Radial engine - RC Groups
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Nov 24, 2012, 09:38 PM
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Radial engine

Building a 1/3 scale Sopwith pup. I would like to puy the new Evalution 77cc radial on this plane.Has anybody used this motor? and are they hard to keep running?
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Nov 26, 2012, 07:05 AM
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DarZeelon's Avatar

The maximum reasonable size for a glow engine is about 10cc...
Running any engine on gasoline uses ~40% of the fuel, which costs about 1/10...

And it is 'Evolution'. This engine is modestly priced, compared to Technopower... It is a novelty.
Nov 27, 2012, 03:38 PM
the great Gassif´er
Not really.... the maximum reasonable cylinder size (if there is such a thing) is 10~15 cc for glow....

There is thermodynamically and mechanically not much difference between 7 single cylinder 11 cc fourstroke engines and one 77 cc 7 cylinder radial (except for the crankcase, crankshaft and conrods of course).

It would be a whole other story if it was concerning a 77 cc 2 cylinder or single cylinder, but the problem is in the physical dimensions, not in the total number of displacement.

So a 77 cc radial might be a very feasible project on glow, and a very thermodynamically challenged project on gas.

Brgds, Bert
Nov 27, 2012, 03:59 PM
Registered User
DarZeelon's Avatar

I was referring to total engine displacement and actual fuel consumption (and cost).

Besides, there are glow engines with ~50cc displacement cylinders; specifically gas engines that some in the U.S.A converted to glow ignition.

Nov 27, 2012, 04:54 PM
the great Gassif´er
I know, and with respect to a 77 cc being not really economical on Methanol you are completely right.... (never meant to contradict that)

But with respect to how small a cylinder unit you can operate on gas, that is a completely different thing.... for an engine to be economical you first need it to be able to run. And the smaller the cylinder units become, the harder it gets to run it on gas....

OP was asking about a 77 cc radial, not a 77 cc single.
Economical or not, methanol might be the best solution still, if OP still prefers a radial instead of an economical but very unscale single cylinder gasser .

these big glow engines, they were done mainly when magneto's were still big and heavy, CDI units not readily availlable, and gassers did not develop really heaps of power like nowadays. Than a glow-conversion gives an instant weight saving of up to 50% of the engine weight and an immediate power boost of 20% (at the cost of a very high fuel bill)

Brgds, Bert
Nov 27, 2012, 05:11 PM
Registered User
earlwb's Avatar
That is sort of a new engine and I think there has been somewhat limited availability with it here in the USA. Siedel had made a number of them before, but I don't think any of them made it into the USA. When I took a look around I didn't see anything but the marketing videos for the engine. But the videos I saw did show the engine being run quite well on a test stand though.

Now there is a guy at our local hobby shop who is putting one of these engines in a large 3D aerobatic plane. But he seems to have stalled on finishing it so far.

DarZeelon, I can agree with a large displacement glow engine can consume glow fuel at a prodigious rate. But if one isn't using full throttle all the time the fuel consumption is a lot more manageable. I do that with a big 30cc glow engine powered plane and it does quite well with a 16 ounce fuel tank like that. But also glow fuel provides a considerable amount of cooling for a glow engine that you don't get using gasoline. So with a big radial engine, the glow fuel could be a benefit in a cowled engine setup on a plane.

One other issue is getting a spark ignition system for a radial engine is a real problem. There just aren't any out there so far. I know some people have been working on radial engine ignition systems that are all electronic (no distributor), but I don't think they are ready for production yet. So the radial engines are mostly limited to glow ignition at this time. Albeit there are a few exceptions where the engine has a distributor built into it for spark ignition.
Nov 28, 2012, 02:35 AM
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DarZeelon's Avatar

The smallest current production gas engine that I know of; is the NGH 9cc.
In the far past, before the advent of the glow-plug, all engines; even as small as 0.5cc, had spark ignition and used gasoline.

The boost in actual output by converting an engine to glow, is 24% (Stoichiometric ratios).
A .52 gas engine makes the same power as a .40 glow; and is virtually the same size and weight; so this is hardly a problem.

Earl, you are right regarding the ignition issue. It is a problem for small multi-cylinder engines...
Nov 28, 2012, 08:49 AM
ARFs Are Me
TomCrump's Avatar
I figure, that if you can afford one of these radials, the cost of fuel is a mute point.

Crashwilson: Many who operate large, multi cylinder glow engines, use onboard glow systems to aid in operational reliabilty. Incomparison to the cost of the engine, these units are inexpensive, and provide piece of mind .

These units have proven to be reliable. http://www.sonictronics.com/xcart/home.php?cat=308
Nov 28, 2012, 12:51 PM
Dieselized User
gkamysz's Avatar
Bert, what are your concerns about gasoline in a small engine?

Nov 28, 2012, 11:41 PM
Registered User

Radial Engine

this is crashwilson calling!!! Thanks all you guys out there who took the time to try and help me out with my questions on the Evalution 77cc Radial.I don't mind spending a few bucks for fuel for that engine if that is the biggest concern.I just want to build this plane as true to scale as possible, and that engine would be the icing on the cake.I just don't want to get into an engine that I have to work on every time I fly it.Again thanks for the replys.
Nov 29, 2012, 09:54 AM
Dieselized User
gkamysz's Avatar
A club member has asked for advice on his, but hasn't finished the airplane yet, so I haven't seen the engine. These engine burn 0-10% nitromethane and 6-8% oil after break in, so the fuel isn't particularly expensive.


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