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Helicopter Propwash  
User currently offlineESGG From Sweden, joined Feb 2006, 51 posts, RR: 0
Posted (5 years 6 months 2 weeks 5 days 5 hours ago) and read 3714 times:


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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?

5 replies: All unread, jump to last
 
User currently offline3MilesToWRO From Poland, joined Mar 2006, 280 posts, RR: 0
Reply 1, posted (5 years 6 months 2 weeks 5 days 2 hours ago) and read 3674 times:



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.


User currently offlineUH60FtRucker From , joined Dec 1969, posts, RR:
Reply 2, posted (5 years 6 months 2 weeks 5 days ago) and read 3645 times:



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


User currently offlineKELPkid From United States of America, joined Nov 2005, 6408 posts, RR: 3
Reply 3, posted (5 years 6 months 2 weeks 5 days ago) and read 3641 times:



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 :-)
User currently offlineESGG From Sweden, joined Feb 2006, 51 posts, RR: 0
Reply 4, posted (5 years 6 months 2 weeks 3 days 20 hours ago) and read 3462 times:

Thanks.
The total knowledge of the A-net members never fails!!


User currently offlineYWG From Canada, joined Feb 2001, 1146 posts, RR: 2
Reply 5, posted (5 years 6 months 1 week 1 day 12 hours ago) and read 3130 times:



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



Contact Winnipeg center now on 134.4, good day.
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