SMALL - espritmodel.com SMALL - Telemetry SMALL - Radio
Reply
Thread Tools
Old Aug 22, 2014, 04:54 PM
Registered User
United Kingdom, England, Keighley
Joined Nov 2012
296 Posts
Discussion
What makes all the noise?

Thought I'd post this here as when we're flying in the park, often we don't want to attract any more attention than necessary.

So I wondered what is making all the noise in planes, or more specifically, can you make a plane quieter and what attributes make for a quiet plane?

With the motor on, some planes make more noise than others - is it the quality of motor? how big the motor is? Prop size? Pitch? Something else?
Stu L is offline Find More Posts by Stu L
Reply With Quote
Sign up now
to remove ads between posts
Old Aug 22, 2014, 05:10 PM
Y=C+I+G
cmdl's Avatar
United States, CA, Rosemead
Joined Jan 2012
8,830 Posts
the prop. a larger (diameter) prop should also make more noise. i imagine noise also increases with rpm (hence motor kv) and pitch. never gave it too much thought though. most planes on my field are IC so i'm the quiet one.
cmdl is offline Find More Posts by cmdl
Reply With Quote
Old Aug 22, 2014, 06:30 PM
Shelter Kitty "Orange Death"
bartricky's Avatar
United States, FL, Monroe
Joined Jan 2008
3,165 Posts
On some of the pushers such as the Stryker noise comes from the air rushing off the fuse just prior to reaching the prop. Mods were done to the trailing edge of the fuse to reduce this noise.
bartricky is offline Find More Posts by bartricky
Reply With Quote
Old Aug 23, 2014, 02:17 AM
Registered User
Joe Perrone's Avatar
doha Qatar
Joined Jan 2004
402 Posts
I've run up the motors on ground, and I've run up motors a bit with no prop. I believe the sources, in order of noise contribution are

1) Motor; geared systems more so than non-geared
2) Prop
3) airframe

Those are the continuous noise sources. The loudest on an occasional basis is the anguished cries of the pilot as the plane merges with ground
Joe Perrone is offline Find More Posts by Joe Perrone
Reply With Quote
Old Aug 23, 2014, 03:34 PM
Registered User
United Kingdom, England, Keighley
Joined Nov 2012
296 Posts
Hmm, interesting. So do you think that different brands of the same size and kv motor are likely to be different too?
Stu L is offline Find More Posts by Stu L
Reply With Quote
Old Aug 23, 2014, 05:17 PM
yank and bank!!
Joined May 2013
2,322 Posts
Quote:
Originally Posted by Stu L View Post
Hmm, interesting. So do you think that different brands of the same size and kv motor are likely to be different too?
I do..... my current scratchbuilt flies nicely but sounds like some motorized tool.... maybe like it's owner
failboat is offline Find More Posts by failboat
Reply With Quote
Old Aug 24, 2014, 01:24 AM
Wake up, feel pulse, be happy!
C₄H₁₀'s Avatar
United States, AK, Fairbanks
Joined Aug 2009
12,444 Posts
Balance the prop, motor, and spinner/adapter. Most of the noise from most "noisy" models comes from a poorly-balanced rotating assembly. Some guys buy props and just bolt them on without even checking to see if they're balanced, much less actually balancing them, nevermind balancing them well. It's horrible.

The model should make a continuous "whoosh" noise with the motor running. If you expect your park flyer to sound like an airplane (buzzing, roaring, or humming), you're expecting the sound of a poorly-balanced prop.
C₄H₁₀ is offline Find More Posts by C₄H₁₀
Reply With Quote
Old Aug 24, 2014, 08:57 AM
Canadian Bacon
flypaper 2's Avatar
Kingston, Canada
Joined Jun 2004
13,062 Posts
The "prop in a slot" type planes make quite a noise. It's the same principle of the way a siren works. Some of the larger props make a lot of noise when doing gyrations such as flatspins.

Gord.
flypaper 2 is online now Find More Posts by flypaper 2
Reply With Quote
Old Aug 24, 2014, 08:58 PM
Registered User
semperfi1970's Avatar
Joined Feb 2012
1,402 Posts
The obvious answer is a unbalanced prop and poor quality motor with bad bearings. All of this is true but when you have a balanced prop and balanced motor with good bearings then what? Well its the most overlooked and most misunderstood phenomena regarding fixed pitch props. Its called cavitation. When the rpm and pitch of the prop blade exceed forward velocity the blade stalls. More so than not this is created by under propping not over propping a motor. The noise that cavitation produces mimics an unbalanced prop, the prop is balanced but the forces exerted on either blade at any point in time are not balanced. Then there is blade flex unequal between the blades causing pitch effect. This can be found even in slower blade rotation throughout the whole rpm range. Then you have that really cool popping, cracking and snapping noise created by the prop blade tips breaking the sound barrier. Few of us will ever deal with this effect unless we are turning in the range of 30,000 rpm,s with the little props we use.
semperfi1970 is offline Find More Posts by semperfi1970
Reply With Quote
Old Aug 25, 2014, 12:15 AM
Wake up, feel pulse, be happy!
C₄H₁₀'s Avatar
United States, AK, Fairbanks
Joined Aug 2009
12,444 Posts
Quote:
Well its the most overlooked and most misunderstood phenomena regarding fixed pitch props.
You're absolutely right about it being misunderstood Cavitation occurs when a boat prop creates an area of such low pressure in front of the blade that the water boils into vapor. The term is often used, never correctly, to describe RC props that make weird noises. It has nothing to do with stalled blades, and indeed nothing to do with aircraft props at all.

Much more commonly, the "cavitation" sound is caused by a prop which flexes and deforms under the loads present at high RPMs. GWS props are notorious for it since they're very soft to begin with, but other brands and types will do it if you spin them fast enough.

Quote:
Few of us will ever deal with this effect unless we are turning in the range of 30,000 rpm,s with the little props we use.
The actual RPM required to take a prop transsonic is entirely dependent on its diameter. 30k will get you there with anything about 8.5" or bigger.
C₄H₁₀ is offline Find More Posts by C₄H₁₀
Reply With Quote
Old Aug 25, 2014, 07:55 PM
Registered User
semperfi1970's Avatar
Joined Feb 2012
1,402 Posts
Ok we wont call it cavitation then How about we call it when the spinny thing on the front of the plane can no longer propel the plane any faster because the drag of the plane out weighs the spinny things and motors ability to pull forward. She is spinning and just cant get enough air to pull so she shutters or stalls over and over. The bumber to high pitch props
semperfi1970 is offline Find More Posts by semperfi1970
Reply With Quote
Old Aug 26, 2014, 07:38 AM
Registered User
United Kingdom, England, Keighley
Joined Nov 2012
296 Posts
Hmm, so should we favour a smaller prop with a bigger motor or a bigger prop with a smaller motor?
Does it work like that it am I over simplifying?
I'm not looking to change but the theory interests me.
Stu L is offline Find More Posts by Stu L
Reply With Quote
Old Aug 27, 2014, 02:01 PM
Registered User
Canada, QC, Laval
Joined Jun 2014
47 Posts
Quote:
Originally Posted by semperfi1970 View Post
Ok we wont call it cavitation then How about we call it when the spinny thing on the front of the plane can no longer propel the plane any faster because the drag of the plane out weighs the spinny things and motors ability to pull forward. She is spinning and just cant get enough air to pull so she shutters or stalls over and over. The bumber to high pitch props
This board needs a like button lol
wwdragon is offline Find More Posts by wwdragon
Reply With Quote
Old Aug 27, 2014, 06:57 PM
Shelter Kitty "Orange Death"
bartricky's Avatar
United States, FL, Monroe
Joined Jan 2008
3,165 Posts
Quote:
Originally Posted by wwdragon View Post
This board needs a like button lol
xxx
bartricky is offline Find More Posts by bartricky
Reply With Quote
Old Aug 28, 2014, 10:54 AM
Y=C+I+G
cmdl's Avatar
United States, CA, Rosemead
Joined Jan 2012
8,830 Posts
Quote:
Originally Posted by Stu L View Post
Hmm, so should we favour a smaller prop with a bigger motor or a bigger prop with a smaller motor?
Does it work like that it am I over simplifying?
I'm not looking to change but the theory interests me.
i'd guess the smaller prop - just a guess. butane or others would have to weigh-in.

Quote:
Originally Posted by wwdragon View Post
This board needs a like button lol
see attached pic.
cmdl is offline Find More Posts by cmdl
Reply With Quote
Reply


Thread Tools

Similar Threads
Category Thread Thread Starter Forum Replies Last Post
Sold 4 Engines. all NEW IN BOX, make an offer on 1 or all shooboy Aircraft - Fuel - Engines and Accessories (FS/W) 25 Mar 12, 2014 02:33 PM
Discussion What makes a "rare" kit so valuable ? epoxyearl Trader Talk 40 Nov 10, 2013 09:05 PM
Question What makes a good snow ski? iceburg47 Foamies (Scratchbuilt) 8 Nov 10, 2013 09:11 AM
Discussion What are all the parts used in making an cnc rcniteshrc CAD/CAM 1 Sep 28, 2013 04:39 AM
Discussion Just want to make sure all of you Obama supporters know what you've been condoning .. logan5 Life, The Universe, and Politics 64 Dec 18, 2012 03:40 AM