Wednesday, 14 October 2020
The most under-rated Soviet combat aircraft?
Speaking to a former Soviet air force pilot convinced me the Su-15 was far better, and certainly more significant, than is commonly thought. The Soviet Sukhoi Su-15 was one of the best interceptors of the 1960s and '70s. It had better acceleration and initial climb rate than the US F-106; compared to the British Lightning it had double the weapon-load and double the endurance. Vitally, this supersonic warplane was available in far larger numbers than either its British or American counterparts.
Before interviewing former 'Flagon' pilot Valeri Shatrov I had a vague idea of the Su-15 as a primitive interceptor with obsolete systems that lacked agility. I found his opinions and recollections absolutely fascinating, and in some case revelatory.
I should also note that I do not take any pilot's opinions as entirely objective as most pilots have a bias towards their machine, but Shatrov's answers were candid - and at times critical enough to be credible.
The Soviet approach
The West's opinions of Soviet warplanes have often been wrong. Some overestimated, some are underestimated – and some misunderstood. Analysts often saw Soviet aircraft as inferior facsimiles of Western types, or else wildly inflated their true capabilities. To be fair, the facsimile claims have a meaningful historical origin. The Tupolev Tu-4 was a reverse-engineered B-29 Superfortress. The Tu-4 was an epic project. It was no easy thing to copy the most sophisticated aircraft in the world. It took the expertise of over 850 factories and institutes, and involved the creation of over 105,000 drawings. However, with the brutal determination of Stalin driving its completion, quick work was made of it. The design was completed in less than a year and it entered service in 1947. The Tu-4's (and so B-29's) design informed the Tu-95 that remains in service today. 70 odd years later, the Russian Air Force's 'Bear's carries Superfortress 'DNA' in its fuselage dimensions, circular cross-section, the pressurised shell fore of the wings and its thick wing roots.
This idea of Russia or the USSR lagging behind or aping the NATO nations' weapons technology is misleading and far from a universal truth. Operational helmet-cued thrust vectoring weapons, true 2D IRST sensors, electronically scanning fighter radars and post-stall manoeuvrability were all Soviet innovations. But Russia has long had a bit of a chip on its shoulder about its technological sophistication compared to Western Europe, or rather lack of it. The Steel Flea by the Russian author Nikolay Leskov is a comical short story from 1881. In it Leskov makes light of a Russian inferiority complex and an envious competition with advanced British technologies. Of course there is also a great deal of pride in Russian and Soviet innovations, but the most cursory glance at YouTube comments beneath a film about a Russian military hardware subject will reveal an aggressively defensive position from Russophiles and Russians – revealing a deep insecurity. The opposite is true of America, with a historical tendency to overestimate their strengths (a sweeping generalisation but one with some truth, see the underestimation of Japanese aircraft and pilots in World War II as an example).
Then there is the Russian philosophy of robust reliability over exquisite technology, something inherited from the Soviet era. This is sometimes viewed as a result of technological inferiority rather than a considered approach. A Western-centric view of the Su-57 may see it as bad F-22, but that is a conceptual misunderstanding: it is a different kind of machine intended to fight in a different kind of way. High stealth is at odds with the Russian philosophy acceptance of the dirtiness of real wartime operations. The Su-57 is however an 'anti-stealth' fighter and its revolutionary low band width radar antennae may be useful in detecting F-35s and F-22s at longer ranges than X-band radars. If, and this is a big if, Russia gets the Su-57 right it will offer an adequate counter to the F-22 and F-35 without the pitiful availability rates of the US aircraft. Indians withdrawal from the project is not necessarily a sign that it is a bad programme, it may also be partly due to unfair Indian expectations of a radar cross section akin to a US fifth generation type.
To go back to the 20th century, the philosopher Bertrand Russell noted 'The Russian Government has a different conception of the ends of life. The individual is thought of no importance; he is expendable. What is important is the state, which is regarded as something almost divine and having a welfare of its own not consisting in the welfare of citizens. This view, which Marx took from Hegel, is fundamentally opposed to the Christian ethic, which in the West is accepted by free thinkers as much as by Christians. In the Soviet world human dignity counts for nothing." It could be argued that this outlook is reflected in the doctrine of massed inexpensive warplanes and the acceptance of high fatalities in military operations. Compare this to the culture of USAF between Korea and Vietnam. According to Frederick Corbin 'Boots' Blesse, a United States Air Force major general and flying ace, "Safety became more important the tactics, more important than gunnery, more important anything. Safety was king. Safety took over*."
*Tiger Check, Automating the USAF pilot in air-to-air combat, 1950-1980
In the United States (in the air force at least) the pilot was precious and the increasingly expensive aeroplane was also precious. The same can be not said of the USSR at this time. The pilot was not precious and the aircraft itself was more disposable with an airframe, and especially engine, built for a shorter life. The new Russia's first fighter, the Sukhoi Su-30, was an awkward half-way house between Soviet simplicity and Western complexity and proved (and still proves) labour intensive to maintain and operate (its small arm contemporary, the AN-94 assault rifle shared the new Russia’s brief flirtation with complexity).
Before the Su-57 and before the Su-27 'Flanker', there was the Sukhoi Su-15, Su-11 and Su-9. These were similar in configuration to the MiG-21, tailed deltas with a nose intake. Nose intakes were becoming unfashionable as they limited both the radar size and internal fuselage volume compared to a cheek or shoulder-mounted intake. Entering service in 1965, the time had the unenviable task of defending the largest nation on earth against NATO, arguably the most powerful combined force in history. It was supported by the obsolete Yak-28, the extremely long ranged Tu-28 and later the extremely fast MiG-25.
The Su-15 would operate as an area defence interceptor, in an environment where any unknown aircraft crossing the air defence boundary could be treated as hostile. The intention was for the Su-15 to be guided to the interception point by a ground controller, using its relatively high-powered radar at the point of engagement to defeat any electronic jamming and to allow its radar guided missile to lock on to the target.
Key attributes for the interceptor role are rapid climb and acceleration, a good long-range radar, coupled with good air-to-air missiles, preferably of the fire and forget variety. The targets of greatest importance for the Su-15 would probably be the US B-52 Stratofortress, given its role in delivering the US nuclear deterrent. Aircraft manoeuvre performance in these circumstances is perhaps less important, unless your missile requires continuous radar illumination, when good turning performance is required once the missile goes active.
The Su-15 is best known today for its infamous accidental shoot-down of Korean Air Lines KAL007 in 1983 (another sad note: a recklessly flown Su-15 may have been responsible for the tragic loss of Yuri Gagarin's MiG-15). It performed poorly against Turkish incursions, but this speaks more of the failure of integrated air defences of the time than the aircraft itself. Indeed a look at the long list of Cold War aerial defections shows that air defence networks in a peacetime posture were generally pretty hopeless.
Soviet interceptors were not widely exported, being too specialised and their capabilities too strategically sensitive. So the Su-15 has not the fame of the extremely popular MiG-21, nor the eye-popping performance that made the MiG-25 a flying myth. But is was a vitally important aircraft. The Soviet Union had a huge number of these interceptors — over 1290 were produced, which is a lot more than its closest US analogue, the F-106, of which there was only 340. According to Shatrov, the type was extremely reliable which would further enhance the available 'air mass'.
Comparison with Western interceptors
"It was a good plane and exceptionally reliable. I always said that I loved it like a woman. And when you turned on the afterburner on take-off, you got a hefty push in the back from the ferocious power of two engines. The relatively long fuselage and delta wings allowed you to make a large number of barrel rolls from any rotation speed. What I like most about Su–15 was its ability to perform complex aerobatics at full power."
The excellent handling off the later T-10 ('Flanker') series did not come from nowhere.
"The aircraft was manoeuvrable, as I have already mentioned. With the engines set at maximum thrust the Su–15 allowed you to perform a turn with a roll of almost 90 degrees. As for the service ceiling of the aircraft I personally gained a height of 23,000 metres (75,459 feet) where ‘a little higher – space begins’ as we joked in those days.The instantaneous turn rate was very good, with a G-force of up to 6. The high alpha of the aircraft was limited to this maximum overload, but the thrust of the engines allowed any horizontal aerobatics figures without loss of speed. ‘Split ‘S manoeuvres were allowed from a minimum altitude of 2.5 km up to the practical service ceiling."
When one compares the Su-15 with the Lightning, Phantom and Delta Dart, there are some significant differences and some similarities. The largest numerical difference is in wing loading, where the large wing and relatively light weight of the F-106 suggests that this aircraft would have good instantaneous turn-rate compared to the others, although, with the lowest aspect ratio, and lower thrust to weight ratio, it is likely the F-106 sustained turn rate would be less impressive. The Phantom also has a large wing area compared to both the Su-15 and the Lightning, perhaps because its origins as a naval multi-role aircraft included a requirement to carry larger external loads than the other aircraft.
As might be expected, the Lightning emerges with the lowest endurance of the four aircraft. While stressing that this is a comparative rather than an absolute assessment, my estimates suggest quite comparable endurance for the other three aircraft, but that the Lightning, even in the F6 variant, offers the shorter endurance for which it was renowned.
In terms of claimed maximum speed, in the face of considerable discrepancies in the data, I can only suggest that the F-106 was likely to be slightly faster than the other aircraft, but overall, the differences in maximum Mach number appear relatively small. In practice, the speeds available would be highly dependent on the weapons loaded, and on any other applicable limitations, for example depending on whether drop tanks were retained or not.
Let us start with the wing. The closest Western analogue to the Su-15 was the US F-106. Whereas the F-106 had a large pure delta, from 1969 Flagons had a small compound tailed delta with the angle of sweep shallower on the outer wing (it started life as tailed pure delta). The wing planform is largely a measure to get some more lift out of the wing to reduce the landing speed, and possibly improve handling in manoeuvring flight. I asked Jim Smith his opinion, he noted: "It was introduced from the 11th aircraft, so the need was probably pretty compelling. The F-106 wing, in comparison, is huge. The F-106 weighs a bit less, but has nearly double the wing area. So I'd expect better instantaneous turn rate, and better performance at altitude from the 106, and better acceleration and initial climb rate from the Su-15, which has 24% higher thrust-weight ratio." He also opined that "Compared to F-4, I'd expect better acceleration and climb rate due to slightly higher T/W. I'd also expect inferior manoeuvre performance due to higher wing loading, and I'd also expect to be somewhat out-gunned, with up to 4 Sparrow + 4 Sidewinder. But the Su-15 is primarily an anti-bomber aircraft, and would not be expecting B-52s to be escorted over Russia (bit of a one-way mission, that). "
The type had an impressive thrust-to-weight ratio for its generation. In combat configuration it was around 0.84. This compares well with the F-4 (0.77) and is far superior to the F-106 (0.68). Sukhoi’s taste for high thrust-to-weight ratios is also seen in the later ‘Flanker’ series.
It is likely that expect more than double the endurance. Early Su-15s had a similar weapons fit, with one IR and one radar guided. According to Shartrov, "the first serial Su–15 modifications (the Su-15TM Flagon-F) were called ‘Hound dog’ (Гончая in Russian) for their extremely high landing speed and ‘Dove of Peace’ (Голубь Мира in Russian) for having only two air-to-air missiles. I was lucky – I flew and was on duty with four missiles and two cannon pods. And that version had leading edge extension on the wing, somewhat reducing the landing speed."
Later aircraft had four MRAAM or 2MRAAM + 2 SRAAM plus a gun pod. So probably one kill per engagement for early aircraft, two per engagement for later aircraft. These were big missiles and probably had a big warhead. The Lightning carried two large infra-red missiles of two differing types, Firestreak and Red Top. Of the two, Red Top was the more effective, but could only be carried by ‘big fin’ Mk 3 and Mk 6 Lightnings, resulting in Firestreak remaining in service to arm the ‘small fin’ earlier aircraft. Late Mark Lightnings could also carry a gun pack, at the expense of trading away some of its limited internal fuel.
The Delta Dart carried four Falcon missiles, but these seem to have not had a very good reputation. The F-4 carried four Sparrow MRAAM, and could also carry Sidewinder IR SRAAM. Experience in Vietnam showed that a gun was also required, and this was introduced in the F-4E model. From an armament perspective, it’s probably fair to say that all four aircraft did the best they could with the somewhat limited capability available at the time. It is an interesting detail that all were fitted with additional gun armament, having at one time or another had none.
The Sukhoi Su-15 is an impressive aircraft, whose role was essentially area air defence for the Soviet Union. Given this role, it might be expected to be a large, supersonic aircraft with a large radar and air-to-air missiles, and this is very much what we find. The aircraft (strictly weapon system) is very much optimised for high-speed interception, with small wings and relatively high wing-loading.
Contemporary aircraft might be the BAC Lightning, although this is very much a point-defence interceptor; the F-4 Phantom II, originally designed as a multi-role fighter-bomber for the US Navy; and the Convair F-106 Delta Dart.
Comparing these aircraft, in the absence of authoritative data, turns out to be somewhat difficult. In a former role, with access to aerodynamic modelling and weight estimation tools, this would be a breeze, but without these, and relying on somewhat doubtful estimates, I’ll simply make some observations, with which readers will doubtless disagree.
To illustrate the data problem, if you look at the Wikipedia entry for the F-4, you will find a quoted gross weight of 18824 kg, and an empty weight of 13757 kg. The difference between these is 5067kg, which is insufficient to account for the quoted internal fuel of 7550 litres (approx. 6040 kg), let alone 4 Sparrow missiles (~800kg), pilot and equipment, and gun ammunition. Even if the ‘empty’ weight is an empty equipped weight, there is still not enough margin to account for full internal fuel plus the pilot and his kit.
As indicated in the interview with the Su-15 pilot, the high wing loading of the aircraft will result in high take-off, approach and landing speeds. In this respect, the data suggests that the Lightning would need equal care, while the large wing area of the F-106, and the naval design heritage of the F-4, are likely to mean these two would be a little easier to land.
The wings of all four aircraft underwent modification in service, with conical camber being introduced to the Delta Dart; a conically-cambered leading-edge extension being fitted to the Lightning; introduction of manoeuvre slats on the F-4E; and introduction of a reduced sweep outer panel on the Su-15, at the position of the air-to-air missile pylon. For the Su-15, this discontinuity would introduce a highly-swept vortex, with similar beneficial effects to those seen on aircraft with leading edge root extensions like the F-16. The primary effect would be to maintain lift to a higher angle of incidence, with a secondary effect of improving the flow over the outer wing at high incidence.
The modifications to the Delta Dart and the Lightning were principally to reduce supersonic drag due to lift, and, in the case of the Lightning, to add a little more fuel, whereas for the F-4 and the Su-15, increases in lift and manoeuvrability appear to have been the main objective.
"Armament varies widely across the four aircraft. With 4 Sparrows plus sidewinders and a gun, the F-4E appears best equipped, although early Sparrows definitely had their limitations. The Su-15 could be flown with a mix of radar and Infra-Red (IR) MRAAM, and later models could carry IR SRAAM or gun pods if required." Were Soviet missiles more reliable? This is hard to ascertain but they could barely be worse than British and US missiles of the time for probability of kill. It should be noted that at this time Soviet rocket propulsion technology was probably superior.
Overall, the Su-15 seems to have been well suited to its task as an air defence interceptor. Fast, with good climb performance and acceleration, a big radar and a mixed IR and radar missile capability, it was well equipped to deter and defeat airborne attack on the homeland, focussing on the US and NATO bomber threat.
It was not designed as an air superiority aircraft capable of gaining control over contested airspace against Western fighter aircraft, and might well have found the manoeuvrable and heavily-armed Phantom a bit of a handful. In a defensive situation, the F-4 would be met by a massed armada of more agile MiG-21s and this in a forest of surface-to-air missiles and anti-air artillery, leaving the Su-15s to perform their intended role of destroying bombers.
I imagine a properly trained pilot would have found it an exciting aircraft to fly, and, with its size, high power, and relatively small wing span, must have made a good display aircraft – big, noisy, with high rate of roll, good acceleration and an impressively purposeful appearance.
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