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Coanda or Bernouli, which describes lift?

  1. May 1, 2005 #1
    When firing my pulse jet I tried various approaches at increasing its' performance without significantly increasing its' weight. When (while holding a piece of larger diameter pipe with channel locks) introducing a larger diameter than the jet diameter pipe into and partially allowing the larger dia, pipe to find its' natural location I discovered (felt) something that was described as 'the Coanda Effect' . A database search reveals disagreements among 'people in the know' regarding the mechanism for describing 'LIFT'.Is there a definitive answer??

    frank MR. P
  2. jcsd
  3. May 1, 2005 #2


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    Staff: Mentor

    While Bernouli doesn't tell the whole story, it does form the foundation. The Coanda effect has a minimal impact on lift. For one thing, that cohesion force doesn't increase with flow velocity. Its essentially a static force.

    Also, your description of what you observed isn't all that clear, but it sounds like normal aerodynamic forces - not the Coanda effect.
  4. May 2, 2005 #3
    thank you for your responce russ.......The effect I felt was simiar to the feel you sense when two magnets are in close proximity to each other when attracting. I also noted that by keeping the larger diameter constant, the effect always appeared at the midpoint of the length i was using here's some data:

    Pulse jet tail pipe diameter 1 1/8"
    Pulse jet length 27"
    pulse jet inlet diameter 2 1/2"
    length of inlet & combustion chamber 6 1/2"
    length of reducer 2 1/2" to 1 1/8" 1 1/2"
    stand alone operating frequency ~230 pulses/sec
    reflected standing wave frequency ~365 pulses/sec
    normal acoustic output >120 db
    augmented/ducted acoustic output <100 db with a 3 1/8" X 4" duct

    I was firing this thing at my friends' subaru repair shop in Monrovia Ca. in 1993
    way before 9-11 even then the police would come by and shut me down after 15 min of continuous operation each time I fired it. In totality I managed to get 10 firings in 10 days to discover whatever. When I started ,it produced ~6 lbs of thrust when I finished I was producing close to 60 lbs mostly due to the increased operating frequency. These machines posess a doubling cubing relationship or thereabouts in that dubling the operating frequency cubes the output power. This was the most rewarding engine and experience I've ever had and I'm still looking for another.
    I'd be a rich man if scaling worked, however, it was the unique combination and the physics of the mass flows that produced the high thrust and a yet unresolved observation during the last firing of a 'reflected standing wave' that I believe affected the higher operating frequency in combination with the reduced acoustic output.

    frank MR. P
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