page_title: Deflected slipstream
section_title: The Ryan Model 92 Vertiplane VZ-3RY
hierarchical_section_title: Deflected slipstream / Prototypes / The Ryan Model 92 Vertiplane VZ-3RY
caption_attribution_description: English: Deflected Slipstream prototype VZ-3RY on runway, flaps down
context_page_description: Deflected slipstream is an approach to creating an aircraft that can take off and land vertically, or at least with a very short runway. The basic principle is to deflect the slipstream from one or more propellers approximately 90 degrees, to create an upward thrust for vertical takeoff and a downward air cushion for landing. Once airborne, the flaps are retracted so the airplane can fly horizontally.
context_section_description: The Ryan VZ-3 was a deflected-slipstream aircraft intended for total VTOL capability.   The VZ-3RY project started in 1957 when Ryan Aeronautical Company was contracted by the U.S. Army to develop and build a flying craft with V/STOL capability.
  The airplane had a short wingspan with large-chord double-slotted flaps, powered by a 825 horsepower (615 kW) shaft turbine. The engine drove the opposite rotating twin wooden propellers.  Each prop was 9 feet 2 inches (2.79 m) diameter.
  Results of the testing of this  craft were first published November 1959 in the NASA TN D-89  of the Ames Research Center at Moffett Field, California. In Figure 12 above, the airplane is mounted with the trailing edge of the flaps at an altitude of 17 feet (out of ground effect). To quote the authors of TN D-89,
   “The major objectives of the wind-tunnel study were to determine if the machine could achieve steady-state VTOL operation; to determine under what conditions  operation would become impossible or unsafe from either an aerodynamic or structural limit; and to obtain the information necessary for the piloted motion simulation of the aircraft…. The major portion of the tests was directed toward conditions and forces simulating level unaccelerated flight, that is, lift about equal to the airplane weight (2625 lb) and drag about equal to the horizontal thrust component.”
  
  They found that a diving moment materialized as the aircraft in hover mode approaches the ground from 16 feet (4.9 m) or less, even if the flaps are not fully employed. When those flaps are deployed, the diving moment becomes even more serious: 
  “The primary effect of approaching the ground during hovering was a pitch-down moment beyond the trimming capabilities of the longitudinal control. This moment was brought under control by the addition of a leading-edge slat.”
  But, the addition of this slat also created pitch instability when forward flight was attempted.
  
  In a later technical note, in 1963, designated NASA TN-D-1891, authors Howard L. Turner and Fred J. Drinkwater III  concluded: 
  “The Ryan VZ-3RY test vehicle was flight tested over the airspeed range from 80 knots to below 6 knots. The deflected slipstream concept proved to be better suited to STOL than VTOL operation. Adverse ground effects prevented operation close to the ground at speeds less than 20 knots and below approximately 15 feet in altitude. Steep glide slopes to landing (up to –16°) at approximately 40 knots were achieved, but steep, slow, descending flight did not appear feasible. Full-span leading-edge slats markedly increased the descent capability and reduced the minimum level flight speed.”
  The inability to descend in true vertical fashion and unresolved issues as the craft approach the ground, known as “adverse ground effect”, seemed to eliminate consideration of this craft as a VTOL contender.  As they investigated the vehicle's behavior as it approached the ground, and became subject to the “ground effect”, they found:
  “The mechanism of the ground effect appears to be that the deflected slipstream is recirculated through the propeller disc as turbulent air, producing in part, a loss in propeller efficiency, hence, a loss in slipstream velocity and a reduction in turning effectiveness. A loss in lift results from the lowered slipstream velocity and the aircraft sinks rapidly into the ground. It was not possible to check the descent with application of power. A loud slapping noise from the propellers accompanies this loss in lift. The aircraft did not exhibit any tendency to pitch abruptly when entering into ground effect. However, under cross-wind conditions, asymmetric losses in lift were experienced, resulting in abrupt sideslip or abrupt banking of the aircraft just prior to ground contact.”
  
  The VZ-3RY did exhibit strong STOL features, as can be seen in the photo above, where the airplane takes off in a very short distance.  But, there were a number of obstacles to true vertical (or VTOL) flight, and research on the craft did not continue to see if these obstacles could be overcome.  The las
caption: Deflected slipstream prototype VZ-3RY on runway, flaps down
exif: {}