Trimmable Tail Kit Rudder Drag Reduction
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Solution Overview
Problem
Conventional tail kit assemblies for guided munitions suffer from significant drag due to aggressive strakes and rudders, leading to a substantial reduction in the effective range of gun-fired, medium caliber munitions, as they require large profiles to counter high rotational rates, which increases air resistance and complicates rotational orientation determination.
Innovation Solution
A tail kit assembly with trimmable control surfaces, rudders, flaps, or tabs that can be actuated by an onboard guidance system to modulate between retracted and extended orientations, reducing drag by allowing independent control of the tail kit base's rotation and reducing the dynamic pressure on strakes, thereby increasing the munition's range and mission effectiveness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If aggressive strakes with large surface area are used to counter high rotational rates, then the rotational control is improved, but the drag force increases significantly
Solution Approach 1:
The patent applies the dynamics principle by making the control surfaces (strakes and rudders) movable rather than fixed. The trimmable rudders can be adjusted between retracted and extended positions, and the strakes can be trimmed to optimize their angle of attack. This dynamic adjustment allows the system to achieve effective rotational control at lower surface areas, thereby reducing drag while maintaining reliability.
Solution Approach 2:
The patent implements parameter changes by allowing the control surfaces to vary their geometric parameters (surface area exposed to airflow, angle of attack) during flight. The trimmable rudders can change their effective area and orientation relative to the airstream, enabling the system to achieve the necessary aerodynamic moments with reduced drag compared to fixed aggressive strakes.
2Ease of operation
If fixed geometry rudders are used for trajectory control, then the guidance function is achieved, but the drag forces reduce the effective range
Solution Approach 1:
The patent applies dynamics by making the rudders trimmable rather than fixed. The rudders can be adjusted to optimal positions for different flight phases and conditions, allowing effective trajectory control only when needed. This reduces the time-averaged drag force compared to fixed rudders that must maintain control authority throughout the entire flight, thereby extending effective range.
3Difficulty of detecting and measuring
If the tail kit assembly is rotationally decoupled from the munition, then the rotational orientation determination is simplified, but the device complexity increases
Solution Approach 1:
The patent applies segmentation by dividing the tail kit assembly into a rotatable base and a non-rotating or differently rotating control surface assembly. This decoupling allows the control surfaces to maintain a stable reference frame for orientation determination while the base can rotate independently. The segmentation simplifies the measurement of rotational orientation of the control surfaces relative to the airstream, despite the increased structural complexity of the decoupled assembly.
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
The trimmable control surfaces significantly reduce overall drag, allowing the munition to maintain a higher velocity and extend its range by up to 30% compared to conventional systems, while simplifying the determination of rotational orientation and improving trajectory control.
Implementation Method 1
the strakes that are fixed to such a tail kit assembly can be angled or curved relative to the longitudinal axis, which generally corresponds to the direction of flight, so as to generate a rotational force on the base that is counter to rotation of the munition
Implementation Method 2
the air resistance of the strakes and rudder produce counter rotation and transverse forces on the tail end of the munition in a desired manner thereby guiding or controlling the flight of the munition through the air
Data Source
AI summary
A tail kit assembly of a guided munition having a tail kit base connected to a trailing end of a projectile body. The tail kit base is rotatable relative to the projectile body. A trimmable rudder has forward and rearward ends. The forward end is pivotally coupled to the tail kit base, such that the trimmable rudder can, relative to the tail kit base, between retracted and extended orientations. An actuator is fixed between the tail kit base and the rearward end of the trimmable rudder. The actuator is electrically coupled to an onboard guidance system that controls actuation of the actuator to pivot the trimmable rudder between the retracted orientation and the extended orientation.