turbulator tape vs VG's

[Dplunkt]

Good reading here as well..... http://phys.org/news/2012-09-scienti...se-vortex.html

I read that article too, not bad. To Ron's point there is really limited comparison from a golf ball to a wing for a variety of reasons including the ball is spinning. Where dimples made sense to me was not in dimpling the entire surface but like zigzag tape, putting a couple rows along the length of the airfoil at a strategic location just in front of the separation bubble to keep the air attached longer. For example Aircraft spruce sell a turbulator tape kit for cessna struts.

To your points Ron, if the boundary layer is only say 1/8 or less at the location where VGs are applied why do they need to be 1/4"+ tall? The other thing that i like about the delta shaped vg is that deltas create a strong vortices at higher angles so this shape might be effective (I've not tested it though). I'm thinking that, as you noted, that the airflow goes into the VG and thus "compresses" a little causing a stronger "exit" over the top of the delta shaped sides creating a stronger vortex than it would otherwise. i have no clue if I'm right about that though.

When the weather turns better (we got 5 inches of snow last night) I'm going attach temporarily some of these as try to document any change in flight characteristics. if I see any good results I'll post those back here.

[Ron Blum]

Sounds like you have a good plan. I am interested to know the results. Strength of the vortices are a result of the airflow energy. Looking at a typical profile of the boundary layer, most of it is at a higher airspeed (it's only the flow really, really close to the surface that is greatly slowed.

[raytoews]

I tried dimple tape on my Grumman Cheetah (don't panic it's in the OM category) and found no or virtually no difference. I put it at the high point of the wing as per instructions.
Now I have a set of VG's I'm going to try. Grumman guys don't think it will help but nobody has ever tried.
First I'm going to do some tuft testing to see what it really does, the videos are pretty impressive.
Has anybody tried tufting the bottom of the wing, I know there is no "lift" generated there but tufting looks for turbulence,,,,right?
If I get time I will try it and screw a gopro to the bottom of the wing and have a look see.
The same for the back of the canopy, there is about a 1/8 transition between the back of the canopy and the fuselage.
I understand the VG's are supposed to re-attach the laminar flow, is this not correct?

Ray

[Ron Blum]

Now you're talking! If you find anything on the bottom of the wing, I would be shocked (except behind gear legs, etc.). If something like that happens, it would be in cruise and not near stall. BTW, contrary to popular belief (low pressure on top of the wing and high pressure on the bottom of the wing), both sides are actually lower than ambient pressure (for most of the surface) until you get to some pretty high angles of attack. I am jealous of what you're doing. Again, have fun ... safely.

[Ron Blum]

Just looking real quick, but I see 4 draggy things on the Cheetah (besides the back edge of the canopy like you mentioned): exhaust stack, nose gear strut, round antennas (you would be surprised) and the beacon on top of the vertical.

[Bill Greenwood]

There is a great article on Vortex Generators in the June 2012 issue of AVIATION CONSUMER magazine with the subtitle Real Bang For The Buck. It covers 5 brand on 16 different airplanes, and is especaially recommended for extra safety on light twins. Also says, "not an option for modern high performance aircraft like a Cirrus SR 22", but as to why, it really seems that no one has tried it on Cirrus. They did try them on a Lancair IV which is very high performance and stall speed came down so that it really would not stall, but cruise speed lost 11 mph. This was with the vg at 11 % back on wing chord.
If the vg is too far forward, it will lower stall speed but penalize high speed, and if too far rearward the reverse so that it may not help stall speed.
The main company seems to be Micro Aerodynamics.

[Ron Blum]

Yes! You don't get something for nothing ... except if you're fixing a problem (which new airplanes, designed with high performance CFD programs should not have. This is a great forum. Thanks!

[Victor Bravo]

In another lifetime, in a previous century, I was a sailplane racer. Although not a trained aerodynamicist by any means, I do know that the difference between the "turbulator tape" and the "VG's" is the intention and effect of the modification, and an order of magnitude difference in the amount of air they affect.

VG's are there to put additional energy into the boundary layer, to prevent or delay airflow separation over adverse gradients. The VG's do create parasite drag, which was considered an acceptable loss in return for the delayed separation. The fact that VG's wound up not costing anything (or much) in speed was an unexpected benefit, icing on the cake.

Turbulator tape is there to force the transition between laminar flow and turbulent flow at a certain point, in a controlled manner, so as to prevent random separation bubbles from forming. These act like TINY little VG's, but they only affect the air within the boundary layer, maybe 1/16 to 1/8 inch. We used the stuff on the bottom of glider wings mostly. The differences were very small,and the performance of a racing glider was one of the few areas where you could actually measure some benefit.

VG's will delay separation on just about any airfoil, although they will instantly turn a low drag airfoil into a high drag airfoil. VG's on a high drag airfoil (Cubs, Cessnas) will deliver a noticeable benefit, but not make the high drag airfoil any more draggy.

Turbulator tape needs a really smooth, laminar airfoil to accomplish their job. Gliders, maybe laminar power-planes like a Lancair, Glasair, etc. Put them on a Cub wing and you would probably never see a difference.