Why are small single engined airplanes so noisy?

I mean those small planes that fit two or three or four people, that people fly for fun in the summer. They fly thousands of feet up in the air, but you can hear them very clearly on the ground. While a far more powerfull modern car is pretty silent when it passes you by at the same distance. Is it just that sound travels much better without any obstacles inbetween, or do these flying machines have such bad mufflers?

i dont think any airplanes have mufflers… that is wasting room, adding extra weight, and no one really cares when youre up in the sky anyway :slight_smile:

Most of the noise you hear isn’t from the engine, but from the shockwave the propeller leaves as it spirals through the air. Turbo-prop planes can also be extremely loud in that buzzy propeller way, even though the sound the engines themselves make is very different. (If you ever witness a C-130 takeoff, for example, you may not think of a Cessna as noisy any more.)

A single engine plane is likely to be flying (as planes go) relatively low - 5k to 15k feet, perhaps, so it’s relatively close to the annoyed bystanders on the ground.

Whatever power it has has to come from that single propeller - so it may be driven harder than the props in a multi-engine plane.

I’d also guess that sounds tend to travel pretty well from high up in the air. Noises that originate on the ground are more likely to be absorbed, reflected, and otherwise disrupted by trees, buildings, fields full of grass, etc.

There are at least a couple of Doper regulars who are licensed pilots - they may very well offer some better explanations soon.

Yeah, the props are pretty noise. I wouldn’t say “shockwave” though, as propellor and engine manufacturers put a lot of effor into making shure the tips don’t exceed the speed of sound. (Loss of efficiency and increased noise, otherwise.)

Most of the noise from helicopters comes from the tail rotor, BTW. A slowly descending heli may make a “slapping” sound with the main rotor blades, and a Huey has the famous “wop! wop! wop!”, but you’ll notice that even jet helicopters (as used by police departments and the Media) often sound a little like airplanes. If you ever see the MD-500 NOTAR, you’ll notice it is much quieter because it does not have a tail rotor.

Not much to add, except that some prop tips do go supersonic on takeoff, despite the efforts on manufacturer to avoid it. It’s VERY loud when this happens. Also, most light aircraft don’t have mufflers, and use 360-540 cubic inch engines running at high power settings. That powerful car you speak of doesn’t put out 75% power for any great length of time, and has a full exhaust system with mufflers, catalytic converters, 10 feet of pipe, and so on.

What about attack helicopters? Does the lack of a tail rotor and the use of a second main rotor instead cause an effect close to a MD-500 NOTAR? Honestly, I don’t even know what a MD-500 NOTAR is.

What “attack” helicopters have a second main rotor?

An MD-500 NOTAR is a McDonald Douglas 500 NO TAilRotor helicopter. It is a very much updated version of the old Hughes 500 (as seen on Magnum PI) and uses vectored exhaust at the end of the tail boom to offset the torque produced by the main rotor.

This is a NOTAR. (It seems to have some other designations, but it’s based on the MD-500.)

What do you mean by “attack helicopters”? There are AH-1 SeaCobras or SuperCobras that fly around here, and they’re not at all quiet.

Are you sure? The helis I fly have them, as did the Cessna 172 and 182 I used to fly. So did the PA-28 Dakota I flew once. Other aircraft I’ve heard around airports seem to have mufflers.

Okay, maybe I wasn’t clear. Aren’t there helicopters that, instead of using a tail rotor, use two top-mounted rotors for speed and manuverability?

Joey G, where do you get your information? Just curious, because so much of it is wrong.

The only aircraft I’m aware of that have prop tips “go supersonic” are poorly designed ultralights, or instances where some doofus mounts a prop too long for the engine. It is VERY important to avoid this, because going above Mach 1 causes immense stress on the prop, which can lead to cracks or even losing pieces of the prop. You don’t want to have chunks of prop depart. It can do horrible things to the aircraft.

Also, I’ve never seen an airplane without a muffler. That includes the fixed-wing ultralights I used to fly. Some early 1980’s models did utilize a “tuned” exhaust pipe, but they are extremely rare these days.

Also, plenty of light aircraft have engines with less than 360 cubic inches. I don’t happen to have my manuals handy, but if you ask nicely I might get the information for you and other curious folks.

You are correct that car engines are not normally run at 75% (or higher) power for extended periods of time. Comparison with cars on a racetrack might be more fair than slow-moving cars on a road.

However, I agree with others in stating that most of the noise you’re hearing with a small plane is prop noise. The sound of air being beaten into service. A badly dented or out of balance prop will be even more noisey than usual.

A couple other factors - as pointed out, there are fewer things like bushes and trees and what not to dilute the noise when it’s overhead. People are conditioned to expect airplanes to be noisy. The engines running the ultralights I used to fly were Rotax engines - essentially snowmobile engines in the 22 - 50 hp range. The same engines used in many jetskis and ski-doos. Yet the ones in the airplanes are perceived to be louder by many people, even when idling. It’s conditioning. And that prop noise.

Another thing - the stuff between and airplane engine - the engine compartment walls, the “accessories” - are much less substantial than in a car. There’s less on the machine to muffle the noise. Run your car engine, then lift the hood - it sounds louder, right? Same engine, though.

So… mostly it’s the prop, a little bit the less “stuff” around the engine to muffle the noise, and somewhat peoples’ expectations.

Sorry, I should have said that some of them don’t have mufflers. certainly not “most” of them.

Can’t choppers run ‘quiet’? I’ve probably gotten this idea from cop movies, but if it’s doable, how do you do it?

**There are several aircraft who can run their prop tips into the supersonic range. North American AT-6s, Early Bonanzas and Cessna 210s, Cessna 185s, Beech Debonair, some R-985 equipped planes like the Beaver, etc. It’s far from uncommon. It’s not good, but it does sometimes happen on takeoff with the prop lever full forward. Just because you are unaware of this does not make it wrong.

**I already told Johnny L.A. that I shouldn’t have said most, I don’t even know why I did. Not every aircraft has one, but some do not.

**I knooooooow there are plenty of airplanes that have less than 360 cubic inches. I never said there weren’t. He was asking a question about 2,3, or 4 seat aircraft in general, so I picked the most popular engines. The 320/360 series engine is by far the most popular piston aircraft engine in use today, and the 540 isn’t too far behind it. By saying 360 and 540 I wasn’t setting hard and fast limits for light aircraft engines, I was trying to comment on what he mostly likely would have come into contact with.

Yes. Although the single main rotor/tail rotor configuration is, by far the most used, there are several other configurations that have been tried out for helicopters.

The most familiar (at least to Americans) would be the CH-46 Sea Knight and the CH-47 Chinook, both of which use the inline tandem rotor configuration. With two “main” rotors, each rotating in a different direction, the helicopter avoids the tendency for the body to rotate around the axis of a single rotor. The ridiculously large MIL MI-12 Homer* used a side-by-side tandem rotor setup, although it was never put into production. The V-22 Osprey has the same configuration, but adds tilting rotors to the mix.

The synchropter or intermeshing tandem rotor design uses two rotors, close together with intermeshing blades. Charles Kaman was one of the biggest proponents, using them in the HOK-1 Huskie among others and the company he founded Kaman Corporation is using the design in the K-Max “arial truck”.

The Kamov Design Beaureau designed maritime helicopters for the Soviet navy and favored a coaxial rotor configuration. The contrarotating rotors eliminated the need for a tail rotor and the small space taking by two rotors in the space normally required for one was a major advantage aboard ship. The Ka-25 Hormone* and [all used the coaxial design, as well as the two new land-based gunship designs the [url=“http://www.fas.org/man/dod-101/sys/ac/row/ka-50.htm”]Ka-50 Hokum*/Ka-52 Hokum B*](http://www.fas.org/man/dod-101/sys/ac/row/ka-29.htm"Ka-27/29/32 Helix*[/url)

*NATO designation

My father designed engines for Piper and Cessna aircraft at Avco Lycoming. (The last engine he designed, or at least led the design team for, was the L3C5D.) When I asked him a similar question a while back, he said: “To make them quieter would make them a lot heavier and more expensive.”

He’s always been a man of few words. But at least you’ve got it from the horse’s mouth.

Oh, yeah, one other thing. If I understand correctly, that Cessna 182 you flew probably had an Avco Lycoming engine that my dad helped design. I’ll ask him tomorrow.

Sorry, I guess I used the wrong terminology and that we’re not talking about attack helicopters but transport helicopters. I’m not a big aviation nut or a big military nut, so I was just going off memory. Anyway, let me reask my question. Do these tandam-rotor configurations, or any other for that matter, have an effect on noise or the sounds described earlier by Johnny L.A.?

Small Plane, Small Dog, Small motorbike.

All noisy.

Oh, I’m sorry, I thought we were talking about the most common single engine airplanes. And I was rashly assuming they would be flown by competant pilots who would know better than to abuse their machines. How foolish of me. :rolleyes:

3-seat aircraft? Yeah, I’m sure they exist but I’ve yet to see one. Heck, I’ve seen a 5 seat aircraft, but never a 3 seater…

Cessna 150 , Piper Cherokee, Piper Warrior I & II all have less than 360 cu in engines. I don’t know what the C172 has, don’t have a manual for it on hand, but I expect it’s not any bigger than the Warrior, especially the 145 hp pre-1964 models. Pretty sure the Warrior III falls into that category, too. Those are by far the most commonly seen and heard single-engine “small” airplanes in the 4 seat and under category. You have to move up to at least a Piper Archer or a Cessna 185 to get into the 360 and up cu in range. Unless you live in Alaska or Canada, you don’t see that many Beavers.

And you didn’t say 320/360 in your post, you said 360 and 540. What airport do you live next to where those models you listed off outnumber the C150s, C172s, and PA-28’s?

“Most likely” is what I listed, not the more expensive and complex aircraft you named. Geez, might as well throw the Cessna Skymaster into the mix - I can hear the sound of one of THEM over the sound of the 320 cu in Lycoming in the Warrior I fly. Now THAT’s a loud airplane! Oh, wait - that’s a twin engine aircraft, maybe that’s one reason it’s so darn noisy…