Vortex generators, slow the plane down?

[rogerh12]

Howdy All;

I was thinking about shortining my model 4 wings a bit, and installing vortex generators to bring the stall speed back down. I thought shorter wings would let the plane go faster in cruise. However, won't the vortex generators just add more drag again and even things out?

Any hard facts on this?

Thanks
Roger

[Newkid]

The two won't make up for each other. The shorter wing only goes 2-3 mph faster but raises the stall considerably. The VGs won't make up for not having the longer wing. The short wing will role a lot faster and give you a better ride in turbulence, and you will still probably be able to go everywhere you go now. I've never heard of VGs slowing a plane down on the top end. Everyone one has different opinions on what installing VGs did for their plane.

[catz631]

I have VG's on my plane but can't say they do much. Look cool though.

[jtpitkin06]

Catz,

The vortex generators in your photo look like they are mounted too far aft.

It is likely the air has already separated from the airfoil by the time it gets to the generators. Did anyone do flight testing of these VG in other positions before selling them to you. Or did they just "wing it" in the mounting instructions? There are several suppliers making generators for experimental airplanes who have never tested them on a Kitfox and market them as good "for any airplane".

I have a Cardinal RG and there are some STCs for VGs on them. All of them are mounted much further forward, and yes, they do slow the airplane down a bit in cruise. The owners who install VGs are looking for slower approach speeds and shorter landing distance for the airfields they fly in and out of. They are willing to give up some on the top end.

I suspect the same is true for the Kitfox.

We're still looking for that free lunch.

John Pitkin
Greenville, TX

[akflyer]

I have VG's on my plane but can't say they do much. Look cool though.


WAY too far aft and the spacing is effed up too..

[kitfoxnick]

Way to far back. I seem to remember 8% of wing cord. I love mine no decrease in top end. My stall speed wasn't drastically reduced maybe a knot or two. Totally different plane at slow speed.

[BigJohn]

I would agree that your's are way to far aft. I put VG's on my KF-5 and found significant improvement. 4-5mph on light loading and upto 9mph at full gross in lower stall speeds and significant improvement on handling.

Here a a couple of photo's on Mine. Also I noticed no change in Cruise Speed, However my Max Speed did loose approx 3mph, Not an issue and the benefit was worth all the effort.

[avidflyer]

At first glance, Catz's VGs do look like they are quite a ways back, but if you look at the leading edge which shows through the fabric, and use that as a measure, I would say the VGs on both planes shown are at about the same place on the wing. In the second picture because of the angle and the dark blue strip, you kind of don't see most of the wing. Take care, Jim Chuk

[catz631]

Actually the VG's are right where they should be . If you will look at the photo closer you will see the rest of the wing. The photo is an illusion due to the wing stripeing. I almost mentioned that but decided to see if anyone would see it.
The VG's are roughly about 6 inches back from the leading edge.I am not at the hanger so cannot give you the exact distance. Before I mounted them I followed the dirrections with the kit and the info here at this site (as well as others)
I had VG's on my prior Piper Pacer and they worked very well but on my Kitfox well....not so much but,I will keep them.The effect,if any,is more subtle I think than on my Pacer(death cruiser)
The wing is a low speed wing anyway and I knew,from prior reports, that they wouldn't do much .
I am constently working on my aircraft and making small improvements as I go along. Some of the improvements were major such as the bush gear and elevator trim system. The VG's eeehhhh.... make for good conversation as you see on this site. Everyone has an opinion on them.
Dick

[kitfoxnick]

Just went out to the plane and measured mine they start at 3.75" from the leading edge, using a framing square held against the bottom of the rib tight to the leading edge and then using a tape measure to measure horizontally to the front of the vg. Further aft seamed to be less effective and further foward only seamed to slow the plane down with no dramatic change in handling. I certainly didn't mean to offend you it's just your coment about not much change that peaked my interest as my change seemed dramatic. With the vgs I can power off stall with the stick full back and the plane will stall and recover and stall and recover without ever letting the stick foward. My vgs are the metal pacific Northwest Aero.

[BigJohn]

I'm with Nick and also did not indend to offend, the VG's just looked way to far back and the spacing seemed off that is why I sent pics of mine. They by the kit NW Aero LLC start at 5" back from the leading edge. It may be the VG kit and there design that just isn't working for you on the Fox. As I said Mine did wonders.

[catz631]

For the "what it's worth" dept. I measured how far back the vg's were from the leading edge and it was 5 inches. This was also done with a framing square.

Dick

[tomec]

installed VGs over the weekend 3.75 back, Wow, new airplane!!

[Geowitz]

In what ways did you notice a change?

[akflyer]

When I installed the VG's on mine, I talked to the manufacture and he said to include the flaperons for the over all width of the wing. After talking to several others, I think that including the flaperons for the wing cord is not correct as they are slung below the wing and are in effect thier "own wing". The 3.75" is alot more inline with where they should be versus the 5" that myself and others have used.

I have flown alot of different supercubs with several different VG's and some STC's call for them to be alot further back on the wing than others. By far the most difference you can tell on a cub is the ones with the VG's closest to the wing leading edge, however, you have to get the nose at a rediculously high AOA to really get the full benifit and most people wont fly it that nose high cause you cant see where the heck your going.

On my old pacer with VG's on the wing and tail I could fly it around at 35 MPH with lots of power but the deck angle was pretty stupid, however, flying a pacer on floats with a final approach speed at 50 MPH was very nice!

[tomec]

very stable at low speed, still testing, will let u know more after test.