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  • Stolspeed VG's

    Is anyone using the Stolspeed vortex generators? If so, how do you like them?

  • #2
    Yes, see my post about the same topic here:
    https://bearhawkforums.com/forum/fly...sing-vgs/page3

    Comment


    • #3
      I read every word of Batson's essay! Great info!
      Amusing story to share: A while back, I picked up a BRAND NEW Husky, with a friend. While at the factory, I mentioned that my plane, a Husky A-1, had VG's. Everyone around scoffed and snickered... "VG's", they declared, "only cover up flaws, in inferior airfoils and don't do anything on Huskys." I really couldn't summons much of a retort, since the plane had the VG's when I bought it. So, I didn't have a baseline to compare. I just knew it flew nicely. The amusing thing (to me) is that, the last two years, that I visited the Aviat display in Oshkosh, EVERY HUSKY ON DISPLAY had VG's. Evidently, properly done VG's can augment the performance of well designed airfoils, as well! As 'Commander Batson' discovered.

      Bill

      Comment


      • #4
        Good information. As I reported in another thread, my LSA will slowly roll off to one side or the other when truly stalled. There is a bit of a burble that accompanies the stall, but not a lot. I was thinking about using the Stolspeed VG's on the outer 1/3 of each wing, only. I'm thinking that would allow aileron control deeper into the stall, and result in the inboard section of the wing stalling first. That should theoretically cause more buffeting as disturbed air would be flowing over the tail. A lot of certified aircraft use washout or stall strips to get the inboard section of the wing to stall first. The thing is, though, my LSA flies so well now that I don't want to mess it up. So, would the Stolspeed VG's be removable without messing up the paint if I don't like them? Thx, Bob

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        • #5
          I used them on my Rans S7 and was impressed. Stall speed decreased 4 kts to 28kts, no change in cruise, but a slower plane than the Patrol. I will probably mess around with them on the Patrol when finished. They can be fastened with tape, so you can play around with location before permanent install.

          Comment


          • #6
            Interesting topic, I'm a bit confused tho'. I thought that VG's, albeit proven to work, the data shows that the improvement is closer to 3-7% for a given airfoil, so for a 37KIAS (already an anomaly since the variance in IAS has a margen or error of +-4KTS) would be closer to 1.1 KIAS (well inside the KIAS tolerance of +-4KIAS so almost negligible) as to the high water mark, or there about, 2.59 KIAS, is also with in that range, practically KIAS margin of error, so very hard to use as a proof point.

            Another factor is this range of efficiency is very well define to several factors, Reynolds numbers, airfoil type, and AoA, so defining all there of those factor will define placement of the VG's on the airfoil upper surface, so you get the improvement with in an envelop of performance. So, at a given speed, and a given AoA, and a given location, the VG's have measurable performance gains, no argument behind the science and the data, my question is, will and average pilot reap the benefits of VG's, considering their low margin of improvements?

            You need to be flying very near the edge of the performance envelop of the airplane, like a STOL competition as an example to reap those benefits. Sure, if you are flying regularly, you get a margin of error improvement as the exited airflow with keep laminar separation from happening.

            So how des one find the right placements for the VG's, well a wing tunnel, or you could spay some cold wax on your wing (pledge)near the root, then make some flow viz solution (google it) paint it generously on the area with wax, go up and in a safe altitud, play with AOA and stall, if possible, record the high AOA ad you will see something like this: OilFlowTypes.jpg

            The clear area at the front will show you where the VG's go, where they stat to apear is the area of separation of laminar flow, if you need the extra ~4KIAS on your approach

            Comment


            • #7
              Originally posted by SpainCub View Post
              Interesting topic, I'm a bit confused tho'. I thought that VG's, albeit proven to work, the data shows that the improvement is closer to 3-7% for a given airfoil, so for a 37KIAS (already an anomaly since the variance in IAS has a margen or error of +-4KTS) would be closer to 1.1 KIAS (well inside the KIAS tolerance of +-4KIAS so almost negligible) as to the high water mark, or there about, 2.59 KIAS, is also with in that range, practically KIAS margin of error, so very hard to use as a proof point.
              ...
              if you need the extra ~4KIAS on your approach
              To restate the above in a different way, 7% subtracted from 37 KIAS is 34KIAS, so the empirical evidence is supported by the theoretical. A range of tolerance for a given instrument and a statistically likely outcome based on a distribution of results after repeated tests are two different things.

              The difference between flying my friend's Bearhawk without VGs and mine with was a most enlightening reminder about their importance. I would never own a Bearhawk without adding VGs, they are the best and most cost-effective way to improve STOL performance. The extra kinetic energy at landing (velocity squared) means you need almost 20% more room to land without them fitted. Once again, the practice agreed with that theory when I was landing my friend's Bearhawk. It is more challenging aircraft to land well and land short. Those last few knots at touchdown make all the difference.
              Last edited by Battson; 03-14-2017, 08:37 PM.

              Comment


              • #8
                I'm just curious enough to spend the money and time to try the Stolspeed VG's now that I know they can be removed without damage. Anecdotally, a friend who has used them on two different airplanes said that they made both airplanes better. Neither of those airplanes were Bearhawk though so, I'll find out what, if anything, they will do for the LSA. This is not a priority though, so it may be a while. Bob

                Comment


                • #9
                  Originally posted by Battson View Post
                  To restate the above in a different way, 7% subtracted from 37 KIAS is 34KIAS, so the empirical evidence is supported by the theoretical. A range of tolerance for a given instrument and a statistically likely outcome based on a distribution of results after repeated tests are two different things.

                  The difference between flying my friend's Bearhawk without VGs and mine with was a most enlightening reminder about their importance. I would never own a Bearhawk without adding VGs, they are the best and most cost-effective way to improve STOL performance. The extra kinetic energy at landing (velocity squared) means you need almost 20% more room to land without them fitted. Once again, the practice agreed with that theory when I was landing my friend's Bearhawk. It is more challenging aircraft to land well and land short. Those last few knots at touchdown make all the difference.
                  Two quick comments:

                  Empirical data is there, however, measurement in KIAS is a mistake to validate empirical data, factors or error are also important, so a highly sensitive equipment is needed to substantiate the claims. leaving all other variable factors aside from a empirical perspective (temperature, barometric, air density, humidity, air direction, airspeed) considering that at 0<50KIAS there is a tolerance or error or roughly 10% in the equipment used. This means that as you take measurements, the empirical value of those measurements must account for the error. To limit these, you take several measurements with in a 10 mins span (looking for stall entry values.) then average those and account for margin of error in a normalised curve, you will find that 4KIAS is with in that margin of error, you get Relative Error, so your delta of 4KIAS and 4KIAS+- of the equipments looks rather odd mathematically which is the point I was making: (4 - 4)/ 4 If you look at it from Relative Uncertainty, then 4/4 = 1 or 100% uncertainty of the data.

                  As far as your subjective valuation of with vs no VG, not much I can say other than there are percibable difference is the preasusure distribution of the wing, particularly on the tips where most of the improvements of the VGs come into play, keeping the laminar bubble from separation and re attachment (hysteresis) of this particular airfoil (and most airfoils of the type in their lower Re operation at the tips) so they do work to stabilise that aspect of the flight characteristic of the wing, giving you less input to adjust for small imbalance of aileron input.

                  I hope we are in agreement and pls understand that was not trying to contradict anyone. I have but the deepest respect to all the builders in this site, just sharing my thoughts on the subject from my own understanding of the technology.

                  Comment


                  • #10
                    Originally posted by SpainCub View Post

                    Two quick comments:

                    Empirical data is there, however, measurement in KIAS is a mistake to validate empirical data, factors or error are also important, so a highly sensitive equipment is needed to substantiate the claims. leaving all other variable factors aside from a empirical perspective (temperature, barometric, air density, humidity, air direction, airspeed) considering that at 0<50KIAS there is a tolerance or error or roughly 10% in the equipment used. This means that as you take measurements, the empirical value of those measurements must account for the error. To limit these, you take several measurements with in a 10 mins span (looking for stall entry values.) then average those and account for margin of error in a normalised curve, you will find that 4KIAS is with in that margin of error, you get Relative Error, so your delta of 4KIAS and 4KIAS+- of the equipments looks rather odd mathematically which is the point I was making: (4 - 4)/ 4 If you look at it from Relative Uncertainty, then 4/4 = 1 or 100% uncertainty of the data.

                    As far as your subjective valuation of with vs no VG, not much I can say other than there are percibable difference is the preasusure distribution of the wing, particularly on the tips where most of the improvements of the VGs come into play, keeping the laminar bubble from separation and re attachment (hysteresis) of this particular airfoil (and most airfoils of the type in their lower Re operation at the tips) so they do work to stabilise that aspect of the flight characteristic of the wing, giving you less input to adjust for small imbalance of aileron input.

                    I hope we are in agreement and pls understand that was not trying to contradict anyone. I have but the deepest respect to all the builders in this site, just sharing my thoughts on the subject from my own understanding of the technology.
                    I can understand your reasons for being skeptical. Clearly you've got a good grasp on the theory behind VGs.
                    That said, all evidence did point to a clear reduction in stall speed and increased margin of safety at a given approach speed. The acid test for me was the stall behaviour, approach / touchdown speeds, and landing distance. All evidence points to performance improvement, so that's the logical conclusion to draw. Only the outcome matters in the end, the exact numbers are indicative only.

                    The outcome is, after fitting the VGs, I could fly almost 10 KIAS slower on approach for the same margin over the stall AoA, which is a massive practical advantage. The reduction in stall speeds translates to shorter landing rollout in STOL ops.

                    Comment


                    • Dave Roberts
                      Dave Roberts commented
                      Editing a comment
                      I agree with Battson 100%. I've had vg's on my bearhawk for about 600 hrs. Every thing Battson said is right on.

                  • #11
                    I installed VGs on a Cessna 340 some years ago. They definitely work; reduced stall speed, improved rudder function in single-engine ops, and improved roll control at slow speeds. I plan to put them on my Bearhawk.

                    Comment


                    • #12
                      While I am quite satisfied with the performance of the wing on my LSA, it does stall with little to no buffet. The stall is very gentle , but if held long enough, it will eventually roll slowly off into a spin. It does this quicker as the CG is moved to the rear, but it is still pretty slow. When stalled in a hard slip, with the CG forward, it buffets a lot with no tendency to roll "over the top" into a spin. With the CG to the rear, it will roll over the top when stalled in a hard slip, but the rate is very slow.

                      I am wondering if installing the Stolspeed VG's on the outer 2/3's or so of the wings will delay the stall there while allowing the center section to go far enough into the stall to produce a buffet. What I don't want to do is mess up what I consider superior stall characteristics when the wing is stalled in a slip. Also , I don't want to lower the cruise speed. I think the Stolspeed VG's can be temporarily installed with double sided tape so that I can experiment without concern about removing them if I don't like the result. I'm ordering some today. Bob

                      Comment


                      • #13
                        Today, I removed the STOLspeed VG's from the horizontal stab of my Patrol. I hadn't installed them yet on the wings but will get on that this weekend. I cant get all technical with you but I will tell you that they create an unstable tail and I'm sure it raised my Stall speed by 5mph. My slow speed approaches felt very "Loose" and uncomfortable if that makes any sense. I put a total of 6 hours on them before removing them . I jumped in and flew for 4 hours today with them off and its sure nice to have my sweetheart back.

                        Comment


                        • #14
                          Originally posted by Isilverone View Post
                          Today, I removed the STOLspeed VG's from the horizontal stab of my Patrol. I hadn't installed them yet on the wings but will get on that this weekend. I cant get all technical with you but I will tell you that they create an unstable tail and I'm sure it raised my Stall speed by 5mph. My slow speed approaches felt very "Loose" and uncomfortable if that makes any sense. I put a total of 6 hours on them before removing them . I jumped in and flew for 4 hours today with them off and its sure nice to have my sweetheart back.
                          I'd be interested to hear the details of how they were installed. I love the STOLspeed VG's under my stab, in combination with a gap seal.

                          Comment


                          • #15
                            Correct me if Im wrong but I think your flying a 4-place?

                            I also have VG's and gap seals on my 4-place tail ( A model with slab tail) and love them. Im talking the Patrol

                            Comment


                            • Mark Goldberg
                              Mark Goldberg commented
                              Editing a comment
                              There is a Patrol owner who did very extensive testing on placement of VG's on his wings. My memory of his testing results is not 100% clear, but I believe the best position was more forward than the recommended placement from the manufacturers. I seem to remember it was pretty close to where Jonathan placed his - even though they are different airfoils. Mark
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