I have a puzzling question.

[TacitBlue]

And the reason that the GPS and the Air Speed Indicator are different is that the GPS displays your speed in relation to the ground. The ASI displays your speed in relation to the air around your aircraft. Both instruments measure speed in Knots, or Nauticle Miles Per Hour.

[Papa9571]

Now that we have defined KIAS and ground speed I have a question.

What is KEAS?

[TacitBlue]

After much google-ing I found that KEAS stands for Knots Equivalent Air Speed. I have no idea what it means exactly, equivalent to what, I don't know. Also, in the course of this search I found a helpful dicionary of aeronautical terms - KEAS wastn't in it - but lots of other stuff is.http://www.aeroplanemonthly.com/glossary/glossary_A.htm

[TSC.]

"...Knots Equivalent AirSpeed. ..."

That is factoring in the thinner air at altitude. The vehicle may be actually moving at Mach 2 (for example), but it is feeling pressures equal to only a few hundred mph in a standard atmosphere lower down.

PS: Thats a really handy glossary on that site Tacit, here's another one that is similar:

http://www.airodyssey.net/reference/glossary.html

Cheers,

TSC.

[Papa9571]

I found this definition after a lot of searching


For the non-pilot readers, KEAS is Knots Equivalent Airspeed. Knots are Nautical Miles per Hour in pilotese. To place this in perspective, my old Cessna 172, (N3892S circa 1981), was quite happy cruising along at 120 KIAS, or 120 Knots Indicated Airspeed. Airspeed is how fast the wind is going past your wings. If you were in a 120 Knot headwind, you could be flying 120 KIAS and sitting over someone's head like you were the ball on top of a flagpole. Indicated means it is what you read off the dial in the cockpit; Equivalent means that the air over your wings has the equivalent effect after accounting for speed and density of the air.

[Calb]

Interesting discussion, especially the past few posts about KEAS.

For the interest of the original poster, I dug out my trusty E6B (Dalton) Computer (it's essentially an aviation specific circular sliderule) and plugged in some values.

In order to calulate TAS (True Air Speed), you need 3 things -- pressure (indicated) altitude, OAT (Outside Air Tempterature) and IAS.

In this example, I plugged in -15C at 25,000 ft. At 300 KIAS, the TAS is 468 Kts which is equivalent to 540 MPH or 864 Km/h. When I plug in -30C at 30,000 ft, 300 KIAS is 507 Kts.

As you can see, both altitude and temperature affect TAS. Now you know why airliners have OATs -- in case you've ever wondered.

Cal (CYXX)

[AK_Airborne]

While this subject has been pretty well discussed in this thread, I'll go ahead and throw in my 2 cents on all these airspeed issues to help make some sense of it.

-KIAS-
First of all, what you read on your airspeed indicator is KIAS or (Knots Indicated Airspeed).

[A/SGT.Mav316]

The original poster is being overwhelmed with information! Thank you for all your input guys, I have a good understanding of everything now.

Again thank you for all your input. I am obviously just an enthusiasts and not a real pilot. I just enjoy the sensation of flight. I grew up creating make beleive simulators out of my bed (since I was a kid) and when I discovered Flight Simulator I put away the model plane kits and took up the hobby of imagination of flight on my pc. But I am sure when I finally do decide to go to a flight school they are going to cram all this stuff into my cranium