Slide 1

MOUNTING OF ENGINES ON AIRCRAFTLOADS ACTING ON ENGINE MOUNTING POINTS

GE 414 low by pass turbofanFront Mounting point Rolls Royce RB 211 turbofan

Forward attachment Rear attachment

Typical attachment of turbofan engine on wing pylonTransport aeroplane

pylon

Wing-mounted nacelles can be placed so that the gas generator is forward of the front spar to minimize wing structural damage in the event of a disk or blade failure. Engine installations that do not permit this, such as the original 737 arrangement may require additional protection such as armoring of the nacelle, to prevent catastrophic results following turbine blade failure.

Attachment of gas turbine on engine pod Front mount

Gas turbine engine on the aircraft Front mountTruss structureLoads acting on engine mounting points

Forces are due to i) Thrust generated by the turbine ii) Weight of the engine and inertia force due to load factor iii) Aerodynamic forces - side ward during slide slip motion iv) Gyroscopic forces of the rotating masses during pitch and yaw motions of the aero plane

Gyroscopic effect or precession of axi - symmetric rotating bodies

Axis of spin of the wheel = zAxis of nutation = x about which moment Mx will have to be applied to cause precessionAxis of precession of the shaft = y

Gyroscopic effect

xzyRight hand screw concept

Propeller rotatesclockwise lookingfrom rear Aircraft is turned Left by rudder inputUpward force is required at tail to maintain level flightSpin direction is constantThe three vectors, spin velocity, input angular velocity and output angular velocity follow right hand thumb ruleA torque applied perpendicular to the axis of rotation, and therefore perpendicular to L, results in a rotation about an axis perpendicular to both and L. This motion is called precession. The angular velocity of precession P is given by the cross product (vector product) = P x L where L is the angular momentum of the shaft

LPGyroscopic effectExample of a car

The gyroscope/engine is spinning at a fairly high speed in a clockwise direction, as seen from the back of the car and as shown in the diagram above. When the car is turned to the left, the torque applied to the shaft by the support is along y axis.Reactions to forces A and B are applied to the Structure of the car forcing the front end of the car up and the rear end down. If the gyroscope is spinning in the opposite direction then the reverse will happen.xZ (left turn) Y torque axis forces acting on the shaftGyroscopic effect

zxy Precession Along z axis Additional informationFrom US patent Engine mount system for a turbofan gas turbine engine US 8267349 B2

A gas turbine engine may be mounted at various points on an aircraft such as a pylon integrated with an aircraft structure. An engine mounting configuration ensures the transmission of loads between the engine and the aircraft structure. The loads typically include the weight of the engine, thrust, aerodynamic side loads, and rotary torque about the engine axis. The engine mount configuration must also absorb the deformations to which the engine is subjected during different flight phases and the dimensional variations due to thermal expansion and retraction.One conventional engine mounting configuration includes a pylon having a forward mount and an aft mount with relatively long thrust links which extend forward from the aft mount to the engine intermediate case structure. Although effective, one disadvantage of this conventional type mounting arrangement is the relatively large punch loads into the engine cases from the thrust links which react the thrust from the engine and couple the thrust to the pylon. These loads tend to distort the intermediate case and the low pressure compressor (LPC) cases. The distortion may cause the clearances between the static cases and rotating blade tips to increase which may negatively affect engine performance and increase fuel burn.