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Aerospace engineering

Anonymous69 Wed 17 Mar 23:50:12 2021 No.12847654 View Reply Original Report

Quoted By: >>12847733 >>12847788 >>12848713

hey my intelligent anons, why is propeller efficiency low at both high and low advance ratio?

Anonymous

Anonymous Thu 18 Mar 2021 00:09:12 No.12847733 Report

Quoted By:

>>12847654
just think about it. At zero, the prop is doing nothing. On the other hand, when V approaches the order of nD or larger (that is, V/nD => ~1 or greater depending on pitch) then the propeller is pushing against nothing and all energy is wasted.

Anonymous

Anonymous Thu 18 Mar 2021 00:25:26 No.12847788 Report

Quoted By: >>12847804

>>12847654
Not a planefag but a boatfag but if a prop for is turning too slowly it won't be able to effectively move water but if it's moving so quickly that water cavitates around it it won't be making any thrust either. Think of it as like a car spinning its tires. Planes are probably no different.

Anonymous

Anonymous Thu 18 Mar 2021 00:29:48 No.12847804 Report

Quoted By: >>12847848 >>12847858

>>12847788
but how do you calculate the "about right" speed?

Anonymous

Anonymous Thu 18 Mar 2021 00:44:59 No.12847848 Report

Quoted By:

>>12847804
No clue, probably a combination of blade airfoil and aspect ratio and chord and RPM.

Anonymous

Anonymous Thu 18 Mar 2021 00:47:28 No.12847858 Report

Quoted By:

>>12847804
this, i want to know this as well

Anonymous

Anonymous Thu 18 Mar 2021 05:30:24 No.12848713 Report

Quoted By:

>>12847654
Because the AoA on the blades is too high at low speeds and too low at high speeds. The highest efficiency is when the blades achieve L/Dmax for a given airspeed/RPM combination; any other speed or RPM will result in inefficient thrust development unless it’s a constant speed propeller configuration.

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