Total Exhaustion From Smitty

Stubby

Stubby

Famous Member
VIP
Seattle Smitty has brought us some fuel for the brain.

"A couple of years ago I mentioned this article when we were talking about exhaust system efficiency, and said I would post it if I could find it. I was pretty sure I had it, but I have been watching for it to surface since the late-60s!! Note the magazine was dated Sept'62.

All thanks to the estimable Gary Stubbs, Texas good-guy, who offered to scan these pages and blow up the diagrams to readable size, as needed. I'm always about two generations slow in any technology, and probably shouldn't be allowed on this forum"

Smitty, I realy didn't feel comfortable writing that second paragraph, but I will honor your request, since you provided us with a realy good article. Now we will see how good I did on scaning and uploading. I had to cut them up a little to keep them small enough. If anyone wants, I can email a zip file.









 
I did a quick internet search, and came up with this: cafefoundation.org tests of various exhausts. They reported that there wasn't any increase in power, but that the exhaust tone was mellower. Interesting reading though...
 
Nice job, Gary, thanks again.

I'm about to try to get the computer to print out that article so I can study it, Chuck.

I have a single-cylinder 125cc outboard racemotor I built thirty years ago using a '73 Yamaha motocross engine (I water-jacketed it). This winter I plan to dyno-test some pipes with it, and I'm going to build a Coanda extractor. Instead of the cone being fixed, however, I'm going to suspend it from a length of all-thread so I can run it in and out. But it will behave differently on a 2-stroke expansion chamber than on an un-tuned automobile tailpipe or aircraft exhaust. I won't be expecting any particular outcome, just satisfying curiousity.
 
I didn't mean to sound so negative in my earlier post, sorry about that. The pics in your article got me to thinking about the design of aircraft jet exhausts, I thought I'd seen a coanda extractor before, but couldn't find it. I'd be interested in that kind of setup to get a mellow tone, even if it didn't help (or inhibit) performance. Food for thought...
 
(the next day)

Chuck, after making a black-&-white copy I read through the CAFE Foundation article, and will do so again after taking some notes on the color-code for the pressure-maps . . . .

Two observations: First, while the graphs they generated are quite interesting for the physics of pressure waves in resonant chambers, they aren't of direct practical use. Proving that tuned exhausts work on an aircraft engine just as they do on any other engine is hardly a revelation ( although some of the more mechanically-clueless private pilots I've met may think it is). Their own conclusions, that tuned exhaust "should" produce more power, efficiency, etc., could have been reached by reading any of the established works on the subject. Undoubtedly, getting real-world torque, horsepower, and fuel consumption figures is subject to the complications of running a pressure-cowled aircooled engine on a dyno stand. And trying to account for the uncontrollable variables of flight-testing can't be easy.

But dyno and vehicle testing is worth more than all the hunches, theories, computer simulations, and pressure-maps, and any pipe-builder (including moi) can tell you how he has been surprised and usually disappointed when the cold hard facts appear. Besides, there are issues beyond mere pipe performance: How are jetting and spark-timing requirements changed by the pipes, will this void the engine warranty, and what will the FAA have to say about it? Is the power increase worth the extra weight and installation complexity of the tuned exhaust system? Can this assemblage of tubes and maybe mufflers be attached to the aircraft in a way that it won't buzz, add to parasite drag, or shed pieces (and when it does will it melt holes in the aeroplane?)?

Still, the graphs are interesting.

Second, their specific tests of the Coanda extractor were insufficient to prove/disprove the validity of the concept. Obviously, Coanda's own testing showed different results. Once again, dyno-testing, with a range of nozzle configurations and adjustments, on a range of exhaust systems, using a range of camshafts, would get us closer to knowing when or if the Coanda concept has value.

I'm going to see if I can find anything else about Coanda's snarky-looking gizmo, and will get back to you with anything interesting. Unless someone has been there before me, I'll do some 2-stroke tests myself, probably late-winter or spring. I already have some ideas (but I ain't telling yet!!!!!!).
 
I'm surprised and disappointed that this subject drew so little comment! I was looking forward to see our engineers and tech-mavens chewing on it.

Apparently the '20s and '30s saw a lot of interest in the properties of vortices, with the usual cranks promoting perpetual motion, etc. For a modern group looking for useful ideas amongst the dross, Google "Viktor Schaunberger, The Inventions."
 
Thanks, Smitty!

I've been on holiday for Spring Equinox, Yiddish New Year, Blossom Festival in my home town of Alexandra. Before I left, I got your article, Smitty, so I've had a nice quiet time reading and doing calculations!

The numbers show anything from 5 to 16% power gain, but there are many, many subsidary issues to contend with.

Three of my outcomes from the article.

No. 1. Based on a one pipe per Coanda, there is an iipe diameter is around 3.75 times stock pipe size. So a typical 2" internal diameter pipe found on a big 4 5 4 will need eight 7.5" exit unless the Coanda (heron called the tuner) is pancaked down to manageable proportions. Bad stuff.

No. 2. Midrange torque is influenced by pipe length. Brake specific fuel consumption is hurt when the back pressure is set up for maximum power. The calculations set by Coanda are based only on the pipe diameter decided on by the orignator of the engine. Hence some engines have one pipe, others, like the Leyland bus or Plymouth engines and aditional tests by the Conservatory of Arts and Trades are engines with one grouped pipe. Each invalidates the premise Coanda worked from, because they cannot physically employ a Coanda extension, nor operate under his strictures, unless it is a grouped pipe. On planes or dragsters or boats, sweet as, but unpackageable on a conventional car

No. 3. There is a premise that the tuner can be tuned for both back pressure and maximum power, so the true schedule of testing, in order to cover the apples with apples, must cover the amount of back pressure present, and must practically work on each exhast outlet. Hence a six or eight cyl engine needs 6 or 8 of them.

My summary is that, one tuner could do a great job if it was used like a tuned muffler on a motorbike. Sadly, it has to be packaged for an automobile, and then modern day testing on a single or dual pipe car with 95 dbA noise, Federal 200 ton block crash tests and California style emissions regs has to take place. I've got a few ideas on how to package it, but the exhast pipe would be a real expensive item.
 
What you called the "tuner," I'll call the "extractor." Or, the "gizmo." All of us are the tuners!

Why do we need one extractor per cylinder? Why do we have to place it at the point of the tuned-length of the system? We aren't using it to control positive/negative waves to clear the cylinder; we are only attempting to lower back-pressure at the outlet, and all we need is some pressure and flow to operate the extractor. So, why can't we have a good set of headers, equal-length to the collector if you please, followed by a single pipe terminating in a muffler at the point of the desired tuned length (what, 36-44'' for most of our uses?), then a tailpipe to the extractor at the back of the car. I would think a set of six evenly-spaced pulses would keep the hoped-for vortex rolling over itself better than single pulses one-sixth as often. Enlighten me. I don't see why the length of the tailpipe aft of the muffler matters at all, with the exception that I imagine it would be better to have the entire system thermo-wrapped and/or coated to retain energy in the exhaust charge.

I do think that hanging one of these gizmoes on a two-stroke is a different kettle of fish. But (if it actually works in the way Coanda claimed), the extractor could be incorporated into an expansion chamber (rather than merely affixed to the end of the stinger) in a possibly synergistic manner. (I wish I could make drawings here; maybe I'll mail you something).

As far as the final outside diameter of the gizmo, Dean, you oughta see some of the rice-rockets around here!!

(Okay, I printed your post, now I have to go study it and think some more).
 
The extractor can be flattened into an oval (Ford oval?) section, and pacakged to suit.

I'll look at making two up to fit in my Cortina station wagon. (It's got dual exhasts, just like a wheelbarrow).

I love the idea, but have issues with packaging it. Pipe A maps to pipe A' to do a back to back control test, and I can't see any way of doing it. My goodness, its gotta make a beautiful noise, though!
 
Come on, Dean, talk to my questions! How am I ever gonna become any more than a dumb welder unless you clue me in?

Another question or two: Evidently the vortex rolls itself up over the periphery of the outer cone, becoming a fast-rolling doughnut of exhaust gases. I wonder how, exactly, the exhaust ultimately comes away form the vortex. Among other things, this would tell me if I can make a truncated cone (flat plate on the trailing end) rather than a pointed cone, which is harder to roll and fabricate. Also, IF I am envisioning the rolling vortex correctly, I would think your idea of an oval-shaped megaphone and cone would have a lot of extra resistance to forming and sustaining that vortex . . . .

Now here's another notion. Before I understood (I think) the kind of vortex Coanda was trying to generate, I envisioned something rather different, a swirling vortex that spiraled out through the first half of the cone, in the manner of water draining out of your bathtub. If this were a desireable thing it could be enhanced by "aiming" the little sheetmetal vanes that support the cone inside the megaphone. But IS this desireable? For all I know, the vortex in my bathtub drain SLOWS the flow . . . where are our physics-majors??
 
I don't think it has or needs any swirl. I think it will act similar to a venturi. I feel there will be a low pressure area around the cone just aft of the transition between the inner and outer cones.

I keep getting stuck on the notion that, it takes something to get something. The air flow will create some vacume. The vacume can be measured and used for something, but can it be used to evacuate the source that creates it? I am inclined to think not.

If we add the pressure waves then we might get something. We would be combining the normal pulse tuning with the Coanda effect.

I think the real gain might be to introduce the high speed airflow on the outside also. Picture a couple of over the transom headers with the cones.
The airflow along the outside of the cones might help amplify the vacume.

It would be interesting to run a steadystate test and a pulsing test with smoke to observe the airflow.

Smoke! I am intrigued with the possible sound and the possibility of blowing smoke rings. Big cam, radical idle, add smoke and puff smoke rings.
 
Yeeehoooo. Mysteron exhast system

New%20Captain%20Scarlet009.jpg
 
You must log in or register to reply here.
Back
Top