Model Attitude Measurement

Introduction

The technique used to measure model attitude for a particular test campaign depends upon the type of test.

Drag Tests

For drag tests measurement of the model angle of attack or “alpha” is just as important as accurate measurement of the total model loads – this is because lift and drag are calculated from both the model loads and the model angle of attack.

For drag tests an electronic incidence meter or "inclinometer" mounted inside the model (usually the nose) is used to measure model incidence or "alpha".

Stability and Control Tests

For stability and control tests where very large loads are expected and the model can experience considerable buffeting, the model angle of attack "alpha" and sideslip (or yaw) "beta" must be calculated by a computer using the loads measured by the model balance, the known bending characteristics of the model support system, and the pitch and roll of the sting which are measured inside the model support cart. 

An inclinometer mounted inside the model cannot be used in heavy buffeting because inclinometers use an internal pendulum weight which behaves like an accelerometer if moved quickly making any incidence measurements unreliable.

Technical Information

Drag Tests:

• Model inclinometer accuracy is ±0.003˚ within range ±10˚ in benign flow conditions

Stability and Control Tests:

• Sting pitch "theta" measured by inclinometer mounted inside model cart
• Sting roll "phi" measured by roll synchro-converter mounted inside model cart
• Model cart inclinometer accuracy is ±0.003˚ within range ±10˚
• Model cart synchro-converter accuracy is ±0.08˚ for entire roll range ±180˚