Vortex Ring State in gyros?

Ed L

Newbie
Hi All correct me if I am wrong. I also thought no way untill I stopped and really thought about it. to create lift there must be a downward flow of air. without a downward flow of air there can be no lift. in autorotation there is a downward flow of air creating lift otherwise we would just drop out of the air.

Doug

Are you saying/thinking for a fixed wing there must therefore also be a “downward flow of air”? I don’t think that’s true. For both there’s an upward vector of lift, caused by the aerodynamic forces at play.

Again, I don’t believe there is a VRS for a gyro and have seen no credible source suggest otherwise.

Jean Claude

Junior Member
Are you saying/thinking for a fixed wing there must therefore also be a “downward flow of air”? I don’t think that’s true.
Of course it is true: Aft, the angle of deflection is 2 Cl /πA radians with A = Aspect ratio
For example if A = 5 and Cl = 0.5, then Deflection = 3.6 degrees down

For the lifting disc of a rotary wing, A = 1.27 and when CL of the disc is 0.5, then Deflection is about 0.25 rad or 14 degrees
For both there’s an upward vector of lift, caused by the aerodynamic forces at play.
It's also true. Just more local. The sum of all the local pressures on the walls produces on the one hand the lift vector, and on the other hand the deflection of the air flow

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DASBUR

Member
An article at Skybrary states that for a vortex ring state to occur:
The aircraft has to be in powered flight. If the engines are not producing power, the aircraft is in autorotation and the upflow of air (rather than engine power) is being used to drive the rotor motion. It is not possible to enter the vortex ring state whilst the helicopter is in autorotation.

Now it makes sense because one of the ways to get out of VRS was autorotation

Doug

Ed L

Newbie
Of course it is true: Aft, the angle of deflection is 2 Cl /πA radians with A = Aspect ratio
For example if A = 5 and Cl = 0.5, then Deflection = 3.6 degrees down
View attachment 1146787
For the lifting disc of a rotary wing, A = 1.27 and when CL of the disc is 0.5, then Deflection is about 0.25 rad or 14 degrees

It's also true. Just more local. The sum of all the local pressures on the walls produces on the one hand the lift vector, and on the other hand the deflection of the air flow

Fair enough.
Stepping back, though, it still seems like “we” are trying to rationalize that VRS can occur in a gyro. Best I can tell, the scientific answer still seems to be no. Failing to respect the H/V curve, for example, does not mean a VRS was induced in a gyro.

ferranrosello

Member
Hi, gents. I'm late in this post... However, the vortex ring state in helicopters implies a very fast induced flow, and this was learnt by experience. Nobody was able to anticipate in by understanding the rotors. I don`t have a suitable explanation however, gyros cannot get this high induced speed, because the pitch angle is very low. And the cure to exit VRS in helicopter is very close to enter an autorotation, because we know (by experience) that is totally impossible to get a VRS in autorotation...

And of course, the autorotative rotor has an induced flow (induced velocity) too. But only in the outer section of the rotor disc is producing downwards induced flow. The medium part of the rotor is producing induced flow in a direction close to the rotor dis disc plane...(in helicopters rotor mode all the disc is producing induced flow.

In fact, when a helicopter has a reasonable forward speed, the rotor induced flow is "less vertical" and much more closed to horizontal... And then is not possible to get a VRS.

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