Tuning a radial

Apr 22, 2011 No Comments by

After reading the latest Engine Clinic column regarding the Fox flat twin flameout problem, I decided to ask you about a Laser V200 four-stroke V-twin that I bought last year.  It has a dual carb setup (each cylinder has its own carb), and during break-in I noticed a tendency for one cylinder to flameout at low throttle.  I tried to tune each carb separately by using a smaller prop and removing the plug from the other cylinder, which may or may not have been the best way to tune it, but I thought it would at least give me a reference between the two cylinders.  When I installed the engine in my airplane I installed a Sullivan dual on-board glow ignitor which has seemed to work pretty well, and I haven’t had any real problems with it for the few times I’ve managed to get out to the flying field (I never get out there as much as I’d like).  So my first question is: would an on-board glow setup have been a valid alternative approach for the Fox flat twin?  (And does my approach with my Laser seem reasonable?)
But my real reason for writing is about the new OS 7 cylinder radial.  It looks like a very impressive piece of machinery, but for that kind of investment I would like to be reasonable certain that it would work well on a large scale model, by which I mean having a reasonable power output and keeping all the cylinders firing.  Based on my experience with the Laser, I can’t see any other way than with an on-board glow setup.  I’m not aware of a 7-plug device on the market, but with a little investigation I think I could figure out the necessary battery capacity to power 7 plugs at once.  The power output, based on the prop and rpm figures from OS, seem to be roughly equivalent to my Zenoah G-62, which would be quite adequate for my intended application (i.e., a big WW1 biplane).
I seem to remember reading that there would be an engine review of the OS radial, but I never saw it.  Did I miss it?  How about a comparison of the various radials out there in the 3 to 4 cubic inch range?  OS had a 5 cylinder 3.0,  Saito has a 5 cylinder 3.25, the German make of 5 and 7 cylinder engines whose name escapes me at the moment, and others like Technopower who seem to have come and gone over the years.  Are these really practical engines for flying or are they best meant to just sit on a collector’s shelf? Thanks for your  opinion! –Jack

Dear Jack,
The only problem with running each cylinder individually is the additional load placed on the running cylinder causes the mixture to run richer than normal. However, this is a good way to determine if each cylinder is developing the same power.

Sure, an onboard ignition system would have helped the Fox twin problem. but just rotating the cylinder base gasket 180° worked well and was a lot cheaper. Incidentally, note in the article that 1800 got printed rather than 180°.

Having not run the new O.S. 7 cylinder radial, I can not comment on its reliability or performance. However, judging by the

FR-5 I reviewed back in the Oct. 86 issue of R/c Modeler it should work fine. McDaniel R/c has an ignition unit available for 7 cylinder engines. www.mcdanielr/c.com

Back in the March 87 issue of R/C Modeler I reviewed the Saito FA-115 radial. Neither a Technopower nor one of the German radials have ever come our way. We requested engines from both companies and never got a reply from the Technopower people.

The Germans just sent us some literature. Needless to say, purchasing these engines would be a bit costly. Something that neither I nor the magazine could afford. Then too, I am no longer doing engine reviews. I stopped doing so when signing on with MAN.

Best regards
Clarence Lee

Clarence Lee, Editors Blogs, Glow

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