Japanman

To try to cut down the noise a bit, keep more oil off the (future) plane, and because it is fun, I made a mousse can for my BigMig/ norvel.

The mousse can is from a marker, and is 23mm diameter (probably could be smaller) and could be a bit longer. If I can find another, I`ll try it, in the mean time, this one works pretty well.

With the norvel, the hard bit is making a heder pipe: In the past I have tried tapping the crankcase directly, after filing off the lip. That failed and the holes for the mounting screws have to be so close together making the heder with a 90deg turn is a pain.
This time I made a tapped L shaped plate from 2024, and used the cylinder bolts to hold it from underneath, as well as judiciously applied JB weld.
It seems a bit stronger and allows the heder to be braised on without worrying about the steek'in mounting screws being in the way.

I screwed up and made it too short for big props, but as I made it runs well with the apc 5x3 (25.8K- +300rpm? ) and a glass 5x2.8 (29K +1K)

When I have it on the plane I`ll go for a heder extension for bigger props. I might be able to find a new pen or something to try before then anyway.

I am pretty happy so far. [sm=tongue_smile.gif]

J.M

BMatthews

Nice work!

I remember looking at alloy felt markers at one point and thinking of this sort of thing. Then I got side tracked by something shiney and never got back to it.

Mr Cox

Looks good.
I've made a few out off tiny spray cans and felt pen markers myself, tried to get something similar to the MVVS minipipes. End result is something with lower resistance than stock muffler but the preformance is still below an open exhaust.

Is your's working like a tuned pipe so that it give higher revs than an open exhaust?

combatpigg

My Feedback: (3)

The interesting thing is knowing that some guys are capable of attaching a paper thin marking pen body to a pipe without turning it into a molten blob.
The .40 sized MCP shown at the spadtothebone site is a modern marvel. It uses run of the mill junk and creates a 1300 [10%] boost over the stock muffler. I don't remember what the improvement is over open exhaust, though. It has an inner chamber made from aluminum tubing that forces the gas to travel the full distance, then the gas exits the inner tube and has to doubleback the full distance of the outer chamber of the moussecan before exiting a single hole towards the front of the can. This muffler improves throttle response [torque] with a big 3D prop.

DeviousDave

Mr Cox, did you tune the length of the header pipe? The MVVS pipes are "magic mufflers", basically a 1/4 wave pipe with a can around it.

Mr Cox

Hrmm, I have been cheating and simply used JB weld for the ones I've made.
I didn't tune the header length and have had too short headers (didn't want to add too much weight), I guess the length should be similar to the MVVS one but with a smaller diameter.
The only thing I tuned was the distance from the inner tube to the "stinger", turned out the shorter the better. Implying that there is no use for the can I guess when the header is that short.

Japanman

Mr Cox: it is all in the tuning I think. Your pipe looks really short: check my calcs and you`ll see why.

In all my playing with pipes I have found that by far the most important thing is the total length (to the end of the can with the stinger/outlet pipe.)
Assuming the exhaust timing is about the same as a norvel 061 (the CS/ N074/ AP /new brodak should be close enough)

These are about the lengths you want, measured from the piston to the end of the cannister:

20K (6x3 props?) 25cm
25K (5x3 props?) 21cm
30K (4X3 props [>:] ) 16cm

Ideally, the heder should be about 1/3 of the total length, but it is not critical, so don`t let it put you off, just try it and if the total length is right, it will deliver [8D]

Also, there is a fudge factor of about 3K with the numbers I have given, so try them with two or three props if you see no result at first.

J.M

DeviousDave

If it's of any value to you, the 1/4 wave pipe used on the Shuriken was 3.0" from the center of the glow plug, and they ran in the same rpm range your engine is now with the glass prop.

Mr Cox

1/4 wave and 3" sounds good. I haven't looked much into the distances but can also measure the length of the MVVS for instance. Another thing to tune is the size of the stinger relative to the header, I only went with what looked about right to me...

25cm and 25000rpm sounds a bit like a "regular" 1/2 wave tuned pipe?

Japanman

I suspect when you start to operate in harmonics, (1/2 wave/ 1/4 wave) it starts to get more difficult to get a positive effect, because you depend on a body wave in the pipe maintaining it's power during reflection against something (the piston at tdc? or maybe in the body of the canister) and then working next time around. So the shapes of the canister etc start to get more critical.
That said I bet there are some cool tricks out there. I was looking at your muffler MR Cox, and I like the way the heder goes right in to almost the other side: It makes me wonder if the pressure wave exits the heder inside the canister and immediately reflects, and travels up the canister towards the engine, then back and some of it up the heder. This makes the whole thing nice and short.

Guys have been thinking about this since before I was born!




J.M

DeviousDave

Walter Kaden was the first to use a tuned pipe on a two stroke as far as I know.

combatpigg

My Feedback: (3)

Whoever it was......

probably crapped his pants the first time the engine hit the sweet spot.....

probably didn't make a penny off it before some rodent cashed in on it ahead of him.

I think MJD has a sliding trombone header meant for fine tuning a large model engine system. I've always thought that would be clever to have a way to quickly cob together test pipes. I think wax molds for FG cloth and high temp resin would be a way to do that.

DeviousDave

I was wrong, but he finished devloping them-the famous part of the story was when his rider defected from Communism at a race, landing at Suzuki and sharing their secrets.

Walter Kaaden
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Walter Kaaden (1 September 1919 – 3 March 1996) was a German engineer who improved the performance of two-stroke engines by understanding the role of resonance waves in the exhaust system. Working for the MZ Motorrad- und Zweiradwerk part of the Industrieverband Fahrzeugbau (IFA), he laid the foundations of the modern two-stroke engine. His understanding of gas flow and resonance enabled him to make the first engine to achieve 200BHP/litre with his 1961 125cc racer[1]. His motorcycle engines were ridden to 13 Grand Prix victories and a further 105 podium finishes between 1955 and 1976[2].

Walter Kaaden was born in Pobershau, Saxony, Germany. His father worked as chauffeur to the sales manager at the DKW factory. At eight years old he attended the opening of the Nürburgring racing circuit, a formative event to which he later attributed his enthusiasm for engineering[2].

Kaaden studied at the Technical Academy in Chemnitz. He then worked at the Henschel aircraft factory at Berlin-Schoenefeld under Professor Herbert Wagner who invented the HS 293 radio-guided rocket-propelled missile. At the end of the war he was interned by the Americans before eventually returning to Zschopau.

In 1953, the IFA asked Kaaden to take over the racing department from Kurt Kampf but he soon found his factory IFA racers were being outclassed by Bernhard Petruschke riding the private ZPH (Zimmermann-Petruschke-Henkel) machine.

Engineer Daniel Zimmermann based his ZPH engine on the pre-war DKW which he heavily modified by adding a disc valve that allowed asymmetric port timing with a longer duration inlet phase. Zimmermann also used a new crankshaft providing 'square' bore and stroke dimensions (54mm x 54mm) that used stuffing rings to boost the primary compression ratio. However, the East German government didn't like the competition between the two East Germans and persuaded Zimmermann to reveal his engine's secrets to Kaaden. The result was the 1953 IFA racer.

Working with extremely limited resources, Kaaden began to develop the expansion chambers invented by Erich Wolf that had first appeared on his 1951 DKW racers. In 1952 Kurt Kampf copied this DKW innovation and fitted them on the IFA racers [3]. Kaaden used an oscilloscope to examine the resonance in the exhaust system and devised profiles to maximise the engine's efficiency. The net result of this development programme was that by 1954, Kaaden's two stroke 125cc racing engine was producing 13 bhp, more than 100 bhp/litre. This engine was further developed to produce 25 bhp at 10,800rev/min[4].

Japanman

I got to admit it , i love two-strokes and tuned pipes.
Lately I have been truly happy just running engines in my garage: I have two young kids, and this has reduced my time a bit, but really I do like these noisy little beasts (the engines).

I read a book about Walter Kaaden, and when he was working on improving the resonance right through the engine, he once had a disc valve engine suffer a disc seizure, with the disc seizing wide open. The amazing thing was the engine did not stop, or lose any power, it kept running making the same power. That is cool bananas if you ask me.

Mr Cox, i was thinking, maybe you meant you wondered why I don`t just run a full monty pipe? I have had problems with norvels when running a full form pipe: and I think now it is because of the (relatively) low silicon piston (I think) norvel used. I found when they came up on the pipe, you would get a mysterious and sudden catastrophic loss in rpms. with the hard anodised cyclinder of the 074 the compression was getting toasted. What I think happened was the piston would rapidly heat, expand and get really tight in the bore, putting the brakes on big time. Hence going to a more crude pipe with a softer hit.

I made a new longer and higher volume cannister pipe to try. i also found a low suction pipe in my box of bits I`ll let rip when i get the engine on the plane. i need to fly something!

J.M

Mr Cox

Yes, engines are fun and perhaps the main reason for being in this hobby to me.

The title of the thread made me think of the folded pipes rather than a full pipe, so thanks for clarifying that.
A little odd that they don't like full pipes, AAC engine are fine with it as far as I know so maybe there is something different with the anodizing then.

combatpigg

My Feedback: (3)

JM, I don't know if the Norvels are up to the task of running any harder than they can on their own, but there's a couple things I've learned since frying a few G&Zs.
First, is to set the compression as low as possible to just run. Like the way you approach tuning a diesel. You can't say you've tried everything until you've backed the compression off to the point where it won't run, then carefully increase until it just runs.

Too much prop for the system design is just like being over compressed, same symptoms, same result. Minute changes in blade size can make a huge difference at 600-700 beats per second.

If the fuel system isn't capable of ramping up to meet demand when the demand almost instantaneously doubles....a backplate system might not be able to produce the required change, even though it provides a surplus when you don't need it. A well placed tap in the exhaust system is where the true representation of demand is seen. It still would be nice to have inflight mixture control / shut-off capability.

If the system design is too reflective, it will heat the lower end of the engine....[according to what I've read, the concept is kind of abstract for me]. I guess the factors would be system too short, closing ramp angle to steep, stinger too long or narrow.

If everything is working right in a speed application, the launch is made at the forward edge of staging on the pipe and the first dive provides just enough extra push to get the engine able to handle the over rich mixture you launched it with...then you should witness up to a 25% jump in rpm.

You figure in this day and age, a Cyclon with open exhaust can take a usable prop [not some irrelevant 80 mph 5x2 prop] and almost hit 40,000 rpm......so for any piped engine to earn it's keep with the added weight, complexity, etc., you can see where the bar has been already set.

Japanman

CP. what you say about an overly strong reflection by the pipe is interesting. Also Cyclons are simply amazing- I gotta say a free flight timed GZ will run almost the same as a cyclon, depending on what the underlying "personality" of your cyclon and GZ are. But as of the last production run of GZ`s it may be a bit like re-working a volkswagon to run with a porshe....
(just a word of warning: the GZ`s I got direct from the factory require re-work so don`t think yours will run right out of the box. they also suffer from P/C quality issues so as much as i like them, I can`t recommend them for the average guy.)
i really wish GZ would get their act together with these engines: they are close to a really hot product.

Mr Cox, I don`t think it is the AAc nature of the engines, more the low silicon content of the piston and sleeve. From what I have heard, normal AAC engines have sleeves made of 30%silicon to keep the expansion down.
I can only guess, but it starts to get very hard to hard anodise aluminium with a high silicon content, and given the way norvels lose compression when they overheat, I think the cyclinder is low silicon/high expansion. To match that you want to run a piston with a slightly higher silicon content to have a slightly lower expansion co effcient, so it does not sieze if it overheats, as the piston runs hotter than the sleeve.
J.M

Toad

Back when I was playing around with making a few sleeves, I was told by several builders that they use 13% (4032) aluminum for the sleeves (chromed of course) and the std 25% si content stuff for the pistons with 30% being better.
the combo works well. I couldn't get the chrome right, I scraped a bunch of sleeves, and got discouraged about chroming.
That job is really tricky. Too many harsh chemicals involved with trying to chrome aluminum. I gave up on that.
The idea is the lower si content sleeve will expand a bit more than the piston, the piston gets hotter anyway, I'm pretty sure the combo matches in expansion at running temps.
I'm amazed the chrome don't peel off the softer sub-strate material during the expansion anyway. It must be Magic.

Japanman

Toad:
Thanks for the info. I think I got the 30% silicon number from a fora or cyclon 15? But now i think about it i am not at all sure of the figure.
You and me both.

J.M

AndyW

My Feedback: (1)

I recall even OS having problems with chrome peeling. I think too, that their solution was first a nickle plate with chrome on top of that. Or that might be stock practice. Electroless nickle plating does so evenly all over, even in blind holes. Chrome needs a final honing to size.

I've been thinking of getting another nickle plating kit from Caswell. I had tried plating cranks but the plating peeled easily. Where I went wrong was in not getting the part completely clean. I'd use dish soap and the part would come out all shiny with beads of water on it. From there, it would go immediately into the plating bath. When you wash your car, you get beads of water on it and it really looks good and clean. But beading is a sign that there's an oily residue. Wash the part several times and when the water WON'T bead, your part is truly clean. I think it's called the water break test.

For years I was afraid to modify the porting in sleeves in fear of compromising the integrity of the plating. Then I ran into threads on pocket bikes and how the guys were modifying them to insane levels of power. Part of that was grinding at the ports with no concern over peeling. So I tried that on an ABC sleeve and it worked just fine. Tons of bench running with no problems at all. This was on an old Royal .25 sleeve which was stuffed into a Norvel .15

Wish they would invent an electroless chrome plate. []

Japanman

I have made a plane.... and just for good measure I made another pipe to try. This one is potentially like yours, Mr Cox: the heder fits right down inside. I did a bit of a search around online and found that one camp of mousse can makers recomend running the heder right into the canister, but it runs as a full wave pipe but at nearly half the length.
I decided to make one so that it could be run as a "normal" full wave pipe, but then once I verify it goes, i can slide in the heder on the fly and see what happens.
Should be fun.

J.M

PS heres an OS muffler that uses the same kind of concept to make a more compact, and probably easy to tune pipe:

Japanman

Cool, it works!

I ran it on the bench on a very hot and humid day, four shims in the head.

I had a piece of silicon tube sealing the cannister/heder joint so i could slide it in like a trombone. What happened was, it ran best when like a pipe: the heder just in the cannister, but only by 200rpms.
As I slid the cannister up the heder, the revs dropped off (fell off the pipe) but when the heder was nearly all the way in, past the outlet of the stinger (the stinger is brazed in at half it`s length) the exhaust note changed and it came up on the pipe again.

I think the cannister is just a little narrow, and maybe if I made it maybe 20% bigger, I could make the stinger bigger and get a few more rpms, and cooler engine temps. but the I would need to make another one..
As it is, it is almost 500 rpms up on stock with the apc 5x3 at just under 26K, and I think the pipe is a bit short, so it should unload in the air a lot.

Mr cox, what are the dimensions of your pipe? Here are the dimensions of this one: the cannister is 18mm diameter and 75mm long and the heder is 90mm. the stinger has a 4mm id and is about 25mm long. the heder is 9mm id.

J.M

combatpigg

My Feedback: (3)

Nice work JM!

One thing that impressed me last summer was seeing for myself that cool running and huge power are both possible with tuned exhaust. If the combustion chamber tends to build up dry soot quickly, then you've got it dialed in just right. Even with a fixed size exhaust system, you have an infinite amount of possible compression, exhaust timing, nitro% and prop load combos to try.

Japanman

Today I flew my plane with the mousse can on it: The plane is thrown together from junk i had kicking around: an old wing, an some fishing rod parts.
It flew really well though, and the mousse can just topped it off: highly recommended to anyone. the plane had low wing area and was fairly light (10oz wet) but all the same if flew well with the apc 5x3 which really unloaded in the air from over 25.5K on the ground. I have done some more mods to my engine, so it is not a stock Bigmig anymore: but the mods are not hugely significant.
Really i have to say it was the mcp that was ringing the bell [8D] I ran 4 shims and 15% nitro, and it would come up on the pipe with all of these props and was running over 25k with any of them: apc 4.2x4, 5x3, 6x2. cox rubber ducky 5x3. The cox surprised me, as it seemed to bog the engine down on the test stand, but in the air, it unloaded a lot and as soon as it was up on the pipe it never lost it. I tried some glass fiber props but they seemed to be trying to take the engine where it did not want to go: it didn`t fly slower, just not faster either for a lot more rpms. The apc 5x3 seemed the best prop, though with some streamlining work i think more pitch might help. but even with the 4.2x4 it seemed to have unlimited vertical: I was doing humungous loops. i think it was seeing about 70MPH in most orientations.

i could not say enough good things about how the engine ran today.

Stefan

combatpigg

My Feedback: (3)

That's a mighty fine report, JM!

I'll bet it sounds very cool as well.

Does it leave a pretty good vapor trail?