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Thu Oct 25, 2001 12:32 pm

Is the speedometer in a car the same as groundspeed in an aircraft?
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RE: Groundspeed

Thu Oct 25, 2001 12:49 pm

>>Is the speedometer in a car the same as groundspeed in an aircraft?

If you're asking if the speed measured by the auto speedometer is the same thing as groundspeed in an aircraft, yep, conceptually they're the same.

Autos are pretty straightforward, but the two main factors that influence aircraft groundspeed (GS) are true airspeed (TAS) and wind component (WC). Take a TAS and subtract a headwind (HW) component, and you'll have a lower GS than you would if there was no wind, or if you had a tailwind (TW) helping you along.

ALL views, opinions expressed are mine ONLY and are NOT representative of those shared by Southwest Airlines Co.
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RE: Groundspeed

Fri Oct 26, 2001 3:52 am

Adding to that, TAS is IAS compensated for airpressure (IAS decreases as pressure decreases, TAS remains constant).
I wish I were flying
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RE: Groundspeed

Fri Oct 26, 2001 4:04 am


Calibrated - Indicated corrected for installation errors
Equivalent - Calibrated corrected for compressability
True - Calibrated corrected for Temp (not pressure)
Mr Spaceman
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RE: Groundspeed

Fri Oct 26, 2001 4:33 am

Hi Wardialer.

Just to expand on what OPNLguy said. If you have a true airspeed (TAS) through the air of 300 mph, and the wind is calm, then your speed over the ground (Groundspeed) will also be 300 mph. However, if you're flying with a TAS of 300 mph into a headwind of 50 mph, then your Groundspeed (GS) will only be 250 mph. (thus making your flight take longer). Likewise, if you're flying with a TAS of 300 mph, and you have a tailwind of 50 mph, your GS will be 350 mph. (thus making your flight shorter).

The shorter your flight...the less fuel you burn, plus you arrive sooner! That's why pilots LOVE tailwinds  Big thumbs up and HATE headwinds.  Pissed

Chris  Smile

"Just a minute while I re-invent myself"
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RE: Groundspeed

Fri Oct 26, 2001 5:07 am

In answer to the original question...........YES.  Big thumbs up
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RE: Groundspeed

Fri Oct 26, 2001 8:49 am

Well GS is actually ETAS+Wind Component.

(Effective true airspeed.)

A wind vector relative to an aircraft has 2 components, HW/TW and XW. To fly straight along your track, naturally, you have to correct into wind. Therefore, reducing the forward velocity of the aircraft, the new forward velocity is what we call ETAS. Then when you add your HW or TW, you get your ground speed, basically the same as what everyone has already said and rarely is there much difference. But its there and it phas to be considered.

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