Author: Joe Wagner
Edition: Model Aviation - 2009/08
Page Numbers: 66,67,68,69,70
,
,
,
,

Saito’s Four-Stroke CL Engines

by Joe Wagner

When I was offered the opportunity to test Saito's newly issued four-stroke engines—the FA-40CL AAC, FA-56CL, FA-62ACL, and FA-72CL—made specifically for powering CL Precision Aerobatics (Stunt) models, I was skeptical. Two-strokers have been hauling CL models around effectively since 1941: they're lighter, simpler, and less costly than four-stroke engines. So why change?

I found out why. I won't dwell at length on the exquisite yet almost bulletproof packaging Saito uses or the company's thoughtfulness in providing the proper-size Allen wrenches and even a tiny valve-adjustment wrench with each engine. Every Saito package serves as an effective "quality statement."

I read the instruction booklets (two come with each engine) twice. I've been using model-airplane power plants since before World War II—I have decades of experience—and one thing I've learned is to read the instructions. Model engine factories want satisfied customers; their manuals are prepared with that purpose in mind. Yes, directions can contain errors, but they're more helpful than not.

The smaller Saito booklet shows in detail how to change the air-inlet venturi size. Since these are CL engines, they don't have throttles. They come with intake restrictors in their venturi bodies; after break-in, these can be removed to provide extra power and rpm. The well-illustrated manual shows exactly how to do that. I stayed with the small-diameter inlets throughout my tests.

I followed the break-in instructions in the larger booklet. One paragraph recommends oiling the engine before its first run. Besides injecting oil through the crankcase breather, Saito advises putting a few drops down the pushrod tubes to lubricate the camshaft area. That requires removing the rocker-arm covers. While the covers were off I admired the valve mechanisms' Swiss-watchlike precision. When considering switching to four-stroke power, some two-stroke users worry about valves needing constant readjustment; that was a problem with earlier four-strokers—but not with Saitos.

I mounted the Saito .62 on my test stand for break-in. Saito's instructions for its CL engines advise using fuel with 10%–15% nitro and 20%–22% oil—no more than half of that castor. I used 15% nitro and 22% oil. The instructions warn not to exceed 4,000 rpm for the first 10 minutes of break-in. But with the recommended 13 x 6 propeller and small venturi insert, the slowest I could get the .62 to run was 6,200 rpm—even with the needle set "slobbering rich." Yet the .62 showed no sign of distress or overheating, and its exhaust oil came out undarkened—an excellent indicator of mild operating temperatures. I had similar results with the .56 and .72. Neither would run as slow as 4,000 rpm, but no problems resulted from exceeding the prescribed "top limit." As I understand it, the 4,000 rpm limit is for the RC line of engines, which can easily adjust power output with the throttle.

The Saito .72 weighs 17 1/4 ounces and differs most noticeably from its smaller-displacement siblings because its carburetor is offset from the centerline.

Flight-Test Vehicles

My helper and I decided to try one of John Brodak’s biggest ARF kits—the Cardinal—for our first attempt with Saito power. The kit was designed to be powered with a Brodak .40 two-stroke: a lightweight, mostly aluminum engine. With its muffler and 11 x 5 Master Airscrew propeller, the Brodak .40 weighs 9.7 ounces. The Saito .56 weighs 16.1 ounces with its muffler and propeller.

Substituting a four-stroke engine for a two-stroke in a modern CL aircraft is more than swapping power plants. Following is one way to calculate how much to shorten a model’s nose to accommodate a heavier engine:

  1. Measure the distance (on plans if possible) from the design’s balance point (CG) to the centerline of the cylinder of the engine the model was designed to use.
  2. Multiply that engine’s weight by its distance from the balance point (inch-ounces).
  3. Divide that number by the heavier engine’s weight. The result is the distance from the model’s balance point to the heavier engine’s cylinder centerline.
  4. Shorten the nose by the difference between the original cylinder centerline location and the new location.

Example (Brodak Mauler):

  • The Mauler was designed for a Fox .35 which weighs 10 ounces; with an added 1-ounce spinner to correct tail-heaviness, gross weight is 11 ounces.
  • On the plans the Fox cylinder centerline is 8 1/4 inches ahead of the CG.
  • Calculation: 11 x 8 1/4 = 90 3/4 inch-ounces.
  • Divide by the Saito .62’s weight plus propeller: 17 1/2 ounces → 90 3/4 ÷ 17 1/2 = 5 3/16 inches.
  • To maintain the same CG with the Saito, the Mauler’s nose should be shortened by approximately 3 inches (difference between original and new). That’s often too much to allow room for a fuel tank.

On my Mauler I compromised: I shortened the nose only 1 1/2 inches, leaving barely room for a 3 1/2-ounce Oval Profile Uniflow tank. To balance the Mauler properly I planned to leave the aft end of the profile body untapered, extend the tail by close to an inch, and probably install a heavy brass-hub tail wheel on a 3/32-inch-diameter wire strut.

The Cardinal was a different story. Since it had a longer nose, it was readily possible to shorten it enough for proper balance. I fully assembled the model except for the power system, tied the propped Saito .56 to a loop of string, and hung it beneath the Cardinal’s nose. Sliding the loop fore and aft until the model balanced showed precisely where the Saito’s cylinder centerline belonged. The engine-mounting process was straightforward from there.

Another consideration was propeller clearance. Brodak’s Cardinal ARF comes with 1 3/4-inch wheels intended for paved surfaces, but they didn’t provide enough propeller clearance for the 12-inch propeller with which the Saito .56 performs best. Installing 3-inch SkyLite wheels and rebending the Cardinal’s aluminum landing gear struts inward a tad solved that problem and eliminated takeoff and landing difficulties at the grassy field I typically use for CL flying.

When the Cardinal’s engine installation was complete, I tried hand-starting the Saito in the model; I much prefer hand-starting because it gives a feel for the engine and avoids lugging heavy equipment to the flying circle. Initially I couldn’t get the Saito to perk because of the narrow gap between its intake and the side of the Cardinal’s profile fuselage. Finger-choking was impossible, and so was squirting fuel into the carburetor inlet.

I solved this problem by adding an extension to the .56’s intake: a 2-inch length of brass tubing through a hole in the Cardinal’s side did the trick. That not only made hand-starting easy but also added a couple hundred rpm, likely due to a tuned intake effect. I’ve seen the same improvement from extensions on many other two- and four-stroke engines, and I recommend it for the Saito.

Later I found another way to add an intake extender using a length of 3/8-inch-OD rigid plastic pipe (available at home-improvement stores). The pipe’s wall is thick enough to allow the end to be tapered to match the Saito intake’s internal taper. Do this on a drill press, using file-to-fit methods and checking for proper fit as the pipe is shaped with a file and sanding tools. Bell-mouth the pipe’s outer entry to eliminate inlet stall and the power loss that can cause.

Surprise Performance

An interesting possibility occurred to me regarding models for the Saito FA-72CL: it develops approximately the same power as some of the best Class C spark-ignition two-stroke engines of the late 1940s (Anderson Spitfire .65, Atwood Champion .60, Orwick .64). With their ignition components—coil, condenser, battery packs, and wiring—plus propeller, those old ignition-powered setups weighed close to the big Saito four-stroker’s 19 1/2 ounces.

Many 60-powered Old Time Stunt models were fine performers in their day (e.g., Jim Saftig’s big Zilch; J.C. Yates’s Madman; Hal deBolt’s Stunt Wagon; Bob Palmer’s Go-Devil Sr.; and the scale model of Sammy Mason’s aerobatic Stearman). The Saito .72 would make an ideal modern power provider for those airplanes and should require little or no nose shortening.

Flight Performance

To make valid performance comparisons between the Saito .56 and a two-stroke engine with similar power, I installed a well-broken-in Brodak .40 in my longstanding Stunter design—the Vanga Shrike—that I’d flown for years with a mild-mannered McCoy .35 Redhead. The Shrike and the Cardinal have almost identical aerodynamic setups; I had also altered the Cardinal wing’s leading-edge radius to a more rounded contour I prefer.

Weights and wing loading:

  • Shrike ready-to-takeoff: 2 lb, 15 oz.
  • Cardinal: 5 oz heavier.
  • Both models have 4 sq ft of working wing area (including flaps), so wing-loading difference is negligible—about 1.25 oz per sq ft.

Conditions for tests were near ideal: temperature about 70°F, humidity near 60%, and just enough wind to keep the lines taut in severe maneuvers. I flew both models on 70-foot .015 braided steel lines. For sound-level comparisons, I also flew my Flite Streak powered with an O.S. .25 LA-S.

First up was the Shrike. I’d flown it many times with its original McCoy .35 (which never needed an intake extension). The Brodak .40 has a muffler and, with the needle set to a steady but not fully leaned condition, the Shrike flew shoulder-level laps at 4.8 seconds—nearly 95 ft/s (65 mph). At that speed the Shrike pulled the lines almost straight between handle and wingtip without requiring extreme pilot posture.

Sound measurements by my helper, Yana Sarai:

  • Shrike (Brodak .40): 110 dBA at ground takeoff, 90 dBA as it passed her on the side of the circle, 70 dBA on the far side. Ambient was close to 60 dBA. Sound quality was not annoying.

The Saito-powered Cardinal performed flawlessly. With a 52-ounce flying weight, it flew at a good speed but maneuvered more briskly; Saitos are potent. The not-completely-broken-in Saito .56 turned a 12 x 6 Master Airscrew at 9,450 rpm on the ground—450 rpm faster than the factory obtained with a 12 x 6 APC and the small venturi insert, likely owing to my intake extension.

I ran the .56 with the same 15% nitro/22% oil fuel I used to break in the other Saitos and used earlier for the Brodak .40 and O.S. .25 LA-S. The .56 ran steadily through its flights; as expected for a four-stroke, there was no "two-four break" effect in maneuvering. It drew fuel from a standard Uniflow tank setup; switching to muffler pressure made no difference.

The Saito .56-powered Cardinal performed as well as any high-powered Stunt model I've flown. Its extra weight compared to the Shrike's had no noticeable adverse effect. Flying speed was close to the Shrike's. I did notice a small difference in control response, but that could have been caused by the Cardinal's control setup—the up-line ahead of the down-line was a first for me.

Yana measured the Saito's sound output as:

  • 110 dBA at takeoff (same as the Brodak),
  • approximately 80 dBA as it passed her in flight,
  • about 60 dBA on the far side of the circle (near ambient).

Considering background noise, the Saito was amazingly quiet in flight. The only real difference in sound quality between the two-stroker and the Saito was the latter's lower tone. A comparison flight with the .25-powered Flite Streak confirmed similar sound-meter readings.

Fuel consumption:

  • Both Shrike and Cardinal used 3-1/2-ounce fuel tanks.
  • Shrike’s Brodak .40 ran about 6.5 minutes from startup to in-flight shutoff on average.
  • Saito .56 ran almost a minute longer.

Conclusion and Recommendation

Saito's CL four-stroke engines are marvelous for round-the-circle aerobatic flying—or for sport. Their steady running, low sound output for their size, and "businesslike attitude" seem well worth the extra cost. The only improvement I suggest is for Saito to supply a 2-inch-long intake extension with each engine—this addition makes a real difference.

Joe Wagner [email protected]

Sources:

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