Helix angle the helix angle. The efficiency can be plotted versus the helix angle for a constant friction, as shown in the adjacent diagram. The maximum efficiency is a helix angle between 40 and 45 degrees, however a reasonable efficiency is achieved above 15°. Due to difficulties in forming the thread, helix angle greater than 30° are rarely used. Moreover, above 30° the friction angle becomes smaller than the helix angle and the nut is no longer self-locking and the mechanical advantage disappears. In helical and worm gears, the helix angle denotes the standard pitch circle unless otherwise specified. Application of the
Type 90 Kyū-maru tank made Type 90 more challenging to operate outside Hokkaido. Some politicians therefore criticized the effectiveness of Type 90 due to difficulty in transportation. In fact, more than 65% of major bridges in Japan were still considered passable for Type 90 while overseas main battle tanks such as Challenger 2 and Leopard 2 could only use 40% of bridges in Japan. Type 90 Kyū-maru The is a main battle tank (MBT) of the Japan Ground Self-Defense Force (JGSDF). It was designed and built by Mitsubishi Heavy Industries as a replacement for all deployed Type 61 and Type 74 tanks, and