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Scale exhaust for glow engine


Danny Fenton
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Over the years many of our customers have tried this, and most have failed. Vibration loves a scale exhaust! 

 

If you do it, make sure its as light as possible and the whole muffler can is supported with stays down to the engine mount bolts on the crankcase. That way its a much stiffer than if the thing was cantilever and just hanging off the exhaust port. Thin wall stainless would probably be my choice for material as brass is really heavy. 

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6 minutes ago, Nigel R said:

what about

 

standard exhaust elbow

short flex joiner or silicon 

larger can connected to the airframe structure with all the fancy scale outlets

Hi Nigel, yes that's the sort of thing, but what materials would you make the can from and what would you use to join it together? Especially if its aluminium as Jon suggests?

 

Sorry for the daft questions, but I don't normally dabble in I.C.

 

Cheers

Danny

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Copper plumbing bits / tubes + silver solder? Not sure standard lead solder would hold up. Might even need brazing. I'm not an expert but I think if you're fitting a standard can and then making what is essentially a diverter, then silver would be enough.

 

Might also be worth looking at whether JB weld would hold up. I've used a few aluminium tube cans made by my dad before, but only on two strokes, basic dumpy silencer type things, they were just held together with 24hr epoxy. Could be an easy option.

 

I guess the easy if expensive option is giving your flexible friend some exercise and taking him somewhere like JE or Weston.

 

edit:

have a search around for RC car bits, there might be something already out there to split your exhaust?

 

maybe like:

 

https://www.aliexpress.com/item/32751058834.html

 

Edited by Nigel R
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4 stroke exhaust can temperatures can be in excess of 300'c and i managed to melt an aluminium baffle in an exhaust i made for an enya 155 so that is what, 600'c?! Although smaller, things like JB weld are not likely to cut it even on an 82. You might get away with a silicone adaptor on an 82, but it wont last long and i suspect you will be changing them on an almost weekly basis as it will be right next to the head and the hot gasses will rot it from the inside out. My OS FF240 is just 4 60's on a crankcase and the cylinders regularly burn through my silicone exhaust adaptors. I need to make up some metal ones as im quite sick of replacing them. 

 

Grab some thin wall stainless tube from ebay and use that. Copper will crack and is very heavy. Depending on what you make you might also be able to ditch the saito muffler as you will have built one. 

 

Again though, keep it light. The saito exhaust already weighs a ton so i wouldnt be adding more. Although the knuckles and things you have look lovely, they do not look like they are especially light. 

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The full size Stampe I modelled mine on had four exhaust stubs protuding from the bottom of the engine bay; so rather than fuss with a purpose made exhaust I just cut three alloy stubs from some tubing and set them poking out to line up with the straight exhaust extension on the Laser 180. With  any exhaust smoke I get in flight it is impossible to see which pipe it is coming from. Added to that the lower oil fuel now recommended for Lasers burns so cleanly there is barely any smoke to observe.

i fired up my new 180 in the P47 for the first time today with it’s carefully split and routed exhaust (mostly silicon apart from the elbow and splitter (a plumbing Y coupler)). After five mins taxiing around the lawn there was a clear smell of heat build up so have decided to ditch the system as it is just too close to the fuel tank and cowl base. The Laser exhaust  straight pipe extension now protrudes 10mm outside the bottom of the cowl and I can sleep easily and the model.will be as easy to keep clean as an electric powered model 

image.jpeg

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I  use stainless bendy pipe sleeved with silver soldered brass on a few of my Laser set ups and it works well . One of the keys with longer exhaust is not to make the clamping too rigid. Coating the inside of clamps with high temp silicone and letting it set before clamping works well. All engines move at high frequency and totally rigid pipes will crack . We used to have similar issues in model boats where we also used rubber engine mounts. The key is restraining and exhaust with a limited damped movement. High temp silicone inside clamps works well . It’s also not a good idea to clamp the exhaust too near the engine for  obvious reasons. 
 

75FBE0B2-CC3F-488F-B097-1D8A2DB3D369.jpeg

Edited by Tim Flyer
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Hi Danny sure I will do. As you said earlier correct flux and Silver Solder is key. What I did was use K&S Brass tubing in various diameters . Each size down fits inside the next so it’s quite easy to make a tapered insert into the bendy pipe . I will check but I think this is also 10mm stainless bendy pipe as used on some domestic equipment. I used the standard Laser exhaust clamp as I soldered the brass tube on each end of the bendy pipe. I left about an inch for the sleeve that goes into the engine .

The Engine in my photo is a Laser 200v and didn’t need extra cans . As long as your bendy pipe is long enough an extra can isn’t really necessary unless you have very strict noise limits. 

The pipe into the cylinder head fits perfectly and I simple put a smear of high temp silicone on it before clamping it . I have the size in my shed but I do remember it is an imperial rather than metric size that fits in snugly into the cylinder head . In my experience the seal has worked even better than the standard system . I silk reply with the exact size if u need. 

Edited by Tim Flyer
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Thanks Tim, that is excellent info and I have enough to form a plan. I was not lucky enough to get a Laser, but the Saito 82 does look a lovely bit of kit, the exhaust is a threaded fitment

As I have a lathe, I know very lucky, I think I may be able to turn some end fittings to silver solder to the 10mm flex pipe.

Thanks again.

 

Cheers

Danny

Edited by Danny Fenton
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Some of the guys on a model engineering site sugfested Tenacity 5 flux for Stainless, i have some on order ?

I did last night stumble on a web page that gave part numbers for Saito exhaust flexi with ends fitted. They suggest 12mm i.d. for the 82.

Thanks for all your suggestions

And sorry for all the daft questions, but as I said I havent run an i.c. for many decades.

Cheers 

Danny

Edited by Danny Fenton
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Hi chaps here is some info that might help laser users silver soldering stainless to brass .

The ID for laser 70 -100 exhausts (and that includes 160v and 200v) I have found to be 7/16” . I use K&S brass tubes going down by 1/32 each which then fit nicely inside each other to make a tapered insert into the stainless pipe. I include a photo of pipes needed and the correct powder flux . 
 

 

09E36C22-95C4-48E0-A477-7558D4CD86D5.jpeg

315E93DB-56D9-497D-BE9B-09BB973F6E73.jpeg

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Silver soldered stainless seems to work very well.  This was my solution for an ASP 160 in my 1/4 scale Cub and it's probably 10 years old now.

 

large_0044.jpg.0435f50c88a344e1b5925a1c2bf05db8.jpg

 

The main chamber was the salt pot from a 50p cruet set bought at a car boot sale for the purpose!  Each inlet is a length of drilled tubing running full width which I crimped at its end.and the single bottom outlet is of similar construction.

 

This highly effective alternative came to me on a second hand model attached to a Zenoah 38 - shown with the lid of the die cast aluminium project box it was built from removed.

large.831861.jpg.0d2d188cd5089cdc481589eaea6ac955.jpg

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