Would this be something our SP140 could also benefit from?
Interesting question. In what ways do you think it could be useful for ePPG? Variable-pitch props usually improve efficiency for different regimes of flight, particularly distinguishing between the greater demands of takeoff and climb and the nominal demands of cruise flight. Do you expect that this could extend flight endurance by reducing battery power demand during cruise? Since ePPG does not need to run the motor continuously, but effectively manages demand by means of intermittent or proportional operation, it seems to me that it might best use a “climbing prop” at all times. Moreover, endurance that is already limited to only about an hour at best does not admit of much cruising. An ePPG flight consists almost entirely of climbing to some altitude and gliding back down, perhaps several times in a flight session, but not really in a cruising cross-country flight regime. Variable props are traditionally heavier than fixed props, and that is a weight penalty that ePPG cannot afford for its limited flight regime. I think ePPG would prefer to favor devoting all discretionary weight to additional battery endurance, if possible, particularly for foot-launched platforms. Is this particular variable prop very light? How is its pitch controlled? [Edit: Allow me to apologize, please, that I failed to notice that the above picture was actually a link to a YouTube video which answered some of these questions, at least in the context of a continuously-running fueled engine system for which “changing gears” is of benefit to engine efficiency. Nonetheless, the efficiency of electric motors does not follow the same power curve over a range of RPM as an ICE. It does not benefit from “changing gears”, even in a continuously-variable scheme.] Let me return to my initial question: How do you envision such a prop benefiting an ePPG?
It wasn’t clear to me how much of the efficiency was from an inherently more efficient angle of lift, vs keeping the motor closer to its ideal band. If the lift angle is more efficient, that helps even with an electric.
For example, max power requires shoving every fixed magnetic pole with max volt/amp any time it would push in the right direction, subject only to how fast you can switch. But that same voltage and amperage will make a bigger difference when a pole is just past the wire (whose current is doing the pushing) then when it is halfway to the next wire. Maybe after tilting to the efficiency setting, you can power the motor 10% less, and maybe that takes 20% off the duty cycle, because you can choose the 20% where it is least efficient. If so, that drains the battery 20% more slowly.
He also mentioned that it is much quieter, and that may be even more important with electric than with gas, because the rotors represent an even greater percentage of the noise.
Many modern ICE cars have 5 or more gear ratios to keep the motor in the power band or efficiency band. CVTs have even been implemented and if done right are worth the power loss due to slippage. Tesla and most other electric cars have one gear ratio.
The concept of positioning the center of lift behind the center of rotation of the blade and using a counter spring system could be applied to EPPG if it were to feather the prop when unpowered.
That could actually provide some revolutionary performance gains.
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Yeah that would definitely increase the glide ratio. Thermaling PPG and powered gliders have successfully used folding propellers. A spring activated feathering would probably work just as well.
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