In cowl exhaust solutions?

[Craig Spence]

Hi all,
I've talked about this before on here but now theres different problems.
Basically I can't fit my exhaust in the cowl, I have looked at getting a 90% manifold and then just attaching the exaisting silencer. I still think this won't fit.
The other option is to use a knuckle, female to female adapter and flexible pipe to the silencer.
This option will be expensive for a twin though.

So I thought of this, get a 90% knuckle and use a silencer from a 30 four stroke which is alot shorter and has a smaller OD.
The engines I am useing are SC52FS, would the smaller silencer effect the engine performance at all?, will it put stress on it or make it consume more fuel?.

Help and advice needed. If need be I will post pics tomorrow.

Cheers all.

[andy watson]

Do you need a silencer at all?

 

I had one hanging out of the bottom of my stuka. I took it off for asthetic reasons- only leaving the short manifold pipe protruding. There wasn't any real difference in volume if I remember correctly. It certainly wasn't noticeable enough to make me put it back on.

 

[Craig Spence]

Hi Andy, I have thought of the same thing, leaving it off, but what about tank compression?, if you remove the silencer you have no nipple to put back pressure on the tank.
Also noise is going to be an issue?.

I'd still need a 90% manifold either way, as the other manifold will be too big.

I also thought of just getting the flexible pipe going straight onto the silencer and forfitting the manifold. But I have been told the flexible pipe shouldn't be bent that much from the engine?, lol, flexible pipe?.

[andy watson]

You can put the nipple into the manifold rather than the silencer. I have just gone with an unpressurised tank as 4 strokes are supposed to be fine without it. I am not hugely convinced by how big an increase in pressure you actually get anyway.

 

Mick Reeves does a stainless steel flexible pipe that might be more flexible than the commercial ones. You will need to silver solder the thread onto the ends.

 

Noise- well that's for you to know if it's an issue- although as I said the difference on a Saito 1.20 wasn't really noticeable.

[Biggles' Elder Brother - Moderator]

I've run both a 91 and a 56 OS four stroke without exhaust silencers and I'd say the difference in sound volume is absolutely minimal. Most 4 strokes are pretty quiet anyway - well within the 82dB max guideline.

 

Also I've found the lack of tank pressure to have no real effect. You may have to open the HS needle valve a fraction that's all. But I would add that that was on a scale job that wasn't thrown about wildly!

 

BEB

[Craig Spence]

Sorry for the late reply guys, I've been sanding like mad.
Anyways, it's reassuring that you've run them without the nipples.
It's a worry for me for two main reasons,
1; my twin had 6 ounce tanks but I've had ti change to small 4 ounce slec tanks. I've asked a few people and they think with the engines I have I should have approximately 8 to 10mins max.
So if there is a difference I will know.
2; if I loose an engine I potentially loose the plane.

BEB I think you showed me a solution before which looked good.
I think I'm gonna try with the knuckles and silencer, if that fails I'll use smaller silencers.
I plan to get some rubber tube on the end of the silencer and route it through to the dummy exhaust stacks.

Thoughts guys.

Cheers for the help I appreciate it.

[Reno Racer]

I'll second the Mick Reeves fleixble pipe, it comes fitted with screw on threads, so is just' plug an play' as they say.

 

Worked a treat in moving my ASP 91 FS exhaust so it didn't stick out the side of my Revolver 70 cowl, but smartly came out of the bottom of the cowl like a pitts style muffler. Plus you can still use the pressure nipple as normal to feed tank pressure.

[Craig Spence]

Hi Christian, I didn't realise it came fitted with threads on each end I thought you had to solder the ends on.
I may have a look right now.
Cheers.

[andy watson]

The flexible pipe I bought needed silver soldering. You cut the existing manifold in half to give the 2 ends, then solder them in place. My attempt wasn't successfull- but that was due to my soldering skills I think! I ended up going the "official" route and buying the expensive OS one which was premade. I have had no problems with that at all- including a fairly sharp 90 degree bend exiting the engine.

 

One route I considered, but was warned off before I actually installed it was silicon exhaust tubes. These are thick walled "heatproof" exhausts used for cars. My LHS (car based) told me they would be fine, but a lot of people said they wouldn't cope with high 4 stroke exhaust temperatures. It might be worth giving it a go- especially for your ducting through the dummy exhausts.

[Craig Spence]

Hi Andy,
That's the only thing that puts me off, soldering the ends etc..., but it's far cheaper than just engines pipe, ?18.99 for one fully made up.
I think I'll go for it, I'll take my existing manifolds to work and cut them down on the big band saw.
It's bending the pipe through 90% that worries me as some people advise against it.

The other thing is having something with a slightly smaller OD to fit inside the pipe and manifold to solder.
Although it sais you can but it up, not sure if that's a great idea. As for soldering my father has an industrial soldering iron, just heat up the metal add flux and solder.
Or so goes the theory, I'll measure up tonight and get the head scratching going.

As for rubber tubing, I think it's a viable option.

Cheers, Craig.

[Reno Racer]

Actually, Now I think about it. I got mine from Just Engines.. Check them out the pipe is really good. Here you go, about 3/4 of the way down.

[Malcolm Fisher]

Craig,

Soldering an exhaust by using a soldering iron with ordinary solder won't stand up to the exhaust temperature. You need hard solder which needs a much higher temperature than a soldering iron will give, A good butane torch will suffice or find someone who has access to oxy-acetylene equipment.

Malcolm

[Craig Spence]

Hi Christian, I'm going back and forth now lol.
I think I may try the 90% knuckle and connect a tube to the end if the silencer to exit the cowl.
All will know next month when I'll buy something.

Hi malcom,
The soldering iron my father has is as I said industrial, this is used for some heavy plant equipment and gives off a good bit of heat.
With the light metal I'll be useing the iron would heat it to the point of glowing, then silver solder.
If I had a blow torch I'd use it but money's a prob at the moment.
Out of interest would you use internal tubing between joints?.

Thanks for the help guys.
Cheers, Craig.

[andy watson]

If you check through my DVII build blog you will see how I installed my flexible pipe, and the 90 degree bend it has. I also got it from JE, and it has run perfectly.

 

I am worried about your reference to rubber though- do you really mean the flexible "heatproof" silicon pipe. It would be worth checking out whether it works on the bench before committing it to an installation. My flexipipe gets so hot it is actually scorching the firewall, and I am thinking about adding a metal plate to soak up some heat.

[Craig Spence]

Hi Andy, I'll check your build after this.

As for the "rubber" yes I meant heat proof silicon lol!.
And yes your right, I looked at one solution but the silencer would be next to the servo and I don't want to melt that.

This is going to become a real pain lol.

[Craig Spence]

Andy, had a look at your build, very good.
I'll know next month when I try the parts.
Thanks.

[Stefan Hafner]

Craig, I've used sillicone tube for an exhaust extension in one of my installations. On mine I have a 1.20 FS connected to a metal flexi pip and then the silencer, and from the silencer i connected the flexipipe to the actual scale exhaust, bit of a long system but it kept it all hidden, this seems to be able to handle the temperature ok, but them its been cooling throughout the flexpip already, and not sure how it would hold up straight off the engine

[Craig Spence]

Hi stefan,
That's probably the way I'm gonna go I think.
Silver solder mote flex pipe to the end of the silencer and route it to cowl exhaust.
Cheers.

[Shaun K]

Hi Craig,

 

The esteemed Wizard of Oz reviewed the RCS Turbo Muffler and gave them a good report. See the link below.

 

RCS Turbo Muffler from Christian Traders in Australia.

 

Shaun.

[Craig Spence]

Hi Shaun,
Thanks for the link. It looks excellent but it's no good for me.
After going the LMS I found out that the SC30FS silencer thread is too small for the tubing, meaning I'd have to butt two different ID's of tubing together to fit the silencer.

So after the info and help I've got from here I'm looking at two options now.
1; Just buy the flexible pipe, go straight from the engine and route through the cowl. Forfitting the back pressure nipple.
2; Or buy the knuckle, drill it, tap it and add a nipple to it for back presssure. Then add flexible pipe and run through cowl.

I think I'll go for the cheaper option lol.
Cheers all.

[Craig Spence]

Hi all,
Been a long time and no progress, bit of a head scrathcher really.
I got some flexi pipe from just engines and it's no good for this application, it's not flexible enough and I have to make two sharp bends like an s which would need to be supported on the engine itself.
So I think I will have to buy the 90% manifold now, it's the only option as the cowl is so close to the exhaust outlet.

I have a few questions if you could help.
1; could I cut the silencer just below the nipple and then again just above the taper of the outlet, remove the centre peice and then solder just the two tapers together creating like a little bell with a nipple.?
2; can I silver solder brass/ copper pipe to the silencer.?

Here's the latest plan and I would appreciate your feedback.

I plan to use a 90% manifold, the outlet will face downwards in relation to the engine.
Then I will cut a two inch cylinder from the centre of the silencer, the remaining two ends will be silver soldered together (this will have the pressure nipple on it).
So the 90% manifold will be screwed into position then the bell silencer screwed on the end of this.

I then plan to again silver solder a short length of brass/ copper tube to the end of the bell silencer.
Once this is in place I will simply attach an exhaust deflector (heat proof silicon tubing) and route through the scale exhaust shroud.

Thoughts please.

Cheers all.

[Craig Spence]

I was wondering with the above set up, could I create too much back pressure?.

[andy watson]

Craig, I am struggling to see how you can't use the flexi pipe with the 90 degree knuckle. I am wondering if you are getting yourself tied in knots a bit!

 

Remeber by using a nut you can screw it tight at any angle, so the pipe can be pointed at the direction you are going.

 

A photo might be a real help here

[Steve Hargreaves - Moderator]

Hi Craig, like Andy I'm struggling a bit to see the problem here.....if you have room for the 90 degree knuckle why not the pipe? Will it simply not make the bend radius needed?

 

They say a picture is worth a thousand words so maybe a sketch or a photo might help...

[Allan Bennett]

Just a couple of comments, which I hope might be relevant: I didn't have much luck with flexible pipes on my OS48FS and OS120FS -- official OS flexible, 3rd-party flexible (can't remember who, so I won't guess a name), and "heatproof" silicone tubing. They all burned through close to the engine eventually, but the OS one lasted longest; the 3rd-party and the silicone tube only lasted a handful of flights. So my recommendation is to use the stock rigid components as far as possible. If I remember correctly (I'm all converted to electric now) I used a right-angle bend with the stock silencer connected directly to it, and then used a much larger diameter heatproof silicone tube to direct the exhaust out of the bottom of the cowl. At one point I think I used a metal plate as a deflector instead.

 

So far as back pressure is concerned, I think there's a danger if you put the nipple into the header pipe and don't use a silencer, as was mentioned several posts back, you run the risk of getting suction instead of pressure. The pressure in a silencer is generated by the fact that the outlet is smaller than the body of the silencer and, possibly, the outlet is slightly smaller than the inlet.