Measuring and testing – Navigation – Ship's log
Reexamination Certificate
1998-01-08
2001-01-23
Fuller, Benjamin R. (Department: 2855)
Measuring and testing
Navigation
Ship's log
Reexamination Certificate
active
06176130
ABSTRACT:
BACKGROUND OF THE INVENTION
(1) Field of the Invention
The present invention relates to a flight velocity vector measuring system in a wide velocity region using a truncated-shape probe, and more particularly to a flight velocity measuring system in a wide velocity region using a square truncated pyramid-shape probe capable of measuring a flight velocity vector by a calculation process on the basis of air data obtained by the square truncated pyramid-shape probe in a wide velocity region from a low velocity to a supersonic velocity.
(2) Description of the Related Art
A flight velocity vector measuring system for measuring a flight velocity vector using a square truncated pyramid-shape probe so far known has been proposed by the present inventors (see U.S. Pat. No. 5,423,209 specification). In the conventional flight velocity vector measuring system using a square truncated pyramid-shape probe, the probe is mainly directed at the low speed region which is not affected by compressibility and shock wave. The calculation of the flight velocity vector is done on the basis of dynamic pressure. The flight velocity vector is computed by substituting five pressure information (that is, a total pressure and four pressures on a truncated pyramid-shape surface) obtained from the square truncated pyramid-shape probe and pressure calibration coefficients obtained in advance into a polynomial approximation and using a Newton-Raphson method (a repetition computing method). Further, the pressure calibration coefficients are calculated on the basis of the dynamic pressure in the flight change and five pressure information every change of probe angle.
In general, for definition of velocity representative of the magnitude of velocity in a region from low velocity to supersonic velocity, Mach number is applied taking a concept of sonic velocity into consideration. Since the air current is changed into an incompressible flow, a compressible flow and a flow caused by a shock wave according to the velocity region, the Mach number is obtained by separate operational expressions corresponding to these flows. That is, in the low velocity flight, the velocity is simply obtained from the dynamic pressure obtained by a difference between total pressure and static pressure without taking the compressibility into consideration. Further, since the compressibility influences on the probe as the velocity comes close to the sonic velocity, the velocity should be obtained by an expression which takes the compressibility into consideration. Furthermore, in the case of the flight beyond the sonic velocity, the shock wave is generated in front of the probe so that the pressure information detected before and behind the shock wave. Therefore, the velocity is obtained by using an operational expressing which takes these into consideration. In the case of flight at a large attitude angle in velocity regions, it is important to take an influence of all pressure differentials caused by a movement of a stagnation point of the probe into consideration.
From the above-described fact, in the case of flight at a high attitude angle in a wide velocity region, in the flight velocity vector calculation process according to a set of pressure calibration coefficients, it is difficult to enhance the measuring accuracy. Further, when the probe calibration coefficient every velocity is used in order to secure the accuracy, the process time increases, making it difficult to put to practical use.
SUMMARY OF THE INVENTION
An object of the present invention is to provide, by further improving the conventional flight velocity vector calculation processing system using the truncated pyramid-shape probe, a flight velocity vector calculation processing system capable of obtaining a flight velocity vector with high accuracy and high velocity even in the case of flight at a large attitude angle in a wide velocity region from a low velocity to a supersonic velocity.
The flight velocity vector measuring system in a wide velocity region according to the present invention includes a primary calculation processing and a secondary calculation processing. In the primary calculation processing, five pressure information items detected by the square truncated pyramid-shape probe an extreme end of which has a truncated pyramid-shape and which has a total pressure hole at the apex, said probe being provided with pressure holes in each truncated pyramid-shape surface, are converted into electrical signals and incorporated into a calculation processor. An attack angle pressure coefficient C&agr; of an air current is obtained from pressure differential information of upper and lower pressure holes of the probe and a sideslip angle pressure coefficient C&bgr; is obtained from pressure differential information of left and right pressure holes, and an air current angle pressure coefficient C&ggr; is obtained from the obtained attack angle pressure coefficient C&agr; and sideslip angle pressure coefficient C&bgr;.
In the secondary calculation processing, the attack angle pressure coefficient C&agr;, the sideslip angle pressure coefficient C&bgr; and the air current angle pressure coefficient C&ggr;, pressure calibration coefficients with respect to the Mach number M, the attack angle &agr; and the sideslip angle &bgr; of the probe every velocity region obtained by dividing the wide velocity region pre-stored in the calculation processor into a plurality of regions, and the unknown-quantity Mach number M, the attack angle &agr; and the sideslip angle &bgr; constitute an operational expression comprising a polynomial approximation to determine the magnitude of Mach number. The velocity region is then determined by the obtained Mach number, the pressure calibration coefficients in the velocity region are called, and the flight vector (M, &agr;, &bgr;) is calculated by the polynomial approximation.
The calculation processes include a successive computation method which executes in accordance with the calculation process determined every updating, and a table conversion system, which computes Mach number from an air current angle pressure coefficient C&ggr; and a Mach pressure coefficient Cm obtained in advance, omitting an intermediate solution by way of a tertiary equation for calculating Mach number, to prepare a Mach number table TM whereby the Mach number is directly read. In the latter method, the air current angle pressure coefficient C&ggr; and the Mach pressure coefficient Cm are first simultaneously obtained from five pressure information, and the flight pressure coefficient to determine a divisional region k. After velocity region when updating is grasped from the value of the Mach determination of the velocity region, the Mach number is obtained on the basis of the air current angle pressure coefficient C&ggr; and the Mach pressure coefficient Cm from the Mach number table TM in the region.
REFERENCES:
patent: 5423209 (1995-06-01), Nakaya et al.
patent: 5756891 (1998-05-01), Nakaya et al.
patent: 5866813 (1999-02-01), Nakaya et al.
Hanzawa Asao
Kuwano Naoaki
Nakamura Seigou
Nakaya Teruomi
Armstrong, Westerman Hattori, McLeland & Naughton
Fuller Benjamin R.
National Aerospace Laboratory of Science & Technology Agency
Thompson Jewel V.
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