Airspeed Indicators

[Pips]

I find that as I fly FSX more and more, I try to make it as real a possible. No HUD's, no GPS; just flight maps, the Mark One eyeball and the instruments on the panel of the aircraft I'm flying .

Which are invariably almost always pre-1945 era, if not positively Vintage. :) And one of the toughest things I having to come to grips with is using the Airspeed Indicator as a navigational tool.

Aircraft of that era were equipped with an airspeed dial that measured Indicated Airspeed ie air density, not airspeed over the ground. Indicated airspeed is crucial for a pilot to know, to ensure he stays within the boundaries of the aircraft's performance eg stall speeds, airframe limits etc. But at anything other than sea level they are no indication of his true through the air speed ie TAS. And it's TAS that the pilot needs to know to determine how fast he is travelling and how far he has come. Admittedly it won't tell him wind speed or direction, that he has to get from weather reports before he takes off. And then rely on said Mark One eyeball.

So a couple of questions.
* IAS is as old as flight itself. But when was TAS first understood/discovered and how was it quantitified?
* Once known, how did pilots determine their TAS? Was/is there a rule of thumb? No computers in those days.
* Why wasn't an airspeed indicator developed that measured True Airspeed?
* And finally are aircraft - GA or otherwise - equipped with such now?

[paulb]

You might find the information here of interest -

http://aafcollection.info/items/detail.php?key=198&pkg=ls!title!!198!1!title!up!20

Cheers

Paul

[normb]

Wow! What a great link to those old documents. Thanks!

Indicated Airspeed is still what the pilot sees. Based on altitude and temperature the TAS can be estimated. Add 2% of IAS per thousand feet altitude for TAS. Then use time/speed distance over terrain to estimate winds ( or reliable winds aloft forcasts, if avialable.) That's where the old reliable E6B computers (circular slide rules) came into play.

Now adays the fancy air data computers and nav gear provide all that info.

[Brett_Henderson]

For aircraft that normally cruise below 10,000msl, and are not capable of IAS much above 150kts.. the 2%/1000ft works well enough for planning. After all.. forecast winds aloft are never dead-on as far as direction and velocity.

Enroute, you can obviously monitor your overall/average groundspeed by elpased time between known checkpoints... and with a little experience, you can interpolate (to a useful, albeit rough degree) the actual wind direction and strength, by the your calculated ground-speed, and the heading you've had to hold.

VORs (sans DME)can be used too, for 'tricky' ground-speed and wind calculations. Like.. if you're tracking a radial inbound; you can select a radial X degrees either side of the one you're tracking, and then change heading the same X degrees, and time how long it takes to 're-center' the OBS.. On long legs you can do tat both sides of your original radial, and by geometry, come up with all sorts of info ..

[Pips]

Cheers guys.

So I gather then that airmen back in the 1930's knew of and used the 2% rule? Great, that's fine. So when was TAS discovered? And anyone know by who or which organisation?