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  1. LostCosmonaut

    Advanced MiG-3 Variants

    Intro The MiG-3. All flying aircraft today have been re-engined with the V1710, and look slightly different. The MiG-3 was one of the first fighters developed by the famous Mikoyan-Gurevich design bureau. An improvement on the troubled MiG-1, the MiG-3 was designed for combat at high altitude. Introduced in 1941, it gained less fame than its contemporaries like the Yakovlev and Lavochkin fighters. Germany's virtually nonexistent strategic bomber force, and the low-altitude nature of combat on the Eastern Front meant the MiG-3 was forced out of its element, and its performance suffered. Combined with the MiG's difficult flight characteristics and the horrible strategic situation for the Soviets in 1941, this meant the MiG-3 achieved little success. While the MiG-3 did not spawn a successful series of fighters (like the Yak-1, Yak-9, and Yak-3, for instance), numerous variants were considered, and many of them were built in at least prototype form. However, for many reasons, such as lack of need or nTheonavailability of suitable engines, none of these variants entered large scale production. I-230/MiG-3U The resemblance to the baseline MiG-3 is easily seen. via aviastar The I-230 was one of the more straightforward developments of the MiG-3. Development on the I-230 (also known as the MiG-3U) began in late 1941, with the objective to correct numerous flaws identified in the MiG-3. First was the armament; the MiG-3 had only two 7.62mm ShKAS machine guns and a single 12.7 Berezen (BS) machine gun, firing through the propeller. On the I-230, these were replaced with two 20mm ShVAK cannons (again synchronized to fire through the propeller). Outwardly, the I-230 looked very similar to the production MiG-3, although the new aircraft was made mostly of wood instead of steel tubing and duralumin. The wing area and wingspan were increased (to 18 m^2 and 11 meters, versus 17.4 m^2 and 10.2 meters for the production MiG-3), and the fuselage was lengthened by .37 meters. Soviet engineers originally intended to fit the I-230 with the AM-39 engine. However, by the time the I-230 airframe was completed in early 1942, the AM-39 was not yet available. As a result, the first I-230 was forced to use an engine built from both AM-38 and AM-35 parts (designated AM-35A). This engine was roughly 40 kilograms heavier than the intended engine, but produced a respectable 1350 horsepower. Even with such an odd engine, the I-230 flew by the end of 1942, achieving a top speed of over 650 km/hr at altitude. (Some sources say the I-230 first flew in May 1943, this is likely for the machines with AM-35A engines). Four more prototypes were built with AM-35A engines. These aircraft would serve in defense of the Moscow region while undergoing flight testing. While the design showed promise, by this point the AM-35 was obsolete and out of production. Additionally, some other deficiencies were identified. The I-230 was found to be difficult to land (a flaw shared with the MiG-3), and the engine tended to leak oil into the rest of the aircraft at high altitudes. As a result, the I-230 was not built. I-231 The I-231 was a further evolution of the I-230, using the AM-39 engine that had originally been intended for use in the I-230. One of the I-230 aircraft had its engine replaced with the more powerful AM-39. This required modification of the cooling system; the radiator was enlarged, with another secondary radiator installed. There were also a few other modifications, such as moving the horizontal tail surfaces downward slightly, the fuselage fuel tank was enlarged and some modifications to the radios. Armament was the same as the I-230; two 20mm ShVAK cannons. First flight of the I-231 was in October 1943. However, in early November, the prototype was forced to make an emergency landing after the supercharger failed at high altitude. Two weeks later, flight testing of the repaired I-231 resumed. The prototype, with the more powerful AM-39 (1800 horsepower), reached a top speed of 707 km/hr at an altitude of about 7000 meters. It also climbed to 5000 meters in under 5 minutes. Flight testing continued in early 1944, and in March, the I-231 was damaged after overrunning the runway during landing. The program suffered another setback when the repaired I-231 suffered an engine failure, damaging the precious AM-39 engine. Following this last mishap, work on the I-231 was discontinued. The similarities between the radial and inline engined models are still visible. via airvectors I-210/MiG-9 M-82 I-210 with radial engine. via airpages.ru The I-210 was a more substantial modification of the MiG-3 which began in the summer of 1941. Production of the Shvestsov M-82 radial engine had recently begun, and many design bureaus, including MiG, were instructed to find ways to incorporate the engine into their designs. In the case of the MiG-3, this was especially important, as the Soviet government sought to discontinue the AM-35 to free up production space for the AM-38 used by the all-important Il-2. In theory, the M-82, with 1700 horsepower, would provide a significant performance increase over the AM-35. Soviet engineers projected that the M-82 equipped MiG-3 (now known as the I-210) would reach nearly 650 km/hr at altitude. It was also projected that performance would be massively improved at low altitude, important for combat on the Eastern Front. The new aircraft was received the designation “MiG-9 M-82”, denoting that it was a substantially new type (this designation would later be reused for a twin-jet fighter in the late 1940s). In addition to fitting of the M-82, there were several other differences between the MiG-3 and the I-210. Armament was increased to three 12.7mm UBS machine guns (two 7.62mm ShKAS were fitted initially, but soon removed). Several systems related to the engine, including the oil coolers and fuel system were also updated. The fuselage was widened slightly to accommodate the new engine. The I-210 first flew in July 1941. However, it became quickly apparent that it was not meeting its performance targets. The top speed at an altitude of 5000 meters was a mere 540 km/hr, far inferior to to projects (as well as the production MiG-3!). Part of this was due to having a different model of propeller installed than what was intended. However, wind tunnel testing and inspection showed that the engine cowling was poorly designed and sealed to the rest of the airframe, causing significant drag. Several months were required to correct the various defects, and it was not until June 1942 that three I-210s were ready for trails. During testing, the three aircraft were assigned to the PVO for use on the front. State trials began in September, and the I-210 fared poorly. Maximum speed was still only 565 km/hr, far inferior to existing types. Overall, the I-210 was judged to be unsatisfactory and inferior to the La-5 and Yak-7. The aircraft did not enter production, although the three completed prototypes would serve in Karelia until 1944. I-211/MiG-9E The failure of the I-210 was not the end of efforts to install a radial engine into the MiG-3 airframe. In late 1942, work on the I-211 began. A new Ash-82 engine, an improved variant of the M-82 installed on the I-210, was fitted. With the help of the Shvetsov bureau, the aerodynamics of the engine and its cowling were substantially improved. Further modifications reduced the empty weight of the “MiG-9E” by 170 kg. The three 12.7mm machine guns were replaced by two 20mm ShVAK cannons. Testing of the I-211 began in August 1942 (other sources variously say that testing did not begin until early 1943, my interpretation is that this is when state trials officially happened). Performance was markedly superior to the I-210; the I-211 reached a top speed of 670 km/hr, and was able to climb to altitudes in excess of 11000 meters. However, the La-5, which was already in production using the M-82 engine, had similar performance. Moreover, the La-7 was in development, and was felt to have better potential. In all, only ten I-211s were built. Interestingly, at least one source claims that a variant of the I-211 equipped with a Lend-Lease R-2800 engine was considered. There is no evidence that such an aircraft was actually built. I-220/MiG-11 The I-220 (and the rest of its series up to the I-225) were substantially different from the production MiG-3, sharing little aside from the basic design and concept. These aircraft took the original mission of the MiG-3, interception of targets at high altitude, to the ultimate extreme. The initial request that led to development of the I-220 was issued in July 1941, in response to high-altitude overflights by Ju-86P reconnaissance aircraft. These aircraft, capable of operating at over 13000 meters, were outside the reach of almost any Soviet fighter. A few Ju-86Ps at slightly lower altitude were intercepted by MiG-3s before the start of the war, so the MiG-3 was a natural starting point for a high-altitude interceptor. Work on the I-220 prototype began in late 1942. Originally, it had been planned to install the AM-39 engine, but it was not ready at the time construction began on the prototype. Instead, one source (OKB MiG, Page 48) states anAM-38F engine was installed, which still provided more power (1700 hp) than the AM-35 on the MiG-3. However, it had the drawback of losing power at high-altitudes; the AM-38F would be an interim installation at best. A different source reports that an AM-37 was the first engine installed. In addition to the new engine, the wingspan was lengthened by .80 meters, with a slight sweep added to the outer portion of the leading edge. The radiator was relocated from the belly of the aircraft to inside the wing center section, with new air intakes added at the wing roots. Armament was increased to four ShVAKs, making the I-220 one of the heaviest armed Soviet fighters. The I-220 first flew in January 1943. Testing of the aircraft proceeded, as the AM-39 was still not yet ready. Despite being handicapped by the AM-38F engine, the I-220 prototype was still able to reach 650 km/hr during testing in January 1944. It was agreed that the aircraft had potential, but would need the AM-39 to reach its maximum performance. The second I-220 prototype was eventually fitted with the AM-39, but by that point it had been decided to substantially redesign the aircraft. I-220 vs. I-221 I-221/MiG-7 While the I-220 had done well, it had not been able to reach the altitudes its designers had hoped for. Numerous changes would be required to get the best possible performance out of the airframe. The most obvious area for improvement was the engine. Rather than the AM-38F, an AM-39A with a turbocharger was installed. Not only was the AM-39 more powerful than the AM-38, but the twin turbocharger would allow the engine to continue developing power at altitude. Additionally, the wingspan was increased further, to 13 meters. Armament was reduced to two ShVAK cannons, to save weight. Significantly, the I-221 was fitted with a pressurized cockpit, to allow the pilot to survive at extreme altitude. By the time the I-221 made its first flight in December 1943, the Ju-86 threat had disappeared. One of the high-altitude intruders had been intercepted by a Yak-9PD (a high-altitude version of the Yak-9 designed and built in three weeks), though it had not been destroyed, overflights ceased. Nevertheless, the Yak-9PD was very much an interim solution, armed with only one ShVAK and requiring 25 minutes to climb to 12000 meters. So, development of the I-221 continued. The test program of the I-221 was cut very short. On the eighth flight of the aircraft, in February 1944, the pilot bailed out at altitude, after seeing flames coming from the turbocharger and smoke in the cockpit. The pilot survived unharmed, but obviously the I-221 was completely destroyed. I-222/MiG-7 Side view of I-222. via ruslet.webnode.cz The I-222 was a continued development of the I-221. Not only did it have several additional performance improvements, but it was the closest of MiG's high altitude fighters to a “production ready” aircraft. The AM-39A engine was replaced with a more powerful AM-39B, with twin turbo-superchargers, plus a new four-bladed propeller. An improved intercooler was also installed (clearly visible under the central fuselage). To improve the I-222's potential utility as a combat aircraft, 64mm of armored glass was installed in the windscreen, and the cockpit pressure bulkheads were reinforced with armor plate. The fuselage contours were also modified to give the pilot better rearward visibility. Armament was two B-20 cannons, replacing the ShVAKs. The I-222 made its first flight in May 1944. Relatively little testing was done before the aircraft went to the TSAGI wind tunnel for further refinement. It emerged in September and underwent further testing. Test flights proved that the I-222 had truly exceptional performance. A speed of 691 km/hr was reached, quite respectable for a piston-powered aircraft. The truly astonishing performance figure was the ceiling of 14500 meters, well in excess of any German aircraft (save for the rare and latecoming Ta-152H). Though the I-222 could likely have been put into production, Soviet authorities assessed (correctly) that by late 1944 there was little threat from high-altitude German aircraft. Nuisance flights by Ju-86s were of little consequence, and German bomber programs such as the He-274 universally failed to bear fruit. Testing of the I-222 continued through late 1945, when the program was cancelled. I-224/Mig-7 As can be seen the I-224 is similar to the I-222. From OKB MiG by Butowski and Miller The I-224 was a development of the I-222 with an improved AM-39FB engine. Several other minor improvements, such as an improved propeller and modified cooling system. The new aircraft first flew in September 1944. After five flights, it was heavily damaged in an emergency landing. Difficulties continued after the aircraft was repaired in December; the engine had to be replaced in February due to the presence of metal particles in the oil. Like the I-222, the I-224 demonstrated very good performance at altitude, also climbing to over 14000 meters and recording speeds over 690 km/hr. But by now, it was October 1945, and the war was over. It was decided to fit the I-224 with a fuel-injected AM-44 engine. This was not completed until July of 1946, and by then the time of the piston-engine fighter had passed. Both the I-222 and I-224 programs were shut down in November. I-225/MiG-11 From OKB MiG by Butowski & Miller The I-225 was born from the second I-220 prototype. Although the I-225 was still designed for operation at high-altitude, it was decided not to optimize the aircraft for such extreme heights as the I-222 and I-224. It was hoped that this would allow for a higher top speed and heavier armament, among other improvements. A turbocharged variant of the AM-42 engine (similar to that used on the Il-10 ground attack aircraft) was fitted, providing 2200 horsepower at takeoff. The pressurized cabin was deleted to save weight, and allow the cockpit to be optimized for better visibility. Armament was the same as the I-220; four ShVAK cannons. Armor was added to the windscreen, as well as the pilot's headrest. Improved instrumentation and a new radio system was also added. As predicted, the I-225 had exceptional performance. The aircraft was capable of speeds in excess of 720 km/hr, and demonstrated good handling characteristics. Unfortunately, the first I-225 prototype was lost after only 15 flights, due to an engine fire. A second prototype was completed with an AM-42FB engine, and first flew in March 1945. This second prototype was fitted with four B-20 cannons instead of ShVAKs, This prototype was also reported to be capable of over 720 km/hr, as well as able to climb to 5000 meters in under 4 minutes. However, due to continued vibrations, the AM-42 was replaced with an AM-44 in January 1946. This did not solve the issues though, and the I-225, like its predecessors, was not selected for production. All work on the I-225 was shut down in March 1947. Remarks While none of the advanced MiG-3 variants entered production, they did provide the Mikoyan-Gurevich bureau with valuable engineering and design experience. In a different world, one might imagine that some of their designs could have found a niche. The I-210/1 and I-230/1 would have little reason to be built in a world where Yakovlev and Lavochkin fighters exist in the way they did. However, if Germany or another enemy had a developed strategic bombing arm, then the I-220 series fighters could have found a use. Either way, by 1945, it was clear that jet aircraft were the future. Even the Soviets, who had a relatively late start on jet engines, quickly developed aircraft like the MiG-9 and Yak-15 whose performance exceeded any of the MiG-3 variants. Sources: OKB MiG, a History of the Design Bureau and its Aircraft, by Piotr Butowski and Jay Miller http://www.airvectors.net/avmig3.html http://www.aviastar.org/air/russia/a_mikoyan-gurevich.php https://ruslet.webnode.cz/technika/ruska-technika/letecka-technika/a-i-mikojan-a-m-i-gurjevic/ (I-230, I-210, I-211, I-220, I-221, I-222, I-224, and I-225 pages) http://www.airwar.ru/fighterww2.html (I-230, I-231, I-210, I-211, I-220, I-221, I-222, I-224, and I-225 pages) http://soviethammer.blogspot.com/2015/02/mig-fighter-aircraft-development-wwii.html
  2. Basic History State of PVO before MiG-25 During the middle part of the 1950s, the PVO (Soviet air defense forces) were poorly equipped to deal with future threats. The majority of its interceptors consisted of aircraft such as the MiG-15, MiG-17, MiG-19, and Yak-25. These aircraft possessed sufficient performance to take on American bombers such as the B-29 and B-50, and were at least marginally capable of intercepting jets like the B-47 or B-52. However, they were horribly inadequate against coming bombers, such as the B-58 Hustler (which first flew in 1956). The arrival of Mach 2 capable interceptors such as the Su-9, and later the MiG-21 in the latter portion of the 1950s evened the playing field somewhat. However, these interceptors suffered from severe deficiencies. The Su-9 (and to a lesser extent the MiG-21) had a cripplingly short range, a major shortcoming when defending a country as large as the Soviet Union. The Yak-27, a development of the Yak-25, had better range than either of the deltas, but was inferior in terms of speed and altitude. In addition to various performance issues, the PVO’s interceptors were also handicapped by poor armaments. The Kaliningrad K-5 (NATO AA-1) radar guided missile was equipped by most PVO interceptors following its introduction in 1955. Though decent for its time, it was limited by its beam riding guidance and short range. The infrared guided K-13 (AA-2) was introduced in 1960 after being hurried copied from a captured AIM-9B. Like the K-5, the K-13 suffered from poor range, and was also limited to being fired at the rear of a target. These systems would clearly not be sufficient to reliably destroy the B-58, let alone the Mach 3 capable XB-70 (which began development in the late 1950s). The introduction of surface to air missiles such as the S-25 and S-75 had some promise (as demonstrated by the destruction of a U-2 reconnaissance aircraft by an S-75 on May 1 1960 at over 18,000 meters). However, these missiles required large fixed launch sites, leaving them incapable of covering large swaths of territory. In an environment where a single bomber was capable of destroying a whole city, the situation was clearly unacceptable. It was clear that a new interceptor was needed to equip the PVO. Numerous solutions were tried. A modified variant of the MiG-19, the MiG-19SU was tested. This aircraft was fitted with liquid rocket engines in addition to the two RD-9s, giving (briefly) improved speed and altitude capability. This allowed flights to over 20,000 meters , however, the aircraft suffered severe controllability issues. In any case, it was clearly a temporarily solution. Another program was the development of various ‘heavy interceptors’, capable of engaging NATO bombers at extreme range, well away from populated areas or strategic targets. These included the abortive La-250, and more successful Tu-128 (developed from the Tu-98 bomber prototype). Though the Tu-128 entered service (indeed, it continued on into the early 1990s), it did not arrive until the middle of the 1960s. Even then, it was a large and ponderous aircraft, capable only of transonic speeds and completely lacking maneuverability. It could not serve as the PVO’s primary interceptor. An effort with more potential was the Sukhoi T-37. This aircraft was broadly similar in planform to the Su-9 (being a tailed delta) but was much larger. Powered by an R-15-300 engine, it was planned to reach speeds near 3,000 km/h at altitudes approaching 25,000 meters. Interestingly, it was also to have been fitted with equipment enabling it to be flown automatically under ground control (the US had the SemiAutomatic Ground Environment, a similar system capable of directing F-106s). However, it was plagued by numerous issues, and was scrapped in 1960 before it ever flew. Requirements The requirements for the MiG-25 were greatly determined by its potential adversaries. The main threat was the B-58 Hustler, capable of Mach 2 at altitudes approaching 18,000 meters. In 1960, the Soviets became aware of yet another threat; a Mach 3 successor to the U-2 was under development (this was the A-12/SR-71, though the Soviets did not know this initially). As a result, it was decided that the new interceptor should be capable of flight at up to Mach 3, and at altitudes in excess of 20,000 meters. Coincidentally, the VVS (Soviet Air Force, separate from air defense forces) was looking for a new high speed reconnaissance aircraft during the late 1950s. At the time, most of the VVS reconnaissance force consisted of variants of the Il-28 or Yak-25. The survivability of these aircraft against new NATO fighters such as the F-104 or Lightning was marginal at best. The Yak-25RV was in development, and promised comparable performance to the U-2 (it did not fully deliver), but this was an incremental step at best. A wholly new aircraft with exceptional performance was needed. By 1960, it was realized that the new recon aircraft had broadly similar requirements to the new PVO interceptor program (by then in development for over a year), so the programs were merged. The ability to carry photorecon equipment was added as a requirement to the interceptor program. Development The Ye-150/152 can be considered the direct ancestor of the MiG-25. Developed in the late 1950s and first flying in 1960, the Ye-150 was broadly similar in appearance to the MiG-21, but was significantly larger and was capable of reaching much higher speeds. The Ye-152 was a further development; it was fitted with R-15-300 engines, the same R-15s which would be fitted to the MiG-25. Like the Ye-150, it represented a massive performance leap over the MiG-21, but it was very much a testbed. The R-15s were supremely unreliable (early models had an average engine lifetime of roughly 20 hours), and the weapons system was tempermental. There was also the Ye-152A, which was fitted with two R-11 turbojets (the same engine as the MiG-21) instead of a single R-15. Though these aircraft did not enter production, they provided the Mikoyan-Gurevich design bureau with valuable data on high speed flight and the R-15 engine. There is some uncertainty about the initial genesis of the MiG-25 program. There are rumors that Mikoyan instructed chief designed Seletisky to develop an interceptor similar to the North American A-5 Vigilante (which had first flow in late 1958) powered by two R-15-300s. Other sources state that work began before the first flight of the A-5. While there are obvious similarities in layout between the A-5 and MiG-25, there are also massive differences. At most, the MiG-25 was somewhat inspired by the A-5, and is very much not a ‘clone’ or reverse engineered copy. (Later proposed Vigilante derivatives such as the NR-349 or rumored J58 powered version would have been much more analogous to the MiG-25). The new aircraft was assigned the designation Ye-155 by Mikoyan (the prefix Ye for yedinitsa denoting a prototype or testbed aircraft). It was decided very early to use the R-15-300 engine. However, there remained uncertainty as to the layout of the engines. Though a conventional side by side layout was ultimately chosen, a vertically stacked layout (such as on the English Electric Lightning) was also considered, as was a staggered engine arrangement (as on the I-320 prototype). Unlike previous Mikoyan-Gurevich designs, it was decided not to utilize a nose mounted intake, but instead place the intakes under the wings. This allowed for a smaller fuselage (in both length and cross section). The underwing intake placement worked well with the shoulder mounted wing placement, which was needed to allow for the carriage of very large AAMs. This wing layout also allowed the wings to be constructed in one piece, simplifying constructing and improving structural rigidity. Numerous planforms were proposed for the wing before the design of the prototype was finalized. At one point variable geometry designs were considered (this would have significantly predated the introduction of the Su-17, though variable sweep designs had been studied at least since 1945). The variable sweep design was seriously considered enough that a model of a recon MiG-25 with variable geometry was made, it somewhat resembles an F-14. One of the benefits of the variable geometry design would have been improved takeoff and landing performance, however, it was decided that this was not worth the added complexity and weight associated with such a design. Following numerous wind tunnel tests, a trapezoidal wing of low aspect ratio was chosen. As with many Soviet designs in the 1950s and 1960s, lift jets were considered for use to improve takeoff and landing distance. The proposed STOL design would have used two small RD36-35 lift engines, mounted in a slightly staggered arrangement in the fuselage, with intakes along the back of the aircraft. While the lift jets would likely have improved takeoff and landing distances greatly, they also decreased the internal volume available for fuel. This was a serious drawback, especially for the reconnaissance version. As a result, the lift jets were discarded, with the STOL design not progressing beyond the model stage. As the MiG-25’s design grew closer to being finalized, materials selection became a serious issue. The leading edges of the wings, inlets, and nose of the aircraft would experience extremely high temperatures at Mach 3, well above the melting point of conventional aluminum alloys commonly used in aircraft construction. Alternative materials had to be found, and many were considered. At first, titanium seemed a logical choice. It has excellent thermal properties, is quite strong for its weight, and the Soviet Union possessed large reserves of the material. However, the Soviet aircraft industry had little experience working with titanium, which was notoriously temperamental (for instance, when manufacturing the SR-71, Lockheed engineers were forced to use special tools, as normal tools contained cadmium, which made the titanium brittle). In particular, the automated welding methods commonly used in Soviet aircraft manufacturing plants would not be suitable for titanium. As a result, it was decided to use steel alloys for the majority of the MiG-25s structure (titanium was used in some areas, but at much lower quantities). Initially, there were some doubts as to whether certain components (such as the integrated fuel tanks) could be made strong enough without seriously increasing weight, or absorbing the cyclical flight loads. Tests showed that this was not the case, and the MiG-25 ended up being built using large quantities. In addition to the issues with materials selection for the aircraft structure, the thermal loads associated with high speed flight caused trouble in other areas. Normal lubricants and hydraulic fluid would break down at the temperatures the MiG-25 would experience, and normal canopy glass would melt. In many ways, this mirrors the problems faced by the Skunk Works team designing the A-12 at around the same time. Throughout 1962 and 1963, the design of the MiG-25 was further refined. In 1963, construction began on the first prototype, Ye-155R1. Its completion took most of the year, and it was not rolled out from the Zenit Machinery Works (the common name for the MiG bureau’s experimental aircraft factory) until December. Despite this, Ye-155R-1, a prototype of the reconnaissance variant, was missing much of its operational equipment. Still, it had more than enough to validate the basic flight characteristics of the airframe. In addition to lacking various pieces of equipment, Ye-155R-1 differed from production MiG-25s in several ways. For one, the aircraft had a pair of 600 liter fuel tanks mounted at the wingtips. These both increased fuel capacity, and prevented flutter. Ventral fins were attached to the fuel tanks, to improve lateral stability at high speeds. Both of these features would be absent from production MiG-25s. Ye-155R-1 also had provisions for the fitment of canards to the sides of the forward portion of the air intakes; these would have been used for pitch control at high Mach numbers, but they were never installed. The first prototype suffered from numerous issues. Among the most serious of these was roll control issues in the transonic regime, in some cases severe enough to render the aircraft uncontrollable. The wingtip fuel tanks caused vibration as fuel was depleted and sloshed about. The intakes were inefficient at high Mach numbers, and the aircraft’s static margin decreased as well. Finally, Ye-155R-1 was overweight, causing its range to fall short of the target. The second prototype, Ye-155R-2, was also a prototype of the recon MiG-25. This aircraft was broadly similar to the previous prototype, though it did incorporate some refinements. There was one immediately obvious difference; the wingtip fuel tanks were deleted. This would be the last prototype built at the Zenit plant; the factory was tasked with producing the first MiG-23 prototypes, and had no more room for further Ye-155s. As a result, it was decided to build prototypes from Ye-155R-3 onward at Mikoyan’s Gorkii plant, the same as would produce the production aircraft. This resulted in a delay in producing Ye-155R-3 as the factory was retooled, but it would ultimately allow production to commence quicker. Ye-155R-3 was a milestone in and of itself; it was fitted with a full suite of photorecon equipment, and would be used for testing various camera arrangements (among other things). Belenko Defection Later Variants Post-Soviet service Variants Prototypes Ye-155 models Operational MiG-25P/PD/PDS Export MiG-25P MiG-25RB MiG-25R MiG-25BM MiG-25PU Other Ye-266M Ye-155MP Buran testbeds / training aircraft Various other concepts and variants Production In Red Air Force Service Other Operators Combat Performance Egypt vs. Israel Iraq MiG-25 vs. SR-71 Structure Materials Engines Electronics Radar Early versions vs. Later Recon variants - cameras Armaments Air to Air MiG-25P MiG-25PD Ground MiG-25RB MiG-25BM Other Systems of Note Citations http://www.kamov.net/russian-aircraft/mig-19su/ http://www.kamov.net/russian-aircraft/sukhoi-t-37/ MiG-25 'Foxbat', MiG-31 'Foxhound': Russia's defensive front line By: Gordon, Yefim. Aerofax 1997 Skunk Works: a personal memoir of my years at Lockheed By: Rich, Ben R., and Leo Janos. Little, Brown 1994