Root vortices

[StanFoster]

Much has been written about tip vortices, but seldom are root vortices covered. Ray Proutys Helicopter Aerodynamics has an interesting sketch which I took a picture of and posted here. The tip vortices have the high pressure air under the outer tip of the rotorblade swirling outward and upward from the bottom of the blade as the air rapidly travels to the low pressure on the top of the rotor tip. This of course causes the spiraling vortice to trail off the tips........................................The inside root of the blade also has an inboard edge to the rotor blade,and here there are vortices being formed turning upward and inward this time, causing a vortice to be created that turns the opposite direction as the one on the outer tip.................................There also is a hole at the root ends where there are no rotorblade section to fill in to the rotorshaft. Smoke tests show that there is a flow of high pressure air going up right around the rotorshaft, going above the rotorhead and then making a fountain like return downward flow right back through the rotor and down to the ground when hovering. This racetrack loop of circulating air picks up dust and debris from the ground and keeps recirculating it alongside the cabin . I see small particles following this pattern and have them come inside my cabin when I am hovering sometimes. I love to hover but watch this debris closely and move on if the conditions are right and I am locked into a dirty vortice. I don't like my turbine ingesting debris, so this is part of my job to watch for while hovering. Usually there is enough wind that the root vortice isn't picking up much debris, but the right conditions happen once in awhile, and I will get moving out of my hover............................................. ................................ There is a meandering root vortice that travels from the rotorhead, twists down around the rotorshaft towards the ground, then like a snake, makes a serpentine path along the ground, getting moved outward by the recirculating outer tip airflow that is coming downward through the rotor, then outward. This outward flow pulls this serpentine root vortice to randomly interact with the tail rotor. At just the right hover height, it can cause fluctuations in the tail rotor thrust which keeps the pilot busy on the pedals. There are also tip votlces hitting the tail rotor at certain clock positions, but this root vortice is just another perturbance to keep the feet busy. There are times when the hover is locked in and very little pedal movement is needed, then other times the pedals are going ack and frth like a fish tail. .....................................To me, reading about this stuff, then actually experiencing it first hand gives me endless excitement. Stan

[All_In]

Hi Buddy!!!
Thank you for posting this the drawing helps. Having not experience with it I'm struggling to really understand it. This helps!!!

[Rotor Rooter]

Stan you are bring up an interesting topic; particularly as to how it might apply to a gyrocopter.

The idea of placing a solid disk in between the roots of the blades to stop the fountainhead effect has been an intriguing one. On a helicopter the front of the rotor disk must be tipped downward during forward flight.

However, on the gyrocopter it will be tilted back and the disk can act as a small lifting body.

Perhaps it has never been considered for the gyrocopter because it might create a slight resistance to pitch change, due to its inertia and aerodynamics.


It is a little, very little, likeVranek's idea.

Vranek Disk Rotor Helicopter concept - YouTube


Dave

[kolibri282]

Dave and Stan,

interesting thoughts! Perhaps the effect of a root disk wouldn't be very noticeable for its lift effect but the losses (vortices) at the root would be diminished. Would be very interesting to see if the effect could be measured. Uhmmm... Dave... didn't you talk about a laboratory van once ...???... After all ..... if you can't measure things you can't tell if you are making progress....;-)

Cheers,

Juergen

[jebthereb]

Stan as you know i have one whole entire hour as a student helicopter pilot.

How do you correct/react to this situation to resolve this.

Do you increase altitude or just move out of it and find a different place to hover?

You talk about clock positions. Is this in relation to the wind direction?

[Rotor Rooter]

..... if you can't measure things you can't tell if you are making progress....;-)

Juergen,

That's the advantage of working on helicopters instead of gyrocopters. If the idea does not work, then in a helicopter you can always back up and take another run at it.


Dave

[birdy]

Usually there is enough wind that the root vortice isn't picking up much debris,
Stan, just wundern, [ slightly off track] , at wot wind speed can you land/TO without feeln translation?
Light choppys like your dont have a very powerfull wash compared to sumthn like a R44, so a strong wind will have you landn before any translation occurs.

[StanFoster]

Jeb- I just watch for recirculating debris, and move out of the hover if its excessive. Most of my hovering is over grass, and its not much of a problem. I won't hover over sand or gravel as this is just too rough on the blades and turbine. The fields have been extra dry lately and I won't hover and create a dust storm, but instead just keep moving along fast enough to keep from recirculating the debris. .........................Birdy- You can take off in winds around 20 mph or greater and be above the speed that produces the shudder the rotor feels when its running into its tip vortices. Stan