The Engine Shop
Joe Wagner | [email protected]
There's a new Double Star in the heavens
AN UNUSUAL NEW model engine is on the market: the Double Star .54. Specially designed for powering competition CL Precision Aerobatics (Stunt) airplanes, this power plant is being made in "limited edition" numbers. Tom Dixon (Box 671166, Marietta GA 30066; Tel.: [770] 592-3279; Web site: http://members.tripod.com/~TomDixon/tomdixon.htm) is the exclusive US importer of this made-in-Moldova engine.
The Double Star is expensive! However, its $350 price tag seems reasonable, and not just because of its limited availability. (Only 50 are being made in 2005.) This new .54 is supplied with five interchangeable venturis. Each has a different intake-passage diameter. Exchanging these permits accurate fine-tuning for various atmospheric conditions.
This Double Star's package includes a multipage instruction manual that Tom Dixon wrote. It describes in detail the engine-tuning techniques that top-level competition Stunt fliers use and tells how to determine which of the five venturis should be used. (You might want to use one on a cool morning and change to another when the weather warms up in the afternoon.) There are also specific fuel, glow plug, head shim, and propeller recommendations.
The Double Star .54 comes with two mufflers, one of which is the common expansion sort. The other is a much smaller "tongue type," for use when the expansion muffler would be too bulky for use on your model. Extra O-rings, head shims, and a spare glow plug are included.
This engine needs no break-in! According to Tom, "... with AAC [aluminum-aluminum chrome] construction, bench running does not simulate the loads and temperatures this engine will see in flight. While bench running doesn't hurt anything, it really provides no benefits either. It's just a waste of time and fuel."
The Double Star weighs less than 10 ounces with its larger muffler. That light weight is owed to its mostly aluminum construction. Only the shaft, double ball bearings, and "hardware" are steel. A scaled-down-to-.40-displacement version of this engine (which should be available by the time you read this) weighs only 7 ounces with a "tongue" muffler attached.
One unusual non-feature of the Double Star is its lack of a fancy, multicolor package.
"With such small numbers being produced, it's not economical to have boxes specially designed and manufactured for this use," said Tom. "Also, since these engines are not destined to sit on hobby shop shelves, 'artistic packaging' isn't really necessary or useful."
There seems to be quite a number of miniature-engine enthusiasts these days with only minor interest in flying with model power plants. Many of these people are collectors, but others enjoy the challenge of making their own engines the most.
Doing that used to be popular decades ago, when most American high schools had metalworking shops and encouraged students to work on individual projects such as model engines.
(Also included in this column:
- How to build your own model engines
- How to make a quick-disconnect adapter for lighting 1/2A glow plugs)
(The famous Morton M-5 started out as a school metal-shop project.)
Interest in personally made model engines declined greatly along with the staggering reduction in school metalworking classes since 1950. (There used to be more than 10,000; now fewer than 700 exist.)
However, today's growing availability of reasonably priced precision metal lathes and milling machines—from mail-order dealers such as Grizzly and Smithy—has brought home-constructed model engines back from near-oblivion.
Approaches to home-building miniature engines vary widely. Some hobbyists use components from commercial engines for hard-to-make parts such as cylinders and pistons. I handled an impressive example of that last month at a Little Rock, Arkansas, model-airplane meet. It was a five-cylinder radial of unique design. Builder Ralph Barnette (Coldwater MS) used five Webra .40 cylinders, pistons, and heads. That makes its displacement 2.0 cu. in.
Yes, it's a two-stroke engine! Because of that, the five moving pistons don't produce pressure or vacuum within their crankcase while the engine runs, as other two-strokers do. Instead, a vane pump at the rear, driven by the crankshaft, does the job of supplying the fuel/air mixture.
This ingenious project weighs 3 pounds, 9 ounces, and turns an 18 x 6 propeller at approximately 7,500 rpm. Ralph has it installed in an 80-inch-wingspan Balsa USA Fokker Eindecker. He says it runs roughly six minutes on an 8-ounce fuel tank,—but I didn't find out whether or not that was at full throttle.
If you would like to try this aspect of model engines, a superb place to get further information is Roger P. Schroeder's online "booklet" (spiral binding and all) Building A Model Airplane Engine That Runs. It is posted at http://archive.ctsnet.edu.au/~BDU/staff/nor/rcsr/build.html.
The booklet, and Roger's online catalog (which you can access from the Web site), tells a novice almost everything needed to make a start. For those without a computer, Roger can be reached at 4111 W. 98th St., Overland Park KS 66207; Tel.: (913) 648-4265.
He also sells drawings and casting kits for a variety of do-it-yourself model power plants. One of these, which is specially designed for beginners, is the "Simple Single" .049. This glow engine uses a Cox cylinder, piston, and glow head. A highly detailed set of CAD drawings and instructions covers everything a novice engine builder needs to know to construct one.
Another attractive and sweet-running project, using Cox pistons and cylinders, is the Schroeder Twin. An opposed-cylinder design, it's the smallest internal-combustion twin I know of, at .040 displacement. It uses Cox Pee Wee components and a crankcase and three-piece crankshaft that you machine from bar stock.
Roger's casting kits include several antique engines such as the original Brown, a reduced-size (.19) version of the famous Brown Junior, Irwin Ohlsson's first engine design, and the Lindberg Hornet. There are diesels, spark-ignition types, and glows—14 engines in all. Prices range from $11 (for the .040 Twin's drawings and instructions) to $33.50 for the .104 "Midget Gas Engine" complete casting kit.
I almost forgot to mention another valuable and interesting resource for home-workshop model-engine makers: the Motor Boys Plan Book, available from AMA (catalog number 3148) and priced at $34.35 postpaid. Several casting kits that Roger Schroeder sells require the use of this book for the machining drawings.
Another source for do-it-yourself model-engine casting kits is George Genevro, at 1955 Dallas Hwy NW #517, Salem OR 97304; Tel.: (503) 363-5032. He sells a complete set of drawings, castings, and bar-stock materials for his Titan .60 engine for $44 postpaid. This is far from a beginner's project, but when properly completed results in a sturdy, well-designed, reliable-running power plant.
The Titan was originally intended for single-speed operation, mainly for CL flying. However, it's easy to adapt to use a commercially available RC carburetor assembly, such as one of the larger Perry, Fox, O.S., or SuperTigres.
As mentioned in the previous column, lately I had been rebuilding some 1950s-era 1/2A engines for me and my friends to use at this year's Nats. But none of these little power plants are compatible with today's Ni-Cd "glow lighters." That's because their plugs nestle far down into the heads. In trying to figure out some sort of quick-disconnect adapter for lighting these 1/2A glow plugs, it dawned on me that the venerable Cox glow-head clip will work for that. However, I stopped using stock Cox glow-head clips years ago because the way they're wired often results in high-resistance problems and difficult starting. Instead, I rework them. Here's how.
Carefully slit through one side of the yellow plastic "handle," then spread the plastic enough to let you remove the two beryllium-copper contact arms. Pull their wires free and throw those away; they're too small for the amperage they need to carry. Scour or scrub the contact arms with a wire brush until they gleam brightly all over.
Take a length of "lamp cord," and solder each conductor firmly to one of the contact arms, preferably in the same area where the original wires were crimped. Put the contact arms back in the yellow plastic "handle," and bundle everything back together with a length of shrink tubing.
For "powering" the reworked clip, I've stolen a method from my friend Don Garry (Cocoa FL). He uses a 3-D-cell battery holder from RadioShack and rewires it to hook up all three cells in parallel. That provides long-lasting power for lighting glow plugs and glow heads—and no recharging is needed. You merely replace the D alkalines whenever necessary.
Using a Cox-type glow clip requires that you take precautions, regardless of how it's powered. Accidental short circuits at the "business end" can happen easily. I think I'll revise my three-cell battery holder by putting it inside one of RadioShack's plastic boxes and add a switch to that. Accidents can happen; guess how I know. MA
Transcribed from original scans by AI. Minor OCR errors may remain.
