Sentry IP,
Yes, I understand the definition. At this stage in my career, it would be a little late to be trying to figure out the basics. Reread the post, and you'll note that I clearly stated that reference was made to engines which are critical in the conventional sense, and those which are critical for other reasons.
Critical refers not only to the aerodynamic assymetrical thrust situation which would most adversely affect the handling qualities of the airplane, but "the engine whose failure would most adversely affect the performance or handling qualities of the aircraft." See FAR 1.1
Additionally, in aircraft which are not affected aerodynamically by the loss of one engine over the other, the loss of one engine may present other issues such as loss of hydraulic, vacum, electrical, or other concerns. In such cases, loss of that engine may effect the operation of the aircraft more than the loss of any other powerplant, and that engine may be considered critical.
Critical is conventionally taken to mean an engine affected by assymetrical thrust caused by the descending propeller, however, there are clearly other reasons that an engine may be critical. I made reference to the P-2V/SP2H, in which failure of either jet created a more critical thrust situation, in terms of total thrust, and in terms of assymetrical thrust, than either recip.
Simply because you are not familiar with contra-rotating propellers with the descending blade on the outside, doesn't mean they don't exist, or haven't been designed. Certain of the Aerostar series had this feature, as did the P-38 lightening. Both engines were critical. If I'm not mistaken, I believe the F7F also utilized this arrangement. I may have confused you previously by referring to them as "counterrotating", but you understood the intent. The descending blade is on the outside of the arc, with the left engine turning counterclockwise as viewed from the rear, and the right engine turning clockwise.
In the non-conventional sense, both engines on most light twins are critical, in that the loss of either engine results in very undesirable performance (eg, the inabilty to maintain altitude, or serious erosion of climb performance). The reference in this case is clearly outside the conventional definition, and I so stated in the previous post. It is more tongue in cheek than a specific reference to the critical engine.
In this sense, even counterrotating props such as on a beech duchess become critical at high density altitudes and gross weights; the airplane is seriously impaired with the loss of either engine, and both engines are critical to operation of the aircraft.
Years ago I spoke with an A-10 IP who was extolling the virtues of the A-10. He stated that it was his idea of a fighter aircraft (spare me the role-lecture). He stated that it was fast (relatively speaking), maneuverable, single seat, and single engine. I commented that the airplane did indeed appear to have two engines. No, he replied. It had one. It just had a half engine on either side. Humor aside, the same thing may be said for most light twins, except that rather than a half-engine on either side, when one fails, the other resorts to a 1/5 engine, yielding only 20% of the necessary performance.
