• DRONE IN A WIND TUNNEL

physical quantities of the forces
of the relative motion of a drone

• DRONE – PHYSICS MEASUREMENTS

the impact of crosswind
active horizontal force

Horizontal velocity

Direction of the vector defining the velocity of drone's horizontal motion is presented by the relative air velocity through the wind tunnel. We expected results and stated hypothesis.
Matej and Domen constructed brackets and a frame for the fitting of the drone and force sensor Vernier.
Sensor was attached vertically to the vessel's air buoyancy.

Does horizontal velocity of vessel's motion influence the amount of force of air buoyancy during the flight? We assumed that it does.
We predicted: HORIZONTAL VELOCITY WILL DECREASE AIR BUOYANCY AND THUS DISABLE THE LIFT-OFF OF THE VESSEL.

The results of the measurements were surprising. Namely, the measurements showed that side component increases the force of buoyancy, which enables the lifting of the vessel. Our hypothesis was disproved. We found the reason for that in the aerodynamic shape of rotors.
• PHYSICS MEASUREMENTS

Vertical force is measured at the time of the launch of drone's rotors and influences the horizontal components of relative velocity.
Force sensor Dual-Range Force Sensor DFS-BTA Vernier is connected via interface to the computer programme Logger Pro. Measurement period is 30 seconds and the measurement frequency 50/s.

• RESULT ANALYSIS

The gauge accuracy at 0.001 N combined with a high frequency of measurements results in a diagram, which needs to be evaluated according to the average segments of measurements.
Vessel launching force is therefore increased from -0.1093 N to -0.209 N. It is increased by almost 52 %.

• MEASUREMENT DIAGRAM

Diagram presents measurement section A, where no impact of air velocity in the wind tunnel is detected. At this time gauge records only the force of drone's rotors rotation (uplift force)..
Section B presents data related to the wind tunnel launching and the impact of the horizontal air force (relative velocity).
The result is an average force of uplift. The speed of air mass increased the uplift force. Air buoyancy of the vessel increased.

MEASUREMENTS – FORCE COMPONENTS

MEASUREMENT SERIES

The picture shows air velocity vectors (v), which represent relative movement. The uplift force (F) of a drone is directed vertically at the gauge.
In Series 1 and Series 2 tabs there are two charts from all measurements.

Series 1

The series of measurements show constant increase of the aerodynamic drag force. Force Fp is the result of drone's motor power. This force is, however, limited due to a fixation of the drone to the measurement instrument. We can observe a very constant change of force caused by the air flow of the wind tunnel. Measurment Nr4 is an exception, therefore we believe it could be applied to an error in measuring. It was probably caused by the contact of the beam and the measurement chamber.

Series 2

In the second series we have measured at a lower speed of 2,92m/s. We also improved the beam connection, which caused an even bigger change of force and thus an even bigger change of aerodynamic drag force at a relative side-movement of drone. This force increases the buoyancy of a drone by approximately 80% . It also confirms our assumption that such influence is the highest at a lower speed.

LIMITATIONS

Force gauge Dual -Range Force Sensor DFS-BTA Vernier yet again proved to be a very reliable piece of equipment. Accuracy of measurements exceeds our requirements.
Measurements could be improved with improved mounting (a stand) of a gauge and improved rigidity of the system. Some differences in measurements could be attributed to the bus, upon which the drone was fitted. The friction between the bus and the opening in a measuring chamber could be reduced with a special sliding lead-in.

PROBLEMS

The greatest problem with all measurements was the continuity of drone's power supply. Battery providing supply for the drive and the steering of a vessel has a very small capacity. Drone as a machine consumes too much electricity in comparison with the power supply capacity. The voltage in batteries rapidly dropped to the minimum thus enabling only short-term relevant measurements. Charged battery's maximum voltage was 4.2V. As the voltage dropped to merely 3.8V, there were problems with the remote signal reception and the constancy of rotor frequency. The picture shows air velocity vectors (v), which represent relative movement. The uplift force (F) of a drone is directed vertically at the gauge. In Series 1 and Series 2 tabs there are two charts from all measurements.

AERODYNAMIC DRAG

AERODYNAMIC DRAG FORCE IN DIFFERENT POSITIONS

While moving and flying, drone assumes various positions due to its orientation and inclinations at the changes of course as well as the relative situations such as the impact of wind.
Measurement 2 encompasses the impact of aerodynamic drag in the measuring chamber of the wind tunnel in different positions of the vessel.

AERODYNAMIC DRAG

MEASUREMENTS – AERODYNAMIC DRAG

MEASUREMENT SERIES OF AERODYNAMIC DRAG

X-shaped drones are the most common. Our model has four symmetrically positioned rotors as well. With such shapes we can expect relatively high aerodynamic drag.
We wanted to prove how important drone position during the flight is. Series of measurements show the correlation between the aerodynamic drag force and the angle – inclination of a vessel as well as the relative velocity of motion.

Series 1

The first series shows three main positions of flying. Horizontal position is mostly theoretic as this kind of movement results in additional force components, which move the drone in a vertical way. Angle 45° is common but not permanent. Angle 90° means vertical movement. At this angle the measured air drag force is at its highest value.

Series 2

The frame of the drone used in this measurement allowed us to measure random drone inclinations. We selected several values and observed the changes in the resistance dependent on the angles presented in the chart.

INCLINATIONS

Each series of measurements at different speed was adjusted manually with a barycentric protractor.

THE TOUCH OF A SENSOR

The accuracy of aerodynamic drag force measurements depends on the transfer of a body's area (intersection) directly upon the gauge. In order to nullify the impact of the force gauge itself upon the measurements, the measurement was conducted in the section between a bracket over the angle bus to the connection with the gauge Dual-Range Force Sensor DFS – BTA Vernier. The obstruction of a drag and static friction force in the bus were prevented by respective separation of the measured part from a sensor. Separation X in picture A enables the movement of measurement system to the force gauge (picture B) merely due to the impact of the aerodynamic drag caused by air mass in the wind tunnel.