Rate-Based Autopilot Gravity Bias for Lofted Projectile Trajectories
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Solution Overview
Problem
Current guidance systems for guided projectiles result in flat trajectories at longer ranges, leading to reduced accuracy, increased collateral damage, and limited maximum range due to inherent gravity bias values below 1.0, which cause ground impacts and warhead malfunctions.
Innovation Solution
The introduction of an Additional Gravity Bias (Gbias) component, calculated as the difference between the Desired Gbias and Inherent Gbias, is used to reshape the projectile's trajectory by modifying the rate commands for lateral control loops, allowing for improved trajectory lofting and terminal flight path angles without increasing airframe maneuverability demands.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If inherent Gbias of 0.7 to 0.9 is used in rate based autopilot, then the guidance system is simple and low cost, but the trajectory becomes flat at longer ranges causing ground impacts and reduced accuracy
Solution Approach 1:
The patent modifies the gravity bias parameter from the inherent 0.7-0.9 value to a desired value of 1.0 or higher by adding an additional Gbias term. This parameter change transforms the trajectory shape from flat to lofted, enabling accurate long-range engagement without increasing system complexity or cost.
Solution Approach 2:
The patent calculates and applies the additional Gbias in advance based on the difference between desired and inherent gravity bias values. This preliminary adjustment to the rate commands ensures the projectile achieves the correct lofted trajectory shape before engagement, preventing ground impacts and improving accuracy.
2Shape
If low proportional navigation gain is used to shape trajectory, then the rocket stays higher earlier in engagement, but the terminal flight path angle is reduced and maximum range is limited
Solution Approach 1:
The patent changes the gravity bias parameter to achieve trajectory lofting without relying on low proportional navigation gain. This allows the rocket to maintain higher altitude earlier in engagement while also achieving steeper terminal flight path angles and extended maximum range, resolving the trade-off between trajectory shaping and terminal performance.
3Length of moving object
If additional Gbias is applied to loft trajectory, then maximum range and terminal flight path angle are improved, but airframe maneuverability demands increase
Solution Approach 1:
The patent applies the additional Gbias as a preliminary adjustment to the rate commands before engagement. This advance adjustment shapes the trajectory to achieve extended range and steep terminal angles while distributing the maneuverability demands throughout the flight, preventing excessive G requirements during the terminal phase.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach significantly increases the maximum effective range, enhances warhead precision, and reduces collateral damage by achieving steeper terminal flight path angles, improving the probability of hit and warhead effectiveness without increasing complexity or cost.
Implementation Method 1
Gravity influences the guidance of projectiles by modifying the trajectory downward compared to the trajectory in the absence of gravity. Gbias compensates for the effects of gravity.
Data Source
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AI summary
A device, system, and method for shaping the trajectory of a projectile employing a Gravity bias, Gbias. The system includes a seeker, a guidance filter, a pitch rate filter, an actuator, pitch/yaw/roll coupled aerodynamics, and lateral rate sensors. It receives roll orientation input to a guidance and control autopilot; it applies Additional Gbias to that produced by the null rate command to the lateral control loops of the guidance and control autopilot device. The lateral rate command is equal to the desired Additional Gbias divided by an estimate of the projectile velocity. The Additional Gbias is translated to a rate command and incorporated into guidance loop commands to boost an Inherent Gbias to shape the trajectory of the projectile to the target.