In anticipation of the RFP, all interested manufacturers had preliminary designs underway that could meet the anticipated RFP performance requirements.  Chance Vought assembled a team of aircraft companies with VTOL aircraft experience.  They were Hiller Aircraft Company and Ryan Aeronautical company. The applicable experience of this team was as follows:

• Chance Vought: A Navy prime contractor with major program management experience and with large, skilled engineering and manufacturing departments.
• Hiller:  Had flown a tilt-wing concept demonstrator (X-18) which flew conventionally but with wing-tilt constrained by flow separation over the wing causing unacceptable vibration. Also had gear box design and manufacturing capabilities.
• Ryan:  Successfully designed and flew a V/STOL concept demonstrator (XV-5A) lift fan.

The V/STOL transport proposed to the three services was given a Chance Vought designation “VHR-447”. VHR was the acronym for Vought-Hiller-Ryan, the proposal team. The number "447" was the Vought preliminary design sequence number given to company major configuration studies.

Previous design studies by Vought had determined that a tilt-wing aircraft configuration would meet the anticipated RFP requirements. Four engines and propellers provided the necessary power with a tail propeller added for low- speed control.  A typical RFP aircraft-sizing requirement is shown below:

• Warm-up, take-off, accelerate, 5 minutes at normal power
• Cruise out; 200 nautical miles, sea level, 250 knots
• Hover; sea level, 10 minutes, unload half of payload
• Cruise back; 200 nautical miles, sea level, 250 knots
• Reserve; 10 percent of initial fuel
• Payload; 8,000 pounds

The Navy requirement for a V/STOL aircraft that was “carrier suitable” was a major constraint on the aircraft size and shape. Navy carrier aircraft must fit on a carrier elevator, which absolutely constrains aircraft length, width and height.  The VHR-447 was proposed with a rather flat nose and with wing, tail and tail propeller- boom fold features that satisfied this requirement.

The VHR-447 proposal included mechanisms that would allow the pilot’s flight controls to function identically in both forward flight (wing down) and hover (wing up). In hover, aileron control surfaces provided yaw power, differential propeller thrust provided roll control, and collective propeller thrust provided altitude control by means of a helicopter-type collective-pitch stick. Horizontal tail incidence was positioned leading edge up.

Flight Control Utilization

Control Function Cockpit Function Flight Mode Hover              Transition              Cruise Roll Lateral Stick Differential Collective Differential Collective & Ailerons Ailerons Yaw Pedals Ailerons Differential Collective, Ailerons & Rudder Rudder Pitch Longitudinal Stick Tail Propeller Tail Propeller & Horizontal Tail Horizontal Tail

Pitch power was provided by a tail propeller powered by a hydraulic clutch from the main cross-shaft system.  All of these flight control functional changes were accomplished with a mechanical “mixing linkage’ slaved to wing position except that  the tail propeller clutch was activated by the pilot through separate clutch controls.A cross-shaft system between the engines provided power to all four propellers in the event one or more engines were shut down.  Two engines powering four propellers was the most efficient cruise configuration.

As a result of the Tri-Service evaluation of all proposals, the design development contract for five airplanes was awarded to Vought for the VHR-447.  The aircraft military designation was XC-142A. The U.S. Air Force was the procuring activity. The contract was signed in early 1962 with first flight specified for July 1964.

During the XC-142A program, a total of 420 hours were flown in 488 flights.  The five  XC-142A’s were flown by 39 different military and civilian pilots.

 XC-142A:

VHR-447 V/STOL Proposal
XC-142A Design/Development Program
The Military Operational Test Program
NASA Operations