meowy84

This goes out to all the gugus. I was just curious why the Norvels (.049 Norvels even) have so many more cooling find than the Cox engines? I realize the Norvels run higher rpms and so generate more heat but that big a difference? Might it have something to do with the cylinder materials? If I recall steel (as per leaded steel of Cox) conducts heat better than aluminum (as per Norvel)...unless the fins of Norvel's engines are steel as well which looking at mine I think they might be.

Incidentally, what is the reason for the leaded cylinder of the Cox engines? Is it for lubrication sort of like lead in gas used to lubricate the valve guides and seats and when they switched you now have to have hardened seats if you run unleaded fuel in say your musclecar?

DICKEYBIRD

Well, I definitely ain't a gugu, or a guru even but the leaded steel is used for it's great machining qualities. The high speed screw machines used by Cox love the stuff. It's called "Leadloy" I believe.

As far as the thermal qualities, I dunno. [sm=confused.gif] Many refer to having excessive cooling problems with Cox engines but I've never had that problem! I always seem to be trying to solve heating issues. The Norvels I've run seem to thrive on heat and rpms. YMMV

Larry Driskill

Hey Meowy, Good Evening from Texas!

Interesting you should question the cooling area on the Norvels. So have I. When I was running AMEs in CL Combat I sometimes turned some of the fin area off, and those were the pre RevLite cylinders.

I don't have the math handy, but there is a good deal more cooling circumference available per unit of displacement on a 1/2A engine than on a .40.

I have also ran into problems with 1/2As in the winter related to keeping them warm enough to hold a good needle setting. My "Field Expedient Fix" (that became the formal fix) was to wrap a piece of business card around the cylinder and hold it on with a nylon tie. The cold day I first tried it, I discovered keeping the heat up a bit solved my problems and I have used it many times since when the mercury dropped below 50 F.

Here is one of my old 'turned AMEs compared with a RevLite cylinder and a VA with a business card muff (well really a Rotary club card).

ajcoholic

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DB's correct - the reason leaded steels are used is they are the most free cutting steels, and therefore can be machined at high rates of speed with low stresses on the tooling. Since the case hardened stamped steel pistons are so much harder than the leaded steel, it also makes good engine metalurgy (dissimilar hardness works really well for lapped piston/cylinders).

Anyone who has turned leadloy on a lathe knows immediately how awesome it is for machining. And even a few cents machining less time on each engine meant much $$ saved by Cox since the engines were made in such vast quantities.

AJC

CoosBayLumber

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I got explained different some time ago.

The reason for so much of a diameter and fins on Norvel is strength. They want to hold heat distortion down to a minimum, and thus by adding more fins and diameter, and strength, which will keep the cylinder round, and per original taper. As with most aluminums, they expand more than steels as the heat increases. The Norvel uses a tapered cylinder, not a straight one, for as it heats up, it grows to round and grows to non-tapered.


Wm.

meowy84

DickeyBird, LOL, 'gugu=guru' and 'cooling find=cooling fins'....now that I re-read my post I'm surprised you understood what I was talking about. Guess it pays to proof-read...I was just so hyped about my question and I wanted to get it out there so fast that I guess I forgot my grammar/syntax. I can hear my English teacher screaming at me already!

Larry, interesting stuff and theory...any idea what the Cox's and Norvels should run at temperature wise? I have a heat sensor (the type the use on r/c cars to check head temp) and would be very interested to measure the Cox and Norvel in stock form and note the differences. I too have a pre-revlite Norvel .049 and even though it has tons more cooling fins than my Cox reedies it is still absolutely dwarfed by the cooling head of my .061 Revlite (sorta like the difference in your picture).

CoosBayLumber, do you know why the top of the cylinder (where the taper is) would expand more than say the center? I understand that the explosion occurs right at the top of piston travel and so that's the hottest area of the combustion chamber so more expansion at the top than in the middle but then if that's the case then on most other engines which aren't tapered (this is just an assumption) as the Norvel (is the Cox tapered...anyone?) wouldn't you expect the top to expand and some loss of compression to result? Or is it (and this is my theory) that the Norvels are tapered because of the thermal qualities of the aluminum/aluminum construction (as we know aluminum expands more than steel)?

ZAGNUT

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exactly twice as much for an .049 when compared to a .40.
and considering that the average .40 gets around half it's cooling from the intake charge then theoretically the 1/2A engines really don't need cooling fins. in practice i've found that cox cylinders and heads with the fins totally mangled, clogged or missing run just fine.


dave

Japanman

Dave and others- this has got me thinking that quite possibly problems with heat are more a symptom of over advanced ignition from over compression or too 'hot' a plug.

That said I do wonder if part of the reason that norvels are reputed to be ablr to run leaner than other engines and so save fuel is in part because of the aluminium cylinder ( able to conduct heat away from the piston quickly) and the massive finning.
I know in larger, (petrol or gasoline to you N.American guys) motorbike two stroke engines switching from aircooled to water cooled allows for leaner jetting due to the reduced cooling requirements.

I found a small blurb on a high performance 1/2A engine (1cc?) who`s maker claimed a 1500 to 2000 rpm boost simply by switching to hard chromed aluminium liners as apposed to a hard chromed brass one. ( I would assume because of the heat dissapating qualities.)

http://www.gregorie.demon.co.uk/free...f_engines.html

One thing I have been thinking about for a long time is that a water cooled glow engine- I am really talking a high power engine here- may make for quite a bit of power.
I wonder how many people have tried this with a larger engine by swapping heads with a water cooled marine version of the same engine?

Stefan

ZAGNUT

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JM, i agree that heat issues on most small glow engines are ignition related and curable with correct nitro content, compression ratio and plug heat.

water cooling on the big gasoline two-strokes means much more consistent cooling and allows tighter tolerances and higher compression without fear of detonation. look at how powerful the porsche boxers became one they dropped air cooling. on a glow engine it doesn't really help a whole lot because so much of the cooling is already done by the methanol.

a better way to make power in a glow engine is a spark ignition system. compression can be jacked up and the mixture leaned since they no longer affect ignition timing. nitro is also no longer needed for a reliable idle and transition. i have a homebrew ignition that weighs under 1.5 oz. and only needs a single lipo to run, it works great on the little engines but i have yet to play with compression ratios and retuning the pipes. might be a bit heavy for 1/2A but for .09-.15 it is tolerable.


dave

Japanman

Dave- I came to the same conclusion about spark ignition- I wonder how small and light a coil could be made- what are you using?

but dam it, glow is geniously simple!

Stefan

Larry Driskill

Wow, even more pronounced than I expected. Spark, water cooled, or whatever . . . I'm thinkin' it is relatively easy to get into a situation where a 1/2A engine is overcooled.

Larry Driskill

Makes good sense to me. So, I should stop turning the fins off and increase production on the muff assembly line?

Larry Driskill

[quote]ORIGINAL: meowy84



Larry, interesting stuff and theory...any idea what the Cox's and Norvels should run at temperature wise? I have a heat sensor (the type the use on r/c cars to check head temp) and would be very interested to measure the Cox and Norvel in stock form and note the differences. I too have a pre-revlite Norvel .049 and even though it has tons more cooling fins than my Cox reedies it is still absolutely dwarfed by the cooling head of my .061 Revlite (sorta like the difference in your picture).

[quote]


Sorry, I don't know. But some of the folks here will, or at least know where you can find the answer.

meowy84

More , more, more. This is what I like. I really get off on engine theory.

WATER COOLING: In addition to being into planes (a newbie admittedly) I like tinkering with cars and I was thinking of building a water cooler r/c car in the .15-.40 engine size, perhaps using one of those Octura Kool-clamps that they used to make for boat cooling or making my own clamp. Anyways, the clamp isn't the problem. The problem is suplying enough cold water in a plane or car setup. I thought I could build a miniature radiator/cooling system BUT I have a feeling that physics is against us on this one because of the specific heat of water. Bottom line: It works great in full scale (real cars, real bikes) but in scale you might just end up boiling the water out of your miniature cooling system and the air passing over the miniature radiator would not be able to keep up in cooling the water sufficiently. I think that water cooling would work better for model airplanes than for model cars simply because planes are exposed to a higher, cooler air up in the sky but even so the whole system would add weight so that any power advantages obtained with water cooling would be offset by the added weight of a miniature cooling system the engine would have to pull around. I think you'd at least have to have a 20 cc (1.2 cubic inch) engine for the miniature water cooling to be a viable proposition.

But then again I could be wrong on this. LOL Any physicists out there with some data of how much heat a little model 2 stroke puts out and how much water volume would be needed to cool it sufficiently given a given air volume passing over the fins of the cooling system? (don't forget to factor in the heating/cooling properties of the material you build your radiator out of...most likely brass or copper as per full size autos...Copper I believe is the most efficient heat exchanger)

Jim Thomerson

Dave, just run diesel fuel in your glow engine. It runs much leaner and, as near as I could tell on my one test, puts out similar power. Running compression for a 40-size glow engine is pretty close to right for a 40-size diesel. On the other hand glow fuel is cheap and easier to get.

Jim

ZAGNUT

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tried playing with a PAW once and gave up on it, maybe the fuel was just bad but then finding anything fresh would also be a major hassle....and it stinks

JM, the coil i used was rescued from a dead 3W ignition, after carving away the potting compound it is about 13mm diameter by 13mm long and weightless. the DC-DC converter and capacitor take up more room than the coil.

right now i have some similar sized coils that are designed for strobe lights and are cheap and easy to buy, still need to try them out though. another problem is the advance curve, because small glow engines are so diverse in their RPM ranges a single curve won't fit every application like with the big gas engines. trying to come up with something that's user programmable without having a lot of additional circuitry....but my PIC skills still suck

if and when i get everything ironed out i will share the schematics and code and maybe even sell built units if i can keep the price attractive enough.


dave

Japanman

Dave- that sounds great- I`d be really interested in any schematic for making your own (miniature) ignition system. I have a chainsaw engine in N.Z that I made a water cooled head for but the ignition is a major problem- I had to make my own flywheel with magnets included because the stock one was much to big and weak to rev like the new porting wants too. I used a cdi/coil off a homelite if you are familiar with them- but the spark gets weak at about 12K abd causes a misfire.

I`m going to head beack to N.Z over christmas and I plan to get that particular boat out and get it going, so any schematics would be great.

Stefan