On Jun 17, 7:39*pm, Hellman wrote:
I've been flying gliders for years, but the following question only
occurred to me recently: In mechanically compensated varios, the TE
pressure is supposed to be as much below static as pitot is above
that. That makes sense since "ram air pressure" increases as v^2, as
does the kinetic energy of the ship. But pitot pressure is
proportional to IAS, whereas the kinetic energy of the ship would seem
to need TAS. If I haven't made a mistake (and please correct me if I
have), TE compensation will only be correct at one altitude. At higher
altitudes it will be under compensated, and at lower altitudes over
compensated. Comments please!

Martin

I predict this will be a long thread.

First principles:

Total energy vario systems sum the kinetic energy of speed and the
potential energy of height and display the rate at which that sum is
changing with time in knots or meters per second.

This calculation must be done in the same domain and in the same
units. i.e. true airspeed + true rate of climb or indicated airspeed
+ indicated rate of climb in the air-data domain. TE calculations can
also be done entirely in the inertial domain though no such system
exists to my knowledge. Don't mix units or domains.

An example is the Borgelt B50/B500 varios which are altitude
compensated to give true rate of climb and which calculate TE with
true airspeed to produce a fast, smooth and accurate TE vario.

These varios, like most, use a probe which may be regarded as a
special static port which is carefully crafted to respond in a precise
way to airspeed changes while being relatively insensitive to yaw and
pitch angles. The real 'magic' of an air-data TE vario is in the
probe.

You could, if so inclined, connect the TE port on the vario to regular
static ports and have a perfectly workable, if non-compensated, vario.