Measuring and testing – Volume or rate of flow – Using differential pressure
Reexamination Certificate
1999-09-24
2003-07-08
Patel, Harshad (Department: 2855)
Measuring and testing
Volume or rate of flow
Using differential pressure
C073S170020
Reexamination Certificate
active
06588285
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
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 or gas.
The measurement of flight parameters is one of the most important tasks of the aeromechanics and aerodynamics of flying vehicles (FVs). At the present time, in order to measure the flight (flow) parameters use is made of Pitot-static tubes (PSTs) which are, frequently, mounted directly on the fuselage of the aircraft or on the body of any other flying vehicle, and these PSTs actually measure parameters of the local flow, which is close to laminar. As a rule, several such PSTs are mounted on the flying vehicle and measure the local flow parameters. The true flight parameters are determined on the basis of preliminary calibrations.
2. Description of the Related Art
A Pitot-static tube mounted on the body or fuselage of an FV is known from WO 94/02858. The known PST has a cylindrical tube mounted on a strut having curved leading and trailing edges which approach one another as the tube is neared from the base of the strut. The leading edge of the strut can be rounded off. The pitot-static tube has an orifice in the nose part of the tube for sensing the total pressure, and an orifice for sensing the static pressure at a certain distance from the nose of the tube. The tube has a heater for preventing the formation of ice. However, this Pitot-static tube cannot be applied for determining the angle of attack, since it lacks orifices for sensing pressure with the aid of which the angle of attack can be measured. In fact, as follows from the abovementioned patent, this tube is not intended for these purposes. Moreover, the tapering of the strut, seen from the side, as the tube is approached leads, in conjunction with maintaining the internal volumes required for installing airways and heaters, to a marked increase in the relative thickness of the profiles of the transverse cross-sections of the strut. This leads, in turn, in the case of high subsonic speeds (Mach numbers of M=0.8-0.9) to the earlier appearance of local pressure shocks and a marked increase in the shock drag of such a Pitot-static tube.
A fuselage Pitot-static tube according to U.S. Pat. No. 4,615,213 is known for determining the flight (flow) parameters—angle of attack, total pressure Po and static pressure Ps and, consequently, also the Mach number M; it is an elongated axisymmetric body having a head part in the form of a hemisphere with groups of orifices on the axisymmetric body for measuring pressures by means of which the flight (flow) parameters are determined with the aid of calibrations. At the same time, the orifices for measuring the pressures by means of which the total pressure and angle of attack are determined are arranged on the hemispherical head part, while the orifices for measuring the static pressure are arranged on the lateral (cylindrical) surface of the axisymmetric body. For the purpose of mounting on the fuselage or body of the flying vehicle, this PST has a strut, the profile of which has a lens-shaped transverse cross-section. The given PST has the following disadvantages:
a complicated design;
increased overall dimensions of the axisymmetric body;
increased aerodynamic drag in subsonic flight regimes;
increased required power for the heater of the anti-icing system;
increased design weight;
increased sensitivity of the total pressure, measured with the aid of the central orifice on the spherical head part, to variation in angle of attack, which leads to additional errors in measurement of the total pressure; such a dependence of the total pressure on the angle of attack for a range of FVs is unacceptable.
The closest of the known technical solutions is disclosed in U.S. Pat. No. 4,378,696 for determining flight (flow) parameters—angle of attack, total pressure Po and static pressure Ps, and thus the Mach number M, which is an elongated axisymmetric body with a conical or ogival head part where an orifice is arranged for sensing total pressure, and which merges into a circular cylinder on whose surface orifices are arranged for sensing static pressure. Later, this cylindrical surface merges into a conical one, on which orifices are arranged for sensing pressure for which the angle of attack is set up correspondingly, and then merges again into the cylindrical surface. For the purpose of being mounted on the fuselage or the body of an FV, the tube has a strut whose cross-section has lens-shaped profile. The given PST has the following disadvantages:
complicated design;
increased overall dimensions;
increased aerodynamic drag in subsonic flight regimes;
increased required power for the heating anti-icing system;
increased design weight;
low sensitivity of pressures, measured in orifices arranged on a conical part (and intended for determining &agr;), to the angle of attack, which leads to increased errors in determining the angle of attack. This is caused by the following factors:
1. As in the case described above, the given PST has an increased mid-section of the axisymmetric body. Moreover, the increased dimension of the mid-section is caused in the given instance by two circumstances. The first is that the cylindrical part of the axisymmetric body merges into a conical one on which orifices are arranged for sensing the pressure by which the angle of attack is determined. In order to increase a little the sensitivity of the pressure sensed by means of these orifices of the angle of attack, the angle of taper must be sufficiently large to lead to the necessity of increasing significantly the diameter of the axisymmetric body behind the given conical part.
The second circumstance is bound up with the fact that although groups of orifices for measuring pressure, which are used to determine total pressure, static pressure and angle of attack, are dispersed in the given configuration, they are all situated on the same axisymmetric body. There is a need to arrange inside the latter airways emerging from all the indicated groups of orifices, a static pressure chamber and also tubular electric heaters for the anti-icing system. The diameters of the airways and the TEHs cannot be less than a certain minimum values which for the airways are determined by the magnitude of the hydrodynamic lag and for the TEHs by the limiting 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 complicated design of the axisymmetric body of the PST.
The circumstances indicated lead to an increase in the area of the mid-section, and consequently to an increase in the design weight, aerodynamic drag and power of the anti-icing system.
It should also be pointed out that transition from the cylindrical part to the conical one, and then again to the cylindrical one, can lead to separation of the flow behind the conical part and to an earlier appearance (in terms of the Mach number) of local pressure shocks. This, in turn, must lead to an increase in the aerodynamic drag. Moreover, the increased diameter of the axisymmetric body and the non-optimum form of its tail part in conjunction with the strut also lends [sic] an unfavourable aerodynamic interference (separation of the flow and earlier appearance of pressure shocks) in the area of the joint of the contracting tail part of the axisymmetric body of the PST behind the line of maximum thickness of the lens-shaped aerodynamic profile of the strut. This also leads to a certain increase in the aerodynamic drag of such a PST.
It may also be noted that the presence of a conical part on the axisymmetric body of a PST leads to the realization of additional support on the cylindrical part lying in front, where the orifices for measuring static pressure are arranged. As a result, the precise determination (without the introduction of corrections) of static pressure requires that the orifices for sensing it must be sufficiently far from this conical part. Thi
Efremov Andrei Aleksandrovich
Golovkin Mikhail Alekseevich
Golovkin Vladimir Alekseevich
Guskov Valentin Ivanovich
Kohler Heinz-Gerhard
Harter Secrest & Emery LLP
Nord-Micro Elektronik Feinmechanik AG
Patel Harshad
Salai Esq. Stephen B.
Shaw Esq. Brian B.
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