SPECIFICATION OF THE INVENTION

1. Title of the invention

Improved method for High Altitude Release of unguided Air-to-Surface weapon from fighter aircraft

2. Field of Invention

This invention relates to a method for improving the accuracy of weapon delivery from fighter aircraft in particular for unguided Air to Surface weapon released from high altitude. The invention uses a wind model to account for the effect of winds at different altitude bands of the weapon trajectory and a mechanism to display the cues on Head Up Display (HUD) to perform weapon aiming.

3. Prior art and Draw backs of prior art

The weapon aiming systems facilitates a pilot to accurately release ballistic weapons at the target by computing the weapon trajectory (time of flight, horizontal range, impact point, impact angle and impact velocity, etc) using position and velocity of the aircraft and the weapon physical characteristics. The weapon aiming systems drives the Head Up Display for displaying the computed parameters in the form of cues of impact point for performing weapon release.

The conventional unguided air-to-ground weapon aiming system computes the ballistic trajectory based on instantaneous wind velocity at the time of weapon release. But in the real scenario, if the weapon is released from the high altitude (approximately >2km), the effect of the wind is more predominant and the weapon trajectory changes as the weapon travels through different altitude bands having different wind profile. Hence, the solution provided by conventional method is not accurate for the weapon released from high altitude. Also, for a typical higher altitude release condition, the weapon impact point coordinates remains outside the field of view of the Head Up Display, hence it is displayed at limited position to HUD display boundary. Hence, the conventional method of display provides only limited information to pilot to perform the high altitude weapon release.

4. Aim of the Invention

The main objective of this invention is to provide improved weapon aiming solutions, by inventing a wind model to cater for the effect of wind variation at different altitudes of weapon trajectory for high altitude release of weapon.

Further objective of the invention is to provide a method for dynamic wind recording and storage of the winds for entire weapon trajectory.

Yet further aspect of the invention is to provide a method to improve the accuracy of weapon ballistic computation by taking into account the drift acceptance rate of the weapon in different airmass (winds) encountered by the weapon during its trajectory.
Still further objective of the invention is to provide improved mechanism to display weapon aiming cues on Head Up Display when the impact point coordinates are outside the HUD display area.

5. Summary of the present invention

This invention presents an improved method for the computation of impact point for accurate release of air-to-surface ballistic weapon at higher altitude. A wind model is invented to cater for drift of the weapon taking into account the prevailing winds through the weapon trajectory and the drift acceptance rate of the weapon. The wind velocity is processed by obtaining the required data from Air Data module 110 and Inertia I Navigation module 730. The database of the processed winds for the different bands of altitude is created and stored in linear format in Wind Processing and Storage module 120.

The ballistic trajectory of the weapon is generated by High Altitude Release (HAR) Ballistic Trajectory module 150. The winds are extracted from the database using the Wind Extractor module 140. The across distance travelled by the weapon is obtained by using the weightage of drift from the Drift Acceptance Rate (DAR) module?60 due to the winds. The along and vertical distance travelled by the weapon is obtained by the effect of change in drag by wind.

For displaying the impact point on HUD, the impact point in terms of HUD coordinate system is computed by Impact Point module 170 based on the distance travelled by the weapon. The Display Generation module 180 displays the weapon aiming cues (gapped Bomb Fall Line (BFL) and marker) on HUD to facilitate the pilot in carrying out the accurate weapon aiming from high altitude.

6. Brief Description of the Drawings

Figure 1 is a block diagram of the Weapon Aiming System for computing the weapon Impact Point for High Altitude Release and its display on HUD.

Figure 2 is a plot of drift acceptance rate against the time of fall of the weapon.

Figure 3a depicts the format of recording the winds at different altitudes.

Figure 3b depicts the weapon trajectory of the freefall bomb with extracted winds at different altitudes.

Figure 4a is a view of a Bomb Fall Line with limited impact point display on HUD.

Figure 4b is a view of a typical head-up-display Bomb Fall Line with gap representing the actual impact point to perform high altitude release.

Figure 5 is a representation of the weapon along, across and vertical distance travelled from aircraft.

Figure 6 is a flow chart of the steps illustrating an improved method of storing the winds.

Figure 7 is a flow chart of the steps illustrating the improved method of determining the impact point coordinates.

7. Detailed Description of the Invention

In the present invention, the impact point of the air to surface unguided weapon for high altitude release is generated from the wind model developed using the winds prevailing at different altitudes through-out its trajectory. This wind model caters for the drift acceptance rate of the weapon. The invention also displays the aiming cue when the impact point is out of field of view of the HUD. The invention, aids the pilot to carry out the high altitude release with improved accuracy, consists of air data module 110, inertial navigation module 130, wind processing and storage module 120, wind extractor module 140, High Altitude Release Ballistic Trajectory module 150, Drift Acceptance Rate module 760, Impact Point module 170 and Display Generation module 180.

The Figure 6 shows the flow diagram illustrating the operation of the weapon aiming system 100 for the recordation of the winds at different altitudes. In step 500, the Wind Processing and Storage Module 120 receives the HAR Recordation Status. The HAR recordation status is activated by the pilot when the high altitude release mission is initiated. In step 507, the recordation status is checked; if not set, the winds are not recorded in step 502 and if set, the winds are recorded as in step 503.

In step 503, the Wind Processing and Storage Module 120 creates the height bands from a minimum height (Hmin) of -1,000ft to a maximum height (Hmax) of 25,000ft with the altitude difference (AH) of 1,000ft between the bands. The Hmini Hmax and AH can be varying for different aircrafts.

In step 504, the Module 120 obtains the Aircraft Altitude from the Inertial Navigation Module 130, which in-turn receives the Aircraft altitude from Inertial Navigation and Global Positioning sensors. When the Aircraft Altitude is within ±2.5% of the particular altitude band i.e.A/C Altitude >= Altitude band - 25ft and A/C Altitude <= Attitude band + 25ft (1)

then in step 505, the winds are computed from the inputs i.e. True Air Speed and Air Density Ratio (a) received from Air Data Module 110, Angle of Attack (a) and Side Slip

In step 506, the winds, Wn and We are stored by Module 120 as the linear function, y = mx + c in memory for the particular altitude with respect to. the previous altitude band winds by computing the slope and offset. Refer Figure 3a. Here the winds for the height below the Hmjn and above Hmax are same as that of the winds at Hmin and Hmax respectively.

The Figure 7 shows the flow diagram illustrating the operation of the system 100 computations and display of impact point by extracting the winds recorded by the Module 120. In step 600, the High Altitude Release Ballistic Trajectory Module 150 receives the HAR Attack mode Status. In step 601, the attack mode is checked; if not set, the attack will not be engaged as in step 502 and if set, the attack will be engaged. During this mode of attack the wind recordation also takes place as in Figure 6 and the recent winds are updated in the memory for the specific altitude bands.

In step 603, the Target Altitude from the sea level is determined by the High Altitude Release Ballistic Trajectory Module 150 as the difference of Aircraft Inertial Altitude received from Inertial Navigation Module 130 and Height above Target received from Radar or Laser.

In step 604, the Module 150 computes the bomb's initial altitude, along, across and vertical velocities. Initially, the bomb acquires the velocities of the aircraft taking into consideration the ejection speed and the mounting angle of the weapon. The Module 150 determines whether the weapon altitude is above the target altitude in step 605.

When the weapon altitude is above the target altitude, in step 606, the entire trajectory of the weapon is divided into intervals (Refer Figure 3b) based on the total time taken by the weapon to reach the target taking into account the weapon altitude and velocity.

Subsequently, each interval time is computed which will be nothing but the time of flight of weapon for the particular interval.

In step 607, the Wind Extractor Module 140 computes the winds (Wx & Wy) by extracting the winds (Wn & We) stored in memory for the particular interval weapon altitude - Wait (Refer Figure 3b) and provides it to the HAR Ballistic Trajectory Module 150. The module 140 searches the weapon altitude from the bands of altitudes, obtains
the corresponding winds from the particular y = mx+c format and computes the winds, Wx and Wy by receiving heading, ¥ from Inertial Navigation Module 130.

In step 608, the module 150 obtains the weapon across velocity by computing the drift acceptance rate of the weapon. The Drift Acceptance plot (Refer Figure 2) shows drift acceptance rate in % versus the time of fall of the weapon which rn-turn explains that if the bomb had been in a cluster of wind for 30secs, then the bomb accepts a 100% Drift.

When a bomb moves from one parcel of air to another with a different wind velocity or direction, it will take time to pick up the new drift and establish co-ordinated flight in the new air-mass.

The bomb travelling in the cluster of winds is accelerated or de-accelerated depending on the across wind magnitude and direction in step 608 by module 150. Here the relative velocity of the weapon in across direction is determined at each interval considering the weightage of the drift from the DAR Module 160 due to winds on the initial bomb velocity. Subsequently in step 610, the weapon across distance (Sy - Refer Figure 5) in ground axes is obtained by the resultant weapon across velocity and time of flight.

In step 609, the module 150 computes the along and vertical component of velocities of the weapon using the effect of drag on the frontal cross sectional area of the weapon by the numerical computational method. The wind effect on the weapon in vertical and along direction is modeled by change in drag by wind in each interval of the weapon trajectory. Subsequently in step 611, the distance travelled by the weapon in ground axes (Sx and Sz - Refer Figure 5) is computed by the module 150 from the along and vertical velocity, drag, etc using the numerical computational method.

In step 612, the Impact Point Module 170 determines the impact point coordinates in terms of azimuth (Az) and depression (El) in aircraft body axes from the weapon along (Sx), across (Sy) and vertical (Sz) distances and then converts the coordinates on to the Head Up Display system (HUD) axes for display of the weapon aiming cues like marker and BFL on to the HUD.

In step 613, the Display Generation Module 180 displays the BFL on the HUD (Refer Figure 4b). As the aircraft altitude is high, the marker coordinates will be out of the HUD Field of View (FOV) (Refer Figure 4a). Hence, the bomb impact point indication (marker) on the HUD will be limited at the HUD display boundary and the impact point will be displayed as flashing. To indicate the true depression of impact point, a gap will be indicated on the BFL where the position of gap represents the actual depression of impact point which is out of FOV (Refer Figure 4b). The symbology is generated in the form of X and Y deflection by the module 180 for display on HUD.

CLAIMS

We claim

1. An improved method for generation of real time impact point by weapon aiming system for accurate delivery of a ballistic weapon at high altitude from fighter aircraft platform. The method is characterized by wind processing and storage module, wind extractor module, High Altitude Release Ballistic Trajectory module, Drift Acceptance Rate module, Impact Point module and Display Generation module.

2. Wind Processing & Storage module, as claimed in Claim 1, processes and records the winds for different altitude bands in the linearised format.

3. Wind Extractor module, as claimed in Claim 1, extracts the winds stored at different altitude bands of weapon trajectory using the linearised format.

4. Drift Acceptance Rate module, as claimed in Claim 1, computes the drift acceptance rate of the weapon according to the time of fall of the weapon for each interval of weapon trajectory.

5. High Altitude Release Ballistic Trajectory module, as claimed in Claim 1, computes the distance travelled by the weapon based on the drift acceptance rate with respect to the time of fall of weapon and drag of weapon.

6. Impact Point module, as claimed in Claim 1, generates impact point coordinates of the weapon in the Head Up Display axes.

7. Display Generation module, as claimed in Claim 1, generates a cue represented by Bomb Fall Line with a gap and the marker for display on Head Up Display.