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Prop extension or not?

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  • Prop extension or not?

    O360 with kitset motor mount. I am contemplating intalling a 4 inch sabre prop extension to help with cg as it will be hanging a hartzell CS prop. I know its only 4 inches ahead of the prop but i am concerned about a tailheavy cg. I could have extended motor mount but already purchased the kitset O360 mount before i read the threads about the lighter O360 out front. Opinions are encouraged. Thanks all again. Im almost thinking it would be too little difference compared to the extra cost and extra work. It would look nice i believe with the longer nose though

  • #2
    I guess it depends on what you want with your build. If flying qualities are more important, having a far forward CG is not what you want. If useful load is your primary objective, then if it were me and I was using an O-36,0 I think I would take the time to make a little longer motor mount. I want to carry stuff.

    I also used Oratex, and spruce stringers. The Oratex is half or less than regular cloth, and the stringers are half the weight of the kit aluminum ones. All of the cloth is aft of the CG other than the landing gear covers.

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    • #3
      I wouldn’t do it but if you run the numbers and it gets you where you want to be then I think it would be fine.

      My wife hates the long nose of the BH. Literally every time I show her a pic to ask her opinion of some change we made she comments about how much she dislikes the nose. If it were longer she’d probly make me sell it😉

      There might be better ways to help your CG. Metal prop, firewall battery, regular sized tailwheel, weight conscious interior, not screwing up the paint and correcting it by adding more paint, accuratly balancing the elevators (make sure you have enough lead but not more than necessary), don’t put the ELT in the tail, etc. Every little bit helps and is even more significant on a O360 airplane. You also have to accept the ‘limitation’ of the engine you chose. An O360 BH is a nice flying airplane and will haul a great load but you really need to watch the CG.
      Scratch Built 4-place Bearhawk. Continental IO-360, 88” C203 McCauley prop.

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      • #4
        I hate the idea of adding weight anywhere. If I do, I better get something out of it. No free rides. I think adding a skylight and glass in the lower door cost me 20-25 lbs. EFI about 8. Everything else I went "lightest" so far. Using Oratex even saved 4 lbs of elevator and aileron balance weight. 2 of those are in the tail.
        I think maybe the only place to add weight that might make sense for a 360 powered BH might be a metal prop. That also saves money. I haven't bought the prop yet. I might make the same choice. Anywhere else and I think you are adding weight at a faster rate than helping your CG.

        Like Whee said, mount everything possible in front of your butt. And as far in front as possible. That is about all you can do save a longer engine mount, or changing your mind and putting a big honking motor in it.

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        • whee
          whee commented
          Editing a comment
          How much lead did you have to pour in your elevators? I’ll see if I can find were I wrote down how much I put in mine. I think it would be interesting to know.

          EDIT: I'm almost positive I used 4lbs for each counterweight but I can't find were I wrote it down or the thread discussing it. Looks like you used 3 lbs, that's a nice savings.
          Last edited by whee; 11-25-2019, 11:17 AM.

        • svyolo
          svyolo commented
          Editing a comment
          I would have to look up what I posted. I don't know if I wrote it down. I just calculated it and actually balanced it out on an aileron a few weeks ago. Oratex was 68 oz or something close. Heavy fabric was more painful on the ailerons as the balance weight isn't that far forward. Easily a pound or more saved on each aileron.

      • #5
        I guess moving the oil cooler to the intake, and using a belt driven alternator also moves some weight forward a couple of feet. 12-15lbs X 24-36 inches.

        I think the only wires on my build aft of the CG are to the wingtip lights, and the audio panel right behind the front seats in the wing roots. I think every other wire is in front of the CG. So far anyway. I am starting out with no AP servos, and stock manual trim.

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        • #6
          Here is a picture of a spread sheet for my plane that I keep on my iPhone. Each time I load passengers into the back seat I can run the spread sheet to see if I need to move things around. One time I did have to ask a passenger to move from the rear to the front to keep weight and balance more comfortable. It was not that you could not fly safely it was that I could feel the pitch sensitivity and it was more comfortable with that passenger in the front. It was going to be a night arrival back home and I did not want to deal with the sensitivity at night. There are somethings that are important about this document:
          180 Hp Lycoming MTV 210 15B prop

          1 The plane is set up with 2700 lb gross weight
          2 It has a light MT propeller. If I had a heavier prop the numbers would be better.
          3 The plane is a little heavier than I wanted but it is what I wanted. Weight could easily be removed as it has a heavy carpet on the floor that could easily be removed.
          4 I was out at night this week with it. 70% power 117kts true airspeed

          Is it a 250 hp. with all the performance of a sports car, no, but it flies great and I am happy with the performance compromise. With the 180 hp. move everything reasonably possible, forward as far as possible and you will have a good plane.

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          • JimParker256
            JimParker256 commented
            Editing a comment
            Maybe it's just me, but all I see is the thumbnail, even if I open it in a new browser window.

        • #7
          I will make a excel spreadsheet of my weight and balance this evening and post it.

          The news group will not except a spread sheet. I expect it is a security concern in which case I think it is a important concern to keep our group safe.
          Last edited by tailwind; 11-26-2019, 06:52 PM.

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          • #8
            Originally posted by whee View Post
            My wife hates the long nose of the BH. Literally every time I show her a pic to ask her opinion of some change we made she comments about how much she dislikes the nose. If it were longer she’d probly make me sell it😉
            Pro tip - the nose looks shorter with 29 inch tires or larger

            Comment


            • svyolo
              svyolo commented
              Editing a comment
              I flew something with a long pointy nose for a long time. Nothing to be ashamed of. I got over it quickly.
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