Vortex generators on laminar flow airfoils

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geosnooker2000

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I'm not aware of a data base the lists stall characteristics, but there is more to the stall behavior than just the 2D airfoil selection. Reference all the discussion about the "deadly" NACA 23012, which behaves very nicely in the real world.

One example that I have flown is the LS(1)-0413 aka GA(W)-2 that is used on the Glasair series (likely meets the definition of laminar) and the GlaStar and Sportsman which do not, with riveted the metal wings, have laminar flow. The Sportsman and the Glasair both have benign stall characteristics IMO.


BJC
So, again, I am relegated to "asking around". I'm not saying that is a bad thing. Just that it does not exist in database form... correct?
 

TFF

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I have never seen a database for stall. Unluckily there are probably thousands of great airfoils that will never see the light of day. Cant build an airplane for each for the proof in the pudding test. You pretty much have to pole what is already flying as that is what someone stuck their neck out and built. There is no one trying to hide the magic airfoil until they can make millions on it, at lest not this day and age. Usually it’s not that an airfoil is bad, it’s being used in the wrong application. If one is not building a laminar wing, the classics are hard to beat. If one is laminar , use the Cirrus airfoil. Not real original. If any known better airfoil existed it would be flying. What ends up flying is the best average airfoil. Good in most ranges, not excellent in one and fails at others, hence why they are the classics.
 

Lendo

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It would be educational to know , the reasons for the differences of opinion. I'm sure both opinions are valid, but may vary due to design/ performance of different aircraft. Personally I don't know.
George
 

Hot Wings

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So, again, I am relegated to "asking around". I'm not saying that is a bad thing. Just that it does not exist in database form... correct?
There is no database, that I know of, for how nicely a particular airfoil stalls. The general rule of thumb is to look at the wind tunnel data just before and after the stall.
A high second derivative in that area, or sharp curve of the 2D airfoil data, indicates an abrupt stall. As noted above there is more to it than just the 2D data.

Airfoil tools is a good place to do basic evaluation.
 

Norman

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I have never seen a database for stall.
True that stall characteristics are not often listed in text databases but a pile of pictures (or in our case polars) is also a form of database. TOWS has a great dateset of wind tunnel data of pre-50s airfoil profiles. In order to get reliable stall data you need either actual tunnel data or real CFD. Unfortunately both of those are expensive.

Cant build an airplane for each for the proof in the pudding test.
Actually building an airplane wouldn't give you the 2D airfoil data. A 3D wing has several geometric parameters that can mask the 2D airfoil characteristics. Knowing the 2D airfoil characteristics is only one element of wing design and none of those characteristics will apply directly the finished wing. CLmax will be lower, CDmin will be higher, L/D will be a lot lower (typically L/D of an airplane is 1/4 of the airfoil L/D because of induced drag and the parasite drag of the fuselage), and the stall could be better or worse than the polars indicate depending on taper ratio and washout. There are correction factors for all of these things published in books and web pages.
You pretty much have to pole what is already flying as that is what someone stuck their neck out and built.
Monkey see monkey do does work but if you don't actually understand it well enough to design it yourself you run the risk of leaving out something important or adding something bad.

There is no one trying to hide the magic airfoil until they can make millions on it, at lest not this day and age.
Actually the big aircraft companies hide their airfoils. So do race plane teems.

Usually it’s not that an airfoil is bad, it’s being used in the wrong application.
Bingo!

If one is not building a laminar wing, the classics are hard to beat.
Actually the "classics" (no more than 20% laminar) are easy to beat if at least the front half of the wing's skin is stiff enough. Metal can start out with a lot of laminar flow but will slowly get more draggy as it ages and wrinkles. A fabric covered wooden wing can sustain laminar flow back to the edge of the D-tube (say 30 or 40%) if you put enough elbow grease into the finish, that's why sailplanes started using 40% laminar airfoils back in the 1950s. Fiberglass wings can sustain laminar flow to 80% on top and over 90% on the bottom. A smooth fiberglass wing with a "classic" airfoil will make at least twice as much drag as the same wing with a highly laminar airfoil cross section, that will cut into your rate of climb, angle of climb, rate of descent, top speed, and power required at low speed.

If one is laminar , use the Cirrus airfoil. Not real original. If any known better airfoil existed it would be flying. What ends up flying is the best average airfoil. Good in most ranges, not excellent in one and fails at others, hence why they are the classics.
 
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allonsye

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So what else happened when you got the huge
increase in speed?
Quieter? Smoother?Effects on controlability?
Any more info would be very interesting.
That’s hard to quantify because I has also added them underneath stab fwd of elv. I have to be careful in descents because it wants to hit VNE in a hurry. Handling in all respects is more fluid/linear.
 
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