3 ms·

On gliders, the airspeed indicator is even simpler - just a pitot tube connected to a (very sensitive) pressure gauge. The variometer (a vertical speed indicato

On gliders, the airspeed indicator is even simpler - just a pitot tube connected to a (very sensitive) pressure gauge. The variometer (a vertical speed indicator) uses an internal air reservoir and a calibrated restriction to derive rate of climb or descent. So, all the main instruments (altimeter, airspeed, vario) are worked by atmospheric pressure, no batteries needed.

mannykannot 5y ago
Modern variometers are more sophisticated than this. The first major modification was the total energy variometer, which takes account of the fact that you can trade speed for altitude and vice-versa. It gives a figure (expressed as an equivalent rate of climb) that corresponds to whether the sum of your potential and kinetic energy is increasing or decreasing. This is particularly useful in rough air, where, with a simple variometer, it is difficult to center on the strongest updraft. As the performance of gliders improved, and the speed for optimal glide angle diverged from that for minimum sink rate, it became useful to know the vertical speed of the airmass, as, when flying fast, your descent rate is quite high even if the air is rising. Netto / airmass variometers compensate for the still-air rate of descent you would have at the current airspeed. Relative netto variometers show the difference between this and the minimum sink rate. All of this can be achieved by clever plumbing, though electrical instruments can have less lag, and potentially adjust for flap setting and ballast weight. One orthogonal development that requires electricity is the audio variometer, which emits a sound of varying pitch to indicate rate of climb or descent - an important safety issue, as you can monitor this datum while looking outside of the cockpit. Another thing that variometers are usually equipped with is the speed-to-fly ring, invented by Paul McCready of 'Gossamer Albatross' fame. It gives a useful (even though imprecise, on account of the parameters that have to be estimated) indication of the optimal speed to be flying at for the current variometer reading. As in the case of indicated vs. true airspeed, it is important to understand what you need the information for.
- flyinghamster 5y ago
  Wow, a lot has happened since I dipped my feet into those waters. The lessons I took before my feet got too cold :-) were in old-school Schweizer ships (a 2-22 and a 2-33) with just the bare basics. Naturally, a yaw string was one of them.

mannykannot 5y ago

Modern variometers are more sophisticated than this. The first major modification was the total energy variometer, which takes account of the fact that you can trade speed for altitude and vice-versa. It gives a figure (expressed as an equivalent rate of climb) that corresponds to whether the sum of your potential and kinetic energy is increasing or decreasing. This is particularly useful in rough air, where, with a simple variometer, it is difficult to center on the strongest updraft. As the performance of gliders improved, and the speed for optimal glide angle diverged from that for minimum sink rate, it became useful to know the vertical speed of the airmass, as, when flying fast, your descent rate is quite high even if the air is rising. Netto / airmass variometers compensate for the still-air rate of descent you would have at the current airspeed. Relative netto variometers show the difference between this and the minimum sink rate. All of this can be achieved by clever plumbing, though electrical instruments can have less lag, and potentially adjust for flap setting and ballast weight. One orthogonal development that requires electricity is the audio variometer, which emits a sound of varying pitch to indicate rate of climb or descent - an important safety issue, as you can monitor this datum while looking outside of the cockpit. Another thing that variometers are usually equipped with is the speed-to-fly ring, invented by Paul McCready of 'Gossamer Albatross' fame. It gives a useful (even though imprecise, on account of the parameters that have to be estimated) indication of the optimal speed to be flying at for the current variometer reading. As in the case of indicated vs. true airspeed, it is important to understand what you need the information for.

flyinghamster 5y ago
Wow, a lot has happened since I dipped my feet into those waters. The lessons I took before my feet got too cold :-) were in old-school Schweizer ships (a 2-22 and a 2-33) with just the bare basics. Naturally, a yaw string was one of them.