This was the lowest mass solution at the time of P1127 development.
Remember that weight is at a premium for vertical take off. The first hover tests of the P1127 prototype were only possible with fuel for only 3 minutes in the tanks and 700 lbs of equipment stripped from the airframe. A conventional landing gear would had made hovering impossible in 1960.
But be warned that this gear layout will not be easy to get right. It took until 1967 to get it to behave well. What went wrong?
- In the first tests, the main gear oleo strut had more travel than the outriggers, so the airplane would tilt over to one side as soon as one of the outriggers would be lifted from the ground. The sideways component of thrust thus set free would let the plane skid sideways, which in turn resulted in a rotation around the nose gear. With thrust being equal to weight, even 6° of tilt will produce a sideways acceleration of 0.1 g!
- So for the next test the outriggers were placed on platforms. While lift off was possible this way, landing inevitably took place without those platforms, and the same dramatic sequence unfolded at all subsequent takeoffs. Bleed air was at a premium, so roll control was insufficient to keep the airplane level.
- The first successful hovers were possible after the outriggers were fitted with temporary extensions. Now it was time to try a conventional takeoff, starting with taxi tests. The landing gear fought back hard by exhibiting a large deadband in the nosewheel steering mechanism, followed by far too great sensitivity once control inputs exceeded this deadband. The resulting weaving made takeoffs impossible.
- When that was fixed, the main wheel brakes took over in prohibiting takeoffs. During the next taxi tests, a brake induced torsional oscillation developed and broke a main leg.
- After that it was the turn of the outriggers to act up. They were initially castoring, but showed a tendency to shimmy and finally had to be locked for flight.
Only in May 1961 was the first conventional take-off possible. The nosewheel steering system was barely useable, the brake judder was severe, the anti-skid often failed and the pilot could not feel that the wheels were skidding at any time. Several tyres were burst.
Source: John Farley's Harrier Development lecture.