Aircraft General Discussion

[Bill PudneyParticipant @billpudney37759]

Model Engineering as a sit com?…..why am I thinking of "Dads Army"?

cheers

Bill

[Perko7Participant @perko7]

Perhaps the aircraft enthusiasts on this site can answer a dumb question for me:

Why don't piston-engined aircraft have silencers on their exhausts?

I've had plenty of light aircraft fly over our house from time to time (we are about 10km from Archerfield airport which is the major light aircraft facility in Brisbane) and the racket they make is many times greater than the commercial jets that also fly over at times. Sure they are at a lower altitude, and i'm aware that prop noise is a major contributor, but the light aircraft with turbo-prop engines don't seem anywhere near as noisy as the piston-engined ones.

Are there technical issues, or is it just customary?

[Trevor Crossman 1Participant @trevorcrossman1]

I quite agree Perko, many light aircraft do make a lot more noise than others, sometimes due to propeller sometimes largely from the engine, usually it's a combination though. Back in the later 30's some British light planes, I forget the manufacturers, were sold with a very long exhaust pipe along the bottom of the fuselage, maybe also some of the DH Moth series too.

Several years ago when I was member of, and an aircraft inspector for, the then Popular Flying Association (now Light Aircraft Association), the Chief Engineer asked members to forward ideas and designs for effective and practical silencing systems particularly for homebuilt type aircraft that were not under prescribed FAA/ CAA regulations. Despite some promising work ,both science based and home workshop style practical efforts, done by a few members, the whole idea fizzled out much to the delight of the more ''traditional'' light aircraft owners who were quite unsurprisingly by far the loudest in rubbishing the project before it even started, often equating noise with power/performance and scornful of the public's dislike of light aircraft droning slowly across the sky, usually citing' safety' concerns to support their negative views. I dare say that manufacturers of certificated aircraft would say the same, plus of course the ever important added costs.

Trevor.

[Perko7Participant @perko7]

Thanks Trevor. I can't see why it should cost a whole lot more, particularly considering the total cost of a light plane. Cars and trucks are being forced to comply with ever-increasing restrictions on vehicle exhaust emissions, plus the switch from leaded to unleaded fuel, as well as noise restrictions, yet the light aircraft industry seems to be spared. Even commercial passenger jet aircraft are required to meet certain noise emission limits as far as i know.

I would be surprised if a properly designed exhaust system with silencer would decrease the power available from an aircraft engine, in theory it should be able to increase it, particularly when they operate within a fairly narrow rpm range to suit the diameter and pitch of the propellor. I would think a good set of extractors with a sports muffler should be able to provide the same if not better power, and a nicer sound as well.

[Mike PooleParticipant @mikepoole82104]

From a power point of view I think a tuned length of pipe is all an engine needs, all silencing is for the comfort of the driver/pilot and others. F1 fans complained when the turbos sapped the volume of the exhaust.

Mike

[Ian S CParticipant @iansc]

All the light aircraft that I have worked on, except most of the British ones, have a silencer, some Tigermoths have an extended exhaust with a silencer. I think some of the modern composite props are a bit quieter, Andrew might be able to say, I think he has one on the Pawnee. The propeller needs to be quite near the speed of sound to get the maximum thrust for minimum power.

Near Christchurch, at the RNZAF station of Wigram flight training was conducted with NA Harvards, and the locals didn't like the noise. They thought they had won when the Harvards came to the end of their life, and were replaced with the NZ made Airtrainers, wrong, although only about a 1/3rd the horse power, they made almost as much noise, and being quite a bit slower, made the noise for a longer time. Love that noise, but the government closed the base.

Never seen a silencer on a radial engine, and you won't find one on a Merlin, or the like.

Ian S C

Edited By Ian S C on 21/09/2018 12:18:01

[Trevor Crossman 1Participant @trevorcrossman1]

Yes tuned pipes are indeed effective, but remember that although whilst at cruise the rpm may be relatively constant, an aircraft engine requires instant response at the critical times such as take off and landing, aerobatic machines also require instant responses. Much of this can be overcome at little cost as is seen in modern sports bike road performances ( far beyond my motorcycling capabilities now I might add!) , but one is still left with the psychological aspects of aircraft enthusiasts, who, like many bikers and F1 watchers , link volume of noise with power, speed and excitement. On the other hand I used to enjoy burning of the ''racing striped, logo bearing, tunnel sized exhaust, over sized tyre type boy race'' with my pretty standard looking but well sorted machines. Just look at most car/bike ads where the ''macho-ness'' of the vehicle is exaggerated.

Although many production light aircraft have some sort of sound attenuating collector box within their exhaust system they do not make a massive difference , though the Avions Robin DR 400 types that I once helped maintain, were quieter than many.

Trevor

[davidkParticipant @davidk]

Hi Ian

Funnily enough, the one aircraft that I saw fitted with silencers, many years ago was a PZL Wilga with an Ivchenko radial engine. This was at Lydd Airport in Kent, UK. Probably 30 years ago, but the image stuck in my mind!

There are a few pictures on the internet of Wilgas fitted with silencers. Googling G-BUNC or SP-FZE for example will find some.

I've just found an NZ registered example as well!  ZK-PZN

Regards

David

Edited By davidk on 21/09/2018 13:04:58

[Barnaby WildeParticipant @barnabywilde70941]

Posted by Neil Wyatt on 20/09/2018 22:46:37:

Sometimes when we feature a tool build in MEW, a supplier tells me they have had a small 'run' on that item ready-made.

Neil

So why not work with them?

Celebrity endorsement is a massive business, just drop the celebrity bit & get someone making something with tools. Instead of spending £xx's on a few inches of advert, why not get a Co' to supply a tool to a maker who then writes the article or films the video of how they used it?

[Cornish JackParticipant @cornishjack]

Re. silencers, when I was running the Boscombe Down Model Aircraft Club, one of our members (a test engineer) did a lot of experimental work on model silencers but without conclusive results. The use of tuned pipes is essential for such as Pylon racing and, at the Nationals at Barkston Heath, we lap-counters would be treated to the sound of these thoroughbred engines coming 'on the pipe' – spine tingling sound effects!! Still got a couple of unused pipes and manifolds in the shed – a bit past that side of model aircraft nowadays!!

rgds

Bill

[Robert Atkinson 2Participant @robertatkinson2]

So why not work with them?

Celebrity endorsement is a massive business, just drop the celebrity bit & get someone making something with tools. Instead of spending £xx's on a few inches of advert, why not get a Co' to supply a tool to a maker who then writes the article or films the video of how they used it?

There starts the slippery slope of loosing independence. I see it in amateur radio publications, Dealers supply much of their income though advertising. Review equipment is often loaned and the editors don't want to publish bad reviews for fear of loosing the advertising.

Robert.

[Barnaby WildeParticipant @barnabywilde70941]

Posted by Robert Atkinson 2 on 21/09/2018 16:39:37:

So why not work with them?

Celebrity endorsement is a massive business, just drop the celebrity bit & get someone making something with tools. Instead of spending £xx's on a few inches of advert, why not get a Co' to supply a tool to a maker who then writes the article or films the video of how they used it?

There starts the slippery slope of loosing independence. I see it in amateur radio publications, Dealers supply much of their income though advertising. Review equipment is often loaned and the editors don't want to publish bad reviews for fear of loosing the advertising.

Robert.

I agree. It would take people with high moral standards & impeccable integrity to be on both sides. But the way the market is going . . . I think it would survive the coming changes.

[not done it yetParticipant @notdoneityet]

While most Merlin engines have stub exhausts, those fitted to Hamdens did have a single exhaust manifold pipe. No actual silencer fitted, but must have at least softened the tone a little?

[MuzzerParticipant @muzzer]

Posted by Robert Atkinson 2 on 21/09/2018 16:39:37:

So why not work with them?

Celebrity endorsement is a massive business, just drop the celebrity bit & get someone making something with tools. Instead of spending £xx's on a few inches of advert, why not get a Co' to supply a tool to a maker who then writes the article or films the video of how they used it?

There starts the slippery slope of loosing independence. I see it in amateur radio publications, Dealers supply much of their income though advertising. Review equipment is often loaned and the editors don't want to publish bad reviews for fear of loosing the advertising.

Robert.

Or god forbid the audio snake oil magazines who have to endorse the latest emperor's new clothes. Enough engineers on here to put a stop to that kind of nonsense here at least!

Murray

[NimbleParticipant @nimble]

Who would want to silence the most beautiful mechanical noise with a silencer?

For me what mechanical noise is more beautiful than that of a Spitfire doing a “BeatUp”

The sound of the V12 Merlin with stub exhausts, the whine of the supercharger, Doppler effect of the aircraft approaching and receding, combined with the subtle and varied propeller wash and general wind noise!

I have not seen the movie “Spitfire” yet but look forward to doing so.

I live within 3km of the Ardmore Aerodrome home of the NZ Warbirds Organisation where there are 5 Harvards based, Catalina, DC3 Yak and many other aircraft. There is currently I think the third rebuild of a Mosquito being undertaken I believe it is due to take to the air within the next two months. Then the fourth rebuild will commence. Lately the Spitfire has been going out once or twice a week, always a joy to see and hear, unfortunately no “Beat Ups”

Nimble Neil.

[Tim ChambersParticipant @timchambers76147]

During the testing of the Mosquito prototype DH experimented with "saxophone" exhaust pipes that gave the aeroplane an extra 8 mph but they added a lot of extra complication so they were not used in production aircraft.

I remember an article in Pilot magazine about a pilot who owned a company making performance exhaust systems for cars and motorcycles. He realised he could improve the performance of light aircraft engines with a carefully designed exhaust system (quieter too).But if you fit a different exhaust to a Lycoming, its no longer a Lycoming, it becomes an experimental engine in the USA.

[Neil WyattModerator @neilwyatt]

Coolest bike I ever saw was matt black BIG and almost inaudible, as it came into a roundabout I could hear the chain clicking and it barely grumbled as it ripped out of the turn.

Still love to hear a Merlin though.

Neil

[Ian S CParticipant @iansc]

ndiy, The Handley Page Hamden had two 980 hp Bristol Pegasus XVIII 9 cylinder radials.

Ian S C

Edited By Ian S C on 22/09/2018 14:13:37

[not done it yetParticipant @notdoneityet]

Ian,

I stand corrected! I knew it was a Handley Page and it began with an ‘H’. It was the Halifax, which of course had 4 of these marvellous engines with the saxophone exhausts.

One of the reasons for this arrangement, instead of stubs, was to remove/reduce the flames from the exhaust, which was a bit of a give-away when night-fighters were looking for targets on clear nights.

[Ian S CParticipant @iansc]

By about 1943 it was found that the Halifax with Merlin engines was under powered, and the newer ones were fitted with Bristol Hercules engines which bought the performance up to near that of the Lancaster, but they had the problem of a small bomb bay compared to the Lancaster, and could not fit the 4000lb bombs, I think that's why they got jobs like coastal command, glider tug, and dropping SOE agents in France.

Ian S C

[Neil WyattModerator @neilwyatt]

Apologies to twitter haters but I'm not going to upload and type this all twice

Neil

It must be #Halloween because I saw a #Vampire today! I was at Brandon Marsh near Coventry when I heard a #jet making an odd whistling sound approaching. I though that sounds like an old one… long nose so a two-seat trainer version. #aircraft #planespotting pic.twitter.com/MU6vmaGZM2

— Model Engineer (@ModelEngineers) October 31, 2018

[martin perman 1Participant @martinperman1]

Could have been a NF MK10.

Martin P

[Neil WyattModerator @neilwyatt]

Posted by martin perman on 31/10/2018 18:37:38:

Could have been a NF MK10.

Martin P

No looks like there's a training version at Coventry:

"WZ507 – T.11 airworthy with the Vampire Preservation Group in Coventry, Warwickshire."

Neil

<edit> It's the only airworthy Vampire in the UK.

Edited By Neil Wyatt on 31/10/2018 19:08:43

[martin perman 1Participant @martinperman1]

what do all the #words mean

[Ian S CParticipant @iansc]

Looks like a T 11 to me, there are a couple of them here in NZ on the War Bird circuit, a nice machine. There is some regret that there are no FB 5 single seaters flying in NZ, as we had quite a number that served well in the RNZAF, but it seems that they were a maintenance headache in latter years, and the range / endurance very short. At least the T 11 has a bang seat if you have to get out in a hurry, something the single seat FB 5 did without.

Vampire, one of my favourite aeroplanes. This is as near as you get here, a model about 5ft wing span.

[Author]

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