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

Helicopter Propwash

View Large View Medium

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: 259
Joined: Sun Mar 12, 2006 2:08 am

RE: Helicopter Propwash

 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

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.

-UH60

KELPkid
Posts: 5247
Joined: Wed Nov 02, 2005 5:33 am

RE: Helicopter Propwash

 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?

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...
Celebrating the birth of KELPkidJR on August 5, 2009 :-)

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

RE: Helicopter Propwash

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

 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....
Contact Winnipeg center now on 134.4, good day.

Who is online

Users browsing this forum: No registered users and 2 guests

Popular Searches On Airliners.net

Top Photos of Last:   24 Hours  •  48 Hours  •  7 Days  •  30 Days  •  180 Days  •  365 Days  •  All Time

Military Aircraft Every type from fighters to helicopters from air forces around the globe

Classic Airliners Props and jets from the good old days

Flight Decks Views from inside the cockpit

Aircraft Cabins Passenger cabin shots showing seat arrangements as well as cargo aircraft interior

Cargo Aircraft Pictures of great freighter aircraft

Government Aircraft Aircraft flying government officials

Helicopters Our large helicopter section. Both military and civil versions

Blimps / Airships Everything from the Goodyear blimp to the Zeppelin

Night Photos Beautiful shots taken while the sun is below the horizon

Accidents Accident, incident and crash related photos

Air to Air Photos taken by airborne photographers of airborne aircraft

Special Paint Schemes Aircraft painted in beautiful and original liveries

Airport Overviews Airport overviews from the air or ground

Tails and Winglets Tail and Winglet closeups with beautiful airline logos