Mercy! Mercy! That Dang Nabed PERCY!

Power Isn't Everything

This Thursday when I go back to Pope’s Hobby Land in Wausau I plan to get six props that are the OS manufacture’s recommended ones for a Sixty-Sized engine and run a string of test data using this new thrust measuring device I've acquired.

Already I’m wondering what the significance of the data would be. For example suppose one of the six proved to be the one that maximized thrust. So what? Would that mean this propeller is the best for all Sixty-Sized aircraft or would there still be conditions where one of the other ones would be better.

For example the prop generating the most torque might be best for one type of airplane but not necessarily for another. Allow me to explain. On Friday night our club has indoor flying at the gym of a High School in Wisconsin Rapids. I have this ultra-light indoor electric model called an “Ember.“ Once it is trimmed out it virtually flies itself and requires only some rudder inputs to get it to circle the gym. It runs best at half throttle. This means it came with an engine and prop that matched the lightweight construction and wing loading of the model.

So there are at least two variables introduced that have a greater influence on the model's flight characteristics than how much maximum torque the engine generates. So it becomes apparent that in the range of fuselage and wing possibilities some airframes would require a different propeller to meet both the design and power requirements of the engine and airframe.

As a rule of thumb I plan to begin with the hypothesis that the right engine and prop are those that make the plane fly best at half throttle. I'll also be capturing RPM data and heat data for each of test run series. For example the engine being tested will be run with a different prop for each series. The series will consist of data taken at idle, quarter throttle, half throttle, three quarter throttle and full throttle. In addition to the torque reading there will be an RPM and heat measurement.

It seems to me that an airplane that is light and aerodynamically streamlined will require a different propeller than one that is heavier and with more surface area. For example the prop to run a sport aircraft, a war-bird, a glider and a biplane each might require a greater size and pitch... even though they all might require a given sized motor..