Complex sentence: The design was intended to be a multi-engine aircraft that in the event of failure of a single engine would not, because of assymetric thrust become dangerously difficult to control; the result is an asymmetrical aircraft with a very distinct appearance.
Split into simpler sentences: The design was intended to be a multi-engine aircraft that would not become dangerously difficult to control in the event of failure of a single engine. The result is an asymmetrical aircraft with a very distinct appearance.