# Research on the Performance of an Aircraft Landing
## 4 Unlocking Performance Analysis
### The Influence of the Landing Gear Weight on the Unlocking Force  
In the process of unlocking, the load applied to the hook by the uplock roller changes from the original impact force of the upper lock \(M_{Impact}\) to the weight of the landing gear \(M_{\omega}\), which is greatly influential for the unlocking force \(F_{Uunlock}\). To consider the influence of the landing gear weight on the stability performance of the upper lock, the corresponding weight moment equation should be added:  
\[M_{w}=w\times\xi\times\left[\tan\hfrac{2.5\times(\theta_{3}-\varphi)}{v}+1 \right]/2, \tag{11}\]  
where \(M_{w}\) is the locking moment corresponding to the weight of the landing gear; \(\xi\) is the distance from rotation point D of linkage 3 to the action line of the hitting force between the lock roller and hook; \(\varphi\) is the value of the angle \(\theta_{3}\) at which the landing gear weight begins to take effect; and \(v\) is a weight parameter related to the speed at which the weight of the landing gear acts on the lock. The results are shown in Figure 7, into which the results without landing gear weight (light gray line) are integrated. Figure 7 clearly shows that \(w\) has a great impact on the stability performance of the lock mechanism. Influenced by the weight of the landing gear, the unlocking bifurcation curves of the lock mechanism undergo marked changes, and the unlocking force of upper lock \(F_{Uunlock}\) also increases quickly with the increasing overload factor. As is known, the upper lock mechanism should never be unlocked automatically, no matter how large the aircraft maneuvering overload. The lock mechanism can be unlocked automatically in the following case. When \(F_{Uunlock}=~{}0\), if the position of lock mechanism linkage 1 is less than a particular angle, the lock mechanism can jump automatically to the unlocked state from the locked state, even in the absence of an external driving force. Taking the computational result of a 1 g overload as an example (thick black line), the specific angle at which the lock mechanism can be unlocked automatically is \(\theta_{1}=99^{\circ}\) (the angle corresponding to the circular dot in Figure 7) in this scenario. That is, for the 1 g overload case, the position of the limit stopper should be greater than \(99^{\circ}\). To study the variation trend of this specific angle, the limit stopper mounting position that satisfies all operating conditions was investigated. We calculated the unlocking curves under the following four conditions: 0.5 g, 1 g, 1.5 g, and 2 g. The results reveal that the specific unlocking angle tends to have a critical position of 101.3\({}^{\circ}\) with the increasing overload of the landing gear. Hence, it can be inferred that the specific angle will be infinitely close to 101.3\({}^{\circ}\) (the angle corresponding to a triangle in the figure) when the overload is infinite in theory. Accordingly, the lock mechanism can be in a completely locked state without being accidentally unlocked as long as its stopper position is greater than 101.3\({}^{\circ}\), unless there are any external disturbances such as the maloperation of an unlocking actuator. When \(\theta_{1}\) is between 99\({}^{\circ}\) and 101.3\({}^{\circ}\), the landing gear is in a pseudolocked state, wherein the lock mechanism tends to be unlocked due to disturbances (e.g., overload on the landing gear due to supermaneuvering flight), despite the seemingly locked landing gear. Therefore, the pseudolocked state is dangerous. For the upper lock mechanism of the actual aircraft landing gear discussed in this paper, the limit stopper is at \(\theta_{1}=105^{\circ}\) (the angle corresponding to a square in the figure). The unlocking process is explained by taking the scenario of a 1 g overload as an example. When \(F_{Unlock}\) begins to increase from 0, the angle \(\theta_{1}\) remains unchanged because of the action of the limit stopper (rightward arrow line in the partial view of Figure 7).