No new questions on POA so here is a new old question - prop tip speed and noise

Discussion in 'Flight Following' started by k9medic, Sep 12, 2021.

  1. k9medic

    k9medic Line Up and Wait

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    I recently sold by Cherokee 6/260 and moved into a C310Q. During the past couple of flights, passengers have mentioned how much louder the 310 is compared to the 6/260.

    Given this, I decided to do some math to calculate tip speeds and see if there is a true noise increase or if it is just circumstantial.

    The 6/260 tip speed at cruise (2400 rpm) calculated to .744 mach.
    The 310Q tip speed at cruise (2450 rpm) calculated to .747 mach.
    The 310Q tip speed at cruise (2300 rpm) calculated to .701 mach.

    Measuring the distance from the cockpit to the blade tip on both aircraft, the distance is similar. The only thing I can think of that would make the perceived difference in noise would be the fact that there are now 2 engines making noise and the relationship of the seats to the tip path plane.

    Thoughts?
     
  2. flyingron

    flyingron Touchdown! Greaser! PoA Supporter

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    There's more to prop noise in the cabin than prop tip speed. But then there's the fact that the passengers are sitting a lot closer to the engines in the 310 than they are in the single.
     
  3. WDD

    WDD En-Route

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    Vintage Snazzy (so my adult children say)
    And harmonics. And wave patterns. And cabin noise insulation. And as mentioned you have two vs one engine.

    Solution -
    • Tell them how cool they look in a twin and stop complaining:cool:
    • Spend more of the kids’ inheritance and add more sound insulation.
    • Only use one engine. :)
     
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  4. Doug Reid

    Doug Reid Cleared for Takeoff

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    My friend flys a 310..it is way louder than my 195 or my Bonanza.
     
  5. sarangan

    sarangan Pattern Altitude

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    The tip speeds of the props might be the same, but the 310 is producing twice as much power as the other one. In other words, the frequency could be the same, but if you increase the amplitude the noise will go up.
     
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  6. Doc Holliday

    Doc Holliday Pattern Altitude

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    Forty five year old insulation, which wasn’t that good from the factory.
     
  7. k9medic

    k9medic Line Up and Wait

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    I have already mentioned the cool factor. The biggest selling point for my wife was the fact that we can get to our destination 45 minutes quicker.
     
  8. Doug Reid

    Doug Reid Cleared for Takeoff

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    A C310 is a cool SkyKing machine...buy a couple good headsets and grin :)

    Cabin insulation might help to some degree, but my friend spent a lot of time insulating his 310 with that black foam and foil system..it is still very loud inside.
     
  9. Domenick

    Domenick Cleared for Takeoff

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    I can't help but note, that contrary to expectations, the Q-tips are noisier.
     
  10. WDD

    WDD En-Route

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    Have your passengers wear ear plugs under the head sets and boost the head set volume to max. Works especially well with ANR sets.
     
  11. WDD

    WDD En-Route

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    In addition, that’s going to be very painful putting headphones over them. Better options for reducing noise vs cotton swabs on a stick……….
     
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  12. Lachlan

    Lachlan En-Route

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    Remind them that more airplane noise means more fun!
     
  13. 455 Bravo Uniform

    455 Bravo Uniform En-Route

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    I’d guess that it’s the difference between sitting behind the prop vs sitting on the side of the prop (actually between two props). The tip path plane, as you say.
     
  14. Dan Thomas

    Dan Thomas Final Approach

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    The sonic shock wave off the prop seems to travel straight out sideways from the prop. You'll notice that as an airplane flies past you on takeoff. Loudest snarl is when you are close to in line with the prop plane of rotation. Coming at you, or going away, it's quieter. Now, that shock wave in a twin hits the side of the fuselage and creates lots of racket inside.




    Jump ahead to 00:48 or so

    [​IMG]
     
    Last edited: Sep 12, 2021
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  15. Doc Holliday

    Doc Holliday Pattern Altitude

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    Strategically placed sound deadoning material glued to the skin of the fuselage interior directly across from the props reduce the noise.
     
  16. skier

    skier Line Up and Wait

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    I suggest better headsets. Easiest, cheapest solution.
     
  17. pmanton

    pmanton En-Route PoA Supporter

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    feather both props ergo noise stops. :p
     
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  18. hindsight2020

    hindsight2020 Final Approach

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    No, the cheapest solution would have been a retract single. :stirpot::biggrin:
     
  19. N747JB

    N747JB Final Approach

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    The exterior noise stops, the noise inside would get considerably louder! :D
     
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  20. WDD

    WDD En-Route

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    261A6188-E992-4A22-8BDC-5EEF8A777647.jpeg Waiting for someone -no one has mentioned it yet —
     
    Last edited: Sep 12, 2021
  21. Shepherd

    Shepherd Final Approach

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    Fly a 336/337.
    Then the 310 will seem positively silent.
     
  22. Checkout_my_Six

    Checkout_my_Six Touchdown! Greaser!

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    Better windows can help….thicker and new side panel insulation.
     
  23. Matthew Johnson

    Matthew Johnson Pre-Flight PoA Supporter

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    Username checks out!
    (actually just jealous of a 310)
     
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  24. k9medic

    k9medic Line Up and Wait

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    I got a call yesterday from a buddy of mine asking if I could fly his 310 to pick him up so I figured that it would be a good chance to see if there was a DB change when the prop is pulled back.

    Here is what I got -

    2300rpm
    [​IMG]

    2450rpm
    [​IMG]