Title of Invention	"A DEVICE FOR THE DIRECT MEASUREMENT OF AERODYNAMIC LOADS OF STRUCTURES"
Abstract	A device for direct measurement of aerodynamic loads of structures which comprises an elastic metal plate (EMP) having an integral load end (A), and mount end (B), characterized in that the said metal plate being provided with strain gauges located at four corners of top surface of the said EMP (NF1 to NF4) and bottom surface of the said EMP (PM1 TO PM4), the mid region of the said EMP being also provided with strain gauges (RMl, RM3) on top surface and strain gauges (RM2, RM4) on bottom surface, the said st-jin gauges being connected in Wheatstone bridege configuration essentially consisting of there bridges such as NF1 to NF4, PM1 TO PM4, and RMl to RM4.

Title of Invention

"A DEVICE FOR THE DIRECT MEASUREMENT OF AERODYNAMIC LOADS OF STRUCTURES"

Abstract

A device for direct measurement of aerodynamic loads of structures which comprises an elastic metal plate (EMP) having an integral load end (A), and mount end (B), characterized in that the said metal plate being provided with strain gauges located at four corners of top surface of the said EMP (NF1 to NF4) and bottom surface of the said EMP (PM1 TO PM4), the mid region of the said EMP being also provided with strain gauges (RMl, RM3) on top surface and strain gauges (RM2, RM4) on bottom surface, the said st-jin gauges being connected in Wheatstone bridege configuration essentially consisting of there bridges such as NF1 to NF4, PM1 TO PM4, and RMl to RM4.

Full Text	The present invention relates to a device for the direct measurement of aerodynamic loads of structures. The main usage of the device is for measuring aerodynamic forces and moments on the structure of various geometry such as control surfaces, wings, scaled models of aircraft, axi-symmetric bodies, external stores, automobile configurations and civil structures accurately without causing any obstruction to the flow of medium. The present invention is a device for the direct measurement of aerodynamic loads of structures, wherein the device can be used for all ranges of speed- Subsonic, Transonic, Supersonic and Hypersonic speed with sufficient accuracy within the specified limits. Prior art literature and patent search reveals that no device is available for direct measurements of aerodynamic loads of structures. Earlier designs of device gives indirect measurements of aerodynamic loads, in addition there are certain drawbacks such as support system interference, long length of the sensing element and space constraints in the models. Further, earlier designs of both external /internal mounted balances, due to their inherent geometry had a tendency to increase the errors in measurement. One example of external mounted strain gauge balance is given in " On the use of Special Balances for force measurements on control surfaces of a missile model" -Proceedings of the one day discussion meeting on Flight Vehicle Aerodynamics, August 14, 1997, Department of Aerospace Engineering, I.I.Sc, Bangalore. Designed balance is of fixed-fixed beam type and centre line is located midway between forward, Nl and aft N2 gauge stations. Four arm active strain gauge bridges are formed for the element Nl and N2 and separate strain gauge torque element for the measurements of the rolling moment RM. From bridge outputs Nl, N2 and RM, Normal force is derived by sum of the Nl and N2, Pitching moment is derived by difference of Nl and N2 and RM directly obtained from the output of the RM bridge. The drawbacks of balance are: it needs in-situ calibration, it has long length of sensing element and occupy more space volume of the model. Other example of internal mounted strain gauge balance is given in "Special Wind Tunnel Balances "Aerodynamic Testing and Structural Dynamics Conference, 21-22 October, 1994, I.I.Sc. Bangalore. The design principle adapted is: loads are acting at the reference centre of the balance, Fig 3 of sheet 1 of 3 of the drawings shows the wiring diagram. Accordingly, the present invention provides a device for direct measurement of aerodynamic loads of structures which comprises an elastic metal plate (EMP) having an integral load end (A), and mount end (B), characterized in that the said metal plate being provided with strain gauges located at four corners of top surface of the said EMP (NF1 to NF4) and bottom surface of the said EMP (PM1 TO PM4), the mid region of the said EMP being also provided with strain gauges (RM1, RM3) on top surface and strain gauges (RM2, RM4) on bottom surface, the said strain gauges being connected in Wheatstone bridege configuration essentially consisting of there bridges such as NF1 to NF4, PM1 TO PM4, and RM1 to RM4. In an embodiment of present invention one or more strain gauges may be used at each location. In another embodiment of present invention, mount end (non-metric) and load (metric) end geometry is selected to suit the testing models. The device of the present invention provides a device for the direct measurement of aerodynamic loads of structure's which comprises a main element with network of electronic circuitry (strain gfauge bridges) and load (metric) and mount (non-metric) ends, which is sensitive for all three loads as well as rigid enough to minimize the deflations compared to other configurations, the main element being rectangular in cross-section, which can be machined accurately with any conventional machining process for the required dimensional accuracy and desired surface finish. The device of the present invention, the device my be adapted for measurement of loads on plurality of surfaces. The device for the direct measurements of aerodynamic load of structures is an Electro-mechanical device for measuring aerodynamic loads on thin sections, configurations such as wing, fin, control surface and other aerodynamic bodies. This device is very compact which is capable of measuring loads directly. Due to its unique constructional features, it minimizes non-linearity and thermal gradient effects in outputs. Dimensional accuracy of main element and its flat surfaces, locai8ton of the strain gauges and Wheatstone networks minimizes the linear interactions, where minimum deflection avoids the non-linear interactions. The novelty of the device of the present invention is that it is capable of providing direct aerodynamic load measurement on structures. The inventive step lies in gauge location selections and formation of Wheatstone Bridge networks and each bridge is formed in such a way it is most sensitive to the particular load and shows insensitivity to the other loads. A single small size element also reduces the thermal gradient effects. General practice is to measure the force and moment as referred in prior art. In the device of present invention, moments are directly measured. In the device of present invention, all the gauges of the normal force bridge are lying on the same surface and bridge is very sensitive to normal force and linear interaction is avoided. In this way error due to deflection is minimized giving the another feature of novelty. Where as, in other type of balance design normal force is measured at two separate stations and added to get the total load. In the device of present invention, all the gauges of the pitching moment is lying on the same surface and bridge is very sensitive to pitching moment and linear interactions are avoided. Where as, in other type of balances, normal force and pitching moment is derived from Nl and N2. The slopes at Nl and N2 are different, which change the orientation of load. In the device of present invention, slope is not coming into picture. Therefore, error due to balance deflection and gauge positioning is minimized, which adds once again to another feature of novelty. The following examples of calibration are given by way of illustrations and therefore should not be construed to limit the scope of the present invention. The balance is calibrated to measure accurately the normal force, pitching and rolling moments. The sign convention of loads and moment is shown in fig 4 and 5 in sheet 2 of 3. Fig. 5 shows the normal force direction. Fig. 4 shows the pitching moment and rolling moment acting on the balance. The said device is calibrated for the normal force, pitching moment and rolling moment by applying standard calibrated weights under gravity vector and as an example of an output in graphical form is shown in Fig 6, 7 and 8 in Sheet 3 of 3. The following examples of loads in kgs applied to the balance during a trial calibration and corresponding outputs in mV per volt of excitation in main element as well as secondary elements. The sign convention for the Normal force is shown in sheet 2 of 3 in Fig. 5. Example 1 Loading: Normal Force, + ve (Table Removed) The sign convention for the Pitching moment is shown in sheet 2 of 3 in Fig. 4 Example 2 Loading: Pitching Moment, + ve (Table Removed) The sign convention for the Rolling moment is shown in sheet 2 of 3 in Fig. 4 Example 3 Loading: Rolling Moment, + ve (Table Removed) All the above examples and illustrations indicate that the calibration data obtained by using a device for direct measurement of aerodynamic loads of structures has a good linearity in the main component as well as secondary component interactions. Main advantages of present invention are: (1) It is a compact device compared to earlier models. Hence the error in measurements is reduced due to minimum deflection of the element. (2) In this device, the device configuration is such that the entire strain gauge network is located at one place thereby avoiding thermal gradient effect. (3) In this device, respective bridges directly measure loads. (4) Eliminates drawbacks as support system interference. (5) Minimizes space needed to accommodate the device. (6) Reduces the tendency to increase the errors in measurement. (7) Obviates long length of sensing element. We Claim: 1. A device for direct measurement of aerodynamic loads of structures which comprises an elastic metal plate (EMP) having an integral load end (A), and mount end (B), characterized in that the said metal plate being provided with strain gauges located at four corners of top surface of the said EMP (NF1 to NF4) and bottom surface of the said EMP (PM1 TO PM4), the mid region of the said EMP being also provided with strain gauges (RM1, RM3) on top surface and strain gauges (RM2, RM4) on bottom surface, the said strain gauges being connected in Wheatstone bridege configuration essentially consisting of there bridges such as NF1 to NF4, PM1 TO PM4, and RM1 to RM4. 2. A device as claimed in claim 1, wherein in one or more strain gauges are used at each location. 3. A device for the direct measurement of aerodynamic loads of structures substantially as herein described with reference to the examples and drawings accompanying this specification.

Full Text

The present invention relates to a device for the direct measurement of aerodynamic loads of structures.
The main usage of the device is for measuring aerodynamic forces and moments on the structure of various geometry such as control surfaces, wings, scaled models of aircraft, axi-symmetric bodies, external stores, automobile configurations and civil structures accurately without causing any obstruction to the flow of medium.
The present invention is a device for the direct measurement of aerodynamic loads of structures, wherein the device can be used for all ranges of speed- Subsonic, Transonic, Supersonic and Hypersonic speed with sufficient accuracy within the specified limits.
Prior art literature and patent search reveals that no device is available for direct measurements of aerodynamic loads of structures. Earlier designs of device gives indirect measurements of aerodynamic loads, in addition there are certain drawbacks such as support system interference, long length of the sensing element and space constraints in the models. Further, earlier designs of both external /internal mounted balances, due to their inherent geometry had a tendency to increase the errors in measurement. One example of external mounted strain gauge balance is given in " On the use of Special Balances for force measurements on control surfaces of a missile model" -Proceedings of the one day discussion meeting on Flight Vehicle Aerodynamics, August 14, 1997, Department of Aerospace Engineering, I.I.Sc, Bangalore. Designed balance is of fixed-fixed beam type and centre line is located midway between forward, Nl and aft N2 gauge stations. Four arm active strain gauge bridges are formed for the element Nl and N2 and separate strain gauge torque element for the measurements of the rolling moment RM. From bridge outputs Nl, N2 and RM, Normal force is derived by sum of the Nl and N2, Pitching moment is derived by difference of Nl and N2 and RM directly obtained from the output of the RM bridge. The drawbacks of balance are: it needs in-situ calibration, it has long length of sensing element and occupy more space volume of the model.
Other example of internal mounted strain gauge balance is given in "Special Wind Tunnel Balances "Aerodynamic Testing and Structural Dynamics Conference, 21-22 October, 1994, I.I.Sc. Bangalore. The design principle adapted is: loads are acting at the reference centre of the balance,
Fig 3 of sheet 1 of 3 of the drawings shows the wiring diagram.
Accordingly, the present invention provides a device for direct measurement of aerodynamic loads of structures which comprises an elastic metal plate (EMP) having an integral load end (A), and mount end (B), characterized in that the said metal plate being provided with strain gauges located at four corners of top surface of the said EMP (NF1 to NF4) and bottom surface of the said EMP (PM1 TO PM4), the mid region of the said EMP being also provided with strain gauges (RM1, RM3) on top surface and strain gauges (RM2, RM4) on bottom surface, the said strain gauges being connected in Wheatstone bridege configuration essentially consisting of there bridges such as NF1 to NF4, PM1 TO PM4, and RM1 to RM4.
In an embodiment of present invention one or more strain gauges may be used at each location.
In another embodiment of present invention, mount end (non-metric) and load (metric) end geometry is selected to suit the testing models.
The device of the present invention provides a device for the direct measurement of aerodynamic loads of structure's which comprises a main element with network of electronic circuitry (strain gfauge bridges) and load (metric) and mount (non-metric) ends, which is sensitive for all three loads as well as rigid enough to minimize the deflations compared to other configurations, the main element being rectangular in cross-section, which can be machined accurately with any conventional machining process for the required dimensional accuracy and desired surface finish.
The device of the present invention, the device my be adapted for measurement of loads on plurality of surfaces.
The device for the direct measurements of aerodynamic load of structures is an Electro-mechanical device for measuring aerodynamic loads on thin sections, configurations such as wing, fin, control surface and other aerodynamic bodies. This device is very compact which is capable of measuring loads directly. Due to its unique constructional features, it minimizes non-linearity and thermal gradient effects in outputs. Dimensional accuracy of main element and its flat surfaces, locai8ton of the strain gauges and Wheatstone networks minimizes the linear interactions, where minimum deflection avoids the non-linear interactions.
The novelty of the device of the present invention is that it is capable of providing direct aerodynamic load measurement on structures.
The inventive step lies in gauge location selections and formation of Wheatstone Bridge networks and each bridge is formed in such a way it is most sensitive to the particular load and shows insensitivity to the other loads. A single small size element also reduces the thermal gradient effects.
General practice is to measure the force and moment as referred in prior art. In the device of present invention, moments are directly measured.
In the device of present invention, all the gauges of the normal force bridge are lying on the same surface and bridge is very sensitive to normal force and linear interaction is avoided. In this way error due to deflection is minimized giving the another feature of novelty. Where as, in other type of balance design normal force is measured at two separate stations and added to get the total load.
In the device of present invention, all the gauges of the pitching moment is lying on the same surface and bridge is very sensitive to pitching moment and linear interactions are avoided. Where as, in other type of balances, normal force and pitching moment is derived from Nl and N2. The slopes at Nl and N2 are different, which change the orientation of load. In the device of present invention, slope is not coming into picture. Therefore, error due to balance deflection and gauge positioning is minimized, which adds once again to another feature of novelty.
The following examples of calibration are given by way of illustrations and therefore should not be construed to limit the scope of the present invention. The balance is calibrated to measure accurately the normal force, pitching and rolling moments. The sign convention of loads and moment is shown in fig 4 and 5 in sheet 2 of 3. Fig. 5 shows the normal force direction. Fig. 4 shows the pitching moment and rolling moment acting on the balance. The said device is calibrated for the normal force, pitching moment and rolling moment by applying standard calibrated weights under gravity vector and as an example of an output in graphical form is shown in Fig 6, 7 and 8 in Sheet 3 of 3.
The following examples of loads in kgs applied to the balance during a trial calibration and corresponding outputs in mV per volt of excitation in main element as well as secondary elements.
The sign convention for the Normal force is shown in sheet 2 of 3 in Fig. 5.
Example 1 Loading: Normal Force, + ve

(Table Removed)
The sign convention for the Pitching moment is shown in sheet 2 of 3 in Fig. 4
Example 2 Loading: Pitching Moment, + ve

(Table Removed)
The sign convention for the Rolling moment is shown in sheet 2 of 3 in Fig. 4
Example 3 Loading: Rolling Moment, + ve

(Table Removed)
All the above examples and illustrations indicate that the calibration data obtained by using a device for direct measurement of aerodynamic loads of structures has a good linearity in the main component as well as secondary component interactions.
Main advantages of present invention are:
(1) It is a compact device compared to earlier models. Hence the error in
measurements is reduced due to minimum deflection of the element.
(2) In this device, the device configuration is such that the entire strain
gauge network is located at one place thereby avoiding thermal
gradient effect.
(3) In this device, respective bridges directly measure loads.
(4) Eliminates drawbacks as support system interference.
(5) Minimizes space needed to accommodate the device.
(6) Reduces the tendency to increase the errors in measurement.
(7) Obviates long length of sensing element.

We Claim:
1. A device for direct measurement of aerodynamic loads of structures which
comprises an elastic metal plate (EMP) having an integral load end (A), and mount
end (B), characterized in that the said metal plate being provided with strain
gauges located at four corners of top surface of the said EMP (NF1 to NF4) and
bottom surface of the said EMP (PM1 TO PM4), the mid region of the said EMP
being also provided with strain gauges (RM1, RM3) on top surface and strain
gauges (RM2, RM4) on bottom surface, the said strain gauges being connected in
Wheatstone bridege configuration essentially consisting of there bridges such as
NF1 to NF4, PM1 TO PM4, and RM1 to RM4.
2. A device as claimed in claim 1, wherein in one or more strain gauges are used at
each location.
3. A device for the direct measurement of aerodynamic loads of structures
substantially as herein described with reference to the examples and drawings
accompanying this specification.

Documents:

276-del-2001-abstract.pdf

276-del-2001-claims.pdf

276-del-2001-correspondence-others.pdf

276-del-2001-correspondence-po.pdf

276-del-2001-description (complete).pdf

276-del-2001-drawings.pdf

276-del-2001-form-1.pdf

276-del-2001-form-19.pdf

276-del-2001-form-2.pdf

276-del-2001-form-3.pdf

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Patent Number

218310

Indian Patent Application Number

276/DEL/2001

PG Journal Number

24/2008

Publication Date

13-Jun-2008

Grant Date

31-Mar-2008

Date of Filing

12-Mar-2001

Name of Patentee

COUNCIL OF SCIENTIFIC AND INDUSTRIAL RESEARCH

Applicant Address

RAFI MARG, NEW DELHI - 110 001, INDIA

Inventors:

#	Inventor's Name	Inventor's Address
1	RAM SINGH VERMA	NATIONAL AEROSPACE LABORATORIES, POST BAG NO.-1779, BANGALORE - 560 017, INDIA
2	RAMA RAO RAMESH	NATIONAL AEROSPACE LABORATORIES, POST BAG NO.-1779, BANGALORE - 560 017, INDIA
3	NARENDRA BEHARI MATHUR	NATIONAL AEROSPACE LABORATORIES, POST BAG NO.-1779, BANGALORE - 560 017, INDIA

PCT International Classification Number

B64C 73/00

PCT International Application Number

N/A

PCT International Filing date

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1			NA