Optics: measuring and testing – Velocity or velocity/height measuring – With light detector
Reexamination Certificate
2001-12-06
2003-05-06
Buczinski, Stephen C. (Department: 3662)
Optics: measuring and testing
Velocity or velocity/height measuring
With light detector
C356S005010, C356S005100, C356S141100
Reexamination Certificate
active
06559933
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATIONS
Not Applicable.
Federally Sponsored Research or Development
Not Applicable.
BACKGROUND OF THE INVENTION
1. Technical Field
This invention relates to the field of surveillance and more specifically to the detection of helicopters that potentially represent a threat.
2. Background Art
In the field of electronic surveillance, particularly on the modern battle field, helicopters such as the American Apache helicopter, the European Tiger helicopter as well as undoubtedly Russian and other countries' helicopters use mast-mounted sights and terrain masking as a way of acquiring a target while remaining undetected. A typical flight scenario would be for a reconnaissance helicopter to fly very low to the ground while approaching a potential target. The helicopter would then expose a minimal portion of itself, such as a mast-mounted sight, which is analogous to observing a surface ship from a submarine. In the case of the helicopter, terrain between the helicopter and the intended target ‘masks’ the helicopter's approach.
In the unrelated field of aerodynamics, the operation of a helicopter is fairly well understood. It is an immutable principle of physics that helicopters—indeed any ‘heavier-than-air-craft’—can only fly because the airfoils, at any given instant, accelerate a mass of air downward that is at least equal to the mass of the aircraft.
On airplanes, the airfoils (called ‘wings’) are bolted firmly to the fuselage at a fixed angle and the entire craft is accelerated along the runway until sufficient ‘relative airflow’ is generated over the wings that they can deflect a sufficient mass of air to take off. “Lift” is the equal and opposite reaction to that downward deflection of the air.
Helicopter airfoils (called ‘main rotors’) are rotated about a hub with a feathering hinge at the root, which allows the ‘angle of attack’ to be increased or decreased, both ‘cyclically’ and ‘collectively’. Because these rotating wings are capable of generating ‘relative airflow’ solely due to the speed of rotation, it is not necessary for helicopters to have forward speed in order to fly.
But whether we talk about ‘rotary-wing’ or ‘fixed-wing’ aircraft, the greater the forward speed with which the aircraft flies through the air, the greater the volume of air per unit of time that the lifting airfoils will act upon. The greater the mass of air deflected, the less vertical acceleration must be imparted to that air mass in order to provide the ‘lift’ necessary to fly. For example, a crop-spraying airplane flying over a field at only one or two meters above the vegetation will barely rustle the leaves.
On the other hand, slow flying aircraft interact with a smaller volume of air per unit of time and therefore it is necessary to accelerate that air to a greater downward velocity in order to sustain lift. This is the case with a hovering helicopter—particularly a helicopter hovering well clear of the ground—where there is invariably a column of descending air beneath the craft. Hovering a helicopter ‘out-of-ground-effect’ requires more power than is required for forward flight or hover ‘in-ground-effect’ and is akin to trying to swim up a waterfall.
Referring to
FIG. 1
, the vertical velocity of the column of air, also known as the ‘rotor intake’ region
15
, above a hovering or slow moving helicopter
10
depends upon several factors including surface wind, main rotor radius, and ‘disc loading’ (that is—the weight of the helicopter divided by the ‘swept’ area of the rotor disc). The mass of air entering the rotor intake region is necessarily equal to the mass of air exiting the rotor ‘down wash’ region
16
from the helicopter
10
, where helicopter rotor down wash is a fairly well understood phenomenon. Larger helicopters not only have greater mass, but they generally have a higher ‘disc loading’ when compared to smaller helicopters. This is because other design influences limit the practical main rotor radius on large helicopters.
We have discovered a means of protecting a potential target by detecting helicopters that are using terrain masking to approach the target. Our invention uses the aerodynamic principles of helicopter flight to detect these helicopters before they have observed the target. Advantageously, our invention reveals the position of the helicopter to the potential target before the helicopter is aware that it has been detected. This invention addresses a long-felt need by ground troops for protection from approaching low flying helicopters.
SUMMARY OF THE INVENTION
A robot sentry with a scanning laser observes the sky just above the geographic skyline looking for a vertical airflow pattern characteristic of the rotor inflow to a helicopter rotor. The presence of this vertical airflow pattern indicates the probable presence of a reconnaissance helicopter that is using terrain masking. The robot sentry can be set up to survey the surrounding terrain, using for example a video camera to detect the contrast difference between a darker terrain and lighter sky. The robot sentry can automatically establish an ‘observation line’ by laser ranging to the geographic skyline or an operator can set the observation line based on local terrain features should as can be determined from a topographic map.
The helicopter is detected by drawing an imaginary line in space, aiming very short duration and small diameter laser pulses at various points along that line, detecting return signals from individual aerosol particles on that line, and correlating an area of vertically descending particles with the area of a helicopter rotor. Once the helicopter is detected, personnel in the area are alerted to the potential threat.
REFERENCES:
patent: 4652122 (1987-03-01), Zincone et al.
patent: 4729737 (1988-03-01), Reagan et al.
patent: RE33152 (1990-01-01), Atlas
patent: 5049756 (1991-09-01), Colstoun et al.
patent: 5208600 (1993-05-01), Rubin
patent: 5424823 (1995-06-01), Nettles et al.
patent: 6070461 (2000-06-01), Gjessing et al.
patent: 2001263994 (2001-09-01), None
patent: 2001264440 (2001-09-01), None
Kirkpatrick Philip L.
Krulis Richard P.
Buczinski Stephen C.
Honeywell International , Inc.
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