From the Rolls-Royce experimental archive: a quarter of a million communications from Rolls-Royce, 1906 to 1960's. Documents from the Sir Henry Royce Memorial Foundation (SHRMF).
Study on engine vibration frequency and the location of the principal axis of rotation, with associated calculations, diagrams, and data.
| Identifier | ExFiles\Box 126\4\ scan0140 | |
| Date | 1st April 1934 guessed | |
| 138 S. A.{Mr Adams} E.{Mr Elliott - Chief Engineer} JOURNAL (Transactions) Fig. 1—Frequency of the Engine Due to the Support "The mass of the body, reduced to radius R, is m = I/R². Substituting the foregoing values gives m = 65/126.6 = 0.5135 lb.-in. sec.² "The inherent speed of the system, V, is √(c/m) = √(1600/0.5135) = √3118 = 55.8 radians per sec. "The frequency, f, = V/2π = 55.8/2(3.1416) = 8.88 per sec. "The frequency, f1, = 60 f = 60 X 8.88 = 533 per min. "The engine will vibrate, due to this suspension, at an engine speed n = 533 r.p.m. "By transformation, frequency f1, is f1 = √c R (9.55/√I) per min. "For the values I = 65 lb.-in. sec.² and R = 11.25 in., f1, = 13.33 √c per min. From this equation a chart for varying spring constants, c, can be drawn. For a radius r, instead of R, the ordinates should be multiplied by r/R, or r/11.25 in this instance." Polar Axis Discussed Perhaps at this point it would be well to discuss the principal axis, or polar axis, of an engine. There has been much discussion of the location of this axis and the factors controlling its position. Obviously, the position is greatly affected by the resistance and location of the engine mountings. Broadly speaking, on a unit powerplant, the longitudinal principal axis will run through the center of the U-joint and intersect the center of gravity. This is not exact but is much closer than the actual axes of rotation will be when the engine is rotating on its mountings, no matter how accurately placed. We have carefully checked the axes of rotation of many engines in cars and rechecked the engines free of their Diagram Labels (Side Elevation): Axis of Rotation Longest Principal Axis Center of Rear Mounting top Centerline of Crankshaft Front A, B, C, F Bottom Center of Gravity SIDE ELEVATION Diagram Labels (Plan View): Axis of Rotation Longest Principal Axis Front Machined Face of Clutch Housing Center of Rear Mounting Centerline of Crankshaft Right Side Front α, β, θ, ε A, B, C, F Left Side Center of Gravity PLAN VIEW Engine Data Table: Engine | α (Deg. Min.) | β (Min.) | θ (Deg. Min.) | φ (Deg. Min.) | C | D | E | F 1 | 7 45 | 0 | 9 1 | 1 4 | 8 5/32 | 4 21/64 | 1/8 | 18 21/64 2 | 9 15 | 44 | 10 51 | 1 43 | 6 19/64 | 3 21/32 | 43/64 | 17 3/16 3 | 6 25 | 59 | 8 38 | 1 51 | 8 21/32 | 3 57/64 | 17/32 | 17 7/32 4 | 6 4 | 22½ | 7 2½ | 1 30 | 9 9/16 | 4 1/32 | 23/32 | 20 7/16 Fig. 2—Variation of the Position of the True Principal-Axis Location Location of longest principal axis, axis of rotation, and center of gravity of engine and transmission assemblies. Vol. 34, No. 4 | ||