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Autorotation Aerodynamics


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Phil Croucher -------- just remember this then. All the adult Spanish females wearing totally black clothes all the time are in forever mourning for deceased husbands............NO TOUCH!!!. :lol: ..........AND get 'outta Dodge BEFORE you use up all that Single Malt.

 

Oh yeah... Ontario and 'corn whiskey'. Remember 'corn' is the main ingredient of American Whiskey. Might not be as 'local content' you imagined.

 

 

 

Freefall --------- who cares about that anyway? If it requires an Act of Parliament, Senate or some other form of State government before an engine will fail, then how a particular R/W autorotates means nothing. :lol:

 

 

 

 

 

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I'm told that the blades on the Wessex were put into a large vice and twisted!

 

cheers

 

Phil

 

Phil,

 

That sounds more like a Russian engineering technique.

 

I once toured a Russian space exhibit about twenty-five years ago in the conference center in Winnipeg, Manitoba, Canada. I swear that all of the hardware on display was built with a monkey wrench and a ball peen hammer.

 

IG

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I found Phils answers as usual to be great.

One must remember that relativity has a large part in anything moving. As the helicopter is descending at a high rate, you must look at the blade pitch angle never as in relation to the plane of rotation but always as the cord pitch relative to the airflow at any given segment of the blade. With a high rate of descent it is impossible for any portion of the blade to be in negative pitch.

 

The fact that it will not autorotate straight down as all the blades segments are stalled nor if we have the pitch set high are the same problem. There is a narrow band of speed that you have to maintain to keep the balance of driving and driven.

 

Next is the formula for lift that is just as important in the the part of velocity squared. Speed of the blade greatly changes the angle of attack as we all experiment with while training for stuck pedal etc. (the m/r and t/r are mechanically linked at ratios that have the t/r spinning much faster. Any reduction of m/r speed sees a much larger reduction in t/r speed resulting in a far less efficient t/r and therefore a different 'spin' of the helicopter at the same collective setting)

 

Back to the blades, the vary reason for twist was to address the problem of velocity as did taper did with area (another important component of lift) all were trying to get lift more evenly spread across the blade. This could only be done though to the extent that is did not reduce autorotational abilities.

 

clear as mud?

 

Hey Windslapper,

 

Your avatar is very cool. It looks like something that Jules Verne would have dreamed up; or more probably Leonardo Da Vinci.

 

I was able to follow, and agree with most of your explanation.

 

Specifically with regards to your last paragraph, so far as I have been able to figure out helicopter blade design, it seems that every manufacturer strikes a balance at some point between a blade's efficiency when driven by the motor and its efficiency when in autorotation mode; because the two design goals are at odds with one another.

 

Thanks for your input.

 

 

 

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.............AND you can call that thing(s) that drivesa R/W or F/W either an 'engine' or a 'motor', BUT you better be darn particular which word you choose and around what group of people you use it amongst. One of those two words is something that runs a washing machine and the like, while the other word is used to describe the item that powers an a/c.

 

 

ISN'T THAT RIGHT, Splitpin? :lol:

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.............AND you can call that thing(s) that drivesa R/W or F/W either an 'engine' or a 'motor', BUT you better be darn particular which word you choose and around what group of people you use it amongst. One of those two words is something that runs a washing machine and the like, while the other word is used to describe the item that powers an a/c.

 

 

ISN'T THAT RIGHT, Splitpin? :lol:

 

What kind of a man would call a 212 a 'two motored chopper' If I heard that I would twist his head off and shyte in the resultant cavity! :D:D

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