Tech News: An Alternative Pitot for Drones

Alternative Pitot-Solution for Airspeed-Measurement of a drone.
Germandrones new Pitot solution compared to a classical pitot tube on a UAV

New "Pitot-Wing" und classical pitot tube side by side.

Principle of a pitot-static-tube

Schematic of a pitot-static tube.

Static pressure port on an airliner

Static port of an airliner. (License CC BY 3.0, Author SempreVolando)

Germandrones has developed a new type of pitot-probe with significant advantages over the competitors’ classical tubes: It is small and elastic, making it robust in everyday use while providing reliable data. Measuring its airspeed is vital for any fixed-wing UAV as it is decisive for the flight-physics and bares information about the wind conditions when compared to the ground speed.

 

Why doesn’t everybody do this?

It is not so easy. To determine the airspeed, the static pressure of the environment p∞ is compared to the ram-air-pressure (or “total pressure”, p0) caused by the vehicle’s movement. The difference between these two is called the “dynamic pressure” q and can be used to calculate the airspeed as follows:

formula for airspeed from pressure measurements

(with the air density ρ)

Take a look at the pressure distribution around a streamlined object: While the maximum pressure p0 is present at the very front where it may be measured, the displacement of the body causes an acceleration and therefore a pressure-drop alongside the surface. To determine the static pressure, a sensor port must be placed exactly where cp = 0, which is dependent on the shape of the object.

pressure distribution around an object

Note: the image shows the distribution of the pressure coefficient cp which is made dimensionless by dividing through the dynamic pressure q and therefore valid for any airspeed. It is determined by

formula for the pressure coefficient

In case of a pitot-static tube (or “Prandtl-tube”) this static pressure port is integrated in the shaft by the manufacturer (see image on the right), allowing it to collect both values with a single probe and making it easy to integrate into any UAV. Other aircraft on the other hand, e.g. airliners, have a separate static port in a carefully selected location on the fuselage.

 

Hundreds of operating hours have shown that the classical pitot tubes are prone to be damaged when working on the aircraft or when transportation to a new deployment site gets a bit rough. The new design by Germandrones consists of a streamlined pillar (resembling a small vertical wing). It is smaller and made from a flexible material, making it very robust in everyday use. And several hours of flight tests in various conditions have proven that the accuracy of its measurements is excellent.

The new pitot tubes will be delivered with all Songbirds of the upcoming release version and can also be retrofitted to existing systems if desired.

 

Contact:

Dr. Klaus Scho, CEO

Mail:

Tel. + 49 (0)30 34 78 12 81

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