V 
3.0. 
4.0. 
5.0. 
sheet 4. 
contd ++... 
are used to define a measurement position within the profile. 
A confidence interval of 0.05 mm can be obtained with this 
method, (Fig. 7). 
Example - Examination of Air Seals by HEIR Technique 
  
Dynamic radiography can be used to investigate virtually 
all seal areas within gas turbines without modification. For 
this reason, a minimum of 'a priori' knowledge is required 
with respect to the components to be investigated. A develop- 
ment engine experiencing difficulty can be radiographed within 
a few days of problem identification and most areas of the 
engine investigated. The technique provides essentially trans- 
parent walls to the engine. 
Of course there are limitations. A radiograph is a shadow- 
graph, and thus only a two-dimensional plane may be presently 
produced (normally an engine vertical centreline profile). Exa- 
mination of other planes is achieved by moving the accelerator 
and imaging system positions. The measurement is limited to an 
area around the X-ray beam axis. Further, off-centre measure- 
ments may be made but geometric corrections may be required. 
Eventually, ellipsing of objects in the image renders measure- 
ment unsuitable although qualitative data may still be derived. 
Thus large format radiographs are used to obtain the greatest 
information in a single exposure. For example, a radiograph of 
a turbine tip seal will also yield data on all associated disk 
seals and guide vanes. 
Labyrinth air and oil seals can be readily imaged in most 
areas of the engine. Good data can be obtained on axial and 
radial movements of both static and rotating components. This 
data can be used to obtain optimum build settings of the seal, 
and also for profiling of the static component. 
Shrouded turbine blades are examined in a similar manner 
and only on the larger engines does the metal path thickness 
become a severe restriction. 
Unshrouded blades present a different problem, the metal 
path thickness of the blade being small relative to the total 
thickness. Close approximations can be obtained using the 
blade platform position as a datum. 
Cost Effectiveness of the Technique 
  
This technique using a high energy linear accelerator was 
first attempted by Rolls Royce and Harwell with assistance by 
staff from Radiation Dynamics Ltd., on an Olympus 593 engine 
for Concorde at R.R. Bristol in September 1970. 
Since this time, at Rolls Royce, the accelerator has been 
installed for radiography on over 70 engines of 20 different 
engine types. A total of approximately 20,000 radiographs 
have been produced for analysis.