esgg
Posts: 43
Joined: Sun Feb 26, 2006 3:43 am

Helicopter Propwash

Wed Apr 08, 2009 9:58 am


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Photo © Alfredo La Marca - SpotIT



Judging from this picture there are two separate wortexes from this helicopter. I thought that the body of the helicopter was so small compared to the rotordisc that there would only be one wortex under the helicopter.

Can anyone explain?
 
3MilesToWRO
Posts: 258
Joined: Sun Mar 12, 2006 2:08 am

RE: Helicopter Propwash

Wed Apr 08, 2009 12:34 pm



Quoting ESGG (Thread starter):
I thought that the body of the helicopter was so small compared to the rotordisc that there would only be one wortex under the helicopter.

Erm, why "so small"? The fuselage is not so small and in this case divides the airflow quite well in two parts. I guess if the helicopter was higher, the two halves would indeed join below the fuselage, but this time they apparently didn't have time/space to do this.
 
UH60FtRucker
Posts: 3252
Joined: Tue Mar 29, 2005 9:15 am

RE: Helicopter Propwash

Wed Apr 08, 2009 2:37 pm



Quoting ESGG (Thread starter):

It's simple rotary wing aerodynamics, at work.

Rotary wing aerodynamics shows us that when blades rotate, it creates induced flow through the rotor disc, forcing air downward. To fixed wing guys... it's akin to "prop wash", but we call it "rotor wash."

Now lets look at the photo. The rotor blades are rotating counter-clockwise, and if you look... you'll see that the vortices being created by the rotating blades, are also rotating in the same counter-clockwise motion. If you look on the right side of the aircraft (starboard side), the blades are pushing that vortex up against the main fuselage... which serves to "contain" that vortex. In comparison, the left side (port side) has no fuselage to push the vortex against, so that vortex is larger and more spread out. Also... notice that the left vortex is more forward of the aircraft, whereas the right vortex is more aft of the aircraft. This is simply because of the direction of the rotating blades, which "pushes" those vortices in their direction.

If this aircraft was out of ground-effect, and maintaining a higher hover, then the two vortices will spill out, becoming larger, and eventually blending together.

What's interesting, is that at a hover, and especially with high power applications, you can feel the vortices buffeting against the side of the aircraft, and making a slight rocking motion.

Hope that helped.  Smile

-UH60
Your men have to follow your orders. They don't have to go to your funeral.
 
KELPkid
Posts: 5247
Joined: Wed Nov 02, 2005 5:33 am

RE: Helicopter Propwash

Wed Apr 08, 2009 2:50 pm



Quoting UH60FtRucker (Reply 2):
it's akin to "prop wash", but we call it "rotor wash."

Is it available in buckets for fooling unsuspecting but naive ground and maintenance personnel, too?  Wink

When I worked at the airport, a favorite joke to play on a new hire was to ask them to go fetch a bucket of prop wash... Big grin
Celebrating the birth of KELPkidJR on August 5, 2009 :-)
 
esgg
Posts: 43
Joined: Sun Feb 26, 2006 3:43 am

RE: Helicopter Propwash

Thu Apr 09, 2009 6:49 pm

Thanks.
The total knowledge of the A-net members never fails!!
 
YWG
Posts: 1055
Joined: Wed Feb 07, 2001 11:29 am

RE: Helicopter Propwash

Sun Apr 19, 2009 2:32 am



Quoting KELPkid (Reply 3):
a favorite joke to play on a new hire was to ask them to go fetch a bucket of prop wash...

...from one of the more serious mechanics who doesn't think the joke is funny.

It never gets old.... Big grin
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