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Re: [pop-pop-steamboats] improving thrust

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  • William Abernathy
    This is an intriguing idea. A casual search turns up many hits for thrust augmentation in jet engines, but not a lot for water designs. My theory (read
    Message 1 of 4 , Jan 8, 2012
      This is an intriguing idea. A casual search turns up many hits for thrust
      augmentation in jet engines, but not a lot for water designs. My theory (read
      "wild-ass guess") about this, which anyone with A) empirical experience B) an
      actual education in fluid dynamics is more than welcome to dispatch, is that
      thrust augmentors work better with compressible fluids than incompressible ones.
      Such augmenters work by using the Bernoulli effect to increase the coherence and
      the velocity of the fluid being pumped. In the case of pulse/ram jets, this
      fluid is a gas, which is highly compressible. Water, on the other hand, is
      relatively incompressible.

      Pop-pop boats alternate an incoherent intake with a coherent exhaust stream. A
      thrust augmentor might well lengthen the coherent stream, and might speed it up;
      however, for most of the time between thrust impulses, the augmentor will still
      be hanging out there creating drag. I can't prove it, and will happily be proven
      wrong, but my trick knee suggests that this approach, net-net, is going to cost
      more drag than it gives back in thrust.

      --William

      x022435b wrote:
      > hi this is my first message.i made a popop boat years ago from memory of one
      > i got in a lucky dip when i was a kid .i was on you tube and sawn experiment
      > to inccease the speed of popops by using multi tubes and engines.i then had a
      > flashback to my young experiences with jetex modfl planes,there waswhat they
      > called an augmenter tube to increase the thrust.it was a tube with a bell
      > like end and the jetex motor out let was mounted with the otputend in thre
      > center of the bellmouth .what happened was the thrust from the jetex drew air
      > into the tube and added to the thrust.the point is i think you can do the
      > same wiyh the popop egine and it would act like a ventury pipe i do not have
      > the equipment to make this to try it but some of you may.let me know what you
      > think of the idea


      --
      William Abernathy
      Berkeley, CA
      http://yourwritereditor.com
    • papypp44
      Thrust augmenters are well known but...you cannot win everywhere. The thrust evolves with the mass flow and with the jet velocity. If you increase the mass
      Message 2 of 4 , Jan 12, 2012
        Thrust augmenters are well known but...you cannot win everywhere. The thrust evolves with the mass flow and with the jet velocity. If you increase the mass flow (for instance with a ventury) the jet velocity will be less. It means that at low speed or at bollard pull you could increase the thrust, but the maximum attainable speed for the boat will be less. And the pop-pop jet velocity is already so slow...

        --- In pop-pop-steamboats@yahoogroups.com, "x022435b" <x022435b@...> wrote:
        >
        > hi this is my first message.i made a popop boat years ago from memory of one i got in a lucky dip when i was a kid .i was on you tube and sawn experiment to inccease the speed of popops by using multi tubes and engines.i then had a flashback to my young experiences with jetex modfl planes,there waswhat they called an augmenter tube to increase the thrust.it was a tube with a bell like end and the jetex motor out let was mounted with the otputend in thre center of the bellmouth .what happened was the thrust from the jetex drew air into the tube and added to the thrust.the point is i think you can do the same wiyh the popop egine and it would act like a ventury pipe i do not have the equipment to make this to try it but some of you may.let me know what you think of the idea
        >
      • Frank McNeill
        You can provide more thrust by providing more engines though. In files, see a Pulse Projection article by Len Stevens from the April 1996 issue of Model
        Message 3 of 4 , Jan 16, 2012
          You can provide more thrust by providing more engines though. In files, see a "Pulse Projection" article by Len Stevens from the April 1996 issue of Model Boats magazine.

          --- In pop-pop-steamboats@yahoogroups.com, "papypp44" <papypp44@...> wrote:
          >
          > Thrust augmenters are well known but...you cannot win everywhere. The thrust evolves with the mass flow and with the jet velocity. If you increase the mass flow (for instance with a ventury) the jet velocity will be less. It means that at low speed or at bollard pull you could increase the thrust, but the maximum attainable speed for the boat will be less. And the pop-pop jet velocity is already so slow...
          >
          > --- In pop-pop-steamboats@yahoogroups.com, "x022435b" <x022435b@> wrote:
          > >
          > > hi this is my first message.i made a popop boat years ago from memory of one i got in a lucky dip when i was a kid .i was on you tube and sawn experiment to inccease the speed of popops by using multi tubes and engines.i then had a flashback to my young experiences with jetex modfl planes,there waswhat they called an augmenter tube to increase the thrust.it was a tube with a bell like end and the jetex motor out let was mounted with the otputend in thre center of the bellmouth .what happened was the thrust from the jetex drew air into the tube and added to the thrust.the point is i think you can do the same wiyh the popop egine and it would act like a ventury pipe i do not have the equipment to make this to try it but some of you may.let me know what you think of the idea
          > >
          >
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