The historical Kipp rotary-piston engine used a broad rotating pulley containing four single-acting cylinders. Opposite pistons were connected by yoked rods, while a fixed eccentric crank pin and slide blocks produced successive piston displacement as the pulley turned.
Kipp Rotary Piston Engine Interactive Calculator
Calculate cycle-average power from entered mean effective pressure, combined swept volume per revolution, speed and assumed efficiency. The drawing does not determine these inputs.
Equation Used
- Use mean effective pressure and the combined swept volume for one revolution; these quantities are entered assumptions.
- Efficiency is an entered assumption.
- No steam admission/exhaust timing, disc-valve geometry, leakage, condensation, friction, heat transfer or strength model.
The four cylinders turn around a fixed eccentric pin. Crossed sliding yokes keep each piston on its cylinder axis; valve timing and pressure are not animated.
Rotating cylinders around a fixed pin
Hiscox describes a broad pulley containing four single-acting cylinders. Opposite pistons are joined by yoked rods, with an eccentric stationary crank pin and slide block producing successive displacement. Steam enters and leaves through the hollow shaft and ports in a disc valve.
In the cutaway animation, a fixed eccentric pin passes through slide blocks in two perpendicular yokes. Each yoke joins an opposite pair of pistons, which slide along their rotating cylinder axes. The two yokes occupy separate axial layers; the drawing uses illustrative dimensions.
A historical rotary steam-engine arrangement
This arrangement places reciprocating pistons inside a rotating housing. It differs from a Wankel engine, whose rotor turns within a shaped chamber. Hiscox illustrates the Kipp arrangement in entries 345–346; this page does not establish its operating performance or suitability for a modern application.
Cycle-average power
IHP=pVn/(12×33000), where p is mean effective pressure in psi, V is combined swept volume in cubic inches per revolution and n is revolutions per minute. The factor 12 converts inch-pounds to foot-pounds; 33,000 foot-pounds per minute is one mechanical horsepower.
Shaft power is η×IHP, using the entered efficiency as a decimal. Mean shaft torque is shaft horsepower×33,000/(2πn), in pound-feet. Loss power is the difference between indicated and assumed shaft power. These results do not come from the sketch’s geometry.
Worked power example
For p=80 psi, V=72 in³/rev and n=300 rpm, indicated power is approximately 4.36 hp. At an assumed efficiency of 85%, shaft power is approximately 3.71 hp, mean shaft torque 64.94 lb·ft and the difference 0.65 hp.
These are results of the entered cycle averages, not measured Kipp engine ratings. Changing speed changes power; at fixed pressure, volume and efficiency it leaves calculated mean torque unchanged.
What the model leaves out
The calculator assumes entered cycle-average pressure and volume and an entered mechanical efficiency. It does not predict valve timing, condensation, leakage, friction, pressure histories or structural strength. The drawing runs at a fixed display rate and does not change geometry with these inputs.
The animation shows the piston-and-yoke motion at a fixed display rate. It does not show the disc-valve passages or steam-pressure cycle. Use the calculator for the stated cycle-average power arithmetic.
Frequently asked questions
Does the drawing show correct piston travel?
Yes. Each piston slides on its cylinder axis, and the crossed yokes accommodate the fixed eccentric pin as the housing rotates. The dimensions are illustrative; valve timing and steam pressure are not animated.
What volume should be entered?
The combined swept volume associated with one shaft revolution, in cubic inches per revolution, consistent with the entered mean effective pressure.
Is efficiency predicted?
No. The entered percentage scales indicated power to an assumed shaft-power value.
Why does torque stay constant when speed changes?
At fixed mean pressure, volume per revolution and efficiency, calculated shaft power is proportional to speed. Dividing that power by angular speed gives the same mean torque.
Is the separate four-stroke video the Kipp steam engine?
No. It is a related rotating-cylinder example, with a different operating cycle and arrangement.
Historical reference
Gardner Dexter Hiscox, Mechanical Movements, Powers, Devices and Appliances, entries 345–346, describes and illustrates the Kipp rotary-piston engine, its yoked rods, fixed crank pin and disc-valve steam passages.
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