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. #111
    Ed -
    Yea, noticed that too. Here’s a 40 hp right angle gearbox on ebay (Chinese of course, but maybe good enough for testing) It has 1"shafts and max input of 1800 rpm, and probably weighs 18 or 20 lbs - ouch. But the gears, shafts and universal joints ain't gonna be light either.

    Also, if limited to 2000 rpm main shaft speed anyway, 1800 would give us a 4:1 ratio, or 550 ft lb reduced to 137, coincidentally the max torque of the engine but at 4400 not 1800 rpm, so will the torque converter with no lockup allow running the engine at 2.5 times the output shaft speed? Maybe? You can sit in a car, put it in drive, lock the brake and rev it pretty high. So can we just watch the rotor tach and add more throttle as required during the wind-up? This would give us 1:1 ratio at the engine and 4:1 at the head.

    Wait -- the prop is also turning and eating power and only have enough engine for one, not both - have to figure a way to disconnect the prop. Gets more complicated.

    Have also been working on what to use for drive shafts and universal joints.

  2. #112
    Gear box for testing should be good 40 hp x 5252 / 1800 = 116 ft lb vs 137 ft lb (post # 111) close enough for test.
    Torque converter not running in lockup will over heat in short order unless you have a 10X bigger transmission cooler on it. I'm guessing this is a sealed unit so you just have case heat rejection.
    Drive shafts can be made to turn faster - shorter lengths, carrier bearings and bigger tubes between ujoints. it just gets more expensive.

    For testing no prop so maybe a 2 : 1 gear box on the engine?
    spitballing for the real thing a clutch system that clutches the rotor and when it unclutches the rotor it clutches the prop. A double cone clutch 2 cones back to back?
    Do you have machining capability? Might have to build your own aluminum gear box cases to get lighter weight.

    Have fun
    Ed L.

  3. #113
    maybe a couple of motorcycle clutches - they are spring loaded and mechanically shifted. brain won't stop....
    Ed L.

  4. #114
    This maybe built of unattainium but something like this MAXITORQ clutch brake double clutch, hook rotor to one side and propeller to the other side.

    See page 3.
    Torque range 10 lb. ft. - 2400 lb. ft.
    1 HP to 150 HP capacity
    Positive engagement / disengagement possible at any speed
    All units run in oil or dry applications

  5. #115

  6. #116
    Kevin - you may see photos on pp 3 and 5 for progress.

    Ed - Have considered overheating of torque converter but not in depth. Just top of the head thoughts that experience with what I’ve got and how fast it overheats will give me an idea of the problem. Already have a cooler for the hydraulic system which I can use and can get more if needed. 10 times will be quite a lot though. Have read that TQs only lock up at higher speeds and taxi cabs drive around the city all day without problems, but they’re not working continuously at high rpm.

    Big Harley gets around 110 lb ft of torque and that’s the newer engines. If I found a couple at a junk yard think they could be stacked to provide the capacity needed, but probably still too pricey and hard to find but am looking anyway.

    Maxitorq ? wow, beautiful, but unattainium is to put it mildly, 2500 bucks each. There is a king kong motorcycle clutch with 20 plates that sells for only 1500 clams :-) -- yeah, right.

    Also took some measurements - to run the drive shaft past the engine will have to have 14" between the center of the TQ and the center of the drive shaft so will have to use belts or chain drive.

    Just had a flash, no thought. Think I’ll go back and figure what I’d get if used my 11 gpm hyd pump to power the 21 gpm one. Half speed but more torque? Naah. If 2 big ones won't do it, less sure won't.

    Gettin’ too late - back to it tomorrow.
    Last edited by James J. Judge 42935; 06-13-2018 at 08:43 PM.

  7. #117
    In the you tube on the hydraulic prerotator they said they only went to 300 rpm - 50% over normal? Because your so close maybe try to get your rotor turning with what you have and minimal cost to find out the "rest of the story" like the actual hp needed and if you have any unanticipated problems.

    Car transmissions lock up at almost all times except when starting to move and when shifting gears which is a very small percentage of time.

    Big harley clutches at 110 ft lb, so remember 500 ftlb at the rotor through a 5:1 reduction becomes 100 ftlb on the drive shaft. The rpm likewise goes from 450 X 5 = 2250 rpm in the ball park operating range on the drive shaft.

    Further down the road musings.
    If you can find a belt style torque converter (snow mobiles - 4 wheelers) from a wrecked unit. They are good for upwards of 80 hp and will provide a variable transmission.
    A jaw clutch like old model A ford engine crank that clutches one way but disengages the other way for rotor engagement are much cheaper. Clutch in while it is stopped and will disengage at speed. Somehow don't know about the gear engagement.
    Drive off the front of the engine for the rotor and the back of the engine for the prop?

    Ed L.

  8. #118
    Ed -
    Rotor RPM will vary depending the blades and plane weight, but a round number for average rpm at flying speed is 300 rpm. In the Air Command video --
    they say winding up to 50% over flying speed, then say that is 375 rpm, which would mean their flying speed is only 250 rpm. I guess possible since plane looks lightweight and rotor is probably only 25 foot or so. For me, a 2 place plane, 30 foot rotor, and very heavy blades plus heavy rotor head, I may be lucky to get away with 300. However, those heavy blades will store more energy so may get away with less than the standard 150%, and if I can make it spin the test apparatus will give the answers.

    I do suspect our 550 lb ft may be quite high, since the drag is based on the Polish pdf which used a fixed pitch of 2 degrees, which means it’s consuming enough power to lift the plane, whereas my zero pitch is not, and that sounds like quite a bit of power difference. 25% ? would be 137 lb ft. Yet the Polish chart that shows that it takes 10 times as much power to get from 250 to 450 rpm, as it takes to get up to 250, makes for a serious pause. Yettt - Those higher rpm’s are exactly where more lift is created so more power required -- and I’m not creating that lift, so the power not required? Yes, we sure do still have that get a ‘real’ number problem.

    Still looking for a big Harley clutch, also working on a way to get around a clutch altogether. Noticed that Air Command used a spring operated shift and a manual pin for pitch change. If I can get just a little friction to the prop to get it turning just a little, might get away with a no clutch connection? Driving a semi, I could go thru 11 gears and never touch the clutch.

    Have been shying away from running off the front of the engine, even though much more efficient. (Actually the hydraulic pump does run off the front but shock is not a problem). Concerned that without a little slip in a clutch the application of power would be too sudden and would bust something, unless drive train was built very heavy, and then it would probably stall the engine. The TQ gives a soft start.

    For belt drive, have some info indicating that 3 C grade belts would handle the 137 lb torque, but confidence level is kind of low. Since the right angle drive is limited to 1800 rpm, am trying to limit shaft speed to that, which yields 1:1 ratio at engine and 4:1 at the head. Hold on now -- have been wanting to hold down engine rpm because didn’t want to spin the prop so fast couldn’t hold the plane back - but now am disconnecting the prop, so why not run the engine harder to get more power. The 2:1 you suggested would get 3600 on the engine, why not? Would the belts handle it? Would it make any difference in the heat generated in the no-lock TQ? Much to work on.

  9. #119
    I get it. Rotor RPM will vary with a lot of different factors. The spinup on all these versions of prerotation is at a fixed blade pitch and some are holding the total rotor pitch relative to the fuselage at a neutral angle - yes? Been looking for a book that puts some numbers to the perception this one seems to be one of those. Modern Gyroplane Design 4th Edition by Martin Hollmann and Dr. Eric M. Hollmann Any feedback from any body that has seen this book?

    "I do suspect our 550 lb ft may be quite high," yea, you are probably over building it but who knows till someone spins it up to speed.

    Belts handle over 3600 rpm all the time you have to just go through the design parameters laid out by the manufacturers.

    Ed L.

  10. #120
    Ed -
    Yes, maybe about 99.99% of gyros have a fixed blade pitch between 1 and 5 degrees. Adjustable blade pitch is extremely rare. Total rotor disc pitch (many call it angle of attack just to differentiate) in flight is normally about 9 degrees back to keep the relative wind flowing into the bottom. If you push the stick too far forward, too close to a neutral angle, and the relative wind comes in from the top, you have unloaded the disc and will experience a non-recoverable somersault into a very nasty dirt bath.

    My understanding is that the drag from the rotor disc is the primary limitation on flight speed, and currently the way to reduce that drag is to push the stick forward but you can only go so far. I hope that drag may be reduced by reducing blade pitch in flight, and that more forward speed will compensate for reduced lift resulting from reduced pitch. That would eliminate the danger of pushing the stick too far, and too much loss of lift would be seen in your altimeter. Of course there is a limit to how much blade pitch can be reduced as well.

    I suspect that for spin-up, for best stability, the spindle of the rotor head should be parallel with the force of gravity, regardless of fuselage or topography, but just my opine. I don't have the Hollmann's book.

    I look upon any overbuild as more power to speed up the pre-rotation, and that's a good thing, unless, of course, it makes the project unworkable.

    Have been researching motorcycle clutches, think I'm to the point where I need to meet one personally. Some designs look to be easier to work with. Will need a little luck to find one of those.

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