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sheet 2 
Solution 
The application of high energy X-radiography has been 
pioneered by Rolls Royce to provide more detailed studies of 
component flexures and two dimensional clearances, not possible 
with standard devices. It has the ability to penetrate the 
thick metal sections up to twelve inches of steel existing on 
aero and industrial gas turbines so that, in conjunction with a 
suitable image recording system, the small movements may be re- 
vealed, recorded and analysed. 
It has been a philosophy of our work that it should be 
possible to use the equipment on any engine for problem identi- 
fication and study, with no special engine modification. The 
possession of such a capability furnishes us with and excellent 
front line diagnostic instrument in gas turbine engine develop- 
ment. 
The Radiation Dynamics Ltd., 'Super X' Linear Accelerator, 
(Fig. 2), is mounted on a simple transportable mount. It has 
an X-ray output of 1500 Roentgens per minute at a meter at a 
fixed energy level of 8 Megavolts (Fig. 3). The X-rays are 
emitted from a focal spot of less than 2 mm (nominally circular). 
The accelerator is a pulsed machine with pulse repetition fre- 
quencies between 50 and 500 pulses per second. Thus strobo- 
scopic techniques may be used in which sensed engine rotational 
speeds trigger single pulses to build up images of specific 
components. 
The accelerator is mounted at a distance of approximately 
3.3 meters from the engine vertical centreline and the imaging 
plane is situated on the opposite side about 0.6 meters from 
the engine (Fig. 4). This radiographic geometry, together with 
the X-ray source size imposes a limitation on the sharpness 
obtainable on the radiographic image. Besides geometric un- 
sharpness there are also other inherent unsharpnesses in the 
imaging system used. For most engineering situations, happily, 
this is not a great problem. 
In recording internal changes of component configuration 
within gas turbines it is our practice to first radiograph the 
engine as received i.e. 'cold' and 'static'. This provides an 
image which serves as a reference. Any subsequent radiographs 
made with the engine running are compared with the 'cold static' 
reference and the relative movements of the components are 
determined. This technique assumes that the radiographic para- 
meters are maintained constant for subsequent exposures.  There- 
fore the making and development of the stored images requires 
considerable attention to detail and close quality control. 
The main sources of engine configuration change in a sea 
level test are the rotational speed of the engine, the component 
temperatures and the internal gas pressure loadings. The gas 
pressure loadings are a function of rotational speed, but the 
thermal changes are not as closely related. 
Thus speed dependent changes may be examined by means of 
short duration exposures during transient engine handling con- 
ditions such as accelerations or decelerations. Temperature