Smith’s rotary engine has four sector-ended arms turning about the center of a cylindrical shell. Pins on an eccentric head disc act through slots in the arms, changing the spacing between them during each revolution. The animation illustrates that motion. The separate calculator applies selected mean effective pressure to swept volume per revolution: work is pV, indicated power is pVN/60 and mean indicated torque is pV/(2π).
Smith Rotary Engine · Selected Indicated-Power Ledger
Explore the four-arm mechanism and calculate indicated work, power and mean torque from selected pressure, volume and speed.
Equation Used
- Selected swept volume is volume per revolution.
- Selected mean effective pressure applies to that volume event.
- One selected volume event occurs per revolution.
- Lift does not alter the entered IMEP unless supported by separate measured data.
- Leakage, friction, timing, heat loss, strength and safety are excluded.
The lift control reports an independent entered dimension. It does not set the Smith mechanism’s geometry or predict seal leakage.
How the four arms move
Hiscox’s item 336 shows four arms with cylindrical sectors rotating about the shell center, with the driven shaft and head discs eccentric to the shell. In the cutaway animation, four equally spaced pins turn with the blue head disc. Each pin slides along a gold arm as that arm pivots about the casing center. The changing arm spacing illustrates the changing chamber geometry. The dimensions are illustrative; steam admission, exhaust and sealing are not simulated.
What the calculator determines
Select mean effective pressure, swept volume per revolution and speed to calculate indicated work, power and mean torque. The separate lift input reports an entered dimension only and does not affect the power calculation or illustrated geometry.
Selected indicated-work identities
Wrev=pV; Pi=pVN/60; τi=Wrev/(2π). Selected lift is passed through unchanged.
Selected-input example
At 5 bar, 5 L/rev and 350 rpm, selected work is 2500 J/rev, power is 14.58 kW and indicated torque is 397.9 N·m.
Interpreting indicated power
Actual IMEP already reflects the measured pressure-volume cycle. Lift alone cannot determine leakage, IMEP collapse or efficiency without seal geometry, pressure ratio, timing and flow data. Strength and safety are excluded.
Questions
Can an entered lift determine leakage loss?
No. Leakage also depends on seal geometry, pressure ratio, temperature and how long the passage is open. The lift input here is independent of the illustrated Smith engine.
Does the drawing reproduce a surviving Smith engine?
The animation follows the four-arm arrangement in Hiscox’s item 336, using illustrative proportions rather than measurements from a surviving engine.
References & Further Reading
Gardner D. Hiscox, Mechanical Movements, Powers, Devices and Appliances (1901), page 92, item 336: Smith rotary engine.
- Wikipedia contributors. Rotary steam engine. Wikipedia
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