[Tlhingan-hol] Propellers and rotors

[Will Martin]

The blade of an airplane propeller generates lift, like a wing, by creating pressure differences between the two major surfaces of the blade. Water is not compressible, so a water propeller works more through the redirection of momentum of mass. This is why water propellers use such remarkably steep angle of attack (typically around 45 degrees), which would stall the blade of an airplane propeller, making it ineffectual for taxi or takeoff. 

This is also why adjustable pitch propellers exist for aircraft — because the angle of attack changes as the airspeed of the aircraft changes, and it’s better to pitch more shallow to get the airplane started on the ground and to climb, then pitch deeper to cruise efficiently without over-revving the engine. Less expensive aircraft are limited by fixed pitch propellers that have a single pitch, compromised between these two angles, less effective at either.

Nobody changes the pitch of a water propeller. There’s no real advantage to doing so, since water propeller blades can’t stall.

But hey, they both spin and they both push. I get it.

pItlh
lojmIt tI'wI'nuv



> On Nov 4, 2015, at 1:35 AM, Bellerophon, modeler <bellerophon.modeler at gmail.com> wrote:
> 
> ghunchu'wI', jIQochlaw'. muDDujDaq, bIQDujDaq je nIbbe' bIngtaHbogh vo'wI', 'a rurbej.
> cha' tel rav ghaj ngIq vo'wI'. telvamvaD 'etlh ponglu' je.
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