C2 (Accessories) Flashcards
Drives that may be present on the Helicopter engine
a). Starter motor
b). Fuel control unit
c).engine oil pump
d).tacho generator
e).alternator/generator
d). Centrifugal Breather
Alongside the driven components fitted to the accessories gearbox several non-driven item from the oil system are found. Name these items:
a). Scavenge filter
b). Drain plugs
c). Oil temperature bulbs
d). Magnetic plugs
The drive for the accessory units are typically taken from;
a). A rotating shaft
b). Internal gearbox
c). External gearbox
How are shafts connected together
-spline drive (provides a sliding fit)
-serrated drive (triangular projections)
Internal Gearbox is made from:
Aluminium
External Gearbox made from:
Magnesium
The location of the external gearbox is governed by what?
by the size and shape of the engine casings.
Where can the external gearbox be found
Front, center or rear of the engine.
All gear meshes are designed with “hunting tooth” ratios which ensures what:
that each tooth of a gear does not engage between the same set of opposing teeth on each revolution.
Spread any wear evenly across all teeth
Extra tooth so it doesnt hit the other tooth
What are accessory units in engine designs?
Accessory units provide power for ancillary systems needed for engine operation, including various pumps and control systems.
What drives may be present on the engine of a helicopter?
The following drives may be present:
- Starter Motor
- Fuel Control Unit
- Engine Oil Pumps
- Tacho Generator
- Alternator/Generator
- Centrifugal Breather
What is the function of the Starter Motor?
The Starter Motor is used to start spool rotation.
What does the Fuel Control Unit contain?
The Fuel Control Unit contains many components of the fuel system.
What is the purpose of the Tacho Generator?
The Tacho Generator measures and transmits engine RPM to the pilot.
What does the Alternator/Generator do?
The Alternator/Generator generates electricity for avionic systems.
What items are typically found alongside the driven components in the oil system?
Non-driven items typically include:
- Scavenge Filter
- Drain plugs
- Oil Temperature Bulbs
- Magnetic plugs
How is the drive for the accessory units typically taken?
The drive is typically taken from:
- A rotating shaft
- Via an internal gearbox
- To an external gearbox
What are splines and serrated drives used for?
They are used for keying together rotating components, transmitting high power, and allowing easy fitting and removal.
What is a spline drive?
A spline drive is an integral feather key machined on a shaft or in a hub to provide a sliding fit, usually with at least four splines.
What is a serrated drive?
A serrated drive is similar to a spline drive but uses triangular projections, mainly used on tapered and parallel shafts.
What is a Splined Drive Shaft?
A type of drive shaft with splines that allow for torque transfer.
What is a Serrated Drive Shaft?
A type of drive shaft with serrations that provide a grip for torque transfer.
What is the internal gearbox made from?
Usually made from Aluminium.
What dictates the location of the internal gearbox within an engine?
The difficulties of bringing a driveshaft radially outwards and the space available within the engine core.
What is the external gearbox usually made from?
Usually made from Magnesium to reduce GTE weight.
What does the external gearbox contain?
-The drives for the accessories,
-the drive from
-the starter, and
-provides a mounting face for each accessory unit.
What governs the location of the external gearbox?
The size and shape of the engine casings.
Where can the external gearbox be found?
At the front, centre, or rear of the engine.
How are the spur gears of the external gear train mounted?
They are mounted between bearings supported by the front and rear casings which are bolted together.
What is the typical RPM range for accessory units driven by the external gear train?
Normally between 5000 and 6000 Ri.
What design feature do all gearmashes have?
They are designed with ‘hunting tooth’ ratios to ensure even wear across all teeth.
