Total energy compensation, explained.

The stick thermal.

Cruise at 160 km/h and slow smoothly to 100. The glider zooms about 61 m upward, and for those few seconds an uncompensated needle slams to full deflection — a strong, wide, perfectly convincing thermal that you manufactured with your right hand.

Pilots call it the stick thermal, and it poisons every reading. Each speed correction fakes lift or sink; every gust response looks like air movement. Trying to centre a real thermal with such an instrument means chasing your own inputs around the sky — the needle rewards exactly the wrong behaviour, pulling up.

Total energy: the sum that stays honest.

A glider in flight holds two kinds of energy: potential, from altitude, and kinetic, from speed. Divide their sum by weight and you get a single number in metres — the energy height: your altitude plus v²/2g. It is the altitude you would reach if you traded every knot of speed for height.

A pull-up or a pushover merely moves energy between the two accounts. The sum does not change — only drag spends it, and only two things top it up: an engine, or air that is going up. Watch the sum instead of the altitude alone, and everything the pilot does with the stick cancels out of the reading.

That is the whole idea of a total energy vario: it differentiates energy height instead of altitude. During a pure zoom the result is zero. In a thermal it is the true airmass climb. And the kinetic account is no rounding error — at 160 km/h you are carrying roughly 100 m of energy height in speed alone.

Two ways to build one.

The classic solution is entirely pneumatic: the TE probe, the small tube standing on the fin of nearly every sailplane. Its orifices face aft, so airflow past it generates suction almost exactly equal to dynamic pressure. Plumb the vario to the probe instead of pure static and it sees static pressure minus dynamic pressure — the speed term subtracts itself, mechanically, with no electronics anywhere. Fly faster and the extra suction mimics exactly the altitude you would gain by slowing down.

The modern solution is electronic: measure static and pitot with fast digital sensors, compute energy height in firmware, differentiate and filter. This is what LX digital varios do. There is no extra plumbing to leak, the degree of compensation is adjustable in software, and the same sensors feed airspeed, netto and speed to fly — but it stands or falls with a healthy, leak-free pitot-static installation.

Why it is never perfect.

There is one thing no total energy system can fix: a horizontal gust. Fly into a sudden 10 km/h headwind gust and your airspeed jumps without the elevator moving — a genuine rise in energy height the instrument cannot tell apart from entering a thermal, so even a perfect TE vario spikes on a gust front. That is physics, not a defect; the energy really did change.

Everything else is installation. A probe needs clean air — the fin tip, clear of the fuselage and propeller pressure field — and its tubing must be tight: a leak lets raw static bleed in and the stick thermals creep quietly back. Electronic systems inherit every fault of the pitot and static ports they read.

The last trade-off is filtering. Heavier filtering rejects gust spikes but delays the real thermal; a lighter filter answers instantly and jitters. This is why the response time of a good vario is adjustable — it is not one correct number, it is a choice about the air you fly in.

In your cockpit.

Every LX vario compensates electronically from pitot and static, with the compensation degree and response time set in the instrument — and it can use a TE probe instead where the airframe has a good one. If the needle moves when you pull in still morning air, the installation is telling you something: check the percentage, then check the tubing.

Once the vario finally tells the truth about the air, the next question is what to do with it — how fast to fly between the climbs it reports. That is the MacCready article.