Popping the Prop

Unless youre sure you know what youre doing, think twice before you hand-prop your airplane


When I was a new flyer, an old instructor named Tony Stubby Azzetti taught me how to hand-prop an airplane. Despite the lack of three fingers on one hand, he made it look easy, as though hed been swinging props to start airplane engines for decades. Always remember, he said as I took the propeller blade for the first time, that propeller cant see you and wont feel a thing if your melon gets in the way. Old Stubby sure knew how to teach.

Safety-conscious pilots will shake their heads in disbelief that anyone would intentionally grab a propeller and swing it. Good. Keep that attitude and youll live to be an old pilot. But some day, when your guard is down, you may be tempted to twist the prop. Frankly, its no sin unless you screw up.

There are two reasons to spin a propeller by hand. Either the engine has no starter or it has a starter but the battery is dead. Hand-propping isnt something you do for fun, such as sky-diving or alligator wrestling. Its the aviation equivalent of pushing your college roommates VW down a hill, then jumping inside to pop the clutch.

In the average piston engine airplane, the ignition spark is supplied by magnetos, which are completely independent of the battery and the master switch. This is Neanderthal technology in the electronic age. Beneath the cowling, your $250,000 Archer IV isnt much different than the ratty old Cherokee 180 parked in the weeds.

Magnetos are something farmers gave up using on their tractors 20 years ago. Think of them as magnets in a box that when rotated make a spark. This is primary theory, but important if youre to understand what happens when your hands are used to start an airplane.

Most single engine airplanes have two mags, both for redundancy and for a more even burn of fuel. Some have an impulse coupler that retards the spark for starting. Its usually found on one mag only and disengages through centrifugal force once the engine is running. At that point the spark advances.

The snap you hear when you pull the propeller through by hand is the impulse coupler activating. With the magneto switch on (not grounded), the engine should fire when that snap occurs. So, if you turn a propeller and hear that snap, think of it as the sound of a firing pin snapping against an empty shell casing. Add gunpowder – or in our case avgas – plus a hot mag switch or ungrounded mag – and it fires.

Like a gun, the propeller should be considered loaded at all times. Whenever youre near the propeller expect it to want to kill you. I cringe when I see pilots blithely pull their airplanes by the propeller, as though it was some big handle. Same with pilots who move the propeller during preflight to peer inside the cowling. They poke their nose inches from the propellers deadly arc and pull the blade. All it takes is one spark and theyll call you Flatface.

There I go scaring away customers again. Lets return to the legitimate reason to hand-prop an airplane, which is usually restricted to the antique division, the ones without electrical systems and starters.

Cub, Champ, Luscombe, Taylorcraft … the list is long of certified airplanes that need to be wound up by hand before flight. We wont try to teach you how to hand-prop any of these because no magazine article can. For that you must be taught by a master, someone (instructor, mechanic, Orville Wright) whos done it more times than youve tied your shoes.

Every style engine – four cylinder, six, radial – has a unique way of starting. The bigger the engine the more mass the hand-propper has to get into motion. A baby 65-hp Continental with bad rings is a breeze to spin by hand, but a Lycoming O-360 180-hp engine with decent compression is a bear to pull through. Each requires a different technique. We cant assume that since weve propped our buddys Cessna 120, then we can hand-prop a Cessna 195.

Propeller type effects hand-propping characteristics, too. Three-bladed propellers are a definite avoid item. Yes, theres the pilots lounge myth about someone who hand-started a three-bladed Bonanza and if you want to join that crowd, my hats off to you … at your funeral. Do the math. With one extra blade, you have less time to get clear.

Propeller composition affects the start, too. Wooden propeller blades have less mass and take a different swing than an aluminum blade. Knowing where to place your hands along the propeller is critical. Standard rookie technique is to grasp the propeller with fingers curled over the trailing edge of the blade like youre about to do chin-ups. This allows for a firm grip, but some day the engine will kick back. Usually this doesnt result in too many missing digits, but it hurts.

Once bitten, the newly shy hand-propper tends to stand too far away from the prop and gingerly grasp it by the tip. Balance is the key. If you hold the prop too far out youll have to pull it through a longer arc to reach the firing point. This unnecessarily increases your exposure to danger. Too close to the hub requires more muscle, which, again, increases risk. Theres risk in everything, and proper hand-propping can be done with relatively low risk exposure. But get flaky on technique and the risk equation inverts.

The other semi-legitimate reason to hand-prop an airplane arises when, like the hapless VW owner mentioned earlier, you find yourself on a windswept ramp in North Dakota with a dead battery in both your airplane and your cellphone and you must get the serum through. Then, you will be tempted to start by hand. Lots of pilots do it without any trouble. If you mess up, you could cause serious damage or be left standing on the ramp as your airplane heads to Fargo, alone. We snicker up our sleeves and think what nit-wits those type pilots must be. Until, to paraphrase Pogo, they be us. It only takes a few seconds or less to make the transition.

Its not only the brand new private pilot whos subject to error. Theres a tendency for seasoned veterans to get careless around propellers. When propping is standard fare, it loses its threat after a few hundred twists. Those of us who spin a prop before every flight can become jaded about the danger. Even the old hands need to step back now and then to review technique.

The Rules
Although it seems as though theres an FAR for everything else, theres little official guidance for hand-propping.

Partially, thats because the airplanes of yesteryear were designed to start by hand; the CAA (now FAA) couldnt regulate every facet of the start. A huge dollop of common sense applies.

But think about your Cessna 172 with a dead battery. Sure you can hand-prop it to life, but under FAR 91.7, you, the PIC, are required to determine if that aircraft is in an airworthy condition. Paragraph (b) says the PIC shall discontinue the flight when unairworthy electrical conditions occur.

That 172 was designed to start by turning a key. If you have to monkey with the prop, is it airworthy? I wont answer that for you, but perhaps you have more than a dead battery to worry about. Your call.

There is no FAR Part 91 paragraph called Hand-Propping. FAR 91.3 says, Youre PIC so act like one and take the heat if you dont. Should you send your pilotless Citabria winging into a passing Citation, youll probably get sued. But the FAA will also probably cite you under 91.13 for careless and reckless behavior. Frankly, I wouldnt sweat the lawyers, because as PIC you have to make decisions. Cant handle that? Dont fly.

The FAAs opinion of what they call hand-cranking an engine is found in two Advisory Circulars – AC 91-42 and AC 90. Boiled down it comes to this:

1) Only experienced persons should (not shall) do the hand-cranking with a reliable person in the cockpit. No mention is made of needing a licensed pilot at the controls. The other strand of FAA advice from AC-90 is: Never PROP an engine on uneven or wet/snow covered ground. I once had to hand-crank my airplane on a frozen lake, because thats where I was stuck and didnt want the long frozen walk home. Under normal circumstances Id have to agree with the FAAs advice.

Safety is what its all about. Regardless of credentials, things can get squirrelly if the person at the controls and the person at the propeller arent communicating. Before you take the blade in hand, work out the signals. Discuss what each player will do and whatll be said. Its suggested that the person at blade be in charge and call the commands. Have the pilot at the inside controls repeat them verbatim. Agree on phraseology. One pilots, Contact! is another pilots, Switch off.

As Stubby Azzetti says, When the magneto switch says OFF, it means … you can read. Never trust either the magneto switch or the pilot.

Generally, the older airplanes that need to be propped will be tailwheel types. In that configuration, the airplanes nose is naturally pointed skyward, which brings the propeller into good position for cranking. Tricycle gear airplanes, by contrast, are stinkers to prop. The propeller sits lower, which means less room to swing it. The hand-cranker has to contort into a hunched over position leaning into the propeller.

Weve seen the old newsreels of mechanics kicking a leg high like a Las Vegas chorus girl before heaving down on a prop blade. It looks cool in the films, and old Hissos and Liberty motors took a huge heave, but its no good. All that dancing around on one leg throws you off balance and can result in an unplanned tumble into the chopping blades.

Your goal is to be moving away from the blades, not toward them. True, the swinging leg fandango is meant to swing you away but it can throw you off balance. Have someone show you how to do it with less drama – someone like Stubby, whose moniker came from his habit of smoking cheap cigars right down to the stubs, not from the fact that hed lost those fingers in snowblower. Those snowblowers are dangerous, which is probably why he moved to Florida.

-by Paul Berge

Paul Berge, editor of IFR, owns a 1946 Champ with no electrical system, hence no starter.


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