Sukhoi Su-15 Flagon - History, Design, Performance & Dissection

This is a continuation of the Su-9/11 thread

I had originally created it on the old forum: Sukhoi Su-15 Flagon - History, Design, Performance & Dissection - Soviet Union - War Thunder - Official Forum

The Su-15 is one of my favorite old interceptors. The delta wing design, the early SARH missiles that I find interesting, high performance, and it’s known for the unfortunate encounter with a civilian airliner (check the end of the post)


Origins

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(T-37 heavy interceptor, a promising project to replace the Su-9 and Su-11 which was unexpectedly canceled)

As everyone knows, the 1950s was a very troubled climate for the Soviet Union, since the West had began fielding new airborne-strike systems and long-ranged strategic bombers. The PVO was comprised mainly of MiG-17A/F and Yak-25 jets at that time (later the Yak-27 and MiG-19PM). Such jets weren’t capable of intercepting strategic bombers with inadequate performance and cannons only. This is why jets such as the Yakovlev Yak-28, Sukhoi Su-9 and Su-11 were developed: high-speed, missile-armed aircraft were needed to counter the threat.

However, there was an issue… Nikita Khrushchev was the head of state at that time, and he had little respect for the military aviation. During his era, 35 aircraft projects were terminated, and 21 engine programs alone in 1958 - 1959. He had a soft spot for SAM systems instead to defend the country, and when it came to desgining new aircraft, only conversions or upgrades of existing aircraft were allowed. Khrushchev’s “missilisation” of the Soviet Union had a big blow on the Soviet aircraft industry that took six years to recover.

Despite this climate, favor was still found in OKB-51 (Sukhoi OKB), since the Su-7 tactical fighter had been put into production and then converted to a fighter-bomber under the designation of Su-7B, while the Su-9 had just completed its acceptance trials, entering production henceforth, and the Su-11’s trials had begun.

Now, there was an issue with the Su-7 and Su-9. A very BIG issue. The Lyulka AL-7F and its derivatives suffered from reliability issues, mainly the AL-7F-1. In the first 1 year and a half of the Su-7’s service entry, 20+ Su-7 and Su-9 examples crashed. More than half of the accidents were attributed to random engine failures, and the time between overhauls was just 25 to 50 hours. The engine was very expensive to produce, thus was available in short numbers. Moreover, the very promising and nearly complete T-37 heavy interceptor with the more reliable and powerful Tumansky R-15-300 and forming the T-3-9A interception system was very unexpectedly canceled alongside the K-9 missiles, a sad end to what was going to be a remarkable aircraft. It was obvious in 1961 that the situation was not good.

Sukhoi faced yet another setback in the early 1960s: the PVO began leaning towards the new Yak-28P twin-engined interceptor, as it showed more engine reliability and safer flying. To this end, MAP (the Soviet Ministry of Aircraft Industry) demanded that the Su-11’s production be cut short in heavy favor of the Yak-28P and the new Tu-128. Even more, the promising MiG-21PF from MiG began its trials. This was a blow to the Su-11, and only 108 examples were produced in total. Now Sukhoi was facing the possibility of being closed altogether again.

Considering Khrushchev’s attitude towards the military aviation at the time, chances of developing all-new manned combat aircraft were close to zero, and all Sukhoi could do was modernize existing designs, with hopes of them being accepted only if state-of-the-art missile systems were incorporated. (Fun fact, this is why the Su-24 was actually at first a delta-winged interceptor with a 150 - 170 km-capable radar with different proposed missile designs! When Khrushchev was ousted and replaced by Brezhnev who favored the military aviation, it was no longer disguised as an aircraft derived from the Su-15 prototype family under the designation T-58M and then became its own thing; Sukhoi finally freely explored the tactical bomber role)

This is exactly the situation which led to the start of the Su-15. At that time, they weren’t quite aware of it yet though. They started developing a new single-engined interceptor at their own risk under the in-house designation of “T-58”. To win the support of the higher ups and avoid possible negative consequences, it was disguised as a further upgrade of the existing T-3-8M weapons system, the system which was formed by the Su-11 (see the previous thread). It was to be armed with a radar offering longer range than the RP-11 Oryol of the Su-11, and missiles with lethality increased in the kill probability and range department. OKB-339 offered the Oryol-2, a further upgrade of the RP-11, and an all-new Vikhr (Whirlwhind), a scaled down version of the Tu-128’s Smerch. However, both of them were too bulky to fit inside the axisymmetrical air intake of the Su-11 so the only option was to use the entire nose section aft of the cockpit for the radar and to use lateral air intakes, which OKB-51 had gained experience in from the P-1 and T-49 experimental projects.

Still, the T-58’s air intake design ended up differently, featuring two-dimensional with vertical airflow control ramps, found on the F-4 Phantom and F-106 Delta Dagger. But in the Soviet Union, this design was not yet fully explored. It should also be noted that the sector-shaped isoenthropic air intakes found on the T-49 had a staunch support at TsAGI; Prof. Gersch Grodzovski, who once visited Pavel Sukhoi urging him to use such intakes on his T-58 project forming the seemingly upcoming T-3-8M3 weapons interception system, but he refused as it seemed risky. He then instructed his designers only to change the fuselage structure as far as the section after the cockpit, to ensure maximum commonalities with the Su-9 and Su-11, and minimizing production costs, to ensure the same No.153 factory would keep on producing his jets.

Development was rapid, and as early as July 1960 the first piece of metal on the T-58’s prototype was placed, and its forward fuselage assembly began. The project was still a private venture at that time, not being officially sanctioned by the government.

However at this time the appetite of the military started growing. They demanded that the new aircraft has all-aspect engagement capabilities against targets flying at up to 27,000 m (!) and speeds up to 2,500 km/h. To appease the missile-minded leaders of the USSR at that time, they informed them that the upcoming design will only feature two air-to-air missiles. In November the same year, the Council of Ministers issued an order to equip the new jet with the Vikhr-P radar and the Polyot GCI system. The missiles were going to be 2 x K-40 air-to-air missiles in SARH and IR versions (what would later become the R-40R and R-40T of the MiG-25). In this configuration, the designation T-3-8M3 was used as the in-house designation and allocated as part of the Su-15-40 aerial weapons interception system. This is when the designation “Su-15” was used for the first time.

Time passed, but the promising K-40 missile was nowhere near to be sighted, neither the CofM’s anticipation of the project with the Vikhr-P radar. Hence, they continued the aircraft’s development with the Oryol-2 radar and K-8M2 missiles; upgraded R-8MR and R-8MT missiles (which did not find success, however the K-8M2 was developed into the K-8M1P which came in IR and SARH, what became the R-98T and R-98T later). In the project’s documents, this config was called the Su-11M, while the aerial intercept weapons system was allocated the designation “T-3-8M2”.

The T-58 was due for completion in September 1961, but work on it was canceled during that year’s summer. Apparently, it was the specific related divisions within the government thought that hope was lost in an AAM-equipped fighter. Sukhoi struck back and proved them wrong.

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(T-58 blueprint from one of the ADP documents)


Sukhoi T-58D - Pavel’s Retaliation

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(T-58D-1 prototype, the first prototype of the Su-15, under final assembly)

As previously mentioned, the AL-7F-1 was a very troublesome engine. It’s why the Su-9 and Su-11 had a negative reputation at first, before they had the AL-7F-1 replaced with the AL-7F-100, -150 and -250 later on.

As an insurance policy, Sukhoi decided in late 1960 to prepare a new project derived from the T-58, characterized by the installation of two Tumansky R-21F-300 axial-flow afterburning turbojets in the side-by-side fuselage configuration. This was an advanced engine type rated at 7,200 kgf on full power (afterburner).

The new project was designated T-58D (“D” could stand for either “dvigateli” (“two engines”) or “dorabotani” (“updated”), it is still unsure which is correct), but was still to be equipped with the Vikhr-P radar, Polyot GCI and K-40 air-to-air missiles, and officially known as the Su-15 at this point. This indicates how differently the Su-15 could have turned out had the missiles been developed in time! Though, the PVO was still adamant about the radar and missiles, despite MAP indicating that with the Oryol-2 and K-8M2s it would enter service much sooner.

However, the R-21F-300’s serious design flaws were eventually discovered. It was then decided to replace it with the R-11F2-300, found on the MiG-21F/F-13. OKB-51 already had experience with these engines in the twin configuration since they had meddled with them on the Sukhoi T-5 (see chapter 2 in the Su-9 and Su-11 thread). In any case, the twin-engine configuration significantly increased reliability over the single-engine design as originally planned for the older T-58.

To speed up the development process, they decided to borrow the tail and wings of the Su-11. However, with all the new changes, it proved to be a lot heavier than the production Su-11. To redeem this, the designers resorted to installing blown flaps.

The T-58D was enivisioned to become an interceptor that would have to deal with single, unmaneuverable targets flying between 20,000 - 24,000 m and speeds up to 2,500 km/h. Because it also seemed that it would stand no chance in engaging targets in pursuit mode since it didn’t offer speed advantages due to the weight increase, they devised head-on tactics. The minimum missile launch range was limited to certain altitudes because the radar lacked LD/SD.

To maximize the efficiency of the weapons system, they included an automatic flight control system (AFCS) with an AP-28T-1 autopilot with heading adjustment command modules and pre-programmed optimum climb profiles.

The in-house reviews of the ADP and review commission were deemed unnecessary since at that time the T-58D was still considered to be no more than an upgraded Su-11.

Wind tunnel tests were of course still held, as well as ground rigs were built to test the T-58D’s electric hydraulic systems. After the AFCS was fully developed, it was designated SAU-58, and was actually tested on the seventh prototype of the Su-11 (T-47-7).

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(Here, the T-58D can be seen taking shape at MMZ No.51; Sukhoi’s experimental shop at Moscow-Khodynka)


Sukhoi T-58D-1 / T-58D-2 / T-58D-3 - Tests Execution

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(T-58D-1, the first prototype of the Su-15, properly coded “58-1” and seen with R-98R & R-98T missiles)

In early 1962, the first prototype, designated T-58D-1, was rolled out of the factory. As an aerodynamic testbed, it lacked the intended radar and test equipment occupied the radar’s place of installation. It was mainly intended to test stability/handling and performance to test top speed, acceleration, range, service ceiling and fuel consumption rates, with and without drop tanks.

It was trucked to the LII testing airfield and on the 30th of May, 1962, after R. Yarmakov checked and passed the T-58D-1’s ground system checks and taxying tests, it performed its maiden flight under the hands of Vladimir S. Ilyushin, a Sukhoi OKB test pilot and the son of no other than Sergei Ilyushin, the aeronautics engineer and founder of Ilyushin OKB. He praised the aircraft for its flying for the most part, except that it had poor directional stability in comparison with the Su-11, an issue that was fixed by installing a 400mm “plug” at the base of the fin.

By the end of the year, the prototype had completed 56 test flights under the manufacturer’s test program and its “58-1” code was changed to “31 Blue”. It displayed good performance and handling, meeting the expectations for the most part.

Suddenly, even during these early stages, MAP issued an order to fit the aircraft with the Smerch-AS radar and to arm the prototype with K-8M2 air-to-air missiles. This decision was going to lead to the outcome of installing the same radar to the three advanced interceptors at that time: the Ye-155P (MiG-25P prototype), the Tu-128 and the T-58D.

Despite the order, it was clear that the forward fuselage design would have to be radically changed, and since there was no prototype radar available for fitting, Pavel Sukhoi and Matus R. Bisnovat (head of Bisnovat OKB, designer of the RS-2US, R-8 and R-98 missiles) worked together to prove their point to MAP and the Commanders in Chief for the VVS and PVO and were successful in doing so; to install the upgraded Oryol radar instead, at least only initially. On the 13th of March, 1963, Dimitri F. Ustinov, CofM Vice-Chairmain wrote back in agreement to Pavel O. Sukhoi but also highlighting that the Smerch-AS would have to be used later. The military also agreed to reduce the size of their demands, stating that it would be fine if the requirements were changed to a maximum interception altitude of 23,000 m for targets at speeds up to 2,000 km/h instead.

The initial stages of the State Acceptance Trials were to be held with the upgraded Oryol radar, and were to finish in November 1963.

Since the first prototype was merely an aerodynamic testbed, the second and third prototypes (T-58D-2 and T-58D-3) were tasked with radar testing. There was a “Sobol” radar in development but it was canceled, so once again they resorted back to the original option, now designated Oryol-D (“D” against standing for “dorabotani” which is Russian for “modified”). At this stage, the brake chute was also relocated from the rear fuselage to the base of the rudder, and the KT104 nosewheel was replaced with the larger KT-61/3, while the main KT-69/4 landing gears were replaced with the identically-sized KT-117s but with more effective braking. In early 1963, the T-58D-1 underwent modifications to match the same standards as the T-58D-2 and T-58D-3.

Until the end of 1963, Vladimir S. Ilyushin alongside two other test pilots kept on performing test flights, reaching 104 in the modified T-58D-1.

Because it took them too long to decide which radar model should be used for testing, the T-58D-2 / second prototype did not begin its test program until April 1963. On the 4th of May the same year, it performed its maiden flight under the hands of Ilyushin again. The second prototype differed from the first by having a longer and more pointed nose radome with a cone angle of 28 degrees but the vertical tail was still unmodified and the brake chute was accordingly located ventrally. However, it featured a complete avionics fit, with the Oryol-D58 (izdeliye 303D) radar installed.

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(Not only the only rare photograph of the T-58D-2 in flight, but also colorized!)

As part of the manufacturer’s test program, tests of the avionics suite lasted till June, and in August the second prototype was submitted for the State Acceptance Trials. The trials began on the 5th of August, and since the SAU-58 AFCS was running late in development, it was decided that another and separate trials schedule would be considered.

To speed up the process, instead of the State Acceptance Trials incorporating two stages as usual (Stage A and B), it was decided to join them both together as one stage instead.

The T-58D-3 (the third prototype) had its maiden flight on the 2nd of October, 1963. It differed from the previous two in the new AP-46 autopilot and a higher internal fuel capacity by 180 liters.

The Air Force pilots were generally pleased with the T-58D-3, however they criticized it for the following:

  1. Decreased aileron authority at low speeds
  2. The engines ran roughly during certain vigorous movements with sideslipping
  3. High takeoff and landing speeds
  4. Deteriorated acceleration compared to the Su-11
  5. 1.5 tons heavier than the Su-11 (10,060 kg vs 8,560 kg)
  6. Instability during landing between 340 - 450 km/h

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(T-58D-3)

Anyhow, on the 8th and 11th of October respectively, the second and third prototypes were flown to the GK NII VVS facility at Vladimirovka AB to continue the trials; more specifically to perform live missile launches against real targets. For starters, the radar’s performance was tested against real targets such as Tu-16 and IL-28 bomber, Yak-25RV recon aircraft and a special Su-9L development aircraft (L.02-10) with an angle reflector to decrease the RCS.

The State Acceptance Trials in general lasted from August 1963 till June 1964. They did not involve just the aircraft, but also the entire aerial weapons system built around it; designated Su-15-98, it comprised the Su-15 of course, the R-11F2-300 turbojets, the Oryol-D58 search and tracking radar and modernized K-8M1P air-to-air missiles which came in IR and SARH versions respectively; entering service as the R-98T and R-98R. Of course, the Vozdukh-1M GCI was also incorporated. The first K-8M1P / K-98 missiles were delivered in early 1964, and live missile launches were conducted. They met all expectations, except the inability to guarantee kills against high speed targets since at that time the fuse could not detonate the warhead in time at closing high speeds. The verdict was that in a head-on situation, the missiles were able to score kills against targets flying up to 1,200 km/h.

The trials of the Su-15-98 system were so smooth, that the PVO expressed almost no criticism regarding it. A total of 87 flights had been made during the trials; 53 accepted “for the record”, 13 training flights, 16 flights “off the record” and five tests for positioning and checkout. All of the aircraft’s systems and equipment had been fully explored, meeting the requirements of the higher ups and the manufacturer’s estimates. All three prototypes in total, under the trials, completed over 300 flights without malfunctioning, demonstrating the reliability of the aircraft design. It was quite well-made, to the point it received the acknowledgement of Air Marshall Savitskiy; a highly experienced WW2 pilot with strict standards.

However, its range fell quite short in comparison to the intended estimate; 1,260 km instead of 2,100 km. In order to solve this issue, OKB-51 decided to eliminate the waist of the area-ruled fuselage to increase fuel capacity. The new modifications were tested on the T-58D-1, proving to be viable changes and were thus highly recommended; the internal fuel capacity had been upgraded to 6,860 liters, more than the original capacity with drop tanks(!). Also, to improve stability and handling, the aileron travel was increased from 15 degrees to 18x30 and the air intake ramp adjustment time was reduced from 12 to 5 - 6 seconds. On the 2nd of June 1964, till the 16th, the modified T-58D-1 underwent a special tests program and the T-58D-3 soon followed with the changes. The trials were officially completed on the 25th of June, 1964, after the last test flight was made by Savitskiy in the T-58D-2 on the 19th.

The final report of the State Acceptance Trials (which referred to the weapons system as the Su-11-8M - stage one upgrade) indicated that the new aircraft offered significant advantages over the Su-11, especially in head-on engagement capabilities. It was recommended that the third prototype be the standard production version. And thus, the Su-15 was born.

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(The second production Su-15, “67 Blue”, during trials)

In early 1965, the first prototype was explored with a new cranked delta design with increased area and longer span to improve handling and stability. These changes were incorporated to the late Su-15TM. Moreover, the first prototype was also used to test short take-off and landing (STOL), much like the MiG-21PD and MiG-23PD. It was designated T-58VD .

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(T-58D-3, obviously the third prototype from the longer and more pointed nose radome and the taller vertical tail with an SPO-2 RWR)


Sukhoi Su-15 Early izdeliye 37 - The Saving Grace Inducted

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(One of the first Su-15s produced, production code (c/n 031506), armed with one R-98R and one R-98T)

In 1966, the Su-15’s production officially began. The first pre-production example was rolled out of the factory on the 21st of February, 1966 and was code-named “34 Red”. With the Su-15 finally in production, Sukhoi was finally relieved. The trials were quite successful that any possibiltiy of the OKB facing entire closure a second time no longer seemed realistic.

With the Su-15 in production, the new radar was redesignated to RP-15 Oryol-D58 and the missiles bore the new designations of R-98T and R-98R (IR and SARH respectively). Actually, they came improved compared to how they were during the prototype stages; they received the PRD-143 rocket motor with a thrust of 13,400 kgf and a burn time of 2.5 - 6 seconds, an improvement over the previous PRD-141 found on the R-8s. They were Mach 2-capable missiles with a kill range of 2 - 14 km in pursuit and 8 - 18 km head-on (this head-on range was achieved only by the SARH version, the IR version on the other hand did have all-aspect capabilities still). The R-98T received a new TGS-14T seeker head with liquid nitrogen cooling and all-aspect engagement (limited), similar to the Red Top and the late R-60M. The plane came equipped with two pylons with PU-1-8 launch rails, and usually had one IR and one SARH loaded.

Moreover, much like the R-8MR and R-8MT, both the R-98R and R-98T were capable of pulling 14G, and their pylon and target G limits were 3G. Their tracking rate was 12°/s.

The RP-15 Oryol-D58 was a capable, non-LD/SD radar, with a detection range of 15 - 35 km at low and high altitude respectively, and a tracking range of 10 km at low altitude and 30 km at high altitude. Detection and tracking of targets were also influenced by the size of the engaged aircraft, scanning at an azimuth of ±60° and elevations of +31°/-15°.

The rest of the avionics suite is listed as the following: RSIU-5 two-way VHF, MRP-56P marker beacon receiver, RV-UM low-range radio altimeter, ARK-10 ADF, SOD-57M distance measuring equipment, Lazour datalink, SRZO-2M IFF transponder, SPO-2 Sirena-2 radar-warning-receiver (RWR), KSI-5 compass system and an AGD-1 artificial horizon.

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(The first ever production Su-15, coded “34 Red”, before pre-production examples were delivered)

With the more reliable R-11FS-300s becoming available, the Su-15 was re-engined with those. No changes ocurred to thrust, only reliability was improved. The top speed of the Su-15 was 2,230 km/h at 11,000 m, and an unfortunate 1,100 km/h IAS at sea level. The climb rate remained more or less the same as the Su-11: 190 - 200 m/s. The maximum Mach speed was Mach 2.1.

This early production model was purely delta-winged, unlike the later Su-15 sans suffix examples that were produced with cranked / double delta wings starting in 1968. Speaking of which, their limit was just 6G.

Cannon armament was largely excluded. A later production example was used as a cannon testbed; the military kept demanding that the Su-15 should have at least one cannon. Sukhoi originally wanted the GP-9 gunpod, and ten aircraft from Batch 12 had the appropriate fittings and carried it at the Marneuli-Sandar AB where the 166th GvIAP were stationed. But by then, requirements were changed, and the UPK-23-250 gunpod with 250 rounds instead of 200 became the dominant option. The GP-9 gunpod on those ten aircraft was considered an experimental fitting.

Game Equivalents: Su-7B, J35A, F-100 (suggested BR: 9.0 - 9.3)

Pros:

  • Fast at high altitude (2,230 km/h) with a limit of Mach 2.1
  • Good radar with decent range (15 - 35 km detection, 10 - 30 km tracking)
  • Equipped with RWR
  • Rocket-fast climb rate (190 - 200 m/s)
  • Effective R-98R and R-98T air-to-air missiles with 2 - 14 km of range from the rear and 8 - 18 km from the front
  • Limited all-aspect heat-seekers (R-98T)

Cons:

  • Two missile pylons only
  • Older gunpod with fewer rounds
  • Old, rear-aspect-only RWR, with little identification capabilities
  • Lack of dogfight missiles to remedy the cannon-less issue
  • Non-LD/SD radar, reliable starting from 2,100 m
  • Transonic at sea level (1,100 km/h IAS)
  • Not capable of CAS
  • BVR missiles with low maneuverability
  • Low 6G wing limit

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(“01 Red”, the first pre-production Su-15)


Sukhoi Su-15 Late izdeliye 37 - Recommended Changes

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In 1968, it was recommended to incorporate the double delta wing design onto later production Su-15 examples. Moreover, gunpods were tested and officially inducted into service in 1971. The usual loadout became two R-98R/T air-to-air missiles and 2 x 23mm GSh-23 housed in two UPK-23-250 gunpods with 500 rounds in total.

Despite the recommendation to produce the Su-15 with double delta wings, they were still produced with the older pure delta design for the time being. In 1969, from c/n 1115301 onwards, blown flaps were introduced to the pure delta wing design. The first Su-15 to be completed with double delta wings was c/n 1115331.

Moreover, from c/n 1115336 onwards, all late Su-15s could be re-engined with the Tumansky R-13-300s with 4,100 kgf on normal power and 6,600 kgf afterburner, and from batch 11 all Su-15s had the SARPP-12V-1 flight data recorder. The new engines, while being more reliable, lowered the aircraft’s ceiling by 400 m. Because of this, they were not widely used. In addition, a production Su-15 c/n 0615327 was tested with R-60 AAMs, and after testing was completed all late Su-15 sans suffix production models were retrofitted with them. The APP-50 chaff/flare dispenser with 50mm PPI-50 and PPR-50 flare and chaff cartridges was also tested, but it took the place of the gunpods.

To summarize, late Su-15s usually came with two gunpods, two R-98R/T air-to-air missiles, two R-60s, blown flaps and with either pure delta or cranked delta wings. The cranked delta design had a wing limit of 6.5G.

Production of the Su-15 late lasted from 1968 - 1971, and the production of the Su-15 sans suffix all in all lasted from February 1966 till 1971. It was succeeded by the more advanced Su-15TM.

Game Equivalents: F-4C, F-100, MiG-19, F-104A/C/G, J35A, Su-7B/BKL (suggested BR: 10.3)

Pros:

  • Fast at high altitude (2,230 km/h) with a limit of Mach 2.1
  • Good radar with decent range (15 - 35 km detection, 10 - 30 km tracking)
  • Equipped with RWR
  • Rocket-fast climb rate (190 - 200 m/s)
  • Effective R-98R and R-98T air-to-air missiles with 2 - 14 km of range from the rear and 8 - 18 km from the front
  • All-aspect heat-seekers (R-98T)
  • Gunpods inducted: two 23mm GSh-23 with 500 rounds
  • R-60s introduced
  • Countermeasures available
  • Missile count increased from 2 to 4
  • Improved 6.5G wing limit with cranked wing design

Cons:

  • No internal cannons; gunpods increase drag
  • Old, rear-aspect-only RWR
  • Non-LD/SD radar, reliable starting from 2,100 m
  • Transonic at sea level (1,100 km/h IAS)
  • Only two R-60s
  • No CAS loadouts
  • Countermeasures pod took the place of cannons
  • High energy loss in turns with pure delta design
  • BVR missiles with low maneuverability
  • Low 6G wing limit with pure delta wing design
  • 6.5G wing limit with cranked design still underwhelming

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(Late Su-15 production model with two UPK-23-250 gunpods, one R-98R and one R-98T missiles, note the pure delta wing design)


Sukhoi Su-15T izdeliye 37M / izdeliye 38 - Huge Upgrade Program

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Because the performance of the Su-15 did not fully satisfy the military, it was due for a mid-life upgrade. As a matter of fact, the reason why the Su-15 turned out the way it was is attributed to Sukhoi OKB being overloaded with work, as they were working on many projects at that time and the Su-15’s prototype did not receive the most attention. It was supposed to be a lot more capable from the start, had it not been to the design bureau being overloaded with other projects at the time.

In mid-1966, several months after the Su-15 entered production, they envisioned it with a Korshun-58 radar, the SAU-58 was finally ready and the RSBN-5S Iskra short-range navigation system had just been developed at that time.

However, the new radar could not provide the intended performance, so all attention was directed towards the Smerch-A of the Ye-155P (the MiG-25P’s prototype) and the project was canceled. Because of this, they decided to arm the Su-15 with the RP-26 Taifoon; a derived radar from the Smerch-A.

The TP-26 Taifoon was a more capable radar than the RP-15 Oryol-D58, with a detection range of up to 70 - 75 km against bombers at high altitude and up to 60 km against fighters, 15 km and 10 km respectively at low altitudes. Tracking range was 50 - 55 km against bombers and 40 - 45 km against fighters, 10 km at low altitude for both sizes, scanning with ±70° azimuth and +30°/-10° elevation.

Moreover, the new R-832M communications radio replaced the older R-802V, the Pion-GT antenna feeder system was introduced, the RBNS-5S Iskra short-range navigation system was inducted alongside an upgraded Lazour-SM datalink, a new SPO-10 Sirena-3 RWR and the long-awaited SAU-58.

The military also demanded that it receives CAS loadouts to make them useful for the Soviet Air Force’s tactical arm; to this end the Su-15T could be loaded with 1 - 2 500 kg bombs, or four 100 or 250 kg bombs, up to two UB-16-157U rocketpods each with 16 x 57mm S-5K unguided rockets or two S-24 heavy unguided rockets. They actually also considered an internal cannon, and it happened, but remained only a prototype configuration.

The new and formerly tested R-13-300 engines also made their way. As they were more powerful than the previous R-11FS-300s, the top speed at sea level was increased from 1,100 to 1,300 km/h at sea level, and the climb rate from 190 - 200 m/s to 228 m/s.

Despite the enhancements, the Su-15T had only 20 examples produced, mainly because of issues which protracted its development and deliveries. The Su-15TM replaced it in October 1971 in production (but did not see service till 1975).

Game Equivalents: F-4C, F-100, MiG-19, MiG-21F-13, F-104A/C/G, J35A (suggested BR: 10.3)

Pros:

  • Fast at high altitude (2,230 km/h) with a limit of Mach 2.1
  • Vastly improved radar
  • Top speed at sea level increased from 1,100 to 1,300 km/h
  • Upgraded SPO-10 Sirena-3 RWR with more aspects
  • Climb rate improved from 190 - 200 m/s to 228 m/s
  • Has 2 x 23mm UPK-23-250 gunpods
  • Equipped with R-60s and R-98R/Ts
  • Countermeasures available
  • CAS loadouts became available

Cons:

  • No internal cannons; gunpods increase drag
  • New radar, but not capable of LD/SD
  • Only two R-60s at once
  • No CAS loadouts
  • Four missile count poor in comparison to other aircraft
  • No countermeasures
  • BVR missiles with low maneuverability
  • Improved wing limit from 6G to 6.5G, but still low

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Sukhoi Su-15TM izdeliye 37M - Finest Modernization

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The best and final version of the Su-15, the Su-15TM. With more than 400 produced, this is the most definitive and lethal variant.

Following the comprehensive Stage A and B of the State Acceptance Trials, the Su-15TM with the new radar was introduced to service, and the upgraded aerial intercept weapons system was designated “Su-15-98M”. The new radar was the RP-26M Taifoon(-M); while it had to be designed with an ogival radome which negatively affected its range because conical design of the previous RP-26 proved troublesome, it was more reliable and was capable of ±70° in azimuth and elevations of +30°/-10°.

Range data as follows:

Detection range at high altitude: 65 - 70 km (bomber-sized targets), 45 - 55 km (fighter-sized targets)
Tracking range at high altitude: 40 - 45 km (bomber-sized targets), 35 - 40km (fighter-sized targets)
Detection range at low altitudes: 15 km (bomber-sized targets) 10 - 15 km (fighter-sized targets)
Tracking range at low altitudes: 10 km (bomber-sized targets), 5 -10 km (fighter-sized targets)

With the new radar also came the improved R-98MR/T air-to-air missiles. These had improved kill ranges; 5 - 24 km head-on and 2 - 15 km in pursuit; improved over the previous kill ranges of 8 - 18 km head-on and 2 - 14 km for the R-98R and R-98T respectively. They were loaded under updated PU-2-8 racks.

RTGVEsM.png

(Su-15TM firing an R-98MR missile)

The SAU-58 AFCS was replaced with the modernized SAU-58-2, and the number of R-60s was increased from 2 to 4, as an Su-15TM example was tested with the APU-60-2 launcher (though it did not enter service with the Su-15 in general). In the 80s, it was retrofitted with improved R-60M AAMs. It also retained the possibility of loading the APP-50 chaff/flare dispenser, which unfortunately had to take the place of the aircraft’s gunpods when it was to be fitted.

Much like the previous Su-15T, it had basic CAS loadouts ranging from 100, 250 and 500 kg bombs, in addition to 32 S-5K unguided rockets or two S-24s. The fuel capacity was also improved.

The Su-15TM stayed in service till the 90s until it was finally retired from service. It’s infamous for the shooting of the Korean airliner.

Game Equivalents: MiG-21MF, MiG-21SMT, J35D, F-104J/S, F-4C

Pros:

  • Fast at high altitude (2,230 km/h) with a limit of Mach 2.16
  • Vastly improved radar
  • Fast at sea level; 1,300 km/h
  • Equipped with SPO-10 Sirena-3 RWR
  • Very good climb rate of 228 m/s
  • Has 2 x 23mm UPK-23-250 gunpods
  • New R-98MR/T missiles with higher kill ranges
  • All-aspect heat-seeking AAMs (R-98T + R-98MT)
  • Access to the APU-60-2 launcher providing up to four R-60 air-to-air missiles
  • R-60M retrofitted
  • Countermeasures available
  • CAS loadouts retained
  • Higher range than the previous models (1,380 km vs 1,260 km)

Cons:

  • No internal cannons; gunpods increase drag
  • New radar, but not capable of LD/SD
  • New radar with higher reliability but worse range in comparison to the Su-15T’s RP-26
  • BVR missiles with low maneuverability
  • Inferior to F-4 Phantoms, Mirages and other Western aircraft in speed at sea level
  • Outmaneuvered by aircraft such as the MiG-21 and Mirage
  • Underwhelming 6.5G wing limit

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Sukhoi Su-15bis - Lost High-speed Potential

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(The Su-15bis’ sole prototype, a conversion from the fifth production Su-15TM “25 Blue”, c/n 0306)

In the early 70s, a new powerful engine was developed: the Gavrilov / Tumansky R-25-300 with a second stage afterburner (or a contingency rating/power boost). Shortly after the Su-15TM’s Stage A of the SAT (State Acceptance Trials) came to an end on the 25th of February, 1971, the CofM (Council of Ministers) issued a directive followed by a joint ruling from MAP and the Air Force to re-engine the Su-15TM with the latest R-25-300s.

These new changes offered a thrust of up to 4,100 kgf on normal power, 6,850 kgf on afterburner and 7,100 kgf on full boost. An Su-15TM coded “25 Blue” (with the production code c/n 0306) was used as the prototype of what became known in-house as the T-58bis (and Su-15bis as the official service designation). The conversion was completed in the first half of the year at the Novosibirsk No.153 factory (which is the one that mainly produced early Sukhoi jets such as the Su-7, Su-9 and Su-11) and the prototype made its maiden flight on the 3rd of July, 1971.

Flight tests continued until the 20th of December the same year and they’ve proven that the Su-15bis had impressive and obvious acceleration improvements over the Su-15TM and a higher top speed, especially at low and medium altitudes with the contingency rating the engines provided. With the second stage afterburner, the Flagon could now intercept targets flying up to 1,000 km/h at 4,000 m in pursuit mode.

Unfortunately, despite recommendation for production, it never received the status of a production aircraft. Instead, the Su-15TM remained the top variant, and the R-25-300 powered the MiG-21bis.

Game Equivalents: MiG-21MF, MiG-21SMT, J35D, F-104J/S, F-4C

Pros:

  • Top speed, acceleration and climb rate vastly improved in comparison with the Su-15TM, thanks to the R-25-300 engines (the same engine type as the MiG-21bis’)
  • Decent, high-ranged radar
  • Equipped with SPO-10 Sirena-3 RWR
  • Has 2 x 23mm UPK-23-250 gunpods
  • Access to the APU-60-2 launcher providing up to four R-60 air-to-air missiles
  • R-60M available
  • CAS loadouts retained
  • Effective (range-wise) R-98MR/T missiles
  • All-aspect heat-seekers (R-98T and R-98MT)

Cons:

  • No internal cannons; gunpods increase drag
  • New radar, but not capable of LD/SD
  • New radar with higher reliability but worse range in comparison to the Su-15T’s RP-26
  • BVR missiles with low maneuverability
  • Inferior to F-4 Phantoms, Mirages and other Western aircraft in speed at sea level
  • Outmaneuvered by aircraft such as the MiG-21 and Mirage
  • Underwhelming 6.5G wing limit
  • Flight range reduced especially on second stage afterburner

nO1oxhI.png

(Another view of the same Su-15bis prototype)

Some variants are not included as they were trainers, such as the Su-15UT and Su-15UM, and testbeds with internal cannons, engine testbeds, avionics testbeds etc.

Thanks for reading.

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Audio transcript of that infamous incident in English

Spoiler

“P” refers to the pilot, Maj. Osipovich, his callsign was “805”
“CC” refers to “command center”, and “Deputat” is “Deputy” (the PVO’s deputy commander)

5:56 AM

P: Deputat, this is 805, heading 45°, climbing to 8,000 m/26,250 ft - authorization…
CC: 805, roger, stay on this heading.
P: Copy that.
CC: 805, Deputat here, the target is 5° to port, port range 130 km/80.75 mi. Target follows a heading of 240°, 5° to port, range 120 km/74.5 mi.

5:58 AM

CC: 805, Deputat here, target straight ahead, range 70 km/43.5 mi, flight level 10,000 m/32,800 ft.

6:02 AM

P: Target in sight, flying at 8,000 m.

6:03 AM

CC: Roger, target straight ahead, range 12 - 15 km (7.5 - 9.3 mi).

6:04 AM

CC: 805, Deputat here, target coded hostile, to be destroyed in the event of an incursion.
P: Roger, wilco.

6:10 AM

CC: 805, can you identify the aircraft type?
P: Of course no.

6:11 AM

CC: 805, interrogate the targets [by means of IFF].
P: Roger.

6:13 AM

P: No [‘friendly’] response.
CC: Roger, activate the special system (i.e weapons system).
P: System active.
CC: 805, Deputat here, keep an eye on the heading.
P: Roger, so far it matches the heading.

6:14 AM

CC: 805, Deputat here, get ready to fire, get ready.
P: Roger. I’ll need to use afterburners.
CC: What’s your fuel status?
P: I got 2,700 kg (5,950 lbs).
CC: Engage afterburners when ordered.

6:15 AM

CC: 805, do you have a good lock-on?
P: I got a stable lock-on.

6:17 AM

CC: Do you see the adversary?
P: Target in sight.
CC: Roger. Destroy!
P: Repeat that, please!

6:18 AM

CC: 805, the target has violated the state border. Destroy the target!
P: Roger, wilco.
CC: Does the target have navigation lights on?
P: Affirmative, the nav lights are switched on… a flashing beacon is on.
CC: Roger.

6:19 AM

CC: 805, flash your nav lights.
CC: 805, flash your nav lights briefly.
CC: 805, force the target to land on our airfield! (this command overrules the one to destroy)
P: … I got my missile launch indicators on!
CC: 805?..
P: 805 here.

6:20 AM

CC: 805, fire a warning shot! Give a cannon blast!
P: … I have to move in closer. I’m cancelling lock-on, moving in.
CC: Give a cannon blast!
CC: 805! Comply!
P: Lock-on cancelled, I’m firing the cannons.
CC: Have you fired, 805?
P: Affirmative.
CC: Do you see the target?

6:21 AM

P: Yes, I’m closing in, moving closer.
CC: Roger.
P: The target is descending; I’m within 2 km (1.25 mi) or so.
CC: Is the target descending?
P: Negative, it is still flying at 10,000 m.
AP (another pilot, callsign “163”): I see you both, about 10 - 15 km (6.2 - 9.3 mi) out.
P: The target is decelerating. I’m passing… passing… I’m ahead now.
CC: Roger, 805. Reduce speed, 805.

6:22 AM

CC: Flash your nav lights.
P: Roger, wilco. Speeding up now.
CC: Has the target increased speed?
P: Negative, it is reducing speed.
CC: 805, open fire!
P: I cannot! You should have told me earlier… I’m off the target’s wing now.
CC: Roger. Move into attacking position if you can.
P: I’ll have to fall behind now.
CC: Report relative target position, 805.
P: Repeat that, please!
CC: What is the target’s altitude?
P: 10,000 m.
CC: What’s the relative target position? Relative to you?
P: Relative target position? Let me see… 70° to port.
CC: Roger.

6:23 AM

CC: 805, try to destroy the target with cannon fire.
P: I’m falling behind, I’ll try missiles.
CC: Roger.
CC: 805, approach the target, destroy the target!
P: Roger, wilco. I got a good lock-on.

6:24 AM

CC: 805, are you closing in?
P: Target ahead, I have lock-on, range 8 km (5 mi).
CC: Engage afterburners!
P: 'Burners on.
CC: Fire!
P: Missiles fired. Target destroyed.
CC: Break off the attack, turn right on heading 75°.
P: Attack interrupted.

10 Likes

Very nice, I didn’t know the old forums had this already and I made a topic about it here too, albeit it pales in comparison to how much you have written.

Spoiler

Sukhoi -15 'Flagon', the Russian J-8

Not yet accepted suggestion

image
Introducing the Su-15 Flagon, the older, Russian brother, to the Chinese J-8 fighter jet.
The flagon predates the j-8 by around 6 years and was a step towards a heavy fighter with a focus on high altitude high speed interception capability.
With around 1,290 airframes having been produced, its a wonder this jet isn’t in game already.

History

After realising the limitations of the Su-9 and Su-11 supersonic interceptor aircraft specifically for intercepting the, at the time, new B-52 Stratofortress, Sukhoi was on the prowl to develop a new and capable interceptor.
Initial development took a great amount of design from the Su-11 and essentially redesigned the tail to accommodate two engines and the nose to accommodate a larger and better radar.

The aircraft suffered from internal political infighting with the Yakovlev bureau and hence had a delayed testing and production.

After production ramped up, the flaws, particularly the poor take-off and landing handling were addressed with the redesign of the wings into a double delta configuration, much like the J-7E in game, as well as incorporating a boundary layer control system onto the aircraft.

This aircraft was later upgraded as the ‘Su-15T’ by giving it the Volkov taifun radar (based on the MiG 25’s radar), but this was not to be and only 10 airframes were put into this configuration. However, hope wasn’t lost as in 1971, the Taifun-M radar (improved) was fitted onto the jet as well as UPK-23-250 gun pods and R-60 missiles.

The Flagon would typically sortie using a mixed loadout of 2 R-60 missiles and 2 K-8 missiles on the 4 wing pylons, of which, one would be the SARH variant and the other would be the IR guided variant. The IR variant was often fired first in order to not have it decoyed by the SARH missile. Both missiles were usually fired at a target in order to secure the kill.

On the underside of the fuselage it had 2 more pylons which were normally used by the UPPK-23-250 gun pods. Hence giving it a full loadout of 4 missiles and 2 guns.
It was also capable of carrying air to ground ordinance.

The powerful radar allowed it to ‘burn through’ any ECM resistance it would encounter. thus giving it great capability and for this very reason this aircraft was very sensitive and was never exported even to the Warsaw pact nations.

Being more known for shooting down a particular Korean passenger airliner, this jet was capable of Mach 2 and could carry medium range standoff weapons to engage enemy fighters.

Interestingly, this aircraft is accredited with the death of Yuri Gagarin, when an Su-15 flew by at supersonic speeds next to Yuri’s Mig-15.

Note

The K-8 was also called the R-8 or the R-98 and did indeed come in both SARH and IR variants.

Armament

4 under wing hardpoints and 2 fuselage hardpoints:

  • 2 x K-8 missiles (IR and SARH)
  • 2 x R-60 missiles
  • 2 x 23mm guns in UPK gunpods
  • S-5 Rockets
  • FAB-500 bombs Specifications
**General characteristics**
  • Crew: 1
  • Length: 19.5 m
  • Wingspan: 9.4 m
  • Height: 4.8 m
  • Wing area: 36.6 m^2
  • Empty weight: 10,760 kg
  • Gross weight: 17,200 kg
  • Maximum take-off weight: 17,900 kg
  • Powerplant: 2 × Tumansky R-13 F-300 afterburning turbojet engines, both produced 40.21kN thrust dry and 70kN while on afterburner
**Performance**
  • Maximum speed: 2,230 km/h
  • Maximum speed: Mach 2.1
  • Range: 1,380 km (860 mi, 750 nmi)
  • Combat range: 725 km (450 mi, 391 nmi)
  • Ferry range: 1,700 km (1,100 mi, 920 nmi)
  • Service ceiling: 18,100 m (59,400 ft)
  • g limits: + 6.5
  • Rate of climb: 228 m/s (44,900 ft/min)
  • Wing loading: 555 kg/m2 (114 lb/sq ft)
**Radar**
  • Radar: Taifun-M
  • high-flying targets detection: 70 km
  • low-flying targets: 15 km
  • high-flying targets: 45 km
  • low-flying targets: 10 km
    Radar limits:
  • vertical: +30°/-10°
  • horizontal: +/- 70°
Pictures








image
^ as you can see, the R-60’s were mounted on the inner pylons while the K-8 was on the outer. i don’t know if they could switch places or not.
image
^ here is an image showing the same loadout format as well as the IR version of the K-8 and the SARH mounted at the same time.

Sources

feel free to use this ^ data for your suggestion if mine gets rejected lol

2 Likes

You can use the data I’ve provided for your suggestion if you’d like^^

nah you got there first ^^ id hate to steal

I’d love to see the TM at 10.7. It’s such a good looking, interesting, and historically significant aircraft that would be a perfect counterpart to the F-104G.

3 Likes

“…No cannon armament was included. A later production example was used as a cannon testbed; the military kept demanding that the Su-15 should have at least one cannon. Sukhoi originally wanted the GP-9 gunpod, and ten aircraft from Batch 12 had the appropriate fittings, but none were actually equipped with them…”
1.At the old forum, in my opinion, guns were discussed-all 10 pieces of Su-15 with GP-9 were in 166 Gv.IAP (Sandar airfield.Marneuli)…Photo the beginning of the 1980s…

Spoiler


1 Like

Very odd but fantastic pictures. Post was updated thank you!

They look similar but with the delta wing design it was quite a bit more maneuverable I imagine

Don’t worry about it just link to my post if needed :)

1 Like

“wing limit of 6.5G”

I’m not an aero scientist, but I understand that aerodynamically, G load may vary from design to design. An F-104 pulling 13G at supersonic speeds with those small wings for example is not the same performance the MiG-29 has if it were pulling the same Gs. The Su-15 had double delta wings that are more fitted to maneuvering than what the F-104 had.

The wings would snap off at 6.5g. That is what the g limit is referring to. It might be maneuverable, sure, but its wings will fall off at 6.5g.
Someone correct me if my math is wrong, but at 6.5g of acceleration, the Su-15TM would have the following turn times at various speeds assuming constant speed:
46.6s, 1700km/h (cruising speed)
61.1s, 2230km/h (max speed)
10.1s, 370km/h (takeoff speed)
21.9s, 800km/h (for reference)
For comparison, the F-104G can pull 12g. At 12g, that gives the following turn times:
12.2s, 821km/h (cruising speed)
35.4s, 2387km/h (max speed)
5.2s, 352km/h (takeoff speed)
11.9s, 800km/h (for reference)

The Su-15TM would not be maneuverable. It may be effective in a long 1-circle rolling scissor with good AoA capabilities, but otherwise any significant turn sustained for more than a second or so would blow the wings off. It makes up for this with great climb rate, acceleration, and missile options, making a superb BnZ fighter.

By the way, I was inattentive myself earlier…One of the photos is in the book by V. Markovsky…And according to the terms of the game, you can add a built-in cannon…

Spoiler

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1 Like
  1. The game does not take into account many factors affecting overload…Therefore, the actual behavior in the game will depend on the setting of the FM Model …
    2.F-104G-it is better to compare with the MiG-21Bis (by the value of the maximum take-off weight) …
    3.The maximum operational overload of the F-104G is 7.3G …Su-15 is 6.5G …
    4.For fighters of the 1-2-3-4 generation when conducting maneuverable air combat, it is the Main Factor (The specific load on the Wing is the Ratio of the mass of the aircraft to the area of the bearing surface).
  2. The parameters of the overload cutoff for the Su-15 (Su-15UT) are not set according to the parameters of the airframe strength…and according to the parameters (Strength of the engine compressor/The strength of Outboard fuel tanks/The efforts of the stabilizer boosters and the Strength of the suspension armament (The main factor of the R-98 missile)…All these parameters are not taken into account in the game …
  3. I will give examples based on the F-4E (17,965 kg.)-Su-15/Su-15UT/Su-15TM/Su-15UM (17,200-17,900 kg.)
  4. Since the Su-15/Su-15TM are interceptors with a small weight of suspended weapons, the main parameter for overloading is the remaining fuel…-For example, F-4E (Empty weight-13,400 kg.)-Su-15TM (Empty weight-10,760 kg.) …
    7.Since the Su-15/Su-15TM are interceptors, the maximum overload is calculated for supersonic speed (pay attention to the parameter in the table-The number of M for the R-98_M rocket = 1.75)…For the F-4E, this parameter = M-1.05 …
    8.The limitation for the F-4E at maximum operational load will be AIM-9 missiles (1,390 km/h) …
    9.Try to Extrapolate this data-F-4E /Su-15…
  5. Most likely, all this is not taken into account in the game-therefore, the FM model for the Su-15 can be calculated based on the data regarding the F-4E…
Spoiler


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Gaijin multiply the structural limit from the manual by 1.5 on all aircraft to get the g that the wings break at in game. That’s done because the flight manual figures include a factor of safety.

So if the flight manual states the limit for the Su-15 is 6.5g, then in game the wings will rip off at around 9.75 g.

2 Likes

Gaijin use the figure from the flight manual multiplied by 1.5 to get the in game rip g. So if the Su-15 flight manual says the maximum g allowed is 6.5 then the wings will break in game at about 9.75 g.

Hi there! Would you allow me to write a suggestion post and use the info gathered here as part of it? I’ll be sure to credit you, as this is some really amazing research.

3 Likes

No problem!

1 Like

Thank you very much!

1 Like