A/C Powerplant: Reciprocating Engine Construction and Nomenclature (CH.3)

Crankcase

• Must support self

• Contains bearings in which the crankshaft revolves

• Provides tight enclosure for lubricating oil

• Supports internal and external mechanisms

• Provides mountings for attachment to
  airplane

• Provides support for attachment of cylinders

• Prevents misalignment of crankshaft and bearings

Opposed-Engine Crankcase

• Two matching halves

• Propeller gear reduction (if installed) separate

• Machined bearing bores

• Oil passages and galleries drilled
  throughout

• Provides mount for accessories at rear

Radial-Engine Crankcase

• Divided into sections

• As few as 3, as many as 7

• Typical is 4

Nose Section - Radial

• Houses prop shaft and bearings

• Gear reduction (if installed)

• Magnetos (improved cooling)

Power Section - Radial

• Cylinder Mounts

• May be divided into multiple parts

Supercharger Section - Radial

• Houses impeller

• Induction air is ducted and distributed

Accessory Section

 Mountings for accessory units

In-Line and V-Type crankcase

• Nose Section

• Power Section

• Supercharger Section

• Accessory Section

Bearings

• A part in which a journal, pivot pin, shaft, or other device revolves

• Must be strong enough to withstand pressure of load imposed on it

• Allow other surface to move freely

• Tight tolerances for quiet and smooth operation

Crankshaft

• Transforms reciprocating action to rotary motion

• Composed of offset cranks or throws

• Subject of total engine force

• Must be strong enough to withstand load imposed by engine
  

Main Journal

• Supported by and rotates in main bearing

• Center of rotation

Crankpin

• Also called connecting-rod-bearing journal or a throw

• Connecting rod for piston attaches here

• Hollow to reduce weight, allow oil, and collect deposits

Crank Cheek

• Aka crank arm or web

• Connects crankpin to main journal

• May extend on the other side of main journal for counterweight

Counterweights

• Provide balance

• Dynamic dampers are attached to crank cheeks

  • Movable, slotted steel counterweight
    

Propeller shafts:Tapered

• Used on older, low power engines

• Milled with a key slot to position prop

• Threaded end for retaining nut
  Propeller shafts

Propeller shafts: Spline

• Rectangular grooves mate with grooves in prop hub

• Retaining nut on front threaded portion

Propeller shafts: Flange-type

• Common on modern opposed engine

• Bolts or studs secure prop

Connecting Rod Assemblies

• Connect Piston to crankpin

  • Large end or crankpin end

  • Small end or piston-pin end

• Must be lightweight and strong

Piston

• Plunger which reciprocates inside cylinder

• The head is the top surface

• The sides form the skirt

  • Large side area to transfer heat to cylinder

• Grooves in the side for piston rings

  • Compression rings prevent gasses from escaping

  • Oil Rings prevent oil entering the combustion chamber
    

Cylinder

• Contains piston in cylinder barrel

• Contains valves and spark plugs in cylinder head

• Cylinder wall will have cooling fins if air cooled and passages for coolants if water cooled

Valves

• Poppet-type intake port and exhaust port valves

• Valve-springs hold valves closed

• Opened by a pushrod actuated by the camshaft

Camshaft

• The rear of the crankshaft has the
  crankshaft timing gear

• Connects to the camshaft gear to
  rotate camshaft

• Radial engines use a cam plate with
  cam lobes around

Accessory Section

• Houses and drives accessories

  • Oil Pump

  • Fuel Pump

  • Vacuum Pump

  • Hydraulic pump

Propeller Reduction Gears

• Allow prop to rotate at most efficient
  RPM for phase of flight

• Engine Maintains full power at much higher RPM

• Allows engine to be efficient power
  generator without propeller becoming
  transonic

Propeller Gear Reduction Units

• Typically found on small engines,
  automotive engines, or very powerful engines

• Small and automotive engines have
  much less engine displacement

• Need higher engine RPM to develop
  peak power

• Very powerful engines

• Need higher engine RPM to develop
  peak power

• Modern direct drive engines are a
  compromise

• Would develop more power at higher
  RPM