Aces High Bulletin Board

General Forums => Aircraft and Vehicles => Topic started by: Flyboy on August 01, 2003, 01:19:16 AM

Title: true air speed
Post by: Flyboy on August 01, 2003, 01:19:16 AM

how does the true air speed (TAS) is calculated?

and did ww2 planes had a TAS indeecator?

Title: true air speed
Post by: LLv34_Snefens on August 01, 2003, 05:46:02 AM

An approximation could be:

TAS = IAS + (Alt[Kft] * IAS/50)

So IAS of 400 mph at an alt of 15000 ft gives an approx TAS of 520.

An accurate equation that takes in account both temperature and pressure would be more complex.

No, WWII-planes didn't have a TAS indicator

Title: TAS
Post by: gwshaw on August 01, 2003, 08:03:13 AM

I use 1/sqrt(density ratio) * IAS

That will be fairly close, but it doesn't take into account position or compressibility errors.

You have to get the density ratio from a standard atmosphere chart. There is an excellent one at:

http://www.aeromech.usyd.edu.au/aero/atmos/atmtab.html

Note: That is a 1976 standard atmosphere and might be slightly different from whatever was being used by various countries in the 30's and 40's.

Greg Shaw

Title: true air speed
Post by: Toad on August 01, 2003, 08:47:46 AM

AH has a TAS indicator (the red mini-line) because back at the beginning there were a few vocal players that didn't understand the difference between TAS and IAS and were forever claiming that their planes were modeled "too slow".

HT just got tired of listening to it and put in the TAS indicator.

IIRC.

Title: Re: true air speed
Post by: HoHun on August 01, 2003, 01:34:52 PM

Hi Flyboy,

>and did ww2 planes had a TAS indeecator?

It was very unusual, but some WW2 planes did have one.

At the German Museum at Munich, I just saw a Messerschmitt Me 262 speed indicator on display that indicated IAS for low speeds and TAS for high speeds. (The dial had two sections with two hands.)

I don't think it was meant for navigational purposes, though - which is what TAS is usually good for - but rather to help the pilot to stay clear of the Mach limit of the jet.

They could have used a Mach indicator for that, which was available WW2 technology, but I guess it's value hadn't been recognized yet, and it was only used for prototypes and test aircraft.

Regards,

Henning (HoHun)