DarZeelon wrote:
>For pipe equipped two-strokes, the soft mounts allow the engine to vibrate to a much larger amplitude, than would a rigid mount.

Most, if not all pilots that compete in F3A (FAI pattern competition) use soft mounts regardless if they are using 4-stroke or 2-stroke engines.

>The cost could be exhaust headers that break, at the weld of the tube to the flange.

Yes, but there are ways around this: Support the free end of the exhaust header from the soft mount itself instead of supporing it from the fuselage. I have seen bad examples of people soft mounting their engines only to rigidly attach the free end of the exhaust header to the fuselage, don't do this! Also use as short exhaust header as possible and select a longer pipe instead.

>I have never seen engine vibrations, with engine mounted rigidly enough, that have caused any airframe damage.

The point here was to reduce noise. And I can assure you that if switch harnesses, servos and Rx:s could speak thay would thank you for a soft mounted engine.