[32起落架] 关于737NG低速刹车时的问题

Several operators have reported that while taxiing at very slow speeds, airplane shudder/vibration would occur while applying brakes.

一些运营商报告说，当以非常慢的速度滑行时，飞机在刹车时会发生抖动/振动。

The vibration is known as "Gear Walk." Gear walk, sometimes called "Brake Shudder," is a known and temporary phenomenon which can occur when performing low speed taxi stops with warm or hot brakes. Gear walk can occur with either steel or carbon brakes.

这种振动被称为“起落架移位”。起落架移位，有时称为“刹车抖动”，是一种已知的暂时现象，在刹车是温的或热的情况下，进行低速滑行刹停时，可能会出现这种现象。起落架移位在钢刹车或碳刹车上都可能发生。

Gear walk was first reported during the 737NG Flight Test Program in 1997. Since then, gear walk has occasionally been reported during taxi stops before airplane delivery or in service. Gear walk typically occurs at low speeds with warm or hot brakes and with light brake pedal application. Gear walk is a low-frequency vibration mode in which the brake and tire response couples with the natural frequency of the main landing gear. While the vibration may be noticeable in the cabin, there have been no reports of airplane damage due to this vibration mode.

在1997年737NG飞行测试项目中首次发现了起落架移位。从那时起，在飞机交付或运营中的滑行刹停时，偶尔会出现起落架移位的情况。起落架移位通常发生在低速时，此时刹车是温的或热的，并轻踩刹车脚蹬。起落架移位是一种低频振动模式，其中刹车和轮胎响应与主起落架的固有频率耦合。虽然机舱内的振动可能很明显，但还没有关于这种振动模式导致飞机损坏的报告。

With steel brakes, when the brakes become hot, the brake lining surfaces develop a "glaze" which creates a stick-slip condition when the brakes are applied gently at slow taxi speeds. The stick-slip condition will continue until the brakes are applied firmly a few times. The application of the brakes in this manner eliminates the glaze from the linings and restores the brakes back to normal.

对于钢制刹车，当刹车变热时，刹车片表面会形成“釉面”，当低速滑行时，轻轻踩下刹车脚蹬，会产生粘滑状况。粘滑状况将持续，直到用力踩下几次刹车。以这种方式刹车可消除刹车片上的釉面，并使刹车恢复正常。

With carbon brakes, vibration is more likely to occur when the brake heat sinks (rotor and stator disks) are new. After a small number of moderately aggressive landing stops, the rubbing surfaces develop a friction film that stabilizes the brake friction coefficient, thereby reducing the likelihood of vibration. The brake friction coefficient can be higher than normal until this friction film develops. When brakes are applied gently at low speeds, a stick-slip condition can occur as the rubbing surfaces alternate between grabbing (sticking) due to high friction coefficient and rotating (slipping) under the low applied brake spanssure. This condition is more likely to occur when the brakes are warm or hot because increased temperature tends to increase the brake friction coefficient.

对于碳刹车，当刹车散热片（转子和定子盘）是新的时，更容易发生振动。在经过一些着陆刹车后，摩擦表面会形成一层摩擦膜，使刹车摩擦系数稳定，从而降低振动的可能性。在摩擦膜形成之前，刹车摩擦系数可能高于正常值。当在低速时轻轻地踩下刹车，由于摩擦系数高，可能会出现粘滑情况，摩擦表面交替出现抱死（粘住）和在低刹车压力下旋转（打滑）。当刹车片温度较高或较热时，更容易出现这种情况，因为温度升高会增加刹车器摩擦系数。

If an airplane experiences a gear walk condition, it is our experience that the problem will diminish after several slightly more aggressive braking maneuvers (such as a normal landing stops). The problem may also be avoided by applying the brakes more firmly at low speeds. As a result, Boeing recommends that no maintenance actions be taken, unless the gear walk continues at an unacceptable level for passenger comfort/perception. If it is determined that a maintenance action is necessary, the brakes may be replaced at a convenient opportunity.

如果飞机遇到了起落架移位的情况，根据我们的经验，在猛踩几次刹车（如正常的着陆刹车）后，问题将减少。也可以通过在低速需要刹车时，猛的踩下刹车来避免该问题。因此，波音公司建议不采取任何维护措施，除非起落架移位持续到了乘客舒适度不可接受的水平。如果确定有必要进行维护，可在方便的时候更换刹车毂。