Letters to the Editor
All letters will be carefully considered; those of general interest will be used. Send to Model Aviation, 815 15th St., N.W., Washington, D.C. 20005
CDI Ignition Systems
Due to the recent interest in CDI (capacitor discharge ignition) systems, I thought I would let you know about my experiences.
About 12 years ago, after seeing many ads for CDIs for motorcycles, I decided to try one. The ads then sounded just like they do now: low power consumption, fires a fouled plug, no points (or at least minimal current through existing points), etc.
The system I purchased was manufactured by Sydmur. Being familiar with bikes and especially with electronics, it installed easily. Problems turned up right away — occasional hard starting, and stopping of one cylinder for no apparent reason. I consulted the manufacturer, and his suggestion was to purchase a new set of automotive coils, thinking the stock coils in the bike were breaking down under the extra voltage. Two new coils didn't help at all.
After much costly experimenting, I finally decided the cause was the short duration of the spark. The system was stuck in a box and shoved in a corner — and the standard ignition was reinstalled in the bike.
Of course, I had no way to tell if my theory was correct until recently. In the May 1981 issue of Cycle magazine, in an article on ignition systems, they came to the same conclusion. I have enclosed a copy of the portion of this article pertaining to CDI systems.
Kawasaki, about the same time, came out with a three-cylinder 500cc, two-cycle bike. It came with CDI as standard and surface-gap plugs. Soon the surface-gap plugs were abandoned and standard plugs were recommended; then the whole CDI was replaced in favor of a more conventional system.
It seems that CDI will work if conditions are correct, but after the hassle I went through, I am not convinced that they are the "cure-all" that they're supposed to be.
Brian K. Grim Lenhartsville, PA
Comment by Emil Svercl
Brian is correct! A CDI is not a cure-all. These systems can have their own set of pitfalls. A well-designed, integrated system is needed to take full advantage of the capacitive discharge concept. The coil needs a ratio of approximately 200-to-1 with a ferrite core that responds to a short electrical pulse with rapid magnetic buildup. The conventional coil is about 400-to-1, and its heavy iron core gives slow magnetic response to the short electrical pulse characteristics of the discharging capacitor.
The high-tension wire must be of low capacitance, or it will "absorb" much of the energy that goes in at the coil end. I used a rather fine inner wire with low-capacitance insulation. Even so, about 25% more energy input was needed when full high-tension shielding was added. Keeping in mind these principles and those outlined in the August 1982 MA article, a reliable and very efficient system can be constructed. However, for some applications a conventional system may be a better choice.
Emil Svercl Cedar Rapids, IA
Bull by the Horns — And They Pulled It Off!
Central Connecticut RC Club President Richard Belanger was relaxed and at ease when his phone started ringing. He answered with the usual hello, listened carefully, gulped a few times, and said: "Can we? You bet we can!"
The caller was the program director of PM Magazine, a nationally syndicated TV program.
Dick had a bull by the horns, because they wanted our club to demonstrate RC flying for the cameras — and wanted it done the following Wednesday, just five days to try to convince the members to take an afternoon off from work. Would their bosses okay the time off for a guy to go fly his models?
Dick put in hours of frantic phone calling to alert the members. But nothing would be positive until the afternoon of the filming.
Results: the biggest turnout for an event the club ever has had. Talk about pride — everybody brought a plane—or two! There must have been about 40 ready-to-go planes in the pits before noontime.
PM's truck showed up at around three o'clock — two hours late, but no one griped. The PM Magazine director had a pre-flight meeting to see if we could fly his way — aerobatics, balloon busting, ribbon cuttings, and general takeoffs/landings, with a few fly-bys thrown in.
Keith Palmer was chosen to do the balloon bust, and he must have made 10 passes for the camera with a Quickee 500. Bob Joslyn got the task of flying directly into the camera lens for a dramatic head-on shot. Dick Hasslick pulled off the aerobatics portion of the program with some superb stick-smashing.
The whole program of filming took about three hours — and would be cut to about six minutes for showing. It was a lot of hard work, but well worth it. The film has been aired several times to the pride of the Central Connecticut group.
Bud Gay Bristol, CT
Printed are several pictures from the filming that were sent to us:
- The Spirit of St. Louis, shown in two of the pictures, belongs to Bud Gay. It was built from a Royal kit.
- The Catalina model belongs to Leon Kusic.
- The plane-to-camera takeoff is performed by a Sportmaster being flown by Bob Joslyn.
Photos by Bud Gay.
It's nice whenever modeling can be shown in a favorable way, especially before PM Magazine's large audience.
Transcribed from original scans by AI. Minor OCR errors may remain.
