Welcome to the second part of my JBA 52. I covered the basics in
Part One, so I'll now move on to how it performed.
Bolting the JBA 52 to my trusty (if very oily and battle damaged) test rig, I affixed an APC 11 x 6" glass nylon propeller to the business end. Since there's no plug supplied (black mark, I hate that - it's like buying a car without a steering wheel; useless 'til you have one) I fitted a trusty Enya No.3, hooked up the plumbing and filled the tank with 4oz of Weston Prosynth 10%, my favourite brew. The instructions recommend 'a medium hot plug and any commercial glow fuel containing 10% nitromethane'; a little more enlightening than some instructions I've come across over the years, but still a bit light on detail.
ABC engines are tight at the top of their stroke, which is normal as they're supposed to be like that. Some even squeak and squeal when new as you turn them over. Worry not, the JBA was neither tight nor sloppy, again falling into the 'just right' category. Choking the thing with a wide open throttle to draw fuel into the engine, before hooking up the glow lead, produced an immediate result. A couple of flips with a gloved hand and the 52 started easily. You can use a starter if you prefer but I always hand-start new engines, I prefer to 'feel' the engine and know what it's about. Glow engines of smaller capacity should never be bullied into life with a starter when new, as damage may occur unless they're well run-in and the correct settings are known. Of course, when an engine is run-in and set up correctly hand starts are so easily achieved that you don't need to resort to a starter anyway!
ABC engines should be run-in quickly, using short bursts of full throttle for a few seconds at a time and stopping the engine frequently, thereby allowing cooling to take place. About two or three five minute runs will suffice, and I usually fly my engines after the first half tank or so of fuel has passed through, setting the needle very slightly rich and using the throttle sympathetically. Running engines in when airborne is very good for the unit as cooling is optimised, but don't let me talk you into risking a model with a dead-stick if you're a newbie to the game. Other than that, go right ahead. Bench running is for fiddlers, rather than modellers!
RESULTS
I was extremely happy with the propeller figures (13,000 max. rpm with a 12 x 4" RAM, 11,100 with an 11.5 x 7" Bolly, and 11,700 with an 11.5 x 6" Bolly), which were taken after about fifteen minutes of running. 'In the ball park' probably sums up the figures. The idle and throttle-up was exemplary, and the engine's behaviour couldn't be faulted. These days there's no such thing as a poor engine review; an oft-levied moan by the one-make cognoscenti, but what is a bloke supposed to do when all modern engines are made to this high standard?
To sum up, then, the JBA 52 is a lusty performer. It does exactly what it says on the tin (well, the box!), being no better and no worse than 99% of similar engines on the market. Whether you choose this one over its competitors will largely depend on whether you favour its looks allied to the price and availability of the engines in your locale.
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