1. I am after an indicator diagram for a Rotax 582, i.e. torque versus crank angle. Does anyone know where one might be, (I've tried the factory to no avail)? Failing this, does anyone know where I could get a representative indicator diagram for a twin cylinder two stroke, or even a single cylinder engine?
2. I want to put an rpm limiter into the ignition circuit on a Rotax 582, i.e. so the sparks dies if rpm goes beyond 6800. Does anyone have any knowledge of how to do this?
1. Thanks for your reply. Where can I get an indicator diagram for a Rotax 582, or representative engine?
2. Regarding the rpm limit I am going to build an Arduino unit to go between the ignition unit and the plug. This'll give me a very quick way of stopping the unit should the load disappear.
Hi, sorry, I misinterpreted your Y reply. The reason i want an indicator diagram is so that I know the maximum peak torque coming out of the crankshaft. This will allow me to size other drive train components. Regards Mark
1 day 16 hours ago - 1 day 16 hours ago#15351by Bill Hertzel
He is looking for Instantaneous Torque vs Crank Angle, not average Torque vs Rpm.
A quick Google search of "Engine Torque vs Crank Angle" shows the peak torque is 300-400% of the average torque, depending on the engine.
I would be hesitant in installing anything that has the capability of disabling the ignition in an aircraft.
Even Rotax allows "Military Power" (105% Max RPM) for a few seconds.
A High RPM alarm, Sound and Lights, Might serve the same purpose.
If you exceed Max RPMs in a dive the alarm would remind you to back off the throttle.
A throttle servo that could be manually overridden would be another option.
I would hate to see the ignition be disabled in flight due to a failure in the safety circuit.
generally manufacturers do not develop indicator diagrams for engines. You can grab a standard 2 stroke indicator diagram and scale the area under the curve to match the continuous torque. This would give you and indication of the peak.
However this is not what you actually need. The torque is modified by the inertia of all the moving components from the pistons, rings, con rods, cranks, bearings crankshaft windage, gear train etc. to the peak and trough of the output on the output shaft is far less that the peak would indicate.
I once measures instantaneous cylinder pressure at each degree of rotation and went through the exercise of calculating the resultant based on all of the above. Interesting exercise...
However If I really wanted to know the peaks for design purposes it gets even more complicated.
A designer I worked with when working for one of the major aircraft engine manufacturers said the drive train was designed for a worst case of a backfire pulse at the worst rpm then they added a 100% margin.
Most people seem to base the size on experience and testing.
Naturally torsionally soft couplings in the drive train decrease the peak loads enormously
As to RPM limit there are several very good and cheap aftermarket 2 stroke ignition systems you do not need to develop your own.