User:Dr Bertelsen/Sandbox

I. Principle
Deflected Slipstream is a an approach to creating an airplane that can take off and land vertically (VTOL), or at least with a very short runway (STOL). 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.

II. History
A. Preliminary'

The beginning of this approach to vertical flight was the wing  flaps developed during the period of WWI and afterwards. These flaps were designed to add lift to the plane.

B. Research sponsored by NACA in the USA

In the period after WWII, when the U.S. National Advisory Committee on Aeronautics (NACA) ponsored research on a fairly large number of approaches to vertical flight, the deflected slipstream approach was investigated through models, wind tunnel tests and construction of full scale aircraft. It was one of a number of S/VTOL technologies that  NACA sponsored in the 1950s, which have been summarized by Mike Hirschberg in his “Wheel of Misfortune" chart.

1. Wind Tunnel Explorations

In 1956 Robert Kirby explored the effectiveness of wings with large-chord flaps in deflecting propeller slipstream downward through the large angles needed for vertical takeoff.

The tests were carried out at the NACA Langley in Virginia on a model situated  in the free-flight wind tunnel facility. The span of the model's wings was approximately equal to the theoretical diameter of the propeller slipstream, i.e. 70% of the propeller diameter (24 inches [61 cm]). Robert Kirby summarized his research on deflected slipstream in NACA Technical Note [TN] 3800 : “The investigation showed that it was possible to turn the propeller slipstream 90° so that the resultant-force vector of the wing-propeller combination was normal to the propeller shaft and was 80 percent of the magnitude of the propeller thrust. When the model was near the ground, the slipstream was turned only about 75°, but the resultant force increased to about 88 percent of the thrust. The resultant force was reduced about 10 percent when a fuselage was added to the wing system.” He added in his conclusion, “End plates with an approximately semicircular shape on each wing (defined by the upper surface of the wing with the flaps deflected and a tie between the leading and trailing edge) were essential for obtaining high turning angles and efficiency. Larger end plates showed no improvement in the turning effectiveness of the wing system”.

Below is the schematic he used to illustrate the deflected slipstream principle.

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 last word on this craft remained: “Flight tests with the Ryan VZ-3RY V/STOL deflected-slipstream test vehicle have indicated that the concept has some outstanding advantages as a STOL aircraft where very short take-off and landing characteristics are desired. An adverse ground effect, brought about by the recirculation of the propeller slipstream,severely restricted operation at very low airspeeds.”

b. The Fairchild M-224-1VZ-5FA

Fairchild Aviation, which had been building aircraft since the 1920s was contracted by the US Army in the late 1950s build the VZ-5, another airplane attempting vertical flight with the deflected slipstream principle. NASA Technical Memorandum, TM SX-805, authored by Marvin P. Fink describes the results of the testing of this deflected slipstream aircraft at the Langley wind tunnel.

The summary of the investigation said the testing results for the VZ-5 were not favorable: The investigation showed that the airplane was unstable over the speed range and could not be trimmed about the actual center of gravity at 0.64 chord for the low speed. In order to provide a reasonable degree of longitudinal stability for the basic airplane configuration and a bare capability of trim over the flap deflection range, it would be necessary to ballast the airplane to move the center of gravity far ahead of its actual location. About 700 pounds of weight added to the cockpit area would be necessary to move the center of gravity the required amount. The airplane can develop a hovering lift of about 4,000 pounds which is approximately equal to its weight. The airplane had very high effective dihedral which, coupled with the certain directional instabilities, would be expected to produce highly undesirable flying qualities.”

Since the VZ-5 was only ground and wind tunnel tested, exactly how those “undesirable flying qualities” would have become manifest in test fights never became known.

c. The Robertson VTOL

A third attempt to utilize deflected slipstream to give an airplane VTOL capabilities was built by the Robertson Aircraft Corporation in 1956 and 1957. It was never flown off tether.

III. Current Efforts
The three craft presented above represent NASA's efforts to employ the deflected slipstream approach to vertical and short take off take offs and landings (V/STOL). Since only the Ryan VZ-3RY left the ground and its did not perform well in purely vertical operations, no true VTOL craft based on the deflected slipstream was developed during the period of NACA and NASA research in the 1950s and 1960s.

One researcher, operating on his own resources has continued to look at this approach to a VTOL airplane, and has spent over five decades of his time in a quest for a deflected slipstream  airplane with vertical capabilities. In those years, he has proposed a radically different wing shape – which he calls the arc wing – and has performed his own tests, augmented by university wind tunnel tests, to determine the viability of his approach.

This researcher, Dr. William Bertelsen, and his son William D. Bertelsen, continue to experiment with the deflected slipstream method of vertical flight, and have built small models, kites, parasails and ultra lights as part of their research. To date, they have not built a full scale model of the design, which is shown below:

Features of the craft, such as the arc wing, and the flaps to deflect the propeller slipstream can be seen in this drawing.

IV. Footnotes
1. U.S. Centennial of Flight Commission, “Slotted Wings, Flaps, and High Lift Devices”, Centennial of Flight http://www.centennialofflight.gov/essay/Evolution_of_Technology/High_Lift_Devices/Tech6.htm

2. Hirschberg, Michael J., “V/STOL History Overview Brief”, http://www.vstol.org/brief.htm

3 Kirby, Robert H., NACA TN 3800 “Exploratory Investigation of the Effectiveness of Biplane Wings with Large-Chord Double Slotted Flaps in Redirecting a Propeller Slipstream Downward for Vertical Take-Off”, http://cafefoundation.org/v2/pav_tech_lib.php

4 Draper, John W; Kuhn, Richard E, “Some effects of propeller operation and location on ability of a wing with plain flaps to deflect propeller slipstreams downward for vertical take-off”, NACA TN 3600, 1955. http://hdl.handle.net/2060/19930084500

5 James, Harry A., Wingrove, Rodney C., Holzhauser, Curt A., Drinkwater, Fred J. III, “Wind-Tunnel and Piloted Flight Simulator Investigation of a Deflected-Slipstream VTOL Airplane, The Ryan VZ-3RY”, NASA TN D-89, November 1959. http://hdl.handle.net/2060/19890068209

6 Turner, Howard L. and Drinkwater, Fred J. III, “Some Flight Characteristics of a Deflected Slipstream V/STOL Aircraft”, NASA TN D-1891, 1963. http://hdl.handle.net/2060/19630008786

7 Fink, Marvin P., “Full-Scale Wind-Tunnel Investigation of the VZ-5 Four-Propeller Deflected-Slipstream VTOL Airplane”, NASA TM February 1963, SX-805,    http://hdl.handle.net/2060/19980228393

8 Hirschberg, Michael J., “V/STOL History Overview Brief”, http://www.vstol.org/brief.htm

9 Bertelsen, William R., “50 Years of Aeronautical Research by Aeromobile Inc",American Institute of Aeronautics and Astronautics (AIAA)Aerospace Sciences Meeting and Exhibit,            Reno, NV, Jan 2007. http://www.aeromobile.com/50%20Years%20of%20Aeronautical%20Research%20by%20Aeromobile%20Inc.pdf

V. External References
http://www.vstol.org International V/STOL Historical Society

http://cafefoundation.org Cafe Foundation

http://ntrs.nasa.gov/search.jsp NASA National Technical Reports Server

http://www.centennialofflight.gov/index.cfm US Centennial of Flight Commemoration

http://www.aeromobile.com/History%20of%20Deflected%20Slipstream%20VTOL%20Aircraft.pdf History of Deflected Slipstream VTOL Aircraft, by William D. Bertelsen, delivered at The American Helicopter Society, 61st AnnualForum, Grapevine, TX, June 1-3, 2005

http://www.aeromobile.com Aeromobile Inc.