I believe the concern about damaging an engine by operating LOP dates back to the days of the airliners with large radial engines and flight engineers. In order to obtain maximum advantage from operating LOP on these engines it is necessary to advance the ignition timing to about 40degrees BTDC. This produces a significant reduction in specific fuel consumption and extended the range of the old airliners. The timing was controlled by an extra lever in the care of the flight engineer. The procedure was to set up the desired RPM and MAP, weaken the mixture to LOP and then advance the ignition to restore power without additional fuel consumption.
The risk to the engine arose from the consequence of inadvertently enriching the mixture without first retarding the ignition to about 20 - 25 degrees BTDC. Detonation would almost certainly occur and the engine would be seriously damaged. Current GA aircraft do not usually carry flight engineers and are therefore not permitted to have a means of advancing ignition timing to 40 degrees BTDC and we are prevented from damaging our engines by its misuse.
What we need is an electronic ignition system that will monitor RPM, MAP, air flow and fuel flow and calculate the optimum ignition advance and implement the advance with no pilot intervention. This would give us a real fuel saving with a small loss of speed, if the authorities would approve it.
Roger
