Relay-Version: B 2.11 6/12/87; site scorn Path: uunet!zephyr.ens.tek.com!uw-beaver!fluke!ssc-vax!wanttaja From: wanttaja@ssc-vax.UUCP (Ronald J Wanttaja) Newsgroups: rec.aviation Subject: It Slices! It Dices! Keywords: Hand prop, engine basics, article Message-ID: <3314@ssc-vax.UUCP> Date: Thu, 26 Apr 90 19:28:16 PDT Organization: Boeing Aerospace & Electronics, Seattle WA Lines: 312 As there's been some discussion about magneto operation and turning the prop by hand lately, I thought I'd post the following article. It was published in Jim Campbell's _The_US_Aviator_ magazine in January. Two side issues of note. The first is the style of the article. I wrote it for Campbell when he was editor of _Sport_Pilot_, and hence tilted the style toward the radical to match the magazine. It shows in a lot of "golly-gee-whiz" phrasology and a bit of FAA bashing. Those who read my KITPLANES articles will notice the difference. The second issue is related... in that I probably won't be writing too many more articles for Campbell. You see: 1. He published it without telling me (I happened to call to check its status in February, and was told "it was in last month's issue". 2. He still hasn't paid me for it. 3. He lost the photos I sent with the article... and I had sent the *negatives*, per his requirement. Anyway, enough bitching. On to the article! ------------------------------------------------------------------------- IT SLICES! IT DICES! By Ron Wanttaja (Copyright 1989 by Ronald J. Wanttja. All Rights Reserved) Upset by the new Mode C regulations? Most aircraft flown within 30 miles of a primary TCA airport must now have altitude-encoding transponders. The cost of building your dream ship goes up a thousand bucks, and all you'll have to show for it is a black box. The buck-sucking vampires of Washington have struck again. A string of garlic won't help, but the rule includes this silver bullet: "...except for aircraft without engine-driven electrical systems." If you don't install a generator, the transponder isn't required unless you actually enter a TCA. And without the generator, why install the rest of the electrical system? Elminate that twenty-pound battery and fifteen-pound starter as well as ten pounds of alternator. Buy a twenty-ounce handheld instead of five pounds of nav-com. Goodbye switches, so long battery box, farewell circuit breakers and ammeter. No cable bundles, no firewall pass-throughs, no crimping, no soldering. Shave up to a hundred pounds of weight, and save countless hours of installation and troubleshooting. The idea isn't unique to the Mode C era. The homebuilder's main enemies have always been weight, cost, and complexity. Removal of the electrical system is a victory over all three. But usually, it's a victory only until the builder realizes, "No starter? That means I gotta hand-prop that thing!" Back goes the starter, the generator, the battery, etc. etc. Out comes the charge card to pay for the transponder. All that additional weight and cost for something that's used only ten seconds a flight. Why not hand-prop? General aviation got along without starters for years. Sure, it's safer to sit in the cockpit and mash the button labeled "start." But smaller homebuilts can save 10% of their empty weight by deleting the electrical system. Which performs better, a plane weighing a thousand pounds, or an identical one weighing nine hundred? Each carries a starter. But in the second case, the starter is you. I know... you've never learned how to hand-prop, have you? The thought of touching that six-foot Veg-a-matic just gives you the willies. No matter. It's not that tough. With proper precautions and procedures, the typical lightplane engine can be easily... and safely... started by hand. A few basics, first: Three things are necessary to start an aircraft engine: Fuel, air, and spark. Rotation, as such, isn't needed. Squirt the proper fuel-air mix into a cylinder, position the prop to exactly the right spot, and fire a spark. The engine will kick over and start on its own. [There are some antique airplanes that start exactly this way... I didn't mention them because I don't remember their names.] Providing that spark is the problem. Aircraft magnetos generate their own electricity. But like an alternator or generator, they only produce power while turning. Since the mags are geared to the engine crankshaft, the prop must be rotating for the magneto to supply a spark. It doesn't matter if this rotation is provided by Bendix, Delco, or Harry Handpropper. But Bendix and Delco can't say "Ouch!" To keep this word (and stronger turns of phrase) from one's vocabulary, a deeper understanding of aircraft magnetos is necessary. Proper spark timing is vital to any internal combustion engine. Magnetos fire the plug at about 25 to 30 degrees before the piston reaches the top of the compression stroke (called top dead center, or TDC). At cruise RPM, this allows the right amount of time for the fuel-air explosion to build prior to the power stroke. But at starting speeds, 30 degrees before TDC is too early... the force of the explosion kicks the prop backward. Magneto impulse couplings solve this problem. At speeds less than four hundred RPM or so, the impulse coupling retards the spark (i.e., makes it later) for easier starting. When engine RPM approaches idling speed, timing shifts back to normal. Impulse magnetos make electric starters feasible for small aircraft; otherwise, the starter motor has to be big enough to turn the prop at near-idle speeds. When hand-propping, it's important to know which, if any, mags have impulse couplings. Slowly rotate the prop and listen for a click. The sound is produced by the other function of impulse couplings: they momentarily snap the magneto forward to produce a hotter spark. If there's only a single click, only one mag (probably the left) has a coupling. When in doubt, ask an A&P. Impulse couplings make hand-propping a breeze. The prop doesn't have to be turned quickly; just fast enough so inertia carries it through the compression stroke. In fact, flip it too fast and the coupling won't work. With only one impulse coupling, turn the other mag off during start. Engines without couplings require special care. If the prop isn't turned fast enough, the spark will sometimes kick the propeller backwards. This kickback can actually turn the engine backwards several turns. Poor hand-propping procedure can result in bruised or broken hands and wrists. Let's look at starting the garden-variety Continentals and Lycomings. These procedures work on VWs and Rotaxes as well, but reverse all references to "left" to "right" since these engines rotate in the opposite direction. Antique and classic engines like Kinners and Rangers may require special procedures. Before you touch the prop, check your footing. You're going to be standing near a sharp, rapid-turning (hopefully) object. Slip and you're sushi. Ice is an obvious hazard, but loose gravel or wet grass can be just as bad. Clear the ground or roll the plane somewhere else. Set the parking brake, if the plane has one. Normally, props will stop just before they reach a compression stroke. This places one blade at about the ten o'clock position as viewed from in front (two o'clock for VWs and Rotaxes). On a typical taildragger, the blade ends up at about shoulder height or a little higher. If the prop has stopped in some other position, turn off the mags and gingerly move the prop backwards. Remember, the mags are turned off by shorting the primary coils. While flying, that's great... if the switch wire breaks, the engine keeps running. But on the ground, the mag can fire anytime the prop is moved. Always assume the mags are hot: never casually touch a prop, and never place any part of your body where the prop can reach. Turning the engine backwards prevents the impulse coupling from firing. Stand in front of the prop to the left of the hub (your left, not the aircraft's), with your left foot slightly forward. Stand close enough so that you can comfortably reach the prop by leaning forward slightly. Being a little scared is natural and healthy, but stand too far away and a loss of balance might pitch you into the cleaver. Place both hands on the blade about two-thirds the distance out from the hub. This gives the best mechanical advantage; a small arm motion moves the prop over a wide angle. It's also typically the widest part of the blade. Don't wrap your fingers around the trailing edge. That's bad news if the prop kicks back. Instead, move the prop by the friction between your palm and the blade. The propeller's angle of incidence and downward hand pressure combines to give a very good grip. Bare hands work best. To prop the engine, sweep your arms in a short arc downward, curving your hands clear in the follow-through. Experience will show how much movement is necessary to get the prop past the compression peak. Use slight hand pressure against the blade to rock backwards and get your torso moving away from the prop. There's nothing wrong in turning this motion into a step or two backwards. This action is quite natural in a taildragger, as the tilted prop plane tends to bring your arms towards you as they're brought downward. If the engine doesn't have an impulse mag, turn the prop as rapidly as possible, while still maintaining your balance. If the aircraft has an impulse coupler, just a gentle flip will do. Pretty simple, eh? The point is to move your arms away when the prop's own momentum is enough to complete the stroke. You aren't trying to spin the engine over several times; just enough to move it past one cylinder's compression stroke. By the time the fuel-air mixture fires, your hands should be already clear of the prop. Practice with the switch off until you get the hang of it. Of course, hand-propping is much more than just turning the propeller. Let's assume you don't have a qualified person to sit in the cockpit, and go through the entire starting procedure. (See the sidebar for the legal aspects of this, and for two-person start procedures.) Too often, pilots are so worried about being hit by the prop that they ignore the other major danger of hand- propping: the runaway aircraft. Tie it down! Period. Locally in the last couple of years, a J-3 chewed up an airport office, a dead-batteried Bonanza creamed a Baron, a nose-dragging Varieze centerpunched a Cherokee, and a Cessna 180 bounced between two rows of aircraft for a half hour until the prop finally hit something hard enough to stop it. At the very minimum, tie the tail and use a pair of chocks. Even better, install a glider hook and cockpit release. They cost only a hundred bucks or so, and allow you to release the tail rope from the pilot's seat. Installation on a certified airplane requires only a weight and balance recalculation and a Form 337. The ground is clear, the airplane is secure, and we're finally ready for start. If the engine is cold, a few shots of prime will be necessary. All engines are different, but our club Fly Baby's C-85 likes one shot if the air temperature is between 60 and 85 F, two shots between 45 and 60, and three below 45 F. Don't prime if the engine has run in the last couple hours or so. Make sure the mags are off and the throttle is closed. Walk to the front of the airplane and pull on the prop near the hub to verify the plane is secure. Flip the prop through about six or seven blades to distribute the priming charge and loosen the oil. Walk back to the cockpit. Set the throttle closed or slightly cracked. Turn the appropriate mag(s) to the "On" position. Glance at the chocks and the tiedowns to ensure everything's secure. Then back to the front. Tug on the hub again. Take your stance and flip the prop, remembering to follow- through smoothly. Unless it starts, the prop will bounce between two compression strokes for a moment. Take care... when the engine is balky, it's too easy to automatically reach forward after each pull. The engine can fire anytime the prop is moving, and you might end up with broken hands or worse. Wait until it stops completely, then step up for another try. Occasionally the prop will come to a sudden stop... the engine has hung up in the middle of a compression stroke. This is very dangerous; the engine could fire with the least motion. Turn off the mags before repositioning the prop. When the engine finally starts, swing wide around the front end and head towards the cockpit. Get into the habit of walking around the wing, even if the plane is a high-winger. Too many pilots have tried to walk right through the prop. Once at the cockpit, do your normal post-starting tasks... turn on the other mag, adjust idle, check oil pressure, etc. When satisfied, back the throttle to minimum RPM, pull the chocks, and undo the ropes. Our Fly Baby typically starts on the second or third flip. Yours should too, if it's in reasonable shape. But what if it doesn't? Assuming nothing's broken, starting problems are usually traced to one source: Fuel, either too much (flooded) or too little. It's very apparent when the engine is flooded. The engine either doesn't fire or just sputters, and raw gasoline often drips from the air inlet. To clear a flooded engine, turn the mag switches off and open the throttle all the way. Flip the engine backwards for ten or so blades to clear the excess gas. Then close the throttle and turn on the mags. Use care with this procedure... make sure the throttle is pulled back before attempting to start. The engine can and will start at full throttle. I made this mistake once. Fortunately, the plane was tied down, but I went into adrenalin overload before reaching the cockpit. When the engine is starved of fuel, it starts, runs for a little while, then dies. The solution is more gas, either by cracking the throttle or by additional priming. Too much, though, will flood the engine and/or dampen the plugs. Use care... it's easier to add a little more than to clear a flood. In cold weather, don't blast the engine with many shots of prime. The raw gas strips oil from the cylinder walls and causes high wear upon startup. Instead, shoot another dose and leave the primer knob unlocked. Start the engine and add little squirts as the engine starts to falter. If only one mag has an impulse coupling and the engine refuses to fire, the magneto may be a little weak. Try starting on both mags. Flip the prop rapidly, as if neither has a coupling. The first time you hand-start an engine is a real thrill... there's something Waldo-Pepperish about it. But continued safe operation demands good habits as well as good technique. For instance, after turning on the mags, always tug on the throttle to ensure it's closed. On the way to the prop, twang tiedowns to verify the plane's secure. Make a post-starting ritual of patting a wingtip; you'll be less likely to walk into the running prop. Allow no distractions, encourage no conversations. Like every aircraft procedure, currency is important. Many hand-prop accidents involve aircraft with dead batteries. If you're well-practiced, go ahead and prop it. Otherwise, it's far safer to dig up a pair of jumper cables. If you run the battery dead on a Lycoming, expect a struggle. The starter gear remains engaged, and you'll have to fight the drag of the starter while turning the prop. Obviously, hand-propping is far more involved than turning the key to "start." But think of the aircraft problems you've encountered over the years. How often was the electrical system involved? There's a small amount of additional risk involved. But it's minimized by careful preparation and appropriate procedures. Considering the weight, time, and money saved by deleting the electrical system, why not hand-prop? Contact! THE END ------------------------------------------------------------------ SIDEBAR One of the continuing controversies about hand-propping is whether you can legally start an airplane without a pilot or A&P in the cockpit. There are no FARs that specifically address the issue; however, FAR 91.9, "Careless or Reckless Operation" is a useful catchall. Indeed, recently published FAA guidelines specify a license suspension of 30 to 90 days for "Propping an aircraft without a qualified person at the controls." However, no FAA representative I spoke to, in the safety, enforcement, and legal sections, interpreted 91.9 in that fashion. All felt solo starts are safe as long as the aircraft is tied down and chocked. But none would make an official statement to that effect. In addition, all were "good" FAAers... regional staffers active in general aviation, not occupants of Washington offices with 747 models on their desks. Who knows what they think. Or if. It's quite possible that the violation guideline is intended for those cases where an accident results. If you let the plane run away, you deserve a violation. But that still doesn't mean that an FAA enforcer won't file a violation if he catches you propping your plane solo. While it's tough to find someone to prop your engine, it isn't too difficult to find a pilot or mechanic to sit in the cockpit while you do the work. Nothing says he or she actually has to do anything... you can tie down the aircraft and set the switches, etc, as if they weren't there. Brief them on the brakes and engine controls in case something goes awry. If you can trust the person, they can make the whole process easier. Here's the procedure: 1. Brief the helper on the sequence of activities and the commands to be used. 2. Seat him or her in the cockpit. 3. Prime the engine appropriately. 4. Step to the prop. 5. Call out, "Brakes set, throttle closed (or cracked), switches off." 6. The helper checks the brakes, throttle, and switches, and verbally verifies each: "Brakes set, throttle closed (or cracked), switches off." 7. Tug on the prop hub to make sure the brakes are set, and turn the prop through six or seven blades. 8. Call "Brakes set, throttle closed, contact." Note: Use "Contact" instead of "Switches On." It's too easy to mishear a "switches on/off" command. 9. The helper should ensure the brakes and throttle are set, call "brakes set, throttle closed, contact," then turn on the mag switches. 10. Tug on the hub again, then start the engine normally. Should you wish to stop the start procedure, call "switches off." The helper should turn off the mags, then call, "Switches off." One last legal note: If you carry a handheld, the aircraft must have an FCC station license. This is true even if the plane has no provision (external antenna, mike wiring, etc) for the radio. ------------------------------------------------------------------------------ That's all, folks. Ron Wanttaja (ssc-vax!wanttaja) (End of Sidebar)