why are aircraft engines so noisy?

[Guernsey]

It is totally silent because the prop chewed you up into minced meat anticlockwise.

Like I said, the engine would become 'Dead' silent.

 

Alan.

 

 

[facthunter]

You ARE funny Alan.

 

BIG slow props. The Wrightflyer had very slow turning props chain driven, and the first engine was only 16 horsepower. Most ot the "rotaries" ( The real ones, where the engine went around and the crank stayed still,( Gnome et Rhone and all that stuff) They only did 1200 rpm flat out and had a lot of THRUST for the horsepower developed. The props have large diameter and fairly wide blades. They are the go for slow planes. Nev

 

 

[Old Koreelah]

You ARE funny Alan.BIG slow props. The Wrightflyer had very slow turning props chain driven, and the first engine was only 16 horsepower. Most ot the "rotaries" ( The real ones, where the engine went around and the crank stayed still,( Gnome et Rhone and all that stuff) They only did 1200 rpm flat out and had a lot of THRUST for the horsepower developed. The props have large diameter and fairly wide blades. They are the go for slow planes. Nev

Always liked the idea of slow props; have read that 1700 rpm was ideal efficiency (can't recall what power and prop diameter that referred to). This is an area we should keep in mind. Remember the noisy dirt bikes of 70's being banned? The resulting campaign -"less sound = more ground" led to major improvements.

 

 

[facthunter]

Most of our engines run what I call toothpick props. these are ok on clean planes but not so good on things like a Murphy Rebel, or some of the draggy biplanes, where you need thrust. People used to tether the plane and have a scale that showed the thrust. You would have to reinvent the older type of engine with a longstroke higher displacement configuration. Quite a few american manufacturers made quite short runs of motors. Warner made the "Scarab" which wasn't too reliable but put together carefully it went ok. used in the Wacket trainer and some Fairchild aircraft. That was the "Super Scarab " at 165 horsepower. Menasco made short runs too. Any good engineering shop should be able to turn out "something" interesting and basic without spending millions. An inverted V4 should be able to be made very compactly. Nev

 

 

[fly_tornado]

This is a BMW 1150 twin, note the dual exhaust!

 

https://www.youtube.com/watch?v=NJCpHAtVnWQ

 

 

[lark]

wow, some of you guys are full of technical knowledge!

 

 

[nong]

I wouldn't think so, dazza; unless I'm mistaken the Texans ran an R-1340 Wasp engine rated to 600hp or so at 2250rpm. That turned a 9ft / 108in prop through a 3:2 reduction to give 1500rpm at max power. This would give a tip speed of about .61 mach. If you overrev the engine to 2500rpm you'd be at around 1670rpm at the prop, giving .71 mach for tip speed - that is in the transonic region and would be making prodigious amounts of noise... but nowhere near supersonic.Cheers - boingk

R1340s are direct drive on most AT6s so your figures are for WIRRAWAY/CERES

If you had said CERES or WIRRAWAY, yes they have the reduction and are easily identified by the large nose case and three blade prop.

 

And yes, there have been exceptions in each case. One CERES tried direct drive, for instance.

 

CERES/WIRRAWAY...chug chug chug AT6...brrraaaawwwww Same R1340 engine.

 

 

[facthunter]

Ceres was the crop dusting version of the wirraway . Yes? Nev

 

 

[Methusala]

There was one sitting derelict at Coffs Harbour airport back in the early 80's.

 

 

[Guest Maj Millard]

The 'super-quiet' plane shown in the NASA colours was flown as part of the Moffit NAS airshow during the late 80s. This is where they have the NASA/Aimes windtunnel, and many other strange and weird aircraft based. It is at Sunnyvale on the peninsula south of San Francisco.

 

I saw this plane perform a couple of fly-overs at about 200 Ft altitude, and I can tell you it was silent ! They spoke about the muffler running down the side of the fuselage, and the special wood prop which was designed and build by a well known local prop-builder, as being the keys to it's noise reduction. That prop-builder whos' name escapes me has sinced passed.

 

The aircraft was used covertly in Viet Nam at tree-top level, and was fitted with special 'urine sensors' that could pick up the smell of urine for the purposes of locating hidden enemy troop encampments, generally at night. The design was based on a Schweizer sailplane fuselage..........................................................Maj...

 

 

[Sapphire]

MM said: The aircraft was used covertly in Viet Nam at tree-top level, and was fitted with special 'urine sensors' that could pick up the smell of urine for the purposes of locating hidden enemy troop encampments, generally at night

 

Wonder how the vietamese would counteract that-bet they came up with something

 

 

[Guest Maj Millard]

They would have to pee into sealed bags I suppose !....................................Maj...

 

 

[Sapphire]

How about walk two or so miles away, pee there, then come back to base. Wait till the bombs drop there and attack with anti aircraft fire. That and Johnsons "expert" management of the war insured defeat for the Americans.

 

 

[Dieselten]

The Lockheed YO-3 observation aircraft was about the quietest propeller-driven aircraft ever deployed on active service, used in Vietnam by the US Army. Only eleven were built and six are known to survive. In operation they flew at heights of approx 1000-1200 feet at night over areas known to be used by the Vietcong and NVA forces. At these heights they were as quiet or quieter than the background acoustic noise in the area, and none was ever shot down or even suffered a single bullet-hole. They were very successful at detecting movement of troops on the ground but were deployed too late in the conflict to make much of a difference.

 

 

[Guest Maj Millard]

I've decided that I like my aircraft engine to be a bit noisy !!...sure beats silence ......................... ...Maj...

 

 

[Guest Maj Millard]

I've decided that I like my aircraft engine to be a bit noisy !!...sure beats silence ......................... ...Maj...

 

 

[Guest Maj Millard]

I've decided that I like my aircraft engine to be a bit noisy !!...sure beats silence ......................... ...Maj...

 

 

[pudestcon]

I've decided that I like my aircraft engine to be a bit noisy !!...sure beats silence ......................... ...Maj...

What's going on Maj, I've noticed double posts from you lately, and now a 'triple'?

Too much Christmas Cheer is it?

 

Pud

 

 

[Guernsey]

What's going on Maj, I've noticed double posts from you lately, and now a 'triple'?Too much Christmas Cheer is it?

 

Pud

Obviously a mistake....he didn't hear his other two posts.

 

Alan.

 

 

[cooperplace]

The Lockheed YO-3 observation aircraft was about the quietest propeller-driven aircraft ever deployed on active service, used in Vietnam by the US Army. Only eleven were built and six are known to survive. In operation they flew at heights of approx 1000-1200 feet at night over areas known to be used by the Vietcong and NVA forces. At these heights they were as quiet or quieter than the background acoustic noise in the area, and none was ever shot down or even suffered a single bullet-hole. They were very successful at detecting movement of troops on the ground but were deployed too late in the conflict to make much of a difference.

the problems with local residents at strips like Aldinga would mostly go away if the planes were near silent. I can see pressure from regulators, local councils, etc, to make quieter planes. The YO3 shows it can be done, altho' we have no idea of the cost. Looking at the sharp edges on the jabiru prop, and seeing that fancy big paddle on the YO3 makes me think that a re-designed prop might make a big difference.

 

When I was young and silly I had a Ducati 900SS that was very noisy, and I loved the noise. When I got rid of the duke, my family and the neighbours told me how glad they were it was gone. Now that I'm ancient, I hate noise. I'd love the jab to be a lot quieter.

 

 

[boingk]

Everyone loves a good sounding engine, but most don't like a loud one.

 

I find that many general aviation conventional engines like the venerable Continental A-65 and C-85, turning low rpm with low compression ratios, are some of the best sounding engines out there. Must be something to do with the relatively large displacement cylinders and low comp ratio, kinda like a Harley Davidson I suppose.

 

They're also fairly quiet... had two guys on the ground yesterday who didn't even hear me on final until it was time for me to do an emergency go around! (They were inspecting site of a prop strike I later found out)

 

- boingk

 

 

[turboplanner]

the problems with local residents at strips like Aldinga would mostly go away if the planes were near silent. I can see pressure from regulators, local councils, etc, to make quieter planes.

About $15,000.00 for emissions and fly by noise matching cars

 

 

[Sapphire]

Boingk said: Everyone loves a good sounding engine, but most don't like a loud one.

 

I live on what should be a quiet cul de sac except for mature age clowns that live and visit across the road. They and all their friends and any tradesmen who come to do work, have noisy exhausts. Some are earth shaking and I made it plain to them of my "corrective plan". Now they seem to have rented out part of the house and spend time terrorizing elsewhere, but not entirely. Even the tennant has a noisy exhaust probably by punching holes into the muffler of his 1970's Escort, to become part of the family. Usually dopy 16 year olds do that nonsense for for a while, then grow out of it regaining sanity. My foot long list of plate numbers one day may keep the local police working overtime. [that's if they even bother which is a whole new thread]

 

 

[facthunter]

An Auster with 4 stubs barks pretty badly. You don't want this sort of ear damaging racket going on for hours. The quieter the better as far as I'm concerned. Your hearing is valuable. Nev

 

 

[Old Koreelah]

Boingk said: Everyone loves a good sounding engine, but most don't like a loud one.I live on what should be a quiet cul de sac except for mature age clowns that live and visit across the road. They and all their friends and any tradesmen who come to do work, have noisy exhausts... Usually dopy 16 year olds do that nonsense for for a while, then grow out of it regaining sanity...

There is a subjective element to noise pollution. Some of us make an exception for our own particular favourite sound. Hendrix or a Ducati with Conti pipes. I can't understand how so many loud Harleys are left to offend the neighbourhood.