FAA Aviation Mechanic Powerplant (AMP)Reciprocating EnginesEasy
A four-cylinder aircraft engine has a bore of 5.0 inches and a stroke of 4.0 inches. What is the approximate total piston displacement of this engine?
- A628 cubic inches
- B314 cubic inches
- C157 cubic inches
- D78.5 cubic inches
Show answer & explanationAnswer & explanation
Correct answer: B. 314 cubic inches
Displacement per cylinder = 0.7854 x bore^2 x stroke = 0.7854 x 25 x 4 = 78.54 cubic inches. Total displacement for 4 cylinders = 78.54 x 4 = 314.16 cubic inches, approximately 314 cubic inches.
Why the other options are wrong
- A. This is roughly double the correct total displacement.
- C. This equals only two cylinders' worth of displacement.
- D. This is the displacement of only one cylinder, not the whole engine.
Piston Displacement Calculation
Total engine displacement is the swept volume of one cylinder multiplied by the number of cylinders, using the formula 0.7854 x bore^2 x stroke.
- 0.7854 = pi/4, area of a circle formula constant
- Bore is squared, stroke is not
- Multiply per-cylinder displacement by number of cylinders for total
Memory trick: 0.7854 times bore-squared times stroke — the circle's area sweeping through the stroke.