rotor blade. The primary aim of the experiment is to make
a verification of design stress distribution.
Table 1 Rotor blade load increments.
7th June 1995 10th June 1995
h | % design load 96 load
0 10 100
50 11 150
12 175J
13 200
14 200J
15 225J
16 250J
17 250J
A structural test of this type involves loading the blade
according to a design distribution which reflects wind
load. Whilst several suitable test methods exist, in this
case, the blade was firmly fixed at its root to a jig, sand
bags and lead ingots were then incrementally placed on
the blade surface in a configuration designed to reflect
wind loading. Table 1 details the loading increments
applied to the rotor blade. The suffix 'J' on the later
epochs indicates that the angle of the supporting jig was
altered by means of hydraulic jacks to allow the static
load to be applied without the tip of the rotor blade
touching the laboratory floor. The final epoch (17)
consisted of a series of small changes in the hydraulic
jacks as the rotor blade was allowed to fail due to creep.
At each increment in design load, measurements of strain
and deflection were made at strategic locations on and
within the rotor blade. Deflection measurements were
made by conventional intersection survey. Two Zeiss Elta
2 total stations were used to coordinate several pre-
targeted points located at specific points along the blade
length. Table 2 shows the RMS location of these targets
in all three coordinate axes. These values meet the sub-
Graph of deflection against % design load.
200
180
160
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0.5 1.0 1.5
Deflection (m)
Figure 2 Measurements of deflection against design load
for the targeted points along the blade length.
millimetre specification since only deflection
measurements, corresponding to the Z axis, were
required. These measurements are conventionally plotted
against % design load to give the graph in figure 2.
Table 2 Target location precision by survey intersection
Axis X Y Z
Coordinate RMS (mm) | 1.71 2.01 0.70
3. PHOTOGRAMMETRIC DATA ACQUISITION
The research orientated digital photogrammetric system
available at the time of testing was not capable of
measuring the complete length of the blade to sub-
millimetre precision. Instead a small 3m long region of
interest at the major change in section near the root of the
rotor blade was selected. This area was spray painted
with matt-black cellulose paint to reduce surface glare
before targeting with 62 3mm diameter retro-reflective
targets. Ten larger retro-targets were mounted
independently of the test structure and coordinated by
intersection with the Zeiss Elta 2 instruments to provide a
stable control network. Three additional targets were
located on the supporting jig to provide a measure of the
stability of the rotor blade mounting.
=f | Epix Framesiore
at apy
=] 0000 =
caca Ua
7] High resolution
monitor
Five multiplexed pulnix
cameras including ring
lighting equipment.
486DX2 PC
Figure 3 Schematic diagram of the imaging system
Five Pulnix TM6CN interline CCD cameras were used to
image the targeted volume. Figure 4 illustrates the
network used and the relative positions of the structural
components. All five cameras were previously calibrated
using optical bench techniques and straight line arrays at
three different distances coinciding with the near, far ang
intermediate object distances. These data were then used
Camera 5
16mm lens
Camera 2
16mm lens
*
. Camera 4
Z Camera 1 8.5mm lens
8.5mm lens
Camera 3
16mm lens
Figure 4 The photogrammetric network used to measure a
portion of the turbine blade.
494
International Archives of Photogrammetry and Remote Sensing. Vol. XXXI, Part B5. Vienna 1996
Figure 5
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| File Options
Figure 7
and 11a
