takes care of compressibility correction, which is of course a function of your velocity.

[unreasonable]

On 8/7/2018 at 6:08 AM, busdriver said:

The airspeed indicator shows "indicated" airspeed, not true airspeed. The iterations you progress through are Indicated>>>Calibrated>>>Equivalent>>>True. In USAF pilot training this was referred to as the ICE-T problem.

 

Right, but in BoX there is no instrument error or compressibility so Indicated = Equivalent,  so it is just the "IT problem".

 

+2% per 1,000ft of altitude is what I use to get close enough if you have to do work it out in your head while flying, for navigation purposes.  That may not have been accurate enough for your military use, but it is quite enough for me to worry about while I try to work out where I am on the Moscow Map with 8/10 cloud cover with a strong wind blowing!

 

 

[CrazyDuck]

3 hours ago, Bremspropeller said:

CD - just out of curiosity - does this table state at which IAS this conversion is made?

The step CAS => EAS takes care of compressibility correction, which is of course a function of your velocity.

 

No Brems, this is a simple rule of thumb for general speed ranges. I find its compromise between accuracy and simplicity (easy to memorize or calculate in your head) very good. Added correction factors are all squares if you look closely.

 

Also not that far off from what unreasonable described (2% for each 1000 ft).

[busdriver]

You put more effort and brain bytes into that than me.  I simply fly an indicated airspeed that's a multiple of 60 to give me a warm fuzzy sensation (close enough for government work).

 

[For background to folks new around here: Assume your ground speed is approximately your indicated airspeed. Divide that number by 60 to give you the number of units (km if German/Italian/Russian or statute miles for British/American) you will fly in one minute. The equation is Distance = Rate x Time. If you know the distance in km, divide that by your rate in km per hour to find how long it will take you to arrive at your turn point or target.  You do this instinctively already. If you're driving along a highway/autobahn/autostrasse at 120 km/h you know you will travel 2 km every minute. Flying at speeds that are a multiple of 60 makes the math a piece of cake.]

 

In SP I follow my flight lead, in MP just look for the tracers.