Sailors approach their DC electrical systems with a laid back, caviler attitude that has always bothered me for some reason. Most of them understand DC systems a lot better than your average shade-tree car mechanic. They talk about house banks, charging systems, starting batteries and electrical load with the easy familiarity of people who know of what they speak. There is absolutely nothing "wrong" with what they say or how they operate their boats. And yet, as soon as I shut off the engine on any sailboat, this little voice echos in my head, "we are draining the batteries!" It bugs me to no end.
Then, last week, I checked out in a new kind of little single engine airplane. (New to me anyway.) It had an all glass panel and autopilot but only one generator and one battery. And I remember thinking there was no way I would take that thing into a night, cloud-filled, sky. It simply didn’t have enough DC system for all those fancy electronics. Aha!
My internal pilot warning system flashes code red at even the thought of running on battery power only. The first item on the check list for a full DC generator failure in the jet is to switch to “EMERGENCY POWER.” That action severely limits the amount of electrical load on the battery by shutting down all but the most important systems on the airplane. The check list then notes that even with a fully charged battery, there is but 30 minutes remaining before the battery is dead. Given the wrong set of circumstances (see below) everyone on board may well end up the same. "Batteries only” ranks high on the aviator's “up the creek without a paddle” list, topped only by being on fire or having a wing break off. (I did a one engine inoperative, full DC failure in night, IFR skies with an approach to minimums, during my last training session in the simulator. It took me two tries to get it right and yes, that means I crashed on the first try. I owed my training partner a beer that night…for killing him.)
A sailor treats his or her batteries like the driver of a car does a gas tank. Fill it (them) up with petrol (electrical potential) and head off. When it gets close to empty (or they get close to dead) stop and fill it up again (or bring some system online to top them off). A sail boat will run for days and days on battery power only. That is the normal state of affairs. Screw up and run the batteries dead (or the tank empty for that matter) and it will probably be nothing but a bit of an embarrassment. It may be a minor inconvenience. Shoot, it might even be a major pain in the butt. But only in the rarest of circumstances would it put one’s life in immanent danger.
In airplanes battery power (And gas of course!) are life and death consumables.
So I guess I am still an airplane driver pretending to be a sailor. Now that I figured it out though, maybe it won't bug me so much?
No comments:
Post a Comment