Relationship between surface dynamics
and emitted sound
Comparing the results in the two tables, we notice that
while the distributions of normal skin and patched
skin have a large overlap for supported areas (underskin
condition A) in Table 1, a very similar situation exists
for the unsupported areas in Table 2. This means that the
coin-tap test method, either with force measurement only
or with sound measurement only, cannot always distinguish
different airplane skin conditions for some underskin
supporting structure conditions, and the discrimina-