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Any Vortex Generators here?

danny

Well Known Member
This last weekend I helped install vg's on a Stinson 108. It was really easy but gave me the itch to spend some of my hard earned money.
Just wondering if anyone has installed vg's on their RV. I have a -9 and if they live up to the hype they would be worth it. Can I get a PIREP from you if you have them?
thanks
danny
 
What part of your mission with your RV-9 would you like to improve on?

VGs generally enhance maximum lift so they reduce landing speed, and often improve handling and control authority near the stall. This is at the cost of a (usually difficult to measure) penalty in top speed.
 
Yes/No

Advised a friend to add them to his Rocket a while back and he did. That plane has shortened wings and 260HP. Don't want to offend so I'll simply state it was a bit more nose heavy than RVs. It would flat haul and climb as you'd expect but he never felt completely comfortable on approaches to short fields. It bought him ~ 5mph of margin for that config. As you'd expect, he gave up a few knots down low but no noticeable penalty up high.

Don't know that I'd want them on a 9.
 
better handling at lower speeds

I'm looking for more precise/sharper handling at lower speeds like during pattern work.
Steve, why do you want to get rid of them? Pain to wash? Maybe they just don't work for your desired mission?
Thanks for responses
danny
 
They are a pain. They catch cleaning rags and slice open skin! The 9 already has very good handling characteristics at low speeds.
 
No intension of getting involved in what could easily become a debate, so I wont post details of actual flight testing that we have done in the past, but will simply offer this...

The RV community is now quite large, and has numerous means of spreading helpful (und unfortunately, unhelpful) information.

If a particular mod. has been found by a substantial enough users to be beneficial, there is always a lot of easily accessible info about it found with a very simple google search, and when attending a large event like Airventure, you would see a lot of the RV's in attendance, with that particular mod. installed.

I think most people would agree that neither of those things are true about VG's on RV's....
 
Steve, why do you want to get rid of them? Pain to wash? Maybe they just don't work for your desired mission?
Thanks for responses
danny

All of the above. They make cleaning the leading edges harder, I "believe" that they do absolutely nothing to stall speed and stall characteristics and I also "believe", largely due to the article by Nigel Speedy that they cost me at least 3-5 MPH in cruise.

The belief in the stall speed and characteristic, aside from Nigel's article, also comes from real world experience by the person that I bought the airplane from. The previous owner flew it for about 17 years then bought a newer version with a fresher engine. The old one (mine) had VGs, the new one does not. He said he could tell absolutely no difference between the stall characteristics and/or landing performance or feel between the two airplanes.

Now, the RV-8 wing is quite different from the RV-9 wing. Would they help on a -9? Maybe, but I doubt it. Unless you operate mostly at the bottom end of the performance spectrum I think (warning, opinion detected!), that you will find it not worth the trade off in other areas. And don't discount the difficulty in cleaning. They are epoxied on and can be knocked off relatively easily.

Anyway, it's your airplane and you should configure it the way you want.
 
Honest question: what kind of sharper/precise handing at traffic pattern speed are you looking for? And at what airspeeds? I've seen very nice roll rates even at speeds just above stall.

I've not done a whole bunch of testing, but it seems to me that the RV-9 will develop a lot of sink rate at 60 knots and below, and I don't think VGs would help that. My guess is that's the characteristic of the airfoil, but I don't know.

Looking to learn some stuff here...
 
My VG experience - RV-6A

Last year, after about 20 hours in the plane, I installed the Stolspeed VG kit on my RV-6A. On the day of install, at ~5000' AGL, stall speeds reduced from 52 mph to 49 mph power off, and power on went down to 47 mph. I feel the plane is safer to fly. I haven't noticed any reduction in top speed, but my RV is very basic with O320 and wood FP prop. They look a little funny, but for me it was well worth the small ($100) investment and time to install. There is a great review on the STOLspeed site from another RV-6 owner. I followed his installation instructions on spacing.

As I have more time flying the RV now, I wonder if now that I have more experience, I wouldn't notice enough difference to keep the VGs. I am also working to increase speed (who doesn't want more speed?) - so as I switch props, maybe reduce drag, the VGs may be removed.
 
Bear in mind that the -9 has a different airfoil than the other RVs, especially the ones that have published reports on using VGs. Since -9 owners report such satisfaction with their airplanes generally, I'd tend to think that VGs might not be appropriate for that family of airplane.

Dave
 
Well part of "experimental" is learning. Read up, research, study the aerodynamics of VG's. Then get universal VG kit. The VG's tend to be stick on double sided affairs. Then install them and flight test it. Then you can report to everyone what you found. You can always remove them, but the down side is possible paint damage.

BTW Indicated speeds are typically not super accurate especially near stall. There are some tricks and flight test procedures to minimize the error, GPS and trailing static cone. Most A/S error is from the static pressure side not the pitot.

What to expect? I am assuming this is a RV9? Never flew either but it does not really matter. However the -9 was designed to be a slower easier to fly airplanes already (not that an RV3/4/6/7/8/10/14 are hard to fly). Van is a smart guy and optimized the plane for the job. You are not likely going to improve on it much if any, I am guessing. You won't know unless you try, this the first paragraph about experimentation. If you just want to learn and see how they work, great. If you do it for some leap in performance, nope.

However I guarantee you will lose a little cruise and top speed. #1 Aerodynamic Rule - There is no free lunch.... There are trade offs. As said vary well above VG's are the control "boundary flow" and allow the wing to fly at slightly higher critical angle of attack (slower stall), and improve effectivity of flight control (aileron, rudder or elevator) at low speed. Typically VG magic is used on the wing, but look at your jets at SEA, VG's sprout off the tail area as well. Those are for low speed pitch and yaw control improvement.

If you have a problem with too much money I can give you my paypal account. I am accepting donations. :D
 
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Still thinking

I'm still thinking about it. I've got 24 hrs on my -9 so I'm not completely familiar with it. I was hoping to get a variety of opinions and you guys never disappoint.
Thanks
danny
 
Librarian

I'm still thinking about it. I've got 24 hrs on my -9 so I'm not completely familiar with it. I was hoping to get a variety of opinions and you guys never disappoint.
Thanks
danny

I dont have much experience with VGs on small planes. But I have been following VansAirForce for a long time. Occasionally this comes up in the forums. I dont recall anybody reporting they were much happier after installing VGs on their Vans. It seems the Vans planes do not have any bad tendencies that need to be corrected. (except being a little slow: a 390 in a RV 9A? are you nuts? JMHO :)
I know several Cessna STOL kits use them quite effectively, but those are not RVs.
 
wife

Danny, take your wife out for a nice dinner. Leave the nine the way it was designed. And come back when you have a few hundred hours. Then you will see what everyone here is saying.
 
Sounds like the most solid plan so far. Ribeye at the local Outback.
Actually I do plan on getting more hours in before making any changes but food for thought is good too. Just feels "different" going from a 165 cruise to 65 final.
danny
 
VG research

I've been reading VG research papers for a while.

Some of the things I've learned... taller VG's (like an inch) add drag, but it is much easier to locate them at the proper point (where flow changes from laminar to turbulent), and the desired speed. So a shorter VG could do the same job, with less drag. But spacing is typically a function of height, so if shorter there would need to be more of them. Very short "micro" VGs can work. We are talking about maybe 1/4" high or less. But then spaced at 1/2" or so.

The net for me is that putting 400 VGs on my plane looks like a pain.

That said there is potential for putting them in targeted areas where the airflow is going turbulent and detatching (which makes drag). Potentially they can even improve top speed in those cases.

Clearly my purpose isn't to lower stall speed....
 
Airfoil

I've been reading VG research papers for a while.

Some of the things I've learned... taller VG's (like an inch) add drag, but it is much easier to locate them at the proper point (where flow changes from laminar to turbulent), and the desired speed. So a shorter VG could do the same job, with less drag. But spacing is typically a function of height, so if shorter there would need to be more of them. Very short "micro" VGs can work. We are talking about maybe 1/4" high or less. But then spaced at 1/2" or so.

The net for me is that putting 400 VGs on my plane looks like a pain.

That said there is potential for putting them in targeted areas where the airflow is going turbulent and detaching (which makes drag). Potentially they can even improve top speed in those cases.

Clearly my purpose isn't to lower stall speed....

I used to be into sailplanes; the airfoils are laminar by design. There is a transition point where the flow goes turbulent. At that point, if the airflow is tripped, the drag will go down. The tripping is not meant to keep things laminar, just to make the transition from laminar less draggy (a technical term).

The RV airfoils are not laminar, from what I understand. So VGs will do nothing to keep them "laminar".

However saying that, there are parts of the airflow around the RV plane that is probably laminar for a little bit. Looking at that transition may help add a 1/2 knot or so. But this would be best accomplished with a zig zag strip of paper a few hundredths of an inch high. JMHO
 
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A nit?

I believe all airfoils have a laminar flow area. A "laminar wing" is one designed to have a much longer (fore to aft) area of laminar flow. Are RV wings "laminar"? My reading seems to lead me to believe that they do have a (small) laminar area, until we get to the spar, where the leading edge skin terminates (and the wing thickness starts to reduce). And that's a pretty typical point for all metal wings with flush rivets.

On the other hand a fabric wing probably has a much smaller laminar area.

A nit I know :)
 
Give me a few months

Funny you should mention that. When I am flying ina few months, i plan to do some oil drop tests to see how much of the aurfoil is laminar flow, and if there is a transition bubble that would benefit from "trip" tape. I suspect that there is not much just by eyeballing the lower surface. By eyeballing the upper surface, i suspect there is nowhere near laminar flow to the spar, seems like only 3 inches at the most; I think the LE radius is too big for our lower speeds (low RE).
 
bear in mind that, generally speaking, VGs are a fix. Just ask Boeing...

Now, do you think your RV needs a fix? Does it have some kind of aerodynamic flaw? Does it misbehave? Is it lacking performance? Vicious maybe? Yes to any of those, go for 'em little pesky stirrers :D
 
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