Probeless airspeed and angle of attack measurements for propeller driven vehicles

1. A method to determine an airspeed of a powered vehicle comprising a flight computer, the method comprising, during flight:

powering an unmanned aircraft with a fixed pitch propeller along a velocity vector by delivering power from an electric motor to the fixed pitch propeller;

obtaining measurements on the unmanned aircraft of a voltage and current supplied to the electric motor, altitude, and air temperature; and

determining an airspeed value of the unmanned aircraft using an advance ratio for the propeller, comprising:

determining power delivered to the propeller using one or more of the measurements;

determining air density using one or more of the measurements;

determining a propeller power coefficient using the power delivered and the air density;

determining the advance ratio for the propeller using the propeller power coefficient;

further comprising, during flight, determining an angle-of-attack (AOA) of the vehicle using the airspeed value; and

adjusting the power delivered to the propeller based on the air speed value.

2. The method of claim 1 , wherein the airspeed value is determined without the use of a pitot-static probe.

3. The method of claim 1 , wherein the airspeed value is a true airspeed.

4. The method of claim 1 , wherein the determining the power delivered comprises applying a motor efficiency.

5. The method of claim 1 , wherein the determining the advance ratio comprises matching the propeller power coefficient on a lookup curve of a plot comparing propeller power coefficients to advance ratios for the propeller.

6. The method of claim 1 , wherein the airspeed value is a true airspeed and the determining the airspeed value comprises multiplying the advance ratio with a propeller rotational speed and a propeller diameter.

7. The method of claim 1 , wherein the determining the AOA comprises determining a dynamic pressure from the airspeed value.

8. The method of claim 1 , wherein the determining the AOA comprises determining a dynamic pressure from the airspeed value;

determining a body normal coefficient; and

using the body normal coefficient on a lookup curve of a plot comparing body normal coefficients to angles of attack.

9. The method of claim 8 , wherein the body normal coefficient is determined from a body-fixed load measurement and the dynamic pressure.

10. The method of claim 9 , wherein the body-fixed load measurement is obtained from an accelerometer on the unmanned aircraft.

11. A method of determining an angle-of-attack (AOA) of a powered vehicle, the method comprising, during flight:

powering an unmanned aircraft with a fixed pitch propeller along a velocity vector by delivering power from an electric motor to the fixed pitch propeller;

obtaining measurements from one or more sensors on the unmanned aircraft of a voltage and current supplied to the electric motor, altitude, and air temperature;

determining an airspeed value of the unmanned aircraft using an advance ratio and one or more of the measurements;

determining a dynamic pressure from the airspeed value;

determining a body normal coefficient;

determining the AOA by using the body normal coefficient on a lookup curve of a plot comparing body normal coefficients to angles of attack; and

adjusting the power delivered to the propeller based on at least one of the air speed value or the AOA.

12. The method of claim 11 , wherein the body normal coefficient is determined from a body-fixed load measurement and the dynamic pressure.

13. The method of claim 12 , wherein the body-fixed load measurement is obtained from an accelerometer on the unmanned aircraft.

14. The method of claim 11 , further comprising:

determining a body normal force using a body-fixed load measurement from an accelerometer on the unmanned vehicle and a weight of the vehicle; and

using the body normal force and the dynamic pressure to determine the body normal coefficient.