Anyone using the Stolspeed vortex generators?

pboyce · #1 03-30-2009, 04:45 PM

I noticed a blurb in the April 2009 issue of EAA Sport Aviation regarding vortex generators from Stolspeed. I went to their website and there is a testimonial from a RV6 owner that these VG's lowered his clean stall by 5 knots. He also claims that he has shorter takeoffs and also better climb.

Anyone else had any experience with these VG's ?

http://stolspeed.com/rv6

chepburn · #2 03-30-2009, 05:15 PM

Just my two cents, but VGs are usually installed to fix an aerodynamicists mistakes, usually to try to get a part of a wing or control to stay flying a -little- bit longer to correct for bad stall-spin characterisitics or insufficient stab power etc.

They do indeed work as advertised...allowing a higher alpha on a wing section because the turbulent flow is energized and can withstand higher angles of attack. However....there is no 'free' lunch. That same flow energy is still there in cruise ...when you DONT need it, and you will pay the piper on your top end. If your mission is mainly short field work, then maybe it is the right thing to do...but IMHO the RV-8 is a cruise machine..and its top end should not be sacrificed for a few knots at the low end. It already has pretty respectable short field performance.

Regards,
Chris

flyboy1963 · #3 03-30-2009, 07:33 PM

okay, I'm sure this topic has been covered before.....

we all fly in headwinds the majority of the time, right? ( a headwind always affects you much longer than a tailwind, and a x-wind is a net loss of groundspeed!)
so is it worth 2 mph cruise? let's not overstate the top end numbers, unless you cruise for 4 hours at a time, most of the trip is taxi, climb and descent.

for many pilots, having the flow attached at low airspeeds, having solid feel to the controls, and more Margin before the stall is a good thing, no question about it, especially when loaded to rear CG limts, VG's on the bottom of the H.Stab will give you more pitch authority when you need it.

(Test pilots can jump in and correct me.)
Yes our aircraft are wonderful performers, but who wouldn't like stopping 50 feet further from the fence at the end of the field on a hot day.

Aviator168 · #4 03-30-2009, 07:55 PM

Even with 4 hour trips, a lost of 2 mph is only 8 miles

At 55% throttle, that's less than 3 minutes. Trading 5 knots in stall speed for 3 minutes in a 4 hour leg? That's a good trade. Then again, if I am going to land on long and wide runways, why bother.

pierre smith · #5 03-31-2009, 06:21 AM

.....gets hung up on them

Regards,

uk_figs · #6 03-31-2009, 07:11 AM

I put VG's on my Pacer and they had a significant positive impact on low speed flight, stall speed with and without flaps and touchdown flare (better elevator authority) however as noted they did cut about 5 mph off the cruise performance. Net result was a good thing for the Pacer for my flying as I mostly went short trips to high elevation grass/dirt strips in Utah or Idaho, basically I think you have to decide what your mission profile is for your plane and select the choice that fits.

A Pierre stated however it is a pain to clean the leading edge 8>)

flyboy1963 · #7 03-31-2009, 12:27 PM

....now I've read a pretty extensive testing article with a -6, but I notice that some of the VG makers don't offer for the -9, no doubt due to the different airfoil.
any other -9 drivers out there that have the VG's?
Notice the Supersport Cub has them furhter forward in front of the aileron, thus the flow is energized at higher AoA and you retain roll control into the stall. Great idea!
Same with putting them under the HS, and the fin.
IF someone knows or has tested for the correct location on the airfoil, I can certainly get out the saw an make a bunch for $20.
I'm not saying the commercial guys shouldn't recover their R&D, but we are constantly doing mods and experimenting, and sharing the info.

Surely someone has tuft-tested their RV.???

Kevin Horton · #8 03-31-2009, 03:25 PM

Terry Jantzi experimented with VGs on his RV-6. He went to the trouble to install a flight test airspeed boom. in an attempt to better measure the reduction in stall speed (the relationship between IAS and CAS is almost certainly not linear at the stall). He measured a stall speed reduction of 5 kt CAS with flaps retracted, and 3 kt CAS with full flap. It is interesting that with the VGs, he found the stall speed essentially the same, no matter what the flap deflection was.

See Terry's results here.

plehrke · #9 04-01-2009, 04:48 AM

Quote:

Originally Posted by Kevin Horton

Terry Jantzi experimented with VGs on his RV-6. He went to the trouble to install a flight test airspeed boom. in an attempt to better measure the reduction in stall speed (the relationship between IAS and CAS is almost certainly not linear at the stall). He measured a stall speed reduction of 5 kt CAS with flaps retracted, and 3 kt CAS with full flap. It is interesting that with the VGs, he found the stall speed essentially the same, no matter what the flap deflection was.

See Terry's results here.

Don't you just love experimental aircraft and a forum to share that information?

I agree with everything said so far in this thread. I would not make the trade of speed for reduced stall speed as I think the low speed handling and landing characteristics of the RVs is already unbelievable. Your results/opinions may vary.

As an aeronautical engineer, what I would caution you on is you should probably re-do phase 1 flight testing as slapping vortex generators on the plane may effect lots of performance parameters. I would even suggest you need to do a spin test as the vortex generators most likely will have an effect especially if you do not get them symetric and one wing stalls first.