Abstract: An on board secondary propulsion system for an aircraft provides the capability of taxiing the aircraft on the ground without using the main aircraft engine(s). The power system includes a small taxi engine mounted on or in the aircraft at a location suitable to provide a thrust sufficient only to taxi the aircraft. Such a suitable system may be provided as original equipment to an aircraft or retrofitted to existing aircraft. The on board secondary propulsion system, in addition to the taxiing function, can provide electrical power, an environmental control unit, power for the aircraft hydraulic system and an emergency power unit as desired. The system can also be used to supplement the main aircraft engines as necessary during takeoff and climb to further reduce fuel consumption, noise, engine emissions, maintenance costs and extend the life of the main aircraft engines, reduce the required takeoff distance of an aircraft when used in conjunction with the main engines and provide emergency glide support.

Abstract: Thrust systems for passenger aircraft provide at least one flight engine and a taxi engine wherein all flight engines together provide, in total, a takeoff thrust arranged in a takeoff thrust direction and the taxi engine provides a taxi thrust which does not exceed 15% of the takeoff thrust and is directed substantially the same as the takeoff thrust direction. The taxi thrust is thereby sufficient to taxi the aircraft along a taxi path. In a system embodiment, the taxi thrust does not exceed 7.5% of the flight thrust. In another system embodiment, the flight engines have, in total, a flight engine weight and the taxi engine has a taxi engine weight that does not exceed 10% of the flight engine weight. In a system embodiment, the taxi engine weight does not exceed 7.0% of the flight engine weight. In another system embodiment, the taxi engine has a rated thrust and is configured so that the taxi thrust is within 40% and 100% of the rated thrust.