Quiet Flight

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

Help Support HomeBuiltAirplanes Forum by donating:

  1. Feb 27, 2011 #121

    GESchwarz

    GESchwarz

    GESchwarz

    Well-Known Member

    Joined:
    Oct 23, 2007
    Messages:
    1,179
    Likes Received:
    108
    Location:
    Ventura County, California, USofA.
    Here's a picture of my Mazda Renesis Rotary 3-port exhaust manifold that I've trimmed to accept the "can" in which the exhaust pulses will spin around the circumference while the flow exits the can through a perforated pipe (not shown in this photo) that runs down the center of the can.
     

    Attached Files:

    • 076.jpg
      076.jpg
      File size:
      63.3 KB
      Views:
      673
  2. Feb 27, 2011 #122

    Jan Carlsson

    Jan Carlsson

    Jan Carlsson

    Well-Known Member

    Joined:
    Jan 11, 2009
    Messages:
    1,860
    Likes Received:
    387
    Location:
    Sweden
    View attachment HEADERS.xls

    Hi

    Do you have any formula or calculations for the "Swarze" pipe or you just go on ”EAR FOR MUSIC”?

    Here is a spread I made for exhaust headers, collected from several sources, there was more but I took them away that didn't seem to align with the ones that have been tested in practice.

    Jan
    www.jcpropellerdesign.com
     
  3. Feb 27, 2011 #123

    GESchwarz

    GESchwarz

    GESchwarz

    Well-Known Member

    Joined:
    Oct 23, 2007
    Messages:
    1,179
    Likes Received:
    108
    Location:
    Ventura County, California, USofA.
    My goal is the elimination of sound. How do you do that? By converting violent supersonic exhaust pulses into an even, constant flow. My observations of this design on rotary powered airplanes and on my little test tell me that this is the best solution out there. And it does an excelent job of drafting; my test showed that pushing pulses through a narrow pipe is restrictive, therefore headders are restrictive as compared to exhausting directly into a large chamber. Tuned headers do little for reducing noise.
     
    Last edited: Feb 27, 2011
  4. Feb 27, 2011 #124

    Jan Carlsson

    Jan Carlsson

    Jan Carlsson

    Well-Known Member

    Joined:
    Jan 11, 2009
    Messages:
    1,860
    Likes Received:
    387
    Location:
    Sweden
    Yes, the "headers" is for 4 cyl. piston engines, I just bring it for those who want/need it, as I was driving down this road anyway, two flies in one whack.
    I know yours is a Wankel.
    And I think your silencer is brilliant. My thinking was that you might had found a way of calculating the perfect size, or just go with what looks and feels right, and fits under the cowling.

    Jan
     
  5. Feb 27, 2011 #125

    GESchwarz

    GESchwarz

    GESchwarz

    Well-Known Member

    Joined:
    Oct 23, 2007
    Messages:
    1,179
    Likes Received:
    108
    Location:
    Ventura County, California, USofA.
    This isn't my idea to route exhaust tangentialy into a cylinder. Someone else had already done it and others have adopted the deisgn in the rotary engine powered airplane community. My integration of the can as part of the exhaust manifold itself is unique. It should increase exhaust gas scavenging from the combustion chamber and reduce the weight and space of the exhaust system.
     
  6. Sep 13, 2011 #126

    Aircar

    Aircar

    Aircar

    Banned

    Joined:
    Feb 20, 2010
    Messages:
    3,567
    Likes Received:
    367
    Location:
    Melbourne Australia
    just found this thread and read it through but have been keenly interested in quietening aircraft (and Aircars..) for many years --grew up on sailplanes and riding bicycles so not a great fan of noisy travel in any event . Robert Cumberford used to write technical articles for Air progress including one I remember clearly called "You know I can't hear you when the engine is running" which mentioned and illustrated several innovative sound reduction methods . If you really want to go quiet then 1.-- put the propeller as far behind you as possible. 2- put it in clean air (especially don't exhaust into it as on vari ezes etc )
    3. Use a water cooled engine 4. bury the engine inside some substantial structure and attach it to something HEAVY --high inertia eg the wing main spar 5. Have long exhaust pipes (and pay attention to the muffling system as ONE factor involved in quiet ) --then look into some basic sound propagation theory . Placing the human body between the engine and your cockpit is one way to use a viscous mass to attenuate noise (that's you --one time when extra blubber might be helpful) --this all leads to a rear engined pusher with low mounted engine . Encapsulating engines was experimented with by the car industry and found to be an excellent method to drop noise --the "ideal" case would be to have an evacuated box (vaccuum) around the engine with only fuel and coolant lines entering and all controls operating without penetrating the seal --another possibility is to have a box filled with a very light gas --hydrogen is the best but helium for safety (although a sealed box full of hydrogen cannot explode or burn without oxygen ) --one old physics test described the case of an alarm clock going off in an evacuated bell jar in complete silence because there was no air to resonate AND a very similar thing in a bell jar full of hydrogen --can anyone verify this (by test for preference) or suggest any other way to kill the noise at source in a simple fashion ?

    We will need a MAJOR noise reduction to get public acceptability for future aircraft or to operate in large numbers and close to dwellings --why should not an aircraft be as quiet as a car going down the road in the same suburban environment? --electric power is the great white hope for lowered noise but has at present too many shortcomings for practical use and prop noise is still the baseline problem --ducted props (high RPM) or shrouded propellers (low RPM) would seem to be other avenues to explore for really low noise --even if the YO 3s used open propellers and got to very low sound emissions (some wind turbine infrasound health issues have been prominent in curtailing wind farms lately --the tips are travelling at near transonic speeds at under 20 RPM so frequency might be involved rather than just DCbs . Noise reduction will be a critical issue in future. Some sort of stealth (wave reflection and annihilation ) technology for muffler interiors would seem to be an idea along with active anti sound if we are to get to the stage where you can SEE a light aircraft but hear nothing unlike at present where you can HEAR an aircraft right across a major city even though it is too small to see.
     
    Last edited: Sep 13, 2011
  7. Sep 13, 2011 #127

    henryk

    henryk

    henryk

    Well-Known Member

    Joined:
    Mar 8, 2010
    Messages:
    4,714
    Likes Received:
    453
    Location:
    krakow,poland
  8. Sep 14, 2011 #128

    Aircar

    Aircar

    Aircar

    Banned

    Joined:
    Feb 20, 2010
    Messages:
    3,567
    Likes Received:
    367
    Location:
    Melbourne Australia
    This is going to stir some controversy Henryk! --goes way beyond less noise and reminds me of the Bourke engine in some ways . I knew a fellow who built several model sized working Bourke engines but don't know what became of his work --the thermodynamic cycle involved needs to be analyzed and detonation as such is commonly destructive especially if you get preignition --I'll leave it to the engine experts to comment or enquire further --out of my league .
     
  9. Sep 14, 2011 #129

    Hot Wings

    Hot Wings

    Hot Wings

    Well-Known Member HBA Supporter

    Joined:
    Nov 14, 2009
    Messages:
    6,437
    Likes Received:
    2,343
    Location:
    Rocky Mountains
    I didn't see anything new or unusual. The use of water to extract more of the heat energy from the fuel has even been discussed on this forum, if my memory is correct.

    news: Clean Fuels Technology receives California verification for emulsified diesel fuel

    Alternative Petroleum Technologies - Wikipedia, the free encyclopedia

    At his 8/1 ratio that means you would have to carry 64 pounds of water for each gallon of fuel. Even if it gave you 90% efficiency from the fuel it doesn't look like anything useful for aircraft.

    I've heard of fuel used for Caterpillar engines with as much as 50% water. It does cut down on the fuel costs for a given job, and might be a good idea for a stationary power plant.
     
  10. Sep 14, 2011 #130

    henryk

    henryk

    henryk

    Well-Known Member

    Joined:
    Mar 8, 2010
    Messages:
    4,714
    Likes Received:
    453
    Location:
    krakow,poland
    =0,5 l petrol + 4 l water/1h=not so many!\100 HP\...

    in my CITROEN AX 1,5D I mix air and water weapoor\sammade system\=moore power,moore economical...

    Samochody osobowe na adMoto.pl - artykuł
    =example with MERCEDES.

    http://www.technologyreview.com/energy/18304/page2/

    -discussion =water injection=
     
    Last edited: Sep 14, 2011
  11. Sep 14, 2011 #131

    DangerZone

    DangerZone

    DangerZone

    Well-Known Member HBA Supporter

    Joined:
    Sep 5, 2011
    Messages:
    2,107
    Likes Received:
    370
    Location:
    Zagreb HR
    Most of these ideas are great, be it this Gun engine, the Bourke engine or the Dornier opposing piston engines, the rotary engine, all of those might be more efficient than standard ICE engines. Yet, are they practical..? Aircraft engines need to be maximally simple in both construction and function. And reliable too. One of the solutions is an electric motor or other sort of electric propulsion, those are simple, efficient (85% to 95% efficiency as opposed to ICE 25% to 35%) and reliable, the only problem until recently was the battery range. But the solution of having enough electricity for an hour of flight and having a power ICE generator for longer flights proved simple enough for many new electric airplane projects.

    Prop noise on the other hand is harder to resolve. One of the solutions that comes to mind might be to change the noise frequency at the prop tips, to turn the sound into a frequency which is out of the human hearing range. Producing props with perforated tips and winglets with holes at right angles from small to bigger ones, that would alter the frequency of the sound, make it whistle silently. It does sound absurd to do such a thing to an existing prop, it would be feasible only on a new kind of props even without loosing prop efficiency. Then again, the problem that such a prop would be complicated in construction would turn pilots to choose a cheaper and louder solution so it seems like a dead end.

    But technically, it is possible to produce an electric motor with such a prop which would be almost completely silent. Electric motors have a maximum moment from 0 so the variable pitch control would not be needed, allowing the same AOA of blade tips and a constant sound frequency. It might find some use only in military projects or some aircraft that need less noise on approach, thus I guess we won't be seeing many of such solutions in the near future.
     
  12. Sep 14, 2011 #132

    autoreply

    autoreply

    autoreply

    Moderator

    Joined:
    Jul 8, 2009
    Messages:
    10,732
    Likes Received:
    2,542
    Location:
    Rotterdam, Netherlands
    Schempp-Hirth has many aircraft flying with non-symmetrical (5-bladed) props. Helps a lot, but financially it's not a viable alternative, they're astonishingly expensive.
     
  13. Sep 14, 2011 #133

    henryk

    henryk

    henryk

    Well-Known Member

    Joined:
    Mar 8, 2010
    Messages:
    4,714
    Likes Received:
    453
    Location:
    krakow,poland
    [​IMG][​IMG][​IMG][​IMG]

    Lotnia Kasperwing

    ="Z"-propeller= very quiet...

    http://www.spratt103.com/images/photo1.jpg
    http://www.spratt103.com/images/photo2.jpg

    =france variant...
     

    Attached Files:

    Last edited: Sep 14, 2011
  14. Sep 14, 2011 #134

    billyvray

    billyvray

    billyvray

    Well-Known Member

    Joined:
    Aug 17, 2005
    Messages:
    712
    Likes Received:
    224
    Location:
    Newnan, GA
  15. Sep 14, 2011 #135

    Rick McWilliams

    Rick McWilliams

    Rick McWilliams

    Well-Known Member

    Joined:
    Feb 27, 2011
    Messages:
    274
    Likes Received:
    30
    Location:
    Santa Paula CA
    Reversals in the surface pressure gradient are certainly a novel way to design an airfoil. Laminar flow at full scale Re will be very limited.
     
  16. Sep 26, 2011 #136

    Aircar

    Aircar

    Aircar

    Banned

    Joined:
    Feb 20, 2010
    Messages:
    3,567
    Likes Received:
    367
    Location:
    Melbourne Australia
    I posted some stuff a while back on bi cambered props -- there is some possibility of radial flow in the 'groove' that might set up a vortex (spanwise blowing is a known concept for wings ) -- experiment is the ultimate arbiter in these things . that sheetmetal propeller looks like a joined wing ! --does it work or suppress noise in fact -- Autoreply made the good point about assymetric blade layout to discourage resonance (as on car radiator fans of the old type or some Russian helicopter tail rotors also)

    are there no audio experts in the forum who can comment about the immersed engine concept ? (gas shroud) maybe a very heavy gas would do something of use (eg sulphur hexafluoride) or a combination or alternate 'layers' . Helmholtz resonators (tuned thin spherical sheels with one opening ) are another device to absorb sound that is experimented with in helicopters -- a deliberate out of phase rotating mass could tune out vibration if you knew how to design it --like a balance shaft within an engine .

    Noise Vibration and harshness (NVH) are a separate discipline in car design and have advanced far past any level acheived in aircraft so there should be a pool of know how to draw on . It is a disgrace that light aircraft are still made and behave as they did fifty or more years ago -- pushers have regressed in this respect.
     
  17. Sep 26, 2011 #137

    henryk

    henryk

    henryk

    Well-Known Member

    Joined:
    Mar 8, 2010
    Messages:
    4,714
    Likes Received:
    453
    Location:
    krakow,poland
  18. Dec 30, 2011 #138

    Max Torque

    Max Torque

    Max Torque

    Well-Known Member

    Joined:
    Dec 16, 2011
    Messages:
    98
    Likes Received:
    17
    Location:
    Arizona/Alaska/several nasty places around the glo
    GESchwarz,

    Any updates/news on the exhaust system?

    Trying to figure out how I'm going to do something similar on my O-320 Lycoming.

    Thanks
     
  19. Feb 29, 2012 #139

    autoreply

    autoreply

    autoreply

    Moderator

    Joined:
    Jul 8, 2009
    Messages:
    10,732
    Likes Received:
    2,542
    Location:
    Rotterdam, Netherlands
    There's a YO-3a for sale for 85K:
     
  20. Feb 29, 2012 #140

    Aircar

    Aircar

    Aircar

    Banned

    Joined:
    Feb 20, 2010
    Messages:
    3,567
    Likes Received:
    367
    Location:
    Melbourne Australia
    Seems like a bargain at 85K --this aircraft should be used to develop the next generation of ultra quiet civil aircraft --it was used in air to air sound measuring (including with the NOTAR helicopter which was designed also to be very quiet by eliminating the tail prop and the tail/main rotor interaction ) -- a good thing that it was built and revealed also since it provides the best evidence that a real prop powered aircraft CAN be vitually silent (and with all that junk hanging off the outside plus the tail wheel,nose scoop etc it is amazing that it was so quiet --even some sailplanes make an audible whistle at 200 ft and certainly with the wheel out . Irv Culver (homebuilt designer ) was very much involved in the conversion and Ole Fahlin (homebuilt prop maker) did the prop.
    Nice post Auto.
     

Share This Page



arrow_white