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Vortex Generator question...

Doug Rodrigues

Active Member
Okay, the wing kit is on order. I'd also like to purchase a Vortex Generator Kit from a non-Van's source. Question: Has anyone flush rivited the Vortex Generators to an RV wing? What problems did you have? How much trouble to dimple the generators considering the limited available flat surface of the blade? The idea of just sticking/gluing them on a wing surface un-rivited doesn't appeal to me.
 
The magic of adhesives

The "glue" is plenty strong
You don't want to rivet them on (for many reasons)
May I suggest you consider flying first before VG's
Check this site for a realistic benefit and disadvantage of VS's

http://ontariorvators.org/pitot/pitot.htm

You can count on may be -3 kts on the bottom end and TOP end.
This means you are shifting top speed AND bottom speed down.

Your turbulent air penetration should be lower by at least 3 kts.

The magic of adhesives are very good. I used a couple VGs on my NACA scoops on the side of my RV-4's canopy to improve cabin vent airflow. They are still on 6 years later.

Personally I don't want VG's and trade the top end for some bottom since it lands slow enough, but that is your call.

Good Luck.

PS if you don't trust the glue the VG's come with, which I am sure is fine, remove the sticky stuff it comes with and use Prop-seal. Scruff up the aluminum on the VG and the skin where you will place them, clean it very well with a clean rag and MEK. Use the pro-seal, which is tank sealant you will come to love and know soon. It will never come off by accident. However if you decide to remove it0 you can soften it up with some MEK and using a thin sharp razor to "shear it off".
 
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Apparently I had some misconceptions.

I thought that the VG would lower the stall speed by at least 10 mph? Thanks for setting me straight. I didn't realize that smoothing the airflow across the wing would add drag? I had a similiar situation with my previous Cessna product. Added flap gap seals...no change although the advertising promised much. Added an Avcon STOL kit. Great slow speed flying, but they never mentioned that I'd lose 3-4 mph cruise speed! :eek: I'll pass on the Vortex Generators. Thanks again.
 
Not necessarily a representative sample, but I saw one RV with them at Arlington this July and asked the builder about how helpful he thought they were. He just laughed and said, "That was such a waste of my time!"
 
Real aerodynamics

There is no magic and don't want to say they are bad. VG's are wonderful "problem solvers" and are all over aircraft of all kinds from STOL aircraft to Large Jets and fighters. However the RV does not have a problem. The RV is already excellent in the low speed department or high-speed department. In other words the RV is PFM, pure freaking magic, in a way. Van hit upon the right combo of airfoil (NACA 23013.5), wing planform-area, aircraft weight, power and attention to detail. Other planes have more to gain from VG's.

Yes almost any airplane can benefit to a degree, but there is no free lunch. If you gain low-end performance you will loose some top end. I have talked to 3 of the VG sales guys and some are realistic, while others imply that you should get a lower stall while loosing no top end. Right :rolleyes: The link I noted above is fairly accurate. It is from a RV builder who does sell VG's. Measuring low speed difference of a few MPH is always hard to do. This site is the only one to do actual real documented flight test data, and I can't argue with his method.

I found out from a friend who likes to do dogfights that after he added the VG's to his RV-4, he could turn in-side another RVs without VG's. In a RV to RV dogfight what happens is you get into tighter and tighter turns and spirals until you bleed off your airspeed and need to back off or stall. The guy with lower stall will win in this scenario.

Personally I love to experiment with stuff. I would not put this on as I said, because I am optimizing the top end of my RV-7. The Guy?s who love this slow speed VG stuff fly planes that top out at 90-110mph, so they don?t care if they loose a MPH or two.

If you are a real bush pilot and want to get in real short, soft, obstacle mountain fields all the time than VG's might help, a little. However the RV has the ability to get into fields almost shorter than it can take off from. Unless you have the skill to fly on the edge of the envelope, just flying better and light weights will get you shorter landing limits than VG's will get you.

If you make your RV as light as possible (with max thrust to weight ratio) you will get great low speed performance out of the RV. If you build a fat RV with all the bells and whistles, a few VG's will not make it a STOL plane. Keep it light. (The stall speed between solo and gross is 7MPH!)

VG?s is not a great match to a high-speed plane like the RV, IMO, which already has good low speed performance. Van's advice: Build it per plans; keep it light, keep is simple.

Cheers G, RV-4, RV-7 (building)
 
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Doug Rodrigues said:
I thought that the VG would lower the stall speed by at least 10 mph?

I've never heard of a VG's lowering stall by 10mph but I have heard that adding strakes on RV8's (not any other RV's AFAIK) will lower the stall substantially. It supposedly cleans up the air coming off of the mains. I can put you in touch with at least one guy who did before and after tests and was very impressed.




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Chuck
 
VG's can help some aircraft's low end without taking off from the high end. This would be because they can reduce the amount of induced drag just enough to offset the small about of form (parasite) drag they cause. The RV however is much to fast an airplane for this to be the case.
 
VG's

I made a set of VG's to experiment with from a plastic suspended ceiling 'T' I bought from Home Depot for $5.00. Trimed the top on a table saw and cut the angle with scissors. Buffed with a belt sander and attached with silicon caulk. Took about an hour to make two sets of 100. If you like the results you can spend a $100 for CCI's.

FWIW,
Bob
 
flow control

chuck said:
[snip] strakes on RV8's (not any other RV's AFAIK) will lower the stall substantially. [snip] Chuck
Here are some articles on local flow control devices:

http://www.cafefoundation.org/aprs/localflow1.pdf
http://www.cafefoundation.org/aprs/localflow2.pdf
http://www.cafefoundation.org/aprs/localflow3.pdf

The first link above (localflow1, page 3) and third link above (localflow3, page 2) shows strakes and "flow guides". The device on the RV-8 is more a flow guide, but the difference is small. I think the main reason for the RV-8 strake is the turbulance coming off the gear and wing root makes the tail shake like crazy. Not sure how much it lowers the actual stall speed of the RV-8. G
 
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Induced Drag

osxuser said:
VG's can help some aircraft's low end without taking off from the high end. This would be because they can reduce the amount of induced drag just enough to offset the small about of form (parasite) drag they cause. The RV however is much to fast an airplane for this to be the case.

I would be very surprised if VGs can reduce induced drag on a properly designed aircraft such as the RV. Induced drag is a function of the amount of vorticity (swirl) in the wake of the aircraft. Vortex generators work by causing vorticity. They do keep the boundary layer attached longer and thus delay stall, and can be useful in reducing deadzone and flow separation over control surfaces. Certain airfoils will benefit more than others from this. I don't think the 23000 series, which was designed to have a turbulent boundary layer, will benefit much from them.

However, the application of VGs may alter the effective incidence angle of the wing where they are applied. The use of VGs may also change the onset speed of stall buffet. If stall buffet is your measure of when stall occurs, you may be getting a false impression of the effectiveness of VGs simply because the plane is buffetting at a different speed.

When applied to a wing with a poor lift distribution, perhaps the incidence changing effect of the VGs could alter the lift distribution on the wing enough to reduce induced drag, but that seems unlikely to me. Besides, if the lift distribution on the wing is that bad, VGs aren't the best way to fix it.
 
VGs on spam can

My father just had a set of VGs installed on his Beech Musketeer. Installed on wing, HS and VS.

His report is that much better at low end, improved rudder and elevator authority but probably took about 1-2mph off of max speed. Can still get same cruise speed but probably at higher fuel flow.

He claims that his solo weight climb is better, too. I asked him if he checked TAS and DA to be sure. Nah, but he thinks its better.

Surprised me that the STC would have VGs on the VS. Apparently it improves the flow across the back side of the rudder.

I believe I won't be needing them on my RV, but I'm ready to be convinced otherwise.
 
All very good comments. I'm convinced now that the Vortex Generators aren't worth the time and effort to install them, although it's possible that some future experimentation would be interesting.
 
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