Set 8412, released in 1995, was the first "Tech Build" set, and it was a great start. This medium sized helicopter reminds me of Korean War era open cockpit helicopter like a Bell 47. It features a fully articulated main rotor head, a rotating tail rotor, and a simulated turbine engine.
Although this helicopter is not very large, the functionality is really excellent and it features some interesting building techniques. The canopy is made from bent semi-rigid pneumatic tubes. The tail boom is made from exposed axles. The landing skids use axles and angle connectors. The cyclic system for the main rotor head uses the rare Flex System components including the new ball end connectors. There are even hidden parts usually used as control arms of suspension systems. The larger of these controls the pitch axis cyclic and the smaller is a spacer on the tail boom.
A technic figure will fit in the seat in the cockpit even though the set does not come with one.
This small set was an excellent and inexpensive introduction to the complexities of Technic in 1995, and still holds up very well today.
The rotors' rotation is driven by an input crank on the left side. This crank drives a set of 12 tooth bevel gears giving the main rotor a ratio of 1:1. The main rotor axle also drives another set of bevel gears which rotate a simulated turbine engine. One of the turbines, a 24 tooth spur gear, meshes with an 8 tooth gear running to the tail rotor resulting in a 3:1 ratio. A final pair of bevel gears complete the path to the tail rotor.
The input crank uses a rare handle part to make rotation easier.
This helicopter uses a cyclic pitch system very similar to 8856. Real helicopter cyclic works by changing the pitch of individual blades as they rotate using a swashplate. For example, the leading and trailing blades may be at 10 degrees of pitch, while the port and starboard blades are at 5 and 15 degrees respectively. This model pivots the entire rotor head instead. If a real helicopter did this it would risk striking the rotor against the frame.
The rotor axle drives a spherical ball gear. A part with 4 ball joints which is similar to a swashplate connects to a pair of flex cables to allow the head to pivot on two axes. The ball joints also keep the swashplate from rotating. Inside the swashplate is a four blade rotor part. The rotor has tabs on the inside which mate with the ball gear to transmit torque. Because of the shape of the gear, the rotor can pivot on two axes while still rotating.
The control of the cyclic is from a stick at the pilot's position. There is one flex cable and sleeve for each axis. Fore-aft motion of the stick (shown in red) pushes and pulls the cable using a ball joint. The flex cable runs up to a link which lifts the swashplate using a suspension control arm! Lateral motion of the stick rotates an axle which runs aft (shown in green). At the end of the axle is a ball joint and a cam which connects to another flex cable. This flex cable attaches to a ball joint on the side of the swashplate.
The landing skids are quite sturdy and are constructed from toothed connectors, liftarms, and axles.