Bearhawk Aircraft Bearhawk Tailwheels LLC Eric Newton's Builder Manuals Bearhawk Plans Bearhawk Store

Announcement

Collapse
No announcement yet.

Bearhawk STOL mods

Collapse
X
 
  • Filter
  • Time
  • Show
Clear All
new posts

  • Originally posted by Nev View Post
    That all makes sense.

    Out of interest, do you guys normally land with full available flap ? I'm wondering what effect it would have if you flew an approach a few kts faster, with full flap so that the drag took care of the extra speed on round-out. Clearly a work-around. But would the few extra kts lower the approach attitude and increase over-the-nose visibility ?
    Yes, and that's generally what you have to do. The faster you fly, the lower AoA you can fly for a given weight. But energy is mass * velocity^2.

    Comment


    • Nev, in my case, it's tinkering with a well-established design because it's fun to try to eek out a little more. From every account I've read, the stock machine performs wonderfully. But, think of the change from Model A to Model B - reportedly a few knots faster speed in cruise (likely owing to the reduction in tail incidence), and a favorable change in already good stall characteristics. There's nothing wrong (and plenty good!) with the Model A, but the B is "slightly better." Why not try? It's Experimental, it's fun to try something new if it doesn't kill you in the process. But, if you have a flying plane and don't want the down time, or you just want to get your build in the air, keep with what's been proven.

      I think the improvement in stall speed with a slotted flap would be small, but noticeable, and would also help with the deck angle when flying very slow. It would also improve roll control slightly, but again, with the current slotted aileron design, there may little, if any, noticeable improvement. I estimate that the Bearhawk plain flap improves maximum section lift coefficient by about 20-25%; a good slotted flap design could probably double that. It may sound like a lot, but stall speed will go with the square root of the ratio of lift coefficients. So, if I WAG our unflapped airfoil as having a Cl of 1.7 (about what you'd see with a NACA 4412 at this Reynolds number range), a plain flap may be about 2.1, and a slotted flap would be about 2.5, giving the plain flap a stall speed improvement of sqrt(2.1/1.7) = 1.11 (~11% reduction in Vstall) for that section; the slotted flap is then sqrt(2.5/1.7) = 1.21 (~21% reduction). That sounds like a lot, but only about 55% of the Bearhawk span is flapped. So if the outer section stalls at a Cl of 1.7, and the flapped section at 2.1 or 2.5, then, from a 2D flow perspective, the plain flap reduces stall speed by (0.55*1.11 + 0.45*1 = 1.06) about 6%, and the slotted flap by about 12% (or, conversely, a 6% reduction in stall speed from the plain flap). If your unflapped stall speed is 50 knots, that logic says your plain flap stall speed is 47 knots, and your slotted flap stall speed is 44 knots. (All speeds are notional, I don't want to get into a stall speed war at this time. Point is, you're talking *at most* a 6% and 12% reduction in stall speed vs. unflapped for plain and slotted, respectively.)

      Reality won't even be that kind, because that assumes you are hitting maximum lift on both the unflapped and flapped portions of your wing at the same time, and have no 3D losses (vortex at the wingtips or from the flap tip, uneven downwash distribution, etc.). Since the slotted flap will hit maximum lift at an angle of attack that is lower than the unflapped portion with the aileron (which is also slotted, but it won't be deflected as much as the flap unless you're in quite a crosswind!), the aileron portion of the wing won't be at maximum lift when the flapped portion is. However, what you will notice is the potential for a lower deck angle and slightly better aileron effectiveness, since the aileron portion of the wing won't be as close to stall.

      I'm attaching the following picture (not copyrighted) from Aerodynamics for Naval Aviators; a great, practical reference for aerodynamics if you haven't seen it: https://www.faa.gov/regulations_poli.../00-80t-80.pdf. I think it under-represents what you can get from a thicker basic section, but the trends are all good.

      flap_effectiveness.png
      Last edited by nborer; 10-13-2021, 10:18 AM.
      4-Place Model 'B' Serial 1529B (with many years to go...)

      Comment


      • I enjoy nerding out on just about anything. Fun discussion. I basically agree with Nick on my reason to install slotted flaps. Tweaking things is a lot of fun.
        Scratch Built 4-place Bearhawk. Continental IO-360, 88" C203 McCauley prop.

        Comment


        • I'm about ready to cover (which for me is the last part of the fuse), but it's getting to be winter, so I have to wait until spring. Now it's on to firewall forward or wings. I think wings because I don't want to do firewall forward then remove it for the rotisserie. Maybe in the next few weeks I can mock up some lowered flap hinges.

          Comment


          • The B model still has a servoing trim system, there is no reason to believe it will act any different than an A model. Here is the low hanging fruit: https://www.youtube.com/watch?v=mFQ1VcCiBJo
            Woah, that's brilliant ! Removing the servo action and adding electric trim all in one go. Very keen to see the flying result.
            Nev Bailey
            Christchurch, NZ

            BearhawkBlog.com - Safety & Maintenance Notes
            YouTube - Build and flying channel
            Builders Log - We build planes

            Comment


            • schu
              schu commented
              Editing a comment
              Not only that, I have a full autopilot setup which can control the trim servos. This means my AP can trim my airplane. Also, there is a bearhawk flying like this already, it works just fine.
              Last edited by schu; 10-14-2021, 12:11 PM.

          • I checked the flaps on a friends Husky yesterday, the hinge point is moved forward as well, which lowers the flap as it is deployed, to bring the airflow over top. I'm not sure if the Maule hinge point is moved forward or just down.

            Comment


            • Battson
              Battson commented
              Editing a comment
              It's probably a trade-off, if the hinge is aft then the flap moves rearward, which is good. If the hinge if forward, then the flap moves downward, which is good. NACA determined something along the lines of, the best gap size to maximise lift is 2% cord. So that needs to be factored in as well.

          • Hi guys

            I am just at the beginning of my project, nothing done on the wings yet, i'm from Canada and what i need is a decent bush machine, i seriously considering building my Bravo wings at 36 feets,
            so longer flaps and longer ailerons, it will be on amphib floats so i will loose on top speed to begin with, since i'm not an engineer, even less any big knowledge in aerodynamics, i think i will just keep the proportion of the ailerons and the flaps lenghts of the standard Bravo plan, however, i am very tempted to modify the flaps a little bit and make thems more like the Husky ones, i have
            found a design online that is quite interesting and i think it can easily be adapt the Bravo wings, i'm a former machinist and i have a lathe and a milling machine in my garage, i can make the necessary parts myself.

            Check it below and let me know what you think.

            Franky
            You do not have permission to view this gallery.
            This gallery has 1 photos.

            Comment


            • Bdflies
              Bdflies commented
              Editing a comment
              Warning: Incoming!!!

          • Originally posted by Franky139 View Post
            i am very tempted to modify the flaps a little bit and make thems more like the Husky ones
            That doesn't look much like a Husky flap. The Husky flap is very, very simple in comparison.

            Originally posted by Bdflies View Post
            Warning: Incoming!!!

            Comment


            • Have you considered adding wider Horner wing tips, rather than building longer wings, it would be a lot easier.

              Comment


              • Originally posted by Hewko View Post
                Have you considered adding wider Horner wing tips, rather than building longer wings, it would be a lot easier.
                I think robcaldwell is the person to ask about this. I too think the longer tips are way better rather than redesigning wing control surfaces
                N678C
                https://eaabuilderslog.org/?blprojec...=7pfctcIVW&add
                Revo Sunglasses Ambassador
                https://www.youtube.com/channel/UCQ0...tBJLdV8HB_jSIA

                Comment


                • Yes the Husky flaps are differents and much simpler, the similaritee is that they open lower like the ones above, i see the ones above as acting a little bit like the double slots flaps, for sure not as efficient but much less easier to fabricate.

                  Adding a longer wingtip will give you more wing area but will not decrease the stall a lot, improving the flaps will do much more for reducing the landing distance, my wings are not built yet, i have a set of 17 feets spars that i'm planing to use, they were made for a beef up Super cub (see below) so not much work for me the make a longer wing, the other thing is that i'm a garage guy, and i enjoy building things.
                  You do not have permission to view this gallery.
                  This gallery has 1 photos.

                  Comment


                  • I think you are underestimating the level of engineering that this mod is going to require, all the while solving a problem that isn't a problem.

                    Comment


                    • Originally posted by Franky139 View Post
                      Hi guys

                      Check it below and let me know what you think.

                      Franky
                      Franky;

                      Here is what I think.

                      Experimentation is exciting to me. I really look up to fabricators! You guys build really efficiently. I mean fast and good. I see industry best practices come from Fabricators. Being a machinist/fabricator you have decades of skills, background, tools, to visualize and build. Retirement.....now its time to experiment on fun stuff!! I'm curious what you will find out.

                      I think you see a lot of good stuff in the Bearhawk Wing design. I think a flap with some fowler action would improve it. I like the Cessna flap action but your drawing is innovative!

                      It seems like the dimensions of your spar webs will allow you to design a new wing. The flap you designed plus your spars moves the wing away from the Bearhawk prints so this will be your wing, not a modified Barrows Wing. I'm thinking a new flap design would produce different (higher) loads on the rear spar. So thats an engineering problem to investigate, measure, build and break so determine streangth needs.

                      The Barrow Wing on the Patrol, Modle B, Companion and Five has a main spar dimension of 8.25". Thats about 1/3 thicker than your spar. We get good speed with that thick Riblet Airfoil. That kind of jumped out to me.​​

                      I highly respect what Jared said. Are you a designer, builder or flyer? There are enough Bearhawks on floats to determin if the stock wing will meet your expectations. But that might not meet your goals if you are a designer.
                      Last edited by Bcone1381; 05-12-2023, 09:31 AM. Reason: added last paragraph
                      Brooks Cone
                      Southeast Michigan
                      Patrol #303, Kit build

                      Comment


                      • stinger
                        stinger commented
                        Editing a comment
                        Wow, right on Brooks! people forget the Bearhawk only has one wing strut. The loading on the aft wing spar and ribs with flaps is significant. Yes the skin and ribs are carrying a lot of the twisting motion to the main spar. One Strut . Stinger

                    • Guys

                      You are all right in yours comments and they are welcome, i should have start by telling you who i am: helicopter and fixed wings pilot with ATP licences, 18600 hrs of flying, first job was as a machinist, i became a pilot a few years later, i have built a Cyclone airplane in the 90's, it was a copy of the old Cessna 180 in kit form, the main difference was an extra foot of wing at the
                      root, giving us an extra foot of flap, we also add a cuff on the leading edge wich was a copy of the Horton stol kit at the time, theses mods made a big difference we could take off in about 200 to
                      300 feets depending on how loaded we were.

                      I'm half retired, i still fly helicopters on a contract basis and building another airplane is my retirement project, i have a Citabria fuselage and the set of spars mentioned above, In canada, we can used an existing fuselage for a project, as long as we comply with the 51 % rules, my first idea was to build a Super Cub wing or buy the Ribletts ribs made by D&E Aircraft in Florida but when
                      i've heard about the Bearhawk Patrol and the performance that they were getting with it, i tought myself: This it, i will put this wing on the Citabria so here i am,

                      My best buddy's son is an aircraft engineer (a real engineer, not just a mechanic) he can do the necessary structural analysis for me, i can do most of the necessary parts with my lathe and my milling machine, i' guessing you all know Mike Patey with his Draco and Scrappy airplane, well, i'm a bit like him, but without the big wallet and the CNC equipments.

                      I'm not 100% in that project yet, this is why i'm here to get as much positive or not so positive comments before jumping into it.

                      Comment


                      • Daniel
                        Daniel commented
                        Editing a comment
                        Don't forget the crew he has working on his stuff for him day in and day out. It's not just about the $$ and equipment. One person cannot do what he does in the time he does it.
                        Good luck with mods!

                    • Nothing is done yet , i'm still looking, thinking and evaluating, the other thing is weight, 1350 lbs is my maximum for empty weight with an angle valves on the nose.

                      Franky

                      Comment

                      Working...
                      X