ROTFL :D :D. Precious!
There you go. That's where your problem is.
I suspected that. That's hy you were arguing so vehemently, bringing up issues that I did not talk about and that are irrelevant. For future, please be clear about fundamental variables pertinent to the phenomenon behind the technology. A good understanding of some simple high school physics helps too.
If you think what you typed above, I can only express my profound frustration for it's no crime to be ignorant, however irritating it might be to us.
For an aircraft, what's relevant is the airspeed, that ois speed of the aircraft relative o the air. Passengers are interested in the ground speed, speed of the aircraft relative to ground, or to any other object fixed relative to ground, or in the same inertial frame as the earth. If air speed of the aircraft is 500 m.p.h., it's ground speed will be 600.m.p. in tail winds of 100 m.p.h. and 400 m.p.h. in head winds of the same speed. NOw think about what you claimed about there being no diffeence between ground speed and air speed. What you siad makes absolutely no sense. :td:

The GPS doesn't know whether wind is pushing or engine is pushing sir. It just know one speed sir.

Referenced to you earlier comment, what needs to be calibrated sir?

Did I say that GPS does or does not know about the wind?
FT God, give me patience!
I'll try one more time.

When you say your GPS tells you the speed f the aircraft is =, let's say, 500 miles an hour, what speed do you think that is?

If you still maintain that there is no difference between ground speed and air speed, please stop wasting my time. Go look at your physics book, ask some one, look up on the internet and educate yourself before you start arguing.

You need wind speed to calculate airspeed from the ground speed or vice versa.

Thank you for explaining. Now I understand fully what you meant and shall not waste anymore of your time.

Phew!. I am glad you understand.

OK?
 

As an uninformed observer of this discussion I pose this question to the FT's:

Airspeed = Groundspeed + Windspeed.

Or is this too much of a simplification?
And, if the above is true, obviously GPS can't record airspeed?:confused:

As I have stated above, airspeed is same as ground speed for our purposes. Of course some aircraft such as high performance fighters can go vertical. In that case ground speed is almost zero. For our practical purposes during cruising, the airplane is traveling mostly horizontal, thus airspeed is same as ground speed.

The aircraft is designed to fly at certain speed, let's say, 567MPH for a 747-400. If it encounter 200MPH tailwind over Japan, then its speed would be 767MPH.

There is a definition for True Airspeed (TAS, Vt=Vg-Vw). This is speed of the aircraft in relation to the air surrounding it. In the above example of the 747-400, maximum would be 567MPH. This is selected by the pilot in consideration to fuel economy, time schedule etc. GPS receiver cannot measure it, there are no in-device calibration for it, and it is irrelevant to what most people are interested. This is what the other poster is referring.

You got the sign wrong.

It's Ground speed= airspeed + wind speed. That has been so and always be, although Galileo Galilei, was the first to put it down. Strictly speaking, Lorentz Transformations relate velocities of an object in different inertial frames. But at low speeds, like that of an aircraft (even supersonic aircraft) and winds, Galilean transformation are sufficiently accurate.

You are absolutely correct that GPS, that records (measures) position of an object gives the ground speed, which when used with other data, can give us air speed. There is not dearth of uninformed people, who do not understand simple arithmetic. :D

You're still not getting it.

Airspeed = how fast an object is travelling in relation to the air surrounding it.
Groundspeed = how fast an object is travelling in relation to the ground.

These can only differ from eachother if the air is moving in relation to the groud, in other words there is wind.

What you described as true air speed is what airspeed is. True airspeed is a term used to distinguish it from e.g. indicated airspeed, which is basically what the gauge it the cockpit is telling the pilot (and which differs from true airspeed mainly due to air pressure). However, I really don't want to go into that, as long as you can grasp the difference between airspeed and groundspeed.

A jet travelling with an airspeed of 500mph in a tailwind of 100mph has a ground speed of 600mph and in a headwind of 100mph the groundspeed is 400 mph . And this definately does make a difference for our purposes as it makes hours of difference in the travel time on a long haul flight.

The direction of travel makes no difference, so a fighter diving directly towars the earth at 500 mph still has a ground speed of 500 mph, because it has a speed of 500 mph in relation to the ground, just as a plane on level cruising of 500 mph has. The fighter just has more vertical speed.
or..
If you're standing in your backyard in a 30 mph wind, you have an airspeed of 30 mph, and a ground speed of 0 mph.

That's great:
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mkgrip

Join Date: Apr 2009
Posts: 1
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More in disguise.

What are you trying to say?
The number of posts has nothing to do with whether you know what you are talking about. You don't get the simple concept of ground speed air speed and the wind speed. Not only do you not under stand it, you refuse to learn when it is explained to you. There are that describe such attitude, but I shall not use them. :D

You mean worse than these? You can save them for yourself then.

The ones I used are acceptable. ;)

Back to GPS...What type of battery were you using? I used Energizer Lithium batteries in my Etrex Vista HCx and it lasted from DFW-ORD-FCO and for two days on the tour bus after that (with compass off). I would say that I got 32+hrs out of them. And the batteries are lightweight and resistant to cold!

In my eTrex Venture Cx, I use regular AA. It will last the whole trip to NRT, TPE, HKG, PVG, KLA or SIN with some on the ground use.

The FRA-SFO track I posted above was taken with an older Garmin eMap. It also use AA. The proprietary memory card has only about 128MB capacity. I left this unit in taxi's etc several times but was able to get it back. On that FRA-SFO trip, I had an exit row seat and placed it in plain view on the door window. FAs and passengers came and went and never said a thing the whole trip. Some took a look with interest.

While traveling in the U.S., I take a Garmin Quest. This unit has internal lithium rechargeable and I bring a car cradle. On the plane, it has a battery life of about 20 hours. This unit has non-removable internal memory of about 110MB.