Vortex Generators on helicopters?

[rotormandan]

I am a new heli cfi and I am working with a guy who just bought an R22. He's one of those guys who wants to put all the extra little gismos on he can find. His new thing is putting V.G.'s(vortex generators) on the rotor. He says he knows a guy that does them and is certified to do it. Now I've seen these on fixed-wing and they work great but on a heli? It doesn't make sense. It seems like they'd be backwards or sideways during the rotation of the blades and would greatly increase drag. Has any one heard of V.G.'s on a heli? and if so, are they a special shape and how do they affect the aerodynamics and performance? It just doesn't make any sense to me to be on a hei.

 

Please get back to me

[RockyMountainPilot]

I am a new heli cfi and I am working with a guy who just bought an R22. He's one of those guys who wants to put all the extra little gismos on he can find. His new thing is putting V.G.'s(vortex generators) on the rotor. He says he knows a guy that does them and is certified to do it. Now I've seen these on fixed-wing and they work great but on a heli? It doesn't make sense. It seems like they'd be backwards or sideways during the rotation of the blades and would greatly increase drag. Has any one heard of V.G.'s on a heli? and if so, are they a special shape and how do they affect the aerodynamics and performance? It just doesn't make any sense to me to be on a hei.

 

Please get back to me

 

Vortex generators provide most of their benefit at low speed and high AOA by maintaining laminar flow, reducing stall speed, and reducing drag. I have never heard of VG's being used on a helicopter for aerodyanmic benefits, but I do know they are used for noise suppression(Which may have an aerodynamic benefit as well). If VG's reduced the power needed to hover or increased cruise speed significantly, I think they would have been used by the manufacturers years ago.

 

Also, I am certified to install VG's on a rotor system, but it is not legal for me to do so without an STC. Someone could do it with a field approval, but there is no way an inspector would sign it off without massive amounts of experiments and testing, and if that were going to be done, might as well apply for an STC. If there is an STC, it would be the first time it has been heard by me.

[Collective Down!]

I am a new heli cfi and I am working with a guy who just bought an R22. He's one of those guys who wants to put all the extra little gismos on he can find. His new thing is putting V.G.'s(vortex generators) on the rotor. He says he knows a guy that does them and is certified to do it. Now I've seen these on fixed-wing and they work great but on a heli? It doesn't make sense. It seems like they'd be backwards or sideways during the rotation of the blades and would greatly increase drag. Has any one heard of V.G.'s on a heli? and if so, are they a special shape and how do they affect the aerodynamics and performance? It just doesn't make any sense to me to be on a hei.

 

Please get back to me

 

I agree with RMP... If it was so great, Robinson would already be doing it. If the helicopter is still under warranty, I'd look into how that STC would affect the warranty.

 

Without pulling out the text books, I have to raise question regarding how vortex generators work. Vortext generators don't maintain laminar flow, but create a turbulent flow, which sticks to the airfoil better. The trade off is that they add drag, which must increases the power required at any given collective pitch setting. At the safety course, the instructors mentioned that Robinson blades are intended to be laminar flow up to the max camber point, at which point it becomes turbulent flow. Even on an airplane, the VGs are only beneficial at low speeds and high angles of attack. The helicopter's rotor should never even be at low speed (low rotor RPM) and high angles of attack with power applied.

 

 

This is COMPLETELY unrelated to the VG's, but you mentioned that the owner wants add-ons for the R22. I would highly recommend:

1. Fine-wire spark plugs from Champion - I've never had a fouled spark plug since installing them, and I've noticed slightly better performance

2. Airwolf remote mount oil filter kit (STC approved for the R22) if your helicopter doesn't already have an oil filter - It's good for the engine, and extends oil changes to 50 hours (although I'd recommend 35 hour intervals).

3. Challenger air filter (similar construction to K&N) - Less air restriction, which translates to a slightly higher critical altitude at which the throttle is full open (you won't notice it so much at low altitudes). You can clean it 25 times and reuse it instead of constantly replacing the paper filters.

4. Bottle of Avblend with each oil change - It's rediculously expensive, but keeps the engine running tip top. All my compressions went up after a couple oil changes.

 

There has been alot of discussion about the autogas STC on here... I thought about it, but stayed away from it because of the logistics of it all. Also, my insurance company specifically asks if the aircraft uses autogas, so I'm assuming that it would raise an issue with them. I'm not for or against it, because I'm not educated enough to take a side.

Edited July 18, 2007 by Collective Down!

[RockyMountainPilot]

Collective Down,

 

VG's circulate the air over an airfoil in order to mix higher and lower energy air to prevent seperation which is the cause of turbulant air. VG's don't cause turbulance, they postpone it. Turbulence is chaotic air, whereas VG's create a wanted and intended swirl.

 

Also, VG's will reduce drag if they are indeed postponing seperation of the air from the airfoil. The small amount of drag that occurs from their form is offset by the large reduction in drag from postponing the seperation.

[rotormandan]

Thanks for the info. I'll pass along the extras list to the man. Anything to add power and keep the enging running tip top is definatly a must as this guy is a big guy at 233 lbs. Luckly I'm only 140 so we can fly together with about 12-15 gal depending on the oat. Even then we are pushing the limits on MAP chart.

[Shawn Coyle]

To be effective on a rotor blade, the VGs would have to micro-sized, literally machined into the surfaces of the blade. I don't know of anyone who's done that - and I have a patent on VG to reduce aerodynamic drag on trucks.