Quiet Flight

Discussion in 'Aircraft Design / Aerodynamics / New Technology' started by needswings, Dec 9, 2009.

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  1. Dec 9, 2009 #1

    needswings

    needswings

    needswings

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    I came across a picture of a Lockheed YO-3 'Quiet Star', and it got me thinking about what things can be done at design time to make an aeroplane quiet.

    Picture here: (http://home.comcast.net/~bzee1a/Edwards09/DZZ_2066.jpg from http://home.comcast.net/~bzee1a/Edwards09/Edwards09.html)

    To my mind why you'd want to build quiet is fairly easy - these days urban developments are getting closer and closer to airfields, and the less noise the planes make the less complaining the residents will do.

    So what can be done to make a plane quiet, without affecting the perfomance too much? I've heard of tuned exhaust muffler systems before, but I havn't seen anything like the prop on the YO-3. How much of the noise actually comes from the Prop?
     
  2. Dec 9, 2009 #2

    Dana

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    Props make quite a lot of noise. However, the human ear tends to hear only the loudest noise, which means that making the prop quieter does not good if the engine exhaust is louder. Quiet down the engine enough, and you start hearing the prop at which point it makes sense to address prop noise. A big, slow turning prop is quieter than a mall, fast turning prop.

    -Dana

    Gun control: The theory that 110lb. women should have to fistfight with 210lb. rapists.
     
  3. Dec 9, 2009 #3

    bmcj

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  4. Dec 9, 2009 #4

    pie_row

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    I've read a technical description of that airplane. The big boxes on the side of the airplane are a frequency trap for the engine exhaust. The airplane had V-belt re-drive to keep the power pulses out of the prop. You can actually hear the power pulses if you get the rest of the noise down low enough. They went through a lot of R&D on the prop to get it quiet enough. The intake had a special frequency trap as well to reduce the intake noise. The long wing span was to reduce the tip vortex strength so that that source of noise was addressed.

    With a turbo charged engine most of the noise comes from the prop.
     
  5. Dec 9, 2009 #5

    Bart

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    I've corresponded with some of the YO-3 guys over the years. The plane was used in Vietnam (VC never even fired at it) and then by the FBI, including overhead at night during the Patty Hearst kidnapping case in LA in the early 70s. It was based at Pt. Mugu NAS, where I talked to one of the crew chiefs on one occasion in the late 70s. He said at night it could fly overhead at 50' and not be noticed. Others have said it was quiet, but not that quiet. Still others say it was quiet from outside the plane, but sitting inside flying not too quiet.

    One YO-3 is sitting on the ramp, rotting, at Skagit County airport in WA State. What a shame. NASA has another, even further modified for quiet, which they use for aeriel noise testing of helicopters, etc. as the YO-3 had various microphones installed--they fly in formation to record noise. The plane has about 12 (as I recall) V-belts in its belt reduction drive, which reduce the engine to propeller rpm by a factor of about 3. 6 or 3 bladed prop, slow turning, since most light aircraft noise comes off the transonic or supersonic blade tips--mini sonic booms. The wider-bladed 3 blade prop (higher Reynolds number) may be the most recent and presumably most quiet of the lot, but I'm not sure of that. Looks a bit like a McGyver job with canoe paddles. Contact NASA at Moffat near San Franciso for details, or at least Google for such, and pics.

    The Swiss muffler per Tony Bengelis' book works, but one guy who tried that on a BMW boxer motorcycle engine (itself very quiet and efficient) said it was not that great, so he wound up using a motorcycle (Suzuki or Yamaha??) cannister muffler, which was both lighter and quieter, and pretty cheap, too. Such mufflers can be had very cheaply on Craigs List, as kids mod their bikes and then have no use for the stock muffler. Then, there's a huge aftermarket for motorcycle mufflers to consider as well, including carbon fiber. That said, if I were looking to the Swiss muffler idea, I'd use ss or aluminum mesh (conducts heat very well) and mineral wool instead of fiberglass, since mineral wool has already been burned and takes about twice the heat (~2k degrees) of fiberglass, while absorbing much less moisture, meaning less buildup of corrosives inside.

    The YO-3 was too heavy and something of a dog to fly. Still, its quietness ideas and methods can and should be used on other aircraft, both to avoid irritating the general populace around airports and to enhance the fun of flying, in my view.
     
  6. Dec 10, 2009 #6

    needswings

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    Great information, thank you guys.
     
  7. Dec 10, 2009 #7

    GESchwarz

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    I have been waiting for just the right moment to revolutionary muffler design. Basically the design takes each exhaust pulse and causes it to be divided up into numerous micro pulses that are released one at a time, over a period of time.

    Because fluid flow is similar in many ways to the flow of electricity for descriptive purposes. I can describe this muffler as a phase splitter and capacitor. The phase splitting happens by causing the sound shock wave to travel through a long perforated tube. It takes time for the pulse to travel the length of the tube. A small amount of that pulse is released each time it passes over a hole. By the time the pulse reaches the end of the tube, the pulse should have been disipated. At the outlet, those micro pulses are of much less amplitude than the original pulse, and the frequency of the pulses are an order of magnitude higher, i.e. smoother.

    Traditional mufflers primarily rely on a mumbo-jumbo system of baffles and/or acoustic material to convert shock wave energy into heat by shear flow and friction.

    My design relies primarily on taking big pulses and splitting them up into little ones and spreading them out over time.

    I believe the greatest noise reduction will result from a combination of the two methods...phase splitting within an acoustic chamber.

    This is all theory, to be tested in a few years when I get to that point in the construction of my machine.

    Noise reduction is very important to me because I have lost some hearing already. It's especially noticable in noisy environments which make it difficult for me to hear conversations when it is relatively easy for others.
     

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  8. Dec 10, 2009 #8

    pie_row

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    Congratulations you've reinvented the glass pack:ponder:
     
  9. Dec 10, 2009 #9

    GESchwarz

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    pie_row,

    This is really very different than a glass pack. A glass pack is basically a straight perforated tube surrounded with acoustic material. The pulse is free to travel straight through. For every pulse input, there is pulse output of slightly reduced amplitude. A glass pack does not act as a phase splitter. Go back and re-read the description.
     
  10. Dec 10, 2009 #10

    pie_row

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    My bad, I'm sorry. Ya it would work like a phase spliter. I've got my own ideas about how to put the engergy that your trying to get ride of to work. Turbos do a wunderful job of reducing exhaust noise. The rotary that you are planing to use in your airplane can't use the energy recovery idea That I've been talking about on a diferent thread but you've got a good light weight mufler for your very loud engine.
     
  11. Dec 10, 2009 #11

    Dana

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    Gary, I hate to tell ya but it's been done... here's such a muffler built around the converging cone of a 2-stroke tuned pipe, though it's sort of the reverse of what you've sketched:

    [​IMG]

    For the ultimate exhaust noise reduction, though, you need active noise cancellation. It, too, has been done, on cars, and works just like active noise cancellation headphones: A microphone monitors the sound, speaker in the exhaust system produces an identical sound 180° out of phase with the exhaust pulse, effectively canceling it.

    -Dana

    But it's NOT an ASSAULT Weapon, it's a DEFENSE weapon!
     
  12. Dec 10, 2009 #12

    pie_row

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    Actually his design has a different operating principle
     
  13. Dec 10, 2009 #13

    GESchwarz

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    Apparently I didn’t explain how it works very well. As the exhaust pulse travels down the length of the perforated tube, a little bit of the pulse gets bled off through the holes. Look at the drawing. It begins at hole number 1. That pulse that passed through hole #1 is now on it’s way to the outlet. As time goes by, the main pulse continues to travel down the tube, releasing these small pulses as it goes through the holes until it gets to the end, and hole #N. That pulse that passes through hole #N must travel much farther than the pulse that passed through hole #1. Because it traveled so much further, it will take much longer to reach the outlet than did the pulse that passed through hole #1. The big pulse is split up into many little pulses and released at the outlet, not all at once like on most other mufflers, but distributed evenly over an extended period of time.
    In the image the Dana provided you can see that a pulse traveling through the perforated section would pretty much pass through intact as a single pulse, but with reduced energy due to the shear flow caused by the flow through the perforated baffle.
     
    Last edited: Dec 10, 2009
  14. Dec 10, 2009 #14

    GESchwarz

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    The only problem with noise canceling head gear is that it only works for the wearer, meanwhile everyone else within earshot must suffer.
     
    Last edited: Dec 10, 2009
  15. Dec 10, 2009 #15

    Dana

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    No, the center tube isn't open in the front, so the only way into it is through the small holes... at lest that's the way it was in another picture I've seen but don't recall where; the illustration isn't so clear.

    I've also seen one that looks, on the outside, to be exactly what you've sketched. but I didn't take it apart to look inside.

    True, but I wasn't talking about head gear, except to say that the principle is the same; the noise canceling system is built into the exhaust.

    -Dana

    A flying saucer results when a nudist spills his coffee.
     
  16. Dec 10, 2009 #16

    pie_row

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    Dana in the pic you posted the pulses travel in the same direction in both tubes That means that at each opening the pulses reinforce each other. In the other drawing the pulses travel in opposite directions so at each hole they cancel each other. Very efficient. And very light weight.
     
  17. Dec 10, 2009 #17

    BBerson

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    This is the plane at Skagit.
     

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  18. Dec 11, 2009 #18

    GESchwarz

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    Big holes, small holes, it doesn't matter because the sound wave goes through that series of holes as a single pressure wave and exits the muffler as a single wave. My design causes that wave to be segmented and distributed over a period of time. I don't know how else to explain it.

    A traditional muffler converts sound energy into heat energy through shear flow by causing it to flow through acoustic baffles and materials, which include holes.

    My muffler design primarily converts each sound wave into numerous waves of lesser magnitude, which are spread out over time. This has the effect of flattening the oscillating wave as depicted in my drawing above.
     
  19. Dec 11, 2009 #19

    Bart

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    Note wheels sunk up to the axles in the asphalt. sigh.:depressed

    Birds found a nice nesting place, though.
     
  20. Dec 11, 2009 #20

    JimCovington

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    Gary, in the diagram you posted (noise vs time) there's some energy missing. The integral of the two waves should be the same - your "fractured" wave has MUCH less overall energy than the original wave. You show it as being quiter at its highest pulse than the original is between pulses - not likely! The fractured pulse should be higher on the y-axis.

    Other than that - I like the idea.
     

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