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Weight & Balance

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  • #16
    Bergy, Thanks for the program! I am starting to believe that scales in a workshop will improve results of every aircraft. I also ought to plan my empty wt and CG, and know where I stand as I build rather than arrive at it by accident after everything is done.

    Chris and Rollie, One factor that I am familiar with and may contribute to the slope is elevator effectiveness at slow speeds.

    The quantitative element of the the slope on the forward end of the envelope may be the elevator's inability to provide pitch authority at a slow speed (the landing flare) while operating at a forward CG. Forward of the line, I am guessing that the aft stop on the elevator will be contacted during the landing flare.

    I flew a Beech 56TC Baron once upon a time....the very large engine that Beech could put on this four place Baron fuselage moved the CG forward. (Lyc TSIO-541, 380 hp, 46" MAP on takeoff) With one 150 pound pilot and no freight, it required 50lb. ballast in the aft most baggage area to be in the CG envelope. If not, one would be forward of the CG limit, and hit the aft elevator stop during the landing flare resulting in a near three point landing.

    The Flight Test Phase is the time to test this stuff. We can find out "How heavy and how far forward can the CG be and still have satisfactory elevator authority?" I suspect that the Patrol with a carefully targeted empty weight CG is so well designed that the elevator never looses effectiveness in the flare.
    Brooks Cone
    Southeast Michigan
    Patrol #303, Kit build


    • #17
      I asked a question about engines and CG issues a month or two ago. I was thinking that to make the airplane more "useful" , as in useful load, it might make sense to plan to build it so that flown solo, you needed ballast to either put it within the CG envelope, or in a better part of the CG envelope to make it fly better.

      Apparently that is not a unique thought. I was perusing Van's forums and several RV-10 builders do the exact same thing. To increase their "useful" useful load, they carry ballast in the cargo are when flown solo. When they want to carry more people/stuff, they remove the ballast, which takes all of 30 seconds. I was also wondering if this was "legal" per FAR's. Someone mentioned that the US does permit an aircraft to be signed off with a CG forward of the limit and carry removable ballast, but Canada does not.

      For my personal plane, it will be flying over rugged, remote terrain 98% of the time. Having some basic camping/survival stuff, and water, would probably be prudent. Throw in a bit of fishing gear and a case of beer, and an unexpected overnight camping trip could be downright enjoyable. My "ballast" gets heavier every time I think about it.


      • #18
        Someone in my chapter down here (up here?) in Milwaukee has an RV-10 with a Lyc300 in it. Talk about forward CG!
        ​Christopher Owens, EAA #808438
        Project "Expedition"
        Bearhawk 4-Place Scratch Built, Plans #991
        Bearhawk Patrol Scratch Built, Plans #P313
        Germantown, Wisconsin, USA


        • #19
          My first build was a Glasair II TD. Not a IIS, which was the 'stretched' version. It was a 'short one. Being young and foolish, through a series of strange events, I powered it with a Continental IO520D (300hp) and a 3 blade McCauley prop. Can you say "NOSE HEAVY". I put the battery as far to the rear as possible. I ended up molding a 12# lead weight, that I bolted above the tailwheel spring. AS i recall, minimum pilot weight was about 150#. Ideal? No. If I'd known then what I know now, I wouldn't have built it with that power plant. It flew great! If I'd known better, I wouldn't have had the pleasure and excitement of flying a 1180# (empty) plane with a 300 hp engine. Talk about a RUSH! Picture attached.
          I guess my point is not to get too wrapped up in engineering the CG. If you don't stray too far from the designed parameters, you can adjust the CG by common means. My lead ballast was a bit extreme, but produced a plane with no adverse tendancies.



          • #20
            I've enjoyed playing with my online W/B program,

            I am really beginning to appreciate Bob's Ribblet Patrol airfoil. As I've stated earlier, by starting with a basic fuselage without an engine and then positioning the engine with my mathematical model one can really configure the aircraft to haul some fantastic baggage loads and still feel relatively safe.

            As a grade-school kid, my buddies and I would run around the countryside in our old '31 Model-A Ford sedan. The Ford had a gas tank up front not that different from a J-3. The gas-gauge always read "E". Before a jaunt we would jump on the running-board and if the gauge wiggled we assume we had enough gas for our trip. Well if we assume that no pilot is going to try run their aircraft on fumes in like manner, and we assume that if we return home with extremely low fuel only after a cross-country trip and therefore have some baggage we can really configure the Patrol to manage a huge usable load (Example: me at 200#, my wife, full fuel, and 200#+ of baggage). This is accomplished by pushing the engine a bit farther forward, especially if using smaller engines and lightweight props.


            • Mark Goldberg
              Mark Goldberg commented
              Editing a comment
              Moving the engine forward does have the cost of diminished visibility over the nose. MG

          • #21
            Thanks for the program Robin, it will surely be useful in my case too. Hopefully I'll sort out the numbers needed for my four place soon.


            • #22
              Yesterday was a big moment of truth for me: Weigh in day. I knew I was building heavy, especially compared to Bob. I came in at 1269 total, 91 at the tail, empty cg 12.9 That's 8 quarts of oil, unusable fuel, (I had to taxi it to the shop with the scales and drain the fuel) full IFR avionics, two garmin autopilot servos, electric fuel pump with filter, Hatrzell Trailblazer prop.

              I figure the battery, alternator, starter and associated wiring added a significant chunk of the weight over Bob's then the avionics and the few other mods I did account for the rest. Mods like removable belly panels, big cowl flap, plus I insulated the inside of the boot cowl and the bottom of the floor boards and I'm running dual mufflers and dual heat.

              Its a bit heavier than I was hoping for but it has everything I want in my plane and I built up the engine to cover for the expected weight gain. My IO-360 should be putting out around 205-210hp. Hopefully in a couple weeks I'll know how it flies.
              Rollie VanDorn
              Zanesville, OH
              Patrol Quick Build


              • Rollie
                Rollie commented
                Editing a comment
                I just did a few computations and found that there is no way I can exceed the CG envelope without doing something like loading the tail full of stuff. I even tried it with nobody in the front seat, like flying solo from the back, which I don't plane to do, and with full fuel, 150 lb in the baggage and 200lb in the back seat and the front seat empty, it just almost touches the aft cg limit. and with a light pilot, solo, no baggage and low fuel, its still aft of the empty cg, which is within the forward limit. It should fly fine, now I need to get back to work so I can get it inspected next week.