CONTROL LINE SPEED
Glenn Lee, 819 Mandrake Drive, Batavia, IL 60510
This is the Control Line Speed column; however, I find that it's read by modelers who fly other control-line events, as well as R/C fliers. As a result, I try to pass on any engine-related information that I accumulate.
SuperTigre 2500/3000 vibration problem
John Bishop, a member of the suburban Chicago Tri-Village R/Cers club, wanted me to pass along some information about the big SuperTigre 2500 and 3000 engines.
Quite a few fliers have complained about excessive vibration with these engines, and John accidentally figured out the cause. A flier noticed that the spinner backplate (or prop driver plate) that comes with the engine was out of balance, so he drilled several holes in the heavy side to rectify the problem. Someone saw this and wondered why the original plate was so out of balance. He finally figured out that it was designed that way: you are supposed to orient the backplate on the crankshaft so the heavy side is opposite the crankshaft counterbalance.
To correct this problem:
- Put the plate (by itself) on a prop balancer and mark the heavy side.
- When you put the plate back on the engine, make sure this mark lines up with the crankpin. The mark should be straight down when the piston is at bottom dead center (BDC) or straight up at top dead center (TDC).
- Note that there is no information about this in the engine instructions.
If you're skeptical, test the procedure:
- Clamp the end of an 18-inch piece of small-diameter music wire to the side of your fuselage so it sticks straight up.
- Run the engine with the plate in different positions and note how the wire vibrates.
Electroless nickel-plated sleeves (ABN O.S. engines)
Neville Palmer (Palisades, NY) has constructed several of his own engines and asked what I thought about nickel-plated sleeves. He didn't want the problems of setting up a chrome-plating system.
Some O.S. engines have an ABN sleeve-and-piston combination where the piston is high-silicon aluminum alloy and the brass sleeve is nickel-plated. The nickel is not electroplated like chrome but is applied by an electroless process. Clean brass is dipped into a solution where nickel ions attach themselves to the brass—no electric current is necessary.
Differences between electroplated nickel and electroless nickel:
- Electroplated nickel is used where maximum adherence is desired (often as a flash under copper or chrome). This nickel has an extremely active surface and is unsuitable for parts that will rub against another metal: it will gall, have high friction, and may weld itself to the mating part.
- Electroless nickel has a different crystal structure and can be used for rubbing surfaces, but it doesn't have as much peel strength as electroplated nickel. In short, it doesn't stick to brass as well.
Many years ago I wrote an engine article predicting electroless nickel plating for brass sleeves. I was experimenting with plating solutions that had boron as an additive in the nickel to reduce friction and improve wear characteristics. I don't know if the O.S. plating contains boron.
Several speed fliers have tried to use the ABN O.S. .65 engines in D Speed; I've seen a few of them fail when the nickel flaked (or peeled) off. It's my opinion that these failures are a result of pistons' rubbing velocity.
Piston and sleeve experiments
Thirty years ago (before ABC), Dick Hall and I experimented with different sleeve-and-piston alloy and plating combinations. Dick, an avid modeler, is a rocket engineer for the Huntsville Arsenal. He's an acute thinker, an endless tinkerer, and the person who told SuperTigre about the high-silicon aluminum alloy material we use in our engines.
We tried many combinations:
- Sleeves made of: steel, cast iron, copper, and brass.
- Platings: chrome, gold, and silver.
- Pistons made of: cast iron, mild steel, and 4340 steel.
- Pistons plated with: chrome, gold, and silver.
Chrome against silver was one of the best combinations for metal-surface compatibility. Aluminum doesn't run well against most materials; we tried chrome- and gold-plated sleeves and pistons running against chrome and they didn't perform well. If you buy stainless-steel hydraulic fittings today you'll find threads silver-plated to prevent galling against the mating part.
Piston and sleeve materials must have thermally matched characteristics. For instance, cast-iron pistons will work in a steel sleeve because cast iron has a lower coefficient of thermal expansion. I read somewhere that the Dooling brothers' experimental engine would rev up to 30,000 rpm and seize because the parts didn't have proper thermal expansion matching. Bill Wisniewski tried a titanium piston; it would start to seize immediately because of thermal expansion. Some of our engines ran very well, but each combination seemed to have a definite upper-rpm limit (even with a flywheel instead of a propeller).
This led to a theory: a certain alloy piston will operate against its sleeve alloy up to a maximum rubbing velocity. Go any higher and you get galling, flaking, welding, or just refusal to go any faster. Of course, there are other factors that limit rpm—engine design, porting, and timing all help—but the ABC combination gave the biggest jump in performance. The lighter aluminum piston allows a higher rpm, there's no drag or friction from rings, and the thermal expansion of the piston is almost perfectly matched to the sleeve.
I believe the same velocity effect limited the Cox engines—the steel sleeve wouldn't allow them to rev to a high rpm. My neighbor Bob Oge does chrome plating; he's revved Tee Dee .049 engines to 30,000 rpm after chroming and reworking. The parts can't stand the stress for long, however.
Conclusions
It's my opinion that ABN engines work as long as you keep the rpm down. Try them in Speed (or other high-rpm events) and you'll have trouble. Piston fit has an effect too—you need a tight fit for higher power, but some fliers simply strip the nickel and chrome-plate the sleeve, eliminating one more problem.
What's our next Great Leap Forward? I'll tell you in a future column.
Transcribed from original scans by AI. Minor OCR errors may remain.
