Vertical take-off, vertical landing and hovering in the air together with the possibility of achieving high aerodynamic speeds is the ideal of the dream of flying. Reducing the size of large airports, getting rid of long, expensive runways for take-off, making the aircraft as independent of airports as possible and gaining height fast are another dream. In the Sixties, the magic word to solve this problem was known as VTOL (Vertical Take-off and Landing).
Of the three vertical planes built in Germany, two must be pointed out. On the one hand the only VTOL aircraft so far, the Dornier Do31 and on the other hand the only supersonic take-off aircraft, the EWR VJ101C. The design teams of the German companies Bolkow, Heinkel and Messerschmitt formed a consortium in 1959 named Entwicklungsring Sud [Souther Development Circle] to develop a Mach 2 VTOL intercepto. Heinkel left the consortium in 1964, and in the following year the consortium re-formed as a company with the title Entwicklungsring Sud GmbH, known more usually as EWR. [The Entwicklungsring Nord (Northern development circle) - abbreviated ERNO, was a totally underelated consortium of Focke Wulf, Weserflug and Hamburger Flugzeugbau, formed in 1961 for rocket development].
The VJ 101 C featured tilting engines for increased thrust, reheat for takeoff, simple translation, triangular decentralization of the engines for thrust modulation, and moderate ground effects. Two experimental aircraft were built, with and without reheat, capable of Mach 2 and Mach 1.04, respectively. The mechanical flight control system and tests were conducted both for hover rig and flight configurations. Ground suction, acoustic and thermal loading, sodium silicate coatings to avoid ground corrosion, and recirculation were considered. Results of the follow-on project to the VJ 101 C, the AVS, which was developed by NASA, suggested that trends toward thrust-to-weight ratios exceeding one, in concert with low wing loading, favor the development of V/STOL aircraft.
Two thrust units were built in the end of the wings and in the front area of the fuselage. The triangular arrangement resulting from this proved to be beneficial for vertical flight and hovering and also meant that the fuselage was not filled with the thrust units unnecessarily.
Both thrust unit pairs at the wing ends were placed in a cradle which could be swivelled in a horizontal direction. In the vertical position they served as lift jet engines during vertical take-off and after swivelling during the transition into horizontal position they served as cruising engines. The two thrust units behind the cockpit served as pure lift jet engines and were switched off during aerodynamic flight.
All thrust units (during hover flight 6, aerodynamic flight 4) were operated with a joint performance lever. To move the aircraft during hover flights around the longitudinal and transverse axes, the so-called thrust modulation was used for the thrust difference between the cradle and lift jet engines for the entire flight range - hovering, transition and aerodynamic flight. The pilot was supported during hovering by a hover mode autopilot basing on a gyroscope.
Experimental application equipment for the preparation of remote landing and take-off sites for turbo-jet VTOL aircraft was designed, fabricated and demonstrated. Three full scale remote sites were prepared in England and the Federal Republic of Germany. Evaluation of these sites was accomplished with the P.1127 and the VJ101C-X2 aircraft respectively. These remote sites were prepared by spraying a modified chlorinated polyester resin and fiberglass roving over essentially unprepared ground. Modifications to the application equipment, further development of materials and fabrication techniques were made as a result of the experience gained in the preparation and evaluation of these remote sites. Preliminary remote site design criteria were developed for determining site thickness, site size and shape. Experimental pads were prepared over various soil types and tested using typical wheels and tires to obtain data for determining site strength requirements. A methodology for determining site size and shape was further refined by conducting downwash flow field studies using models of the P.1127, VJ101, XC-142 and DO-31 aircraft.
The artificial stabilization of an aircraft requires a fully electrical control system. Such control systems were used in VTOL combat aircraft (VJ 101, VAK 191), although only for short-term use. In conventional aircraft design, the size and position of wings and control surfaces and the arrangement of these surfaces with respect to the aircraft's center of gravity are selected in such a manner that the aircraft exhibits satisfactory maneuverability in all degrees of freedom in any possible flight situation and that the various modes of elastic and flight-mechanics oscillation have an adequate natural stability. It is selfevident that the performance and costs-effectiveness of an aircraft are considerably impaired by the necessity of satisfying these requirements. If the requirement for inherent stability is eliminated, new possibilities for aircraft design arise which promise further performance enhancement.
Control of VTOL aircraft in hover and low-speed flight has been an important item in pacing the development of this type of aircraft. The required reaction forces for attitude control during hover have commonly been achieved by the use of engine compressor bleed air method, used on early jet lift VTOL aircraft such as the Shorts SC-1, Bell X-14A, and Lockheed XV-4, has been successful whenever a sufficient quantity of bleed air was available. Subsequently, particularly forlarger VTOL aircraft such as the EWR VJ-101 and Dornier DO-31, engine thrust was used directly for control. Advantages of improved efficiency and lighter weight, but when it is used, certain items should be considered carefully to insure satisfactory handling qualities.
Up until August 1964 the VJ101C-X1 was thoroughly tested in nearly 130 tests with 40 aerodynamic flights, 24 hover flights and 14 full transitions. During these tests the sound barrier was broken, for the first time by a vertical take-off aircraft. On September 14, 1964 the test aircraft X-1 crashed due to an avionics problem.
The tests were subsequently continued with the 2nd prototype VJ 101C-X2, which differed in many details from the VJ 101C-X1, and in contrast to the X-1 was already equipped with the high performance exhaust reheater jets. The VJ 101C X2 flew its first hovering free flights on 12 June but did not attempt to use its afterburning capabilities for vertical takeoffs until 10 October 1964; within two weeks, the VJ 101C X2 demonstrated complete transitions from vertical to horizontal flight and back to a vertical landing using afterburning. It suffered from high temperature and erosion issues, and crashed when it ingested hot exhaust gases and suffered a significant thrust loss while attempting to land on an elevated platform.
The rotating nacelle design was abandoned, and the proposed follow-on, the VJ 101D, dispensed with the wingtip-mounted engines but retained the lift plus lift/cruise propulsion concept. Its use of RB.162 five lift engines and two aft fuselage RB.153 lift/cruise engines (with internal thrust deflectors) was very complex and the VJ 101D was canceled after engine testing had begun.
EWR VJ 101C-X1
6 Rolls Royce RB-145 with 1,250 kp each (start take-off trust)|
2 thrust units in the fuselage
2 thrust units each in the swivellable thrust cradles at the end of the wings
|Top speed||Mach 1.08|
|Take-off weight||6,000 kg|
EWR VJ 101C-X2
|Power plant||Lift engine (in the fuselage)||2 Rolls Royce RB-145 with 1,250 kp each (start take-off trust)|
2 Rolls Royce RB-145 with exhaust reheater switched on 1,610 kp each (start take-off trust)|
without exhaust reheaters 1,205 kp each (start take-off trust)
2 cruise engines each in swivellable thrust units cradles at the wing ends
|Top speed||upper supersonic range|
|Take-off weight||8,000 kg|
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