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These cookies track visitors across websites and collect information to provide customized ads. Torsional acceleration for internal combustion is typically highly sensitive to engine fuel mixture and is therefore rather uncertain.
Design parameters have been empirically developed to seek reasonable upper bounds for maximum torsional acceleration loads. However, the uncertainty with this sometimes strong especially for racing applications contributor to cyclic stress requires that extensive operational testing be employed to verify structural integrity for high performance applications.
The component of cyclic torsional acceleration is not considered for electric motor applications. Cyclic bending stress induced by precession during rapid loops is also included in the stress computations. However, this effect is very minor, even under extreme pitch rate conditions. In addition, precession stress is normally out-of-phase with torsional vibration effects; therefore, it does not add to peak cyclic stress magnitude.
The bending modulus is sensitive to humidity. Fixed pitch propellers generally have to perform well over a large range of flight conditions. Therefore there is no single design condition that may be used to optimize a propeller shape, even if the model airplane characteristics i. RPM are well known. Therefore, most initial propeller design iterations are verified almost exclusively with extensive flight tests. Once a design is broadly set, interactive optimization algorithms may be used to adjust diameter, pitch and chord distributions to maximize thrust for specified model speed, engine RPM and engine torque.
Two complementary methods have been used to measure engine RPM and model airspeed. These in-flight speed and RPM data are then used to evaluate the propeller performance. After a large database is developed, interpolation between existing designs is used for developing new designs. The telemetry system is a computer controlled data acquisition system that can record up to 30 minutes of data in solid state memory.
The data are played back after flight recovery. While many options exist within the system, it is primarily used for airspeed and RPM measurements. The airspeed and RPM measurements consistently yield data very close to that determined from radar gun and audio recordings, providing considerable confidence in data accuracy. Engine in-flight RPM is determined using a video camera to record engine audio.
Spectral analysis software is then used to determine the dominant harmonic content from the signal. Audio data are collected with the model flying both toward and away from the pilot. Differences in apparent frequency are used to identify and remove Doppler shift effects. Conversion to 3 and 4 bladed propellers is performed by matching the 2-blade torque for specified model speed and RPM conditions.
This method allows efficient use of a rather broad data base that now exists for 2-blade propellers. APC Propellers are also available worldwide from your favorite online supplier or local hobby store.
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