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Sukhoi Su-27 prototypes

Sukhoi Su-27

Venik's Aviationwww.aeronautics.ru / venik.way.to June 19, 2002

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Breakthrough inSupermaneuverability.

The following is a translation of the interview with the chief designer of theSu-27 fighter aircraft recently published in the Russian 'Science & Life'magazine. I also included some of my comments and notes to clear up a fewpoints. 

Even in the age of beyond-visual-range combat the value of maneuverabilityof a fighter remains one of the top priorities for Russian aircraft designers.And not just Russian: the USAF has preferred the more traditional and moremaneuverable YF-22 and X-35 to the more stealthy and unconventionalYF-23 and X-32

Sukhoi is currently working on the design for Russia's next-generation fighter.Nothing is known about this new aircraft other than it will probably have twoengines and will be a fighter-bomber. However, it should be expected that thenew fighter will be truly supermaneuverable with novel aerodynamics andpowerful thrust-vectoring engines. It is also likely that this new fighter will bein the weight class of the Su-27.

An interesting twist in the Russian "fifth-generation" fighter development:originally it was expected that the new Russian fighter will be a directcounterpart to the American F-22 and will be based on either the MikoyanMiG 1.42 or the Sukhoi S-37 'Berkut'. As it turned out this will be a totally newaircraft not based on any previous MFI prototypes and will be the next step

Sukhoi Su-30MK

Sukhoi Su-35

after the F-22, which has been in development for the past 20 years.

Breakthrough in Supermaneuverability

"I will never forget the first display flight of the Su-27 in Paris, organized bythe British Aerospace along with designers and test pilots of the SukhoiDesign Bureau, - recalls John Farlight - a fighter pilot in the Royal Air Force. -Victor Pugachev was turning his Su-27 360-deg in 10 seconds, the averagerate of turn - 36 deg/sec. At that time we could only hope that ournext-generation fighter could achieve 25 deg/sec. This is the kind of speedthat pilot should be able to turn his plane at to have the entire weapons suitready for an attack. If we would imagine that our new plane encounter anSu-27 in combat, after 10 second all it will be able to do is to lower the gearand land, if it's lucky. Much of what I've seen at the airshow can be used inreal aerial combat. To an average observer an airshow is just a superficialaction, but if you are one of the aviation industry experts, a fighter'smaneuvering will tell you about its flight limits. Naturally, when you see thatthere are no limits for an Su-27 or that the aircraft can go vertical, stop, slidesdown and than resumes normal flight and performs this not once, not twicebut time after time, you realize that this is not an exception, not a trick, but astandard. Complexity of this particular maneuver is not in initiating themaneuver but in exiting from it. Usually we are not allowed to exceed20-25-deg. angles of attack: if we go over it, we lose control of the machine...But the Russians perform their maneuvers, while changing the angle ofattack in a wide range, while remaining confident in their control of the aircraftwith absolutely symmetrical aerodynamics. The same applies to the engines.The Western engines "suffer" from the strict limitations on the angle of attack.When flying our fighters one has to think about the enemy's maneuvers andabout one's own limitations from the aerodynamics point of view, about whata pilot should not do. Of course this is not a very comfortable situation for thepilot. For him it's much easier when he can do anything that is necessary totarget the enemy and to pursue him. What the Russians have achieved hasastonished us to the bottom of our souls." With its revolutionary design andaerodynamics, the Su-27 has established new standards in fighter aircraftdesign. The person, who's name is inseparable from the fighter's creation, isthe designer-general of the AOOT "OKB Sukhoi" Mikhail Simonov. In 1995he was awarded the V.G. Shukhov golden medal and in 1998 he was called"the legend of the year" by the Aviation Week & Space Technologymagazine. His name can be found in the Hall of Fame of the NationalAerospace Museum in Washington, D.C., along with the names of IgorSikorsky, S.V. Ilyushin, and Verner von Braun. This is the first interview givenby Mikhail Simonov to the "Science and Life" magazine, even though hereads our magazine since 1946.

Sukhoi Su-37

Mikhail Simonov, Su-27 designer

- Mikhail Petrovich, everybody, who at least once have seen at an airshowwhat Sukhoi aircraft are capable of, or even saw their performances intelevision broadcasts, can't help but wonder why such machines are created?

When I was in the ninth grade, I read a book "Some of the Piloting Mistakes".A pilot can never be guaranteed from mistakes. Aviation has always beenand will remain to be very demanding toward pilots and designers. Becauseof technical malfunctions or crew errors not only the aircraft may die but alsothe crew and the passengers.

spin is one of the most complex and dangerous phenomenon. In essence it isuncontrollable flight most dreadfully oriented in space: the aircraft spins out ofcontrol with its nose pointed toward the ground. Upon impact the "air pocket"explodes and the aircraft is being torn into small pieces. It may seem that allone needs to do to avoid this problem is to teach all the pilots to recognizethe limits after which an aircraft enters a stupor. It should be mentioned thatthere are several similar phenomenon in aviation that begin with aircraftlosing control and rolling on the side, but not all of them result in a stupor.However, despite the fact that all fighter pilots are thought the basic methodsfor exiting from different types of spins, by far not all of them end upvictorious in real-life situations (most often this happens because of pilotingmistakes and less often because of technical problems with the aircraft).There are aircraft that cannot exit from certain types of spins due to theiraerodynamic peculiarities. Such extreme situations are uncommon in civilaviation. However, for combat aircraft maneuverability is a condition forsurvival. This is the reason why all aircraft designers around the world areworking on the issues of maneuverability. It is maneuverability, in conjunctionwith armaments carried by the aircraft, that guarantees the aircraft's ability toperform the set tasks.

- And what tasks are being set?

Maneuverability is the aircraft's capacity to change its position in space.Naturally, the must be a reason for initiating one or another maneuver. Suchreasons appear on their own in various combat situations: you must assumesuch a position in space that the enemy is within the effective range of yourweapons, while your aircraft remains outside the enemy's targeting envelop.It is understood that whoever will be able turn and position his aircraft first willbe the winner. The classic fighter aircraft of the 1940s-60s of the last century

Sukhoi S-37 'Berkut'

experienced serious problems in combat due to the severe limitations on theirability to maneuver. Normally aerial combat was conducted by large groupsof aircraft - say, twenty aircraft - and a huge "swarm" rolled in the air andeveryone wanted to survive. Fighter aircraft of classic design differed littlefrom the enemy's aircraft which resulted in prolonged aerial engagements -5-6 minutes. During that time the engines were pushed to their limits and fuelconsumption was high. And even after a victory was achieved, not everyonewas able to reach home. Every fifth aircraft was lost after the fight was oversimply because it ran out of fuel and had to be dumped. It was good if thepilot was able to eject, but if tried to land - say, on a highway at high speed -the outcome was predetermined.. When entering aerial combat, pilots ofsome countries knew they would not be able to exit from it. To fly out of thearea of combat one would need to expose his "tail", which would beimmediately targeted by the enemy. Such a fight was to the end, and whenthe red fuel light would come on, the pilot would eject from a perfectlyfunctional fighter.

- ...A sort of a single-use aircraft?

A pilot's life is more precious. But one way or another maneuverabilitydrawbacks are very costly. Thus a breakthrough into the realm ofsupermaneuverability, when the risk to the pilot and the aircraft becomesminimal, became our top priority.

- Is possible to predict that the fighter will be supermaneuverable during thedesign stage?

You usually know who will be the most likely opponent. At the time the Su-27was being designed, we were aligned with the Warsaw Pact countriesagainst the NATO. We had to produce and aircraft that would have beensignificantly superior to such fighters as F-14, F-15, F-16 and F-18.

Within our aviation industry we are represented by the Sukhoi Design Bureauand a large number of outside contactor firms. For example, our radars aremade by a number of NII1 and KB2. We do not design engines, we simplyproduce the requirements for one and it is created by the Lyulka DesignBureau. Such is the scientific and technological union which guarantees thedevelopment of a fighter of the highest quality. To make the best plane thatcan defeat any enemy fighter we need to have the best engine in the world,the best radar, the best missiles in the world and everything else also has tobe the best. While working on the Su-27 we created what seemed to be agood aircraft that exceeded capabilities of the F-15, but by how much? Byvery little. And once again in the situation of close combat we can end up in acomplex "carousel", where both fighters will have equal chance of winning.

We realized that in order to obtain a decisive advantage of the opponent ourfighter would have to be not just more maneuverable but several times moremaneuverable. There is such definition as radial rate of turn toward thetarget. In combat the advantage rests with the fighter that is able to turnaround before its adversary. We have decided that if we are able to make outfighter turn at twice the rate of the opponent, we will call thissupermaneuverability.

Supermaneuverability is a fighter's capacity to turn toward its target from anyposition in space with at least twice the rate of turn that the enemy fighter iscapable of.

- It would seem that in such extreme situations much will be demanded fromthe engines as well.

First of all the engines must have superior thrust. A modern military aviationengine is a turbojet with an afterburning chamber. (Afterburning is a mode ofoperation during which additional fuel is injected into the combustionchamber. This achieves a significant increase in the engine's thrust at the

cost of additional fuel.) The thrust produced by the two engines of an Su-27pushes the aircraft with a force equivalent to 25 metric tons (12.5 tons ofthrust per engine). Corresponding engines of American fighters at the timethe F-15 was created could generate 10.8-11 metric tons of thrust. Of coursethere are other requirements as well. It would be helpful, for example, to useengines not just to propel the aircraft but also to steer it using special nozzlescapable of turning about 15 degrees from their normal position. This isespecially important when during combat the plane is pushed beyond thecritical angles of attack (AOA). For the Su-27 the critical AOA is 24 degrees.A combat situation may demand the plane to turn 60-90 or even 120 degreesrelative to the direction of its flight. When the pilot initiates such a maneuver,the engines must respond instantly by deflecting thrust at the required angle.

The nozzles of the two turbojet engines AL-31FP used on the multi-functionalSu-30MK fighter are capable of deflecting 32 degrees in the horizontal planeand 15 degrees in the vertical plane. This enables the aircraft to performmaneuvers unattainable by other fighters: to rabidly slow down and then turnon a dime similar to a helicopter.

AL-31FP turbojet engine

When in 1989 we came to the Paris airshow for the first time with theconclusion of the State Combat Aircraft Testing Institute that flightcharacteristics of our Su-27 are inferior to those of an American F-15, wewere still convinced that our plane was significantly better American aircraft.

American fighters have set a number of time-to-altitude records. (Time ismeasured from the time the aircraft starts its take-off run and until it reachesa predetermined altitude - 3000, 6000, 12000 meters and so forth). Thus froma dead stop the aircraft must reach this altitude in the shortest possible time.All world records at that time were held by the F-15.

We have conducted a series of Su-27 flights that beat all F-15 records, thusproving that our plane is superior to the F-15 in the time-to-altitude aspect ofperformance.3

- How was this accomplished

The aircraft must be standing still like a sprinter on the start line. But whenthe engines are working the wheel brakes alone are not enough to hold theaircraft. To keep the fighter still we tried using a tank. A cable was connectedto the hook on the lower part of the fuselage, but we weren't celebrating forlong. After just a second of afterburners being engaged we heard ascreeching sound and observed how the Su-27 started pulling the tank downthe runway. We had to find something else to hold the plane. A nearbyrunway was under construction and we have noticed a huge "Caterpillar"bulldozer. We attached it to the tank, which was in turn attached to theaircraft. The fighter's start from dead stop was guaranteed.

From the very start, the engines are pushed to their limits. As soon as thecable locking mechanism is released the plane sprints down the runway andstarts gaining altitude in a vertical flight. While flying vertically up the planebreaks the sound barrier. No other aircraft, not even a space booster at suchlow altitude can achieve supersonic speed in vertical climb. Normally thishappens only in the upper regions of the atmosphere where air density isvery low. However, we could achieve supersonic flight at an altitude of just

2000-3000 meters.4

During that airshow we were able to achieve better results than theAmericans.5

In a classic aerial combat two fighters are spinning in a "carousel" until one ofthem can reach the position from which it can attack its target. However, ifcan enter close combat and in the first moment turn our aircraft 90 degreesrelative to the direction of flight, the target can be locked and missiles can befired. Thus we can considerably improve close aerial combat and in second,not minutes, guarantee our victory.

- They say that originally it was believed that the Su-27 cannot exit from astupor.

Yes, such was the conclusion of TsAGI after wind tunnel testing of the model:the aircraft cannot exit from a stupor. Something had to be done about this. Asystem was developed that would not allow the plane to exceed the AOA of24 degrees.

Not a single Su-27 model in TsAGI's wind tunnel was able to exit from thestupor. We challenged this finding by creating a 10-meter half-real-size modelof our aircraft, attached it to the Tu-16 bomber and dropped it from 10,000 m.The model had an automatic guidance system that would force it into the spinand, if the model could not exit from it, a landing parachute would bedeployed. We discovered that in about half of the situations the larger modelwould safely exit from a stupor. However, we could not tell the pilot: "Goahead, everything is fine". And thus we had to agree with TsAGI andestablish limits for the aircraft's performance. This was all very strange: wewanted to achieve high angles of attack but could not produced a planecapable of doing this.

"Cobra" maneuver

The most interesting situation occurred during flight testing. Fighter testing isan enormous work requiring about five thousand test flight, during which themachine is tested for structural strength, its aerodynamic properties, it abilityto deliver and deploy weapons and other aspects of performance. Evenbefore the "Cobra" maneuver, Victor Pugachev was performing high AOAmaneuvers. I was very worried about this because I knew about the problemsexperienced by the American F-16 fighter during high AOA testing, when theaircraft was able to achieve a 60-deg. angle of attack but was only able toexit from this maneuver by using a special anti-spin parachute. We chose adifferent approach to testing our plane, but were still very apprehensive whenPugachev entered a high AOA. However, he was able to exit from it andeverything ended well.

Further testing proved that the Su-27 would not fall into a spin whenperforming high AOA maneuvers. The results have shown that it is possibleto take the plane to high angles of attack and then return it safely to thenormal mode of operation. This finding was what opened the future for

supermaneuverability. But 20 years ago we could not realize this, we wereconducting just the first test flights.

"Cobra" maneuver in combat

During one of such flight conducted by test-pilot V. Kotlov experienced adepressurization of the air pressure sensor 6, which gave him an incorrect airspeed reading. The pilot tried to compensate what he though was very highspeed by increasing the climb angle and finally the aircraft came to rest in avertical position at an altitude of 8000 meters and started sliding down with itstail first. The pilot's hopes that the plane will eventually return to normal flightdid not materialize, instead the aircraft seemed to be "suspended" betweenthe sky and the ground. This was unexpected and baffling: the air speed wasnear zero and the altitude was 8000 meters. The pilot panicked, he switchedoff the afterburners and immediately engaged them again. The plane startedfalling on its tail and the pilot experienced weightlessness - in the future thismaneuver was to be called the "Kolokol", or the "Bell". 7

- And all of that happened in just a few seconds?

About 20 seconds. In the air it seems like much longer. Once the aircraft hasreached the 60-deg. AOA (and we only had the permission for 24 degrees)the aircraft fell into a spin and started spinning with its nose pointed towardthe ground. The pilot then realized what has happened and reported to theground controller: "Stupor!" Since it was believed that an Su-27 cannot exitfrom a stupor, the ground controller's only order for the pilot was as if struckin stone: "Eject at an altitude of no lower than 4,000 meters."

"Kolokol" maneuver in combat

Ejecting is hardly a pilot's favorite thing to do, thus to avoid serious injuriesthe pilots has released the controls and started preparing for the ejection.However, at the last moment he noticed that the aircraft had exited from thespin and now beginning to exit from the dive as well. The Su-27, when left onits own, was able to return to the normal flight. After verifying that the aircraftwas still controllable, Kotlov made a safe landing.

- Perhaps this was just a coincidence?

This was our conclusion at first as well: for the 1000 flights this was the onlysuch situation. On the big count this did not matter. However, a shirt timelater an even more incredible situation occurred in the Far East. An Su-27pilot was performing an automatic intercept exercise. The plane exceededthe critical angle of attack and entered a stupor. Following the order from theground controller the pilot ejected, after which the Su-27 exited from the spinand the autopilot resumed its course until the plane ran out of fuel. Soon aftera third such incident occurred in Lipetsk8. This forced us to establish aspecial research plan to investigate this phenomenon. As it turned out duringthe course of the investigation, the Su-27 exhibited certain instability whenentering the spin and exiting from it. It was established that even the mosteffective aerodynamic methods for exiting from a spin did not always result inthe desired outcome. At the same time in a number of situations the planewould exit from a spin on its own when the position of its control surfaces wasneutral. This was later explained by the peculiarities of the Su-27's air vortexaerodynamics at various angles of glide and attack.

Su-27 doing a "Cobra"

A considerable role in our "victory" over the spin was played by theaccomplished test-pilot, cosmonaut Igor Volk. He conducted a series of testflights and determined that the Su-27 can exit from all variations of a stupor.

- So why did model tests resulted in an opposite conclusion?

It turned out that it wasn't the aircraft's layout but the size of the model thatmattered most in this situation (the Reynolds number9 in fluid dynamicsconnects the speed of flight, the size of the aircraft and the viscosity of airand this number is considerably greater for full-size aircraft than for theirsmall-scale models.)

- How is that that supermaneuverability leads to the reduction of the aircraft'svisibility on the radar screen?

Supermaneuverability should be looked at as a system of maneuvers forclose aerial combat. Once the pilot receives a signal that his plane is beingtracked by an enemy radar, the first thing he needs to do is to go vertical.While gaining altitude and losing speed the aircraft starts to disappear fromthe screens of radars that use the Doppler effect. 10 However, the opponentis no fool either and will counter by pitching his aircraft upward as well. Bythat time our plane is going vertical and its speed approaches zero. But allDoppler radars can recognize only a moving target. If the aircraft speed iszero or simply low enough to prevent the enemy radar from calculating theDoppler component, for the enemy our aircraft will disappear. He may still beable to track us visually, but he will not be able to launch a radar-guidedmissile (either active or semi-active), simply because the missile's seekerwould not pick-up the target.

- Are there any other methods to make a plane invisible to a radar?

The so-called "stealth" aircraft are just beginning to emerge. The greatestimpact of this new technology is expected for the fifth-generation fighters.11The first combat aircraft created using this stealth technology was thefighter-bomber F-117A. Although, the aircraft never became a fighter.12 Theaircraft had very low radar visibility but poor flying characteristics - a sort of aedgy flying steam iron (comprised of many flat panels the aircraft wouldreflect the radar signal away from the receiver.)13

- I read somewhere that, during the creation of the new fighter, you realized aneed for a drastic upgrade of the onboard electronic equipment. How reliableis this equipment on supermaneuverable aircraft?

Generally people discount "Russian" electronics as inconsequential. I have adifferent opinion. We ask from our radar designers what we want and theydeliver. If the radar aboard the F-15 weighs 244 kg, our analog weighsseveral times more. But this does not worry us. Our goal is to be able todetect targets at greater distances. The same can be said about the opticaldetection and targeting systems.

Su-35 doing a "Cobra"

When American SR-71 strategic reconnaissance planes were visiting us fromthe direction of Norway, Su-27s and Su-30s were positioned along the entirecoast up to Novaya Zemlya to guard our northern airspace. When the SR-71appeared once again our fighters were already in the air. We decided to playa trick on the Americans and did not engage onboard radars, instead relyingon optical detection systems, which can "see" targets at considerabledistances in infra-red spectrum. When the SR-71 and our fighters wereclosing in on opposite courses, we were able to track the SR-71 at a greatdistance. The "American" did not violate our airspace, but we still kept it inthe crosshairs.14

So, you cannot say that our electronic equipment is worse. It is exactly whatwe ask for based on our knowledge of the enemy aircraft. And as to makingan aircraft that can lift our electronics - that's not a problem.

- Is it true that to improve the aerodynamic performance the new-generationfighters use a different type of a wing?

In order to reduce the wing's wave resistance during supersonic flight thewing has be swept relative to the velocity vector. If the wing is positioned insuch a way that turbulence causes it to twist and bend downwards, the wing'slifting capacity drops but its structural stability remains high. In the case of aforward-swept wing gusts of air bend it upward, which increases the wing'slifting capability and, as it increases, so does the bending and twisting of thewing. Despite a danger of structural collapse of the wing, aircraft withforward-swept wings show excellent aerodynamic performance.

Americans worked on an experimental forward-swept-wing aircraft called theX-29, but for some reason did not find it's design promising.15 We, on theother hand, believe that this problem can be solved by using compositematerials in the wing's construction. A metal wing cannot withstand thedivergence - high forces created due to the wing being twisted. We hadsituations when metal wings of forward-swept-wing aircraft model wouldbreak during wind tunnel testing. Today we can create a special composite

structure based on carbon fibers, epoxy and organic materials with a highresistance to twisting and pulling forces - some of these materials are used inarmored vests.

- What are your hopes for the fifth-generation fighter in terms ofsupermaneuverability?

I have very high expectations. If our "competitors" are building afifth-generation fighter, then we need one as well. One can say it's a rule ofequilibrium. Not long ago we attended one foreign airshow and the air forcecommander of one of the countries told us: "We need your plane. We havedifferent fighters, but in addition to those we want to have a Russian fighterwith such characteristics so than the enemy would be afraid to attack us."This is the role of the new fighter - to provide political equilibrium in the world.

(source: Science & Life, April 2002, interview taken by T. Novgorodskaya,translated from Russian by Venik)

FOOTNOTES:

1 Abbreviation for Nauchno-Issledovatelski Institut, or Scientific ResearchInstitute.

2 Abbreviation for Konstruktorskoe Buro, or Design Bureau.

3 Time-to-altitude performance is one of the most important flightperformance characteristics of a fighter aircraft, determining how fast anaircraft can respond to the detected violation of the airspace and to interceptusually high-flying targets, such as reconnaissance aircraft and strategicbombers.

4 Keep in mind that Simonov talks about achieving supersonic speed invertical climb to this altitude, not in horizontal flight at this altitude, which canbe done by a number of other fighter aircraft.

5 In June of 1989 the Reuters reported from the Le Bourget airshow: "Lookslike the competition between Soviet and American fighters in the skies of LeBourget has been won by the Soviet Union. The Russians succeeded thanksto their snake-like aircraft whose promising design and ease of controlshocked the experts."

6 The Pitot tube - a long tubular protrusion in the nose cone of a fighterallows to determine the aircraft's speed by measuring the pressure of airinside the receptor. A depressurized air pressure sensor would result in thehigher air speed reading.

7 This is not the same as the "Bell" maneuver in the Western terminology.The maneuver described by Simonov is often refereed to as "Tailslide"maneuver in the West.

8 Russian Air Force Academy is located in Lipetsk.

9 "Fluid flow can be either laminar or turbulent. The factor that determineswhich type of flow is present is the ratio of inertia forces to viscous forceswithin the fluid, expressed by the nondimensional Reynolds Number: R =(rho*V*D/mu), where V and D are a fluid characteristic velocity and distance."(Fluid Mechanics, 2nd ed., by Landau, L.D.)

10 Originally discovered by the Austrian mathematician and physicist,Christian Doppler (1803-53), this change in pitch results from a shift in thefrequency of mechanical compression (i.e. sound waves) andelectromagnetic waves.

11 "Fifth-generation" is a relative term and usually describes the F-22, JSF

and the Russian counterparts in development (MFI and LFS).

12 Actually, the F-117A, despite its "F" (for "fighter") designation, was neverintended to be anything other than a light bomber, even though the aircraftwas tested with AIM-9 Sidewinder air-to-air missiles (without much success).The aircraft was presented as a multi-functional fighter-bomber to thegovernment and the public to justify its high cost and also to place the aircraftunder the USAF command rather than under the command of now defunctSAC (Strategic Air Command was eliminated as a separate organization inJuly of 1992).

13 In 1966 a well-known Soviet mathematician, Pyotr Ufimtsev, published apaper in which he described mathematical methods to predict RCS (actually,the field of dispersion) of two-dimensional objects (that's why the F-117 iscomprised of flat two-dimensional panels: even though Ufimtsev's methodallowed to calculate any type of surfaces, not just flat, his calculationsprovided in the book were limited to such and it took Lockheed andNorthrop-Grumman mathematicians some time to develop methods forcomplex curved surfaces). Ufimtsev's work was directly used by Lockheed'smathematician, Denys Overholser, to develop computer software known as"Echo 1", which could calculate the RCS of an aircraft constructed of flatpanels. This program was used to find the optimum geometry to minimize anaircraft's RCS. The resulting structure became known as "HopelessDiamond", which lies in the basis of F-117A's external construction. Simplyput, the flat, angled external panels of F-117A are designed to reflect radarwaves in all directions but the direction of the radar's receiving antenna. Thismeans that to effectively track F-117A one would have to use multiple radars(or, at least, multiple receivers.) Needless to say that the geometricalrequirements for minimizing the RCS established by "Echo 1" program hadlittle place for considerations of aerodynamics. The resulting aircraft had theaerodynamics of a flying coffin (some of the modern anti-stealth radars takeadvantage of F-117A's poor aerodynamics and target the aircraft by detectingthe considerable trail of turbulent air left by the aircraft's boxy airframe.)

14 SR-71 was originally intercepted by six MiG-31s, and, on one of its laterflights, by Sukhois. During the first intercept by the MiGs, the SR-71 wasactually in violation of the Soviet airspace, but was able to leave it before theMiGs caught up with it. The "Black Bird" was retired by the USAF shortly afterthese intercepts.

15 During a simulated combat exercise the X-29 was flying against an F-18and proved its ability to turn its weapons against the F-18 from any position inspace considerably faster than the F-18 was able to target the X-29. TheF-18 lost all simulated engagements to the X-29, even when the latter wasplaced at a considerable disadvantage in terms of speed and position. Thereare a few likely explanations for the X-29's unrealized potential: first, theforward-swept wing is not compatible with the conventional stealth geometryconcepts; second, X-29's developers had structural problems with the wingand could not come up with the composite material similar to that usedSukhoi S-37 (and the Sukhoi is considerably larger and heavier than the X-29and experiences greater forces acting on its wings); finally, the USAF officialsdid not look favorably on the unorthodox X-29, just as their Russiancounterparts viewed the unusual S-37 with suspicion.

VenikJune 19, 2002