It's nice to see some appreciation for us cargo boys from a Chinook crew chief. One additional thing, While the aft rotors are higher than the fwd rotorhead its not the reason the blades don't hit each other. Both rotors are mechanically linked by the driveshaft so when you rotate one rotor the other one turns at an identical rate in the opposite direction. The rotorheads themselves are phased so each blade always remains the exact same distance from each other. Like the way an old hand crank egg beaters whisks pass through each other but never touch.My son joined the Army and is currently training as a Chinook Mechanic. This is an impressive piece of machinery, I wish I could have worked on one.