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Old 06-16-2013, 11:33 AM
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Default gyro wake

Hi
anyone know anything about gyro wake we leave in the sky ?
I have visited the odd gliding and parachuting site, both are not keen on rotorcraft as the associate them with helicopters and hate helicopter downdrafts, a bit of education and it's all sorted , but it would be nice to know a definitave set of words that alleviates their fears. I also have a microlight and paramotor guy that wants to take some air to air pics. I dont want to collapse the parachute or anything else nasty.
any thoughts ?
Thanks
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Old 06-16-2013, 11:46 AM
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There is definitely a wake as I have chased other gyros around and have been in the wake, a little bumpy but no big deal. Not sure how it would affect a parachute.
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Old 06-16-2013, 11:59 AM
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Wake for a any aircraft is also called induced velocity. Induced velocity reduces with forward speed for rotary wing aircraft and also with disk loading. For a VPM M-16 at 65mph it's about 4 fps. If you want to learn a bit more have a look here:
http://www.rotaryforum.com/forum/sho...53&postcount=4
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Old 06-16-2013, 12:43 PM
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Gyro rotorcraft do not have the same down wash as a helicopter. Remember the helicopter produces thrust the gyro produces lift only with the rotor. Air flow is totally opposite. But a gyro does have prop wash more like a plane. This can be seen when a gyro cuts toilet paper in the sky the streamer does not show a downward thrust as its cut like you would see in a helicopter.

Sounds like you have people that see rotorcraft and just assume things.
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Old 06-16-2013, 12:58 PM
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A helo rotor produces thrust and lift, a gyro rotor drag and lift. You add up both using good old Pythagoras to yield resultant rotor force. If resultant is equal, helo and gyro produce the same downwash (=induced velocity = wake) if disk area is also equal.

Last edited by kolibri282; 06-16-2013 at 01:14 PM.
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Old 06-16-2013, 04:05 PM
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This shows the wake of a small helicopter very well. The rotor clearly shows the down wash before the transition to forward flight. Very interesting view.


http://youtu.be/Mh-tRy2bE14
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Old 06-16-2013, 11:23 PM
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For comparison: This is the same wake a fixed wing of the same weight and the same span at the same forward speed.
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Old 06-17-2013, 03:45 AM
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Good tutorial on wake turbulence!



Wake Turbulence Avoidance - YouTube
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Old 06-17-2013, 03:59 AM
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If you get wing tip votices on a plane and you can make a wing more efficient with winglets, could you put winglets on rotors?
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Old 06-17-2013, 04:20 AM
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Interesting question Peter. Recently doing air to air video with an RAF 2000. Bigger and heavier than the Bensen so treated it very cautiously, more so than when doing it with you and John, though again both were heavier machines than mine.

Any wing/rotor will in the production of lift produce wing tip vortices and having for years practiced extreme caution when following heavier aircraft in the landing sequence (always remaining at, or above their glide slope if close) experienced my most dramatic induced drag turbulence 10nm in trail of a Saudia 747 ahead of me going in to land at Riyadh. His gear was up however he would at that point have had some flap and probably at a speed of about 190kts reducing. I was hand flying and the aircraft was a mid size exec Citation Excel.

As he turned at the VOR I looked at the DME to check our distance to go and at that moment we experienced a sudden and very violent roll to the right. Correction was instinctive and the roll stopped at around 60 degrees of bank. No sooner were wings level when we again rolled, this time the other way equally violently.

To have hit one was unfortunate, to hit two pretty amazing. My only conclusion, we had either crossed both at an angle, or one vortex had opened up and I had crossed through both sides. The power and it's effect was sobering and unforgettable.

As usual with our gyros I would have to believe that the rotor tip vortices left would be quite a complex pattern of disturbed air and vary with what maneuvers the gyro is doing.

It has always been my understanding that high aspect wings leave vortices of greater rotational velocity, these varying in intensity with weight, speed, phase of flight and wing configuration of the originator, and that they sink below the point of origin then stabilize. This would indicate to me that a helicopter or gyro would leave higher speed vortices than a fixed wing aircraft of similar weight.

Been a lot of research into rotor tip technology and the BERP tips on Pumas as well as a number of other shapes are probably better that the winglets commonly seen on fixed wing commercial aircraft.

Desmon that was a fascinating video, thank you for posting.

In forward flight here appeared two principal areas of disturbed air from each side of the rotor, but also a broad swathe of less disturbed air from both front and trailing edge of the rotor disc that appeared to fall below those from the outer edges. The hovering vortices we can discount, but we would be leaving disturbed air above us in the vertical descent.
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Last edited by Resasi; 06-17-2013 at 04:32 AM. Reason: Viewed Desmon's clip
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Old 06-17-2013, 07:25 AM
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Back in my fixed wing days, I would exicute a 360 degree turn and if done properly you would fly through your own wake and feel a little bump.
I have done the same maneuver many times in the gyro; with the same results.
Just a little bump!
I think the wake we leave would be very similar to a fixed wing.
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Old 06-17-2013, 09:08 AM
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That sounds reassuring.
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Old 06-17-2013, 09:54 AM
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Cool video, helicopter wake.
Ground fog, vortices and friends....AND Helicopters! - YouTube
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Old 06-17-2013, 10:38 AM
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There appears to be quite a bit of Helo knowlage and a fair amount on fixed wing, so who is up for taking a video of a gyro flying through a smoke column ? , my guess is there will be rotor wake which will be lower than the gyro then we are talking about prop thrust wake all mixed up, but we are mostly very light weight. so , my guess is we leave quite a mass of turbulent air all boiling like crazy for perhaps 1-3 mins rather than a conventional fixed wing tip vortex
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Old 06-17-2013, 05:15 PM
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Is it true that if you fly a jet into another jets wake, because it oxygen poor it will stall the jet engine?
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