Lesson 4: Reciprocating Engine Design and Construction

1. Lesson 4: Reciprocating Engine Design and Construction

2. Reciprocating Engine Design and Construction • Basic Parts • Crankcase • Cylinders • Pistons • Connecting rods • Valves • Valve-operating mechanism • Crankshaft • Head • Spark plugs

3. Reciprocating Engine Design and Construction • Crankcase • Foundation of the engine, containing the bearings in which the crankshaft revolves.

4. Reciprocating Engine Design and Construction • Crankcase • Tight enclosure for lubricating oil. • Support for attachment of the cylinders and the powerplant to the aircraft. • Must be rigid, strong and light. • Cast of forged aluminum alloy.

5. Reciprocating Engine Design and Construction • Opposed Engine Crankcase Bearings

6. Reciprocating Engine Design and Construction • Crankshafts • Transforms the reciprocating motion of the piston and connecting rod into rotary motion for the propeller.

7. Reciprocating Engine Design and Construction • Crankshaft • Backbone of engine. • Forged from very strong alloy (Chromium-nickel-molybdenum steel). • Single or multi-piece.

8. Reciprocating Engine Design and Construction • Crankshaft • Four-throw used on four-cylinder engines. • Six-throw used on six-cylinder engines. • Three Main Parts • Journal • Crankpin • Crankcheek

9. Reciprocating Engine Design and Construction • Crankshaft Balance • Dynamic dampers are used to reduce vibration during engine operation. • Pendulum which is fastened to the crankshaft.

10. Reciprocating Engine Design and Construction • Connecting Rods • Link which transmits forces between the piston and the crankshaft. Master and Articulated Fork and Blade Plain

11. Reciprocating Engine Design and Construction • Master and Articulated Rod Assembly • Commonly used in radial engines. • One piston in each row is connected to the master rod. Others are connected to the master rod by articulated rods.

12. Reciprocating Engine Design and Construction • Fork And Blade Assembly • Used primarily in V-type engines.

13. Reciprocating Engine Design and Construction • Plain Type Connecting Rod • Used in in-line and opposed engines.

14. Reciprocating Engine Design and Construction • Pistons • Acts as a moving wall within the combustion chamber.

15. Reciprocating Engine Design and Construction • As the piston moves down it draws in fuel/air mixture. • As it moves up it compresses the charge. • Ignition occurs, and expanding gases force the piston down. • This force is transmitted to crankshaft through connecting rod. • On the return upward stroke, the piston forces the exhaust gas out.

16. Reciprocating Engine Design and Construction • Piston Construction • Machined from aluminum alloy forgings. • Grooves machined for piston rings. • Cooling fins inside for greater heat transfer. • Piston pin (wrist pin) joins the piston to the connecting rod.

17. Reciprocating Engine Design and Construction • Piston Types • Trunk Type • Slipper Type • Not used in aircraft Slipper Trunk

18. Reciprocating Engine Design and Construction • Piston Rings • Compression Rings • Oil Control Rings • Oil Scraper Rings Rings Pin boss

19. Reciprocating Engine Design and Construction • Compression Rings • Prevent the escape of gas past the piston during engine operation. • Number used depends on engine design. • Cross section of the ring is either rectangular or wedge shaped

20. Reciprocating Engine Design and Construction • Oil Control Rings • Placed in grooves immediately below the compression rings. • One or more rings per piston. • Regulate the thickness of the oil film on the cylinder wall.

21. Reciprocating Engine Design and Construction • Oil Scraper Ring • Installed in the groove at the bottom of the piston skirt. • Installed with the scraping edge away from the piston head or in the reverse position. • Returns surplus oil to the crankcase.

22. Reciprocating Engine Design and Construction • Cylinders • The portion of the engine in which the power is developed. • Provides a combustion chamber where the burning and expansion of gases take place. • Houses the piston and the connecting rod.

23. Reciprocating Engine Design and Construction • Cylinders • Either produced singly or cast in a block. • Air-cooled engine uses the overhead valve type. • Two major parts: Head, Barrel.

24. Reciprocating Engine Design and Construction • Cylinder Heads • Provides a place for combustion of the fuel/air mixture. • Gives the cylinder more heat conductivity for cooling. • Contains the intake valve, exhaust valve and sparkplugs. • Contains fins for cooling.

25. Reciprocating Engine Design and Construction • Cylinder Barrels • Made of a steel alloy forging with the inner surface hardened to resist wear. (Nitrided) • Worn Cylinder walls can be ground out and re-nitrided or chrome plated. • Chrome plated cylinders can be recognized by orange paint mark on cylinder.

26. Reciprocating Engine Design and Construction • Cylinder Numbering (Opposed Engine) • Propeller (Front) • Accessory (Rear) • Left, right (Pilot’s view)

27. Reciprocating Engine Design and Construction • Cylinder Numbering (Opposed Engine) • Numbering is by no means standard. • Continental starts from rear. • Lycoming starts from front.

28. Reciprocating Engine Design and Construction • Cylinder Numbering (Radial Engine)

29. Reciprocating Engine Design and Construction • Cylinder Numbering (Radial Engine) • Numbered clockwise as viewed from the accessory end. • Single-row, cylinder No. 1 is the top cylinder. • Double-row, all odd-numbered cylinders are in the rear, and all even numbered cylinders are in the front.

30. Reciprocating Engine Design and Construction • Firing Order • The Sequence in which the power event occurs in the different cylinders. • Designed to provide for balance and to eliminate vibration.

31. Reciprocating Engine Design and Construction • Firing Order Single-Row-Radial • First all odd numbered cylinders fire in numerical succession. • Then the even-numbered cylinders fire in numerical succession. 1-3-5-7-9-2-4-6-8

32. Reciprocating Engine Design and Construction • Firing Order Double-Row-Radial • Arranged with the firing impulse occurring in a cylinder in one row and then in a cylinder in the other row. • Two cylinders in the same row never fire in succession.

33. Reciprocating Engine Design and Construction • Firing Order Opposed Engine • Lycoming and Continental number their cylinders differently which gives us two sets of firing orders. • But the firing impulses are the same.

34. Reciprocating Engine Design and Construction • Firing Order Opposed Engine 1-4-2-3

35. Reciprocating Engine Design and Construction Valves

36. Reciprocating Engine Design and Construction • Valves • Fuel/air mixture enters the cylinders through the intake valve. • Burned gases are expelled through the exhaust valve. • Mushroom or tulip type depending on shape.

37. Reciprocating Engine Design and Construction

38. Reciprocating Engine Design and Construction • Valve Construction • Intake valves, because of lower operating temperatures, can be made of chrome-nickel steel. • Exhaust valves are made of exotic metals such as inconel, silicon-chromium or cobalt-chromium alloys.

39. Tip Neck Face Head Reciprocating Engine Design and Construction • Valve Construction Stem

40. Reciprocating Engine Design and Construction • Valve Construction • Valve head has ground face which forms a seal against the ground valve seat in the cylinder head. • Valve face ground to an angle of either 30° or 45°. • Valve face made more durable by the application of stellite (an alloy of cobalt and chromium).

41. Reciprocating Engine Design and Construction • Valve Construction • Valve stem acts as a pilot for the valve head and rides in the valve guide. • Surface-hardened to resist wear. • Some stems are hollow and partially filled with metallic sodium.

42. Reciprocating Engine Design and Construction • Valve Construction • The neck is the part that forms the junction between the head and the stem. • The tip is hardened to with stand the hammering of the valve rocker arm.

43. Reciprocating Engine Design and Construction • Valve Construction • Machined groove near tip receives the split-ring keys which form a lock ring to hold the valve spring retaining washer.

44. Reciprocating Engine Design and Construction • Valve-Operating Mechanism • Each valve must open at the proper time, stay open for the required length of time, and close at the proper time. • Timing of the valves is controlled by the valve-operating mechanism.

45. Reciprocating Engine Design and Construction • Valve-Operating Mechanism • Intake valves open just before the piston reaches top dead center, and exhaust valves remain open after top dead center. • At this particular instant both valves are open at the same time (end of the exhaust stroke and beginning of the intake stroke). • This valve overlap results in better volumetric efficiency and lower operating temperatures.

46. Reciprocating Engine Design and Construction • Valve-Operating Mechanism (Opposed engine)

47. Reciprocating Engine Design and Construction • Valve-Operating Mechanism (Radial engine)

48. Reciprocating Engine Design and Construction • Camshaft • Valve-operating mechanism is operated by a camshaft.

49. Reciprocating Engine Design and Construction • Camshaft • The camshaft is driven by a gear that mates with another gear attached to the crankshaft.

50. Reciprocating Engine Design and Construction • Tappet Assembly • Converts rotational movement of the cam lobe into reciprocating motion. • Transmits this motion to the push rod, rocker arm, and then to the valve tip. • Opening the valve at the proper time.