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Bearhawk in Brazil

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  • Bearhawk in Brazil

    After 6 months and about 50 hours of flying, I think I'm getting the hang of this airplane. I've got a kit built 4-place that I purchased from a builder here in Brazil. It has a Continental IO-360 spinning a variable pitch Hartzell. Since July, I have been "fixing" a few things. New tailwheel, oil pressure gauge wasn't working (I like to have that when I'm flying), Static pressure was vented into the cabin, new VSI, new fuel selector valve, cleaned the dirty fuel out of the tanks, etc.

    My airspeed rarely shows over 120 mph. It seems fine below 100 mph, but at higher speeds I don't trust it. I did some "testing" this week. Very generic, but I'm not seeing the airspeeds that everyone else seems to be getting so I did some flying using GPS groundspeed. I set my throttle and prop at my desired setting and then flew one direction until speed (vertical and horizontal) was stabilized and then noted GS over a period of time. Turned 180 degrees and did the same thing. Here are my results; ground speed MPH at 1500 feet....

    2300 RPM at 23MP: 106 mph
    2400 RPM at 24MP; 115 mph
    2500 RPM at 25MP; 125 mph

    I did one long range flight where I was able to measure fuel burn accurately. At 24 squared I burned 38 Litters / hour (10 gallon). Do these seem to be in-line with those that have a 200 hp 4-place?

    Matt

    A couple landings: https://vimeo.com/182907800
    https://vimeo.com/204669306
    Last edited by MattS; 02-19-2017, 05:52 AM.

  • #2
    Thanks for the update! Those speeds look a little slow, by perhaps 5-10 mph, but not totally out of line. It's hard to say without more info about the conditions. The fuel burn looks just about right for that power setting.

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    • #3
      I could easily be the size of the picture, or just the camera angle, but in that second picture it looks like the main gear leg might be fabric covered only on the outside, leaving the tubing on the inside "exposed" to the air. That's likely just an optical illusion, but if it WERE true, it would add a good bit of drag, which would negatively impact your speed.

      But the "bigger" thing is that when using GPS ground speed to determine true air speed, a 3-leg course works far better than a 2-leg course, unless you are "100% certain" of the wind aloft direction at your altitude during your test flight. Even then, you must fly your 2 legs directly upwind and directly downwind to obtain accuracy. If you have ANY drift correction, your accuracy will be compromised.

      If you want to try the 3-leg method, which corrects for that "wind drift" factor, there is a website (here) that explains the process (basically fly 3 legs with 90 degree turns after each leg) and then does the calculations for you once you've made your flight and got the raw data.

      Finally, don't forget the difference between TAS and IAS. Even at 1500 feet (18C and 29.92 altimeter), a TAS of 125 mph would be indicated as 121 mph on the airspeed indicator, assuming no difference between Indicated and Calibrated airspeed. If you want to convert your "True Airspeed" back to "Calibrated/Indicated" airspeed to confirm the accuracy of your pitot system, you'll need to also record the indicated altitude, altimeter setting, and OAT along with the the headings and indicated airspeeds..

      Hope this is helpful.
      Jim Parker
      Farmersville, TX (NE of Dallas)
      Patrol Quick-Build Serial # P312

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      • #4
        Jim, Yes, that definitely helps! You are correct, they are only covered on the outside. I met with a guy today to see if I can find some dope and fabric and get that fixed. At $10.60 per gallon for Avgas, i get more bang for my buck when I can reduce drag! I will research the 3-leg method and do some testing. I appreciate all the information that everyone posts on the site. Helps me not feel so alone here in the southern hemisphere.

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        • #5
          Cool! Great to see what's happening in a different part of the world.

          If you are looking to save money, I would suggest learning about running the engine lean of peak. That fuel burn is unusually high for the airspeed you mentioned. I am sure you could 100mph for under 30L/hr. Provided you keep the power settings at or below about 23" and 2300 then you can't hurt the engine.
          Last edited by Battson; 02-19-2017, 03:32 PM.

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          • #6
            I have read some about lean of peak and about not hurting the engine if you stay below 65%. The airplane only came with one EGT and one CHT-- neither of which was working. I am planning to go to sun and fun and look at some engine monitoring systems. After I have EGT and CHT for each cylinder I plan to get serious about running LOP.

            Comment


            • #7
              Matt, one other thing you should consider (along with purchasing the all-cylinder digital engine instrument) is taking the Advanced Pilots Seminar, which costs $395 for the online course. The "live" (in person) course is better, but timing and logistics might be difficult. There is a LOT of information presented that is eye-opening, and you will learn how to operate your engine Lean Of Peak, but that's all secondary to learning how to actually use a digital, all-cylinder EGT/CHT instrument to analyze and diagnose issues with the engine. I took the online course, then the "live" course (you get full credit for the money you spent on the online course if you later decide to attend the live course). And, of course, they have a standing offer to refund every penny you spent on the course if you don't feel you got your money's worth.

              To me, it was the best training event I've ever attended, and well worth the money spent.
              Jim Parker
              Farmersville, TX (NE of Dallas)
              Patrol Quick-Build Serial # P312

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              • #8
                Thanks Jim! Planning to come to Sun and fun and hope to make a decision on an engine analyzer there. I will check out that course and definitely take it one way or another.

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                • #9
                  Hi Matt

                  Where are you based in Brazil? I will be in country in early April for work, and if locations work out it would be good to catch up.
                  http://www.mykitlog.com/yadama

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                  • #10
                    Hi Adam,
                    In Santarem, Para. Up on the Amazon River. Come on over and visit! Matt

                    Comment


                    • JimParker256
                      JimParker256 commented
                      Editing a comment
                      Hey, Matt. I lived in Sao Luis, Maranhao for six years, then a few years later we lived in Fortaleza, Ceara for four years. We travelled often to Belem and Recife as well. It wasn't until I was in college that my parents moved to Rio. At least I got to spend a summer with them during school. During that summer, my brother and I took a bus trip to Brasilia for a week, and saw all the federal buildings. Amazing place with amazing architecture and layout planning. But all that was 40 years ago, now! I suspect things have changed pretty radically! Someday, I hope to get back down there for a visit with my wife.
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