AMT 214 – Piston Engines 2
In this course:
Precision Tools - Know how to use and care for measuring tools used in aircraft engines.
Procedures - Including testing and troubleshooting.
Safety Practices - Including safe storage, as well as shipping practices.
Overhaul vs Maintenance.
Instrumentation - Electrical testing and maintenance
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Piston Engine Maintenance: Pwrpnt pg 3-450
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Starting Systems: Pwrpnt pg 451-529
Engine Instruments: Pwrpnt pg 530 to 792
Precision Tools: Pwrpnt pg 793 to 846
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• MAP – Manifold Air Pressure
• CAT – Carburetor Air Temperature
• CHT – Cylinder Head Temperature
• EGT – Exhaust Gas Temperature
• FP – Fuel Pressure
• FF – Fuel Flow
• OAT – Outside Air Temperature
• EICAS – Engine Indicating & Crew Alerting System
• MEMS - Micro Electro Mechanical Systems -
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It all begins with an idea. Maybe you want to launch a business. Maybe you want to turn a hobby into something more.
The Yellow Sheeee
Thermistor:
In short, a Thermistor is a Thermal resistor. There are 2 types:
-Positive Temperature Coefficient
where resistance increases with temperature.
-Negative Temperature Coefficient which uses a semi conductor, and the resistance actually decreases with temperature increases.
Tachometer Probes
A tachometer probe creates a magnetic field that extends through the probe. As a rotating gear wheel moves close to the probe, it changes the magnetic field, generating voltage signals. These signals vary with the speed of the gear wheel, counting RPM.
Wheatstone Bridge
Synchronous Indicating Instruments
Used in RPM, and position indicator for landing gear, etc. Synchro-type remote-indicating instruments use an electric system to transmit information from one location to another. 'Synchro' means 'synchronous' and describes electrical systems that measure, transmit, and display various aircraft parameters over long distances.
Autosyn uses AC and Electromagnets
Magnasyn uses AC and permanent Magnets
Selsyn uses DC and a variable resistor at the sensing end, and a permanent magnet at the indicator end.
Bimetallic strip:
Using two types of metals, a strip can be straight or coiled. Temperatures affect each metal differently causing the the metal to expand or contract at different rates, resulting in a curve. An example being Brass and Steel
Fuel Flow:
On small aircraft, fuel flow is proportional to the fuel pressure in this system. Fuel flow is measured normally in Volume, as in gallons per hour. A little airplane would use a Fuel Pressure Transmitter.
On large aircraft, fuel flow meters measure the Mass, rather than Volume due to changes in temperature. Pounds of fuel per hour.
Troubleshooting
Before Troubleshooting, you must first understand what’s happening in the aircraft systems
First: Follow Maintenance Manual procedures.
Electrical Snags? Cannon plugs are usually to blame
Next: Switch instruments with known serviceable unit.
Does the problem follow the instrument? This is easy on a twin engine aircraft or when you have access to parts..Test pressure systems with calibrated Dead Weight Tester
Test temperature units with a Barfield or JetCal Tester
Bleed air out of wet lines
Indicator lights often have push to test features –which may test the entire circuit, or just the light bulb
Engine Instruments
PSIA - Absolute
Absolute Pressure uses a perfect vacuum. Find it : MAP
Absolute Pressure = Gauge Pressure + Atmospheric Pressure
PSIG - Gauge
Gauge pressure uses ambient air pressure. Find this in Oil Pressures.
Gauge pressure = Absolute Pressure - Atmospheric Pressure.
PSID - Differential
Differential pressure is the difference in pressure between two points. Airspeed Indicator uses Pitot/Static
Instrument Markings
Green Arc: Marks the safe or normal range of operation. Visually marks the maximum and minimum limits for continuous operations.
Blue Arc: Not common, but allowable operation under unique circumstances. For instance, a blue arc would mark acceptable fuel flow at certain altitude.
Blue Line: Not common. The Blue Line marks the maximum or minimum limits under unique circumstances.
Found on some airspeed indicators on twin engine aircraft and would mark the minimum airspeed, one engine out.
Yellow Arc: Precautionary range operation, including the Yellow line alerting operating temps that Carburetor ice may occur.
Red Line: Indicates minimum or maximum safe operating limit, and operation beyond this limit will result in damage
Red Arc: Restricted operating range where excessive vibration or other stresses could endanger the airframe or engine. As found on the RPM range on Lycoming IO-360 with certain propeller combinations.
Index mark: Typically a white line that extends from glass to housing. Any disruption in the line indicates the glass has moved, resulting in unreliable limit markings.
Engine Gauges
To save room on twin engine aircraft often one gauge is used for both engines to indicate parameters such as RPM, oil pressure, oil temperature, fuel pressure/ temperature, MAP,CHT, CAT.
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A bulb in the circuit serves as a variable resistor
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In conjunction to a Bourdon tube sensing pressure it can be used to sense temperature. By having a sealed system filled with an inert gas that will expand as it heats up this will cause the bourdon tube to move from the increased gas pressure. This system is usually found only on a small light aircraft where the engine is close to the cockpit, because if the system fails then the complete system ( gauge, hollow semi-flexible tube, and temperature bulb) must be replaced.
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• Force can be applied to inside or outside
• Built from Brass, Bronze, Stainless steel, beryllium copper
• Diaphragm more accurate than bourdon tube
• Low pressure only
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Bellows contracts and expands like a diaphragm but uses less space and has greater indicating range of movement. • Bellows gages have greater range than
diaphragm
• Generally used for differential pressure
measurements
• Fuel pressure / fuel flow
– Self compensating for altitude
– Fuel pressure / ambient air
• Cabin differential air pressure
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Item description
Dead Weight Tester
Testing Instruments
Barfield Tester
