There are two main types of aircraft hydraulic jacks that are used in aviation— axle and airframe (tripod) jacks. Though different in some capacities, the two operate using similar aircraft jack parts and standardized aircraft hydraulic fluid. Furthermore, both have important safety features in the case of malfunction or overload. Let’s take a look at the different types of aviation aircraft jacks, and the general maintenance protocols for both.
Axle jacks are typically used for the purpose of maintaining tires, wheels, and struts. In order to raise the aircraft, they are attached to the nose gear or main landing gear. For safety, the jack is equipped with a bypass valve. In the event that the applied load exceeds 10% over the specified load capacity, the bypass valve will bypass fluid to prevent damage. There are three variations of an axle jack that are commonly seen in aviation, all of which meet different load requirements. These include hand-carried, horseshoe, and outrigger.
Hand-carried axle jacks are, as their name suggests, relatively easier to transport than the others. They operate using single or double manually operated hydraulic pumps. Horseshoe axle jacks have a stationary piston, and two hydraulic cylinders that power a lifting arm. Lastly, an outrigger axle jack is the largest and heaviest of the three. This jack has a two-speed pump mounted on its frame, which operates the hydraulic cylinder.
Airframe (tripod) jacks are usually employed to lift an entire aircraft. Depending on the type of aircraft, it may require this jack to be placed on the wing, nose, fuselage, or tail.
There are two distinct types of tripod jack, called fixed height and variable height. Given its name, the height of the tripod components on a variable height jack can be adjusted by adding leg extensions.
Preoperational maintenance is critical to ensure that aircraft jacks are safe to operate. A preoperational inspection should occur before every use. There are a few elements that should be inspected regularly regardless of varying type, including fluid level verification, joint damage and fatigue, missing or bent components, and locknut condition. In addition, when performing maintenance, you’ll want to pay attention to the aircraft jack classification numbers. They vary depending on the type of jack and its load capacity and will help you determine the necessary protocols for inspection.
Both aircraft jack varieties are categorized with a specific labeling system to ensure proper care and maintenance. For example, a model might be designated A25-1HS. The “A” indicates axle, the number 25 indicates the load capacity in tons, followed by a specific jack identification number, in this case the number one. The proceeding two letters indicate that the jack is either outrigger (OR), hand carried (HC), or horseshoe (HS). Tripod jacks are labeled similarly to axle jacks. For instance, let’s consider the tripod label “T20-1VH5”. Every identification parameter is the same, excluding the “T”, and the last three items. A tripod is classified as fixed height (FH) or variable height (VH). The additional number at the end of the model designation, represents the number of leg extension kits that can be applied; in this case, there are five.
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