Category Soviet x-plenes

Purpose: To use Tu-16 aircraft for various experimental purposes, and to take the basic design further.

Design Bureau: OKB-156 ofA N Tupolev, Moscow.

This graceful twin-jet bomber sustained what was in financial terms the most important programme in the entire history of the Tupolev design bureau up to that time. Since then, because of inflation, the Tu-154 and Tu-22/Tu-22M have rivalled it, though they were produced in smaller numbers. The pro­totype Tu-16, the Type 88, was a marriage of upgraded B-29 technology in structures, sys­tems and to some degree in avionics, with to­tally new swept-wing aerodynamics and what were in the early 1950s super-power tur­bojet engines. The Tu-16 entered production in 1953 powered by Zubets (Mikulin KB) RD-3M engines of 8,200kg (18,078 Ib) thrust. The second series block had the RD-3M-200 of8,700kg (19,180 Ib) followed by the 9,500kg (20,944 Ib) RD-3M-500, which was then retro­fitted to most earlier aircraft.

From 1953 the basic aircraft was repeated­ly examined against alternatives based as far as possible on the same airframe but using different propulsion systems. Most of the studies had four engines. Tupolev had origi­nally schemed the 88 around two Lyul’ka AL-5 turbojets, but the design grew in weight to match the big AM-3 engine, and this was the key to its win over the smaller Ilyushin with the Lyul’ka engines. In parallel with the
production aircraft one project team led by Dmitri S Markov studied versions of the 88 with not two but four AL-5 engines, and then four of the more powerful (typically 14,330 Ib, 6,500kg) AL-7 engines. These Type 90s would have been excellent bombers, with in­creased power and much better engine-out performance, but the decision was taken not to disrupt production. On the other hand, vir­tually the same inboard wing and engine in­stallation was then used in the Tu-110 transport, two of which were built using the Tu-104 as a basis. Some of the four-engined bomber studies had engines in external na­celles hung on underwing pylons.

From 1954 Type 88 prototypes and a wide range of production Tu-16s were used over a period exceeding 40 years as experimental aircraft. Some carried out pioneer trials in aer­ial refuelling at jet speeds.

One large group of about 20 aircraft was kept busy in the development of avionics, in­cluding navigation, bombing and cartograph­ic guidance, parent control of drones and targets, and the direction of self-defence gun­nery systems.

Probably the most important single duty of Tu-16LL (flying laboratory) aircraft was to air – test new types of turboj et and turbofan engine. In each case the engine on test would be mounted in a nacelle either carried inside the weapon bay or, more often, recessed into it. Usually the test engine would be suspended on vertical hydraulic jacks or a large pivoted beam so that in flight it could be extended
down fully into the airstream, with its efflux well clear of the rear fuselage. In many cases the engine pod or the Tu-16 fuselage ahead of it would be fitted with a fairing or door which could be left behind or opened as the pod was extended for test. Among the engines air-tested under Tu-16LL aircraft were: the Ivchenko (later Progress) AI-25, Lyul’ka AL-7F – 1, AL-7F-2, AL-7F-4 and AL-31F, Solov’yov (Avi – advigatel) D-30, D-30K, D-30KP and D-30F6 (in MiG-31 installation), Lotarev (Ivchenko Progress) D-36, Kuznetsov NK-6 (with and without afterburner) and NK-8-2, Tumanskii (Soyuz)R-l 1 AF-300( Yak-28nacelle)andR-15- 300 (in the Ye-150 and the totally different MiG – 25installation), MetskhvarishviliR-2I-300and R-21F with Ye-8 inlet, Khachaturov R-27 ver­sions (including the vectored R-27V-300 in a complete Yak-36M prototype fuselage, Mikulin (Soyuz) RD-3M (many versions), Kolesov (RKBM) RD-36-41 and RD-36-51, and Dobrynin (RKBM) VD-7, VD-7M and VD-19 (in a pro­posed Tu-128 installation), etc.

One Tu-16 had its entire nose replaced by that intended for the Myasishchev M-55, in order to test the comprehensive suite of sen­sors. Another tested a scaled version of the bogie main landing gear for the Myasishchev M-4 and 3M strategic bombers, replacing the normal nose landing gear. A new twin-wheel truck was added at the tail. According to doc­uments a Tu-16 with outer wings removed tested the complete powerplant of the Yak-38 (presumably in free hovering flight) though photographs have not been discovered.

Purpose: To investigate the use of cryogenic fuels.

Design Bureau: ANTKA N Tupolev,

Moscow. Technical Director Valery Solozobov, cryogenic fuels ChiefDesigner Vladimir Andreyev.

For many years the USSR and its successor states have been replacing petroleum by nat­ural gas, which in 1999 provides over 53 per cent of the total of all Russia’s energy sup­plies. Since 1982 what is today ANTK Tupolev has been investigating the use of natural gas and also hydrogen as fuels for aircraft, because of their availability and clean burn­ing qualities. However, for use in vehicles both have to be liquefied by being cooled to exceedingly low temperatures. Liquid hydro­gen (LH2) boils at -255°C, an unimaginably low temperature at which (for example) all conventional lubricating oils are rock-solid. Moreover, this fuel is very expensive, and haz­ardous from the viewpoints of detonation and fire. On the other hand, liquefied natural gas (LNG) is widely available, at least threefold cheaper in Russia than aviation kerosenes, and also significantly improves flight perfor­mance. It is straightforward to store and han-

Below: Tu-155.

Photographs on the following page:

die, and less fire/explosion hazardous even than today’s kerosenes. After years of labora­tory work an existing civil transport was se­lected for use as an LNG flight test-bed. It has been flying since 1988. All work is now di­rected at the Tu-156, the first LNG aircraft de­signed to go into service.

T o flight-test an LNG sy stemANTKTupolev bailed back a Tu-154, No 85035, and replaced the No 3 (starboard) engine with an NK-88, fed with LNG by a completely separate fuel system. The NK-88 is a derivative of the Kuznetsov NK-8-2 turbofan (still fitted in the Nos 1 and 2 positions), with thrust unchanged at 20,945 Ib (9,500kg). The successor to Kuznetsov’s bureau is Samara/Trud. The complex feed system is shown in a drawing. The main tank, of 10ft 2in (3.1m) diameter and 17ft 81/2in (5.4m) long, is of AMG6 alu­minium alloy, with a 50mm (2in) lagging of foamed polyurethane. The NK-88 engine has a dedicated two-stage centrifugal pump dri­ven by a bleed-air turbine. LNG comes in at -152°C and is passed through a heat ex­
changer to convert it to gas. The engine com­bustion chamber is able to accept either this supply of NG or, on command, to switch to the kerosene supply normally used for the other engines. Work is still underway on a low-emissions chamber which will be used on the improved NK-89 engine to be fitted to the Tu-156. The definitive Tu-156 is expected to have the fuel in giant saddle tanks along the top of the fuselage. Instead, to reduce time and cost, at least the first Tu-156 has a main tank (capacity 28,6601b, 13 tonnes) behind the passenger cabin and, to preserve centre of gravity position, an auxiliary tank (8,377 Ib, 3,800kg) in the forward underfloor baggage hold. This reduces payload from 18 tonnes to 14 (30,864 Ib). Range will be 1,616 miles (2,600km) on LNG only, or 2,051 miles (3,300km) on combined LNG and kerosene.

Eventually the Earth’s store of petroleum will run dry. It is pointless to say ‘More keeps being discovered’. The world’s aircraft will then have no alternative but to switch to an­other fuel, and LNG is the obvious choice.

Purpose: To copy the Lockheed U-2B. Design Bureau: OKB No 49, Taganrog, General Constructor G M Beriev.

On 1 st May 1960 the world was astonished to learn that the missile defences of Sverdlovsk had shot down a Lockheed U-2 of the US Central Intelligence Agency. Parts of the air­craft were put on display in Moscow’s Gorkiy Park. What the world was not told was that for months afterwards a vast area was combed by large squads looking for every fragment of the downed aircraft (which had broken up at high altitude). All the pieces were brought to GK Nil WS, where they were carefully studied. On 28th June 1960 SovMin Directive 702-288 instructed OKB No 16 in Kazan, led by P F Zubets, to copy the J57-P-13 engine. This was a blow to Zubets, whose RD-500 was in the same thrust class, and even more to the several engine designers (Do­brynin, Lyul’ka, Kuznetsov and Tumanskii) who had engines on test which were more
powerful and of much later design than the massive Pratt & Whitney. On 23rd August 1960 Directive 918-383 ordered OKB No 49, assisted by neighbouring No 86, to study the U-2 and produce five copies, designated S-13. These were primarily to support ‘a multi­discipline study of the structural, technical and maintenance aspects of the U-2, and master its technology for use in indigenous aircraft’. It was also expected that the S-13 would be used to collect upper-atmosphere samples, destroy hostile balloons and (using the 73-13, or AFA-60, camera) undertake re­connaissance missions. Despite inexorable increases in weight over the US original, work attempted to meet the first-flight date of first quarter 1962. Much of the supporting equip­ment had already been developed for the Yak-25RV and TsybinRSR (which see). On 1st April 1961 a detailed metal fuselage mock-up was completed, with ‘models of its systems’. A Tu-16 was readied for testing the engine (now designated RD-16-75), landing gears
and other items, while CAHI tunnels con­firmed that the U-2 had the exceptional L/D ratio of25. Out of the blue, on 12th May 1962 Directive 440-191 ordered the whole S-13 project to be terminated.

Purpose: To test previously invented ‘parabola wing’ in a powered aircraft Design Bureau: Not an OKB but a private individual, Boris Ivanovich Cheranovskii (1896-1960). Throughout his life he scratched around for funds to build and test his succession of 30 types of gliders and powered aircraft, all of ‘tailless’ configuration.

In 1924 Cheranovskii tested his BICh-1 ‘Para­bola’ glider and the refined BICh-2, which demonstrated ‘normal longitudinal stability and controllability and is considered to have
been the world’s first successful flying wing’. In 1926 he followed with the BICh-3, which was almost the BICh-2 fitted with an engine. Cheranovskii’s gliders had been flown at the All-Union meetings at Koktebel, Crimea, but most of the flying of his first aeroplane was done by B N Kudrin (later famous) in Moscow.

The BICh-3 was a basically simple aircraft, constructed of wood with thin ply skin over the leading edge, inboard upper surface and landing-gear trousers, and fabric elsewhere. The BICh-2 had flown without a rudder (it was better with one) since turning was
achieved by the ailerons. With the BICh-3 the addition of an engine required a vestigial fuselage with a fin and rudder. The main con­trols remained the trailing-edge elevators and ailerons, operated by rods and bellcranks and hung on inset balanced hinges. The engine was a Blackburne Tomtit, an inverted V-twin of 698 cc rated at 18hp. Skids were provided under the tail and outer wings.

Kudrin described the BICh-3 as ‘not very stable, but controllable’. It was sufficiently successful to lead to the many successors.

Purpose: To modify established jet aircraft in order to test ejection-seats.

Design Bureau: Initially the seats were designed by special teams formed in the jet – aircraft OKBs. However, in 1952 a special organization was created to specialize in life-support and safety-equipment systems, and in 1994 this was transformed into NPP Zvezda (Star) joint-stock company. From the 1960s this organization captured the market until it was providing ejection-seats for virtually all Soviet combat aircraft.

Soviet ejection-seats, called Katapul’tnoye Kreslo, were initially diverse, and drew heav­ily on designs by US, Swedish and, especially, the British Martin-Baker companies. After 1945 a few flight tests took place with German seats, developed in 1944 for such aircraft as the He 219 and Do 335. The detailed history has not been written, but some of the earliest
flight tests were carried out from about mid – 1947. Probably the first Soviet ejection-seat was designed in the MiG OKB from January

1947. On 11th March 1947 this OKB received an order to test this seat in the FT-2, the sec­ond prototype of the M1G-9UTI trainer. After ten test ejections in a ground rig the experi­mental seat, weighing 128.5kg (283 Ib), was initially installed in the considerably modified rear cockpit of FT-1 (the first two-seater which was still with the MiG OKB). Flight test­ing took place throughout the first half of

1948, but only up to 700km/h (435mph). The very similar FT-2 was then fitted with two ejection-seats, the front one at a rail angle of 22.5° and the rear at 18.5°. The modified air­craft was delivered to NIl-WS, the air force flight test institute, on 29th September 1948. After two tests with dummies live testing con­tinued between 7th October and 13th No­vember 1948. An automatic sequence firing
the canopies and seats was then perfected (though ofcourse the FT-2 was never left with both cockpits empty). From the results of these tests the OKB gradually developed the first production seat, called the SK. This was then developed through 14 production series.

Probably the next Soviet aircraft to be used for ejection-seat testing was the Ilyushin IL-28 tactical twin-jet bomber. First flown on 8th July 1948, using the imported Rolls-Royce Nene and later the Nene-derived RD-45 and VK-1 A, this excellent aircraftwas used for sur­prising tests using seats fired from the ex­treme tail. Unlike the very similar British Canberra, which was undefended, for this aircraft the Ilyushin OKB developed a power­ful tail turret with two NR-2 3 guns, manned by the radio operator who had an escape chute. In several aircraft the turret was replaced by a special test installation for an ejection-seat. Both upward – and downward-firing seats

were tested, and cine films showed that in some cases firing the seat imparted to the air­craft a pronounced kick in the pitching plane, either nose-up or nose-down. Some of the IL-28 seat tests were at airspeeds exceeding 800km/h (497mph).

Even higher speeds were reached during seat testing with ST-10 aircraft, which were specially modifiedtwo-seat UTI MiG-15s. This was the principal type used from 1951 on­wards in development of the SK and SK-1 seats which were used in thousands of early MiG jets, and later for the much better KM-1 family used in later MiG fighters, cine films and photographs have shown seats being fired from ST-lOs with callsigns 15, 23, 101U, 102U and 401U. These aircraft were painted with bold horizontal black lines in known po­sitions to assist determination of the seat tra­jectory. What is surprising is that about half the photographs of tests appear to have in­volved firing the test seat from the front cock­pit. Using dummies and human occupants many hundreds of combinations of canopy, seat, ejection gun, stabilizing drogue and parachute system were investigated. Early SK seats were notoriously unreliable, and when they did fire on command the pilot often suf­fered spinal damage. Gradually, and espe­cially after the ST-10 testing began, the SK seats improved. A faceblind was provided to
protect the occupant’s face, additional firing triggers were incorporated in both armrests, improved ejection guns were developed im­parting a precisely repeatable phased accel­eration using different cartridges for summer and winter, and the original restrictive limits of airspeed and altitude were progressively increased. A photograph shows 101U, one of the aircraft with a completely open front cockpit. The final ST-10,401U, was fitted with a new type of front-cockpit canopy which was hinged at the rear to the top of the seat so that on ejection the canopy served as a wind­break to protect the occupant. This became a feature of early MiG-21 fighters.

Photographs have been found of at least two Yak-25L (Laboratoriya) seat-test aircraft. The production night fighter seated the pilot and radar operator in tandem under a large one-piece canopy which opened by sliding on rails 2.2m (7ft Sin) to the rear. Both the seat test-beds had a pressure bulkhead separating the front cockpit from the rear cockpit, from which the seat under test was fired. Aircraft callsign 18 retained the original type of canopy but with the portion over the rear cockpit opaque (on being jettisoned this usu­ally passed perilously close to the tail). Air­craft callsign 01 had a completely modified arrangement, the pilot having a short upward – hinged canopy and the test cockpit having a
prominent light-alloy superstructurewhich in most tests was open at the top. This aircraft was later used to test the Yakovlev OKB’s KYa-1 rocket-boosted seat, the first to have ‘zero/zero’ capability (able to be fired with the aircraft at rest on the ground).

The only Sukhoi aircraft known to have been an ejection-seat test-bed was an Su-9U with callsign Red 10. Liberally covered on the starboard side with black lines for use as tra­jectory references, this Mach-2 aircraft always fired the test seat from the rear cockpit. This was open-topped and sealed from the pres­surized front cockpit. The only photographs released on this aircraft must have been taken since the 1970s, as they show modern Zvezda zero/zero rocket assisted seats, at least one being of the K-36 family. One pho­tograph shows a test at ground level.

While the Su-(U was used for tests at high subsonic Mach numbers, at least on M1G-25U has been used to confirm behaviour in ejec­tions at supersonic speeds. Details of the seats and Mach numbers have yet to be dis­closed, but Zvezda believe this aircraft has been used to check successful ejections at mach numbers significantly higher than any­where else in the world.

Purpose: To make an invisible aeroplane. Design Bureau: Zhukovskii WA, Soviet air force academy; designer Professor Sergei Kozlov.

Professor Kozlov was eager to see to what de­gree it would be possible to construct a ‘transparent’ aeroplane, difficult to see (for example, by enemies on the ground). In 1933 a preliminary experiment was made with a U – 2 biplane whose rear fuselage and tail were stripped of fabric and re-covered with a trans­parent foil called Cellon (unrelated to the British company of that name). In 1935 the WA was assigned Yakovlev’s second AIR-4, which already had experimental status. The airframe was completely stripped of all cov­ering and internal equipment, and reassem­bled as described below. Though it was called the Nevidimyi Samolyot, invisible aero­
plane, it received the unexplained official designation of PS. It first flew on 25th July 1935.

The AIR-4, one of A S Yakovlev’s first de­signs, was a neat parasol monoplane, first flown in 1930. Powered by a 60hp Walter NZ – 60 five-cylinder radial, it had two seats in tan­dem. The structure was almost entirely wood, with skin of ply and fabric. The pairs of wing bracing struts were mild-steel sheet wrapped round to an aerofoil section 64 x 32mm (21/2 x l!4in). Of course, Kozlov could do nothing to hide these struts, nor the rub­ber-sprung divided main landing gears, or the engine, fuel tank and other parts. Virtually the whole airframe was covered in a French transparent plastic called Rodoid. This was cut from sheet, each panel being drilled and secured by aluminium rivets inserted through eyelets. As far as possible the opaque parts

were painted silver-white.

The PS was officially judged to have achieved results which had ‘a measure of im­portance’. Apart from the invisibility effect, the transparent skin was also held to improve the field of view of the occupants, and Kozlov did preliminary studies for a transparent re­connaissance aircraft. On a low-level flypast the PS was said to be not easily seen except by chance, though of course observers could narrow the field of search from judging the source of the aircraft’s sound. After a few weeks, however, the foil skin was of little use, partly because of progressive darkening by solar radiation and partly because of the ef­fect of dust and oil droplets from the engine.

Left: PS accompanied by a U-2.

Design Bureau: OKB-155 of A I Mikoyan

Throughout the massive production of the MiG-15 and MiG-17, with a combined total ex­ceeding 22,000, the MiG OKB was eager to dis­card the British-derived centrifug al engine and build truly supersonic fighters with indigenous axial engines. It achieved this in sensible stages. The M, or I-350, introduced the large TR-3A axial engine and a wing with a leading – edge sweep of 60°. The SM-2, or I-360, pow­ered by twin AM-5 axial engines, at first was fitted with a high T-type tail. Then the tailplane was brought down to the fuselage, the design was refined, and as the SM-9 with afterburning engines (first flown 5th January 1954) achieved production as the MiG-19. The SM-9/3 intro­duced the one-piece ‘slab’ tailplane, with no separate elevator, and this was a feature of the MiG-19S. Powered by two RD-9B engines each with an afterburning rating of 3,250kg (7,1651b), this had the devastating armament of three NR-30 guns, each far more powerful than the British Aden of the same calibre. The following specification is for a typical MiG-19S.

SM-10

Though it had a generally longer range than its predecessors the MiG-19 was required in a decree of May 1954 to be developed with flight-refuelling capability. At that time the only tanker was a version of the piston-en­gined Tu-4, and a series MiG-19, callsign 415, was fitted with a probe above the left (port) wingtip, feeding into a large pipe with divert­ers and non-return valves to fill all the aircraft tanks. By 1956 testing had moved to an extra­ordinary test-bed, callsign 10, fitted with no fewer than four probes. One was at the bot­tom of the nose, another at top left on the nose, a third on the leading edge of the port
wing and the fourth projected with a kink from above the starboard wing.

SM-20

This was a MiG-19S modified as a pilotless aircraft to test the guidance system of the Kh – 20 cruise missile. This huge weapon was de­signed to be carried under a special version of the Tu-95 heavy bomber, and one Tu-95K was modified to carry and release the SM-20. Apart from being equipped with the missile’s guidance system and a special autopilot and various other subsystems, including a receiv­er link for remote-pilot guidance, the fighter was fitted with a position beacon, radar re­flector and destruct package. Suspension lugs were built in above the centre of gravity, and the parent aircraft had pads which pressed on each side of the SM-20 canopy. Tests began in October 1956. SM-20P de­scribed the aircraft after modification with special engines able to vaporise the fuel to ensure reliable starting at high altitudes.

SM-30

This designation applied to MiG-19 and MiG – 19S aircraft modified for ZELL (zero-length launching). Nuclear weapons clearly made it foolish to base combat aircraft on known air­fields, so the ZELL technique was intended to enable aircraft to be fired off short inclined launchers by a large rocket. The launcher was naturally made mobile, and most loca­tions were expected to be in the extreme Arc­tic such as Novaya Zemlya. The aircraft needed a strengthened fuselage, reinforced fuel tanks and mounts, a special pilot head­rest, and (in most cases) extra-large para – brakes or arrester hooks for short landings.

The usual rocket was the PRD-22, with a thrust of40,000kg (88,185 Ib) for 2.5 seconds. Manned firings took place from 13th April 1957, the chief pilots being G Shiyanov and Yu A Anokhin (not the more famous S N Anokhin). Results were satisfactory, but the scheme was judged impractical.

Purpose: To create a fighter able to fly as a biplane or monoplane.

Design Bureau: OKB-30, Chief Designer V V Shevchenko.

There is some dispute over who was respon­sible for the experimental IS fighters. Gener­ally ascribed to VV Nikitin, in more recent accounts he is hardly mentioned and all cred­it is given to Shevchenko who is quoted as saying ‘IS stands for losif Stalin’. In fact, though the conception was indeed Shev­chenko’s, he was an NIl-WS test pilot who was occasionally employed by Nikitin. Design of the IS series was carried out in partnership with Nikitin, and IS actually meant Istrebitel Skladnoi, folding fighter. Surprisingly, it was alsogiventheofficialGUAP designation I-220, even though this was also allocated to a high – altitude MiG fighter. The idea was that the air­craft should take off as a biplane, with a short run, and then fold up the lower wing under­neath the upper wing in order to reach high speed as a monoplane. Shevchenko promot­ed the idea in November 1938, getting an en­thusiastic response, and therefore in 1939 demonstrated a detailed working model built at the Moscow Aviatekhnikum (MAT). His project captivated Stalin and Beria, who wanted the aircraft flying in time for the Oc­tober Revolution parade in November 1939. Shevchenko was given 76 million roubles and
facilities at Factory No 156, while the OKB-30 design team eventually numbered 60. The IS-1 was first flown by V Kulesho v on 29 th May 1940, and the lower wings were first folded by G M Shiyanovon 21st June 1940. Shevchenko states that Shiyanov carried out LII testing and completed his report on 9th January 1941. Ac­cording to Shevchenko, glowing accounts were also written by such famous test pilots as Suprun and Grinchik. In fact, Shavrov records that ‘State tests were considered un­necessary, as the maximum speed was only 453km/h’. As it was so much slower than the LaGG, MiG and Yak fighters, this aircraft was
put into storage after the German invasion, together with the IS-2.

As far as possible the IS-1 resembled the ex­isting production fighter, the I-153. It had the same 900hp M-63 engine, driving a Hamilton VISh propeller of2.8m (9ft 2in) diameter, and apart from the extra ‘wing fold’ lever the cockpits were identical. The airframe was all­metal, the fuselage framework being welded SOKhGSA steel tube, with removable metal panels to the front of the cockpit and fabric aft, while each wing had similar construction for the two spars, but DIG light-alloy ribs and flush-riveted DIG skins. The tail was DIG with

fabric covering. After take-off the pilot select­ed ‘chassis up’, folding the main landing gears inwards by the 60-ata (882 lb/in2) pneu­matic system. He could then select ‘wing fold’, whereupon a pneumatic ram and hinged levers on each side folded the lower wing. The inboard half was then recessed into the fuselage and the hinged outer half (which remained horizontal throughout) was recessed into the upper wing to complete its aerofoil profile. The planned armament was four ShKAS in the inner gull-wing part of the upper wing. There was no cockpit armour.

Though it may have seemed a good idea, the realization was a disappointment. Apart from the overall inferiority of the IS-1 ‘s perfor­mance, it was nonsense to reduce wing area in an aircraft needing the maximum possible combat agility, and moreover to try on the one hand to increase wing area for take-off
and landing whilst simultaneously leaving half the upper (main) wing with a huge hol­low on the underside which destroyed the aerofoil profile. A detail is that with the wings
folded there was nowhere for spent cartridge cases to escape.