The Meat Grinder

I can still remember the awestruck feeling as I stepped back, mesmerized, away from the whirring Cuisinart that the propeller on our friendly yellow J-3 Cub had just become. In that moment I realized just how mighty these slicing scimitars would be against my stumbling, stupefied flesh. My instructor, Jim Beams, had given me careful instruction in the ritual that is the bringing to life of an airplane without an electrical system. There he sat, knowingly, feet on the brakes. He let it sink in a few more seconds, then with a wave of his hand, I was released from the spell, and we got on with the day’s lesson. A strong feeling? Hah! Never mind ‘like it was yesterday’; I can completely re-live it, each time I think about it.

There are, very roughly, 190,000 general aviation aircraft in the United States. According to data from the FAA, NTSB, GAMA, and other sources, a bit under 10% of them — just over 18,000 — have no electrical system. When you consider just general aviation single-engine piston aircraft, of which there are about 140,000, that percentage is actually more like 13%. At some point in many-a-pilot’s career, there will come a time when he or she is introduced to a new kind of starter motor… their own arms. Many of the aircraft that are ultimately engaged by such a motor are ‘conventional gear’ aircraft — conventional in the 1940’s maybe — and better known today as ‘tail draggers.’ If you’ve gotten a tailwheel endorsement… and you have a photographic memory… you may recall that CFR 14, Part 61.31(i) requires that (unless you logged PIC tailwheel time prior to April 15, 1991) you received specific training. Such instruction included learning the skills of normal and crosswind take-offs and landings, wheel landings (if the manufacturer allows them), and go-arounds. The instruction did not include one of the most hazardous operations of all — getting the thing started up.

As we all know — but often forget — for the rest of our airplanes that do have electrical systems, we still must tread gently any time we are near a propeller’s arc. The fact is that most airplanes with electrical systems have engines that are large enough so that ‘compressive resistance‘ in the cylinders would make hand-propping quite an exhaustive proposition. Translation: In most cases, you’d have no business trying — that same compressive resistance makes for an even more violent stroke of the blade should the piston fire. But for those 65-hp J-3 fans out there, as well as all the others, there are some important things to remember. More on that in a moment…

Most of us don’t hand-prop, and most of us have grown less wary of an idle prop — this is a bad thing. In case you forgot, here’s why:

Unlike our cars, an airplane’s ignition system is totally separate from its battery and alternator, because it uses the same principle to generate a spark of electricity that was discovered by Michael Faraday 170 years ago, in the form of magnetos. As we all know, there are two independent ignition systems and two spark plugs in each cylinder, one from each of two magnetos. The ‘off‘ position on our starter switch is supposed to ground out both magnetos, so that any movement of the propeller won’t cause the engine to fire. But if those grounding wires (called P-leads) become disconnected, well… please replace this section’s headline ‘may leave you unprepared,’ with ‘may leave you without an important body part.’

The safety record for hand-propping is poor, only because of the disregard for a few simple precautions. A runaway airplane is about as amusing or vaudevillian as a maniac wandering your airport with a chainsaw. The results are almost always disastrous, sometimes tragic. We’ll start with some rules to live by:

  • Always treat propellers like the mags are hot, and avoid putting any part of your body in the prop arc. That means no leaning on the prop — not for dramatic effect or any other reason.
  • Whenever possible, before you hand-prop an airplane have another knowledgeable person in the cockpit. Call for ‘brakes on‘. And also check that the brakes are working, by pushing near the blade hub … just make sure the prop doesn’t turn. (We’ll assume he or she already knows that a Cub has heel brakes, not toe brakes!) Then it’s the old ‘Contact!’ (which isn’t used much anymore) as you call for switches on.
  • If you’re alone, never, ever prop an airplane without first seeing that the tail is tied down securely. And chock one wheel, for good measure. Confirm fuel, throttle, mags, mixture, etc.
  • You must already be familiar with the throttle controls so that you know what position will provide idle power (or perhaps initially a bit more, on colder days).
  • Check the ground around you for solid footing, so you can beat a hasty retreat. Avoid wet grass and snow!
  • Techniques differ on the finer points of priming. Bad methods: Don’t over-prime, and don’t jockey the throttle to prime a hesitant engine; that’s a better way to start a fire in the induction system. Many smaller engines don’t have accelerator pumps in the carburetor, anyway. Better method: You can spread priming fuel well by pulling the prop through a few compression strokes — with everything OFF — before starting.

If you’re actually going to do this based solely on the knowledge you absorb from this fine piece of writing, that’s a mistake — but keep these steps in mind if and when you seek instruction.

  1. Grasp the prop with your fingertips — but don’t wrap them around the blade — with your thumbs on the front side. (This way if the prop kicks back, it won’t injure your thumbs.) On larger engines, using the prop tip gives you more leverage, but on smaller engines, grasping it further in gives you a faster spin.
  2. Set the prop in the 10 o’clock position with the mags OFF so that you can be sure footed when pulling hardest.
  3. Practice moving your body away as you pull through; lift one leg back, then as you pull through, swing your leg down. This will give you a bit more pull and gives you more momentum away from the action.

Special Notes
General: Despite the natural tendency to want to keep your distance from the propeller, do not stand too far in front of it. In leaning forward, your center of gravity would tend to pull you forward and down, and this is counterproductive. At the end of the stroke, you want everything in your favor to expedite your movement away.

Big Engines: When propping a larger engine, turning the prop back to the previous compression stroke will allow a little more momentum as you swing through the compression resistance of the next cylinder.

Metal Prop: Metal propellers are heavier, so you have more inertia to overcome. However once you get it moving, you then have their momentum in your favor.

All the usual rules apply. Confirm idle power, oil pressure in the green within the requisite amount of time, etc. Finally, resist complacency. Always be overly cautious. And if you ever see someone helping hand-prop an airplane, and it starts right up, but they’re just standing there with that deer-in-the-headlights look… well, it just might be their first time…