Hello

Can anyone please tell the diff b/w turbulated wing and normal wing,How turbulated wings increase performance

thanx

JB

Hmm, a question that might need a book.

Many airfoils develop an unstable flow over the upper surface "just before" that part of the wing stalls. That means for a start that we are dealing with low speed airfoils, or a airfoil operating at the very low point in its effective range.

Very often this instability is accompanied by a "bubble" with reverse flow on the wing surface usually somewheres just back of the high point.

This process is caused by the boundary layer slipping off the wing surface and then re-attaching itself. (If it does not re-attach then you have a full-blooded stall).

The idea of the turbulators is to make the boundary layer turbulent (hence the name). This makes it "sticky" and prevents the partial stall/bubble condition.

In some instances, turbulators have been used to actually generate the surface bubble.



OK having said that we obviously have two different groups.

The first group (preventing b/l detachment) are most frequently found in the front 20% of the wing. The most common on models are thread and "trip tape". The most effective are the "zigzag strip" but note that these are specialised and require some care in building.

The second group can be multi spar wings, step at the high point (tried extensively on ffhlg), and multi strip turbulators. Usually these are found between 30% and 50% C.


How to make?

Strip turbulators - generally less than .5mm high and less than 3mm wide.

Threads - anything from fine terelene thread to knitting wool (dope it on). Personally I dont like these.

The zigzag strip I have tried and it works but it is a B*** to set up. Made mine from 160gm paper for a 130mm chord. It was about 3/8" wide and the zigzag was about 1/4". Glue it on straight edge forward, zigzag back. Leave to dry thoroghly then carefully sand a taper into the paper so that it is wedge shaped. The zigzag edge should finish in a step.

<e> BTW take a look at the series of airfoils that Lissaman developed for Gossamer Condor. The upper surface is actually concave (not a reflexed airfoil). I understand that this feature was developed to encourage and capture the vortex bubble. Made these airfoils effective in a very narrow Reynolds No. and speed range.

I've used turbulators on two models in the past. In both cases they had airfoils designed more for speed than for floating. In both cases they became very "sink-y" when I tried to slow them down. I made turbulators using 1/8 inch wide automotive trim striping tape used two layers thick and the low speed range was greatly helped. If you can't find the automotive tape then you could use regular vinyl electrical tape cut down to 1/8 wide and use two layers again. One layer wasn't enough I found. It helped but not enough. 3 layers had no extra effect and the high speed portion seemed to be affected on the first model I tried them on.

So if your model seems to become draggy and sinky (very technical terms... ) then try some tape turbulators. Start with them about 30% back and move them forward until they help. If you get to about 1/4 inch from the leading edge and they have not helped then either your airfoil didn't need the help.

If your model uses a floaty airfoil then you may not notice any effect. Also on fast airfoils there will be a small penalty from the extra drag but it's very little and the low speed thermalling is so much better that the small loss of speed is not an issue.

Good luck.

All wings involve turbulent flow, but to different degrees.

Laminar flow is analagous to the smooth part of the smoke coming off a cigarette or candle and the point where it begins to curl is where turbulent flow begins.

Airfoils where the flow stays laminar farther aft than about 40% of the wing chord are considered to be laminar flow even though few airfoils maintain laminar flow aft of 60-70% chord. Laminar flow has less drag but also less energy in the boundary layer and the boundary is more prone to separation (ie: a stall) at relatively lower angles of attack.

In the case of a "turbulent flow" wing, the turbulent air flow starts rather early and is present over the vast majority of the airfoil. Turbulent air flow has more energy in the boundary layer and will stay attached at higher angles of attack. Skin friction is also about an order of magnitude higher though, so they can be draggier at higher speeds.

So laminar flow is great for high speed flight, while turbulent flow is preferred at low speeds and higher angles of attack.

At the speeds and reynolds numbers involved in thermal gliding, turbulent flow has many advantages. Turbulators of any type essentially add energy to the boundary layer, induce turbulent flow and assist in keeping the airflow attached to the wing.

The boundary layer in a turbulent flow situation is a little thicker than in laminar flow, but I don't think a "bubble" is a good description as it is still very thin. If you have a bubble of reverse airflow of any significant depth, you have a stall with an attendent loss of lift and increase in drag. That is exactly what a turbulator is designed to prevent.

I have experience with a Drifter II with a pair of turbulator spars deisgned into the leading edge of the wing and particularly at the tips this results in three slightly concave shapes over the top of the first third of the airfoil. It works well as the glider is a floater and designed to thermal at maybe 12 mph. So there is really no parasitic drag penalty and the wing benefits from the improved flow attachment and efficiency at higher angles of attack.

I have other sailplanes where I have used trim striping strategically located to get the same effect. Used correctly with the striping doubled toward the tips, it can be as effective as washout in eliminating tip stalls but without the loss of overall wing efficiency that can occur with washout.