Manufacturer’s Recommendation

By lex, on August 4th, 2011

The idea of the Lancair IV-P is very attractive to the go-fast set: It’s (relatively) inexpensive to build and operate for a pressurized, high performance piston single. With the Continental TSIO-550B under the cowl grunting out 350HP, the plane will carry four real people over a thousand miles in around four and a half hours, averaging 325 MPH at 24,000 feet and 22 gallons per hour.

You can just about see the pride of ownership in this model.

The builder had the foresight to place two batteries on the ignition system for redundancy. Sadly, he wired both to a common bus bar before branching the current into discrete 5 amp automotive fuses. It worked for a while:

The pilot stated that the second flight was uneventful and they flew around the area for about 15 minutes. The downwind and base legs of the landing approach were normal. As the airplane turned onto final, the engine lost power. The pilot stated that the engine “just quit, there was no sputtering or surging.” The pilot switched fuel tanks, activated the fuel boost pump, and cycled the mixture, but was unable to get the engine to restart. The pilot stated that he realized that they were short of the runway and he was going to have to make an off-airport landing. The pilot readied his passengers for the emergency landing. He chose an open area, and left the landing gear in the down position. About 20 feet above the ground, he selected full flaps and activated the speed brakes. The airplane contacted the ground at 70 knots, the landing gear collapsed, and the airplane slid across the hilly desert terrain and came to stop upright.

In order to test the wiring functionality, investigators replicated the ignition system wiring on a test bench. Two 40-watt automotive lamps were used in place of the CDI units. Power was supplied by a variable power supply (PSU) was used to supply power to the left ignition circuit and 12-volt battery for the right ignition circuit. Current draw for the left and right ignition circuit was measured at the input terminal of each lamp. Investigators incrementally varied the voltage at the PSU and recorded the current draw for both the left and right circuits at each voltage increment. At an increment of .1 volts, the right ignition circuit drew 4.7 amps, and the left ignition drew 0.02 amps. At a voltage differential of 0.68 volts, the right ignition circuit drew 7 amps, and the left ignition circuit drew no current. Shortly thereafter, both automotive fuses blew, extinguishing the lamps.

According to the ignition manufacturer, the recommendation for wiring the dual ignition system to independent power sources required a direct current flow-path to each battery without the use of a common bus bar or serially connected Schottky diodes.

Of the four people aboard, all were injured, three seriously. This being America, everyone started suing everyone. The passengers sued the owner/builder, who in turn sued his neighbor and Garmin, the neighbor’s employer. Turned out the neighbor had gotten him a discount on the glass panel you saw if you clicked the link above.

In turn, Garmin is suing back.

So, yeah: I’m thinking certificated is the way to go. If ever I go there

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Filed under Best of Neptunus Lex, by lex, Carroll "Lex" LeFon, Carroll LeFon, Flying, Uncategorized

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