Measuring and testing – Fluid flow direction – Relative to aircraft or watercraft
Reexamination Certificate
2002-05-02
2004-11-09
Patel, Harshad (Department: 2855)
Measuring and testing
Fluid flow direction
Relative to aircraft or watercraft
Reexamination Certificate
active
06813942
ABSTRACT:
The invention relates to the determination of the flight parameters of flying vehicles or to other fields of science and technology which deal with flows of liquid and gas.
The measurement of flight parameters is one of the most important problems in the aeromechanics and aerodynamics of flying vehicles (FVs). At the present time, to measure flight parameters (flow parameters) use is made of Pitot-Static tubes (PSTs) which are frequently mounted directly on the fuselage of the aircraft or the body of some other flying vehicle, and which actually measure the parameters of local flow close to a planar flow. As a rule, some of these PSTs which measure local flow parameters are mounted on the flying vehicles. The actual flight parameters are determined on the basis of prior calibrations.
A Pitot-Static tube is known from WO 94/02858. The known PST is mounted on the body or fuselage of an FV and has a cylindrical tube which is mounted on a strut having curved leading and trailing edges which come together when approaching from the base of the strut to the tube. The leading edge of the strut can be rounded. The Pitot-Static tube has orifices in the nose part of the tube for sensing the total pressure and orifices for sensing the static pressure at a certain distance from the nose of the tube. The Pitot probe has a heater for preventing the formation of ice. However, this PST cannot be applied to determine the angle of attack, since it lacks orifices for sensing pressure with the aid of which the angle of attack can be measured. Strictly, as follows from WO 94/02858, this Pitot probe is not designed for these purposes. Moreover, the convergence of the strut in a side view when the tube is approached leads to a sharp rise in the relative thickness of the profiles of the cross sections of the strut, while maintaining the internal volumes required for constructing the pneumatic paths and heaters. At high subsonic speeds (Mach number M=0.8-0.9), this leads to an earlier occurrence of local shock waves and a sharp rise in the shock-wave drag of such a Pitot-Static tube.
Another device for determining total pressure P
0
, static pressure P
s
, and therefore also the Mach number M, as well as the angle of attack &agr; is known from RU 2 000 561. Said device consists of a body constructed in the form of a plate sharpened at the front whose upper surface is arranged orthogonal to the axis of rotation and is equipped with orifices for measuring static pressure. Arranged in the rear part of the plate on its upper surface is a half-wing with a straight leading edge, which is orthogonal to the upper surface of the plate and on the end of which a total pressure probe is arranged. Orifices for measuring the angle of attack are arranged on the straight leading edge of the half-wing. Orifices for measuring the static pressure, the total pressure probe and orifices for measuring the angle of attack with the aid of corresponding pneumatic paths are connected to pressure transducers. The device is also equipped with a transducer for the angular displacement of the body. The orifices for measuring static pressure can be arranged on a non-rotating disc constructed flush with the upper surface of the plate. In essence, this device combines within itself the functions of an aerodynamic-angle transducer and a Pitot-Static tube. The given device has a number of disadvantages. Firstly, there is the complexity of design, which is caused firstly by the fact that the device is a rotating one. Consequently, it must be equipped with bearings with a very low coefficient of friction, it being necessary for the device to be statically and dynamically balanced. Moreover, it must be equipped with a transducer for the angular displacement of the body. The second disadvantage which, in essence, follows on from the first is an increased design weight. It is also a disadvantage of the given device that because of its design features it is impossible for the total pressure to be transmitted to the fuselage of the flying vehicle, to different consumers, and such a need frequently exists, with the aid of non-rotating pneumatic paths. Transmitting pressure from a rotating part of a device onto a non-rotating one requires the application of special seals and leads to complication of the design and a rise in its weight, to an increase in the friction-force moment and, consequently, to a rise in the minimum magnitude of the rate at which such a device starts to operate.
U.S. Pat. No. 4,378,696 teaches a fuselage PST for determining flight (flow) parameters—the angle of attack &agr;total pressure P
0
and static pressure P
s
and, consequently, Mach number M, which is an elongated axially symmetric body with a conical or ogival head part, where orifices for sensing total pressure are arranged, which merges into a circular cylinder on the surface of which orifices for sensing static pressure are arranged. Furthermore, this cylindrical surface merges into a conical one on which there are arranged orifices for sensing pressure in accordance with which the angle of attack is set, and thereafter into a cylindrical one again. For the purpose of being fastened to the fuselage or to the body of the FV, the Pitot probe has a strut whose cross section has a lenticular profile with a sharp leading edge
The disadvantages of the given PST are:
increased overall dimensions of the axially symmetric body;
complexity of design
increased aerodynamic drag;
increased required power of the heating anti-icing system;
low sensitivity of pressures measured in orifices arranged on the conical part (and intended for determining &agr;, in terms of the angle of attack, and this leads to larger errors in the determination of the angle of attack; and
increased design weight.
This is caused by the following factors:
1. The given PST has an enlarged mid-section of the axially symmetric body. The enlarged dimension of the mid-section is caused in this case by two circumstances.
Firstly, the cylindrical part of the axially symmetric body merges into a conical one on which there are arranged orifices for sensing pressure by means of which the angle of attack is determined. In order to somewhat enhance the sensitivity of the pressure sensed by means of these orifices in accordance with the angle of attack, the cone angle must be sufficiently large, and this leads to the necessity of significantly increasing the diameter of the axially symmetric body downstream of the given conical part. The second circumstance is associated with the fact that although the groups of orifices for measuring pressure, by means of which total pressure, static pressure and the angle of attack are determined, are dispersed in the given configuration, they are all still located on the same axially symmetric body. It is necessary to arrange inside it pneumatic paths, which go out from all the indicated groups of orifices, and also tubular electric heaters (TEHs) of the anti-icing system. The diameters of the pneumatic paths and of the TEHs cannot be less than certain minimum values which are determined for the pneumatic paths by the magnitude of the hydrodynamic lag, and for the TEHS by the maximum values of the heat flux density and the temperature of the surface of the heaters. The result is a high design saturation, that is to say a high design complexity of the axially symmetric body of the PST.
The circumstances indicated lead to an enlargement of the area of the mid-section, and thus to a rise in the design weight, the aerodynamic drag and the power of the anti-icing system. It is also necessary to note that the transition from a cylindrical part to a conical one, and thereafter to a cylindrical one again can lead to flow separation downstream of the conical part and to an earlier appearance (in terms of the Mach number) of local shock waves. In its turn, this must lead to a rise in aerodynamic drag. Moreover, an enlarged diameter of the axially symmetric body and the non-optimum shape of its aerial part in conjunction with the strut also produces unfavourable aerodynamic interf
Efenov Andrei Aleksandrovich
Golovkin Mikhail Alekseevich
Golovkin Vladimir Alekseevich
Kohler Heinz-Gerhard
Pankratov Anatoli Kuzmich
Harter Secrest & Emery LLP
Patel Harshad
Professor N.E. Zhukovsky Central Aerohydrodynamic Institute
Salai Esq. Stephen B.
Shaw Esq. Brian B.
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