Uncontrolled copy not subject to amendment Airframes Revision 1.00 Chapter 8 ENGINE INSTALLATION

Learning Outcomes On completion of this subject you should: Understand the design principles of positioning engines in an airframe. Know the advantages/disadvantages of various engine positions.

Introduction to Engine Installation When the aircraft designer decides what engines will be fitted to an aircraft, he/she has to look at the performance required by the aircraft and so the size of the engine/ engines. Next the position of the engine/engines must be decided considering the following: When the engine position has been decided, the designer then has to strengthen the airframe components that will carry the engine and design the engine mounts. Ease of installation/removal. Position of fuel tanks. Ease of maintenance.

ENGINE POSITIONS For a single engine with propeller, it would normally be mounted in the nose of the aircraft. For a single jet engine, it would normally be mounted in the fuselage of the aircraft near the Centre of Gravity.

For twin engines they can be mounted on the wings or in the fuselage. ENGINE POSITIONS

For 3 or more engines they are usually mounted in or on the wings or attached to the fuselage.

ENGINE POSITIONS There are some exceptions.

ENGINE POSITIONS If an engine fails on a twin or multi engine aircraft with the engines mounted far out on the wings, then a large yawing force is produced. To counteract this yawing force a large rudder must be provided capable of large deflection to keep the aircraft flying straight and level. X Yawing force Counteracting force from Rudder.

ENGINE POSITIONS Positioning of the engines is a balance between the physical size of the engines and the available space on the airframe. On the Tornado they are in the fuselage to give a streamline effect. On the VC10 they are in pods on the rear fuselage which gives less yawing problems and also a clean wing. Propeller driven aircraft need the engines mounted far out on the wing to give clearance between the propeller tips and the fuselage or next propeller. The closer to the fuselage the more noise but the further out on the wing the more yaw problems.

ENGINE POSITIONS Disadvantages of putting engines in the wing (Nimrod) Space taken by the engines can neutralise some of the lifting area of the wing and reduce fuel capacity. The wing must be insulated against engine heat. Engine fire/failure can cause damage to the airframe structure and cause it to fail. i.e. Nimrod crash at Lossiemouth.

ENGINE POSITIONS Placing the engines in a pod and hanging it under the wing eliminates some of these disadvantages and give more advantages. The airflow over the wing is not disturbed. The whole wing can be used to hold fuel. No heat insulation is required. A thinner wing section can be used for higher speeds. Engines are easily accessible for servicing. Reverse thrust is easier to achieve. Weight is moved away from the fuselage, reducing bending loads on the wing in flight

ENGINE POSITIONS There are also disadvantages to hanging the engines under the wing Yaw problems still exist. Heavy loads can be placed on the wing and engine mounts if violent manoeuvres are necessary. Ground debris is more easily ingested into the engine causing damage. Taller and more complex undercarriages are needed to keep pods clear of the ground.

CONCLUSION It can be seen that the positioning of engines varies dramatically with the different roles of aircraft and the size of the engine required. Designers are still coming up with new ideas but for large aircraft the most common place is hung under the wing and for fighters in the fuselage.