C/LCombat T
rying something new: one nice thing about Combat, there can al- ways be something new to try. Right now Speed Limit seems to be the most popular. AMA Fast and Slow have pretty much gone away due to lack of equip- ment; no new engines that are suitable are being made. Anything that is being made (a few car engines might work) generally re- quire machining prop drive parts, and the engines are based on .25 size cases and most use 12 or 13 mm shafts which are likely to break when pushed to 100 mph speeds on a Combat plane. A few years ago I put a Thun- der Tiger .36 Pro engine on a plane with a wide open intake. After half a dozen 90+ mph flights the shaft broke.
To play around with faster speeds, put a ball bearing .28 or so engine on a Speed Lim- it plane and either extend the boom or re- balance the plane. Use large venturi, 25% nitro, an 8–5 or 8–6 prop (maybe trimmed down a bit) to get the rpm up. Try to get the speed up to 88–90 mph. After a few flights, put it on 52.25-foot lines. That will get the lap time down below 2.5 seconds per lap. If you can find some willing local flyers, try some Combat at more serious speeds (don’t forget a fuel shutoff device).
Unfortunately, you will have to do some parts picking to set a motor up to do this. At a minimum the motor will need a new, large venturi and a remote needle valve. There are a few .28 car engines that will take a pro- peller with just a prop washer and nut. I’d give some suggestions, but car engines seem to change daily so it’s hard to recommend a specific model.
One of the things to look for in any engine to use in this caper is a strong shaft. That means one with the intake port in the shaft
by phil cartier You can reach Phil Cartierat 34 Sweet Arrow Dr, Hummelstown, Pennsylvania 17036, or via e-mail at
philcartier@earthlink.net
PHOTOGRAPHY: PHIL CARTIER
Brodak’s Fly-In Combat: Louis Lopez and Tom Skinner battle it out for first and second. In the third round they went head-to-head. Lopez came up two cuts and a few seconds of airtime ahead.
faired into the gas passage. Many engines have the shaft drilled past the shaft port for ease of manufacture. That makes the port very susceptible to cracking. The Magnum series of engines, 28-32-36, and the Evo 36 use a shaft that is already faired in. On the engines that are drilled past the shaft port it is worthwhile to fill in the front of the shaft with JB Weld, other high tem-
perature epoxy, or get a machinist friend to press in a steel or brass insert you can grind into a smooth rounded gas passage. Looking at other engines, try and find a 13 or 14 mm shaft. On a .28 size engine this will be much stronger than a 12 mm shaft.
Of course, you can try some F2D equip- ment. Older engines that run fine with the old 8 mm muffler can still get lap times un- der 2.5 seconds. On the downside, even used, the equipment is liable to be more ex- pensive. Not too many motors in good condi- tion go for less than $150. The F2D engines also seem to take a lot of care keeping them clean. They run at very high rpms. The bear- ings, particularly the main bearing need to be kept spotless.
Foam vs F2D: Dan Banjock and Craig Campbell had a hard fought third round match. One up on cuts, but lots of flying, including a pit stop apiece.
36
The normal routine after a flying session is to run a prime through the engine to make sure no fuel is left inside. Any amount of fuel will be contaminated with acidic combustion products and can ruin the bearing over - night. Flush the dry engine with some kerosene. Simply pour a couple of tea- spoons—say ¼ ounce—into the intake, flip the prop, letting the fuel drain out the ex- haust. Put your blow tube on the intake and blow out the kerosene. Finish up with some air tool oil or sewing machine oil or other high quality lubricant and put it in the in- take, the exhaust port, and the plug seat. Don’t use any lube that will evaporate, such as WD-40 or other household lubes. Another higher speed fiddle is to work with plain bearing Half-A engines. An .061 plain bearing can get considerably better performance than the old standby Tee Dee .049. Norvel is making both a high perform-
AUGUST 2013
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