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 AFV Type 90 AFV The Type 90 is an armoured fighting vehicle produced by Chinese company Norinco; it is the successor for the Type 85 AFV of which it uses some components. The Type 90 series was developed for export, and consists of at least 10 different types; its industrial index is YW535. This new type is rather similar to its predecessors Type 85 AFV and Type 89 AFV, but the hull has a different shape, having a vertical lower side wall and a sloping upper side wall. Overall, the Type 90 is bigger and heavier, yet has a lower profile.