Noise Abatement & Cabin Noise Reduction


7 posts in this topic

Posted (edited)

Reducing noise from Kitfox operations in-general. The three main sources seem to be (in order of significance) exhaust thermal expansion, propeller wash around the slipstream of the cowling, and intake air. Taming Noise is a concern to prevent ordinances from being created to prevent flight operations. While flight with reduced cabin noise contributes to hearing protection and creature comfort.  60dB disturbs sleep.

What are pilot & A&P experiences, and what ideas/suggestions can be provided?

 

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Edited by JimD

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Posted

Swiss Muffler : http://www.piteraq.dk/flight/muffler.html

The Swiss Muffler is home made, and similar to a GlassPack silencer but much lighter: https://www.summitracing.com/parts/sum-630853?seid=srese1&cm_mmc=pla-google-_-shopping-_-srese1-_-summit-racing&gclid=CITa66j39tICFVM8gQodcUgEQQ

Fairing the front and rear to limit drag.

Using aluminum round down spout (nice finish), stainless screen, fiberglass insulation, and stainless chore grill as dampened expansion chamber, the total weight would be around 3 pounds for an 18" muffler without significantly contributing to backpressure. The longer, the quieter.

https://www.guttersupply.com/p-Half-Rnd-Products-Downspouts-Plain-Rnd.gstml?gclid=CPrDksP59tICFUtNfgodJxsOaA

 

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Posted

You must have never heard an Avid or Kitfox from the ground.  They are extremely quiet compared to most certificated aircraft.  Even the two stroke engines.

Ive seen these mufflers befor and they are very effective.  The OEM Rotax muffler is just as good and it fits inside the cowl.  These Swiss mufflers are popular on highlanders and Rans aircraft because they have little to no muffler as part of the fwf in their kits. 

Whats really funny is when these guys muffle the hell out of their planes exhaust, then put a borer or seaplane prop on it!

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Posted (edited)

Quieter Propellers:  

Paddle style propellers seem to be quieter in-general

Off the Shelf: 

The Felix bi-camber propeller: http://a.moirier.free.fr/H%E9lice/Construction/The%20Felix%20propeller.pdf

excerpt: Fred Felix at W-10508 Bell Rd., Camp Douglas, WI 54618, 608/427-6544 or l-800/PROPELR

NASA Stinson & Cub Testing: https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19960008053.pdf

 

Edited by JimD

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Posted

You must have never heard an Avid or Kitfox from the ground.  They are extremely quiet compared to most certificated aircraft.  Even the two stroke engines.

Wow, fast response.

Good to know about the standard muffler.  I'm planning on purchasing a Kitfox with a 670 and am trying to evaluate the best options.  My family owns a place out in the country, and although taking off is around family and they won't complain, I don't want to abuse their hospitality either.

Additionally, I'm planing on doing some operations on ultralight fields, and one in particular is near a neighborhood.

I'm just looking for loads of suggestions to pick and choose from, and I provided what little I have found out so far.

 

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Posted

Gotta take care with Rotax 2 stroke mufflers. The muffler is a tuned part of the exhaust system, and can cause problems where EGT goes sky high if the standing wave frequency mis-tunes with the piston stroke, since the low pressure phase of that standing wave helps exhaust the cylinder. Severe power loss and possible egt problems can be experienced if the muffler system isn't close to the factory one. There are some sites on the web that discuss it a bit more.

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Posted

You must have never heard an Avid or Kitfox from the ground.  They are extremely quiet compared to most certificated aircraft.  Even the two stroke engines.


Good to know about the standard muffler.  I'm planning on purchasing a Kitfox with a 670 and am trying to evaluate the best options.  My family owns a place out in the country, and although taking off is around family and they won't complain, I don't want to abuse their hospitality either.

The 670 (not my favorite engine - story for another time) is a different cat altogether.  Because of the (usually malfunctioning) exhaust valves it requires a much more tuned pipe to work properly (when it works at all - did I say that?).  Without the tuned pipe, you leave all sorts of HP on the table.

When I say two stroke engines, I mean real, reliable, aircraft engines like the 582 or the venerable, lovable, near indestructible 503.

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