Reversible Prop Controls

Discussion in 'Bush / Float flying' started by Chris In Marshfield, Apr 3, 2015.

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  1. Apr 3, 2015 #1

    Chris In Marshfield

    Chris In Marshfield

    Chris In Marshfield

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    Hi all,

    Thinking ahead to when I'll eventually be flying on floats. Does anyone have any photos or references to web sites with photos that would demonstrate how the controls would work for a single-engine piston with a reversible prop? I've found plenty of references to the prop innards itself, but not a single one that shows how the controls are set up. This aircraft is a single-engine high-wing airplane, Bearhawk or similar, typically equipped with a push/pull throttle control. But could go with a quadrant if it's needed for this application (I'm picturing a console shifter with a reverse lockout in my brain).

    Thanks!
    Chris
     
  2. Apr 3, 2015 #2

    Head in the clouds

    Head in the clouds

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    Let me know if you have any success with making one please, I could also do with a reverse lockout in my brain :gig:
     
  3. Apr 4, 2015 #3

    bmcj

    bmcj

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    Perhaps an easier solution would be a small, electric trolling motor on a retractable belly (or float) mounted boom.
     
  4. Apr 4, 2015 #4

    Chris In Marshfield

    Chris In Marshfield

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    That's a pretty great idea, @bmcj. Sure would be cheaper than a reversible prop, that's for sure.
     
  5. Apr 4, 2015 #5

    TFF

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    Im not sure of piston with reverse. All the props I have handled did not allow past feather. It is just a governor action so it the prop can go in reverse. Right parts will make it work. The turboprops usually have reverse locked out until a squat switch is made. I think cropdusters have open reverse, but you have to be careful. A runaway prop into reverse is not recoverable from; the reason for the lockout. The SAABs I worked on had lockouts added after a couple of pilots killed some people when they pulled into reverse in the air.
     
  6. Apr 4, 2015 #6

    don january

    don january

    don january

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    well if it was me I'd start with a new pair of comfortable deck shoes and push the plane away from the beach, and If I was docked in deep water I'd keep an old set of oars straped to the floats. Always carry two ya never know if ya drop one. :gig:
     
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  7. Apr 4, 2015 #7

    Chris In Marshfield

    Chris In Marshfield

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    There are several videos on n YouTube, one of a Husky, and another of a Super Cub, both with an MT reversible. It looks to make docking and other water maneuvers a breeze. But not a single one on how they're controlling it.
     
  8. Apr 4, 2015 #8

    TFF

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    It will be controlled by the govenor. Its just a constant speed prop that can go past feather. The prop lever will be moved to reverse and you would throttle the engine with the power lever. No magic. MTs are not stock props. If they are commercial aircraft, there is an STC. If they are flying them Experimental Exhibition, then they have special paperwork.
     
  9. Apr 4, 2015 #9

    Chris In Marshfield

    Chris In Marshfield

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    Trying to picture the gymnastics between the prop and throttle controls, especially if you're using push/pull controls. A quadrant would make it a little easier, I supsect, to juggle with one hand.
     
  10. Apr 4, 2015 #10

    Toobuilder

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    A reversible prop doesn't go "past" feathered, it goes the other way- "past" max RPM (fine). On the way it goes to zero thrust, then Beta. There are plenty of YouTube videos showing Turbo Porter jump planes using Beta to descend in a vertical dive to get back to the LZ. Some of them even show the airplane passing skydivers in free fall.
     
    Last edited: Apr 4, 2015
  11. Apr 4, 2015 #11

    TFF

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    OOPs your right On the feather. With a vernier control it would not be fun as you would need some detent to tell you where fine would be and over that would be reverse and reverse would be firewall and fine pitch would be out some. Quadrant much easier and a Husky and a Cub will have quadrants. On a turboprop. There is no thrust which is flight idle on the power lever, throttle. Push forward go forward. To go backwards pull finger lock at flight idle and pull backwards. The quadrant does the logic part. On a piston you could come up with a fancy quadrant or I would put it on the prop control lever with a mechanical lock too keep it from going too far untill needed. A plane will drop out of the air and many commuter plane was designed to use reverse in the air as a spoiler system. It got regulated/ADed out of existance as it was killing people. I see cropdusters pull erverse when they are about 4 ft in the air, and the plane just stops flying. If you do have a runaway prop you will come out of the air. The commuter planes I worked on has feather pumps incase the prop would not feather you could force it.
     
  12. Apr 4, 2015 #12

    JamesG

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    Of course you don't want to make it TOO easy...
     
  13. Apr 4, 2015 #13

    Chris In Marshfield

    Chris In Marshfield

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    True enough!
     
  14. Apr 5, 2015 #14

    Toobuilder

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    A quadrant with a gate lockout would be easy enough. Full forward against the gate for normal ops (like a go around) then lift the gate for reverse. The problem however, is all the logic is in the quadrant, and a broken cable may allow the prop to run all the way up against the low pitch stop (which would be reverse in this case). That would make for an interesting go around attempt.
     
  15. Apr 5, 2015 #15

    rv6ejguy

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    On King Airs, you lift the throttles rearward over a gate to engage Beta and further back for reverse if my old brain recalls correctly. These were tied into the prop pitch control mechanism. The prop condition levers gave you in flight pitch control and I believe also a high and low rpm setting for setting up the reverse function. Someone step in and correct me if I stated this wrong, been about 25 years...
     
  16. Apr 5, 2015 #16

    BJC

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  17. Apr 5, 2015 #17

    Toobuilder

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  18. Apr 6, 2015 #18

    Tiger Tim

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    Lifting the principle straight from a turbine may not be the best plan as they do have some unique things going on. For the sake of some background info, a Garrett fixed-shaft turbine as installed on a light twin (non-FADEC) will have three ranges of power lever motion: reverse, beta and flight range. In the MU-2, each range is separated by a gate and most light twins are similar. The range most familiar to piston engine pilots is the flight range, where the power lever is operating a manual fuel valve and prop speed is determined by the prop governor. Lever goes forward, fuel gets added, turbine extracts more power and the prop governor automatically coarsens the prop blade angles to maintain RPM and make more thrust. Just like you'd see in a 182.

    Moving the power lever back into the Beta range makes the power lever control prop blade angle (instead of fuel flow) and RPM is maintained at a constant set by the underspeed fuel governor. The 'disconnect' from the manual fuel valve previously mentioned is because it actually drives it through a cam and that cam has a big flat on it through the beta range. At ground idle the prop blades are effectively at flat pitch. Below ground idle you start to get into the reverse range, which is actually still a form of beta. The power lever still directly controls blade angle except now that angle is getting into the negatives. The only real difference in the reverse range is as you reach maximum reverse there's a cam that increases the underspeed fuel governor's speed to provide a little more of a reverse push.

    For a piston engine, I don't think beta range ever really applies. Idling a constant speed prop-equipped piston engine below its prop governing speed is essentially a fixed-pitch mode that you only see in taxi due to lack of air loads. I think the principle of reverse pick-up (the increase of RPM at max reverse) is a good one to bring over but I'm not sure the massive complexities of fuel governors, prop governors, beta tubes, lockout valves, cam-actuated linkages, etc would come into the homebuilding world without a fight. Instead, I think the simplest answer would be an electrically controlled constant speed prop with reverse controlled by a gated sector of the throttle quadrant. Pull the power back below that gate and a bit of power would be added to keep from stalling the engine as as the prop is electrically driven into reverse. A pitch runaway in flight could be halted with a big emergency switch that makes your prop revert to a fixed pitch long before disaster strikes and then the only real unwanted reverse dangers could happen on the ground (or water, as it may be).

    Or, maybe smarter still would be to look into pre-existing successful light planes with reverse then just copy, copy, copy!
     
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