Posts: 1166
Joined: Fri Sep 14, 2001 1:08 pm


Thu Oct 25, 2001 12:32 pm

Is the speedometer in a car the same as groundspeed in an aircraft?
Posts: 11191
Joined: Tue Jun 15, 1999 11:29 am

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.
Posts: 9973
Joined: Mon Apr 23, 2001 10:12 pm

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
Posts: 1646
Joined: Wed Sep 06, 2000 10:30 pm

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
Posts: 2723
Joined: Thu Mar 15, 2001 5:09 am

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"
Posts: 1589
Joined: Tue Nov 09, 1999 6:20 pm

RE: Groundspeed

Fri Oct 26, 2001 5:07 am

In answer to the original question...........YES.  Big thumbs up
09 F9 11 02 9D 74 E3 5B D8 41 56 C5 63 56 88 C0
Posts: 491
Joined: Mon Nov 01, 1999 4:34 pm

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.

Who is online

Users browsing this forum: No registered users and 1 guest

Popular Searches On Airliners.net

Top Photos of Last:   24 Hours  •  48 Hours  •  7 Days  •  30 Days  •  180 Days  •  365 Days  •  All Time

Military Aircraft Every type from fighters to helicopters from air forces around the globe

Classic Airliners Props and jets from the good old days

Flight Decks Views from inside the cockpit

Aircraft Cabins Passenger cabin shots showing seat arrangements as well as cargo aircraft interior

Cargo Aircraft Pictures of great freighter aircraft

Government Aircraft Aircraft flying government officials

Helicopters Our large helicopter section. Both military and civil versions

Blimps / Airships Everything from the Goodyear blimp to the Zeppelin

Night Photos Beautiful shots taken while the sun is below the horizon

Accidents Accident, incident and crash related photos

Air to Air Photos taken by airborne photographers of airborne aircraft

Special Paint Schemes Aircraft painted in beautiful and original liveries

Airport Overviews Airport overviews from the air or ground

Tails and Winglets Tail and Winglet closeups with beautiful airline logos