Architecture Myths #9: Clean Lines

This post is about how aircraft maker Sukhoi treats every aircraft it makes as a prototype for the better performance of the next one. Go here if you want information on arms and armament control systems. That’s another story. This story is about ROCKET SCIENCE.

Sukhoi SU-27

It begins with the Sukhoi SU-27 of 1985.

The SU-27 was developed as a response to the US’s F-15. Aerodynamic design was by Tsentralniy Aerogidrodinamicheskiy Institut (TsAgI).

The SU-27 had:

• good short-runway performance
• max. speed of Mach 2+
• very low wing-loading (This is the loaded weight of the aircraft ÷ area of the wing. Aircraft with low wing loadings produce more lift per unit area of wing, have better agility and higher landing and take-off speeds. THIS ALSO APPLIES TO BIRDS.)
• large internal fuel tanks leaving more underwing arms space
• two AL-31F afterburning bypass turbojet engines providing:
  1. maximum thrust of 12,500 kgf for excellent thrust-to-weight ratio
  2. excellent agility at all altitudes and speeds
• engine air intakes fitted with mesh guards to prevent bird strikes
• the ability to perform a mission and return on one engine
  1. separate fuel supplies for each engine positioned away from each other so both can’t be destroyed in one hit
  2. a stable power plant that can still function when its gas/air duct is damaged by fragments, bullets, or a shock wave so that shrapnel enters the air intake
• a space between the fuel tanks and air intake channels to prevent fuel from entering the engine inlet from the tanks (when they are shot through)
• wings supported in three places, again to withstand destruction in one hit
• essential parts of the mechanical control system, hydraulic system and electrical system duplicated (and at a distance from each other) for the same reason
• emergency power storage that can control the plane without any hydraulic system

The SU-27 was the first aircraft to perform “The Cobra”, a manoeuvre named after the Soviet test pilot Viktor Pugachev first demonstrated it publicly in 1989 at the Paris Le Bourget air show. 

It is a dramatic and demanding manoeuvre in which an airplane flying at a moderate speed suddenly raises the nose momentarily to the vertical position and slightly beyond, before dropping it back to normal flight. It uses potent engine thrust to maintain approximately constant altitude through the entire move. The manoeuvre supposedly has some use in close range combat, and is an impressive trick to demonstrate an aircraft’s pitch control authority, a high angle of attack stability and engine-versus-inlet compatibility, as well as the pilot’s skill.

The P-42 Record Flanker was an SU-27 remodelled to lower its weight for setting records. Even the paint was removed, the aircraft polished and all drag-producing gaps and joints sealed. The engines were pimped to increase thrust to 2,204lbs, producing a thrust-to-weight ratio of almost 2:1.

Between 1986 and 1988 the P-42 set time-to-height records for 3,000, 6,000, 9,000, 12,000 and 15,000 metres, a height record of 19,335m (63,435 ft) and time-to-height records with various payloads. The aircraft also set the standing take-off record with a run of less than 1,540ft. These records are being constantly challenged and beaten but many were still standing in 2010.

Sukhoi SU-30

The range of the SU-27 was good, but insufficient for the Soviet Union. An aircraft with a larger range and two pilots was needed. (It would take more than seven hours to fly the 9,000 km from Moscow to Vladivostok at an average speed of Mach 2.0.) The SU-27 was the base for two prototypes produced in 1989. The first production aircraft flew in 1992.

It had thrust vectoring. Normally, aircraft use ailerons to change the angle of travel like this

but thrust vectoring controls the direction of travel by changing the direction of thrust of the engine like this.

It allows some very complicated manoeuvres such as The Cobra and the “I-feel-sick-just-even-thinking-about-it” Tailslide.

The point of these manoeuvres is to quickly decelerate the aircraft and cause a pursuing fighter to overshoot. Thrust vectoring is good to have because it means you can do stuff the guy in the other aircraft probably can’t. Here’s an image of an SU-30MKI showing the engine nozzles angled slightly up upon take-off.

Sukhoi SU-33

The SU-33 is a ‘navalized’ SU-27K prototype. Thrust vectoring and the need for less runway are convenient if you want to do this.

Importantly, you can take off without having to depend upon devices such as aircraft catapults. 

The SU-33’s adaptions mainly relate to withstanding the greater structural and undercarriage stresses during quick descents and landings when the aircraft isn’t nose-up prior to touchdown. Other adaptions include

• larger leading edge slats, flaperons and other control surfaces to provide more lift and manoeuvrability at low speeds
• wings with double-slotted flaps, outboard drooping ailerons and other refinements to enlarge the wing area by 10–12%
• wings and stabilators fold to maximise the number of aircraft the carrier can accommodate and to allow ease of movement on deck
• more powerful turbofan engines to increase thrust-to-weight ratio
• In-flight refuelling probes
• canards (the little wings in front of the big wings) to shorten the take-off distance and improve manoeuvrability
• a shorter and reshaped rear radome to prevent it striking the deck during high-Alpha (angle of attack) landings
  

Sukhoi SU-34

The SU-34 is the development of SU-27IB prototype. It shares most of its wing structure, tail, and engine nacelles with the SU-27/SU-30 and has canards like the SU-30MKI/SU-33/SU-27M to improve manoeuvrability and reduce drag. Many design improvements relate to crew comfort for better performance on long distance missions.

The cockpit is unusually large, with side-by-side seating for two – pilot-commander on the left and navigator/weapons operator on the right.

No doubt this is more social on long missions but it also means that instruments don’t need to be duplicated. The cabin is pressurised up to 10,000 metres (32,800 ft) so oxygen masks aren’t used outside of emergency or combat situations. The crew members can stand and move about the cabin and there is space between the seats to have a lie down. Behind the crew seats are a toilet and a galley. No images of these exist (probably because they are hidden by the raised floor when the entry ladder is down).

Sukhoi SU-35

Four converted and six new-build prototypes of the SU-27M were developed in order to test the canards and new flight-control system. The third prototype was called the SU-35 and appeared at the 1993 Dubai Airshow. Although looking similar to the earlier models, it is a ‘deep re-design’. Many of the improvements were used to ugrade the SU-30 as well develop the later SU-37. Here’s an SU-35, formerly the SU-27M.

• The centre of gravity of the SU-35 was further to the rear, making canards unnecessary.
• The vertical stabilisers can be differentially deflected so the SU-27’s dorsal airbrake (see below) is now unnecessary.

• Smaller hardware made it possible to reduce the size of the hump behind the cockpit and to have less of a tail “sting” at the rear. This is the bit that deploys the braking parachute.
• Titanium alloys made it possible to increase the lifespan to 30 years or 6,000 service hours and increase the maximum take-off weight to 34.5 tonnes.
• Internal fuel capacity increased by more than 20% to 11.5 tonnes.
• Fully rotating thrust-vectoring capability with nozzles that, depending on the manoeuvre, can be deflected both synchronously and differentially. This is a big deal because the most critical problem that needs to be solved is how to provide the nozzle reversal joint with a seal strong enough to prevent outblast of gases at temperatures of 2,000°C and pressures of 5–7 kgf/cm2.
  

The TVC (thrust vectoring control) capability of the 117S engine not only enhances turning performance in the close combat high alpha manoeuvre regime, but can also be used to offset supersonic trim drag, reducing thrust and fuel burn requirements in supercruise. 

The SU-35S can sustain supersonic cruise without afterburners. An afterburner is when extra fuel is injected and ignited after the engine turbine. It produces short bursts of extra power for supersonic flight, but uses much fuel to do so. As you can imagine from these Eurofighter Typhoon afterburners.

Not having to use afterburners for supersonic speed means your plane can fly higher and come in faster, as anxiously noted on the website of Air Power Australia, “Australia’s Independent Defence Think Tank”.

The sustained speed, persistence and high acceleration performance produced by the 117S engine will allow the Su-35S to attack slower and less agile opponents, yet remain outside their missile engagement envelopes, thus making this aircraft very difficult to kill. The high thrust at high speeds and altitudes will allow the Su-35S to defeat most conventional BVR missiles by endgame manoeuvre and use of countermeasures.

The SU-35S is a game changer, as it robustly outclasses all competing Western fighter aircraft other than the F-22A Raptor. Deployed in significant numbers it is capable of changing the balance of power in any region where this occurs. This reality does not appear to be widely understood in most Western air forces, or DoD bureaucracies.

Sukhoi SU-37

And here’s a Sukhoi 37.

They’re not the prettiest of things. Kind of droopy at the front, angular underneath and rather ungainly when on the ground. Much like pelicans. This next video was taken on September the 14th, the first day of the 2013 Paris Airshow. (I’m finding the amateur videos better because there are fewer cuts and edits.)

You just saw most of these moves that were made at the Sukhoi SU-37 prototype demonstration flight at Farnborough Air Show in 1996 by Sukhoi test pilot Yevgeni (Ivanovich) Frolov.

1. Take-off  2. Half vertical roll  3. 3/4 loop  4. “Pougatchev Cobra”  5. Heading reversal 90^o x 270° with descend  6. Half loop  7. Pougatchev Cobra with turn  8. Flight at 450 pitch with 90^o turn 9. 1+1/2 roll 10. Turn with reheat  11. Fixed roll 12. Half loop. 13. Somersault (loop with min radius) 14. Heading reversal 90° x 270°  15. Flight at Vmin  16. Tail slide  17. Rolls  18. Heading reversal 90° x 270° and landing

No.13. used to be thought impossible. It is called the Kulbit.

but also known as “Frolov chakra“, after Yevgeni Frolov. It is an aerial in which the aircraft performs an extremely tight loop, often not much wider than the length of the aircraft itself. It is an example of post-stall maneuvering, a type of super-maneuverability. Like most post-stall maneuvers, it demonstrates pitch control outside of the normal flight envelope wherein pitch control is made possible by having aerodynamic flow over the aircraft’s elevators or stabilators. Only the Sukhoi SU-30, Sukhoi SU-35, Sukhoi SU-37, Sukhoi SU-47 Berkut, F-22 Raptor, PAK-FA and MiG-29OVT can do the Kulbit. 

• Modular design of the SU-37 allows for replacement of the nozzle, afterburner, mixer, low-pressure (LP) turbine and compressor, and gearbox as part of post-warranty servicing
• It is possible to repair or replace the blades of the first stage of the LP compressor and all stages of the HP compressor.
• The integral triplane wing layout and its small specific wingload plus the high power-to-weight ratio ensures superagility, increased range and improved takeoff and landing characteristics.
• The thrust vectoring is part of the aircraft flight control loop and makes it possible to minimize flight speed and perform aerobatics at speeds nearing zero without angle-of-attack limitations. 
• The aircraft has virtually no angle-of-attack limitations. It can fly flatwise to the air stream, with its tail forward, i. e., with 90 and even 180 deg angles of attack. It can locate targets with its radars and attack them with its weapons from any position. This feature is useful for air combat and for evading missile attacks.

Sukhoi SU-47

The SU-47 was just mentioned above. Here’s one. It’s not trying to be beautiful.

The swept-forward wing, provides a number of advantages over swept-back wings

• higher lift-to-drag ratio: 
• A substantial part of the lift occurs at the inner portion of the wingspan. This inboard lift is not restricted by wingtip stall and the lift-induced wingtip vortex generation is thus reduced. The problem of wing-twisting is solved by composite materials that resist twisting while still allowing the wing to bend for improved aerodynamics.
• higher capacity in dogfight maneuvers: The ailerons—the wing’s control surfaces—remain effective at the highest angles of attack, and controllability of the aircraft is retained even in the event of airflow separating from the remainder of the wings’ surface.
• higher range at subsonic speed: The high aspect ratio of the forward-swept midwing enhances long-range performance.
• improved stall resistance and anti-spin characteristics
• improved stability at high angles of attack
• a lower minimum flight speed
• a shorter take-off and landing distance

Initially intended as a demonstration aircraft, attempts were made to market it as as something that can take on the F-22. Here’s some footage from Russian television.

Sukhoi T-50

Although a stunning example of techno-logic, the SU-47 took an enormous amount of resources to develop and was inherently impractical as a production aircraft given the degraded defence infrastructure of Russia. Its economic footprint made it unviable. Its US equivalent, the F-22 Raptor, has come ‘under fire’ for the same reasons.

In recognition of these circumstances, in 2006, the Russian authorities approved the final project design for the PAK -FA that would become would become the new prototype.

Again, it uses the basic design of the SU-27, albeit with many modifications. Engines were the proven 117S derivative of the economic and high-performance AL-31 engine traditionally used. The logic is that speed is less important when there is stealth. Nevertheless, supercruise without afterburners is possible. 

The Russian Su-50 is not as stealthy as the F-22 Raptor and its radar is less powerful but it is more economically efficient and requires significantly less maintenance. The F-22 is number one in air-to-air combat but it is expensive.

With stealth aircraft, there is a tradeoff between stealth and performance. Design for the most aerodynamic shape, the most powerful engines, and the best manoeuvrability does not create the most invisible aircraft.

Some future post will cover the implications the unconventional logic of stealth technology has for architecture.

For now, we can learn the following from this story of Sukhoi’s development of the SU-Series:

1. Good design has no need of clean lines. They are a form of decorative ornament. EVEN IN AERONAUTICS, they have little to do with performance. Download your Sukhoi 30MKI vs. Eurofighter Typhoon wallpaper here.
2. Good design is backwards-compatible, retro-fittable. A modular design with components that can be repaired, replaced or upgraded will have a longer life.
3. Good design takes into account the economic footprint for manufacture, as well as (from 2., above) the economic circumstances of the market.
4. Good design takes a successful prototype and improves upon it. If the result is not a clear improvement, then the prototype IS RETURNED for a re-think. The legacy of the successful SU-27 was still being honoured at this September’s Russian International Air Show.
5. THE HISTORY OF GOOD DESIGN IS THE CHRONOLOGY OF INCREMENTAL AND CUMULATIVE IMPROVEMENTS TO SUCCESSFUL PROTOTYPES.
   The history of one-offs that led no-where is the history of one-offs that led nowhere.