Author: Joe Wagner
Edition: Model Aviation - 2010/12
Page Numbers: 97,98,99
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The Engine Shop - 2010/12

Joe Wagner | [email protected]

Brodak Manufacturing: two decades of CL support

For two decades Brodak Manufacturing has been the mainspring of U.S. CL model building and flying activity. The company started in 1991 with aircraft kits and supplies, and in recent years it has begun carrying engines for CL use.

This line of power plants includes 19 types, five for RC, with even more to come. Seven engines bear the Brodak name; they range in size from .049 through .40—and one of the .049s is an RC version with a precision barrel-type carburetor.

Brodak’s 1/2A engines differ from earlier manufacturers (e.g., Cox and Wasp) in several important ways:

  • They are more ruggedly constructed to better withstand “unplanned landings.”
  • They are designed to run well on lower-nitro fuel than the 25% and higher required by other 1/2As.
  • They use standard glow plugs.

The Mark I .049 and .061 come with mufflers. The main benefit is attenuation of the annoying high-frequency note from small-model engine exhaust. The Brodak Mk I .049, complete with its muffler, weighs a mere 1/10 ounce more than a Cox Killer Bee—and puts out the same power.

The .15 and .40 Brodaks

The new .15 (soon to be released in an RC version) appears to be scaled down from the older and popular Brodak .25. I haven’t flown my .15 yet, but I have no doubt it will make an ideal power plant for a Squaw (one of the well-known CL Precision Aerobatics, or Stunt, models I designed for Veco in the early 1950s). The Squaw kit called for a .19 engine; Brodak’s new .15 puts out nearly as much power as the 1951 K&B .19 in my original design prototype—and I considered that model somewhat overpowered.

One key criterion for CL Stunt maneuvering is to keep as close to a constant flying speed as possible. We want just enough flight velocity to keep the lines taut at all times, even when flying in the wind. Too high a flying speed translates to excessive Gs in loops and pullups, which can cause stalling and erratic maneuvers.

Maintaining a near-constant flight speed calls for large-diameter, low-pitch propellers. Stunt fliers never tune their engines for maximum shriek: we set our needles rich, and our models often leave a smoke trail behind them as they pirouette through the sky.

The .40 is the largest of the Brodak lot (so far). Mine has always been a highly reliable performer. It’s in a 600-square-inch flapped Profile Stunt model I designed. Although I’ve made a few changes to that airplane over the years to check their effects on maneuvering, one thing I’ve never needed to alter has been the engine.

Intake design and Aviastar engines

A noticeable feature of the .15 through .40 Brodak power plants is their tall intakes. These provide two advantages: improved power output and increased fuel suction at the spraybar. This results from the momentum of the moving column of intake air, which compensates somewhat for the pulsating flow into the engine caused by the intake port’s continual opening and closing.

I’ve been adding intake extensions to earlier CL engines for years. I’m happy that with Brodak’s engines I don’t need to go to that trouble anymore—particularly with the Aviastar engines the company markets.

Aviastars (Chinese-made) have the tallest intakes of any CL engines on today’s market. They are ABC (aluminum-brass-chrome) designs, with the typical “TDC pinch” when new. After break-in my Aviastars turned out to be easy to hand-start. Their massive straight-through-flow mufflers do an excellent job of decreasing exhaust sound output.

Available Aviastar displacements:

  • .46
  • .53
  • .61

Saito four-strokes for CL and RC

Brodak also carries eight of Saito’s four-strokes, with displacements of .40, .56, .62, and .72. Half of the eight are CL power plants without throttles; the other four are RC types.

Several months ago I tested the three largest Saito CL four-strokes to see what advantages (if any) would come from using a heavier, more expensive, and more complex power plant in my models. Until recently, CL airplanes have almost invariably been powered by two-strokes—so why change?

In-flight comparisons between two similar CL Stunters showed little difference in performance between my Brodak .40-powered Shrike and my much-modified ARF Brodak Cardinal with a Saito .56 in its nose. The Cardinal weighs 5 ounces more than the Shrike. Yet flown on the same lines, alternately on the same day, the models performed almost identically.

A slight difference in maneuverability I noticed was possibly caused by the control setup. The ARF Cardinal has its leadouts reversed from my usual practice of having the “up” line at the rear. I have to admit the Saito-powered Cardinal flew a tad better.

Spectators did notice one significant difference: sound. The four-stroke was both significantly quieter in flight and lower in tone.

Since the two airplanes had essentially the same lap times, I’d say the Saito .56 had a little more power than the Brodak. The Cardinal weighs 11% more than the Shrike, yet both models have the same wing area and general configuration. Therefore, the Saito produced more power in flight at the same speed as its lighter companion.

Castor oil and modern synthetics

I continue to receive readers’ inquiries about model engine fuels. One topic that comes up repeatedly is castor oil.

Although it has been used in high-performance internal-combustion engines for almost a century, many modelers seem to think it’s obsolete now, having been surpassed by modern synthetic lubricants. Not so. It’s true that synthetics produce a less messy exhaust and they won’t congeal inside an engine that hasn’t been used for a while. However, the virtues of castor oil make up for its two less-than-ideal characteristics.

Castor oil is uncannily adherent to metal surfaces, even at high temperatures. Its high film strength doesn’t decline as it gets hot. It doesn’t burn; in fact, it absorbs heat in the combustion chamber, acting somewhat like the “water injection” used in World War II fighter aircraft engines. Castor oil also prevents rust.

The “gumminess” in an engine that has been flown with castor-lubed fuel and then left unused for a while is not caused by “gum.” Gum comes from trees, and there’s none of it in the beans from which castor oil is cold-pressed. “Degummed” castor oil is merely an advertising slogan; it’s as factually meaningless as “decaffeinated bananas.”

What causes the stickiness is oxidation. Castor oil is akin to linseed oil: exposure to heat and air slowly causes it to oxidize and thicken. Both will eventually form a solid film—a well-known property of linseed oil responsible for its use in oil paints for centuries.

To avoid that effect in model engines (other than diesels), copiously inject after-run oil (ARO) into engines if you don't expect to use them again soon.

ARO in diesels will prevent them from running. But model diesel fuel is a good solvent for congealed castor oil, and I’ve never had difficulty loosening a stuck diesel by using its fuel and a hot-air gun to free its moving parts.

Castor oil has a long and honorable history of use in high-performance internal-combustion engines. It was the only lubricant that worked in the rotary radials that powered World War I fighters such as the Sopwith Camel, the French Nieuport biplanes, and the Fokker triplane. Their engines produced more power for their weight than in-line water-cooled types, but they ran hotter and needed the utmost lubrication—castor oil provided just that. It was also the lubricant of choice in the famous Offenhauser-powered racecars of the 1930s and ’40s.

Mechanics would quickly drain the oil from race engines after a run and rinse them internally with solvents to prevent valve stickiness and other problems from castor’s tendency to congeal. For the next day’s race they would fill the Offenhauser’s oil sumps with castor oil again.

You can’t surpass castor oil’s lubricating qualities.

MA

Sources

Transcribed from original scans by AI. Minor OCR errors may remain.