Its front rotor struck the underside of Pier 10, causing the helicopter to rear up vertically and then fall on its side.

It suffered damage to the undercarriage, nose and front rotor, but the crew and 15 soldiers on board were unharmed.

"I saw a Twenty-one lose its front rotor," Stevens said.

And helping to haul its 680-pound heft down from triple-digit speeds were dual stainless-alloy ventilated front rotors - a first for the motorcycle industry.

However, the rear rotor works in the aerodynamic shadow of the front rotor, which reduces its efficiency.

To pitch forward and accelerate, the rear rotor increases collective pitch, raising the tail and the front rotor decreases collective pitch, simultaneously dipping the nose.

To pivot right, the front rotor tilts right and the rear rotor tilts left.

A first for the RL was the use of aluminum 4-piston front brake calipers over 12.6-inch cast-iron ventilated front rotors.

To pitch nose down and accelerate forward, the collective pitch on the front rotor is decreased and the collective pitch on the rear rotor is increased proportionally.

Then my front rotors warped; I had to get those changed.