Has anyone tried "turbulator tape" like that used on gliders instead of the traditional VG's like microaero's? Did it work? results?
thanks
Has anyone tried "turbulator tape" like that used on gliders instead of the traditional VG's like microaero's? Did it work? results?
thanks
I haven't tried it myself, but i know of at least one military drone that uses those tapes and they're cruising at 170 knots so it seems they can take the higher speeds. I don't know why they wouldn't work.
It depends on your airfoil design, your Reynolds number, your boundary layer thickness, how effective you want them to be, and what you are trying to do with them. Some gliders (very low Reynolds numbers) use them to intentionally trip the boundary layer to be turbulent (so a laminar bubble/separation doesn't occur ... that's higher drag). No matter what VG (tape or other mechanical device you use), it will increase drag. Why? Because a VG takes higher energy air above (off) the surface and swirls it into the lower energy air on the surface (in the boundary layer). The trick is to lower more drag than you create.
For example, if air on the aft end of your airfoil is separated (this can happen both at high speed and low speed), you can add a row of VGs before the place where the air is separating. This will give the boundary layer more energy to try to stay attached to the airfoil ... and therefore reduce drag.
As another example for better stall characteristics, if the air is separating before the aileron as you approach stall, a row of VGs ahead of the aileron (and ahead of where the flow is separating) will add energy to the boundary to keep the airflow attached to the airfoil and give you better control. You will see this on several production airplanes.
VGs aren't a silver bullet, but they do fix some airflow problems.
Hi Ron, thanks for the reply. I've been intrigued by VGs for a while. I happen to fly a PA-22 which uses the cub airfoil and responds to VGs well. I've been reading some abstracts regarding micro VGs (Not Microareo brand but smaller designs) that are no higher and in fact lower than the boundary layer and thus don't create as much drag as the ones we see today. Also, they are shaped in a V with the apex down stream and apparently create a larger vortex than traditional VGs given the size, increasing the effectiveness.Originally Posted by Ron Blum
On another note there have been studies, as you say, with putting either dimple tape or zigzag tape just ahead of the separation bubble reducing drag. Piper puts micro Vgs on the flaps of their Meridian for example to increase the flap effectiveness and reduce stall. I would never do this on a certified planebut I have thought about micro VGs at about 10% of the cord from the leading edge, trying to determine the separation and using zigzag tape there and maybe trying it on or near the flaps, etc. just to see if it noticeably affects stall and drag. According to Microaero which has the STC for PA-22s their VGs reduce stall by 8%-11%. I'd like to see if the smaller VGs could match that, etc.
Dan P
Dan: This is cool that you are experimenting! I am not sure what all you can do on a certificated airplane before you need to hang an experimental ticket on it, but ... way cool. (in my line of work I always put an X ticket on the airplanes).
Since your airplane is fabric covered, laminar flow is not possible; you will always have a turbulent boundary layer (not always bad). Tufting the airplane will show you where the airflow transitions from attached to separated, remembering that each little tuft is also a little VG. A GoPro camera (I am not endorsing a brand name, but you get the idea) on top of the vertical will show you flow over the top of the wing and flaps.
Height of the VG is solely the amount of energy that you need to keep the flow attached (if that is even possible). Flaps in the landing position are almost always separated on the upper surfaces. Although this doesn't increase lift, it does increase drag ... which in a landing scenario is good because you can approach more steeply and get rid of it (the excess drag) quickly in a go-around situation.
Be cautious of large performance claims: 1) Production airspeed indicators get less accurate at very, very low speeds because the differential pressures are very low ... on the order of 0.04 at stall. 2) Due to the higher angles of attack, fixed, production pitot tubes are less in alignment with the airflow and are not optimized for off axis flow. In other words, Flight Test departments use calibrated, very expensive, often swivel-head pitot tubes (to align better with the airflow) to get calibrated numbers and 3) OEMs have to be conservative when they draw the curve through stall speeds because every airplane must meet the numbers.
Have fun!
I don't know much about this myself, but recently read an article from several years back in SOARING magazine, where they experimented with turbulator, which was a layer of tape perhpaps 2 in wide or so. I don't have the article, but recall some points.
First, gliders are different from most powered planes in several ways.
1. The are very slow, stall speed is often about 30 knots and best thermalling speed might be only 50.
2. The high performance ones are almost aviation freaks, with very long thin wings, maybe 60 feet and small fuselages.
3. Glide ratios, with normal wings, range from 22 to 1 for a basic Cub like 2-33 trainer to 60 to 1.
4. Trying the turbulator did work, and even hit glide ratios of 100 to 1. BUT, it was only that effective at one speed, in these tests it was right at 50 mph and fell off sharply at other speeds.
Last edited by Bill Greenwood; 03-02-2014 at 10:50 AM.
You're right on, Bill. Sailplanes live in a VERY point designed world at VERY low Reynold numbers. People will say that there is a difference between 80:1 and 100:1, and there is. The pilot flying the 100:1 paid out the wazoo for that little extra, but he probably missed the thermal, didn't center the thermal properly (or stayed in it too long or too little) or didn't interpret the weather well enough to fly the right track to win the contest.
That's why Bob Hoover is one of my favorites. He didn't have the best _____ of anything, but what he does with what he is flying is just ... well ... awe-inspiring.
Hi Guys,
Yea, I fly gliders too and I'm not sure that the turbulator tape would be the choice to replace VGs on the leading edge. As you guys noted the Reynolds number, aspect ration, etc. of gliders makes the comparison to powered apples to oranges. having said that I'm looking for performance enhancements in a couple areas one being slow flight and stall delay which puts me in that 45-60 mph range but high angle of attack.
Tell me if this makes sense; rather than relying on my ASI what I plan to do is to stall or slow flight maneuver noting my GPS speed in all the directions of the compass and then averaging. This is ground speed but averaged in all four directions should give me a consistent basis for comparison.
regarding performance claims; the thing that interests me with boundary layer manipulation is that it has been tested by everyone from NASA, the military, wind turbines, to auto racing with quantifiable results. I've read articles on using these things on everything from props to struts. There are new shapes that claim to equal traditional VG's without intruding into the free stream, etc. Also, given the cost and difficulty of dealing with the FAA i would imagine that has inhibited some adaptation and use of newer ideas. for example these are shapes I've never seen tested in GA:
the small triangular one next to the penny claims to create a stronger vortex than a traditional VG yet is below the boundary layer. We'll see. One more thing...it's just fun messin around with this stuff.
Good reading here as well..... http://phys.org/news/2012-09-scienti...se-vortex.html
Both of the VGs you show want the airflow to go straight into the device. The black one is used on semi tractor-trailers (and I'm not sure what the center raised piece does). The blade VGs on airplanes (either an inverted "T" or an angle), the flow must come into those at an angle. In other words (on airplanes), the optimum is to have the VGs aligned with the flow in cruise (minimum drag) and then be at an angle (due to outflow or inflow on the wing) as the airplane approaches stall.
Boundary layer thickness is a function of the length of the chord and where you are on that length. As real rough estimates on a small GA airplane, it is zero at the leading edge and 1/4" to 1/2" at the trailing edge. The tape is about the only thing smaller than that. As you can tell, we're only touching the surface of this topic.
As for the comparison between VGs on an airplane and dimples on a golf ball, both try to reduce drag under certain conditions, but that is where the comparison ends. Dimpling an airplane will not make it go faster (sorry). On a golf ball, though: 1) it does go further (less drag on a low Reynolds number sphere) 2) it does go further with a more vertical descent path (on a good shot the ball initially rotates bottom side forward, creating lift as the stagnation point moves down and aft on the ball and 3) (for the "these guys are good" - LPGA and PGA folks) Intentionally tailoring (slicing and hooking) your shots are a great way to improve your game.
As you mentioned, this stuff is fun!
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