View Poll Results: Why is jump so rare?

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  • Nobody wants it

    1 12.50%
  • Initial cost too high

    4 50.00%
  • Too much maintenence

    1 12.50%
  • I think it's dangerous

    2 25.00%
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Thread: Jump Rotorhead Dynamics

  1. #121
    Ed - Have ordered a used clutch disc and basket package on ebay, from honda shadow 1100cc rated at 69 hp with 11000 miles on it. With 2:1 ratio at the TQ it should handle the torque. For the prop would need 2 sets stacked, but not until testing is done. So not too expensive and maybe can learn something.

  2. #122
    Jim Alright look forward to seeing that.
    Ed L.

  3. #123
    Ed -
    Lot to learn is right. In planning the direct drive system, and finding the parts for it, realized I had found parts that would make the hydraulics work too, which would definitely be preferable. Have been concerned about running off the TQ, since there is less than a 50% chance that will work for the prop, and if it doesn’t then lose the power for both the prop and the pre-rotator.

    Have figured out how to run that motorcycle clutch, which has a gear on it, on the engine crankshaft, and put a gear on the pump and mount it for a clean gear drive. Will use the 21 gpm, 2900 psi, 3600 rpm pump and buy another to use as motor at the head. Am estimating I’ll need about 2200 rpm and 55 hp from the engine to get the pump to 3600 rpm. (to use the gears that I have from the cycle -- 66 teeth to 38 teeth). There’s a photo of the clutch at

    Have also found gears from the motorcycle tranny to use at the head, no clutch, just engage when still and disengage when power is cut at the pump clutch. A simple pivoting gear plate should do the trick. The size of the gears will require an intermediate gear between the head and the motor. A 4:1 ratio will be easiest, but can make 5:1 work with some more effort.

    Haven’t done all the nitty-gritty math, started to but just got bogged down, and what I got made no sense, and since I have parts to work on am just losing patience with my computationalizing. Since we have twice the volume and rpm at the pump and at the motor there ought to be plenty of power. Your expertise to confirm it , though, would be really appreciated.
    Thanks Ed.
    Last edited by James J. Judge 42935; 07-02-2018 at 09:06 PM. Reason: added

  4. #124
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  5. #125
    Jim and all have a happy 4th.

    21gpm X 2900 psi / 1714 = 35.5 hp
    gear ratio to pump 68:38 teeth guessing big gear on clutch.
    driving pump to 3600 rpm so (3600/68)X38 = 2011 rpm at engine because clutch w/ big gear is on engine.

    using CB2A-F11 hydraulic motor / pump rated at .701 cuin /rev , .701 X 3600 cuin /231 cuin /gallon = 10.924 gpm. you have a bigger pump to get 21 gpm?
    to get 21 gpm at 3600 rpm you need a 21gpm X 231 cuin/gal /3600 rev/min = 1.3475 cuin/rev pump/motor or 2 - CB2A-F11 pumps and 2 - CB2A-F11 motors.

    2 - CB2A-F11 pumps, 2 x .701 cuin/rev = 1.402 cuin/rev
    1.402cuin/rev x 3600 rev/min /231 gal/cuin = 21.8 gpm

    hp required by the engine 21.8 gpm X 2900 psi /1714 = 36.9 hp add losses for one gear mesh 36.9 X 1.02 (2 % per gear mesh) = 37.6 hp
    hp at the motor shaft in the rotor head = 36.9 X .7 = 25.83 hp. (flow loss in for both the pump and motor is ~30% so hp goes down proportionally)

    "Am estimating I’ll need about 2200 rpm and 55 hp from the engine" HP does not change across a gearbox it remains the same minus friction losses.

    hang in there.
    Ed L.

  6. #126
    John, you’re very kind, and something like that is well beyond my imagining, and you can tell I have a pretty wild imagination. I’m just doin’ what I love, havin’ fun, and tryin’ to keep from going to seed in my retirement, with a lot of help from Ed. (thought I posted this 2 days ago but ??)

    Ed - Am beginnng to to wrap my mind around HP, torque, power, speed etc. This lack of understanding is why I thought my computations didn’t make sense. Your line "HP does not change across a gearbox" put it so bluntly as to prod me to more study, and I’m still trying to pound it into my brain. Does age increase density? I already have one 21 gpm pump and am about to order another. Am modifying the crankshaft fitting to handle the clutch, then have to build the frame to carry the pump.
    Am also working on a more complete understanding of how a torque converter works. There’s a complicated little bugger too.
    Last edited by James J. Judge 42935; 07-05-2018 at 11:14 AM.

  7. #127
    Sounds good, keep me posted and send a picture when you get close.

    Ed L.

  8. #128
    Ed - Short update - Have the clutch mounted on the engine, BUT - in the process realized that a motorcycle clutch won’t operate the way I was thinking, that is, running disengaged and only engaging for spin-up. On a bike the clutch is always engaged, and only disengaged momentarily to shift gears. There is so little space between the plates that the friction of running it disengaged would fry the clutch in short order.

    Then there’s the point that on a bike it runs in an oil bath. That one you had found earlier, the $2500 one, could be run wet or dry. Since this is essentially the same design am trusting it will work here too. If it doesn’t I’ll just burn ‘er up :-)

    Which means I’m going to have to mount a shiftable idler gear between the clutch and the pump, and between the motor and the head. Have found a complete set of transmission gears and what I need to get it done, now just gotta build the mountings, shifting mechanisms and controls in the cockpit ... and ... design it all to work with what I’ve already got. No small job for a rube, especially with gears that are too hard to drill even with cobalt, and welding is risky too, but I do have some preliminary drawings done.

    Have abandoned the idea of pivoting mountings as impossible to get an accurate and consistent gear mesh - might work for a quick & dirty test but I hate having to go back and do something over when I could have done it right the first time.
    Last edited by James J. Judge 42935; 07-27-2018 at 02:10 PM. Reason: add

  9. #129
    Is your clutch cable or hydraulically operated? When disengaged is it running on a throw out style bearing? I don't think the clutch will make much heat when disengaged. I worked summers for Wichita Clutch back in the day it takes very little clearance to disengage and if the disks are floating they make very little heat. Running disengaged is probably harder on the throwout bearing than any thing else. As you say they are not built to be running all the time, but if a ball bearing and not a journal bearing you may be surprised how long they will run.

    Shiftable idler gear hummm, I guess manual shift in while static and a spring unshift to keep it away from moving gear. Gear on a spline you might have that in your donor transmissions.

    Sounds like your are making good progress thanks for the update.

    Ed L.

  10. #130
    Ed -
    Haven't decided on cable or lever operation, but not hydraulic. Leaning toward lever since space is tight and that will hold the gears where I want them without springs etc.

    There are no ball bearings in the clutch at all, I guess because it was running in oil anyway. If I run it engaged it turns as one piece with the crankshaft, so no wear at all except for the momentary shifting.

    Didn’t buy the whole transmission, just the gear sets and spline shafts. Will have ball bearings on the idlers and will use one of the spline shafts. Will be interesting to see how well the shifting actually works.

    Mounting the gears on the pumps is a challenge. Have just ordered a couple of taper-lock bushings, but not a clean fit. Will have to modify both the gears (grind a taper) and the bushings (too big for the gears so turn ‘em down and re-cut tapers). Didn’t want to rely on just a press fit to hold the gears on and the taper system should do it.

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