Alternator Reality
In the wiring diagrams in the article “All About Avionics: The Electric Airplane” [May 2008 KITPLANES], the alternator is shown with a fuse between its output and the bus. The diagrams do not show the voltage regulator (VR), but in the text it is said to be an external type with over-voltage protection for use with the SD-20 alternator. I assume that the field supply circuit shown going to the alternator is to the not-shown VR.
If the fuse or circuit breaker in the alternator output opens, the bus voltage will decrease, as it no longer gets the charging current and is now on battery power only. The lower bus voltage will, in turn, cause the voltage regulator to apply current to the alternator field. This current will cause increased depletion of the batterys charge, but with an added consequence: The field current will rise to maximum, and the alternator output with no load will rise to a very high voltage, often in excess of 100 volts. If a circuit breaker is used and it is reset, there will be a very high voltage spike put on the bus, which could damage the avionics.
I recommend that those using an overload protection device, such as a fuse or circuit breaker in the alternator output, connect the VR field source to the alternator side of the fuse/circuit breaker and not the bus side. That way the VR will keep the alternator in regulation and remove the field drain from the battery.
PAUL LIPPS
Fire in the Hole
At the recent Reno Air Races, a biplane had an engine fire and crashed, killing the pilot. I was crew on a Formula One racer in 1995 when Rick Brickert had an engine fire in the Pond racer. He too crashed and lost his life. A friend lost his friend due to an engine fire in a VariEze.
As long as we have carried gas or kerosene in our aircraft, we have had fires.
I was a light plane pilot for 10 years, designed structure on the Ted Smith (Piper) Aerostar and was a flight instructor, and the subject of engine fire extinguishing never came up. I first heard about it in ground school at TWA on the 727. It seems that the FAA and NTSB only require fire suppression equipment for large aircraft. So they want to protect large groups, but not you, your friends and family or the house you flew into!
I had been with TWA for seven years when I started designing and building a homebuilt aircraft. It was a tandem two seat, shoulder wing, mid-engine pusher, with a 5-foot driveshaft to the prop at the tail. I was worried about fire, because it was continually talked about at training. First, I needed a detection system to alert me. I used a probe from the Aerostar and bought from Piper, Radio Shack lights, horn and test button. I looked for a race car extinguishing system and found a three-nozzle system with 7.5 pounds of halon.
When I designed the aircraft, which looked like a shoulder wing F-4, I talked to Molt Taylor about using his Mini Imp drive shaft system with my Lycoming O-320. He said it would be good. It was not! After eight years, 22 flights, and 10 hours, the coupling failed at 3000 feet, east of the airport. I got to the airport, but a quarter-mile short of the runway. The best thing I did was call “Mayday.” When the wreckage stopped, I was trapped due to the bent canopy locking pin. A sheriff heard my call in his hangar and ran to me, getting me out. I feared burning up in my aircraft! When I got out, there was about a 5-foot diameter fuel spill under the engine. I think the discharged fire bottle saved my life!
It is time all homebuilt and certified aircraft carry these systems, just as ELTs are required.
STAN BURAK
Len Us Your Ear
Your May column on Experimental/ Amateur-Built rules [“Around the Patch: Commercial assistance, quickbuilds…babies & bathwater.”] begs the question: What is the FAAs role as assigned in law enacted by a vote of our elected representatives? In a word, its role is safety.
The current and proposed wording of FAR 121.91 (g) and accompanying Advisory Circulars is not in keeping with that assigned role. Regulations written to address safety would try to ascertain
how a plane was built. They would present guidelines focused on structure, building practices, weight and balance and general airworthiness. Any limitations for a homebuilt aircraft would be based on physics, physiology and aerodynamics.Todays regulations ask
why a plane was built and who built it. Asking the first question is an inappropriate function of government. If the Administrator had an infallible mind reader, would any of us pass the criteria of building “solely” for our own education or recreation? Asking the second question sends rulemakers on an exercise in the pretzel logic of trying to define the meaning of “fabricated.” Both questions have a history of generating paranoia. Neither fosters the safe design, construction and operation, which should be mutual goals of the government and the builder.We must address this issue in a way that holds the FAA to account in carrying out its assignment to make rules that ensure safety. If we lose sight of that overlying framework and accept anything less, we will be revisiting this topic in another decade as technology changes the means of fabrication. We will stunt innovation to the extent that the rules discourage new and better designs. We will also fall short of doing our part to establish a principled and logical standard that promotes safety in Experimental aviation.
LEN FOX
