Engine Part 1 Flashcards
What is the primary function of the compressor?
To supply large masses of compressed air to the combustion section
Describe the compressor
The compressor is an 8-stage axial flow unit consisting of two major components, the stator and rotor assemblies.
Where is the engine mounted gearbox located?
It is attached to the bottom of the main frame
Describe the combustion main frame and its purposes:
The combustion main frame is the front part of the combustion section and is the primary structural component of the engine. It serves as a diffuser passage for compressed air entering the combustion section. The mainframe is also a mounting pad for the main fuel nozzles in the combustion section. The mainframe also bleeds air from the 8th stage compressor air to operate the engine and pneumatic systems
What are the 6 major sections of the J85 engine/
- Front Frame
- Compressor Section
- Combustion section
- Turbine Section
- Afterburner Section
- Exhaust nozzle
Each engine accessory is divided into what two sections?
- Engine Accesories (components required to operate the engine)
- Airframe mounted gearbox (components required for aircraft systems)
Each engine accessory is divided into what two sections?
- Engine Accesories (components required to operate the engine) 2. Airframe mounted gearbox (components required for aircraft systems)
What are the accessory sections of the engine driven by?
A power takeoff (PTO) from the engine compressor drive shaft
Where is the engine mounted gearbox located?
It is attached to the bottom of the main frame
Describe the combustion main frame and its purposes:
The combustion main frame is the front part of the combustion section and is the primary structural component of the engine. It serves as a diffuser passage for compressed air entering the combustion section. The mainframe is also a mounting pad for the main fuel nozzles in the combustion section. The mainframe also bleeds air from the 8th stage compressor air to operate the engine and pneumatic systems
What are the 5 major components of the combustion section?
- Igniter Plug.
- Fuel Nozzles
- Combustion Liner
- Inner Casings
- Outer Casings
What percentage of air is used to support combustion?
Less than 25%
What is the purpose of the combustion liner?
The combustion liner provides an efficient flow of air, allowing for combustion, between the inner and outer casings. The combustion liner also allows for air to flow between itself and the casings to provide protective cooling of the combustion chamber components
What is wrapped around the outer combustion casing?
An insulation blanket which shields the airframe components from excessive heat
What is the turbine section comprised of?
Stator and rotors
What is the primary purpose of the turbine section?
Extract energy from the high velocity airstream to drive the compressor and engine accesories.
What does T5 refer to?
Turbine discharge temperature
What does T5 refer to?
Turbine discharge temperature
What is the variable area exhaust nozzle assembly controlled by?
- Hydromechanical System
2. T5 System
What is the basic function of the T5 system?
To prevent excessive EGT beyond the upper 650 C limit
Around what engine RPM do the exhaust nozzles close to their smallest opening?
97%
Describe how the T5 system operates:
As the EGT reaches its maximum range (approx when throttles increase beyond approx 97%) the hydromechanical system is no longer in control and the T5 system takes over nozzle geometry. As power moves from 97% to MAX, the T5 system will maintain the EGT within the 630-650 C limit by opening the nozzles in crease cooling, rather than closing them tighter.
What powers the T5 system?
The T5 alternator
If there is an electrical failure in the T38, will the T5 system fail as well?
No, the T5 alternator is separate from the aircraft electrical system
When the throttles are reduced from MAX through the 97% range, does the T5 system or the hydromechanical system schedule the nozzle geometry?
The hydromechanical system
During all engine operations, what does the afterburner diffuser always do?
Serves to smooth out the airflow elaving the turbine and entering the tailpipe.
How does the J8 optimize engine efficiency and control EGT?
The primary means of controlling EGT and optimizing efficiency is via the variable area exhaust nozzle. The variable area exhuast nozzle is controlled both by a hydromechanical system and the T5 system depending on the throttle setting and EGT.
These two systems adjust the diameter of the exhaust nozzle to optimize engine efficiency and control EGT. Generally, from Idle to ~97%, the exhaust nozzle closes via the hydromechanical system. From ~97% to MAX, the nozzles are opened by the T5 system
How does the J85 maintain compressor stall-free operation?
The variable geometry system assists with compressor stall-free operation. The VGS consits of inlet guide vanes and bleed valves. These two components regulate compressor airflow by automatically being repositioned by fuel pressure, provided by the main fuel control.
How do the variable inlet guide vanes and bleed valves assist with stall-free operation?
The variable inlet guide vanes direct incoming air to the compressor blades at the optimum AOA. At low engine RPM, there is a lot of pressure in the later stages of the compressor seciton. The bleed valves open to release some of that pressure and let out air to provide pressure relief for the 3rd, 4th, and 5th stages of the compressor
Under what malfunction is the engine anti-ice system automatically turned on?
It is automatically turned on with right AC electrical power fails
What should you set your power to to ensure effective anti-ice protection?
80% RPM
How does the engine anti ice system work?
Engine anti-icing directs 8th stage compressor air to the inlet vanes and bullet nose of the engine.
Is the engine anti-ice system DC or AC powered?
AC
When should you use engine anti-ice?
Flying in high-humidity conditions and/or visible moisture with the temperature near or below 32F
How is the engine-mounted accesory seciton attached to the engine?
It is attached at the bottom of the mainframe
What powers the engine-mounted accesory section?
A gear driver fitted to the compressor shaft
All engine driven accesories are powered by the engine mounted accesory section except what 2 items? What are the 2 items powered by?
- AC Generator
- Hydraulic Pump
They are powreed by the airframe mounted gear box.
How does the engine-mounted gearbox power the airframe mounted gearbox?
A PTO shaft extends forward from the engine-mounted accessory section and connects with the airframe mounted gearbox.
How does the oil cooling system work?
As oil leaves the pump, it is cooled through an fuel-oil cooler. This uses oil lines with fuel flowing over them to exchange heat from the engine bearings with the fuel.
How does the fire detection system work to detech a fire?
The system detectors are pneumatically operated by expanding inert gas when high engine bay temperatures occur. As the pressure in the bay increases, the responder diaphragm turns on the circuit to illuminate a left or right enigne fire warning in both cockpits. This system responds to both localized and average temperatures.
Is operation of the fire system in each engine bay independent or dependent on eachotther?
Independent
Through what device is RPM information recieved?
Through an independent tachometer generator mounted on the oil pump shaft along with the T5 alternator.
What can generally cause oil pressure fluctuations?
Generally, low oil quantity can cause fluctuations as well as a clogged oil filter
At a stabilized RPM, a sudden change of what oil PSI indicated a system malfunction?
10 PSI
How long is zero-G flight restricted to due to engine oil supply?
10 seconds
How long is negative-G flight limited to due to engine oil supply and pressure requirements?
30 seconds
Below how many liters of liquid oxygen will sloshing cause the OXYGEN light to momentarily illuminate?
3L
In the event of a DC power failure, the EED is inoperative. All engine indicators except what are also lost?
Hydraulic
How much thrust does the J85 engine produce at sea level, on a standard day in both MIL and MAX?
2200 LBS of thrust at MIL
3300 LBS of thrust at full MAX
How many stages does the J85 compressor section have?
8
What 3 things are required for an engine start?
- Compressor motoring via low-pressure air supply
- DC power to energize the ignition holding relay
- AC power for ignitor firing
When pressing the engine start button, how long does it arm the ignition circuit?
30 seconds
Describe the general operation of an engine start, starting with pressing the ENGINE START button:
- Pressing the engine start button momentarily arms the engines ignition circuit for 30 seconds
- Placing the engines respective throttle in IDL energizes the ignition exciter, firing the main and afterburner igniters and allows for fuel to start flowing into the eninge.
For a battery start, what does that static inverter do?
It supplies AC power to circuits that provide the right fuel flow, and oil pressure indications during the start cycle.
When placing the throttles to off, does it shutoff the engine mechanically or both mechanically and electronically?
Both.
Electronic - Fuel shutoff valves
Mechanical - Closes main fuel control
What is driven by the engine-mounted gearbox?
- Main fuel control
- Main fuel pump
- Afterburner fuel control
- Tachometer generator
- T5 Alternator
