Radio Altimeters?
 

A little bit of bar talk the other evening revealed something I had never thought of before:
Why are we calling radio altimeters radalts?
They do not read altitude. They read instantaneous height. Something quite different.
Radio Height Readers would be a far better suggestion?
It is a serious question as a crewmate (non English) got very confused over this purely because the word altimeter was in it!

Perhaps because years ago when the Radalt was first conceived, it was usual to set QFE when taking off/landing and hence the barometric Altimeter read height? Just a thought.

Look at your instrument pannel.

It has an Altimeter.

When you arrive in the cockpit and it is showing some random indication it is an Altimeter.

When you set QNH for departure, it is an Altimeter

When you set 1013 for enroute climb cruise and descent it is an Altimeter

When you set QFE for landing, it is an Altimeter.

Does your friend get confused and think that is should be called an Altimeter, a Flightlevelometer, and a Heighmeter? :D

The first uses of the radio altimeter was by the Navigator on long over-ocean crossings to work out "D" and over the ocean it most certainly measures Altitude.

Later uses for landing and (E)GPWS do not require us to call it something different.

RADio ALTimeter

[QUOTE]The first uses of the radio altimeter was by the Navigator on long over-ocean crossings to work out "D" and over the ocean it most certainly measures Altitude./QUOTE]

Ah, I considered this but came to the conclusion that it actually still measures height above the water beneath you and not altitude.
Altitude is measured against a datum of "MEAN" sea level not the actual sea level.

The root altus means high. Altimeter is a height meter. Which height? Depends on the instrument and the setting.

:D Best Prune answer in a long long while. :D
Kelly, didn't you do Latin init?

What is 'D' ?

Fourth letter in the modern Latin/English alphabet. Also the third letter in raDar, raDio, and raDiationem.

Heighmeter?
Presumably used for measuring how high the heigh is. Corn is of course measured in elephant's eyes. What is the preferred measure for heigh?

What is D. Something to do with Pressure Pattern Navigation, after which, I'm lost. :bored:

It indeed is an altimeter that reads absolute altitude.

Usually feet, although the Russians prefer metres :E

Simply because only one radalt reports aural warnings/information. Safe thought to crosscheck vital information in TO and land modes of flight.

forget hasn't forgotten much and is on the money.

AP3340 (Air Ministry book of Aviation Meteorology) uses the term "D" to define the difference between the true height (Radalt) and the pressure altitude. "D" is applied to various formulas used in pressure pattern flying calculations. In the northern hemisphere if "D" is increasing drift is to port, if decreasing drift is to starboard.

Let's open this debate a bit more.

Is it a Radio Altimeter or a Radar Altimeter?

Or are they two different things?

Two different things

Radio Altimeter is 'more correct'. Radar comes from RAdio Detection And Ranging and a Rad Alt doesnt really detect anything. (Pedants stay away.)

PS. I've just seen Wodricks post - two different things. How so?

Doesn't a Rad Alt transmit a signal and receive it back in order to determine the height?

It can't give a range to something without detecting it first surely? It detects the ground/water and displays a calculated range.

I said - Radio Altimeter is 'more correct'. Radar comes from RAdio Detection And Ranging and a Rad Alt doesnt really detect anything. (Pedants stay away.)

The point of the discussion was - Radio Alt or Radar Alt. Every other ‘Radar’, Search, Fighter or Weather, needs to detect the direction and range of a target which may, or may not, be there.

Rad Alt doesn’t need to (first) detect anything to work, it bounces off something it knows is there - the earth. That’s the reason it’s Radio Alt rather than Radar Alt - and why I said - Pedants stay away. :)