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8 Measurement of Aerodynamic Forces and Moments
(a) Direct drag measurement
(b) Drag measurement through
deforming parallelogram
Fig. 8.5 Strain gauges arrangement for the measurement of the drag
8.2.2 Sting Type Force Balance
The gauges are fixed to the deformable measurement element of the balance which
is linked downstream to the sting supporting the model. The forces and the moments
to which the model is subjected are transmitted to the rear end of the fixed sting
and this causes the measurement piece to deform under the aerodynamic load (see
Fig. 8.6).
The forces determined with respect to the balance virtual centre can then be
transposed to any other point directly linked to the model. The schematic representations in Fig. 8.7 show the arrangement of the gauges on a balance measuring the
six components of and Fig. 8.8 shows the ONERA 72C sting balance based on this
principle.
The accuracy of such balances are affected by interactions or coupling to a
response from a component of force or moment which is then registered by other
gauges. This results from an imperfect decoupling: for example, the drag force, X,
may cause a response on the bridges measuring Y, Z, L, M, N. These are due to
Fig. 8.6 Installation of a sting balance
8 Measurement of Aerodynamic Forces and Moments
(a) Direct drag measurement
(b) Drag measurement through
deforming parallelogram
Fig. 8.5 Strain gauges arrangement for the measurement of the drag
8.2.2 Sting Type Force Balance
The gauges are fixed to the deformable measurement element of the balance which
is linked downstream to the sting supporting the model. The forces and the moments
to which the model is subjected are transmitted to the rear end of the fixed sting
and this causes the measurement piece to deform under the aerodynamic load (see
Fig. 8.6).
The forces determined with respect to the balance virtual centre can then be
transposed to any other point directly linked to the model. The schematic representations in Fig. 8.7 show the arrangement of the gauges on a balance measuring the
six components of and Fig. 8.8 shows the ONERA 72C sting balance based on this
principle.
The accuracy of such balances are affected by interactions or coupling to a
response from a component of force or moment which is then registered by other
gauges. This results from an imperfect decoupling: for example, the drag force, X,
may cause a response on the bridges measuring Y, Z, L, M, N. These are due to
Fig. 8.6 Installation of a sting balance