METHOD OF DETERMINING A STIFF VALUE OF AN AERODYNAMIC COEFFICIENT

• US 20110046926A1
• Filed: 01/12/2010
• Published: 02/24/2011
• Est. Priority Date: 02/09/2009
• Status: Active Grant

• Current Assignee: Airbus Operations SAS (Airbus SE)
• Original Assignee: Airbus Operations (European Aeronautic Defence and Space Company EADS NV)
• Inventors: CALMELS, Benoit
• Granted Patent: US 8,386,217 B2
• Time in Patent Office: Days
• US Class Current: 703/2
• CPC Class Codes: G01M 9/06 Measuring arrangements specially adapted for aerodynamic testing

Abstract

The invention relates to a method for determination of a rigid value of an aerodynamic coefficient of an aircraft, in which measurements are made in a wind tunnel on a model of the said aircraft and, on the basis of these measurements, at least one value, known as flexible model value, of this aerodynamic coefficient is determined, characterized in that a rigid value of the aerodynamic coefficient is calculated on the basis of the said flexible model value(s) and a correction taking into account the flexibility of the model. A plurality of flexible model values is determined on the basis of measurements made by varying the parameter q/E and maintaining the angle of incidence at a constant value, and the correction consists in an extrapolation operation providing a value of the aerodynamic coefficient corresponding to q/E=0. As a variant, a single flexible model is determined and the correction consists in adjusting the said value with the aid of a correction factor.

Claims

1. Method for determination of a rigid value of an aerodynamic coefficient of an aircraft for a given set of conditions, in which measurements made in a wind tunnel on a model representative of the said aircraft for the set of conditions involved and, on the basis of these measurements at least one experimental value (C_{Z-flexible-model}), known as flexible model value, of the said aerodynamic coefficient is determined, characterized in that a rigid value of the aerodynamic coefficient is calculated on the basis of the said flexible model value or values and a correction taking into account the flexibility of the model.

2. Method according to claim 1, characterized in that a plurality of flexible model values of the aerodynamic coefficient is determined on the basis of measurements made by varying the value of the parameter q/E and maintaining the angle of incidence at a constant value corresponding to the set of conditions involved, and in that the correction consists in an extrapolation operation on the basis of this plurality of flexible model values intended to provide a value of the aerodynamic coefficient (dC_{Z-flexible model} (q/E=0)), considered as being the rigid value sought, corresponding to the value zero of the parameter q/E.

3. Method according to claim 2, characterized in that the said measurements are made while also maintaining the Mach number and the Reynolds number at respective constant values corresponding to the set of conditions involved.

4. Method according to one of claim 2 or 3, characterized in that the said measurements are made in a pressurized and cryogenic wind tunnel.

5. Method according to claim 1, characterized in that the rigid value of the aerodynamic coefficient is calculated on the basis of a single flexible model value (C_{Z-flexible-model)} and a correction factor (Δ

C_Z-model;

KC_Z-model) representative of the effect of the flexibility of the model on the aerodynamic coefficient.

6. Method according to claim 5, characterized in that the correction factor is calculated as follows:

a digit object is generated, known as reference object, representative of the shape that the aircraft assumes under predetermined reference conditions and, with the aid of a digital aerodynamic model, the value (C_{Z-rigid-correction}) of the aerodynamic coefficient of this reference object is calculated for the set of conditions involved, which value is known as rigid correction value of the aerodynamic coefficient,

deformations of the model for the set of conditions involved are measured in a wind tunnel,

on the basis of these deformation measurements, there is generated a digital object, known as experimental flexible object, representative of the shape assumed by the model for this set of conditions and, with the aid of a digital aerodynamic model, the value (C_{Z-flexible-correction}) of the aerodynamic coefficient of the flexible experimental object is calculated for the set of conditions involved, which value is known as flexible correction value of the aerodynamic coefficient,

the correction factor is calculated on the basis of the previously calculated rigid correction value and flexible correction value of the aerodynamic coefficient.

7. Method according to claim 5, characterized in that the correction factor is calculated as follows:

a digital object is generated, known as reference object, representative of the shape that the aircraft assumes under predetermined reference conditions and, with the aid of a digital aerodynamic model, the value C_{Z-rigid-correction} of the aerodynamic coefficient of this reference object is calculated for the set of conditions involved, which value is known as rigid correction value of the aerodynamic coefficient,

on the basis of the reference object and with the aid of a digital aeroelastic model, the value (C_{Z-flexible-correction}) of the aerodynamic coefficient of the reference object considered as flexible is calculated for the set of conditions involved, which value is known as flexible correction value of the aerodynamic coefficient,

the correction factor is calculated on the basis of the previously calculated rigid correction value and flexible correction value of the aerodynamic coefficient.

8. Method according to claim 5, characterized in that the correction factor is calculated on the basis of a rigid correction value (C_{Z-rigid-correction-A320}) and a flexible correction value (C_{Z-flexible-correction-A320}) of the aerodynamic coefficient calculated beforehand for the set of conditions concerned for a model representing another aircraft, known as reference aircraft, that has shapes similar to the aircraft being studied, at least as regards the parts of the aircraft that determine the said aerodynamic coefficient.

9. Method according to one of claims 6 to 8, characterized in that the correction factor (Δ

C_Z-model) is equal to the difference between the rigid correction value and the flexible correction value of the aerodynamic coefficient, and in that the rigid value of the aerodynamic coefficient is equal to the sum of the flexible model value and the correction factor.

10. Method according to one of claims 6 to 8, characterized in that the correction factor (KC_Z-model) is equal to the ratio of the rigid correction value over the flexible correction value of the aerodynamic coefficient, and in that the rigid value of the aerodynamic coefficient is equal to the product of the flexible model value times the correction factor.