Stolspeed VG's

[500AGL]

It’s just one man’s opinion and of course they work different on each aircraft and airfoil.

But, after a lot of time listening, reading and learning from wise old pilots, I installed the stolspeed VG’s on both cubs I had and the factory Patrol using the above chart as my reference. All three aircraft showed the same improvement characteristics over a stock wing.

With the VG’s and tail weight to get the near empty CG back close to the 25% of MAC, I had to use two additional seat cushions to get my vertically challenged torso high enough to see anything on Stol landings.

[AKKen07]

Happy to help :P wouldn’t want you to get bored!

[whee]

Hmm, I might have to rethink my “I like it how it is” position. I have a box of StolSpeed VGs on the sheet for a while but haven’t been able to convince myself I need to spend the time to install them.

Thanks a lot Ken…

[AKKen07]

That is some interesting info. 5 percent is what the Stolspeed manufacturer (JG) recommends and is also the farthest forward I’ve seen until your post. He also mentions that they can’t be too far forward for stall performance but at some point they are more likely to cause cruise speed losses. Maybe less of an issue on a cub than a Bearhawk.

[AKKen07]

No change in cruise whatsoever. I can’t think of a downside other than the obstacle they pose when washing the bugs off the wing. On second thought - previously I could carry a touch extra speed to land then chop the throttle and the plane would plop down and stay down. Now if I have any extra speed it bounces back up and tries to fly again… but that’s just a matter of adapting my landings to the new characteristics.

[500AGL]

I thought I would have responded to this long thread but perhaps I didn’t as so much info was already posted.

They work as described but my suggestion is to use the 5% of chord as the maximum you would want.

The whole purpose is to have them effective when your AOA starts increasing, and quite literally they work the best between 1.1 and 4% of the chord. Many think it’s too far forward but it’s not. Round it out and place them at 2-3% and they work great.

No effect on cruise speed.
As others mentioned there is no stall “break”, just a mush down like an elevator, in full control.

pb

jerry burr’s data on a cub wing IMG_9136.jpg

[Bcone1381]

Is there any down side? Did you see any loss in efficient cruise performance?

[AKKen07]

I put the VGs on my Bearhawk B model wings minus the 18” extended wingtips. Following Stolspeed’s guidance installation was a breeze. I used 5% chord to front of VG. Weather cooperated for a limited window today so I called my fellow test pilot (Dad) to give her a spin. We tested at 2250lbs with a CG slightly forward of center. All speeds are indicated and highly suspect due to high AoAs. Also, wight and CG might be off due to all the changes made since I last weighed her.
I started with two high speed taxi runs to make sure there were no major problems and got airborne briefly - but then the wings just held on! It floated nose up high well after it “should” have landed.
Power off stalls were unrecognizable. Instead of a clear stall at 56 mph (flaps up) as per previous tests at this weight/cg it slowed to 50 and just stayed there, controllably mushing its way to Earth at 1000 fpm. Flaps 2 of 4 notches went from 53 to 48 with the same controllability increase. Wild!
Full flaps now do nothing to the stall speed. It was minor before and now they are just drag.
Power on, flaps up, the plane now sustains a 33 degree nose up attitude at full power and 46 mph. Climbing at roughly 300fpm. In all cases the control stick is fully aft at the stop and the ailerons are effective through the stall.

[Bissetg]

After doing the previously mentioned testing and repositioning of the Stolspeed VGs I found a complete new set of cut adhesives in my mail today sent free of charge by JG at Stolspeed. Outstanding customer service for an outstanding product.

[AKKen07]

My VG experience seconds Bissetg

[Bcone1381]

Thanks Grant. Interesting about the spacing of the VG's!

[Bcone1381]

Thanks Nev!!

[Bissetg]

Hi Brooks, I too have heard that mentioned. It’s not my experience with the Bearhawk or the C172. My experience is that when you reach the critical angle of attack the nose pitches down but no more enthusiastically than without VGs. The difference is that you can hold it in a mushing descent with aileron control with out the pitching oscillations of bouncing in and out of the stall you get without VGs.

The Stolspeed set up requires VGs at 60mm spacing for the 900mm in from the wing tip, then 90mm for the remainder of the wing. My understanding is that this gives the outer 900mm of wing better boundary layer adhesion hence the aileron control.

What I’m going to say next is speculation on my part not based on research I’ve done. I imagine that different wing profiles will produce different results. A P51D has the point of max camber two thirds of the way back from the leading edge of the wing. That was to maximise the low drag laminar flow that will only exist in a decreasing pressure gradient, hence the Mustang went faster than the Spitfire with the same engine. However, I think that the Mustang wing would respond completely differently to VGs for that same reason, if you put them forward you would kill the speed and if you put them aft they wouldn’t help much because the wing area that benefitted from them would be small and likely be less effective. The reason I mention a Mustang wing is it’s the most different wing profile I know of to what we are flying.

What this means to me is that for our aircraft we need to fit and test ourselves. There maybe some wings that do break more positively and without warning but that’s not my experience with my aircraft. Bit long winded but hope that helps.

[Nev]

I've heard (generally speaking and not Bearhawk/Riblet specific) that when a wing with vortex generators stalls, the stall event itself is more sudden and has less warning.

I haven't noticed this with mine Brooks. Perhaps it is more abrupt, but on my B wing before I installed the VG's it was a very docile stall, so maybe it's a very relative thing, I did manage to get the wing to drop a couple of times before putting on the VG's, and I managed to get one wing drop out of it since. The pitch attitude is very high before it breaks, and it dropped to about 10° below the horizon and turned about 15° laterally. It was then fully controllable in all axis immediately after the break. I thought it was unlikely to be placed in this attitude in slow flight ops because I needed a lot of power to achieve it and really had to try hard to get it to break. I'm able to fly around at about 40kts TAS in full control.

I have to mention that the audio AOA feature in the Dynon is an amazing feature, and I would rate it even above the VG's for an increase in safety, awareness, and performance. I'm just a beginner in the slow flight arena, but between the audio AOA and the VG's I certainly feel a lot more comfortable.

Edit to add that in early flight testing the horizontal stabilizer was stalling before the wing, leading to the impression of a docile stall. With power on, the main wing can be stalled at a higher pitch attitude, and will usually drop a wing in a pronounced manner. It is easily recoverable and has sound handling leading up to the stall, especially with VG's installed.

[Bcone1381]

I understand the benefit you experienced....that it handles better at slow speeds, that it lowers stall speed, there is no loss of top end cruise speed.

I've heard (generally speaking and not Bearhawk/Riblet specific) that when a wing with vortex generators stalls, the stall event itself is more sudden and has less warning. I'm curious what your experience was with this event.