THE SOLID STA TE MAGNETO press the point arcing in the past. The elimination of both the points and the

Magneto . . . a self-contained ignition generation and distribution mechanism

First... just what is "solidstate"? "Solid state" is a general term in use in this country to designate various electronic devices which do not have any moving parts or vacuum tubes. Everyone seems to want to question our reasoning when we start talking about the development of a solid state magneto. They seem to think there is really little that can be done to improve a magneto that hasn't already been done. It is one of those things that, "if it ain't broke, don't fix it!" Nothing could be further from the truth. The fact is ... magnetos have been far from perfect. There has been little development in basic magneto technology since WW-I and recent developments in the field of electronics now permit some definite improvements for the conventional magneto. Not only for ordinary systems but in particular for aircraft installations where the service is extremely hard and the conditions for operation are difficult, and where continued operation and troublefree service is essential. Before you can understand what can be improved in a magneto, it is necessary to know why magnetos are used in aircraft. A magneto is a self-contained ignition generation and distribution mechanism that does not require any outside electrical energy to make it function. Thus, you do not need a battery in the aircraft to get spark for the engine to start and run. Since it is common for aircraft to sit around for weeks or months between useages, it is normal for the battery (if there is one) to be run down, making the engine difficult to start. A run down battery will usually not operate an ignition system, particularly if it is also being used to crank a stiff engine that has not been run for a while.

Magnetos overcome these problems since it is usually possible to crank an aircraft engine by turning the propeller by hand and thus get it started with the magneto supplying ignition. For starting, it is important that the ignition be as good as possible, and that dirty spark plugs are obviously avoided.

Due to the problem of spark plug fouling, it is easy to understand that the highest possible high-tension voltage is 64 OCTOBER 1988

by Molt Taylor AEROCAR ASSOCIATES POBox 1171 Longview, WA 98632

desirable in the ignition system. Higher voltage merely burns deposits off the plug points if they form. The higher voltage is now available mainly due to it now being possible to eliminate the "distributor" function within the magneto. The distributor has been an integral part of the older type units, and has been limited in the past to operation at around 30,000 volts. This has been necessary since any higher voltages tend to arc across the distributor points in the rotor cap causing erratic, out of sequence firing of the engine. However, the higher voltage now requires the use of improved insulation and better shielding on the high tension wires.

"It is necessary to know why magnetos are used in aircraft." The new mags use separate hightension coils to generate voltage for each spark plug. This, and the elimination of the distributor, permits the use of higher voltages. Plugs can now be fired in "pairs" through dual high tension coils. These can then fire two cylinders at a time in a 4 cycle engine since one of the cylinders in a pair can have its

condenser are also major improve-

ments. Both have been major trouble spots for years. Usually a magneto is considered to be an entirely self-contained and selfenergizing type of ignition system, and they do not need an outside source of voltage to make them operate. To get them to initially fire, they are often equipped with mechanisms called "impulse couplers" which serve a dual function to both retard the spark for starting and also to initially energize the system. The impulse coupler in effect "spins up the armature to momentarily give it a faster rotation speed." This, then, gives the coils sufficient energy to generate the high voltage needed to provide a good spark for starting. This is why installations without impulse couplers have to be cranked at higher speeds. A magneto system equipped with an impulse coupler doesn't need to be energized from an outside source, and usually will start an engine if it can just barely be turned over. This makes them ideal for aircraft installations where the battery is often almost run down, or where hand cranking means slow turning for the start. If they are not equipped with impulse couplers, some aircraft magnetos (such as the separate type used in older light aircraft) are equipped with a sort of booster to assist in engine starting. These are separate hand-driven auxiliary magnetos or separate battery driven vibrators equipped to supply pulsations of energy to cause the high tension coil in the magneto to provide the necessary high voltage. These boosters do nothing but cause a single spark plug to fire when they are being hand driven or energized.The high voltage caused by these separate vibrators or hand driven magnetos is usually wired into the main magneto through its distributor to direct the high voltage to the

spark occur at the top of the exhaust stroke where it does nothing while its mate will fire the opposite cylinder at the top of the compression stroke. The dual coils can now be triggered by either a magnetic pick-up or a photocell trigger arrangement. Either of these can

proper spark plug. This is delivered, suitably retarded, only during cranking. The distributor in these installations use a separate displaced set of distributor

be used instead of the usual openpoints which have been employed for

A still different type of booster has more recently been devised. This is the so-called "shower of sparks" system. Here the magneto is usually equipped with two sets of points. One set is adjusted for retarded spark for starting and the other set is adjusted for normal

years in most ignition systems. These triggers are considered to be "solidstate" devices. The elimination of the points also permits the deletion of the usual condenser that has always been needed to sup-

cap points to assure that the spark occurs with suitable delay to assure starting.

speed operation. The advanced set of

points is only used after the engine is

running. Such systems always run at

full advance all the time after they get started. The shower of sparks system

requires some sort of vibrator to gener-

ate the necessary alternating or pulsations of current needed to make the high tension coils function and generate the desired high voltage. Some experimental magnetos have been built in the past that have incorporated a mechanical spark advance and retard mechanism in the same physical space where the impulse coupler is normally installed. This serves to retard the timing for starting instead of using a separate set of points, but it does not give the installation the self-generating effect of an impulse coupler so these sys-

tems still need a vibrator to make them function. Thus, they must be powered by a battery or other outside source of power to get them started. However, these systems do have the ability to automatically change the degree of spark advance and retard once the engine is started. The dual point arrangement does not have that capability and only retards the spark during cranking. To further understand these systems, it is well to review the basic idea of a magneto high tension ignition installation. In a magneto, the high voltage is generated by energizing a high tension transformer which has two coils, only one of which can be energized (the primary), and the other (the secondary) has the high voltage induced into it when the voltage in the primary is shut off. The high voltage spark occurs only when the voltage into the transformer (coils) collapses as the points open. Only a single spark is generated at that instant. Thus a vibrator supplying the primary voltage will cause a succession of sparks when such a device is used to energize the ignition coil (transformer). Thus the expression - shower of sparks. A shower of sparks is always more likely to cause an engine to start than the single spark that normally only occurs when the points open.

'Thus . . . the expression: 'shower of sparks'."

With conventional old style magnetos, the dual point arrangement, with one set of points retarded for starting and the other set for running, or a single set of points with the automatic retard of an impulse coupler, are only suitable for gasoline engines that do not need to vary their speed. Or do not operate under a changing load condition, or engines that can always be run at the

same speed and load (such as an aircraft engine). However, it is a well

Recent efforts by this writer to develop a simple solid state magneto

should have its spark timing adjusted in

the art have resulted in several successful demonstration installations. These have included one installation where we attempted to build in the ignition system inside the engine crankcase. The system included the dual coils for the dual-ignition system inside the rear of the crankcase.The alternator was built into the flywheel. The solid state trigger mechanism was mounted on the back of the engine and driven directly from the crankshaft. This installation was finally worked out until it functioned perfectly when run on the ground. However, when we installed the nose cowl over the engine, we discovered that we had trouble keeping the installation cool enough, particularly when the engine was shut down. It was necessary to provide special cooling air ducts to the ignition components in order to get it to operate satisfactorily in flight.

known fact that a gasoline engine

relation to the load condition as well as the speed it is going to be run at. Automobiles do this by having an automa-

tic spark advance and retard mechanism built in to their ignition systems which uses centrifugal force on a governor and a vacuum mechanism to control the degree of advance and retard of the spark. This lack of control of the spark advance and retard (except for starting) has been a shortcoming of the magneto for years, and is something needing improvement. Built in automatic spark advance has been very difficult and expensive to incorporate in a magneto in the past. However, the advance and retard feature can now be built into the electronics or incorporated in the mechanics that drive the alternator and the trigger mechanism. The simple magnetic or photo-electric trigger systems used with electronic ignition installations, such as the solid-state systems, lend themselves readily to the incorporation and use of "automatic" spark control. This can be either mechanical or electronic. Such features can be found in both simple solid state magnetos and ordinary solid state standard ignition installations like those found in lawn mowers, tractors, automobiles, etc.

for light aircraft using the latest state of

"It was necessary to provide special air ducts to the ignition components . . . " Another solid state system was installed on a similar engine, but that time we remembered our cooling difficulties and built the ignition components into sepa-

rate boxes so they could be mounted in

"... a solid state magneto must include some way to generate its own voltage..." However, most aircraft engines have not had such units in the past. This is a very desirable feature that now can be easily incorporated in an aircraft engine for the first time.

In addition to these features, a solid state magneto must include some way to generate its own voltage not only for running but also for starting. It is here that the problem has been difficult to resolve, particularly for a standard separate magneto such as has become

common for aircraft engines. It has only recently been possible to devise an alternator with sufficient output (when it is turned at relatively low velocity) to generate enough energy to fire an electronic ignition system with enough voltage to get reliable starting. This has taken new materials such as improved magnets, coils and electronics to finally get an installation that will start and run a gasoline engine properly. This has been particularly true where the engine already requires high electric current for cranking and the cranking velocity is already slow.

the cooling airstream where they now function perfectly. This work has been done with the cooperation and assistance of associates who have been working on solid state ignition systems for motorcycles. We now feel we can design and build

separate solid state magnetos which

could be directly interchanged with the usual Bendix or Slick type aircraft magnetos usually found on light aircraft engines.

We also feel we can now build a solid state magneto for small aircraft which will offer definite improvements and advantages for small aircraft installations

as well as for builders of new small aircraft engines. This work has been done with the assistance and cooperation of Joe Horvath of the Revmaster Aircraft Engine Co. (7146 Santa Fe Ave., Hesperia, CA 92345, 619/244-3074) and Al D'Alo of the A.R.D. Engineering Corporation (10628 Norwalk Blvd., Santa Fe Springs, CA 90670, 213/941-5842). You may contact either of these individuals or the author for additional information. Whether there is a market for such new technology magnetos remains to be seen. If there is, the A.R.D. people are considering production of such units. SPORT AVIATION 65