can i run a 912 with no muffler

[Rodr]

Can I run a 912 without a muffler ?are there back pressure issues?

 

 

[Guest Maj Millard]

I have run one briefly without a muffler...it ran ok and sounded like an old Cortina...I would not fly one like that though and I would suggest you'd probabily damage the motor if you did..............Maj........

 

 

[cooperplace]

from my experience with motorcycle engines, the problem is that the mixture could well significantly affected, which is a good reason to not do it....

 

 

[bexrbetter]

I've been building engines all my life (a carry over from my father) and I've never understood the term "backpressure" in relation to why people could possibly believe it's a good thing, it's not, you want your exhaust to be as least restrictive as possible. Try breathing thru a straw.

 

Freeing up the system will probably require a mixture change as mentioned above and the danger is in that freeing up the restrictions leans off the mixture whereas if you add a muffler you typically get richer and safer.

 

Very short pipes such as stubs can do some serious damage as wave reversion sucks in air and acts like an air blower on a fire making the coals glow hotter - only in this case the coals are your exhaust valves and pistons.

 

Removing a muffler is not very responsible in this day and age but I'm not your Mum. Well I can be for $100.

 

 

[turboplanner]

Back pressure as some people call it, is a science which includes shock wave travel.

 

You can have a muffler and have less flow restriction than a straight out pipe if the technology and calculations are correct.

 

 

[Hongie]

'Backpressure' per say, is probably not a good thing, but the scavenging effect of having a well designed tuned length exhaust, is.

 

 

[cscotthendry]

I've been building engines all my life (a carry over from my father) and I've never understood the term "backpressure" in relation to why people could possibly believe it's a good thing, it's not, you want your exhaust to be as least restrictive as possible. Try breathing thru a straw.Freeing up the system will probably require a mixture change as mentioned above and the danger is in that freeing up the restrictions leans off the mixture whereas if you add a muffler you typically get richer and safer.

 

Very short pipes such as stubs can do some serious damage as wave reversion sucks in air and acts like an air blower on a fire making the coals glow hotter - only in this case the coals are your exhaust valves and pistons.

 

Removing a muffler is not very responsible in this day and age but I'm not your Mum. Well I can be for $100.

While I'm not knowledgeable about this stuff, your statement about stub pipes got me wondering about all the Rolls Royce Merlins with stub pipes.

 

 

[Rodr]

Thanks to you all, its going in a Fisher Tiger Moth replica and not a lot of room, I run a Jab 3300 and a 5100 without exhaust with no apparent

 

problems apart from noise.

 

 

[kgwilson]

One of the guys here installed a 2nd hand 912 in a Savannah & found the cost of an exhaust system prohibitive so he put 4 exhaust pipes straight down. It didn't seem to affect performance but it sounded like a tractor, in other words horrible.

 

 

[skeptic36]

but it sounded like a tractor, in other words horrible.

Clearly, your driving the wrong sort of tractor..........

 

 

[turboplanner]

One of the guys here installed a 2nd hand 912 in a Savannah & found the cost of an exhaust system prohibitive so he put 4 exhaust pipes straight down. It didn't seem to affect performance but it sounded like a tractor, in other words horrible.

You won't hear one of the key issues which could arise and that's rapid heating/cooling/heating/cooling of the valves - can be very expensive if one lets go.

 

 

[facthunter]

Seeing it is a CV carburettor I can only see the mixture being affected right at the top if the slide goes all the way up. Then it becomes a fixed jet and more airflow means RICHER as the pressure drop increases and fixed jet carbs without correction run richer. Nev

 

 

[M61A1]

Seeing it is a CV carburettor I can only see the mixture being affected right at the top if the slide goes all the way up. Then it becomes a fixed jet and more airflow means RICHER as the pressure drop increases and fixed jet carbs without correction run richer. Nev

Except the excess oxygen comes back in the exhaust port. (if it's a short exhaust)

 

 

[bexrbetter]

While I'm not knowledgeable about this stuff, your statement about stub pipes got me wondering about all the Rolls Royce Merlins with stub pipes.

You will find those stubs combined with a Merlin's exhaust port length actually offer quite a long exhaust tract. It's relative to the speed of sound which doesn't change in a Merlin or a Honda 50 and that would be quite a long header pipe on a Honda 50.

 

Then it becomes a fixed jet and more airflow means RICHER as the pressure drop increases and fixed jet carbs without correction run richer. Nev

Bernoulli may agree with you relative to a steady flow but this is an engine where the airflow stops and accelerates every cycle and air is lighter than fuel and as you cause the air to accelerate faster each cycle ('hot' cams, larger valves, porting, open exhaust, etc.), the more you have to derestrict the fuel flow (eg. larger jets) in order to keep up.

 

 

[facthunter]

Bex, pulsing does affect the jetting but by and large the principle is not changed. If you install a smaller throat carb than desired it WILL richen up as the airflow increases because of the flow characteristics of the two elements. Air corrector jets work at the top flow rates to inject AIR into the mainjet or spray nozzle at the venturi, and emulsify it to prevent this overrichening If there is more airflow there has to more fuel flow to keep the ratio correct. A bigger venturi will need a bigger jet. That is understood . Regarding the fuel to air ratio in FIXED venturi, If it (the venturi)is too small will get richer as the flow increases,(greater pressure drop) unless corrected.. Nev

 

 

[Rodr]

I guess if I run the four pipes into two outlets it may not sound quite like a tractor but then again a tiger moth sounding like a Savannah could be as bad.

 

The Jab 3300 has the Rotec TBI and the 5100 is fuel injected so mixtures are controlled and exhaust notes are great.

 

 

[DonRamsay]

Aircraft noise is one of the main reasons the communities we live in are happy to see airports closed and sold off for housing. If aircraft made no more noise than is allowed by road authorities then there would be no aircraft noise complaints. In Germany, the noise level allowed is very tolerable by the general community. Have a listen to one of the FK aircraft. The Rotax 912 is a lot quieter than pretty well anything else despite working a lot harder (higher revs) than a Jab or Lycoming/Continental.

 

I had a Honda VTR1100 and put Staintune pipes on it. With a little rejetting the top end performance gain was very impressive. But, it was not until I sold it and heard somebody ride it up my long driveway that I realised how tolerant my neighbours had been to my 0600 start-ups and warm ups. I could still hear the VTR when it was a kilometre down the road. It did sound sweet not like a crappy Harley but it was not quiet.

 

 

[Ultralights]

. If aircraft made no more noise than is allowed by road authorities then there would be no aircraft noise complaints. .

Sort of have to disagree with this part, most normal people wouldn't complain if noise levels were lower, but the vast majority, i would say well up to 99% of noise complainers will make a noise complaint on SIGHTING an aircraft, proof is the noise complaints by people at Camden, about Gliders! on a 1000ft downwind! or the recent noise complain/legal stouch at Jaspers brush, the aircraft, a Cherokee, noise levers were indistinguishable from background noise and proven by a court ordered measurement at the residents location.. just as the serial complainer about Sydney and Bankstown airports, 1 person generates about 95% of the complaints, he lives 20nm north of Bankstown and the same from Syd, and he has been caught out using a computer, flight tracking website and an automated dialler to complain about aircraft noise any time a aircraft goes near his property, even when he isnt there..

 

 

[Old Koreelah]

Aircraft noise is one of the main reasons the communities we live in are happy to see airports closed and sold off for housing. If aircraft made no more noise than is allowed by road authorities then there would be no aircraft noise complaints. In Germany, the noise level allowed is very tolerable by the general community.

An old episode of "Inspector Rex" features a Cessna with a big ugly pipe running all the way underneath with an ugly big automotive-style muffler. The prop would still make a racket.

 

 

[bexrbetter]

An old episode of "Inspector Rex" features a Cessna with a big ugly pipe running all the way underneath with an ugly big automotive-style muffler. The prop would still make a racket.

I used to live in Eagleby right down near where the Logan River exits and various craft from Archerfield use to practice directly overhead especially on weekends (the stand out being Barry Hemple) and I know what you are saying but the exhaust noise is certainly a problem.

 

That is one case for direct drive engines, the lower revs do make less disturbance IMO.

 

 

[Ultralights]

An old episode of "Inspector Rex" features a Cessna with a big ugly pipe running all the way underneath with an ugly big automotive-style muffler. The prop would still make a racket.

i think the Cessna's with the big ugly pipe running under the fuselage with an ugly muffler is used for aerial photography and the modified exhausts is to prevent heat haze induced optical distortion.

 

 

[Dafydd Llewellyn]

There's a reason why aircraft noise is not too much of a problem; see http://www.airservicesaustralia.com/services/aircraft-noise-certification/ - Recreational aircraft are NOT in general, exempt from these regulations. Ignorance of the law is no excuse.

 

 

[Guest ozzie]

Are you sure it was a Cessna or an Airedale Beagle?

 

 

[metalman]

I think the noise angle is just an excuse, aircraft aren't that noisy at circuit height, and on final they're usually very quiet, takeoff is probably the noisiest time . Most complainers have ulterior motives ,I've found , whether it be financial ,notoriety or even fear based ( one old bird near YCEM complained that the planes were nearly crashing into her house regularly,turned out she happen to be right where the instructors liked to pull the power for an engine failure simulation, in her mind a quiet aircraft was on the edge of falling out of the sky)

 

I've wondered about running the 912 minus muffler ,for weight of course, would be interested to hear how it goes

 

Matty

 

 

[Old Koreelah]

Are you sure it was a Cessna or an Airedale Beagle?

That breed is new to me Ozzie, but our Teutonic hero jumped out of what sure looked like a C172.