PPT3: CRANKCASE AND BEARINGS - RECIPROCATING ENGINES

Engine Components

- Basic parts: crankcase, cylinders, pistons, connecting rods, valves, valve-operating mechanism, crankshaft.
- Locations:
- Cylinder: valves, pistons, spark plugs.
- Crankcase: valve operating mechanism, crankshaft, connecting rods.

Crankcase

- Function: Foundation of the reciprocating engine, houses internal parts, mounts cylinders and external accessories, provides a tight enclosure for the lubricating oil, and serves as means of attaching a complete engine to an airframe.
- Material: Cast aluminum alloys for strength, rigidity, and light weight.
- Forces: Must be able to absorb internal combustion forces, unbalanced centrifugal, and inertial forces inflicted by a propeller.
- constantly subjected to bending moments, which change continuously in direction and magnitude due to these forces.

Types of Crankcase

- Opposed-engine crankcases
- Radial-engine crankcases
- In-line-engine crankcases
- V-type engine crankcases

Opposed Engine Crankcase

- Structure: Two halves of cast aluminum alloy, manufactured either with sand castings or by using permanent molds, approximately cylindrical with smooth areas and cylinder pads.

- Cylinder pad

A surface where a cylinder is mounted to the crankcase.

- Transverse Webs

Cast directly into the crankcase parallel to its longitudinal axis. These support the crankshaft bearings and add strength to the crankcase.

- Camshaft Bosses

Cast into the crankcase to support the camshaft, part of the valve operating mechanism.

Radial Engine Crankcase

Sections: Divided into distinct sections (3 to 7 depending on engine size type)

1. Nose Section (Radial)

- Mounted at the front, bolts directly to the power section.
- Made of cast aluminum alloy with a domed or convex shape.
- Houses propeller governor drive shaft, propeller shaft, cam ring, and possibly propeller reduction gear assembly.

2. Power Section(Radial)

- Where reciprocating motion of pistons is converted to rotary motion of the crankshaft.
- Absorbs intense stress from the crankshaft assembly and the cylinders.
- Contains machined bosses that rigidly support crankshaft bearings and cylinders.

3. Supercharger Section (diffuser)(Radial)

- Located directly behind the power section.
- Houses the supercharger and related components, made of cast aluminum alloy or magnesium.
- Compresses and distributes air to the engine's cylinders.

4. Accessory Section(Radial)

- Made of aluminum alloy or magnesium.
- Mounts accessories like magnetos, carburetors, pumps, starters, and generators.

1. Front Nose Section(In-Line and V-Type Engine)

- Directly behind the propeller in most tractor-type airplanes.
- Houses propeller shaft, thrust bearing, reduction gear train, and sometimes the propeller governor.

2. Main Power Section(In-Line and V-Type Engine)

- Mounts the cylinders.
- If 2 parts: one part supports one half of each crankshaft bearing and the other supports the opposite half.

3. Fuel Induction and Distribution Section(In-Line and V-Type Engine)

- Located next to the power section.
- Houses diffusers and impeller for internal blower systems.

4. Accessory Section(In-Line and V-Type Engine)

- May be part of the induction section.
- Contains the accessory drive-gear train and mounting pads for various accessories.

Engine Mounting Points

- Opposed Engines: Mounting points (mounting lugs) cast as part of the crankcase.
- Function: Supports entire powerplant, designed to withstand various engine, centrifugal, and gloading conditions.
- A surface that supports and reduces friction between moving parts.
- Used in main journals, crankpins, connecting rod ends, and accessory drive shafts.

Good Bearing Requirements

- Must be composed of strong material to withstand pressure with minimal friction and wear.

1. Plain Bearing

- Used for crankshaft main bearings, cam ring, camshaft bearings, connecting rod end bearings, and accessory drive shaft bearings.
- Made of nonferrous metals (silver, bronze, babbitt, tin, or lead).
- Typically subject to radial loads only.

2. Ball Bearing

- Consists of grooved races, polished steel balls, and a bearing retainer.
- Suitable for thrust loads and used as thrust bearings in large radial and gas turbine engines.
- Construction: Balls are held in place by the bearing retainer; inner and outer bearing races provide a smooth surface for the balls to roll over.

3. Roller Bearing

- Uses polished steel rollers instead of balls.
- Rollers provide a greater contact area and increase rolling friction compared to ball bearings.

- Straight roller bearings

can withstand radial loads only.

- Tapered roller bearings

have cone-shaped inner and outer races and can withstand both radial and thrust loads.