Expandable Arrowhead Spring Element Blade Stability
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Solution Overview
Problem
Conventional blade-opening arrowheads often experience blade movement out of the closed position during launch due to high forces, leading to decreased aerodynamic performance, and existing solutions like elastic bands are unreliable.
Innovation Solution
Incorporating a spring element or O-ring, combined with an interference fit, to maintain blades in the retracted position until impact, using a blade-carrying body with slots for pivotal and translational movement, ensuring blades remain closed during flight and expand upon target contact.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional blade-opening arrowheads are designed to launch in a closed position, then aerodynamic performance is improved, but blades undesirably move out of the closed position due to high forces during launch
Solution Approach 1:
The spring element is pre-loaded during assembly to exert a biasing force that holds the blade in the closed position before launch. This preliminary action ensures the blade remains stable during high-force launch conditions without requiring additional active control mechanisms.
Solution Approach 2:
The spring element applies a counteracting force (biasing force) that opposes the harmful movement of the blade outward during launch. This preliminary anti-action prevents the blade from moving to an open position, thereby maintaining aerodynamic performance while ensuring reliability.
2Reliability
If elastic bands or O-rings are used to hold blades in closed position, then blade stability is improved, but the solution is unreliable under high forces
Solution Approach 1:
The spring element is designed with specific mechanical properties (spring constant, preload force) that enable it to withstand the high forces generated during archery bow launch. By changing the parameters of the elastic element from a simple O-ring to a engineered spring with calculated force characteristics, the system achieves reliable blade holding under extreme conditions.
Solution Approach 2:
The spring element is pre-loaded during assembly to establish a known biasing force before launch. This preliminary action ensures the blade is held firmly in the closed position with a predictable force reserve that can withstand the high G-forces of archery bow launch, making the solution reliable rather than merely functional.
3Reliability
If blades are held firmly in closed position during launch, then aerodynamic performance is maintained, but blade expansion upon impact may be delayed
Solution Approach 1:
The spring element is designed to provide dynamic response characteristics - maintaining firm holding during launch conditions but allowing rapid release when the impact force exceeds the spring's biasing force. The spring's mechanical properties are selected to create a threshold effect where the blade remains closed during normal flight but expands rapidly upon target impact.
Solution Approach 2:
The spring constant and preload force are carefully selected to create a force threshold. During launch and flight, the spring maintains the blade in closed position. Upon impact, the sudden increase in force exceeds the spring's resistance, causing rapid blade expansion. This parameter optimization ensures both reliable closed position maintenance and fast expansion when needed.
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 solution effectively keeps blades closed during launch and flight, enhancing aerodynamic performance and ensuring reliable expansion upon impact, improving the arrowhead's cutting capability and accuracy.
Implementation Method 1
a spring element to hold each blade in the retracted position
Implementation Method 2
a spring element or O-ring, combined with an interference fit, to maintain blades in the retracted position
Implementation Method 3
an O-ring is used in addition to or in lieu of the spring element
Data Source
AI summary
An expandable arrowhead having a blade-carrying body with a slot that houses at least one movably mounted blade. Each blade can be pivotally mounted about a shaft. In some embodiments, the shaft is fixed with respect to the body. In other embodiments, the shaft is movably mounted with respect to the body, for example by mounting a shaft within the slot so that the shaft moves within the slot with respect to the blade-carrying body. In some embodiments of this invention, a spring element positively holds one or more blades in a closed position or a retracted position, particularly during extreme forces encountered when launching an arrow from an archery bow, such as a compound archery bow. The spring element of this invention can be used to improve blade opening capabilities of conventional blade-opening arrowheads or broadheads.