Noise reduction for small aircraft engines

Looking to the electronic muffler or noise suppression.

Two stroke or four stroke?

Either way I think motorcycle exhaust mufflers would be the best place to start. They generally are suppressing noise levels to acceptable levels and are reasonably light.

Frank

OK, I like your humor!

I like 2 cycle for light weight. I like 4 cycle for better reputation for reliability.

I am looking for low noise level in the cockpit, along with low noise impact to the countryside.

Ozzb, any suppliers or vendors with exhaust system experience with active noise cancelation? I know the concept is used to quiet HVAC systems, but thought an exhaust pipe might not work due to nasty environment (heat, soot vibration, corrosion, etc.)

Tuned pipes are ok for a fixed speed. Has anyone experimented with an "adjustable" pipe that could be tuned as the RPM is changed?

Maybe, think off the exhaust pipe as a wave guide, and "filter" stubs to null out the sound at certain wavelengths

What you want is the Aero version of Norton's ( the motorcycle company) 583cc Rotary engine. It can be purchased with all the quite bits and its fully certified. The output is 50 to 150 HP. They are made in both britain and America. You will need to google it as I have forgotten the name of the companies, sorry. From memory they are about $5,000 a pop.

Significant improvement to muffling can be achieved using silicon rubber tube, though I suggest chilling the exhaust first (you can achieve this by running multiple pipes in the slipstream, copper is good for this as it has low friction, high heat tolerance and sink rate and is easily available)

Good luck amd don't forget to read teh rule book!

What rpm change do you anticipate?

2-stoke is light and dependable.

The quietest powerful engines I've not heard are sold at BMW motorcycle shops.

GA, Man.

Stu.

I think active noise reduction is a hideous idea... It maybe ok for specific locations or headsets or carefully controlled acoustic environments...but don't waste your time/money/weight.... it's just more stuff to go wrong...keep it SIMPLE.

Del

Besides, it's only a cure (at best) for the pilot, it doesn't do a thing for the rest of us!

Don't forget to work on prop design and keep the speed of the prop tips down.

That is part of the reason I am thinking of a 2000-2500 rpm speed range. I am not keen on using a 3500-5000 rpm engine and then a speed reduction unit for an acceptable prop speed.

"That is part of the reason I am thinking of a 2000-2500 rpm speed range. I am not keen on using a 3500-5000 rpm engine and then a speed reduction unit for an acceptable prop speed."

Don't rule out a PSRU (Propeller Speed Reduction Unit) before you've done some study. Modern engines virtually all run too fast for a large prop, but that helps a bit with muffling because higher frequencies are produced, and they're more easily damped. In general, water-cooled will also help with sound levels; auto conversions cut costs (and make using auto fuel instead of avgas almost a certain possibility, cutting operating costs). Power density of an engine can be increased by water cooling compared to air, typically around valve areas where overheating is the limiting factor for power. This significantly offsets the extra weight of the cooling system and coolant. Likewise, the additional power available at higher rpms counters the PSRU weight & complexity. Too many tradeoffs, really!

On an air cooled engine, you can also dampen the cooling fins to reduce the "ringing" of the fins from the engine vibrations. Check out some dirt bikes. They just have some type of heat resistant "rubber" plugs jammed between the adjacent fins.

Good answer, it is tough to hear yourself think with screaming and crying passenger!

Seriously though, I have been EAA member for a number of years, I am a licensed (though inactive) pilot, and getting closer to making a plunge back into flying. I will be making the trek to Oshkosh at the end of the month for a couple of days.

Although I haven't picked an aircraft yet, I do know a low noise level is inportant to me.

The 1.0 liter Geo engine (3 cylinder), or up to the the 1.6 liter 4-cylinder versions are all excellent candidates and meet the cost, weight, and noise requirements if appropriately equipped (muffled). Volkswagen and Subaru engines can also work, but are less often muffled, in my experience. Come to Oshkosh (Wisconsin, USA: July 28- August 3) for the FlyIn (AirVenture) and you will see more possibilities and have more folks to talk to than you can handle!

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Contact the EAA. www.eaa.org

These folks are the experts!!!!! If you are really going to build an aircraft, it would be well worth your while to join.

You should also think of what you can do on the INSIDE of the plane to absorb some sound.

I definitely agree there are too many choices (and so little time!) The Piet does have an appeal if I decide to go with a single seat.

There are 2 "versions" of the Piet - the Sky Scout is single seat, the Aircamper is 2-seat tandem. Suggest you just bang Pietenpol into google to find out more - although as I said before there are loads of other worthy aircraft (but only 1 good engine!).

best regards, and remember it is better to aim to enjoy what you do, than aim to do what you enjoy

Will you guys be a OSH?

I saw that in a book when I was a kid, titled "You Can Fly Your Own Aitplane . . . til the rubber band breaks!"

Nice concept, will you wind it for me?

If you want to have it flight certified you are not going to have much choice. You will need an airplane engine for experimentals such as models from rotax. No matter what you do they are going to be noisy unless you have a completely closed cabin with inches thick isolation. One ioption is wearing aviation headsets. they do muff the noise up to -70dB depending on quality and $$$ of course

Good thought. I do want to start at the source and work in from there.

You did have to bring in that four letter word - CA$H

"If you want to have it flight certified you are not going to have much choice. You will need an airplane engine for experimentals such as models from rotax."

Not true. At least, certainly not true in the USA (and the fact that "Ried" plans to attend the Oshkosh event suggests that he or she lives here. I'll be at Oshkosh myself, as I have been most years since 1978). There are airplanes flying legally with a huge variety of non-aircraft engines: Pietenpol (mentioned in this thread) started with a Ford Model A engine (prototype used a four-cylinder Ace water-cooled engine), but has used Corvairs, Ford V-8, and others, and half a dozen different aircraft engines. And that's a single design! More than thirty (yes, 30) different engines have been used on the Pietenpol Air Camper, according to their website). Volkswagen, Subaru, Chevrolet, Ford, and Geo engines will ALL be seen flying at Oshkosh, and probably several others, among the NON-aircraft engines. Airplanes have been flown using motorcycle, ground powerplant, and chainsaw engines (CriCri - see http://www.youtube.com/watch?v=PlV8WJ6N3nU and http://www.cricri.co.uk/cricri_history.htm - but it won't meet the OP's low noise standard, I suspect). VW engines cut in half crosswise, and other VW engines cut lengthwise [both aircooled] have been used for 2-bangers - and that's getting quite a ways away from "aircraft engine", in my book.

"One ioption is wearing aviation headsets. they do muff the noise up to -70dB depending on quality and $$$ of course"

And the noise-cancelling ones, especially, do a fantastic job, permitting conversation and radio use without letting the main aircraft sounds interfere. But I suspect that minimum actual noise generation is the intent.

There are "certified" aircraft engines, and there are various conversions that are not "certified", such as auto engines, 1/2 VWs, motorcycle engines, snowmobile engines, etc.

Please don't ask me to explain the legalese behind the definition. In the US, so far there is a good deal of latitude to allow experimentation with small aircraft construction under certain section of the FAA regulations.

VW engines cut in half crosswise, and other VW engines cut lengthwise [both aircooled] have been used for 2-bangers - and that's getting quite a ways away from "aircraft engine", in my book.

Contrary to popular belief the VW pancake air cooled engine was originally designed as an aircraft engine.

"Contrary to popular belief the VW pancake air cooled engine was originally designed as an aircraft engine"

========================

Back in the 80's I worked for Arthur Stanton the man who imported the first VW back in 1949. I was a member of his technical training department. I was responsible for training dealership personnel in three states; NY, CT and NJ on all three product lines: VW, Porsche and Audi.

I am a pilot, a mechanical designer and an aircraft builder so I naturally listened for anything pertinent to cross applications.

In all those years I never saw any mention of the VW's engine having aviation origins. I might have missed it but given how hungry I was for technical background and my interest in Doctor Porsche's designs. I doubt it

Are you sure your not thinking of Felix Wankel and his rotary design? That one DID get built with aircraft in mind. In fact, in the first versions the crankshaft was bolted to the firewall and the block rotated the prop!

Another reason for suggesting that there is no aircraft history to the VW is that both the crankcase and crankshaft do not lend themselves to attaching a propeller.

The bell-housing is too wide to support an installation with a prop at that end even though the bearings would support it.

The other end is narrow and would work but has a tiny bearing and crank nose sized to the limited loads of driving a fan-generator.

Swinging a prop imposes substantial gyroscope loads on that small bearing. Many a pilot who has failed to address this limitation, has found himself bathed in hot oil, making a dead stick, off-airport landing.

If that engine developed out of an aviation paradigm, you can't tell by looking at it. I suspect you are thinking of the Wankel.

BTW, I built a Watson Windwagon. A single seat aluminum monocoque which was powered by a half VW engine. I know about cutting a VW in half. Never again!

Somewhere during the times we were using VW engines exclusively to power just about everything that aircraft origination was acknowledged. But I could be wrong, It will give me a stroll through yesterday and could be quite fun or not.

Do you have any pictures of your Windwagon. I moderate the yahoo Windwagon group and I'm compiling pictures.

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Pusher type aircraft are reported to be quieter in the cabin.

A copy of a Curtiss-Wright 1930's era pusher also looks like a fun option.

Ried: you seem to pretty much know what to do, and are looking for confirmations. I myself have not flown in years, and always look up to see what is up there. My wife wants to kill birds that wake her up, which disturbs me. The Quest for A Silent Plane is a Worthy Quest. Around here where I live they are trying to eliminate the Local Community Airport. Aircraft noise is a factor that I am constantly updating whatever I know about it. What we really need are quiet heavies. And there have been great strides there. Of all the planes I knew, I hated the most Viscount Turbo Prop for its painful engine prop sound. I think a Paris Jet was there, and I didn't like being around Mitsibushis all around for about every reason. (MU4) The frequency range of a noise is about more important than the decibels in my experience. As well a rythum has bearing. You may need to ask, "What is the Best Sounding Engine?" What is the Best Sounding Engine at Take off RPM? There are a couple of guys around here with Piper Cubs, which I think are about as quiet as a plane gets. It has a pleasing sound on the ground and hardly bothers me up close. Of course a plane made of wood will absorb some sound, and damp some vibrations. I myself want a plane that will at least do speeds as fast as a Tomahawk, or a 152, and I'd like to have a Cherokee, or maybe, maybe, learn to fly a 172. I thought there was something going on with wingtip designs that carried off some sound? What will do what a Beech Baron will do, at half the sound would be important in my fight to save the local airport. Rutan has made some great planes from what I know, and the pusher suggestion for the cabin noise levels was addressed in the Beech Starship design. The mating of a reliable engine to an airframe for character traits, like quiet is not to ever to be a factor allowed to cause a lack of airworthyness. Of course you knew that. I have never blown an engine up in the air, but I have blown up a motorcycle engine. I've been up in Learjets and DC 6s and I liked the Queen Air and the Titian and the 310, Baron, but I never got to go up in the Staggerwing. I almost want to cry thinking that an airplane ought to be quiet, since they inspired hope in me everytime I heard one. P.S. Fast and High is safer.

Some automotive writer had an article where he rhetorically asked how he would burn the last gallon of gas. His answer was to take a highly efficient motor glider and fly as high as possible on the last gallon, then glide to a landing.

Some of the electric experimentals look neat, but that technology needs a bit more development. That would be ideal from a noise consideration though

"Ried: you seem to pretty much know what to do"

You flatter me! In reality if I knew what to do I would be doing it!

I have a glimmer of an idea of what would be nice, but have too many choices. I am casting about for cheap advise to fine tune my thoughts.

Thanks to all the comments so far, and keep them coming!

Unfortunately, noise reduction = power loss + extra weight.

Most light aircraft use a welded thin pipe manifold with minmal muffler, maybe just a 'can'. The direction of the final 'exit' stack can make a big difference in percieved cabin noise.

Remember, there's little you will be able to do about prop noise, and trying to silence the engine below that level is bootless.

Motorccycle mufflers are far too heavy for consideration.

Your local EAA chapter will have better more experienced advice than you'll get here.

I flirted with the idea once and finally decided that I didn't trust anything I'd built quite that much.

liquid cooled 3 main boxer. Simple. vw or subaru. If I am not mistaken: the liquid cooling was advertised in the first subaru ea engines as a noise reducer more than for cooling or heat...and as some jokingly know, the boxer is too efficient to have effective heat without extreme radiator blocking...the ad meant what it said. How is this question even difficult? The liquid 3 main aviator engines been out for several decades. "Ramengines' even makes them for small aviation ....expensive but exotic classics.

I agree the question is not too difficult, I was asking for opinions and recommendations. Liquid cooled engine (Model T I think) was used on the early Pietenpol homebuilts in the 30's I believe. Drawback is carrying the weight of a radiator and water . . . always a trade off when making a design decision!