The SPE 26CC gasoline engine from Cermark
Joe Wagner | [email protected]
CERMARK’S SPE 26CC (1.6 cu. in.) gas engine is a well-made, economically priced power plant for big RC airplanes. It features an electronic spark-ignition system that automatically advances or retards the spark timing to correspond with throttle settings. It also employs a three-bolt positive propeller drive—one that ensures that the propeller can’t come off in flight, but requires precision drill-press work on the propeller to make everything line up properly.
The SPE 26’s multipage instructions included several cautions about balancing—not only the propeller, but even the spinner—and even warned against using a heavy spinner or propellers that sustain any kind of damage. Evidently this is because of the engine’s long overhang from its mounting surface and extended propeller drive assembly. The “cantilever effect” from these would amplify any vibration from rotary unbalance.
In my preliminary examination of this big gas engine before test-running it, I noticed a few anomalies. For instance, I check the tightness of the fasteners on any new engine I receive. Every bolt on the SPE 26 needed at least a quarter turn of further tightening to attain truly firm seating. That’s probably because of gasket compression between the time the engine was assembled and the time I began working with it.
Also, the spark-plug connector’s thin sheet-metal shell split apart as I tried pushing it onto the plug. It’s held together with bent-over tabs. I recrimped those with long-nose Vise-Grip pliers. Then for added strength, I wrapped the shell tightly with a dozen turns of stainless-steel “safety wire.”
To provide as close a simulation as possible to the SPE 26’s installation in an airplane, I made a special mount for test-running and breaking it in. As the photos show, the mount needed to be larger and more elaborate than for a glow engine.
The five-cell (6-volt) Ni-Cd pack, electronic unit, switch, and associated wiring had to be accommodated, just as they would be in an airplane. Allowing any of these vital components to “hang loose” is a definite no-no.
The SPE’s “Auto-Advance Timing Control” unit works from input voltages from 4.8 to 18. I chose to use a five-cell, 6-volt Ni-Cd battery for two reasons. One was to make sure that its output was well above the minimum specified. The other was that I happened to have exactly five spare Ni-Cds on hand. A 1200-1800 mAh-capacity pack is good for a normal day of flying.
The SPE’s instructions warn against using automotive gasoline in the fuel mix. The ethanol content of today’s auto fuel will adversely affect some plastic parts in the SPE’s Walbro carburetor.
As I do in blending the fuel for my old-time spark-ignition engines, I used Coleman Camp Fuel. It’s similar to the low-octane white gas that everyone used in the Good Old Days for running their Ohlssons, Ardens, and Super Cyclones.
For oil I wanted to use a synthetic for running after the initial break-in, as recommended in a recent article in MA. However, I couldn't find that at any of the local auto-parts dealers or home-improvement centers. For the break-in I used Husqvarna XP Premium two-stroke engine oil (found in the chain-saw section at Lowe's).
The SPE requires a 30-to-1 gas-to-oil mixture for break-in. To ensure accuracy when making that mix, I used a glass syringe (more about this later in the column) to measure the oil. Less oil is needed after break-in is complete.
The SPE 26 hand-started for me without much difficulty. However, MA Editor Michael Ramsey ran this engine later, and it showed that the original electronic ignition module wasn't performing optimally. Replacing that with a new unit solved the problem and it started predictably.
Michael recommends that shrink tubing be used to ensure that the battery-plug connection doesn't come apart while the engine is running. A more tightly fitting type of plug could be substituted for the one that comes with the SPE 26.
Another SPE user reported some problems caused by "foreign material" in the Walbro carburetor's primary jet filter. Cleaning that out noticeably improved his engine's performance. There was no gunk in ours, but take this information as a fault diagnosis should engine running become erratic.
As with all spark-ignition engines, a kill switch is needed to shut off the engine. I used a paddle-type automotive switch on my test mount. The sort of miniature slide switches commonly used in RC systems are not adequate for this usage because of vibration conditions and voltage loads. And a paddle-type switch can be operated by an RC servo in an airplane installation.
A far better and more reliable (but more expensive) solution to the kill switch situation is AeroTech's ESW-1 Electronic Switch. It is particularly designed for maximum reliability in RC installations. It employs a photovoltaic relay that optically isolates stray electronic noise from the spark-ignition system and prevents RC interference from that source contaminating the radio signal.
A special feature of AeroTech's ESW-1 is its adaptability to work not only with conventional 50 and 72 MHz radio systems, but with any of the recently introduced 2.4 GHz sets. The ESW's comprehensive instruction sheet covers Spektrum, JR, Futaba, and Airtronics 2.4 GHz transmitters, and it describes how the LED on the switch is used to indicate proper settings when used with one of these various transmitter throttle channels.
The ESW-1 can handle 4.5 amperes. It's small—roughly 1 inch wide and 1 1/2 inches long—and weighs less than 1/4 ounce. It comes encapsulated in a protective plastic sleeve, which was omitted from the unit in the photo for the sake of clarity.
A convenient touch is the ESW-1's screw-type connectors. No soldering is needed for any of the five input/output wires: three for the receiver plug wires and the other two to the ignition circuit.
I asked Marvin Stern, who designed and manufactures the ESW, about employing his unit as a kill switch.
"In using the ESW-1 as a kill switch, just make sure that the hot, or +, side goes to the B (+) 'IN' terminal, and the 'OUT' terminal goes to ground," he said.
AeroTech also makes a more advanced version of the ESW-1. It includes a transistorized spark-ignition circuit for use with old-time model engines. I'll test and report on this unit in my next column.
Now about that glass syringe. For years I've been using one of Larry Davidson's 30-milliliter (1 fluid ounce) glass syringes for fueling my smaller models. I prefer its more rigid and positive feel to that of comparable plastic syringes. However, I neglected to take into account that it's made from glass.
Between uses, I'd customarily put the syringe in the drawer of my field box, unprotected from contact with the various metallic tools in there with it. But the last time I used it for fueling a model, as I was filling the tank I noticed red fluid running down the outside of the syringe.
That's right: blood—my blood! The rim of my syringe's top flange had chipped, leaving a razor-sharp edge. I didn't even feel the cut as it happened.
I told Larry about this, and he suggested putting the syringe back in its original box between uses, to prevent this kind of thing from happening again. He told me that doing so would require removing the plastic fuel tubing from the syringe each time I used it.
Larry said that all he does with the syringe he uses for fueling his FF model tanks is put it in a zip-lock baggie between uses, attached fuel tubing and all. He says that that's all the protection the syringe seems to need. I guess he's recommending the thick, plastic freezer bags.
Larry carries these glass syringes in four sizes: 10, 20, 30, and 50 milliliters. That's .34, .68, 1.0, and 1.7 fluid ounces. MA
The Engine Shop
Joe Wagner
Sources:
Cermark (562) 906-0808 www.cermark.com
AeroTech (732) 928-0884 [email protected]
Larry Davidson (540) 721-4563 www.modelflight.com/larrydavidson.html
Transcribed from original scans by AI. Minor OCR errors may remain.
