Q&A | Aircraft Reciprocating Engine

Fill in the Blanks

1. Reciprocating engines may be classified according to the __________________ or according to the method of __________________.

2. Inline engine may be either __________________ cooled or __________________ cooled and has only __________________ crank shaft, which is located either above or below the cylinders.

3. The Otto-cycle of engine operation is a constant __________________ cycle.

4. Horizontally opposed engine crankcases are usually cast from __________________ alloy.

5. The __________________ engine has two banks of cylinders directly opposite each other with a crankshaft in the center.

6. Radial engines have appeared in two forms: the __________________-radial and the __________________-radial.

7. The __________________ consists of a row, or rows, of cylinders arranged radially about a central
crankcase.

8. Crankcase nose sections are usually cast of either __________________ or __________________.

9. On some of the larger radial engines, a small chamber is located on the __________________ of the nose section to collect the __________________.

10. The crankshaft main bearings must be supported __________________ in the crankcase. This usually is accomplished by means of __________________ in the crankcase, one for each main bearing.

11. The main purpose of the crankshaft is to transform the __________________ motion of the piston and connecting rod into __________________ motion for rotation of the propeller.

12. The outer surface of the crankpins and journals are hardened by __________________.

13. To reduce vibration to a minimum during engine operation, __________________ are incorporated
on the crankshaft.

14. Knuckle pins may also be installed with a __________________ fit so that they can turn in the master rod flange holes, and also turn in the __________________ rod bushings.

15. Pistons may be either the __________________ type or the __________________ type.

True or False

1. If the engine is designed to operate with the cylinders above the crankshaft, it is called an inverted engine. (True/False)

2. In V-type engines, the cylinders are arranged in two in‑line banks generally set 60° apart. (True/False)

3. Cast or forged aluminum alloy is not used for crankcase construction. (True/False)

4. The crankshaft is carried in a position parallel to the vertical axis of the crankcase. (True/False)

5. Crankshafts are balanced for static balance and dynamic balance. (True/False)

6. The master-and-articulated rod assembly is commonly used in radial engines. (True/False)

7. Plain-type connecting rods are not used in inline and opposed engines. (True/False)

8. Slipper-type pistons are used in modern, high-powered engines. (True/False)

9. Gray cast iron is not used in making piston rings. (True/False)

10. Single-row radial engine cylinders are numbered clockwise when viewed from the rear. (True/False)

Knowledge Application Questions

1. Name the basic major components of a reciprocating engine

2. What are the three main parts of a crankshaft?

3. What are the four types of connecting-rod assemblies?

4. What is the purpose of dynamic dampers on crankshafts?

5. Are the connecting rods used in each cylinder of a radial engine the same? Explain

6. Name the different types of piston rings

7. Where should piston ring gaps be installed relative to each other, and why?

8. What could result from incorrectly installed piston rings?

9. What purpose do oil control rings serve?

10. What is used to help prevent valve surge or floating in an aircraft engine?

11. On engines equipped with hydraulic valve lifters, what should the running valve clearance be?

12. What is the purpose of valve overlap?

13. What indications are given in the event of a leaking or open primer while the engine is running?

14. What are the four major factors that need to be considered in the design and construction of the cylinder assembly?

15. What are the two methods commonly used to harden cylinder walls?

Multiple Choice Questions

1. Which statement is true regarding bearings used in high-powered reciprocating aircraft engines?
a. The outer race of a single-row, self-aligning ball bearing will always have a radius equal to the radius of the balls.
b. There is less rolling friction when ball bearings are used than when roller bearings are employed.
c. Crankshaft bearings are generally of the ball-type due to their ability to withstand extreme loads without overheating.

2. A condition that can occur in radial engines but is unlikely to occur in horizontally opposed engines is
a. valve overlap.
b. zero valve clearance.
c. hydraulic lock.

3. Which condition would be the least likely to be caused by failed or failing engine bearings?
a. Excessive oil consumption.
b. High oil temperatures.
c. Low oil temperatures.

4. What is the principal advantage of using propeller reduction gears?
a. To enable the propeller RPM to be increased without an accompanying increase in engine RPM.
b. To enable the engine RPM to be increased with an accompanying increase in power and allow the propeller to remain at a lower, more efficient RPM.
c. To enable the engine RPM to be increased with an accompanying increase in propeller RPM.

5. Which of the following will decrease volumetric efficiency in a reciprocating engine?
1. Full throttle operation.
2. Low cylinder head temperatures.
3. Improper valve timing.
4. Sharp bends in the induction system.
5. High carburetor air temperatures.

a. 2, 4 and 5.
b. l, 2,3 and 4.
c. 3, 4 and 5.

6. Which of the following is a characteristic of a thrust bearing used in most radial engines?
a. Tapered roller.
b. Double-row ball.
c. Deep-groove ball.

7. Which bearing is least likely to be a roller or ball bearing?
a. Rocker arm bearing (overhead valve engine).
b. Master rod bearing (radial engine).
c. Crankshaft main bearing (radial engine).

8. The operating temperature valve clearance of a radial engine as compared to cold valve clearance is
a. greater.
b. less.
c. the same.

9. A nine-cylinder engine with a bore of 5.5 inches and a stroke of 6 inches will have a total piston displacement of
a. 740 cubic inches.
b. 1,425 cubic inches.
c. 1,283 cubic inches.

10. The five events of a four-stroke cycle engine in the order of their occurrence are
a. intake, ignition, compression, power, exhaust.
b. intake, power, compression, ignition, exhaust.
c. intake, compression, ignition, power, exhaust.

11. The primary concern in establishing the firing order for an opposed engine is to
a. provide for balance and eliminate vibration to the greatest extent possible.
b. keep power impulses on adjacent cylinders as far apart as possible in order to obtain the greatest mechanical efficiency.
c. keep the power impulses on adjacent cylinders as close as possible in order to obtain the greatest mechanical efficiency.

12. If fuel/air ratio is proper and ignition timing is correct, the combustion process should be completed
a. 20 to 30' before top center at the end of the compression stroke.
b. when the exhaust valve opens at the end of the power stroke.
c. just after top center at the beginning of the power stroke.

13. Grinding the valves of a reciprocating engine to a feather edge is likely to result in
a. normal operation and long life.
b. excessive valve clearance.
c. preignition and burned valves.

14. Which statement is correct regarding engine crankshafts?
a. Moveable counterweights serve to reduce the torsional vibrations in an aircraft reciprocating engine.
b. Moveable counterweights serve to reduce the dynamic vibrations in an aircraft reciprocating engine.
c. Moveable counterweights are designed to resonate at the natural frequency of the crankshaft.

15. On which strokes are both valves on a four-stroke cycle reciprocating engine open?
a. Power and exhaust.
b. Intake and compression.
c. Exhaust and intake.

16. Master rod bearings are generally what type?
a. Plain.
b. Roller.
c. Ball.

17. The actual power delivered to the propeller of an aircraft engine is called
a. friction horsepower.
b. brake horsepower.
c. indicated horsepower.

18. Cam-ground pistons are installed in some aircraft engines to
a. provide a better fit at operating temperatures.
b. act as a compensating feature so that a compensated magneto is not required.
c. equalize the wear on all pistons.

19. Using the following information, determine how many degrees the crankshaft will rotate with both the intake and exhaust valves seated.
Intake opens 15⁰ BTDC.
Exhaust opens 70⁰ BBDC.
Intake closes 45⁰ ABDC.
Exhaust closes 10⁰ ATDC.

a. 290⁰
b. 245⁰
c. 25⁰

20. Some aircraft engine manufacturers equip their product with choked or taper-ground cylinders in order to
a. provide a straight cylinder bore at operating temperatures.
b. flex the rings slightly during operation and reduce the possibility of the rings sticking in the grooves.
c. increase the compression pressure for starting purposes.

21. An aircraft reciprocating engine using hydraulic valve lifters i s observed to have no clearance in its valve operating mechanism after the minimum inlet oil and cylinder head temperatures for takeoff have been reached. When can this condition be expected?
a. During normal operation.
b. When the lifters become deflated.
c. As a result of carbon and sludge becoming trapped in the lifter and restricting its motion.

22. What tool i s generally used to measure the crankshaft rotation in degrees?
a. Dial indicator.
b. Timing disk.
c. Prop protractor.

23. If an engine with a stroke of 6 inches is operated at 2,000 RPM, the piston movement within the cylinder will be
a. at maximum velocity around TDC.
b. constant during the entire 360⁰ of crankshaft travel.
c. at maximum velocity 90⁰ after TDC.

24. If the intake valve is opened too early in the cycle of operation of a four-stroke cycle engine, it may result in
a. improper scavenging of exhaust gases.
b. engine kickback.
c. backfiring into the induction system.

25. Some cylinder barrels are hardened by
a. nitriding.
b. shot peening.
c. tempering.

26. Which statement is correct regarding a four-stroke cycle aircraft engine?
a. The intake valve closes on the compression stroke.
b. The exhaust valve opens on the exhaust stroke.
c. The intake valve closes on the intake stroke.

27. On which part of the cylinder walls of a normally operating engine will the greatest amount of wear occur?
a. Near the center of the cylinder where piston velocity is greatest.
b. Near the top of the cylinder.
c. Wear is normally evenly distributed.

28. During overhaul, reciprocating engine exhaust valves are checked for stretch
a. with a suitable inside spring caliper.
b. with a contour or radius gauge.
c. by placing the valve on a surface plate and measuring its length with a vernier height gauge.

29. When is the fuellair mixture ignited in a conventional reciprocating engine?
a. When the piston has reached top dead center of the intake stroke.
b. Shortly before the piston reaches the top of the compression stroke.
c. When the piston reaches top dead center on the compression stroke.

30. Ignition occurs at 28⁰ BTDC on a certain four-stroke cycle engine, and the intake valve opens at 15⁰ BTDC. How many degrees of crankshaft travel after ignition does the intake valve open?
(Consider one cylinder only.)
a. 707⁰
b. 373⁰
c. 374⁰

31. What is the purpose of the safety circlet installed on some valve stems?
a. To hold the valve guide in position.
b. To hold the valve spring retaining washer in position.
c. To prevent valves from falling into the combustion chamber.

32. Valve overlap is defined as the number of degrees of crankshaft travel
a. during which both valves are off their seats.
b. between the closing of the intake valve and the opening of the exhaust valve.
c. during which both valves are on their seats.

33. The valve clearance of an engine using hydraulic lifters, when the lifters are completely flat, or empty, should not exceed
a. a specified amount below zero.
b. a specified amount above zero.
c. 0.00 inch.

34. If the exhaust valve of a four-stroke cycle engine is closed and the intake valve is just closed, the piston is on the
a. intake stroke.
b. power stroke.
c. compression stroke.

35. How many of the following are factors in establishing the maximum compression ratio limitations of an aircraft engine?
1. Detonation characteristics of the fuel used.
2. Design limitations of the engine.
3. Degree of supercharging.
4. Spark plug reach.

a. Four.
b. Two.
c. Three.

36. Full-floating piston pins are those which allow motion between the pin and
a. the piston.
b. both the piston and the large end of the connecting rod.
c. both the piston and the small end of the connecting rod.

37. The primary purpose in setting proper valve timing and overlap is to
a. permit the best possible charge of fue/air mixture into the cylinders.
b. gain more thorough exhaust gas scavenging.
c. obtain the best volumetric efficiency and lower cylinder operating temperatures.

38. If the hot clearance is used to set the valves when the engine is cold, what will occur during operation of the engine?
a. The valves will open early and close early.
b. The valves will open late and close early.
c. The valves will open early and close late.

39. The purpose of two or more valve springs in aircraft engines is to
a. equalize side pressure on the valve stems.
b. eliminate valve spring surge.
c. equalize valve face loading.

40. During overhaul, the disassembled parts of an engine are usually degreased with some form of mineral spirits solvent rather than water-mixed degreasers primarily because
a. solvent degreasers are much more effective.
b. water-mixed degreaser residues may cause engine oil contamination in the overhauled engine.
c. water-mixed degreasers cause corrosion.

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ANSWERS

Fill in the blanks
1. cylinder arrangement, cooling.
2. liquid, air, one
3. volume
4. aluminum
5. opposed-type
6. rotary, static
7. radial engine

True or False
1. false
2. true
3. false
4. false
5. true

Knowledge Application
1. crankcase, cylinders, pistons, connecting rods, valves, valve-operating mechanism, and crankshaft.
2. a. Journal, b. Crank pin, c. Crank cheek
3. a. Plain, b. Fork and blade, c. Master and articulated, d. Split-type
4. To reduce vibration to a minimum during engine operation
5. No. Radial engines use master and articulating rod assemblies
6. Oil control, Compression, oil scraper
7. Compression ring gaps should be staggered so that they do not align. This prevents excessive blow-by.
8. Excessive oil consumption

Multiple Choice
1. b
Both ball bearings and roller bearings are used in aircraft engines. However, since the steel balls in a ball bearing offer less surface contact than the rollers of a roller bearing, ball bearings produce less rolling friction. Therefore, ball bearings are generally used in high-powered reciprocating engines to keep friction to a minimum.
2. c
Before starting a radial engine that has been shut-down for more than 30 minutes, the propeller should be pulled through by hand in the direction of normal rotation to detect hydraulic lock. Hydraulic lock is more likely to occur in radial engines because the inverted lower cylinders may allow oil to collect in the combustion chambers.
3. c
If a bearing fails or is in the process of failing, metal to metal contact is occurring. The friction which accompanies this metal to metal contact generates a great deal of heat and can cause high oil temperatures (answer B). The higher the oil temperature, the more oil is consumed (answer A). Since the question asks for the condition that is least likely to be caused by a failed bearing, answer (C) is the best choice.
4. b
The amount of horsepower an engine produces is directly related to the engine's rpm. Therefore, most aircraft engines must run at a speed in excess of 2,000 rprn to develop sufficient power. However, propeller efficiency at these speeds decreases rapidly. Therefore, in order to maintain an acceptable level of propeller efficiency a reduction gear is used. A reduction gear allows an engine to run at the high rprn needed to produce more horsepower while at the same time, allow the propeller to rotate at a lower, more efficient rpm.
5. c
Volumetric efficiency is a comparison of the volume of a fuel/air charge inducted into all cylinders to the total piston displacement. Factors that reduce volumetric efficiency include part-throttle operation, long, small diameter intake pipes, sharp bends in the induction system, excessive carburetor air temperatures, excessive cylinder head temperatures, incomplete scavenging, and improper valve timing. Of the five choices given in the question only #3, #4, and #5 (answer c) affect volumetric efficiency.
6. c
Special deep-groove ball bearings are used as thrust bearings in most radial engines. This type of bearing generates the least amount of friction of all the types of bearings listed while still being able to withstand both the thrust and radial loads.
7. b
Master rod bearings on radial engines are generally subjected to radial loads only and, therefore, plain bearings are used.
8. a
As a radial engine warms up, the aluminum alloy cylinder heads expand causing the rocker arm in the head to move away from the crankcase. At the same time, the pushrod also expands but at a lesser rate than the cylinder head. The difference in expansion amounts between the cylinder head and pushrod effectively increases the space between the valve stem and rocker arm (valve clearance).
9. c
To determine the displacement of the entire engine, multiply the displacement of each cylinder by the total number of cylinders. The total engine displacement is 1,282.95 cubic inches (1 42.55 x 9 = 1,282.95).
10. c
The four-stroke cycle begins when the piston starts moving down in the cylinder on the intake stroke. When the piston reaches bottom center it reverses direction and starts moving up on the compression stroke. Near the top of the compression stroke, the spark plug fires causing ignition of the fuel/air mixture. As soon as the fuel/air mixture begins to burn, the piston is forced down in the power stroke. As the piston approaches bottom center, the exhaust valve opens and the piston reverses direction to begin the exhaust stroke. Therefore, the five events of a four stroke engine are intake, compression, ignition, power, and exhaust.

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