Hi all, I wanted to start a thread to get your favourite examples of unusual engineering solutions where engineers and designers have a solved a problem in a completely different way to the 'standard' way. As an example - I have a background in helicopter aviation. Most helicopters have a large main rotor and by spinning this in one direction the main body body of the helicopter wants to spin equally in the opposite direction. This torque force is usually counteracted by a small tail rotor on the rear of the helicopter, and this is by far the most common solution... However, there are some other more unusual solutions - 1. Probably the most recognisable - counteract one rotor with second rotor - as seen in Chinook helicopters. 2. Use two rotors but mount them along the same axis, one on top of the other. I love this co-axial solution! You see it mainly on a lot of Soviet military helicopters (such as the Kamov Ka-52) but the patent is actually over 150 years old! 3. NOTAR helicopters use the same principle as a tail rotor - which is to use force on the end of a tail, but this force is generated from exhaust gases from the engine, rather than an actual tail rotor. This is apparently quieter and safer, but an interesting way to look at things. Has anyone got any similar sort of examples they'd like to share?