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Re: Yellow Tail Hawk project report

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  • gypsyinvader
    just a two-center... I was going to lighten my briggs cast iron flywheel, but then found cast iron machinings are very abrasive on tooling! Similar to
    Message 1 of 58 , Jul 1, 2011
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      just a two-center... I was going to lighten my briggs cast iron flywheel, but then found cast iron machinings are very abrasive on tooling! Similar to sanding grit into stuff, I guess. No way am I going to expose my (future) new lathe to that, even if it will be an "el-cheapo" Shop Fox jobbie. I'm goung to make an aluminum replacement. Of course, if you hire it done, then what the hey..:-)

      I also "must" have the electric start. Ain't gonna "prop", and my briggs dosn't even have a recoil rope to pull...
      Garry

      --- In Small4-strokeEngines@yahoogroups.com, "Kenneth" <kiweezul@...> wrote:
      >
      > Bill,
      > The flywheel is still installed,it is going to be lightened.
    • goarnaut
      No you did not ask. If you had asked I would have done my best to politely explain, which I have done quite often here, with great patience. A larger chord is
      Message 58 of 58 , Jul 11, 2011
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        No you did not ask.

        If you had asked I would have done my best to politely explain, which I have done quite often here, with great patience.

        A larger chord is necessary with a longer blade in order to maintain stiffness. Also structural strength for the centrifugal loads which increase with diameter.

        This is a very fine prop design method that will give a great-performing prop. I do not think it deserves to be casually dissed.




        --- In Small4-strokeEngines@yahoogroups.com, "williamberson" <whodunit@...> wrote:
        >
        > Actually Gordon, I thought your spreadsheet was pretty cool. I just didn't understand how it was giving the result it did. So I asked.. the author. Well, excuse me.
        > If you take that as lecturing, then I cannot deal with you.
        > I don't trust any computer result, I verify in every way that I can find.
        > Scott Casler is using 60" props on the 1/2 VW (search this forum).
        >
        > Actually, I do have quite a bit of experience making props.
        >
        > But I really don't think you want me to respond to your questions.
        > Bill
        >
        >
        > --- In Small4-strokeEngines@yahoogroups.com, "goarnaut" <goarnaut@> wrote:
        > >
        > > Bill,
        > >
        > > Seeing as you are such an expert that you feel you can lecture me on what is "correct" and what is not, then please go ahead and put together your own prop design spreadsheet.
        > >
        > > Put it up on the files section. I will download it and then I and the other group members can see your better approach. And we can all design our props from now on using the Bill Berson prop design method.
        > >
        > > Really some of your comments are pretty unbelievable. You say my spreadsheet does not seem "correct" to you. How so exactly?
        > >
        > > Please give specific technical details.
        > >
        > > And really what are your qualifications in propeller design? Or aerodynamics? Or any kind of engineering, science or mathematics? I'm just wondering because you seem to be quite sure about the faults you supposedly find in my work.
        > >
        > > A few posts back you similarly said that lightening the flywheel does not seem like it will work. Again, how so?
        > >
        > > I have put up some very good technical explanations on that subject and I think people have actually found it useful and insightful. Just saying "I don't think it will work," amounts to the critique of a 5-year old.
        > >
        > > Really I have to wonder if you are even using the spreadsheet correctly. I have made it very easy to use, but still I have to wonder.
        > >
        > > Assuming you do know how to use the thing and can iterate (guess a number until the two numbers below it are the same), then yes a larger diameter prop will give a bigger chord, all else being equal.
        > >
        > > But guess what? What do the blade angles do? Please report back to us your expert findings. In detail please, as to whether they increase, decrease, by how much, and also your take on why this happens. This I can't wait to hear...
        > >
        > > Also what is the tip speed now with the bigger prop, but leaving rpm the same?
        > >
        > > You are obviously going outside the recommended size if you put in a prop of 60 inches at 3600 rpm.
        > >
        > > The spreadsheet gives you 3 recommended prop sizes and 60 inches is way bigger than any of those three.
        > >
        > > But even still the spreadsheet is almost idiot-proof and will try to match this inane size input with the best recommendation it can.
        > >
        > > Unbelievable...
        > >
        > >
        > >
        > > --- In Small4-strokeEngines@yahoogroups.com, "williamberson" <whodunit@> wrote:
        > > >
        > > > Gordon,
        > > > I tried your prop spreadsheet. I changed your sample 49" diameter prop to my 60" prop and the spreadsheet increased the chord. This doesn't seem correct to me, the blade area should be less, I think.
        > > >
        > > > Also, FAR 33.43 talks about "endurance limit stress" of the crankshaft.
        > > > Do you know what the endurance limit stress is for ordinary forged steel?
        > > > Bill
        > > >
        > > >
        > > >
        > > >
        > > >
        > > >
        > > > --- In Small4-strokeEngines@yahoogroups.com, "goarnaut" <goarnaut@> wrote:
        > > > >
        > > > > Bill,
        > > > >
        > > > > Those industrial engines were not meant to handle gyro loads, but they are meant to handle crank bending loads from a pulley and belt. Both are bending loads, so they are exactly the same---with the exception of magnitude.
        > > > >
        > > > > My prop spreadsheet does the calcs for prop, inertia, gyro loads, and shaft stress. This is what is done in certification.
        > > > >
        > > > > Regards,
        > > > >
        > > > > Gordon.
        > > >
        > >
        >
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