Definition of ground speed
Joined: Sep 1998
Posts: 1,615
Likes: 1
From: wherever
Ground speed. The speed of an aircraft relative to the surface of the earth.
This is from ICAO doc 9426 AIR TRAFFIC SERVICES PLANNING MANUAL PART V TERMS AND REFERENCES.
I think it's pretty clear isn't it?
This is from ICAO doc 9426 AIR TRAFFIC SERVICES PLANNING MANUAL PART V TERMS AND REFERENCES.
I think it's pretty clear isn't it?
Joined: May 2005
Posts: 1,170
Likes: 0
From: Abroad
I think it's pretty clear isn't it?
Kudos to the OP for posting what must be the most interesting question I've read here so far this year. Although aware of it, I'd never consciously thought about it.
Joined: Jul 2001
Posts: 4,960
Likes: 17
From: Australia
Folks,
What we have here is a clash of "Airplane Navigation of Dummies" and something a bit nearer to an engineering solution.
For the average pilot, the simplest definition is all that is required, a bit like the simplistic diagrams we use to illustrate the "forces" acting on an aircraft in cruise, climb and descent ( thrust, drag, lift and the CAA) --- but for an engineer it is not "that simple".
Try arguing with an engineer for an airframe or (particularly) an engine manufacturer about in-flight performance analysis versus contract guarantees --- right down to latitude and Coriolis effect --- that's really getting into the fine print.
Tootle pip!!
What we have here is a clash of "Airplane Navigation of Dummies" and something a bit nearer to an engineering solution.
For the average pilot, the simplest definition is all that is required, a bit like the simplistic diagrams we use to illustrate the "forces" acting on an aircraft in cruise, climb and descent ( thrust, drag, lift and the CAA) --- but for an engineer it is not "that simple".
Try arguing with an engineer for an airframe or (particularly) an engine manufacturer about in-flight performance analysis versus contract guarantees --- right down to latitude and Coriolis effect --- that's really getting into the fine print.
Tootle pip!!
Joined: May 2003
Posts: 412
Likes: 0
Another general situation that may affect the answer is whether the "distance" an aircraft travels **according to its flight plan** is dependent on the altitude of the aircraft. Consider 2 aircraft on long range great circle tracks, zero wind, one at 3000 feet and one at FL450, both to the same destination. Will the flight plan distances be different?
Joined: Sep 2000
Posts: 965
Likes: 110
From: Bielefeld, Germany
ATCast asked for an official definition of groundspeed. Genghis the Engineer thought it is horizontal component of absolute velocity but could not pin a reference.
Pugilistic Animus thinks the two definitions are equivalent. Wizofoz thinks it is not the "horizontal component of absolute velocity" because "absolute velocity" is not defined, although I understood perfectly well what ATCast was asking, as did Genghis.
Tmbstory thinks it is "speed over the ground", and Checkboard "speed over that surface", so FEHoppy "speed relative to the surface of the earth". None of these contributors seem to have picked up that their "definitions" are ambiguous in just the way ATCast explained.
BOAC sees the difference, I think, but considers the discussion "twaddle".
I did what ATCast wanted. I looked it up in Kayton and Fried, Avionics Navigation Systems, 2nd edition, Wiley-Interscience 1997, otherwise known as The Book, when I had the chance.
Ground speed is the horizontal (i.e. tangential to the reference ellipsoid) component of the resultant vector of the air-velocity vector with the wind velocity vector (Figure 2.4, p30, notation Vg). Genghis is right.
As for PA, we may take it he doesn't build inertial nav instruments for a living. Serious nav takes altitude into account, for reasons which I hope I indicated in my earlier post.
PBL
Pugilistic Animus thinks the two definitions are equivalent. Wizofoz thinks it is not the "horizontal component of absolute velocity" because "absolute velocity" is not defined, although I understood perfectly well what ATCast was asking, as did Genghis.
Tmbstory thinks it is "speed over the ground", and Checkboard "speed over that surface", so FEHoppy "speed relative to the surface of the earth". None of these contributors seem to have picked up that their "definitions" are ambiguous in just the way ATCast explained.
BOAC sees the difference, I think, but considers the discussion "twaddle".
I did what ATCast wanted. I looked it up in Kayton and Fried, Avionics Navigation Systems, 2nd edition, Wiley-Interscience 1997, otherwise known as The Book, when I had the chance.
Ground speed is the horizontal (i.e. tangential to the reference ellipsoid) component of the resultant vector of the air-velocity vector with the wind velocity vector (Figure 2.4, p30, notation Vg). Genghis is right.
As for PA, we may take it he doesn't build inertial nav instruments for a living. Serious nav takes altitude into account, for reasons which I hope I indicated in my earlier post.
PBL
Joined: Mar 2000
Posts: 100
Likes: 1
From: Oakland CA USA
"Ground speed. The speed of an aircraft relative to the surface of the earth."
An aircraft that's diving vertically at 500 knots clearly has a speed of 500 knots "relative to the surface of the earth". Is its ground speed 500 knots?
An aircraft that's diving vertically at 500 knots clearly has a speed of 500 knots "relative to the surface of the earth". Is its ground speed 500 knots?
Joined: Jun 2006
Posts: 1,306
Likes: 0
From: Canada
Tim, his ground speed will be about zero, {just watch your GPS next time you are doing aeros} I said about zero so as to avoid those who will find that it wont be quite zero due to many obscure factors, none of which amount to a hill of beans, however if he doesnt pull out it will indeed be zero!
Joined: May 2005
Posts: 1,170
Likes: 0
From: Abroad
Ground speed is the horizontal (i.e. tangential to the reference ellipsoid) component
Joined: Sep 2000
Posts: 965
Likes: 110
From: Bielefeld, Germany
Originally Posted by LH2
Wouldn't that be "perpendicular to the local vertical" or equivalently, "perpendicular to the local gradient of the gravity field"? Is the parenthesised phrase part of the quote from the book, or is that yours?
No, it's not a quote from the book, it is my words saying what Figure 2.4 shows as a vector diagram (triangle with arrows and labels).
PBL
Joined: Jun 2010
Posts: 26
Likes: 0
From: United Kindom
PBL, I agreeI would like to take this chance to say I am not a troll, I do not intend to cause trouble and everybody has pounced on me since I posted my first message, I am a freal pilot and I would like to enjoy my time on here without some of you getting at me