Aircraft Systems: Propping the Plane

This week we’re thinking about aircraft systems. Here’s an excerpt from William Kershner’s textbook The Student Pilot’s Flight Manual.

Nearly all planes have starters these days, but the following is presented for your possible use. If you plan on doing any propping (cranking the propeller by hand), you should receive instruction from someone with experience; it’s an extremely risky business. Another rule is to never prop an airplane without a competent pilot or mechanic, who is familiar with the particular airplane, at the controls. Propping a plane without a competent operator inside is asking for great excitement, tire tracks on your sports jacket, and loss of an airplane.

The idea of starting is the same as with an electric starter except you have manpower instead of electricity turning the prop. There’ll be a little more conversation in this case.

Man out front: “OFF AND CRACKED!” (Meaning switch off and throttle cracked.)

You: (After checking to make sure that the fuel valve is ON, the mags are OFF, and the throttle is cracked) “OFF AND CRACKED.”

Man out front: (After pulling the prop through several times to get the engine ready for start) “BRAKES AND CONTACT!”

You: Check the brakes and say, “BRAKES AND CONTACT,” before turning the switch on. Notice that you’re giving the benefit of the doubt in all cases.

He pulls the prop again and the engine starts. If in hot weather the engine loads up and doesn’t start, the propper will have to clear the cylinders of the excess fuel. If he trusts you, he may say, “Keep it hot and give me half,” meaning for you to leave the switch on and open the throttle halfway, adding that you are expected to hold brakes firmly and pull the throttle back as soon as the engine starts. He may push against the prop hub to see if you are holding the brakes, will then pull the prop through until the engine starts, and will be very, very unhappy if you forget to pull the throttle back and are not holding any brakes. One student chased a mechanic with an airplane for 50 yards one day. Of course, soon afterward the mechanic chased the student with a wrench.

In most cases with students, the person propping will say, “SWITCH OFF AND THROTTLE OPEN,” and you will make sure the switch is off and the throttle is open. When the plane is ready to start, the propper will say, “THROTTLE CLOSED, BRAKES AND CONTACT.” You’ll close the throttle (he can hear it close from the outside), say, “THROTTLE CLOSED, BRAKES AND CONTACT,” hold the brakes, and turn the switch on.

The whole idea in starting an airplane is safety. That prop is a meat cleaver just itching to go to work on somebody. Don’t you be the one who causes it to happen, and don’t be the one that it happens to.

“CONTACT!” may sound dramatic, but unlike “SWITCH ON!” which, on a noisy ramp may sound like “SWITCH OFF!” there is only one meaning to the word (the magnetos are, or are to be, hot). Besides, “CONTACT!” evokes memories of biplanes and barnstorming, helmets, and goggles. (Great!)

When You’re Swinging the Prop
Always figure the switch is on, no matter what the person in the cockpit says. Push against the prop hub to see if the pilot is holding the brakes. He or she may be an old buddy but having no brakes can do you a lot of damage here, so don’t take any chances.

Before you start to prop the plane, look at the ground under the prop. Is there oil, water, or gravel that might cause your feet to slip out from under you? If the ground doesn’t look right, then move the plane — better a tired back than a broken one.


Cockpit: (After checking) “OFF AND CRACKED.”

A lot of nonpilots think that the prop is turned backward and “wound up” and released, but this is wrong. You will turn the prop in its normal direction—that is, clockwise as seen from the cockpit, counterclockwise as seen by you when standing in front of the plane. You’re doing the same thing a starter does—turning the prop over until the engine starts. (Your car starter doesn’t turn the engine backward and then let go to make it start.)

Put both hands close together on the prop about halfway between the hub and the tip (Figure 1). Don’t wrap your fingers around the trailing edge; just have enough of the tips there to pull the prop through, because if the engine should kick back, your fingers would suffer. (You may also be fired into orbit if you hang on tight enough.) Stand at about a 45-degree angle to the prop; this should have your right shoulder pointing in the general direction of the hub. Keep both feet on the ground but have most of your weight on the right foot. As you pull the propeller through, step back on the left foot. This moves you back away from the prop each time. Listen for a sucking sound that tells you the engine is getting fuel. This will be learned from experience; an open or half-open throttle does not have this sound.

Figure 1. Propping the airplane.
Figure 1. Propping the airplane.

When you think the engine is ready, step back and say, “BRAKES AND CONTACT.” After the acknowledgment from the cockpit, step forward and give the prop a sharp snap. Then step backward and to one side as the engine starts.

The starting problems you may encounter have already been discussed.

Don’t stand too far from the prop. This causes you to lean into it each time you pull it through.

If the prop is not at the right position for you to get a good snap, have the person in the cockpit turn the switch off. Then move the prop carefully to the position required. As far as you are concerned, the switch is always on.

As always, check back on Thursday for more from our CFI!

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