When Rotax surprised us last year with the rollout of its new 912 iS engine, we were skeptical of a claimed 20 percent improvement in fuel economy against the old standby 912 ULS. In a four-cylinder, high-RPM geared engine, that sounded like an overpromise. During our factory tour at Rotax, we politely told the engineers we would reserve judgment until the engine hits the field.
Eighteen months later, it has and just as we suspected, Rotax’s initial claims were off the mark. But in the wrong direction, if the company’s recent year-long test of the 912 iS is to be believed. Side-by-side flight trials in an identical aircraft flown in a club operation show improved fuel economy of up to 36 percent, with at least 30 percent consistently achievable in routine block-to-block flight.