A. The angularity of the jack ram (product of the sine of the jack angle).
B. The jack load
(1)
The weight of the airplane on the ground at some point, other than the jack point, can decrease the horizontal forces on the jack. The horizontal forces can also be prevented by other jacks. These jacks must be in the correct position to be resistant to side loads.
(2)
At a point where part of the airplane is on the ground, there is a horizontal force. This force decreases the horizontal force (side load) at the recovery jack point. The ground load force is the result of the multiplication of these factors:
(a)
The coefficient of friction between the ground and the airplane
(b)
The weight of the airplane at that point
(3)
At the other jack position there is a horizontal force. These jacks usually have a horizontal force that is approximately15 percent of the vertical load on the jack.
3.
A different jack (the tripod type recovery jack) has a head that moves in the horizontal direction (by coordinated cylinder extension and retraction). The jack head and the jack point of the airplane align while the jack point moves (within limits through the arc). This prevents large horizontal loads. See SUBJECT 3-30-5 for more data on tripod type and strut type jacks.
3-10-2
WHEN YOU USE JACKS AND TETHERS
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3-10-3 When You Use Pneumatic Bags and Tethers
1.
If you use only pneumatic bags (elevators) to lift the airplane, you must use tethers. Your recovery configuration can be more or less stable with different types of pneumatic bags. Also, different tether configurations are necessary for a different bag height or a different type of pneumatic bag.
2.
Newer style pneumatic bags are designed to give greater lifting power, more stability and safety to lifting damaged airplanes. They are multi-compartment, inflatable lifting elevators. Each elevator consists of compartments bonded together. The top two compartments are further divided into two separate and equal compartments; the top compartment is divided laterally and the compartment second from the top is divided horizontally in order to allow individual inflation to give better support under slanted surfaces.
Older style pneumatic bags, see Figure 3-1 for first-design, balloon type, are more prone to lateral instability then the newer style pneumatic bags.
3.
When you lift only one part of the airplane, the other airplane supports can help to keep it stable. The airplane parts that touch the ground have the same horizontal forces discussed before in SUBJECT 3-10-2. A pneumatic bag is not as stable as a jack and you must be more careful. Some tethers are always necessary.
3-10-3
WHEN YOU USE PNEUMATIC BAGS AND TETHERS Page 3-7 Jul 01/2005 中國航空網 www.k6050.com 航空翻譯 www.aviation.cn 本文鏈接地址：757 Airplane Recovery Document 飛機恢復文件(58)
