How does arresting gear work

These devices, which do not depend on arresting hooks on aircraft, stop an aircraft by absorbing its forward momentum in a landing or aborted takeoff overrun. These systems are most commonly net devices fig. The barriers typically are located in the overrun of the runway, are unidirectional, and can have collocated or interconnected arresting cables as part of their configuration.

They sometimes are used for special purposes, such as stopping the space shuttle. Aircraft arresting cables. Arresting cables span the runway surface and are engaged by the aircraft arresting gear hook fig. Used primarily by aircraft built in the United States and Europe, arresting cables have been used by the military since the late s on aircraft carriers and for land-based runways.

Three main factors determine where cables are located on runways: the direction of engagement unidirectional or bidirectional ; the runout of the system, which is the distance from the cable to the point at which the aircraft stops typically to 1, ft, or to m ; and whether the system is typically used under visual meteorological conditions or instrument meteorological conditions.

Figure 3 shows the typical locations for arresting-cable installations. An aircraft operating on runway 10R would use the cable at the far end for both landing and aborted takeoff unless the aircraft had an emergency, at which point the arresting gear nearest the approach end of the runway would be used.

The installation criteria for cable systems on commercial runways are identified in the U. The location of the cable is marked on the runway by a series of reflective discs 10 ft 3 m in diameter painted "identification yellow. See location identification in "Common Terms". Engineered materials arresting systems EMAS. EMAS, which are constructed of high-energy-absorbing materials of selected strength, are located in the safety area, or overrun, of the runway.

They are designed to crush under the weight of commercial airplanes as they exert deceleration forces on the landing gear. These systems do not affect the normal landing and takeoff of airplanes. Airlines have numerous concerns about operating commercial airplanes on runways with aircraft arresting systems.

These include airplane nosegear interference, trampling of the arresting cable, adjustments to declared distances, dealing with arresting barriers, runway availability, airplane maintenance, and unintentionally engaging arresting systems.

Nosegear interference. Some commercial airplanes have unique nosegear devices to deflect either spray or foreign objects. Normal procedure is for the rubber donuts to be approximately 6 ft 1. For runways wider than ft 61 m , the donuts are placed 8 ft 2. To minimize potential damage to the nosegear deflectors, airplanes with such attachments should slow-taxi over the cable, avoiding the donuts.

If the nosegear spray deflector is damaged and removed, in accordance with the minimum equipment list, the airplane is limited to operating on dry runways until the deflector is replaced. Trampling of the arresting cable. If an operator considers the trampling, or rolling over, of a cable to be too rough on the airplane, the donuts that elevate the arresting cable above the runway surface can be moved to the sides of the runway during commercial operations.

This allows the cable to rest directly on the pavement surface, minimizing the bump effect on the airplane. It is important to note that the cable must be kept under tension, whether lying on the pavement or elevated by the donuts. Otherwise, the cable could be lifted by the airplane landing gear and contact the bottom of the fuselage or antennae located on the lower fuselage.

However, some versions of the system can be retracted by remote control into an adjacent groove in the runway surface when not operationally required and thus the full length of the runway is restored to a normal condition. If these deflectors come into contact with the arrestor cable, they may shatter and create FOD hazardous to subsequent aircraft if not removed.

If a cable is not retractable, it can sometimes be disconnected and moved to the side of the runway when not required or alternatively, the 'donuts' supporting it in the functional or raised position can sometimes be moved along the cable to the sides of the runway, thereby allowing the cable still under tension to lie flush with the surface in a 'rigged and down' condition allowing landing gear to safely pass over it.

The option of a reduction in the declared length of a runway for civil aircraft is also possible by use of displaced landing threshold, but the landing performance must then be re-assessed. The risk of cable interference at the upwind end of the runway in the case of a rejected take off or the end of a landing roll is generally discounted due to the lower groundspeed at that point - typical aircraft manufacturer advice is to ensure that if crossing 'rigged and up' cables is unavoidable, it is done at a groundspeed of not more than 60 knots.

The only widely available requirements for indicating the presence of arrestor gear across runways used by civil aircraft are those published by the FAA. Their requirements for indicating the presence of a permanent aircraft arresting system cable crossing a runway used by civil aircraft are:. The control valve drive system is installed between crosshead and the fixed sheaves, so the relationship between the position of the crosshead and the rotation angle of the cam of the throttle is as follows: where is the transfer coefficient between crosshead position and the rotation angle of cam.

When the association of the area of the throttle and the position of the crosshead is established, the arresting distance of the aircraft can be controlled. Based on the above description, the governing equations of the arresting gear system form a set of differentiation and algebraic equations DAEs. One popular numerical algorithm for solving DAEs with contact problems is the implicit first-order backward differentiation formula BDF.

Assume that we are going to solve at time , which satisfies. Given the values of at time and as and , the first and second time derivative of could be derived through numerical discrete as where is the current time-step. After substituting 29 into 28 , the DAEs are simplified to nonlinear algebraic equations of variables only since both and are known. This nonlinear equation 30 can be solved in terms of the classical Newton-Raphson iteration method, and one possible initial guess of for iteration could be get by assuming that is linear variable and extending and to time There are three cases in which the current time-step will be adjusted.

In this way, the time-step of BDF is automatically adjusted to fit the dynamic properties of the system. The integration method will chose small time-step for the initial impact stage at arresting process and large time-step for the stable deceleration stage. This saves calculation time a lot compared with fixed time-step integration method. In order to verify the established cable element and the collision between the cable and the rigid body, a simple multibody example is presented.

As shown in Figure 8 , considering a cable wrapped around a fixed cylinder with two full circles, it is subjected to vertical forces and at two ends, respectively.

The friction coefficient between cable and cylinder is. Then the analytical solution shows that the cable will be balanced when. The velocity response of the node at the upper end under the external forces and is shown in Figure 9. It is almost stable which agrees with the analytical prediction greatly. Making use of the modeling methodology developed in the Section 2 , we build a full-scale MK7 type hydraulic arresting gear system with parameters shown in Table 1. To determine the mesh size of the cables in arresting gear system, we build a simple supported cable with same physical and geometrical parameters of the purchase cable as shown in Figure The cable is uniformly meshed by elements and elements, respectively.

The maximum displacement difference between these two meshes at center point within the first second is 1. Since both the displacement and stress converged to acceptable accuracies, we decided to use elements every 30 meters to mesh the cables in arresting gear system. In the following context, the aircraft landing along the runway centerline and offset the centerline will be simulated and analyzed, respectively.

The acceleration, velocity, and position of aircraft and the stress within rope are presented. And the functionalities of cable anchor damper and damper sheave installation on the rope stress are analyzed in detail. At the most ideal situation, the landing aircraft velocity is parallel to the runway and the anchor hooks the cable right at the middle point. In this case, the response of aircraft from the initial arrestment to stop and the snapshots of the whole system are shown in Figure And then the aircraft is pulled back a little because of the retraction force generated from the elastic energy stored in deck pendant.

Based on this, we divide the arresting process into three stages: 1 capture shock stage, 2 effective arresting stage, and 3 backward stage. The first stage is caused by the impact between tailhook and deck pendent which happened at 0. It contains three acceleration peaks, and the maximum one is 3.

The character of entering the second stage is that the vibration of impact diminished, and acceleration gots stable. It ends when the velocity reduces to zero, and the elastic force generated by deck pendent leads to the third backward stage. It is interesting to note that the stress at the middle of deck pendent, shown in Figure 12 , performs similar to the acceleration of the aircraft. It also contains three peaks at the initial stage.

It runs to slowly varying stage. This similarity implies that the acceleration of aircraft comes from the stress of cable at contact point. The stress gets its first peak point A once the impact between tailhook and cable happens. Then the stress wave generated by this shock propagates toward and reaches the deck sheave at 0.

When the backward wave reaches tailhook again at 0. Later, the stress wave decays, and the hydraulic force mainly generated by constant runout valve leads to a smooth variable period of stress. We will see later that the decay of the stress wave is caused by the absorbing effect of damper sheave installation and cable anchor damper.

Five points are chosen as the detection points on the deck pendant and purchase cable of the arresting gear system, as is shown in Figure A is the middle point of the deck pendant; B is an arbitrary point in the purchase cable; C and D are the arbitrary two points in the purchase cable between crosshead and fixed sheaves where C is close to point B and D is close to point E; E is an arbitrary point in the cable anchor installation.

The results show that the maximum along the whole cable happens at the middle point of deck pendent. Each stress at the second stage from point A to E varies a little due to the friction between cable and sheaves but shares the same smooth varying process. At the first stage, the point E which is far away from contact point is not notable, influenced by the impact between deck pendent and cable.

The stresses at the middle of deck pendent with these four cases are shown in Figure Figure 14 shows the following cases. Through the above analysis, we conclude that the CAD is far away from the tailhook and it can not generate any effect on the first shock stage, while the DSI is effective at both the first and the second stages. Besides, it is also inspirational to check the cable stress at frequency domain despite that the dynamic behavior of the arresting system keeps changing during arresting process.

The stress at time range [0. As shown in Figure 15 , there are three sharp sparks at 3. This corresponds to the significant stress vibration in time domain. Further, it is interesting to note that the frequencies of second and third sparks are roughly two and three times that of the first spark.

This behavior is very similar with the eigenfrequency character of a tensioned string. Therefore, the fundamental frequency of this tensioned string is which agrees with the frequency of the first spark 3. In addition, these sparks vanished after installing CAD or DSI since the damping force absorbed the vibration in cables severely. Now we discuss the situation of that the aircraft velocity is parallel with the runway centerline, while the landing point is 0. In this case, the stress at the middle point of the deck pendant during the whole process is shown in Figure It is shown from the simulation result that the deck pendant has 5 stress peaks at the first stage.

The first is caused by the instant collision between the arresting hook and the deck pendant at 0. However, the third peak is caused by the reflection and superposition from the right deck sheave of the stress wave after it reached there. The fourth one is caused by the superposition of the transverse wave at the position of the arresting hook of the aircraft after it is reflected from the left deck sheaves.

The fifth one is caused by the superposition of the transverse wave at the position of the arresting hook of the aircraft after it is reflected from the right deck sheaves.

Compared with along centerline landing case, we got five peak values here instead of three. This means that the offline landing case could a little bit reduce the stress peak. The arresting process is a complicated coupling dynamics between rigid bodies, flex bodies, and hydraulic units. It is strong nonlinear and involves both a transient wave propagation process in rope and a smooth decelerating of aircraft.

This fact discounts the calculate efficiency of explicit method since the former process needs small time-step to capture the propagation events, while the later one needs large time-step to speed up.

To solve this problem, in this paper, we proposed to build a multibody dynamic model of a full-scale MK7 type arresting gear system. And the resulting governing algebraic and differentiation equations are solved through a time-variable implicit backward differentiation formula. In the model, a kind of new cable element that is capable of describing the arbitrary large displacement and rotation in three-dimensional space is developed to model the wire cables and damping force is used to simulate the effect of hydraulic system.

Dynamic simulation shows that the cable stress is dominated by the propagation, refection, and superposition of stress waves during the early stage of the arresting process, and later the shock is quickly dissipated by the damper sheave installations and cable anchor dampers.

Simulation results repeat that maximum stress value happens when the stress wave is reflected and superposed between the deck sheaves. And the maximum stress in the off centerline landing case is a little bit smaller than the along centerline landing case. In addition, the multibody approach and arresting gear system model proposed here also provide an efficient way to design and optimize the whole mechanism.

And the authors would also like to thank Dr. Jiawei He for his kind help on visualizing simulation results.