Search the Community
Showing results for tags 'VTOL'.
Found 4 results
During the 1960s, both the USSR and NATO countries had many programs for the development of VTOL aircraft. Most of these never reach flying status, though a few did fly at least in prototype form. One of these was the Ryan XV-5 Vertifan. http://modelingmadness.com/scott/korean/xv5photoa.jpg Development of the XV-5 began on November 10, 1961, when the US Army issued a contract for the development of an aircraft using the lift-fan propulsion system. Primary contractors were General Electric and Ryan Aeronautics. The lift-fan system was quite different from other VTOL systems of the time, such as the lift jets found in the original MiG-23 prototype or contemporary VZ-4, for instance. Rather than the jet exhaust directly providing the thrust for vertical flight, the exhaust drives several fans, which provide the thrust for vertical lift. This has the advantage of not projecting hot exhaust gases downward, however, there are losses in efficiency due to the extensive ducting needed. The XV-5 (orignally designated VZ-11 at the start of the program) was powered by a pair of J85 turbojets, the same engines as found in the F-5. Maximum takeoff weight was 12,500 lb. Space for two crew members was provided. Two large lift fans were located in the wings, which provided most of the thrust for vertical takeoff. A smaller lift fan was located in the nose, which provided additional thrust as well as attitude control. The vanes on each fan could be pitched between -7 and 45 degrees to provide directional control while hovering. As the XV-5 would spend much of its time in hover, the test aircraft were fitted with helicopter style controls, to provide better handling while taking off and landing vertically. Two XV-5A test aircraft were formally accepted by the US Army on January 26, 1965, and began flight testing shortly afterward, at Edwards AFB. http://vertipedia.vtol.org/vstol/images/VSTOLWheel/pics/41.jpg The XV-5A demonstrated the ability to land and take off vertically, as well as successfully transition to horizontal flight (transition took place at about 170 km/h). However, there were some issues. The aircraft's ground attitude meant that taking off perfectly vertically was quite difficult; it require the pilot to release the brakes, adjust pitch controls, and change engine power simultaneously. Additionally, the aircraft was found to be difficult to control during the transition period, as there was no integrated control system for both modes of flight. Often, the XV-5A would pitch up or down for a few seconds as the transition occurred. Numerous other small issues were noted; many instruments were poorly placed, and cockpit temperature control was ineffective. More importantly, visibility downward was very bad when hovering. Oddly, a parking brake was not fitted to the XV-5A, which caused issues during testing. The XV-5A had decent conventional takeoff performance, with a takeoff run of about 800 meters needed. The aircraft also performed well during conventional landings. However, during vertical takeoffs and landings, severe turbulence was noted while in ground effect, making the aircraft difficult to control. This made it difficult to land in a precise spot (a major problem for an operational VTOL aircraft), and limited operations to when winds were less than about 10 km/h, obviously unacceptable for operational use. Another problem noted with vertical flight was that at high loads, the lift fans would reingest exhaust gases, leading to loss of power similar to vortex ring state. Despite these flaws, the XV-5A was judged adequate by the US Army as a research aircraft (however, it was recommended that these issues be fixed in follow-on research aircraft). The first XV-5A aircraft was lost in an accident on April 27, 1965, which unfortunately killed the pilot testing the aircraft. Investigation showed this was likely due to the pilot accidentally switching the aircraft from horizontal to vertical flight mode (the switch was located on the collective control for convenient access, which made it easy to activate accidentally). Testing continued afterward with the second prototype. Later in the testing, the XV-5 was considered by the US Army for use as a close air support aircraft or as a rescue aircraft (the lack of hot exhaust gases meant that it could hover over people without inadvertently frying them). The second fatal accident in the XV-5 program occurred in 1966 during testing of this capability. A rescue harness was ingested into the lift fan on the left wing of the XV-5A, damaging it. The pilot ejected, but was killed as the seat deployed horizontally due to the attitude of the aircraft during ejection. Later investigation showed that the damaged fan was still capable of producing enough lift to slow the XV-5's descent to a survivable rate. The XV-5A following the second crash. Following the crash of the second XV-5A airframe, it was decided to rebuild it into the XV-5B, and continue the test program with that aircraft. Numerous improvements were made to the systems of the XV-5 (including improved control systems and cockpit layout), correcting some of the deficiencies of the XV-5A. The aircraft was also repainted in NASA colors (the XV-5A had been painted in US Army markings.) i http://aviadejavu.ru/Images6/MY/MY77-6/10-3.jpg In addition to being used for testing of the VTOL characteristics and the lift-fan concept, the XV-5B was used for testing of approach procedures for VTOL aircraft. Particularly, the XV-5B was flown at steep approach angles of up to 20 degrees.The aircraft was flown successfully in this role, but it was found to be somewhat difficult for the pilot, as engine throttle, lift fan controls, and conventional flight controls all had to be manipulated to stabilize that approach. Testing of the XV-5B in this role was continued until 1971, when the aircraft was retired. It is currently on display in Fort Rucker, Alabama. http://cdn-www.airliners.net/aviation-photos/photos/7/1/7/2287717.jpg Video footage of the XV-5A Sources: PRELIMINARY PILOT QUALITATIVE EVALUATION OF THE XV-5A RESEARCH AIRCRAFT Lift Fan Aircraft - Lessons from Pilot's Perspective
During the latter part of the Cold War, the Yakovlev design bureau came up with quite a few designs for VTOL combat aircraft. While they weren't the most successful designs, they are pretty interesting, from both a historical and technical standpoint. The first of these is the Yak-36 (Freehand); While the Soviets had come up with numerous other VTOL designs in the 1960s, most of them used dedicated vertically mounted engines to take off vertically. However, the Yak-36 had a more modern arrangement, with two engines that used vectored thrust for both vertical and horizontal flight. The Yak-36 was powered by a pair of R27-300 jet engines (the same engines that powered the MiG-23 'Faithless' VTOL concept). In addition to providing vertical and horizontal thurst, the engines also provided airflow for 'puffers' at the wingtips, nose, and tail, which provided control in hover and low speeds (where aerodynamic controls would not be effective). The Yak-36 suffered from various difficulties during its development, among them the engines reingesting exhaust gases. At least two of the prototypes crashed at somepoint. Though the Yak-36 was at various points displayed with underwing armaments (such as rocket pods), it was never deployed to operational units; it was solely used as a testbed. Following the Yak-36 was the more widely known Yak-38 (Forger). It entered service in the early 1980s. Unlike the Yak-36, the Yak-38 was fitted with lift jets (two RD-36V engines). Though these engines did an adequate job of providing vertical lift, they had the drawback of being dead weight in horizontal flight. Horizontal thrust was provided by a single R27-300. Though the Yak-38 was capable of VTOL, it had highly limited performance; it was strictly subsonic, and had marginal payload capability. (pictured: unrestrained optimism) The Yak-38 was designed from the outset as a combat aircraft, intended to be deployed from the Soviets' Kiev class carriers. In this role, it was shit (much like your favorite anime). The first issue was reliability; many of the Forger's components proved to be horrendously unreliable, especially the lift jets. I've seen figures stating that the lift jets had an average lifetime of less than 25 hours, which leads me to suspect they were actually rebranded Jumo 004s. Engine failures were especially bad in the Yak-38 - a failure of a lift jet on one side would lead to the jet entering a fast, unrecoverable roll. The lift jets also had poor thrust in hot conditions; in many cases, the Yak-38 had to fly with only two pylons filled, rather than all four. Considering that the Yak-38 had no internal armament, this was not optimal. Interestingly, in addition to using it as a carrier aircraft, the Soviets also trialed the Yak-38 as a close air support in Afghanistan. This was less than successful; the Yak-38 was only capable of carrying a pair of 100kg bombs, markedly inferior to dedicated CAS aircraft such as the Su-25. Rumors of the Yak-38 being deployed to Colorado are false; Numerous variants of the Yak-38 were developed, most notably the Yak-38M, which despite having improved engines and other components, was still a dog. There was also the Yak-38U, a serious contender for the title of 'Ugliest Airplane'. In the late 1970s, development of a successor to the Yak-38 began. This aircraft was the Yak-41 (Freestyle). The general configuration of the Yak-41 was similar to the Yak-38, with a pair of lift jets in the fuselage and a single main engine for thrust. However, its capabilities were massively improved. While the Yak-38 was a strictly subsonic aircraft, the Yak-41 was capable of supersonic flight, setting many records for VTOL aircraft (under the fictional designation Yak-141). Additionally, it incorporated far more advanced materials in its structure (including large scale use of composites), as well as improved avionics (such as a radar set which was actually useful). Its payload capacity, in terms of weight, was roughly the same as what the Yak-38 could (theoretically) carry. However, given that the Yak-41 was a dedicated air superiority craft, this was less of a concern than the Yak-38s payload deficiency in the strike role. Unfortunately for the Yak-41, it began testing in the late 1980s, just as the Soviet Union was falling apart. Though some testing continued through the early 90s, the Yak-41 never entered operational service. The second nail in the Yak-41s coffin was the Soviet Union / Russian Federation's acquisition of larger aircraft carrier(s), capable of operating aircraft such as the Su-27K and MiG-29K. Interestingly, for a few years in the early 1990s, Yakovlev collaborated with Lockheed Martin on the development of the Yak-41. This has given rise to many conspiracies about the F-35B being a clone of the Yak-41. While this is obviously false, it wouldn't be outside the realm of possibility that a few bits on the JSF might have drawn inspiration from Yak's design in some way. There was one final successor to the Yak-41; the Yak-43. An even more advanced evolution, the Yak-43 could have been quite capable (had it been built). From what I can find, it dispensed with the extraneous lift jets. Power would have been provided by a modified NK-32 turbofan, the same engine that powers the Tu-160. This would have given the Yak-43 significantly improved performance and payload capacity compared to its predecessors. Additionally, the Yak-43 would have incorporated low observability features into its design, bringing it closer to being a true competitor to aircraft such as the F-35B. In any case, the aircraft remained unbuilt, and I have not heard of any efforts to revive the design.
Just about everyone has heard of the (in)famous F-35B VTOL aircraft, along with its predecessor the Harrier. The Soviets also dabbled in vertical takeoff aircraft throughout the latter half of the Cold War. However, did you know that during the 1960s, NATO seriously considered developing a supersonic VTOL strike fighter? It was thought that airbases would become unusable after the first hours of the war, so having a VTOL strike aircraft would allow NATO to continue striking at Soviet ground forces. Numerous designs were proposed. One of the most sane the P.1154. (a conceptual image of the P.1154) The connection between the P.1154 and the Harrier (via the Kestrel prototype) is easy to see. The P.1154 was itself developed from the earlier P.1150, the original contender for the NATO strike aircraft competition. Like the Harrier, the P.1154 uses a single engine to provide thrust for both vertical takeoff and horizontal flight. This is in contrast to most designs of the era, which used dedicated lift jets. Though the P.1154 was never built, it was a major technological step in the development of VTOL aircraft. The Mirage IIIV is clearly derived from the highly successful Mirage III airframe. However, it can be seen that lift jets have been added in the fuselage aft of the cockpit. No less than eight (!) lift jets are located in the fuselage, in addition to the single main engine. This would certainly have been a maintenance and reliability nightmare, especially in the austere environment of an ongoing (possibly nuclear) conflict. Unlike the P.1154, the Mirage IIIV actually made it to flight status, with two prototypes undergoing testing during the 1960s. The West German VJ101 was an attempt to convert the F-104 Starfighter into a VTOL aircraft. Like the Mirage entry, the VJ101 had lift engines (two in the central fuselage). However, it also had pairs of engines in swiveling pods on the wingtips, which could vary their angle to direct thrust downward or forward (similar to the Bell D-188A. Like the IIIV, the VJ101 made it to flight, and was tested extensively (it has been claimed that the aircraft was capable of supersonic flight without afterburner). With six engines, including four in moving nacelles, the VJ101 would also have been difficult to maintain and keep active. The G.95/6 was the Italian entry (read more about it here). It was the ultimate development of the G.95 VTOL design, which went through several iterations (the G.95/3 resembles a VTOL F-101). In terms of layout, it was closest to the Mirage IIIV, with main engines for forward thrust (two of them) augmented by multiple lift jets (six in this case). Like the other VTOL aircraft, it would have been difficult to maintain, produce and keep reliable. Additionally, like the French and German designs (and the Yak-38), it would have suffered all of the drawbacks associated with lift jets, namely that they are dead weight for 90% of the flight. The failure of the NATO Supersonic VTOL program of the 1960s shows the difficulty in making VTOL practical for a military aircraft. It would take until the 1970s for a subsonic VTOL combat aircraft to be successful (the Harrier), and until the 2010s for a supersonic VTOL aircraft to become workable.