Sukhoi's First Jet Bomber

The Sukhoi Su-10 in its final configuration

Following the end of the Second World War, both the Soviet Union and the West aggressively pursued jet bomber designs after the Luftwaffe had successfully introduced the Arado Ar 234 to combat in the waning months of the war. In the West, many early designs were based on layouts of high-mounted wings with wing-mounted nacelles to allow for a reasonably-sized bomb bay. Similar approaches were taken in the Soviet Union with the design bureaus (called OKBs) of Illyushin, Tupolev, and Sukhoi tapped to develop jet bomber designs to succeed the Soviet Air Force's standard bomber, the piston-powered Tupolev Tu-2. Last summer I had posted about an early Tupolev design that actually did fly, the Tu-12, that was based on the Tu-2 as a matter of expediency pending the arrival of the Tu-14 bomber. While Illyushin and Tupolev both had large aircraft design experience from their own work on twin-engine bombers during the war, Pavel Sukhoi's experience was limited to his prewar tenure at OKB Tupolev. But, given the pace of technological progress and the urgency of rearmament in competition with the West, Sukhoi was ordered on 26 February 1946 to develop a jet bomber powered by four Junkers Jumo 004B turbojets, the same jet engines that powered the Arado Ar 234. Work on Sukhoi's first bomber design began in earnest in April of that year and the aircraft received the official designation of Su-10. 

Several powerplant arrangements were considered along with the use of six engines instead of the four as originally specified. In the Soviet Union, the Central Aerohydrodynamic Institute in Moscow, or TsAGI by its Russian name, did a lot of wind tunnel and theoretical research work to support design efforts at each of the OKBs. At the time that OKB Sukhoi was working on the Su-10, TsAGI had lagged behind Germany and the West in high speed research and as a result, they lacked a significant amount of information on evaluating jet aircraft designs. As a result, much of what laid the basis of TsAGI's high speed aircraft research came about during their work in support of the development of the Su-10 in addition to what had been obtained of German design work following the end of the war. Two leading design variants were evaluated in TsAGI's wind tunnels- one design had four of the jet engines clustered in the mid fuselage and exhausting out the rear with two jet engines under the nose- this was felt to be advantageous design as it left the wings clean. The other leading variant had wing mounted nacelles with a high unswept wing with three engines mounted in clusters on each wing. 

To meet the specified target speed of 528 mph at 26,000 feet, Pavel Sukhoi decided that four engines were insufficient and that six were necessary. Since the Junkers Jumo 004 engine was the only jet engine available to the Soviet Union at the time that had reached production status, the Soviet Politburo placed high priority in reverse-engineering the engine for production- Vladimir Klimov and his OKB were already known for their piston engine designs during the war and he was put in charge of getting the German engine into production as the Klimov RD-10. Klimov's closest aide, Nikolay Kuznetsov, headed the actual reverse-engineering effort- Kuznetsov would go on to form his own engine OKB several years later. 

Inboard layout of the Su-10

With approval from the state authorities to use six engines, design work had settled on a cluster of three engines on each wing as the most efficient layout- the nacelle had two engines side by side with the third RD-10 engine below and slightly ahead of the pair. On 6 May of that year, a full scale mockup was built that was tested in TsAGI's largest wind tunnel with real RD-10 jet engines. Within two months, refinements to the design based on TsAGI's evaluation were in place as full-scale engineering began on the prototype. While two months sounds rapid, development of the Su-10 hit repeated technical hurdles, the biggest of which was that TsAGI lacked a significant portfolio of well-studied high speed airfoils. As a result, while supporting development work on the Su-10, assimilating German design work, TsAGI was also hurriedly developing its on portfolio of high speed airfoils. As a result, Sukhoi's team was constantly having to revise the Su-10 design based on developments from TsAGI. 

By October the full scale mockup had been approved by Soviet Air Force authorities and metal was finally cut for the prototype on 14 October 1946. In the first week of December, the Soviet government commission in charge of aircraft production decreed that the Su-10 would no longer use the Klimov RD-10 engine but instead use the TR-1 engine from the Lyulka OKB, the first indigenous Soviet jet engine design. Since the TR-1 was more powerful than the RD-10, the Su-10 could revert back to a four-engined design and once again Sukhoi and his team had to revise the bomber's design to accommodate the new Lyulka engines. Working at a frantic pace to meet state-decreed deadlines, Sukhoi managed to have a full set of production drawings ready by 23 December 1946 and three days later the OKB's own workshops had completed a static test airframe and production jigs and tooling for the prototype. If things weren't frantic enough as it was, the Minister of Aircraft Industry wanted the Su-10 flying for participation in the air show at Moscow on 18 August 1947! Common sense prevailed and that was one deadline Sukhoi was allowed to ignore. 

Three-view showing the layout of the Su-10 medium bomber

By 15 December 1947 the hydraulic system had been fully tested on a special ground rig (similar to today's "iron bird"), but construction of the prototype was hampered by slow progress from the various subcontractors that were responsible for some of the Su-10's systems. For example, the defensive armament system (which consisted of a manned tail turret, a remotely-operated dorsal turret and forward-firing cannon), the autopilot, the navigation suite and even the Lyulka TR-1 engines were to have all been delivered to Sukhoi's workshops for the prototype but by the end of 1947 none of those items were ready yet. During the delay, studies looked at alternative powerplant options and it was decided that the initial flight tests of the Su-10 would use the TR-1 engine but as soon as the more powerful TR-2 engine developed from the TR-1 became available, the Su-10 prototype would have its engines swapped out and then continue with the flight test program. 

 

These persistent delays led to the Su-10 prototype to sit in the OKB workshops missing various components- by 4 June 1948 the Soviet Council of Ministers ordered that spending had to be reduced on aircraft development programs that year and one of the unlucky programs to get canceled was the Su-10. By that summer OKB Ilyushin had already made the first flight of its Il-28 medium bomber and its performance outstripped what was projected for the Su-10. Not even rolled out, the Su-10 prototype was donated to the Moscow Aviation Institute where it was slowly reduced to parts over time as an instructional airframe. Sukhoi in the years to come devoted its efforts at interceptor, fighter, and ground attack aircraft and it wasn't until the arrival of the Su-24 Fencer in the late 1970s that Sukhoi finally had a production jet bomber. 

Source/Images: OKB Sukhoi: A History of the Design Bureau and Its Aircraft by Yefim Gordon and Dmitriy Komissarov. Midland Publishing, 2010, p93-101.

How Aleksandr Yakovlev's Rivalry with Pavel Sukhoi Did Him In

Aleksandr Yakovlev

The 1950s and 1960s in Russian combat aircraft development were marked by intense rivalries between the various design bureau (OKBs) heads. Nowhere else was this seen than with the rivalries between the respective OKBs of Artem Mikoyan, Pavel Sukhoi, and Aleksandr Yakovlev. During the Second World War, Yakovlev's OKB was one of the dominant forces in Russian aviation, having built thousands of fighters for the Soviet air forces. OKB MiG (Mikoyan and his partner, Mikhail Gurevich) was rapidly rising to prominence during the war. OKB Sukhoi really didn't start to establish itself until well after the war (some say that Stalin had a dislike of Pavel Sukhoi as one reason). As the jet age dawned, Yakovlev took a conservative approach that saw the first Yak jet fighters as jet derivatives of his wartime piston engined designs whereas MiG and Sukhoi were willing to push the envelope and advance the state of the art. A rivalry between Sukhoi and Mikoyan developed with Mikoyan gaining the upper hand against both Yakovlev and Sukhoi with the MiG-15, MiG-17, and MiG-19 fighter designs which outclassed comparable aircraft from Yakovlev. When in the 1950s the Soviet military command wanted a supersonic interceptor, it was Sukhoi's delta winged Su-9 (NATO code name Fishpot) that edged out Mikoyan's design based on an enlarged MiG-21 fighter. First flying in October 1957, the Fishpot was certainly fast, but it was handicapped by the poor reliability of its Lyulka AL-7F turbojet. In those days, it was rare for an AL-7F engine to last beyond 200 flight hours- and that's not time between overhauls, the reliability of the engine was so poor that few engine units lasted past 200 flight hours, an abysmal figure. The radar set in the conical shock cone of the nose inlet was limited as well. 

Sukhoi Su-9 "Fishpot"

Of course, having the Su-9 having much in common with the Su-7 (NATO code name Fitter) tactical fighter did make selecting the Su-9 for production much easier. But the Sukhoi OKB knew that the Soviet Air Defense Forces (PVO) was not pleased with the performance of the Su-9 and with only 924 examples built, an upgraded Su-11 was introduced. But it would be built in very limited numbers. At the time, the Soviet leadership had decreed that the "missile age" had made many aircraft designs obsolete, and like the infamous Duncan Sandys Defence White Paper in the UK that mortally wounded the British aerospace industry, numerous aircraft and engine projects were canceled and only those designs that were developments of existing designs were allowed to continue to develop. As the Yakovlev OKB had already in production the Yak-25/26 interceptor (NATO code name Flashlight) and attack variants, it proceeded with a supersonic design in the Yak-28 (the interceptor variant having the NATO code name Firebar and attack version being the Brewer). Three features made the Yak-28 more attactive than the Su-9/Su-11 family- first, it used the Tumansky R-11 turbojet was showing itself in the MiG-21 to be much more reliable and durable than the Lyulka AL-7F, secondly it had two engines which gave in a perception of safety over the single-engined Su-9/Su-11 family, and thirdly, having a nose free for a larger radar set than what was possible with the nose intake arrangement of the Sukhoi design meant that production was switched over to the Yak-28 instead, the interceptor version being the Yak-28P. 

Yakovlev Yak-28P "Firebar"

Sukhoi wasn't going to be one-upped by Yakovlev, though. Taking as a baseline the limitations of the Su-9/Su-11 family. OKB Sukhoi set about to create a vastly improved interceptor in the shape of of the Su-15 (NATO code name Flagon). The Su-15 was designed from the outset to be superior to the Yak-28P- it used two of the same Tumansky R-11 engines and used lateral box intakes to leave the nose section free for the same large radar set used on the Yak-28P, the Oryol-D radar. Being a development of the Su-9/Su-11 family, though, it managed to avoid cancellation like so many other projects in the 1958-1959 timeframe in the Soviet Union. Interestingly, the Yak-28P and the Su-15 were produced in the same factory- in the Soviet Union, the OKBs only did design and flight test work with workshops for building prototypes. The designs were then handed off to independent factories for production.  At the time, the Novosibirsk aircraft factory No. 153 was responsible for the Yak-28P production and it was assigned production of the Su-15 once it had passed its State acceptance trials in 1962. Given that both the Yak-28P and the Su-15 used the same powerplant and radar, producing both at the same plant made logistical sense. And there was irony in the decision as the same plant built the Su-9/Su-11 interceptors that were replaced in production at that very plant by the Yak-28P. And now the plant was gearing up to produce more Su-15s with the intent of replacing the Yak-28P with the PVO. 

The sole Yakovlev Yak-28-64 prototype

Not willing to lose out to Pavel Sukhoi, Aleksandr Yakovlev dispatched one of his sons to the Novosibirsk plant to learn as much as he could about the Su-15 design (Yakovlev had two sons who worked for him- one would end up designing the Yak-40/42 airliners and the other would be responsible for the Yak-52 trainer). Seeing the threat posed by the Sukhoi design to the Yak-28P, Yakovlev set about designing an upgraded version provisionally designated the Yak-28-64 (due to work on it beginning in 1964). Many of the features of the Su-15 were incorporated into the Yak-28-64, primarily in moving the Tumansky R-11 engines to the rear of the fuselage from the wings. One of the criticisms of the Yak-28P was that having wing-mounted engines gave the aircraft a poor rate of roll and adverse handing characteristics in an single engine-out situation. Moving the engines to the fuselage resolved these concerns. The tail unit and the wings remained close to that of the Yak-28 and the unique bicycle landing gear was retained. The single ventral fin of the Yak-28P was changed over to a twin ventral fin arrangement for stability. Given that OKB Yakovlev had little experience with fuselage-mounted lateral intakes, Yakovlev incorporated a copy of the Su-15's lateral box intake design on the Yak-28-64. 

Yak-28-64

The prototype Yak-28-64 was rolled out in 1966 and it proved in flight tests right off hand to be a dog. In fact, the Yak-28-64's performance was even worse than that of the Yak-28P, the very aircraft that was being superseded by the Su-15. Numerous unpleasant handling characteristics were also uncovered and some of the landing issues present in the Yak-28P thought to be cured in the Yak-28-64 persisted (such as aileron reversal at high speeds). It didn't take long to realize that the Yak-28-64 was a dead end and the project was abandoned by Yakovlev. 

Sukhoi Su-15 Flagon

A look at some of the production figures during this rivalry is telling. Just over 900 Sukhoi Su-9s were built at the Novosibirsk factory. Less than 100 Su-11s were built. Replaced in production at the factory by the Yakovlev Yak-28P, over 400 examples were built before it was completely supplanted by production of the Su-15, of which over 1,200 were built. The attack versions of the Yak-28 had to be continually upgraded with no less than 10 versions, each in relatively small production batches around 200 or so. Having been topped by Sukhoi in the interceptor arena with the Su-15, the Soviet air forces replaced the attack versions of the Yak-28 with another Sukhoi design, the Su-17/Su-22 family (NATO code name Fitter) which proved more reliable and versatile operationally. 

The Yak-28-64 and the rivalry with Pavel Sukhoi damaged OKB Yakovlev for good. His designs were considered by the Soviet air forces to be unreliable and obsolete, at the worst, limited in performance at best. For years no other Yakovlev combat aircraft design was taken seriously by the Soviet military high command and even the VTOL Yak-36 design was supremely limited in its utility. Even Yakovlev's submissions to the  competition that resulted in the MiG-29 Fulcrum and the Sukhoi Su-27 Flanker (Yak-45 and Yak-47, respectively) were decidedly archaic in appearance and failed to use some of the latest advances in aerodynamics. Most Yakovlev designs following the abandonment of the Yak-28-64 were either light aircraft or airliners, areas that were more heavily influenced by his sons than by Aleksandr Yakovlev himself. 

Source: OKB Yakovlev: A History of the Design Bureau and its Aircraft by Yefim Gordon. Midland/Ian Allan Publishing, 2005, p215-230. Additional material from Paul Martell-Mead at the Secret Projects forum.