Aircraft technical Basics: Introduction to Airplanes - Navy Training Courses Edition of 1944: Chapter 13 Fueling and Starting

CHAPTER 13 FUELING AND STARTING

FUELING ASHORE

Keeping the gasoline and oil tanks of an air-plane filled up is more important than you might realize at first thought. The fact is that MOISTURE FROM THE AIR will condense on the exposed interior surfaces of PARTIALLY-FILLED TANKS. Before long there will be WATER in the fuel system, and you will be in a fix. DON'T LET IT HAPPEN.

IMMEDIATELY after any flight, the fuel and oil supply of an airplane should be replenished. Refueling an airplane is a bigger job than taking the family sedan down to the filling station, however.

Be sure you have received COMPLETE AND PROPER INSTRUCTIONS before you tackle it.

First of all, the airplane should be in a SAFE PLACE where there's NO FIRE HAZARD. Be POSITIVE that the switch is "OFF" and that the wheels are chocked carefully. The fuel trucks must be driven carefully into position, and a portable fire extinguisher should be placed near the airplane. Assemble all the necessary equipment for your job and see that every piece of it is cleaned thoroughly. Rinse the funnel with fresh gasoline. Clean the hose nozzle before using it, and keep it from touching the ground or otherwise picking up dirt.

Figure 42.-Grounding nozzle and fuel tank.

Gasoline flowing through a hose builds up a CHARGE OF STATIC ELECTRICITY. When you withdraw a hose nozzle from the tank of an airplane, this charge can easily create a spark that will set the gasoline AFIRE, if you don't take proper precautions in advance. BEFORE YOU start refueling, the hose nozzle and the funnel MUST BE GROUNDED - that is, electrically connected to the earth to remove the charge.

Usually, you'll find that Naval refueling hoses have a GROUND WIRE which automatically makes connection with the earth through a conducting hose. If so, connect that wire to some METAL part of the airplane, such as the tank or engine.

If you're not using a hose that is so equipped, however, you can easily rig a suitable grounding system. A short wire with clips at each end should be obtained. You attach one clip to the nozzle and the other clip to the fuel tank of the airplane, as in figure 42. Then attach another wire to the nozzle or to the airplane, and connect the free end of this wire with the earth. If you're drawing fuel from an underground tank, make an electrical connection between the nozzle and the storage tank.

Danger from static electricity is a lot greater JUST BEFORE - AND DURING - an electrical storm, so avoid doing any refueling at such times except when ABSOLUTELY necessary. If it MUST be done, ground the airplane by running a wire or chain from the engine mounting, or some other metal part of the fuselage, to the earth BEFORE any other operations are started.

One of the big BUGABOOS in refueling is the possibility of getting WATER into the fuel tanks. It's worse than getting salt in the sugar bowl! If there's the slightest chance that water has crept into the gasoline, it must be STRAINED.

Fortunately for you, most refueling trucks and underground storage systems have WATER SEPARATORS which automatically filter the gasoline before delivering it to the airplane tank. These separators should be checked regularly and drained of any accumulated dirt and water. When clean and operating properly they are a big help.

You may, however, have to use a strainer funnel in filling an airplane fuel tank. There are several types made which have patented strainer equipment. Some of these are good, others are not. You'll have to test their effectiveness separately before using any of them for filling an airplane tank.

When an approved patented strainer funnel or regular separator isn't on hand, you can IMPROVISE an excellent strainer by placing a chamois skin loosely over the mouth of a funnel and tying it in position. Chamois skin used for straining must be washed with soap and water to remove the sediment which will tend to clog its pores.

Then it should be AIR DRIED and RINSED thoroughly in clean gasoline before being used.

POOL-TABLE FELT over your funnel also makes a good strainer. You'll find that it strains fuel more quickly than chamois, but will have to be changed more frequently as water accumulates, because the water will eventually pass through.

Gasoline that has been stored in 5- or 10 - gallon cans must ALWAYS be strained before it can be used in an airplane. Such fuel invariably contains water and sediment as the result of condensation and rust.

DOUBLE OR NOTHING on this question! How would you refuel an airplane in the open during a RAINSTORM? No ! You wouldn't wait till it stopped raining. You'd place a waterproof cover over the filler neck of the tank, and work underneath it.

Never remove the filler cap from a fuel tank until everything else is ready. If you're using a funnel, place it in the filler neck so that the weight of the funnel - and its load of gasoline when the fuel is flowing - is not on the neck. It may easily be bent. The tank itself might even buckle or crack.

When you're finished with the actual refueling of all tanks, measure the amount of gasoline in each tank carefully and record it exactly. Use a CLEAN measuring stick, and DON'T RELY ON GAGES.

Inspect all gas tank vents to see that they are open. Check to see that the chain on the filler cap is in good order. Replace the gas tank cap and be certain IT IS SECURE. Then pick up all  rags and gear used during refueling and return them to the places in which they belong.

Here are some valuable tips on gasoline and how to handle it around airplanes

Mixtures of gasoline and air in certain proportions are highly EXPLOSIVE. The slightest spark will ignite them.

Gasoline vapor may cause SICKNESS, or even BE FATAL to persons breathing it. Be cautious.

Aviation gasoline may cause serious injury if spilled on your skin. By all means KEEP IT FROM GETTING IN YOUR EYES OR HAIR.

Learn now to prevent and extinguish gasoline fires BEFORE YOU HANDLE FUEL.

Be EXTREMELY CAREFUL IN HANDLING TOOLS in the vicinity of fuel lines.

Check gasoline piping and tanks daily for LEAKS, and report findings immediately.

NEVER mix gasoline with oil for use in running an air-plane engine. Oil should never be introduced into an airplane fuel system.

Long, unsupported fuel and oil lines in an airplane are likely to VIBRATE loose. The free length of such lines should be cut down as much as possible.

When there is a chance of anything rubbing against a fuel or oil line, FRICTION TAPE or some equivalent insulation must be used.

Carburetor DRIP-PAN DRAINS must ALWAYS be in place, and the discharge from drains must clear the air-plane structure.

Chamois leather will separate water from gasoline for a certain length of time only. Watersaturated chamois WILL DISCHARGE WATER from the under side as fast as the top will absorb it.

Chamois leather should be kept dried out when not in use. DISCARD IT after it becomes hardened and cracked.

Always strain fuel in the SAME DIRECTION through chamois.

Wet chamois MUST NOT BE STOWED in an airplane, as it may become a source of gasoline fumes.

Take SPECIAL PRECAUTIONS to prevent fire if it is necessary to refuel an airplane at night.

Airplanes must not be serviced unless all engines are STOPPED, except in flight.

Inflammable liquids are NEVER to be stored in hangars. Airplane engines are NOT to be run in hangars, unless absolutely necessary.

REFUELING AFLOAT

So far, you've been dealing with the refueling of landplanes, or seaplanes out of water. The job of fueling SEAPLANES AFLOAT is quite a different thing. In general, this can be done in one of two ways - by means of a SMALL BOAT equipped with fuel tanks, or by bringing the plane ALONGSIDE A SEAPLANE TENDER.

Refueling a floating seaplane by means of a small boat brings into use your knowledge on handling small boats around planes. Several kinds of small boats may be used for fueling sea-planes afloat. There's a modern type of 42-foot boat, for instance, that is built expressly for the purpose. More than likely, though, you'll have to use a whaleboat that is equipped with a small BOWSER (fuel tank) and a HAND PUMP.

Getting your boat into position for fueling the seaplane is the first part of the job. The details of reaching position properly will, of course, depend on wind and weather conditions, and will vary with the kind of plane being fueled. The PBM, for instance, has its fuel tanks in the HULL whereas the PBY tanks are in the WINGS and must be fueled from the top.

Naturally, there are a number of positions from which your small boat can fuel a floating seaplane efficiently, and they can't all be considered here. But a discussion of the general principles of refueling from a FEW TYPICAL POSITIONS will furnish you with the basic background for handling the job.

Figure 43.-Passing refueling hose to a seaplane.

Suppose, then, that you're proposing to refuel the PBM - which has its tanks in the hull - from the PORT QUARTER. Don't try to approach with your boat until someone in the plane crew SIGNALS you that the plane is moored. When you've been assured that all's well, bring the boat up AHEAD of the plane and SLIGHTLY TO PORT OF CENTER.

Drop anchor about one boat length ahead of the plane.

When the anchor is fast, pay out the anchor line and back the boat down to a position opposite the port stern quarter. Be sure to KEEP CLEAR OF THE SEAPLANE WHILE YOU'RE BACKING INTO POSITION.

As soon as the boat is where you want it, pass a line to the plane crew man on the tail of the sea-plane to keep the boat from swinging away. If it tends to swing in instead, by all means keep it from hitting. Airplanes are FRAGILE!

Everything should now be ready for passing the gas hose over to the plane. Toss a heaving line to the plane crew, having first attached the hose to YOUR end of the line, as in figure 43. The plane crew then hauls the hose over, taking it in through the after hatch, leading it through the hull and out again through the hatch near the fuel tank. This is done so the plane crew man who is fueling won't have to hold the whole weight of the hose.

Think a moment, now, before you start fueling. Don't forget your precautions against FIRE HAZARD. The plane crew man must "ground" the nose nozzle by trailing a wire from it to the water, or attaching a wire to the nozzle and the side of the plane. The boat crew should stand by with FIRE EXTINGUISHERS - ready for any emergency.

When the fueling is finished, you can cast off the line to the plane and haul in on the anchor line until your boat is clear. As soon as the anchor is weighed, be ready to pull away. It still wouldn't do to let the boat and plane collide.

Another position from which the PBM can be fueled is at the BOW. The bowser boat should be anchored several lengths AHEAD of the plane, and the anchor line paid out until the boat is just forward of the hull. The hose is taken in - by means of a heaving line - through the forward hatch, led through the hull and passed out as before through the hatch near the gas tank.

There are also many positions from which you can refuel a floating PBY. These patrol planes, you remember, have their fuel tanks in the WINGS. Anchor your bowser boat several lengths ahead of the plane, and pay out the anchor line until the boat is JUST FORWARD of the hull. Pass a heaving line to a man on the wing, and the plane crew will haul the hose over the leading edge of the wing to the tanks.

At ADVANCED BASES refueling of seaplanes is usually done from SEAPLANE TENDERS, as shown in figure 44. Depending on the size and type of tender, three methods of fueling are generally employed - FROM THE STERN OF A SMALL TENDER, AT THE END OF A BOOM, Or at the STERN OF A LARGE TENDER.

Figure 44.-Refueling a seaplane from a tender.

It is easiest to fuel a seaplane at the STERN FUELING STATION of a small tender. At this station the seaplane is always clear of the ship - which has a tendency to yaw. A long line, FITTED WITH FLOA'T'S, is taken out astern of the tender and picked up by the plane crew. They then haul the plane up to the stern of the tender. Wing lines may be passed to prevent yawing, and other lines passed to haul over the gas hose. WARNING ! DON'T LET THE, PLANE TOUCH THE SHIP. Use fending poles to keep it off.

FUELING AT THE END OF A BOOM takes training and experience. Tenders have a habit of yawing at the wrong moment when moored or anchored.

The plane crew must keep on its toes to fend off in case the tender swings toward the plane. If you're refueling by this method, a boom is rigged outboard from the tender and the fuel hose is passed along the boom from the fueling station. The plane TIES UP at the end of the boom, and the hose is passed down to the plane crew.

The DECK of a large tender is so far above the water that you had better not bring a seaplane close to the stern for refueling. The plane should taxi in and pick up the end of a floated line - just as when approaching a small tender. But it should not be hauled in too far. Rather, you should secure the plane a short distance astern, so that it can't swing into the ship under any conditions of wind or current. A floated hose is then taken out from the ship by a man in a small boat.

Now, to repeat TWO PRECAUTIONS you've heard before. No matter how, when, or where you're refueling a seaplane afloat, remember that IT IS FRAGILE. And don't forget the EVER-PRESENT FIRE HAZARD. If you're careless, you'll be decorated with a WOODEN CROSS   instead of a NAVY CROSS.

FILLING OIL TANKS

Here are a few words on the subject of OIL. The capacity of airplane oil tanks is clearly marked in conspicuous places on them. You should fill them to this capacity - AND NO MORE. That additional space is for the oil to EXPAND when it gets hot. If you've added too much oil, the tank may overflow in operation.

NEWLY INSTALLED ENGINES, whether just freshly overhauled or brand-new, should have their oil drained and be refilled at the end of the FIRST FIVE HOURS of flight. Thereafter, the interval between oil changes will vary with the type of engine.

Some engines require oil changes after every 60 hours of flight time. Others need draining and refilling after 120 hours of flying. And some models need no change between overhauls, as a general rule. Be sure you know the oil requirements of the engine YOU'RE servicing.

Be sure that NO RAGS OR DIRT get into the tanks to clog up the lines or obstruct the flow of oil when you're refilling or adding lubricant. A clogged oil line can down an airplane as quickly as a broken fuel line.

STARTING

When a pilot gets set for a take-off, he has every right to expect that his ENGINES ARE AS FIT AS A BOXING CHAMPION AT THE OPENING BELL. Anything short of perfection on your end of the line ISN'T GOOD ENOUGH. A slip-up on your part can easily endanger the lives of the entire crew. Their fate is in your hands. There's more to readying an airplane than handling, cleaning and inspecting it. The engines must be in tip-top shape, and running smoothly before the pilot takes over. STARTING THEM, WARMING THEM UP, AND TESTING THEM THOROUGHLY may be part of YOUR job - an interesting and vital part.

Unless you are fully familiar with an engine, DON'T TRY TO START IT for a warm-up and test without consulting a responsible superior for full information on the proper procedure. Improper starting, warming up, and testing of a modern, high-performance engine can result in SERIOUS DAMAGE. Manufacturer's directions should always be followed explicitly. Guesswork will get you a large hunk of grief.

KNOW YOUR ENGINE ! One set of rules for starting will apply only to A PARTICULAR ENGINE, and even then there will be variations, depending upon the kind of accessory equipment installed with it. Here, for instance, starting, warming-up, and ground testing a Pratt & Whitney R-2800 engine will be considered. Since the position of the mixture control in starting depends upon the type of carburetor and other equipment installed with a particular engine, the procedures discussed will apply in all details ONLY to a Pratt & Whitney R-2800 using a Stromberg injection carburetor. However, a careful study of what follows will show you the care with which you must approach all engines in starting and warming up.

In cold weather the oil in an engine should he PREHEATED before you attempt starting, unless an oil dilution system is used. In the latter case, the engine oil should have been diluted with fuel PREVIOUS to stopping the engine after its last run. If the weather is EXTREMELY cold, you may have to PREHEAT THE ENGINE, too, before it will start.

Be positive that the IGNITION SWITCH is turned to "OFF." Turn the engine over four or five revolutions by PULLING THE PROPELLER THROUGH BY HAND. That will clear out any oil or gasoline which might have collected in the lower cylinders while the engine was inactive. It's a good plan to remove the LOWER spark plugs before turning the engine over in this way, if you have reason to think the cylinders might be loaded with gasoline - particularly if the exhaust tail-pipe is raised so as to prevent drainage out of the exhaust ports.

OPEN THE COWL FLAPS. During all ground operations, the adjustable cowl flaps should be fully opened - and LEFT that way.

Set the CARBURETOR HEAT CONTROL in "cold" position, and the PROPELLER CONTROL at "low pitch." The BLOWER RATIO SELECTOR VALVE should be set in the "low" position for all ground operations, unless you're expressly checking it for proper positioning or functioning, or testing the operation of the supercharger drive mechanism in general.

Place the MIXTURE CONTROL in the "idle cut-off" position. Set the THROTTLE according to the kind of starter you'll be using. If it's a DIRECT CRANKING ELECTRIC STARTER, the throttle setting should he between one-tenth and one-fourth open. With an INERTIA or CARTRIDGE STARTER, open the throttle at least one-fourth or perhaps a little farther, as the engine will be turned over initially at a higher speed. CAUTION! As soon as the engine actually starts to run, cut down the throttle opening so as to limit engine rpm to between 600 and 800.

Turn ALL VALVES in the engine fuel line to "ox" and, with the auxiliary or hand wobble pump, till the fuel lines and carburetor with fuel, but don't build up more than 2 or 3 pounds per square inch (psi) pressure. If the engine hasn't been run for several days, a period of two minutes or more may be required to permit air and vapor to escape (or "vent") from the carburetor. Poor starting may be a sign of INCOMPLETE VENTING. If so, just hold your horses ! The trouble will clear up.

You'll generally have to PRIME an engine to get it started easily. The PRIMING PUMP, or PRIMER, draws liquid gasoline from the fuel supply system and forces it into several of the cylinders or to the intake manifold of the engine. The amount of pruning needed for quick starting will depend on the type of engine, its size, the weather and temperature conditions prevailing, and the priming equipment installed. Gasoline coming from the carburetor does not vaporize as quickly when the engine is cold. Hence, if a primer was not used, you'd have to do a lot more propeller cranking to draw gas from the carburetor, through the induction system, and into the cylinders.

TOO MUCH PRIMING will load the cylinders with raw gasoline. So be careful not to overdo it. Loaded cylinders mean difficult starting, and excess gasoline will tend to wash the oil off the cylinder walls, with consequent danger of scoring or of "piston seizure" because of dilution of the lubricating oil. If, ACCIDENTALLY, YOU DO prime cylinders excessively, you should APPLY FRESH OIL TO THE CYLINDER WALLS before starting the engine.

Piston rings and cylinder walls are liable to become rusty if the engine is allowed to stand for a day or so after unsuccessful attempts to start it. FRESH OIL APPLICATIONS in the cylinders are again the answer. If you really overdo the use of the priming pump or valve, fuel may drain back through the intake pipes of the PRIMED cylinders and collect in the intake pipes of the BOTTOM cylinders, without showing any signs of fuel leakage from the blower drain valve. This valve drains ONLY that fuel introduced at the CARBURETOR NOZZLE.

In starting a cold engine, UNDERPRIMING is more often the cause of difficulties than slight over-priming. You can usually recognize underpriming by the BACKFIRING through the intake system - and that presents some hazards you'll want to avoid. As would be expected, cold-weather starting requires a GREATER AMOUNT OF PRIMING and a SLIGHTLY LARGER THROTTLE OPENING than starting in warm or moderate weather. To start a hot engine you probably will have to do no priming at all.

Priming is done either with a HAND PRIMER PUMP or by means of an electrically operated PRIMER VALVE. With either type of equipment, first be sure the mixture control is in "idle cut-off" position. Then, with the hand wobble or electric auxiliary pump, bring the fuel pressure up to 2 or 3 psi. In case your engine is equipped with the hand-type primer pump, don't build up more than 4 psi pressure with the fuel pump while the hand primer is OPEN, or it may become HYDRAULICALLY LOCKED and you won't be able to push in the primer pimp plunger. In fact, you'll have to take the WHOLE primer pump apart to release the mechanism.

If you're using an electrically operated primer valve instead of a hand primer pump, the fuel pressure should be built up to about 8 psi. Then you open the primer valve for as long as is needed to prime the engine adequately. This can be anywhere between 5 and 30 seconds, and depends on the make of primer as well as the engine temperature. Experience is the BEST teacher. In general, remember, if the engine is warm from previous running, or if the outside temperature is 60° F. ( 15° C.) or above, priming probably won't he necessary.

Once any necessary priming has been done, the engine should be ready for starting. Is your THROTTLE open the right amount? Have you set the MIXTURE CONTROL in "idle cut-off" position? Are you keeping the FUEL PRESSURE at about 8 psi? Well and good. If you're using a direct-cranking electric starter and the engine's fairly warm, wait until it has been spun about ONE REVOLUTION before turning the ignition switch to "BOTH ON" position, in order to avoid kick-back. The engine may start immediately, and you'll move the mixture control to "AUTOMATIC RICH" while continuing to operate the wobble pump (or electric auxiliary pump) until the engine is running smoothly. Adjust the throttle to hold engine speed as low as possible for 30 seconds, and watch for an indication of oiL PRESSURE on the gauge. If oil pressure doesn't register almost immediately, you'd better stop and investigate.

What's that? YOUR engine DIDN'T start right off the bat? Well, if you're sure you turned on the ignition switch, and did everything just the way you were supposed to, then just try again. Only, THIS time move the mixture control out of "idle cut-off" and over to "automatic rich" for about three seconds after you've switched the ignition to "on." If that doesn't do it, adjust the mixture control back to "idle cut-off" and continue turning the engine with the starter, keeping the fuel pressure at 8 psi. One to three repetitions of this procedure will USUALLY start her.

When an oil pressure indication has appeared on the gauge, adjust the throttle to about 1,000 rpm.

OVERLOADlNG of a WARM engine with gasoline will show up by a discharge of fuel from the drain valve, located in the lower part of the engine blower. If this symptom appears, keep the mixture control in "idle cut-off" position, discontinue using the auxiliary fuel pump, open the throttle wide, and turn the engine over with the starter to clear out the excess gas. The MOST FREQUENT CAUSE of cylinders loading with gasoline is FAILURE TO LEAVE THE MIXTURE CONTROL IN "IDLE OUT-OFF" POSITION. So keep that in mind.

There are, of course, OTHER REASONS why your engine may not start right away. If there's no drainage of fuel from the blower drain valve, the difficulty is probably NOT clue to overloading. Maybe the engine hasn't obtained sufficient fuel from the carburetor because you forgot to keep up the pressure by using the wobble pump, or didn't richen the mixture for a long enough period. Try again, and keep your EYES and HANDS on the controls this time.

If the engine STILL won't start, chances are you're having IGNITION TROUBLE. Perhaps the booster isn't functioning. Continued operation can OVERHEAT THE COILS and make the booster quit. At any rate, you'd better have a LOOK-SEE and find the trouble.

A cold engine will always have to be primed. An outside temperature lower than 60° F. (15 ° C.) is "cold" to an engine, even if it isn't to you. The cooler the weather, the more priming you'll have to do to get started. A discharge of fuel from the engine blower drain isn't necessarily an indication of overloading in a cold engine. It may mean there's liquid gasoline in the exhaust - probably from primed cylinders. What do you do about it? The SAME as you would do to clear an overloaded WARM engine.

The direct-cranking electric starter will turn the engine at a SLOWER SPEED IN COLD WEATHER, SO you may have to open the throttle wider than usual under such starting conditions to make sure the cylinders are getting an adequate fuel charge. Then, once the engine starts and begins to pick up speed, you can draw back the throttle to keep the rpm down to between 600 and 800.

INERTIA AND CARTRIDGE STARTERS

You'll be following a slightly MODIFIED procedure if you are starting the engine with an INERTIA-TYPE STARTER Or a CARTRIDGE STARTER.

These changes in method are made necessary by the fact that such starters turn the engine over initially at a MUCH HIGHER SPEED than other types. It's important to leave the mixture control in. "idle cut-off" until the engine fires.

Otherwise, if the engine fails to start immediately, large quantities of fuel may be discharged into the engine, draining from the blower section and CREATING A FIRE HAZARD.

It's impractical to use the mixture control to obtain partial priming, as you would with direct cranking starters. It's best to depend on the HAND PRIMER or PRIMING VALVE when you feel the engine is not getting enough fuel for starting. But as soon as the engine fires - and BEFORE THE PRIMING FUEL IS USED UP - move the mixture control quickly to the "automatic rich" position.

WARMING UP

Remember, you're still working with that R-2800 engine you started with. Once the engine starts, you're ready for the WARM-UP. After the first half minute, the engine speed is slowly in-creased to about 1,000 rpm. LEAVE THE COWL FLAPS OPEN. Closing them, even in extremely cold weather, is likely to burn the ignition system insulation, particularly at the spark plug elbows.

OIL COOLER CONTROLS should be in the "hot" position to aid in warming up. The oil pressure relief valve is fitted with a temperature control that forces the oil - when cold - through the engine under high pressure. With very cold oil, the pressure may go up to more than 400 psi but it is AUTOMATICALLY REDUCED when an "oil inlet" temperature of around 104° F. (40° C.) is reached.

AVOID PROLONGED IDLING of the engine at speeds below 800 rpm or you'll probably find yourself with a batch of FOULED SPARK PLUGS. An occasional short run to clear out the engine - at an idling speed of 400 to 500 rpm - won't do any harm, however. Keep the engine speed at 1,000 rpm and by the time the oil temperature starts to rise, the engine will be warm enough. Then you'll be ready for a GROUND TEST.

When the OIL INLET TEMPERATURE gets above 104° F. (40° C.), the throttle may be opened to about 70 percent rated horsepower. Cylinder head temperatures should have reached at least 248° F. (120 ° C.) by now. Move the magneto switch from "both" to "left," and then to "right" in order to check engine operation on each breaker assembly of the dual magneto. You make these checks by noting the LOSS IN RPM when the switch is moved.

In switching from "both" position to either "left" or "right," the normal drop-off is between 50 and 75 rpm. But when you switch from "left" to "right" or vice-versa, the shift in rpm varies with the type of propeller and the original engine speed. Make this check in as SHORT a time as is practicable. Continued running on one switch point with the engine at high speed may cause serious KNOCKING.

You'll probably notice strong VIBRATION of the engine if one or more cylinders are missing fire because of improperly-functioning spark plugs. On the other hand, at low engine speeds with the magneto switch on "both," "left," or "right," freedom from vibration is a mighty good indication that the engine is operating correctly, particularly with respect to the ignition system.

Once in a great while you may run up against uneven engine operation during the regular magneto check, even after the engine has been run so long that you'd think the spark plugs were cleared out. In such a case, you can make a quick check of the dual magneto (at "33 inches Hg" on the manifold pressure gage) to find out what the trouble may be. Such an operation with the magneto switch in either "left" or "right" positions at this high power output, however, must be held to the SHORTEST POSSIBLE TIME, or you'll SERIOUSLY DAMAGE THE ENGINE.

Next, open the throttle until the engine is at 2,000 rpm at "low pitch." OIL PRESSURE (measured at the "pressure gage take-off" on either the upper left or right side of the engine rear section) should be between 75 and 80 psi at 2,000 rpm with the oil inlet temperature at 140° F. (60° C.) The pressure will VARY with their rpm and temperature, so don't be alarmed if it drops to as low as 25 psi, with the engine idling, or jumps to over 100 psi with cool oil at take-off speed.

Check the FUEL PRESSURE which should be between 15 and 17 psi (relative to carburetor air pressure) at 2,000 rpm. At low idling speed the fuel pressure may be as low as 8 or 10 psi, and still be satisfactory if it COMES UP PROPERLY AT HIGHER SPEEDS.

To help PREVENT SLUDGE ACCUMULATION and to check on the OPERATION OF THE TWO-SPEED BLOWER, shift the blower ratio selector valve according to the following directions before each flight and be-fore stopping the engine after long flights.

After the OIL INLET TEMPERATURE is 104°F. (40° C.) or higher, speed up the engine to 1,200-1,400 rpm, with propeller control in "low pitch," so as to obtain the 40 psi minimum oil pressure required for blower clutch operation. Move the blower ratio selector valve to the "high" position. The oil pressure should show a MOMENTARY DROP at this point.

Open the throttle to the prescribed cruising speed (but not more than 2,000 rpm) and lock it. Then shift immediately to "low" blower ratio. Watch the manifold pressure gage for a drop in pressure when you shift from "high" to "low" blower. This drop indicates that the control system is working properly, and prevents the pilot from taking off with the valve in "high" position by mistake. Finally, reduce the engine speed to 1,000 rpm or less after you've made this check.

If the test wasn't satisfactory, run the engine at around 1,000 rpm for two minutes BEFORE repeating the procedure. Prolonged fluctuation or loss of manifold pressure when shifting from "low" to "high" blower ratio indicates POOR CLUTCH ENGAGEMENT. Return the control to "low" and try the shift again. This time be certain to make the shift WITHOUT HESITATION, SO as to avoid dragging or slipping the clutches. MAKE SURE the selector control is in "low" position when ground tests have been completed.

The engine cooling system won't keep cylinder heads and barrels - or ignition harness - cool while running continuously above a specified rpm on the ground. So, while making ground tests, avoid running the engine at high speeds as much as possible and NEVER LET CYLINDER HEAD TEMPERATURE GO HIGHER THAN THAT SPECIFICALLY ALLOWED. Engines vary in allowable ground rpm, manifold pressure, oil temperature, oil pressure, head temperature, etc., so KNOW the engine you're working with BEFORE you operate it.

And here's an old warning all over again : The ADJUSTABLE COWL FLAPS (or "gill") should be FULLY OPEN during all ground operations - warmup, ground test, taxiing - and at least PARTLY OPEN for take-off and climb.