Full size engine silencing

Whilst at Swinderby with Pol, a very noisy plane flew over the airfield. I remarked to Pol that there had to be a reason why they are not silenced better.
The model engine is, and when a tuned pipe is fitted they can be really quiet, but very little loss, or maybe a gain in power.
I asked the question on livechat to our resident full size pilot, Andy, and he didnt know.
So the question is, why arnt they silenced more effectively . Anyone know ???

Garry

so we can here them coming, when we are above 400 foot they have multiple cylinders, and not a lot of room for mufflers, have you HEARD a big, multi cylinder petrol engined model?

Are full sized light aircraft silenced at all?
In general no, although most radials use an exhaust collector ring which reduces the noise considerably..Turbo charged are much quieter (P38 or P47) because of the muffling effect of the exhaust turbine.
Of course the yank 'quiet' planes used in Vietnam were fully silenced.

They were supposed to be inaudible at 1200ft even at night.
I suppose some like the Bristol Fighter had very long pipes which would add a degree of silencing but was really done to duct the exhaust away from the pilot/observer.


I suspect the real reason (apart from cost) is the noise of the prop (Harvard on take off?) is quite significant and you can't do much about that.

That's my two penny'orth.

I can only offer a couple of amateur theories, with a bit of memory from my m/c days,

assuming the engine was a 4 stroke, then the main reason i would think is power, a 4 stroke engine produces its best power when there is little or no restriction on its exhaust, so a short stub or open pipe to direct the flames away is all thats needed, indeed i read somewhere that angling the exhaust stubs backwards helped Spitfires and Hurricanes gain a few MPH, one other reason i suppose is weight as a full exhaust system would not only cost performance but add a lot of weight. whereas a two stroke engine works best with a balanced pressure wave in the exhaust hence the use of "tuned" pipes these can be adjusted to give the ideal length of pipe to give the correct back pressure, this i believe has an effect on the incoming charge into the cylinder and stops a lot of it escaping, if you watch an old glow or diesel engine running in a free flighter you will see that from the exhaust ports comes an awful lot of unburnt fuel, if you want the full story of tuned pipes have a google of Walter Kaaden and particularly Ernst Degner, and how the Japanese motorcycle industry owe him everything!!!

cjp

forgot a bit, even with no silencing the four stroke engines pipes however long they are all need to be the same length for each cylinder hence the "spaghetti" seen on F1 cars.

cjp

Who would dare to silence a Merlin or Griffen or F1 car come to that.

When I was buying japanese imports I bought a Pontiac Firebird.What a beauty of sound.Drove back from the docks with a silly grin.When on the forecourt I would pop out and run it up just to listen to the sound.My truck doesnt have the same effect on me.When in thw air the Firebird Exhaust had no silencer superb

To be fair a 4 stroke handles exhaust back pressure much better than a 2 stroke because it has a proper exhaust stoke that positively pushes the exhaust gas out.
A two stoke can only 'let' the exhaust out and over a much shorter period so has poorer combustion efficiency but it does do it twice as often as a 4 stoke!
I believe it was Stanley Hooker then working for RR on the Merlin who commented a 4 stroke "has one stroke to produce the power and three strokes to wear it out".

Tuned exhausts work on both types but the improved scavenging it provides obviously has more benefit to a 2 stroke.

Now show me such interesting facts about an electric motor, all you do with those is hit a switch, but then, isnt that the brilliance of the electric motor?

alan cantwell wrote: Now show me such interesting facts about an electric motor, all you do with those is hit a switch, but then, isnt that the brilliance of the electric motor?

Of course !!! Its for lazy folks, why do you think I use it

Garry

Very observant of you Eric.I imported several American cars and vans as well as day vans.all American originally from Japan as well as japanese 4x4 and MPV,obviously American vehicles are popular in japan,

Interesting facts about electric motors?
Oh yes there are!
Remember the Ward Leonard DC motor control system. Fully reversible with motor braking in both directions but not quite as light as an ESC!

No,I dont Q can you elaborate please

Garry