Method and apparatus for obtaining improved accuracy and range for air data parameters inferred from independent measurements of interdependent pressures

• US 7,213,454 B2
• Filed: 04/06/2005
• Issued: 05/08/2007
• Est. Priority Date: 04/06/2005
• Status: Active Grant

• Current Assignee: Rosemount Aerospace, Inc. (Rtx Corporation)
• Original Assignee: Rosemount Aerospace, Inc. (Rtx Corporation)
• Inventors: Cronin, Dennis James, Schauer, Travis Jon, Hongerholt, Derrick David
• Primary Examiner(s): Allen; Andre J.
• Application Number:
  US11/099,704
• Publication Number:
  US 20060225496A1
• Time in Patent Office: 762 Days
• Field of Search: 731/80, 731/700.2, 731/82
• US Class Current: 73/170.02
• CPC Class Codes: G01P 13/025 indicating air data, i.e. flight variables of an aircraft, e.g. angle of attack, side slip, shear, yaw
• CPC Class Codes: G01P 5/14 by measuring differences of pressure in the fluid
• CPC Class Codes: G01P 5/16 using Pitot tubes , e.g. Machmeter

Abstract

A method of calculating a system level air data parameter for an aircraft, for example aircraft angle-of-attack (AOA) and/or angle-of-sideslip (AOS), includes measuring a plurality of local static pressures p_i. Next, a plurality of non-dimensional pressure ratios are each generated as a function of one of the plurality of local static pressures p_i, a predicted system static pressure Ps_predicted, and a predicted impact pressure q_{c predicted}. Then, the system level air data parameter is calculated as a function of the generated plurality of non-dimensional pressure ratios. Air data systems having air data computers configured to implement the method are also disclosed. The air data systems can be Flush Air Data Systems (FADS), or other types of air data systems.

Claims

1. A method of calculating a system level air data parameter for an aircraft, the method comprising:

measuring a plurality of local static pressures p_i;

generating a plurality of non-dimensional pressure ratios, with each non-dimensional pressure ratio being generated as a function of one of the plurality of local static pressures p_i, a predicted system static pressure Ps_predicted, and a predicted impact pressure q_{c predicted};

calculating the system level air data parameter as a function of the generated plurality of non-dimensional pressure ratios;

providing the system level air data parameter as an output.

2. The method of claim 1, wherein calculating the system level air data parameter as a function of the generated plurality of non-dimensional pressure ratios further comprises calculating at least one of an aircraft angle-of attack (AOA) and an aircraft angle-of sideslip (AOS).

3. The method of claim 1, wherein generating the plurality of non-dimensional pressure ratios also as a function of the predicted impact pressure q_{c predicted} further comprises generating the plurality of non-dimensional pressure ratios as a function of a predicted system total pressure Pt_predicted, where the predicted impact pressure q_{c predicted} is equal to the predicted system total pressure Pt_predicted minus the predicted system static pressure Ps_predicted.

4. The method of claim 3, wherein generating the plurality of non-dimensional pressure ratios further comprises generating each non-dimensional pressure ratio for a particular local static pressure P_i using a relationship that can be represented by the expression:

(pi-PS_predicted)/(Pt_predicted-Ps_predicted).

5. The method of claim 1, and before generating the plurality of non-dimensional pressure ratios, further comprising:

generating a first plurality of non-dimensional local static pressure values, with each of the first plurality of non-dimensional local static pressure values being generated as a function of one of the plurality of local static pressures P_i and a mean p_i of the plurality of local static pressures p_i; and

producing the predicted system static pressure Ps_predicted as a function of the first plurality of non-dimensional local static pressure values.

6. The method of claim 5, wherein generating the first plurality of non-dimensional local static pressure values further comprises generating each of the first plurality of non-dimensional local static pressure values using a relationship that can be represented by the expression

$\frac{p_i}{{\stackrel{\_}{p}}_i}.$

7. The method of claim 6, wherein producing the predicted system static pressure Ps_predicted as a function of the first plurality of non-dimensional local static pressure values comprises:

producing a non-dimensional predicted static pressure value that can be represented by the expression;

$\frac{{\mathrm{Ps}}_{\mathrm{predicted}}}{{\stackrel{\_}{p}}_i};<br><br>$

 

and

re-dimensionalizing the non-dimensional predicted static pressure value, by multiplying

$\frac{{\mathrm{Ps}}_{\mathrm{predicted}}}{{\stackrel{\_}{p}}_i}$

 

by the mean p_i of the plurality of local static pressures P_i, to produce the predicted system static pressure Ps_predicted.

8. The method of claim 5, and before generating the plurality of non-dimensional pressure ratios, further comprising:

generating a second plurality of non-dimensional local static pressure values, with each of the second plurality of non-dimensional local static pressure values being generated as a function of one of the plurality of local static pressures p_i, and the predicted system static pressure Ps_predicted; and

producing the predicted impact pressure q_{c predicted} as a function of the second plurality of non-dimensional local static pressure values.

9. The method of claim 8, wherein generating the second plurality of non-dimensional local static pressure values further comprises generating each of the second plurality of non-dimensional local static pressure values using a relationship that can be represented by the expression,

$\frac{p_i}{{\mathrm{Ps}}_{\mathrm{predicted}}},$

 

and wherein producing the predicted impact pressure q_{c predicted} further comprises producing a non-dimensional impact pressure value as a function of the second plurality of non-dimensional local static pressure values.

10. The method of claim 9, and further comprising re-dimensionalizing the non-dimensional impact pressure value by multiplying it by the predicted system static pressure Ps_predicted to produce the predicted impact pressure q_{c predicted}.

11. The method of claim 1, wherein measuring the plurality of local static pressures further comprises measuring the plurality of local static pressures using static pressure sensing ports of a flush air data system.

12. A flush air data system having an air data computer configured to implement the method of claim 1.

13. An air data system comprising:

a plurality of static pressure sensing ports each measuring one of a plurality of local static pressures p_i;

an air data computer configured to implement air data parameter calculating steps comprising;

generating a plurality of non-dimensional pressure ratios, with each non-dimensional pressure ratio being generated as a function of one of the plurality of local static pressures p_i, a predicted system static pressure Ps_predicted, and a predicted impact pressure q_{c predicted};

calculating a system level air data parameter as a function of the generated plurality of non-dimensional pressure ratios; and

providing the system level air data parameter as an output.

14. The air data system of claim 13, wherein generating the plurality of non-dimensional pressure ratios also as a function of the predicted impact pressure q_{c predicted} further comprises generating the plurality of non-dimensional pressure ratios as a function of a predicted system total pressure Pt_predicted, where the predicted impact pressure q_{c predicted} is equal to the predicted system total pressure Pt _predicted minus the predicted system static pressure Ps _predicted.

15. The air data system of claim 14, wherein generating the plurality of non-dimensional pressure ratios further comprises generating each non-dimensional pressure ratio for a particular local static pressure P_i using a relationship that can be represented by the expression:

(P_i-Ps_predicted)/(Pt_predicted-Ps_predicted).

16. The air data system of claim 15, wherein the air data computer is further configured to implement additional air data parameter calculating steps, before generating the plurality of non-dimensional pressure ratios, comprising:

generating a first plurality of non-dimensional local static pressure values, with each of the first plurality of non-dimensional local static pressure values being generated as a function of one of the plurality of local static pressures P_i and a mean p_i of the plurality of local static pressures P_i using a relationship that can be represented by the expression

$\frac{p_i}{\stackrel{\_}{p_i}};<br><br>$

 

and

producing the predicted system static pressure Ps_predicted as a function of the first plurality of non-dimensional local static pressure values.

17. The air data system of claim 16, wherein producing the predicted system static pressure Ps_predicted as a function of the first plurality of non-dimensional local static pressure values further comprises:

producing a non-dimensional predicted static pressure value that can be represented by the expression

$\frac{{\mathrm{Ps}}_{\mathrm{predicted}}}{{\stackrel{\_}{p}}_i};<br><br>$

 

and

re-dimensionalizing the non-dimensional predicted static pressure value, by multiplying

$\frac{{\mathrm{Ps}}_{\mathrm{predicted}}}{{\stackrel{\_}{p}}_i}$

 

by the mean p_i of the plurality of local static pressures P_i, to produce the predicted system static pressure Ps_predicted.

18. The air data system of claim 16, wherein the air data computer is further configured to implement additional air data parameter calculating steps, before generating the plurality of non-dimensional pressure ratios, comprising:

generating a second plurality of non-dimensional local static pressure values, with each of the second plurality of non-dimensional local static pressure values being generated as a function of one of the plurality of local static pressures p_i and the predicted system static pressure Ps_predicted; and

producing the predicted impact pressure q_{c predicted} as a function of the second plurality of non-dimensional local static pressure values.

19. The air data system of claim 18, wherein generating the second plurality of non-dimensional local static pressure values further comprises generating each of the second plurality of non-dimensional local static pressure values using a relationship that can be represented by the expression,

$\frac{p_i}{{\mathrm{Ps}}_{\mathrm{predicted}}},$

and wherein producing the predicted impact pressure q_{c predicted} further comprises producing a non-dimensional impact pressure value as a function of the second plurality of non-dimensional local static pressure values.

20. The air data system of claim 19, wherein the air data computer is further configured to implement the additional air data parameter calculating step comprising re-dimensionalizing the non-dimensional impact pressure value by multiplying it by the predicted system static pressure Ps_predicted to produce the predicted impact pressure q_{c predicted}.