Propeller system with two counter-rotating propellers, a method for measuring the thrust of a propeller system with two counter-rotating propellers and wind tunnel with a model positioned therein having a propeller system

A method for calculating the thrust force of a propeller system having a first and a second propeller separated by a first propeller gap and respectively in contact with a second and a third propeller gap, comprising:

• measuring at least one first differential pressure through a first propeller between the adjoining first and second propeller gaps,
• measuring at least one second differential pressure through a second propeller between the adjoining second and third propeller gaps,
• calculating respectively an effectively acting force from the measured pressure difference for each of the first and second propellers, and
• subtracting the effectively acting forces from a measured thrust force of the first and second propellers.

A wind tunnel with a wind tunnel model positioned therein, comprising at least one propeller system, the at least one propeller system comprising:

• first and second propellers positioned one behind the other and separated by a first propeller gap, and having a first and a second propeller hub, respectively, and at least a first and a second rotating force measuring device, respectively,
• at least first and second differential pressure sensors, and
• an evaluation unit,
• wherein the first and second rotating force measuring devices are mechanically connected to the respective first and second propellers and are so configured that they can measure the individual thrust force of the respective propeller;
• wherein at least one of the first and second differential pressure sensors is arranged on or in each of first and second propellers and is configured for measuring a differential pressure between the first propeller gap positioned between the first and second propellers and a second and a third propeller gap on an opposing side of the respective first and second propellers, and
• wherein the evaluation unit is configured for determining a total thrust force of the propeller system by adding the measured individual thrust forces of the first and second propellers and by subtracting the gap area forces based on the respectively measured differential pressures.