Author: Joe Wagner
Edition: Model Aviation - 2010/10
Page Numbers: 79,80,82
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The Engine Shop - 2010/10

Evolution .36 CL engine

ONCE IN AWHILE when I receive a new engine to test and report on, it arrives accompanied by accessories. The Evolution .36 I recently acquired from Hangar 9 did, but those “accessories” turned out to be a complete kit for an ARF CL model—including handle and lines.

Accessories and extras

  • Two mufflers are provided:
  • A conventional type with a large expansion chamber.
  • A much smaller "tongue-type" muffler (so called because it resembles a rectangular tongue protruding from the exhaust port).
  • Three venturis (different lengths and bore sizes) to adapt the engine to a range of model sizes. By interchanging them the user can vary speed and power output. The longest venturi has the smallest ID and produces the lowest rpm; it was installed on the sample I received.
  • Other extras: spinner nut, three-blade propeller, complete mounting hardware, and the various Allen wrenches needed for engine and airframe assembly.
  • Notably absent: operating instructions for the .36 (odd, since Evolution engines have several special features that deserve user attention).

Break‑in and preset needle valve

  • Evolution engines require no break-in. The Evolution .46 User Guide states, "Every Evolution engine has been test run and adjusted at the factory, and is ready to fly with no adjustments or break-in required."
  • The Evolution .36 has preset needle valves with "stops" that limit needle rotation to just less than one full turn.
  • The factory-supplied needle setting on my .36 was correct for my conditions (altitude, ambient temperature) and the fuel I used: 15% nitro, 22% total lube (half castor, half synthetic). High-altitude or other environments may require changing the factory needle setting; the .46 User Guide explains how to do this, and similar guidance should be supplied for the .36 because its performance varies with venturi choice.

Bench testing and running characteristics

  • I bench-tested the engine before and after running six tanks of fuel. For the .46, top speed and lowest reliable idle rpm remained essentially the same through the test. For the .36:
  • It hand-started remarkably easily cold but showed some balkiness on hot restarts.
  • Six tanks of fuel produced no measurable change in performance.
  • Muffler and venturi behavior:
  • The tongue-type muffler measured several dBA quieter than the conventional muffler.
  • With the long, small-bore venturi installed, the Evolution .36 ran reliably with either suction fuel feed or muffler pressure.
  • The shortest, largest-throat venturi requires muffler pressure for dependable running in CL maneuvers.

Fuel system and refueling modification

  • The PT-19 package uses a plastic "clunk tank" with a two-tube outlet arrangement: one tube to the needle valve nipple and the other to the muffler pressure tap. Clearances between the tank front and the engine's rear-mounted needle assembly are limited, making access for refilling awkward.
  • I removed the tank endcap assembly and installed a third tube through it, adding a short external plastic refill line. To seal the refill line when full I pinch it and insert a short aluminum roofing nail as a plug.

Propeller and performance

  • The supplied three-blade propeller runs smoothly and makes the engine easy to hand-start. With the medium venturi installed the three-blade spins a trifle less than 10,000 rpm and appears to be nearly 10 mm (just under 4 inches) in pitch.
  • With that propeller and venturi the model's top speed would be under 40 mph. For better speed in a big CL model like the PT-19 I recommend a Graupner 10 x 5½ two-blade propeller and the Evolution's largest-bore venturi; that combination should yield a flight speed near 60 mph—approximately a 5-second level lap time on the provided control lines. I was unable to perform that test.

PT-19 profile model — construction and flight impressions

  • The profile PT-19 is large (4½-foot span, 520 sq. in. wing area), relatively lightweight at 41 ounces ready to fly, and well built; most parts fit well. Building instructions are copiously illustrated and reasonably complete, though a few places are ambiguous.
  • The PT-19 uses a thick, round-nosed airfoil (as on my Veco designs of the 1950s) and includes George Aldrich's "fixed wing flaps" as used on his Flite Streak and Peacemaker CL aerobatics models.
  • Features I questioned on the stock model:
  • No rudder offset.
  • No right thrust.
  • Only 1/2 ounce of tip weight.
  • I kept the first two stock settings but increased tip weight to a full ounce (my CL experience suggests it's better to have too much tip weight than too little).
  • Flight test: In a 5–7 mph wind the model showed minimal line tension; I couldn't backtrack fast enough to keep the lines taut on the upwind side. Flying over concrete, the lines slackened, the airplane dove in, and further flying that day was impossible. When I repair the PT-19 I will add several degrees of rudder and engine offset and likely increase outboard tip weight.

Fuel tanks and tubing

  • In a recent column I mentioned a small metal fuel tank I modified by replacing brass fuel tubes with aluminum tubes attached with J.B. Weld. Reader Davis Bolin asked where I bought such tanks. I still have old metal tanks from years past, but Brodak Manufacturing now sells almost the full line of Perfect- and Taff-brand fuel tanks. Their site lists them under Fuel -> Fuel Tank (the navigation can be a little tricky).
  • Tygon tubing:
  • Tygon is unaffected by model engine fuel but tends to stiffen with sunlight exposure.
  • Tygon is stiffer than silicone and generally unsuitable for clunk tubing; thinner-walled Tygon introduced years ago kinked easily.
  • "Doctor Diesel" (Eric Clutton) found a source for Tygon that is both flexible and kink-resistant. I bought some and have used it as replacement tubing in Cox reed-valve engines (Black Widow, Babe Bee). Stock tubing in those engines loses elasticity from glow fuel exposure, allowing air leaks at the needle nipple; the improved Tygon solves that problem.

Sources

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