CS vs Fixed Pitch Power

Discussion in 'Steen Skybolt' started by aobt14, Jul 17, 2017.

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  1. Dec 29, 2017 #41

    PittsDriver68

    PittsDriver68

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    The original 200hp Mooneys fly behind the exact same engine that is on the early Pitts S-2A's. IO-360-A1A. Lopresti, as mentioned above, put the Lyco's that have counterweights on the crank into the later Mooneys, and then he had the propeller flange dowels moved to time the propeller to pass by the intake at the time that the intake valves were opening on the cylinders. Then they went to the single drive mag, with that engine being the IO-360-A3B6D. The "3" speaks to the changed indexing of the propeller, the "6" speaks to the counterweights, and the "D" says single drive dual mag.

    The parts book next to me says that the cases are the same for the IO-360 angle valve engines, so if you really want a no counter weights in your engine, trade your counter weighted crank in for a non-counter weighted one. Not a big deal for your engine builder.

    That said, I note that Lyco put a counter weighted crank in the IO-390. As noted above, they did it for a reason, not just to add to the parts count.

    When my engine was last torn down, Tim Hess found that the center main bearing was totaly worn out. 1200 hours of acro with some cross country. Think about what it took to wear out the center main before the others....

    Best of luck,

    Wes
     
  2. Dec 30, 2017 #42

    Lotahp1

    Lotahp1

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    My Ranger center bearing was worn more than the rest. It had a Hartzel “controllable” Aluminum Prop on it. In old Hartzel terms “controllable” meant the pilot had a lever that controlled pitch. The pitch was not governed by anything. It used a hydraulic bladder to move the blades. This was the common Prop on old bonanzas, Navions and Ranger powered Widgeons etc that ran the Hartzel. It was big step above a fixed pitch but not a constant speed. Latter they did use a governor on a T drive to make the controllable Prop into a constant speed by adding a governor and redoing the lever into the cockpit etc etc. this has actually been done on a Widgeon with Rangers I know of but as far as I can tell Hartzel never marketed it to Ranger powered planes but because old controllable setup was the same as the bonanzas etc it worked. There’s some custom pieces involved so I’m sure it took a 337 to do it. (Fat chance you could get it approved today)

    Anyway, I have had several moments when I ask myself “do I want a Aluminum Hartzel that offers the most performance, or Hartzite blades that offers most of the performance but they are 70 year old phenolic or should I just have GT build new blades for the hub? Currently I’m just going with the Aluminum 8833 blades because I found some. And I don’t intend on crazy acro beyond primary level. But eventually I’m very interested in some new GT blades and making it a true constant speed Prop.
     
  3. Dec 30, 2017 #43

    Dennis5678

    Dennis5678

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    How did the first Pitts S-2 compare to the S-2-A ?
    Why did he go to the A ?
     
  4. Dec 30, 2017 #44

    Neil

    Neil

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    There are people here that know this better than I, but the first S2 was a 180hp fixed pitch airplane that became the E as I don't know if any straight S-2 airplanes were produced as certified. The story goes that Curtis got a deal from Lycoming on 200hp C/S engines and thus the 2A was born.
     
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  5. Jul 10, 2018 at 2:41 AM #45

    Skybolt540

    Skybolt540

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    Ha! :) The problem is installation and application dependent. Sometimes, higher order harmonics are starting to creep in as the propeller approaches max rated engine rpm. Stress is still in the ok range at max, but there can be a very steep stress vs. rpm slope out there at the end. That's also why you can only trim so much off the tip for repairs; that blade length reduction gets tested too, it's not just arbitrary. Sometimes even tip shape can be important (rounded vs. elliptical). Propeller design is usually a resonant frequency balancing act.

    You can be confident everything's fine up to rated rpm for a certified propeller/engine combination, but going any higher in engine speed can sometimes start to do bad things to propeller stress. Then again, there are some installations that would be fine at higher revs, it just depends on the prop/engine combination. But regardless of all that, once you hit a certain tip Mach number all you're doing is making more noise anyway, you're not making any more thrust.

    In general, no engine beats up on a propeller worse than an undamped 4-cylinder. I'd definitely keep things by the book if I were flying behind one of those. And anything else for that matter. :)
     

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