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Powerplant
Fuel Metering
| Question | Answer |
|---|---|
| When the mixture is pulled to ICO, a correct mixture is indicated by: | An increase of 10-50 rpm, before decreasing |
| At low altitudes in a fuel-injected engine, Lean mixtures and High cylinder-head temperatures could be caused by what? | The Automatic Mixture Control being stuck in the extended position |
| The Aneroid (Altitude Compensating) valve on Teledyne-Continental Injection systems does what? | It prevents an overly-rich mixture during acceleration on turbocharged engines. Upper deck pressure can't increase fast enough, so it holds bypass orifice open until upper deck pressure rises to match fuel flow. |
| If using an alternate fuel on a turbine engine, what should be adjusted for the performance check? | Fuel Specific Gravity setting |
| What is the function of the Air Bleed? | It aids in emulsifying/vaporizing the fuel |
| One way some engines control detonation is by adding what kind of system? | Water Injection (Allows maximum power without detonation/preignition) |
| Two types of fuel control systems for Turbine Engines | Hydromechanical and Electronic |
| Two types of Electronic Fuel Control | Full Authority, and Supervisory |
| An Increase in Manifold Pressure translates to a _ in airstream pressure (Suction) | Decrease |
| Opening the throttle causes a (Increase/Decrease) in Manifold Pressure? | Increase |
| A Single Diaphragm Accelerator Pump will will discharge fuel with a (Increase/Decrease) in Manifold Pressure? | Increase, since it will decrease the suction on the diaphragm, and allow spring pressure to push the Accelerator fuel into the airstream. |
| What purpose does the metering orifice in a Main Air Bleed serve in a carburetor? | Aids in Vaporizing and controlling the fuel discharge, especially at lower engine speeds. |
| If a Float Carb leaks when the engine is off, a likely cause is: | Worn Needle Valve, or not seating properly |
| If the float in a carburetor sinks, it will cause the fuel level to _, and _ the mixture | Rise, Enrichen (because it will start coming out the Main Discharge Nozzle when the level rises too high. |
| At full throttle, what Carb component limits the max airflow to the engine? | The Carburetor Venturi |
| What controls the Volume of the fuel/air mixture to the cylinders? | Throttle Valve |
| In respect to Injector nozzles, what purpose do Air Bleeds serve? | Aid in Vaporizing the fuel |
| How is ICO achieved in a Back-Suction mixture control Carb? | Low pressure air from the Intake Manifold is introduced into the float chamber, which balances out the low pressure Venturi air that would normally pull fuel from the chamber, and prevent it from flowing. |
| The Carburetor mixture control helps prevent a _ mixture @ high altitudes | Rich |
| In a Supervisory EEC unit, any fault that adversely affects operation leads the system to do what? | Immediately revert to the Hydromechanical fuel control unit |
| A Supervisory EEC receives operating input, and controls the engine by adjust what? | The EEC adjusts the standard Hydromechanical unit for the most effective engine operation |
| Is ambient humidity traditionally an input parameter for turbine engine fuel control units? | No |
| Back-Suction mixture control controls the mixture by adjusting what? | It varies the pressure acting on the fuel in the float chamber (which counteracts the low pressure in the venturi that draws out the fuel). |
| Which is adjusted first, the Idle Mixture, or the Idle speed, when a carb is first installed? | The Idle Mixture is adjusted first, then the speed is set to the desired (Think: Mixture is most crucial, the speed is just adjusting the engine-run itself, and not as crucial) |
| As the velocity of the venturi air increases, how does that affect Temperature and Pressure? | Both temperature and pressure decrease as the air speeds up. |
| As the RPM of an engine changes (From Idle, slowly increases to full throttle), how should the Mixture be adjusted throughout the operation? | Idle: Full rich (Engine can't pull as much fuel out, also to cool) Throttle: Mixture drops off as the airflow increases ----------------- Full Throttle: The mixture should INCREASE towards rich again, to aid in cooling at High RPM (Think Economizer) |
| What two things are adjusted on a Turbine Fuel Control Unit? | Idle RPM, AND Max RPM (This way, Max thrust is obtainable when needed) |
| When equipped with a Pressure Carb, the engine is started with the _, with the Mixture in the _ position. | Primer, ICO. |
| The Continuous Fuel Injection system normally discharges fuel when in the Otto Cycle? | All the time (Continuously during operation) |
| At what location does a Continuous flow injection system normally inject the fuel? | The intake port of each cylinder (Not the combustion chamber itself). |
| The active clearance control system (ACC) in an EEC, controls _ to aid in engine efficiency? | The ACC controls the case temperature (via cooling air through passages in the case), to keep blade clearances at a minimum. |
| What are the two main Continuous Fuel Injection systems that are traditionally used? | Teledyne-Continental, and RSA (Precision Airmotive or Bendix) |
| What is the major difference between Teledyne-Continental, and the RSA continuous-fuel injection systems? | RSA uses a balance of Air AND Fuel pressure for metering, T-C uses fuel pressure ONLY for metering (proportional to engine speed, using engine-driven vane pump and calibrated bypass orifice. |
| What carb component provides an extra burst of fuel during rapid acceleration? | Accelerator Pump |
| If the mixture is too rich to idle, and the Idle-Mixture adjustment can't lean it sufficiently, what could be an underlying cause? | Economizer valve not operating correctly, it could be feeding extra fuel into the engine at low speeds. |
| What's another name for a Carburetor Economizer system? | Power Enrichment System (Enriches at speeds above cruise) |
| Applying Carb heat will (Increase/Decrease) the density of the carburetor air? | Decrease |
| If the bellows inside a Pressure Carb's Automatic Mix. Control ruptures @ altitude, how is the mixture affected? | The mixture becomes richer (The bellows separates inert gas and impact air. As altitude increases, gas pressure overcomes the spring and closes the valve, leaning the mixture. If it ruptured, the spring pushes all the way back, opening the mixture |
| When adjusting fuel control cams, springs and linkages, all final trim adjustments should be made in what direction? (Increase/Decrease) | The Increase direction |
| A radial engine with Multi-Point Priming, will prime which cylinders? | All cylinders above the centerline of the engine. |
| What is used to adjust the ratio of the fuel/air mixture in an aircraft engine? | Mixture Control |
| The Automatic Mixture Control (AMC) serves what function? | It adjusts the richness of the mixture to compensate for density changes from altitude/temperature. |
| Chambers "A" and "B" in a pressure carburetor combine to form the (Air/Fuel) metering force? | The diaphragm between chamber "A" and "B" is the Air Diaphragm, and creates the Air Metering Force |
| Chambers "C" and "D" in a pressure carburetor combine to form the (Air/Fuel) Metering force? | The diaphragm between chamber "C" and "D" is the Fuel Diaphragm, and creates the Fuel Metering Force |
| Chamber "C" in a pressure carburetor consists of (Metered/Unmetered) Fuel pressure? | Metered fuel pressure |
| The Fuel Metering Force in a pressure carburetor is a balance between Chambers "_" and "_". | Chambers "C" and "D". |
| Metered fuel pressure in Chamber "C" in a pressure carburetor will (Vary/Remain Constant) throughout the operation range? | It will remain Constant |
| When making Idle Mixture adjustments, how is the correct adjustment verified? | The Mixture is slowly moved to ICO, while watching for changes in RPM/Manifold Pressure. |
| If a float-carb engine runs excessively rich at full throttle, a possible cause could be? | A clogged Main Air Bleed (Not enough air being mixed with the fuel at high RPMs. Some Economizers enrich the mixture this way as well). |
| In a pressure carb, what device aids fuel delivery during idling? | A spring in the Unmetered "D" Fuel Chamber holds the poppet valve slightly off its seat, so allow fuel flow when the airflow is low. |
| When trimming a turbine engine, the Fuel Control adjusted to set what two parameters? | Idle RPM, and Max Speed (Max EPR) |
| If an engine is running lean, even with the normal amount of fuel present in the mixture, what could be the underlying issue? | The fuel not vaporizing completely (Excess amount of air for the amount of fuel being vaporized). |
| How is fuel discharged in a float-carburetor during idle? | From the Idle Discharge Nozzles, set in the venturi at the edge of the Butterfly Valve |
| What two functions does the Carburetor Venturi serve? | Proportions the fuel/air mixture, and limits the full-throttle airflow |
| When measuring float-bowl fuel levels, where should the measurement be taken? | Using a straightedge over the parting surface, measure away from the walls and float (fuel clings to these surfaces and measures higher than the actual fuel level). |
| What purpose does a turbine engine Dump Valve serve? | It drains the engine manifold lines, preventing fuel boiling (and subsequent deposits) from residual engine heat after shutdown. |
| List some factors that impact a Turbine Fuel Control Unit | Compressor Inlet Air Temp, Power Lever Position, etc. |
| Full-Authority Electronic Engine Control (EEC) controls engine parameters how? | The FA-EEC receives all necessary data, then commands various actuators to control engine parameters. |
| A Supervisory EEC controls the engine how? | It adjusts the standard Hydromechanical FCU to control the engine indirectly, and reverts back to it should the EEC fail. |
| What effect does Humidity have on Jet engine operation? | Little/no effect (Unlike reciprocating engines) |
| A float-carb's Economizer valve serves what purpose? | Provide richer mixtures (for cooling) at power settings above cruise. |
| Mixture Ratios are expressed as (Fuel : Air), or (Air : Fuel)? | Air: Fuel A Mixture of 11:1 refers to 11 parts air, to 1 part fuel (By weight) |
| The mixture required at Idle is richer than at Normal Cruise (T/F)? | True: With the slower airflow at Idle, the mixture is not dispersed properly. It is compensated for with more fuel, which also aids cooling. |
| The mixture required at Full Power is leaner than Normal Cruise (T/F)? | False: The mixture is Richer at full power, to aid in cooling the engine. |
| The engine idle speed and mixture settings should be adjusted when the engine is _? | Warmed up and operating. |
| How is Idle Speed usually adjusted on a Float-Carb? | The Idle Speed is set via an adjustable Throttle-Stop screw, which controls how close the Butterfly-Valve is to the Venturi Walls. |
| With an Increase in altitude (without an AMC), the mixture has a tendency to _ . | Become more rich (As density decreases, the amount of air in the mixture decreases, enriching it). |
| If the Main Air Bleed on a float-carb becomes clogged, how will it affect the mixture @ rated power? Why? What about Idle? | The mixture will become Rich, since not enough air is being mixed with the fuel. The Idle system does not use the Main Air Bleed, so Performance @ Idle is unaffected. |
| Which weighs more? 1 part Dry Air, or 1 part Water Vapor? | Water Vapor weighs only 5/8 as much as Dry Air. |
| What is the purpose of the Vapor Vent Float in a pressure carburetor? | These floats are on top of the fuel in Chambers "D" and "E", and control the flow of vapors/fuel back into the engine. When vapors collect, the float level drops and opens the needle valve. |
| What would happen if a Vapor Vent Float (Pressure Carb) lost its buoyancy? | The float would drop, opening the needle valve and continuously allowing fuel and vapors to return to the tank. It would not affect engine operation, but the fuel flow indication would be incorrect. |
| A Float-Carb with an economizer is adjusted for what setting for normal operation? | The leanest practical mixture for all conditions other than full power. It is then enriched with the economizer at full power. |
| When trimming a turbine engine, all Accessory Bleed Airs and overboard air valves should be what? | They should all be turned off. |
| Why is the Idle Mixture enriched? | The engine may not have enough airflow around the cylinders to properly cool it. |
| How does a Pressure Carb Enrichment Valve operate? | It uses a balance between metered and unmetered fuel pressure to open the valve, and provides an increase of steady-state fuel flow. |
| What is the relationship between the Accelerating Pump, and the Enrichment Valve in a Pressure Carb? | No relation, they operate independently of eachother. |
| How does a Pressure Carb Accelerator Pump operate? | It uses a balance between Manifold Pressure, and spring force. |
| While trimming an engine, if the velocity of the air blowing into the engine intake is excessive, what is the likely result? | The Compression and Turbine Discharge Pressures will be too high, and the trimmed conditions will be too low during operation. |
| If the optimum Idle Mixture is set, what are the indications when pulled to ICO? | Manifold Pressure decreases, and RPM Momentarily increases just before engine shutdown. |
| When the throttle valve is closed and the volume of venturi air reduced, the pressure in the venture will (Increase/Decrease)? | Increase. |
| When adjusting the float level in a Float-Carb, what method is commonly used? | Adding or Removing Shims under the Needle-Valve seat. |
| If fuel is leaking from the Main Discharge Nozzle in a Float Carb after shutdown, what is the likely cause? | The needle valve and seat has failed, and fuel is rising in the bowl above the level of the Discharge Nozzle. The valve and seat should be replaced. |
| If the throttle is not opened enough during startup, what impact will it have on the mixture? | The Mixture will be Rich, as not enough air is being drawn into the engine. |
| The ideal level of the fuel in a Float Carb is slightly (Higher/Lower) than the Main Discharge Nozzle? | Slightly lower (otherwise fuel will leak out of the Discharge Nozzle). |
| What is the main difference between Direct Cylinder Fuel-Injection, and Continuous-Flow Fuel-Injection? | Continuous flow is always injecting fuel into the engine, whereas Direct Cylinder only injects the fuel when needed. |
| Is an engine with Direct Cylinder Fuel-Injections susceptible to Backfiring? Why? | No, since there is no fuel/air mixture in the induction system, and the fuel is directly injected into the combustion chamber. |
| When a Back-Suction mixture control is placed in ICO, what happens? | The float chamber is vented to a negative-pressure area, and the fuel is no longer drawn out of the discharge nozzle. |
| 3 advantages of Dual-ignition for recips | Providing a backup Magneto system Increase power output More complete/faster combustion of fuel |
| What precaution should be taken when using thread lubricant on a tapered pipe plug in a carburetor float bowl? | Engage first thread of the plug, then put small amount of lube on the second thread, then screw in the plug. |
| What is vapor lock? (Fuel systems) | Fuel vapors become trapped in a bend. The vapor pressure is higher than the fuel pressure, and no fuel can flow to the carburetor. |
| In a Low-Tension Ignition system (18 cylinders), how many secondary coils are required? | 36. A Low-Tension system requires a secondary coil for each spark plug. Each cylinder has 2 spark plugs, for a total of 36 secondary coils. |
| When you turn a mag switch off, what is the P-Lead doing? | you’re grounding the ignition circuit, so the P-lead has no power. An Open P-Lead means that the ignition switch cannot ground the leads, and it will keep running. |
| How does a floating thermostat control oil temperature? | Controls the amount of air going through the oil cooler. |
| What type of main bearings are in horizontally-opposed engines? | Soft-metal(Steel-backed Lead-Alloy) |
| How often should float-carbs be overhauled? | Engine overhaul |
| What caused a turbine duplex fuel nozzle divider to open? | Fuel Pressure |
| Where are non-magnetic particles in an oil filter most likely from? | Plain bearings or pistons |
| Undercurrent relay in a starter generator | When you’re starting, when it reaches engine speed the load drops, and it cuts off the starter. |
| Dynafocul engine mounts point inward to what? | The engine’s Center of Gravity |
| Wildly fluctuating oil indications could be a sign of what? | Low oil |
| What is crankshaft RPM if cylinders each fire 200 times a minute? | 400 rpm (2x rotations for each firing) |
| Hissing from exhaust when prop is pulled through indicates what? | Exhaust valve leak/not seated |
| Prop strike classified as anytime there is what? | Drop in RPM (interruption in normal rotation) |
| Two types of Compression checks | Direct & Differential |
| What do the alignment of the marks mean inside a magneto? | The Timing marks are aligned when the rotating magnet is in the E-Gap position. |
| Bright, non-magnetic metallic particles in an oil sump is most likely wear of which components? | If they are no-magnetic, they’re from either the plain bearings, or the pistons. |
| In a twin-spool or dual axial-flow compressor system, the N(2) compressor is the (high) or (low) pressure compressor? | N(2) is the 2nd Stage of compression, or the High-Pressure compressor. it’s driven by the 1st stage turbine. |
| The 1st stage turbine (in dual axial-flow or twin spool compressor system), drives which compressor? | N(2), or “High-pressure” compressor |
| Detonation occurs when the fuel/air mixture _? | Burns too fast (Explodes rather than burning evenly as it should. Causes high cylinder head temps. |
| Type of oil pump most used in turbine engines are classified as? | Positive Displacement (Vane, Spur Gear, Gerotor Types) |
| 3 Types of Positive displacement oil pumps | Vane type, Spur Gear type, Gerotor type |
| If a propellor is in the High RPM position, it is at what pitch-angle? | Low pitch-angle |
| In a “Shower of Sparks” ignition system, at engine start, the spark plug will fire when? | The retard AND advance breaker points are open. -Connected in Parallel -When one or both are closed, current goes through primary winding, points, straight to ground. -When retard points open, high voltage to secondary winding causes continuous spark. |
| What is the purpose of the 2 metering jets in a float-type carburetor? (Main, Idling) | Idling Meter Jet-Meters fuel when @ idle Main Meter Jet-Meters fuel @ all RPMS above idle range. |
| What is the primary function of an Automatic Mixture Control (AMC)? (Pressure Carb or Fuel Injection system) | Responds to changes in air density from Altitude & Temperature. *As either increase, air becomes less dense, AMC decreases amount of fuel metered to engine to keep fuel/air ratio constant. |
| What is the purpose of the diaphragm in most vane-type fuel pumps? | Compensate fuel pressures to altitude changes. *Acted on by atmospheric air pressure to maintain pump output-pressure @ constant value above ambient air pressure. |
| What mechanism allows a pneumatic-starter to disengage once an engine starts? How does it work? | A Sprag-Clutch & ratchet, which automatically disengages when the engine reaches a certain speed. Centrifugal force holds the pawls away from the ratchet when the engine is running. |
| A Pneumatic-starter w/ a sprag-clutch assembly makes a ratcheting noise when the engine is coasting down. What does this mean? Is it cause for concern? | The centrifugal force is too low to hold the pawls up, and they click as they ride over the ratchet. It is normal. |
| Difference between a Supercharger & a Turbocharger? | Supercharger - Compressor driven by a gear train from the crankshaft Turbo(super)charger - compressor turbine driven by exhaust gases |
| Indentations on bearing races from high static loads is known as _? | Brinelling |
| A faulty capacitor will cause the breaker-points to have what kind of appearance? What should they normally look like? | The breaker-points will have a course-grained, and sooty appearance. They normally should have a fine-grained frosty, or silvery appearance. |
| Airworthiness standards for small airplanes (<12,500lbs) & 9 or less passenger seats are found in which CFR? | 14 CFR Part 23 |
| In a turboprop installation, describe the control operation of the propeller. | The Fuel control & prop governor are interconnected. POWER LEVER directs the fuel control for a specific power from the engine. The Fuel control & governor then establish combo of RPM, fuel flow & blade angle for sufficient thrust & desired power |
| The fan rotation speed in a dual axial compressor fwd-fan engine is the same as which other section? | Low-Pressure compressor. The fan is a portion of the low-pressure compressor. |
| How is the strength of a magneto magnet checked? | Hold the points open, check output of primary coil w/ AC ammeter while operating magneto @ specified speed. *Basically an AC generator, output determined by speed of rotor & strength of permanent magnet. |
| In a DC motor circuit, why must you debate a switch from its nominal current rating? | Because of the high inrush of current. The high rate of current flow drops as soon as the motor starts turning and producing back EMF. |
| When a Constant-speed prob being controlled by the governor? | When it is within the range of the mechanical stops. When the blades are against the low-pitch stops, the propeller is no longer being governed. |
| Difference between High and Low-Tension ignition systems? | Low tension has no high voltage in the magnetos or distributors. Transformer coils mounted on inner heads boost voltage @ each spark plug. High tension-high voltage made inside magneto, to distributor, to spark plug via high-tension ignition leads. |
| Describe an Augmenter system and its purpose. | It has several exhaust tubes that open into the lower-rear of an engine cowling which creates a low pressure inside the cowling to draw in air from above the engine through the cooling fins. |
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avandermey
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