Piasecki’s -59 series aircraft proved a promising configuration that was never brought to fruition.
By the early 1960’s evolved models attained speeds of 75 mph, had flown indoors, within trees and under bridges. “While the Airgeep would normally operate close to the ground, it was capable of flying to several thousand feet, proving to be stable in flight.” These vehicles demonstrated the viability of the tandem-duct platform.
Unfortunately, the aircraft possessed the complex aero-mechanics of a helicopter - repeated twice. They utilized the same controls as a helicopter, requiring the same skills to fly, with the difficulty compounded by the intent of low altitude flight. “…the Army decided that the “Flying Jeep concept [was] unsuitable for the modern battlefield”, and concentrated on the development of conventional helicopters.”
Control coupling occurs when a maneuver about one axis is joined by an unwanted rotation about another. An airplane with too much dihedral will roll when commanded to yaw. A helicopter will yaw when pulling collective.
“High-pilot workload” is the euphemism used to describe an aircraft whose control coupling is particularly onerous.
The control system on the test-bed minimizes coupling. A command to pitch nose-up does not induce roll or yaw. No bucking, no spinning. Not very challenging.
The pilot cruises in the direction he wishes to go with little conscious input or training. The vehicle takes cues from his intuitive movements and amplifies them aerodynamically to maintain his level flight path. By applying throttle, he can increase altitude and speed.
Application of power induces torque about the drive axis which must be countered for a flat take-off in any powered lift aircraft. Control surfaces or vanes, although simple, are not effective in countering power-induced torque, unless it is in yaw (rarely the case). This is particularly true when close to the ground - which, coincidentally, is where most take-offs originate.