Van's Air Force
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Vortex Generators
- Thread starter ctbecker
- Start date
Vortex generators are a real mystery to me. It is very interesting how such a small thing can change so much airflow allowing a lower stall speed or better slow flight characteristics. I guess if a small layer of frost can mess you up pretty bad, I can see the possibilities.
I look forward to the discussion here and learning something.
I look forward to the discussion here and learning something.
humptybump
Well Known Member
Charlie - you may wish to use the "search" feature of the forums. Vortex Generators have been discussed a few times.
I will repeat what I said elsewhere - the builder of my RV-8 installed and then removed VGs after deciding they made no appreciable difference.
During the same experimenting period, the builder installed and kept the "strakes" (another forum search will explain these).
I will repeat what I said elsewhere - the builder of my RV-8 installed and then removed VGs after deciding they made no appreciable difference.
During the same experimenting period, the builder installed and kept the "strakes" (another forum search will explain these).
It's all about boundary layer which is the thin layer of air near the surface were the flow goes from a local free stream velocity to zero right at surface. It is those small force at the surfaces slowing down the flow that we call drag. Over large surfaces these forces can add up to a lot. Vortex generators work where the boundary layer flow may have separated from the surface but the turbulence the vortex generators create energizes the flow and keeps the boundary layer attached, delaying separation. Drag can be higher in separated flow then turbulent therefore one use of vortex generators is to reduce drag on highly curved (typically aft body close outs) surfaces where flow may want to separate. Another use is to delay separation on a wing to delay stalls. You can then fly at a higher AOA and therefore reduce stall speed. Penalty thou is increased drag when they are not increasing AOA (meaning all the time).
All that said, my Expert Opinion (trying to remember this all from classes I took 30 years ago but I do play a aero engineer most days on TV) is that they are not needed/required for RVs. They are used to fix problems. RVs have low enough stall speed and very minimal separation drag. Therefore they are a fix where there is no problem.
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They're a mystery to everyone. That's why a complete solution to the fluid flow equations is one of the million dollar millenium prize problems.
I installed two "Hall Type" vortex generators on each wing of my Thorp T-18.
Just a few inches outboard of the inner end of the aileron, and the second a foot outboard of that. What a difference in aileron control at slow speed, yet no noticable decrease in top speed. Now the arrival stall, (throttle closed) with left wing drop is less severe, and the wing can be lifted with aileron and no forward stick. Good aileron control in a deep secondary stall, level decending @ 2,000 fpm; add some throttle and the wing recouples with a whump and starts a 1000 fpm climb.
I know it's not an RV, but the point I'm offering is that just one vortex generator or two can make a big improvement in a particular aspect of control without noticable speed loss.
You can bend one up out of a piece of aluminum, and install it with some double sticky carpet tape. (use some wax remover on the wing, or it won't stay on for long)
Put it on an area of concern, like the wing that drops first in a stall. put it where you think the stall originates. Maybe you don't like the join of the flap to aileron, or think one wing tip is shaped a bit weird?
Is your wing leading edge thicker where a landing light was added? Mine is. That wing is not the one that stalls first, so the thinner wing could get the vortex generator at the thin spot. On my plane, the thin wing is on the same side I sit, so it also carries more weight.
RV-8's are sometimes seen with a vortex generator on the fuselage. Some call them strakes. They effect the airflow disturbance caused by the unique landing gear used on the 8. I haven't flown my RV-8 yet, so I can't comment on that one...
Just a few inches outboard of the inner end of the aileron, and the second a foot outboard of that. What a difference in aileron control at slow speed, yet no noticable decrease in top speed. Now the arrival stall, (throttle closed) with left wing drop is less severe, and the wing can be lifted with aileron and no forward stick. Good aileron control in a deep secondary stall, level decending @ 2,000 fpm; add some throttle and the wing recouples with a whump and starts a 1000 fpm climb.
I know it's not an RV, but the point I'm offering is that just one vortex generator or two can make a big improvement in a particular aspect of control without noticable speed loss.
You can bend one up out of a piece of aluminum, and install it with some double sticky carpet tape. (use some wax remover on the wing, or it won't stay on for long)
Put it on an area of concern, like the wing that drops first in a stall. put it where you think the stall originates. Maybe you don't like the join of the flap to aileron, or think one wing tip is shaped a bit weird?
Is your wing leading edge thicker where a landing light was added? Mine is. That wing is not the one that stalls first, so the thinner wing could get the vortex generator at the thin spot. On my plane, the thin wing is on the same side I sit, so it also carries more weight.
RV-8's are sometimes seen with a vortex generator on the fuselage. Some call them strakes. They effect the airflow disturbance caused by the unique landing gear used on the 8. I haven't flown my RV-8 yet, so I can't comment on that one...
Andy Hill
Well Known Member
Without regenerating the prior threads, the RV-8 specifically (i.e. not even the RV-8A) has a difference in the Gear / Wing intersection area to other RVs. When you then add in the various possibilities of the intersection fairing, it is easy to see why individual RV-8s differ.
I've not seen VGs used, but the strakes some people fit get differing opinions. The questions I would ask are:
I've not seen VGs used, but the strakes some people fit get differing opinions. The questions I would ask are:
- Does this alter the (natural) Stall Warning speed i.e. when buffet felt through airframe and/or stick?
- Does this alter the Stall Speed i.e. the speed where the nose and/or wing drops, or the minimum speed with the stick held fully back?
- Does this alter the IAS margin between the above 2 speeds?
I have them on my RV-6 and just installed them on my RV-3
When I purchased my RV-6 in 2007 it had the Micro Vortex Generators installed on it, so I did not have a chance to fly it pre and post. The builder loved what they did to the stall and aileron control of the 6 in the stall, decreased landing roll etc and expounded the virtues of them. I find the stall slightly under book Vans numbers and good aileron control in the stall. When I did the transition training with Mike Seager (76 circuits in 9.6 hrs), I did find a difference between the two planes in the landing flare. But this is comparing apples to oranges as one is the RV-7 and one is the RV-6 with VGs. The RV-6 seems easier to hold off that last few inches in the flare to make a smoother touchdown but again this may simply be the difference in the two wings. ( I have about 300 hrs in this RV-6)
As to the VGs costing anything on the top end, I can't comment on this either as the RV-6 with 180 hp and ported and flowed cylinders along with a WWRV200 prop, will VNE the airframe TAS at 2500 rpm anyways, so...On my RV-3 I recently installed a set of Stolspeed VGs in the hopes of further slowing my touchdown speed in the flare. Once I test fly the VGs I will have more contructive comments to make on stall speed, any decrease in the top end, etc. Although everything I can read lately seems to discount a perceived "cost" to speed on the top end with VGs. AOPA has a good video which highlights the change the placement of VGs had on an RV-4, as well as this link below which highlights the results of the VG placement in an article. Everything I could find to read on pilot's experiences with VGs was positive, so I figured it couldn't hurt to try another set on the RV-3, for $71.75 CAN (for the Stolspeed VGs at ACS) it's not too much to spend to see how it changes things.
http://www.aopa.org/News-and-Video/.../1/Efficiency-Stuck-on-vortex-generators.aspx
When I purchased my RV-6 in 2007 it had the Micro Vortex Generators installed on it, so I did not have a chance to fly it pre and post. The builder loved what they did to the stall and aileron control of the 6 in the stall, decreased landing roll etc and expounded the virtues of them. I find the stall slightly under book Vans numbers and good aileron control in the stall. When I did the transition training with Mike Seager (76 circuits in 9.6 hrs), I did find a difference between the two planes in the landing flare. But this is comparing apples to oranges as one is the RV-7 and one is the RV-6 with VGs. The RV-6 seems easier to hold off that last few inches in the flare to make a smoother touchdown but again this may simply be the difference in the two wings. ( I have about 300 hrs in this RV-6)
As to the VGs costing anything on the top end, I can't comment on this either as the RV-6 with 180 hp and ported and flowed cylinders along with a WWRV200 prop, will VNE the airframe TAS at 2500 rpm anyways, so...On my RV-3 I recently installed a set of Stolspeed VGs in the hopes of further slowing my touchdown speed in the flare. Once I test fly the VGs I will have more contructive comments to make on stall speed, any decrease in the top end, etc. Although everything I can read lately seems to discount a perceived "cost" to speed on the top end with VGs. AOPA has a good video which highlights the change the placement of VGs had on an RV-4, as well as this link below which highlights the results of the VG placement in an article. Everything I could find to read on pilot's experiences with VGs was positive, so I figured it couldn't hurt to try another set on the RV-3, for $71.75 CAN (for the Stolspeed VGs at ACS) it's not too much to spend to see how it changes things.
http://www.aopa.org/News-and-Video/.../1/Efficiency-Stuck-on-vortex-generators.aspx
PerfTech
Well Known Member
RV-9A ?????
... Has anyone tried these on a 9 and with what results? I had these on my P-210 and they worked very well, with similar results to what was reported in this thread and accompanying links. The biggest draw-back for me was they are really, really, ugly, everyone asks what they are? Do they work? (gets old) Also they almost bankrupted me buying Band-Aids every time I washed the airplane, forget polishing it as that is really dangerous. Allan...
... Has anyone tried these on a 9 and with what results? I had these on my P-210 and they worked very well, with similar results to what was reported in this thread and accompanying links. The biggest draw-back for me was they are really, really, ugly, everyone asks what they are? Do they work? (gets old) Also they almost bankrupted me buying Band-Aids every time I washed the airplane, forget polishing it as that is really dangerous. Allan...
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Eddie P
Well Known Member
General AOPA video that is non specific. Personal email with author as of a few months ago validates he still has them attached and likes the way they improve his "air to air" play with other RV's and traffic pattern manners. Stall is still abrupt with a roll off but at lower speed.
http://www.aopa.org/AOPA-Live.aspx?w...7Wtbp#latest=1
Specific flight test empirical data listed in tab format and explained on a calibrated flight test pitot probe equipped Vans RV-6. Very objective, and shows the loss of upper end speed and gain in lower end stall speed. (no free lunch)
http://www.iwantarocket.com/pitot/pitot.htm
... Has anyone tried these on a 9 and with what results? I had these on my P-210 and they worked very well, with similar results to what was reported in this thread and accompanying links. The biggest draw-back for me was they are really, really, ugly, everyone asks what they are? Do they work? (gets old) Also they almost bankrupted me buying Band-Aids every time I washed the airplane, forget polishing it as that is really dangerous. Allan...
Specific Chat about installation in Vans RV9 airframe:
http://www.vansairforce.com/community/showthread.php?t=102096
