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Thread: Updated photos of Twin JAG

  1. #21

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    Right engine almost finshed. Left engine also in same stage of completion. Bringing both engines to Corvair College first week of November to test run and break in.
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    Measure it with a micrometer, mark it with a grease pencil & cut it with an axe.

  2. #22

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    Front view of engines mounted temporarily.
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    Measure it with a micrometer, mark it with a grease pencil & cut it with an axe.

  3. #23

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    It seems very hard to believe that just stopping an unfeathered prop cuts 94 of the drag, or else it would have been used in other planes, cheaper, simpler than feathering.
    Obviously, once you get to flight testing you can, at a safe altitude, shut down one engine, brake the prop to a stop and try it, and you will know how it flies on one engine. A premium would then be on getting the brake off and restarting.
    It may work, but I'd sure wear a chute and be able to get out. A chute won't help if an engine is lost on takeoff,though.
    You sure have put some work into it.. Good luck.
    Note, I am not any kind of expert on this, and don't even have a multi rating.

  4. #24
    FlyingRon's Avatar
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    Having studied some twin conversions (I'm on the board if the organization that actually holds the TC on one of the twin Navion conversions), did you increase the size of the tail? Rudder trim?

  5. #25

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    Yes, the tail is aproximately 30% larger than the original tail. No rudder trim.
    Last edited by jimdc8; 12-20-2014 at 05:55 PM.
    Measure it with a micrometer, mark it with a grease pencil & cut it with an axe.

  6. #26

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    Bill, you are correct. It is not truly 94%...I was just trying to quantify in simpler terms the reason for my thinking. A feathered prop is more streamlined than a flat blade. Stopping the prop does make a huge effect on drag although my props will probably stop on their own due to low inertia below 100kts. It is just a simple way to reduce drag if the crankshaft broke just behind the prop hub for example.
    Measure it with a micrometer, mark it with a grease pencil & cut it with an axe.

  7. #27

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    Oct 2011
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    Some engine details....still fabricating intake, exhaust, baffling, oil cooler, etc.
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    Last edited by jimdc8; 01-06-2015 at 02:29 PM.
    Measure it with a micrometer, mark it with a grease pencil & cut it with an axe.

  8. #28

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    Oct 2011
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    Designed & carved this 62" x 74" test prop. I will use this prop to test run my engines. I will then tweak it for flyable props. Hope to run the #2 engine on the aircraft before Airventure. I will run the #1 engine shortly after I return from Oshkosh later this summer.
    Measure it with a micrometer, mark it with a grease pencil & cut it with an axe.

  9. #29
    crusty old aviator's Avatar
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    You may see a baggage shelf, and you did a nice job of designing and fabricating it, but I see a rumble seat! I'm not sure how a "light" person would affect the W&B sitting up there, but with a little bubble canopy on the nose cone, instead of just the door on the side, that would make a cool perch!

  10. #30
    crusty old aviator's Avatar
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    Aerodynamically speaking, a spinning prop has the same flat plate area as its entire disc area. This was confirmed by Fred Weick of NACA in the 20's, which is why the feathering prop was developed, as props have little tendency to spin much when feathered. Yes, the blade presents more flat plate area in cruise configuration than when feathered, but only if if it's not turning. What if you have a severed crankshaft, a compression ratio of 20:1 won't keep the prop from turning in flight. If you feather the blades so there's minimal aerodynamic forces acting upon them, you won't have the drag of the entire disk, just "6%" of it. Feathering props are wicked complex and heavy. Jim has created a simple, lightweight system here to help minimize some of the yaw problems associated with an engine-out condition.
    I appreciate other homebuilders posing questions to those showcasing their projects here: it's how we all learn lessons from those who tried and learned something new. The only stupid question is the one that hasn't been typed...that said: what color will she be painted after flight testing?

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