A primary reason for developing pressure-sensitive
paint (PSP) for wind tunnel testing has been
the desire to use PSP in measuring aircraft loads. This
would obviate the need for a separate loads model
and test, as well as make loads data available much
earlier in the design cycle than is presently the case.
However, the ability of PSP to deliver accurate loads
data cannot be validated until integrated pressures
from PSP have been shown to give accurate force
and moment values.
The main objective was to modify the current
PSP data reduction code to support integration of
pressure data over a model surface grid and to
compare PSP-derived force and moment measurements
with those obtained from the balance.
The current PSP data reduction code already
produces pressure maps that are projected onto a
model surface grid. This code was modified to
produce integrated force and moment values by
summing the mean pressure on each surface panel
and multiplying it by the panel area. To verify the
method, forces were computed from PSP data taken
during a test of a semispan wing in the Ames Unitary
Wind Tunnel in October 1993. Figure 1 shows a
view of surface pressures on the wind tunnel model,
together with the surface grid. This test was chosen
because of the relatively simple model geometry, and
because PSP data were available over the top and
bottom of the wing.
The integrated PSP data are compared to balance
data in figure 2, which shows lift coefficient computed
using both methods. Values agree to within
less than 3% except at the high positive and negative
angles of attack. At these angles the model half-body,
which was not coated with PSP and is thus not
included in the pressure integration, begins to
contribute substantially to the lift.
It remains to extend the pressure integration
method to calculating moments, and to calculations
for more complex aerodynamic shapes.
Point of Contact: J. Bell
(650) 604-4142
jhbell@mail.arc.nasa.gov
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