Words of Advice:

"If Something Seems To Be Too Good To Be True, It's Best To Shoot It, Just In Case." -- Fiona Glenanne

"Flying the Airplane is More Important than Radioing Your Plight to a Person on the Ground
Who is Incapable of Understanding or Doing Anything About It." -- Unknown

“Never argue with stupid people, they will drag you down to their level
and then beat you with experience.” -- Mark Twain

"Everything is easy if somebody else is the one doing it." -- Me

"Eck!" -- George the Cat

Tuesday, December 30, 2008

Grounded, Effectively

It's been going on two months since I last flew. Weather was crappy on some weekends, the Thanksgiving weekend was lost to travel.

So a few weeks ago, I was home on a nice weekend day. It was a little cold; I loaded the pre-heater and its gear into the car along with my flight stuff. I had to pump up the tires and then began my preflight.

Now for a necessary detour into a little discourse on engines:

Other than experimental airplanes, piston-engined airplanes have their spark plugs fired by magnetos, which is a very old technology not found in cars since fuel injection and advanced emission controls came into wide use. Magnetos don't require an external electrical supply; they are little generators powered by the rotation of the engine's crankshaft (that's why you can push-start an old car). Magnetos feed electricity to the distributors and the rotor of the distributor routes power to the spark plugs. Airplanes have two spark plugs per cylinder, as well as two distributors and two magnetos. That is so that there can be no "single-point failure" of the ignition system.

Magnetos are always "on." What they have is a wire that shorts out the generator part of the magneto. When you turn an engine with magnetos "off", what you really are doing is closing a switch that is wired into that grounding wire. That wire is known as the "P-lead" and if it breaks, the magneto cannot be shut off.

You can hand-start an airplane by pulling smartly on the propeller, a method known as "hand-propping."



Now imagine this scenario: Some passer-by is walking along a line of airplanes and comes upon a taildragger. He says: "This is how you used to start these things," and he gives the prop a yank. If a P-lead is broken, the engine can start. It will run until someone either breaks into the cabin and shuts the fuel off or pulls the mixture control all the way off. Even if the mixture control is all the way off, enough fuel might slowly creep into the carburetor to allow the engine to fire a few revolutions.

Which is enough to injure or kill a careless fool who didn't expect the engine to start. I shut off the fuel valve from the tanks to the engine and, when I shut down, I do that and let the engine run to drain the line to the carburetor.

In doing the pre-flight, I turned the fuel selector switch back to a tank so I could take a fuel sample. I came around the landing gear to walk to the right side of the airplane (it's easier for me to take a sample from that side) and I smelled aviation gasoline. I looked down and I saw that gas was dripping from the cowling. I shut the fuel control off, secured the airplane, left a phone message on the answering machine of my mechanic and went to lunch.

It might have been something that I could have discovered by looking at the carburetor or maybe lightly tapping on it in case the float had stuck. It was 25degF out with a slight wind, pre-flighting it was miserable enough and the mechanic works in a heated hangar. Easy choice.

It took him about two weeks to get to it, as his priority is to fix airplanes that people use to make money, which I fully understand. He called to say that it wasn't leaking when he looked at it, it started OK, but did I know that there was a pretty good oil leak from the back of the engine?

Um, no. The oil level was were it should be when I checked it.

So the airplane is in his hangar and I'm on the ground.

(Before you comment, read the first word of advice just below the title of this blog.)

11 comments:

One Fly said...

No I don't but you caught it and that's what it's all about.

Mark said...

Seconding One Fly's sentiments. And I can still feel sorry for the plane.

Karen Zipdrive said...

You poor, poor dear.

deadstick said...

A car doesn't have to have mag ignition to be push-started. Westinghouse ignition is actually a very small electrical load, and pushing turns the generator enough to power it. BTDT, many times...

One Fly said...

You can push start a vehicle with an alternator if there is current in the battery.

If the battery is completely dead an alternator cannot produce current unlike a generator which can.

deadstick said...

True, but "completely dead" means COMPLETELY. A battery can deliver enough current to excite the alternator long after it's too flat to pull in the starter solenoid.

One Fly said...

That's correct Deadstick as it only takes a couple volts to do that. But if it's really dead it ain't happening.

One of the benefits of the generator days when the battery was completely dead you knew you could get it running if you could get it moving.

montag said...

You are doing so much better than the guy who hand propped his plane with his granddaughter in the cabin and had the plane get away from him. The plane ran across the field and into some trees and the plane was damaged but there were no serious injuries.

Comrade Misfit said...

Montag, I do have it in mind to write a post on hand-propping.

Anonymous said...

OK, so we are sharing out sad stories. I had the Twinco pulled out of the hanger on Christmas Eve because I couldn't pull it over the small amount of snow. Started up the engines which were already warmed by the heaters, and proceeded with my taxi..There was a maintenance truck parked perpendicular to a hanger along the taxiway and it stuck out too far, so I moved well to the right. When I had successfully passed, I found that I was off the taxiway with my right main. OK, I dodged a bullet, I thought. Taxied out to the runway, did a run up and left. 3 or so hours later, I landed in LaJunta, Colorado for fuel and to use the bathroom...I did the latter first and when I came back to the airplane, Janice and our friend from LHX were standing in front of the right engine.....the prop had both ends bent...but only a bit..HA. Thus, the prop is at the prop shop and I am going to go for a major instead of just a tear down, as the engine has 1300 hours on it. NEVER feel sorry for anyone who owns an airlane.
Gug

Comrade Misfit said...

JG, you win. (wince)