Radio Altimeters?

[glum]

Nothing to do with the frequency of operation then?

[Brian Abraham]

AP3340 again.

Radar altimeter - operates on a pulse system, measures height over a range in the order of 1,000 to 50,000 feet. Error in the absolute measurement is within +-100 feet, but changes of height at a constant level are measurable to within about +-30 feet.

Radio altimeter - operates on frequency modulation and covers the range from zero to about 5,000 feet. Error is proportional to height and may amount to +-3%.

However the AP dates from 1960 and todays manufacturers seem to use the terms radar and radio interchangeably.

[forget]

Here's a remark from a web site which I daren't mention here.

The radio altimeter is often erroneously described as a "radar altimeter". In fact it doesn't use radar principles beyond the fact that it responds to reflected signals.

I think that's what I was saying. OK, I accept that some 50s/60s kit may not fit that bill; but the guy who invented RadAlts did it before Radar was even thought of.

Conclusion, just call it a RadAlt and everyone's happy.

[BOAC]

Greetings from Mr Pedant

Every other ‘Radar’, Search, Fighter or Weather, needs to detect the direction and range of a target which may, or may not, be there.

- not true - a basic ranging radar produces only range, not direction.

NOTHING to do with the OP question, but hey, who cares!

[forget]

- not true - a basic ranging radar produces only range, not direction.

So what's the point? Range without direction? You know it's there - but you don't know where? You happen to have an example of this?

OK. Very Old AI.

[BOAC]

Gunsight ranging? Cue Pantomime mode "It's in front of you.........".......... "Oh no it isn't"

[aterpster]

forget:

So what's the point? Range without direction? You know it's there - but you don't know where? You happen to have an example of this?

I do, since I worked on them in a past life. The radar that was used to provide distance information to day-fighter optical gunsights provided only distance. The location was provided by the optical gunsight. An annunciator light would light when the ranging radar had a lock-on. There was no radar display. In radar parlence, this is known as an "A Scan" radar.

[forget]

Agreed. As I said - OK. Very Old AI; but we weren't talking about museum pieces.

Radar Ranging

[BOAC]

oh dear - not 'AI', please

[galaxy flyer]

One "feature" of a radio altimeter is that it sends out a range only, no azimuth (think a near hemisphere below the plane). In theory, one could fly down the middle of a deep, but narrow, canyon and have a radalt of, say, 300' from the canyon wall, not the floor. Since nearly always the radio signal intercepts the ground first, not a problem, but this does solve low altitude bank angles.

GF

[aterpster]

F-100 Super Sabre optical gunsight.

The ranging radar had a fixed antenna.

http://www.f-100.info/images/cutshal...0f_fpanel1.jpg

[forget]

BOAC, What's wrong with AI? The stuff inside the sharpish end of the Hunter was always called that.

Page 17. Hawker Hunter 1951 to 2007 By David J. Griffin.

'The change of role to Ground Attack did not require the retention of the ranging radar, equipment meant for airborne aircraft intercept'. aka AI.

Hawker Hunter 1951 to 2007 - Google Books

[galaxy flyer]

Didn't know there were TWO Hun Drivers, here!

GF

[BOAC]

Gosh! We have wandered a long way from RadAlts!

The stuff inside the sharpish end of the Hunter was always called that.

- not by most of us. AI means 'Airborne Intercept' and by the time you get to a guns kill the 'intercept' is over. 'Radar Ranging' is a more correct name. I believe the Google book to be incorrect in describing the RR in a Hunter as 'AI'.

Apart from some ex Navy two-seaters (T8?), Hunters, as far as I know (and no doubt John Farley will correct me) never had intercept radar fitted and were vectored into visual range on its targets by ground control. The exception was, I understand, a 'one-off' conversion to train naval Sea Harrier pilots in AI use.

[Brian Abraham]

The radio altimeter is often erroneously described as a "radar altimeter". In fact it doesn't use radar principles beyond the fact that it responds to reflected signals.

Pedant on. Read his post and while he comes across as somewhat knowledgeable his brief of how they operate was not complete. He only talks of modulated frequency and not pulse. As to what they are called the manufacturers these days refer to them mostly as radar altimeters, although the radio is used infrequently. Radio/radar it matters not.

http://search.honeywell.com/search?p...meter&x=7&y=10

FreeFlight Systems Radar Altimeters and Indicators

The manual of the aircraft I flew describes it as a radio altimeter. Depending on the particular piece of kit fitted it operates "to send a signal to the ground, receive an echo, and measure the phase or time difference between the transmitted and received signals. In the pulse system the time may be measured, and in the continuous wave systems the phase is measured".

Pedant off. (Sorry BOAC and forget)