1. CGS Ground School Technical The Variometer © Crown Copyright 2011
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2. THE VARIOMETER The variometer consists of:
which is connected through the instrument,
An insulated capacity flask,
to the static source. 2 4 6 8 10

3. THE VARIOMETER As the aircraft climbs the static pressure reduces.
The capacity flask is now at a higher pressure than the static source.
Air flows from the capacity flask, into the instrument,
then through to the static source, deflecting the needle. Which indicates climb on the calibrated scale. 2 4 6 8 10

4. THE VARIOMETER
A faster rate of climb, causes a bigger pressure change.
The air flows faster, moving the needle further, indicating a higher climb rate. 2 4 6 8 10

5. THE VARIOMETER
In level flight the static pressure and capacity pressure are equal.
No air flow occurs between them and the needle remains at zero, indicating level flight. 2 4 6 8 10

6. THE VARIOMETER
As the aircraft descends static pressure increases. The capacity flask is now at a lower pressure than the static source.
Air flows from the static source, into the instrument,
then through to the capacity flask, deflecting the needle which indicates a descent on the calibrated scale. 2 4 6 8 10

7. THE VARIOMETER
If the static source is blocked, airflow between the static source and the capacity flask can't occur.
The instrument reads zero regardless of the rate of climb
or descent.
The instrument is not connected to the pitot source
and therefore is unaffected by blockages of this system. 2 4 6 8 10

8. X Z THE VARIOMETER Total Energy
In the Viking, and most other gliders, the variometer is connected to the total energy source instead of the static source.
Total energy pressure is a combination of static pressure
and a suction caused by air flowing past the calibrated holes.
The suction varies in proportion to the square of the aircraft's speed.
This is used to overcome the problem of climbs / descents being indicated whenever the aircraft changes speed. X Z
PITOT TUBE
TOTAL ENERGY TUBE 2 4 6 8 10

9. THE VARIOMETER Total Energy A gliders total energy is made up of:
Potential Energy – Energy available due to altitude
Kinetic Energy – Energy available due to speed
When an aircraft speed is increased from 50 kts to 70 kts and then reduced back to 50 kts again the overall total energy remains unchanged.
75kts
50kts X Z
A static sourced variometer would show a increased rate of descent followed by a climb.
A total energy variometer would show only the normal descent rate.

10. = + Total Static Suction THE VARIOMETER Total Energy
This is achieved because:
Total energy pressure = Static pressure + Suction pressure =
Total
Static
Suction
As the nose is lowered the aircraft descends and the static pressure increases.
However the speed also increases, giving an increased suction which reduces the suction pressure.
The overall effect is that the total energy pressure is unchanged and the variometer reading unaffected.
The exact opposite occurs when the nose is raised.

11. THE END
Any Questions?