3. It is to be more efficient. During recent months, I made a little survey on AntiCollision Strobes, and the results were appalling. I found
Don't Buy A Strobe! By Mon K. Lee, EAA 30392 1089 Sterling Ave., Berkeley, California
ON'T BUY A strobe! That's right — don't invest in
D one until you have investigated! Be discriminate, and know precisely what it is that you are buying. Don't buy a strobe because it looks impressive; know what is in it and what it is capable of doing for you. Let us analyze the prime functions of an Electronic Anti-Collision Strobe Beacon:
1. It is to attract attention, thus be seen;
2. It is to save weight, i.e., versus a mechanical rotating beacon; SPECIFICATIONS Input Voltage . . . . . . . . . . . . . . . . . . . . . . 12 VDC ± 3V Input current . . . . . . . . . . . . . . . . . . . . . . 2 A average Flash rate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55/min. Stored energy . . . . . . . . . . . . . . . . . . 9.25 joules/flash Flash duration . . . . . . . . . . . . . . . . 180 microseconds Size . . . . . . . . . . . . . . . . 3 in. OD x 6.5 in. approximate Weight . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24 01.
a vast array of price ranges and quality among those on the market. The prices ranged from $50.00 (with no specifications) to $575.00 each (minimum order of four). I soon realized that the average aircraft owner (weekend or pleasure pilot) either did not get the protection for his money, or does without because of the cost involved. In
view of the situation, I embarked on the task of designing an Electronic Strobe unit bearing two major objectives in mind: 1. Light Output — there is no value in having a strobe when it can only be seen at short range; 2. Price — within the reach of the majority, without sacrificing quality. Before I present the specifications, let us discuss some of the basic principles of an Electronic Strobe in the sequence of the above-mentioned prime functions. Light output has direct relation to energy per flash in units of joules and flash rate. The formula for energy is: J = %CV2 ("J" — joules; "C" — farads; "V" — volts). Thus, fop example, if a strobe unit employs a 100-microfarad capacitor and is charged to 450 volts before it fires, the
energy output will be 10 joules. If the flash rate is one per second, the total output will be 10 watts or 10 wattseconds. Weight, a problem which every pilot is keenly aware of, will not be discussed for quite ostensible reasons. Efficiency — for short duration flashes, the human eye integrates the light, hence the effect of flashing light relating to a continuous source is approximately five to one (Amglo Flashtube Engineering Manual), therefore,
a 10-joules (watt-second) strobe beacon has the equivalent effect of a continuous 50-watt source. There are some who will argue that blinking a 50-watt incandescent bulb V4-second on and %-second off will have the same effect. This argument may appear logical at lirst glance; however, let us analyze it from the power (light output) standpoint. A 50-watt bulb turned on for V4-second will yield only 12.5 watt-seconds. Actually, it will yield less than 12.5 watt-seconds because an incandescent bulb is a thermo device and has finite thermal inertia. In other words, the tungsten filament has to heat to rather-high temperatures, over 1000-degrees absolute, in order to emit visible light. During the time of heating, this is expended energy, which has no visible light output. Now, just suppose this thermal inertia does not exist, and suppose you want a 50-watt-second output in Vi-second (equivalent to 10-watt-second strobe). In the case of a 12-volt electrical system which is actually 14-volts, this requires 14.3 amps. Now, let us think what size wire this will entail in order to carry 14.3 amps. Think — weight.'
Let us now return from our tangential path to my main objective in designing a strobe. I have completed a unit which has the specifications shown here. This strobe incorporates a ferrite DC-to-DC converter operating at a frequency of approximately > 2 khz. The normal charge time of the 90 mfd. capacitor to 45Ovolts is .6-seconds. The timing section employs a separate timing generator and an SCR trigger for greater stability. The flash tube, Amglo HD-2A, is the same type of tube used for the Apollo LEM ground-support system. Thus, I caution you, don't buy a strobe without being selective, scrutinizing and discriminatory. ® SPORT AVIATION
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