- Sep 17, 2008
I've been into homebuilding since 1972. Was a charter member of a new EAA Chapter that year. Got my PPL in 1975. Commercial in 1993, IFR in 1995, Flight Instructor in 1999, Aircraft Maintenance Engineer license in 2000. Had several aircraft projects.If you only worked on certified airplanes you may not be aware of Ellison throttle body injectors, light weight starters, electronic mags, alternators and permanent magnet generators that weight only 3 pounds and put out 30 amps. These all reduce weight by at least 20 lbs. some available 20 years ago. Welcome to the world of homebuilt airplanes! Kitplanes mag is the best source of the latest technology.
How long have you been in homebuilding?
The Ellison was, I believe, an outgrowth of the Posa carb, which was a big deal in the '70s, but it would never fly with certified airplanes because it would dribble fuel when the engine wasn't running, so the fuel had to be shut off at shutdown and turned on right at startup. That's too much to expect of the average pilot. Shoot, they barely understand carb icing and carb heat. The Ellison is famous for being fussy and hard to get set right. Traditional float carbs were settled down a hundred years ago, even the stupid certified Marvel Schebler carbs that persist with a bunch of hassles even after numerous ADs. My ancient 75-year-old Stromberg runs better than those MS things. The Posa was touted as an ice-free carb, which was, of course, totally wrong, and there were problems. Any time you restrict airflow you cause a pressure drop and therefore temperature drop, and anytime you atomize fuel into an airstream you get an evaporative cooling on top of that. Only fuel injection, at the intake ports, is relatively ice-free.
I replaced numerous old starters with lightweight PM starters on many airplanes as a mechanic, all on certified ships. When I retired four years ago, reliable electronic mags were not yet widely available, and from the discussions over on Pilots Of America, it appears they still aren't. Reliable, that is. The Surefly stuff is giving many pilots fits. Some of them quit soon after installation. E-Mag/P-Mag don't appear to be certified but they've been around awhile. They had plenty of troubles early on, too. There are other EI systems, most of them only on Experimentals. Lycoming's iE2 engine is the only certified engine I know of with EI and EFI. All of this points out the difficulty of getting electronic stuff reliable enough to satisfy the regulators. Magnetos are primitive, but that also means they are simple and robust and will not make trouble IF they are properly maintained according to their manufacturers. The only mags I had trouble with were those that had manufacturing defects, or that had not been maintained, and NEITHER of those factors reflect on the magneto's principles. On the other hand, electronic stuff in airplanes gives constant headaches. 90% of all hassles are electrical or electronic. I was taught that in Power Mechanics in high school in 1968, and I have found it true every since.
PM alternators are light, but they get like that by replacing the field coil (rotor coil) with permanent magnets. That means that the only method of regulation is to run the output through a variable resistance, now a big transistor, to regulate the system voltage, and that is a primitive way of doing things that traces its roots back a century or more to a time before there were electromechanical or electronic regulators that vary field current. They used stacked carbon discs, put under varying pressure by a heavy spring, opposed by a big current-sensing coil, to vary the resistance. A PM alternator is at full load all the time, in contrast to a field-regulated alternator or generator. That means wasted power, lost as heat.
I built a tiny PM generator for my Jodel, using a small ball-bearing PM motor, and a regulator designed around an LM117 voltage regulator chip. Spun it with a 3-inch propeller. It produced awesome radio noise no matter how much filtration I put into the system. Took it out and went back to charging the battery occasionally. All it ran was the radio.
Plane Power makes some smaller, lighter alternators, but most serious owners want more power, not less. Alternator outputs are based on some engine RPM, typically at least runup RPM, which means that at idle they won't generate full power, so the alternator has to be larger to accommodate night operations. Glass-panel airplanes also consume more power, day or night. The Garmin G1000 consumes 9 amps from its standby battery when the main system fails, and that's for just the PFD, one Com and the transponder, and the engine instrumentation. The MFD and the rest of the stuff go dark. The whole system likely takes 20 amps, at least, all the time.
Alternators replaced generators a LONG time ago, in the mid 1960s, in both cars and airplanes, when suitable diodes became available. Until then, we were stuck with generators of 25 or 30 or 35 amps that couldn't keep the lights on during night ground operations. (It didn't help that in those days the radios were often still using vacuum tubes, greedy things that ran the battery flat in ten minutes.) Little outputs like that might be fine for today's average puddlejumper homebuilt, but the guy that wants more utility is going to need more power. I have installed the 70-amp Plane Power systems for owners, taking out the larger and heavier 60-amp alternators.
12 years ago I was replacing all the landing and taxi lights on all the flight school's airplanes with the Whelen LED lights. Got tired of the short lives of the incandescents, and the calls at night from the school complaining that a light was dead and they wanted to go flying. Those LEDs fixed everything, and also extended the life of the switches in the panel. I am not unfamiliar with new technologies.
I am waiting for a safe, inexpensive lithium battery. No, not for an airplane. For the electric trolling motor on my canoe. That big heavy lead-acid deep cycle battery is a killer for my old back. And I'd like to put a larger electric troller on my big boat and get rid of the noisy kicker. Rather listen to the birds and breeze in the trees as I troll along, not a constant chatter, along with exhaust fumes.
Edit: Sentence clarified to avoid confusing certain people. One word added:
Any time you restrict airflow you cause a pressure drop and therefore temperature drop...
Sigh. A whole career in ruins due to missing one word. Life is rough.