Use GPS on plane?
 

Is it possible to use a GPS device on a plane? Will it be able to receive a signal through the fuselage?
Thinking about trying it out to follow the route with my Blackberry Curve on a next flight.

Someone can correct me if I am wrong, but I seem to recall a flight attendant in the front of the plane once say that certain devices that send or recieve signal were prohibited during flight.

Rules vary by airline. Here's a web page with a compiled list: http://gpsinformation.net/airgps/airgps.htm.

Even where GPS use is permitted, it will be fairly useless from a Blackberry. You're not supposed to have the cellphone connection on in flight so you won't download any map data to actually show your location. You may get your coordinates but no visual representation.

I tried it one time, and had the FA tell me to shut it down. It was not against that particular airlines policy, but I had to go along with her, as she's the boss. It will work, but mine had a hard time picking up the satellites at cruising altitude and speed. It took a while to get a fix. I had to hold it again the window for it to get any kind of signal. I would not want to do that for the whole flight. I don't know if it was accurate, but the Captain said we were riding a 100mph tail wind going from DFW to PHL. The GPS unit indicated we were doing over 640mph. We left an hour late, and still got in on time, so we must have been going faster that usual.

Yep, Its possible...
 

I can confirm it is possible. I travel alot on work, & was bored one time & pulled my Garmin Nuvi 200 out of my laptop bag & turned it on. Sure enough it picked up a signal & could show me where we were on the map, give a ground speed etc... It was kinda cool (for like 5 minutes) & then I put it away before anyone said anything to me...

On a side note, they can be fun to use on trains too...

Works on the Nokia E71 - 870 km/hr BNE-SYD recently...

I have tried this many times with different devices, a GPS watch, my mobul GPS, and a portable Garmin trakker GPS. Only the latter worked when held VERY close to the window, the watch and my mogul couldn't even get a signal (was going to use local map data on the device for mapping and speed tracking)

It doesn't work great even through the window.

unless you have map data pre installed onto your phone/gps device you wont be able to conventionally download the maps over edge/3g/wifi unless the plane is also equipped with wifi etc

not sure
 

not sure if this was directed at my comment above, but indeed I have all the USA map data on my phone installed, so it will work fine without a data connection at all.

That sounds about right for a Boeing 757 as its cruising speed is .8 mach, about 630 miles per hour. With tail winds of 100 m.p.h, it will give you a ground speed of 630 miles per hour.

Which device, among the ones you mentioned, was the latter? :D

A metal fuselage is a good shield. It works like a faraday cage. The signal and and does get in through the windows, but it's utility will depend on the strength of the signal, which depends on propagation conditions also, and on the quality of your receiver.

Some airlines are picky about gps units, which is just plain stupid. But for those that do allow it, personally I found that I could generally get a reasonable signal for most of the flight in the window seat. I've been able to get it to work well in a window seat by putting the tray table down, using the auto beanbag mount, and then kinda angling the antenna towards the window. That was with my older Garmin 60CS. With my newer 60CSX I'd expect to work a little better, because it's noticeably more sensitive.

I like to know what I'm looking at out the windows, so I like to use it if I get a chance.

I use a Garmin ETrex HCx and it will even get signal from the middle and sometimes aisle seat if it is orientated right and depending on the plane. If you're by the window it's solid. It is best to let it aquire sats at the gate and not while flying. I have tracks from DFW-ORD-FCO and back and all over the US. I especially like using it to know when to see meteor crater on the DFW-LAS flight. Keep it out of sight, I have been scolded.

Good GPS reception need a good antenna. Many phones (e.g. my BB 8830) use so called assisted GPS which reply on basestations and triangulation. So they don't work well in the air if at all.

Some phones (e.g. Nokia N95) are true GPS devices but they use a tiny antenna so reception is poor causing a long satellite lock even not moving on the ground.

True GPS devices use a large antenna about one inch square making an ugly phone or watch. I can get a good reception in the air with a Garmin etrex and Quest. Unless I got a fix on the ground first, even these GPS devices will take a while to get satellite lock once the plane is at cruising speed. Some GPS models (e.g. Garmin eTrex "H" versions) have higher sensitivity and can get a fix even away from windows.

In Northern Hemisphere, south facing windows have view of more satellites than north facing windows and can get a satellite lock easier.

Most true GPS devices can record and export a track even without maps loaded.

Huh?
 

Does this post need to be edited?:confused:

I've used my Garmin Forerunner 205 numerous times and it tells me the airspeed, altitude, etc. I've heard the pilot read our altitude and it was accurate with what my GPS was saying. It has a little bit of a hard time if I'm not near the window.

GPS measures ground speed. The receiver has to be calibrated to calculate the air speed.

The GPS receiver can calculate speed without being on the ground although it will take longer to get a fix while it is moving. Position of the receiver is calculated from position of the satellites and time. So it will work even at airplane altitudes.

http://tycho.usno.navy.mil/gpsinfo.html
http://www.trimble.com/gps/howgps.shtml
http://www8.garmin.com/aboutGPS/

You do know what ground speed is? Ground sped does not mean the object is on the ground. :D

Positioning data alone can only give you ground speed. Other data is needed to calculate air speed.

GPS receiver doesn't know where the ground is and they don't need to be "calibrated". It just know the receiver location calculated from satellite messages it received. Satellites are traveling in fixed orbits. Receiver then calculates its position from the satellite positions with respect to absolute time. Each satellite is essentially a 3rd order time standard. First order being the universal time standard in Paris, 2nd order being the US National time standard at NIST near Denver.

GPS receiver calculates the travel speed from the next position and elapsed time. Each location point is recorded as altitude, longitude, latitude and time. So no calibration on the "ground" is needed. Once it got a fix anywhere, on the ground or in a plane, it is "calibrated" if you want to call it that.

GPS maps are overlays and tied to receiver location via datum set by USGS and other national surveying agencies. The latest one in use in the US is from 1984 thus called WGS84.

Below is a recorded track FRA-SFO. The GPS device was turned on after the plane took off and left on for the entire flight until near SFO. Each leg recorded represents the distance between two points (Alt, Long, Lat, time) and speed is calculated from it.

FRA-SFO

assisted gps simply means it uses the cellular network to shorten the time for the gps to get a fix on its position. instead of 30-60 seconds or more, it's near instant. after that, the gps tracks as it would normally and the cellular network is no longer needed.

if a gps unit can pick up gps satellites, it's a 'true gps.' the antenna has nothing to do with it, although better antennas will obviously help. the gps devices with the sirfstar iii chipset are amazingly sensitive, and i've heard of them getting a fix (no assist either) inside buildings.

that's true.

These are good comments but I won't go so far as antenna has nothing to do with it. No matter how good the chipsets had become, they need an antenna to get signals from the satellites.

High sensitivity is not free either. They have shorter battery life. I use a Garmin eTrex Venture Cx for travel and it has 32 hours of battery life, good enough for a trip across the ocean. The best high sensitivity in the eTrex series (e.g. H, HC, HCx versions) have about 25 hours battery life. So I opt for longer battery life over higher sensitivity.

yes of course. i did not mean that no antenna is needed, just that a true gps does not indicate any particular type of antenna.

Geez. Do you not understand simple English? I never said the GPS needs to know where the ground is. You are the one who brought location of the receiver into play?

You are absoultely confused. There is no way the GPS can give you air speed without other data. Since, GPS,. fundamentally measures position, and the rate of change of position is the ground speed, not air speed, it measures ground speed. It needs airspeed data to calculate airspeed. If you don;t get that simple principle, you need to learn a bit about GPS, and about ground speed, as well as airspeed. :p

The only speed that can be calculated from position data, without any additional input, is the ground speed. That's why I asked you if you knew what ground speed is. You yourself imagined that it had anything to do with location of the receiver.

Yes, I suspected that is what you meant.

Nevertheless there are physical limitations to antennae design. A good antenna takes space and affects aesthetics and design of the end product. There are just no space for a real GPS antenna in cellphones and watches etc.

Satellites are very far away. They use limited power sources such as solar panels and small nuclear power plants. The signal reaching the earth is very weak. Better GPS chipset is not only better sensitivity but also employing DSP technology to separate signal from noise or multi-path issues.

Since cellphone BST tower always has a GPS to serve as a time base, A-GPS works fine. But these devices lacking a true GPS doesn't work in area of no service, such as in foreign countries. My BB8830 is one of these.

I have a Garmin GPS 10 BT pug. It supports cellphone OS such as Palm, Symbian so my Treo and Nokia N72 can load up a mapset on flash cards and work as GPS. But the functionality tends to be quirky thus limiting their usefulness as a real tool. Plus I will need to carry another charger in the travel kit.

If I may ask sir, what is that "other data"?

Let's start from what you know so that we are on the same page.
What do you think you can calculate from position data?
Do you know what ground speed and ow it differs from air speed? I find it unimaginable that someone wouldn't know that.

My sincere apologies sir...

There are no difference between air speed and ground speed as long as direction of travel are parallel.

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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