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Bearhawk Five Flight Testing Continues

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  • #16
    Re: CG range

    A larger tail moment (length or area) will move the aerodynamic center aft. This will move the rear limit for stability aft. The extreme of this is a Long-EZ. A larger tail moment also offers more control authority for flaring/landing, which will move the forward limit forward. A longer tail will result in a steadier airplane on pitch and yaw.

    ....all of this is first order analysis only. There can be many other factors that negate it.

    The 4 place is an excellent machine in crosswinds. I wonder if the Five will be as good with its longer tail?

    In general, the Five is a very attractive airplane.

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    • #17
      I like the ballast system. I was planning on something similar, but instead of using a steel box, I was going to use a very rugged polymer box, and with an adjustable amount of adult survival beverages. If I need a little more weight, I can also add some ice. A proper CG is important, after all.

      The steel box is probably a lot more practical for flight testing. I believe my solution might be more practical in the real world, or at least my real world.

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      • Collin Campbell
        Collin Campbell commented
        Editing a comment
        Actually the ballast box is 1/8" 6061-T6 aluminum. The seams are welded. The box itself weighed 10 lbs. Can see no reason steel wouldn't work though, it's just what Bob wanted. Like your idea of the ballast "beverage" though...

      • svyolo
        svyolo commented
        Editing a comment
        I am shooting for nose heavy. At, or slightly beyond the FW CG limit with me a a tank of gas. I will be flying over mostly very rough and remote areas. I will always have at least 75 lbs back there, just in case. Water, tent, cloths, raingear, and etc........... I am building a B model kit.

    • #18
      So is the gist that even after Bob makes the tweaks at the firewall station that a rather large ballast would be needed for a single pilot with less then 50% of fuel? Or is that requirement likely to be engineered out in the final design? How common is requiring a ballast, I remember from my private pilot training that the citabria I flew required a ballast with a single pilot - we just used a case of water from the flight school office.

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      • zkelley2
        zkelley2 commented
        Editing a comment
        Simple math would probably dictate this to be the case. I'm not aware of any 6 place aircraft or larger that doesn't need ballast when truly empty up to and including large transport category aircraft. If they didn't you wouldn't actually be able to put the full amount of weight in them without running out of CG first. Even 4 place aircraft that don't need ballast rarely can get to mgtow within CG unless a significant amount of the weight is in Fuel.
        I mean... even the 4 place Bearhawk, if the Aft C.G. limit was the same as a part 23 airplane where pitch is dynamically stable, there's no way you could get to mgtow without full fuel or a belly pod or gold bars in the front right seat.

    • #19
      Mr. Corefile - that is a good question and I am not sure Bob has 100% decided. What would seem to be true is that few people will build as light as Collin did. And the set up on the prototype with the IO580 and 3 blade Trailblazer is almost a worst case scenario as far as what builders might do (weight up front and light weight aft) when building the kits. Using a parallel valve 540 would save some 50-60 lbs on the nose. Using a 2 blade Trailblazer saves 25 lbs way out there on the nose. Bob has to evaluate all the options as far as engine/prop combinations and expected weights that builders might come up with. Mark

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      • #20
        A wide CG range is a wonderful thing, not a bad thing. A "perfect" CG is for a single place aircraft. Most aircraft are performing work for a living. Whether paid or not. You load them up, side to side, and front to rear.

        It is hard to describe and explain, but you are reading the about the testing of a new airplane to hopefully expand its' CG range.

        A Citabria is a case study of an airplane with little utility. There are a lot of light aircraft that fall into that category. It doesn't fly very fast. It doesn't land that slow. If flown solo, you might need ballast. But hey, you can do a loop and roll. so that is cool.

        The current flight testing with ballast isn't a limitation, it is a feature. It demonstrates that it can fly with a broad CG range.

        Any model BH can land EXTREMELY slow. They can fly at moderate cruise speeds. They have a wide CG range. The current thread talking about ballast isn't about being CG limited, it is about expanding an already large CG range.

        I am building a 4 place BH. I am installing systems so that if I fly solo I probably need 50-75 lbs of ballast (camping/survival gear) in the rear of the aircraft. If I want to carry 4 people and bags, that allows me to take out that survival gear, and carry more people and bags than if my CG was farther aft lightly loaded.

        It is a choice, not a limitation.

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        • svyolo
          svyolo commented
          Editing a comment
          I did read a post about an RV-10 owner that did the same as me, except he didn't need the survival gear. He did the same as Bob/Collin. He installed a small box in the aft of the baggage space. He filled it with 5 lb scuba weights (the soft kind - lead shot) when flying light. He could remove them in a couple of minutes when he wanted to load it up.

          Most of my flying will be over remote/rough terrain. Basic survival/camping stuff will almost be part of the basic operating weight.

        • AKKen07
          AKKen07 commented
          Editing a comment
          Svyolo, I like your plan, with the exception of my big baggage tube I’m hoping to keep weight forward as well. What good is a bush plane with out a bush kit anyway?

        • auburntsts
          auburntsts commented
          Editing a comment
          In my RV-10 I use a camping type collapsible 5 gal water cube as my ballast when I’m light. What I like about it is I can easily adjust from 40lbs down to zero if I depart light but pickup pax or cargo somewhere along the flight.

      • #21
        Jared, I would love more information on how the horizontal induction is put together. Mark and Bob think it would work on a 4 place so I’m hoping to get some pictures related to the housing and the connection to the cowl. Also the foam bit on the back end of the filter to connect to the fancy collar dealio. Thanks in advance if you have time for this!

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