Created: August 14, 2007
|Wrist Pin Offset:|
|Top of exhaust port from crankshaft axis:|
|Top of port transfer from crankshaft axis:|
|Inlet open radial relative to TDC:|
|Inlet close radial relative to TDC:|
|Rotor Leading Edge radial relative to crankpin:|
|Rotor Trailing Edge radial relative to crankpin:|
|Piston deflector step height:|
|Exhaust port height:|
This form calculates the displacement and timing events for a Rear Rotary Valve (RRV) two-stroke model engine. You need to have an accurate set of measurements for the subject engine. The script called by this form does a reasonable amount of error checking on the parameters supplied, but is probably not fool-proof. If the numbers look valid, the program will calculate the opening and closing angles for the exhaust, transfer, and inlet relative to top and bottom dead center (TDC and BDC). Note that no provision is made (yet) for engines with a "DeSaxe" configuration where the cylinder axis and crankshaft axis (or wrist pin axis) are not all aligned in the same vertical plain.
The almost infinite possibilities for the shape and relative position of the opening in an RRV backplate and the shape of the rotary valve opening may lead to slight errors in the inlet timing calculation. Hopefully, the method chosen for specifying their locations as radials defining their extents should produce either accurate timing, or a very close approximation.
Start by selecting the units of your measurements (inches, or millimetres) using the Radio Buttons at the top of the form. Then enter as many values as required. At a minimum, you need to enter values for the bore and stroke, although this will only calculate the engine displacement. You can click on the label of any of the form fields for an explanation of that parameter. Omitting the heights for a port lip, or the inlet valve data will cause that port's timing to be skipped. The others will still be calculated as all are independent. When entry is complete, press the "Calculate" button at the top right of the form. We recommend that you don't use your browser's "Back" button to return to this form as that may loose your previously entered values. Instead, use the "Return to Input" button on the results page to retain the values for modification and re-use. You can clear the values with the "Clear All Values" button at the top left of the page.
The calculations are performed using a PHP script, so this page requires a working web server for operation. It cannot be used statically in a mere web browser on a local PC (unless you have installed a local web server as detailed in the Model Engine News DVD set-up instructions). For simplicity, angular values are rounded to one decimal place.