An Approach to Involving Testing and Software Computing into the Predictions of Model Aircraft Engine Performance
Autor: Arno Apffelstaedt
Projekt 2
Abstract
The module of aircraft design at the University of Limerick is taught by using the annually
Design/Build/Fly (D/B/F) Competition of the American Institute of Aeronautics and
Astronautics (AIAA). The students are assigned to design an unmanned, electrical powered
and radio controlled aircraft which satisfies best the given mission objectives. In several flight
tests, it was found out that the thrust generated by the propellers does not seem to match
expectations. This report deals with the question how to use testing and software computing to
predict the performance of model aircraft engines accurately. An existing motor test rig was
redesigned to produce accurate measurements on the power system. Two motors, the Hacker
A60-18M and the Plettenberg HP370/50/A3, were chosen to be tested consecutively with two
different propellers, the APC 20x10 and the APC 22x12W. The motors were powered with
battery packs of identical design and capacity. The force of the propeller pulling forward was
measured and recorded. Further, the rotational rate of the propeller, the speed of air exiting
the propeller and the motor voltage and current were measured. The time a power system
could provide a constant thrust value was calculated and named the ‘usable running time’.
The measured performance from static and wind tunnel tests was contrasted to the
equipment’s theoretical performance and to the estimates of computer software called
Propeller Selector. It was found out that the performance measured was close to propeller and
battery discharge theory. The usable running time was found to be a function of the battery
discharge and independent from the motor-propeller combination used. It was further found
out that the estimates of the Propeller Selector were close to the results of the static tests. A
mean down deviation of 5.22 per cent was found. Measurements of the wind tunnel tests were
found to be doubtable. The small diameter of the wind tunnel air stream could not provide a
uniform airflow over the propeller diameter. As a result, the estimates of the Propeller
Selector were far-off the measured performance. The deviation averaged out at 36.24 per cent.
A CD containing test data is included in the appendix.