Editing Tupolev Tu-144 (section)

===Airframe===
[[File:Tupolev Tu-144S, Aeroflot AN1180630.jpg|thumb| Tail surfaces or [[empennage]] showing deflected rudder and no horizontal tailplane.]]
[[File:Tupolev Tu-144 CCCP-77102 LEB 02.06.73 edited-3.jpg|thumb|right|The first production Tu-144S displaying at the 1973 [[Paris Air Show]] on the day before it crashed. The aircraft's planform and canards are clearly shown.]]
The aircraft was assembled from parts machined from large slabs, many over {{convert|19|m|ft|abbr=on}} long and {{convert|0.64|to|1.27|m|ft|abbr=on}} wide. While at the time, this approach was heralded as an advanced feature of the design, it turned out that finished parts contained defects which had not been detected in the [[raw material]]. Cracks formed at the defects at load levels below that which the part was expected to withstand. Once a crack started to grow, it spread quickly over many metres, with no crack-arresting design feature to stop it.<ref name="Fridlyander"/> In 1976, during [[Fatigue testing|repeat-load]] and [[Proof test|static testing]] at [[TsAGI]] (Russia's ''Central Aerohydrodynamic Institute''), a Tu-144S airframe cracked at 70% of the design flight load with cracks running many metres in both directions from their origin.<ref name="bliznyuk2000" /><ref name="Fridlyander"/>

Two Tu-144S airframes suffered structural failures during laboratory testing just prior to the Tu-144 entering passenger service.<ref name="Fridlyander">{{cite journal |last=Fridlyander |first=Iosif Naumovich |title=Печальная эпопея Ту-144 |trans-title=Sad Epic of the Tu-144 |journal=Messenger of Russian Academy of Sciences |year=2002 |volume=72 |issue=1 |pages=70–78 |url=http://vivovoco.rsl.ru/VV/JOURNAL/VRAN/02_01/FRID.HTM |archive-url=https://web.archive.org/web/20110928042757/http://vivovoco.rsl.ru/VV/JOURNAL/VRAN/02_01/FRID.HTM |archive-date=28 September 2011 |language=ru |url-status=dead }}</ref> The problem, discovered in 1976, may have been known prior to this testing; a large crack was discovered in the airframe of the prototype Tu-144 (aircraft 68001) during a stopover in Warsaw following its appearance at the 1971 Paris Air Show. Polish sources say the crack was discovered after the aircraft made an emergency landing due to the failure of both left-hand engines; however, an Aeroflot spokesperson denied the damage and disputed the circumstances of the landing.{{sfn|Moon|1989|p=141}}

Later the same year, a test airframe was subjected to a test simulating the temperatures and pressures occurring during a flight. High skin temperatures of {{convert|110|-|130|C|F|abbr=on|sigfig=2}} were caused by kinetic heating when the boundary layer air reached {{convert|150|-|180|C|F|abbr=on|sigfig=2}} during cruise. The Tu-144 was placed in an [[environmental chamber]] and heated to simulate the skin getting hot quickly, during acceleration to cruising speed, while the underlying structure took a while to reach its equilibrium temperature. This thermal effect caused internal stresses and the situation was reversed while slowing down and descending. The pressure in the cabin, which caused additional stresses, was changed at the same time as the skin heating to simulate climbing to cruise altitude and then descending. Repeatedly cycling the temperature and pressure, as happened with the aircraft in service, caused fatigue damage<ref>Tupolev Tu-144 The Soviet Supersonic Airliner,{{ISBN|978-0-7643-4894-5}}, pp.48,61</ref> and the airframe failed in a similar way to that of the TsAGI load testing.<ref name="bliznyuk2000" /><ref name="Fridlyander"/>

According to {{ill|Iosif Fridlyander|ru|Фридляндер, Иосиф Наумович}}, an aerospace aluminium and beryllium alloys expert,<ref name="AyzatullovaSudakov2020">{{cite journal |last1=Ayzatullova |first1=Alsu Sh. |last2=Sudakov |first2=Mikhail A. |title=История создания и эксплуатации сверхзвукового пассажирского самолёта Ту-144 (по мемуарным источникам) |trans-title=The History of the Creation and Operation of the TU-144 Supersonic Airliner (According to Memoir Sources) |journal=Vestnik of Kostroma State University |date=2020 |volume=26 |issue=3 |pages=87–92 |url=https://vestnik.ksu.edu.ru/2020-t-26-3/ayzatullova-as-sudakov-ma-vestnik-2020-3-ru.html |archive-url=https://web.archive.org/web/20230607000522/https://vestnik.ksu.edu.ru/2020-t-26-3/ayzatullova-as-sudakov-ma-vestnik-2020-3-ru.html |archive-date=7 June 2023 |url-status=live |doi=10.34216/1998-0817-2020-26-3-87-92 |doi-access=free |language=ru}}</ref>{{rp|page=88}} the Tu-144 design allowed a higher incidence of defects in the alloy structure, leading to the fatal in-air breakup of the aircraft in the [[1973 Paris Air Show Tu-144 crash]].<ref name="AyzatullovaSudakov2020" />{{rp|page=91}} This conclusion was supported by some of the designers involved in the aircraft's development. Vadim Razumikhin wrote that the [[Load factor (aeronautics)|load factor]] experienced by the plane at the moment of the break-up was less than the design limit. If the stress tests had been conducted earlier, the disaster may have been averted. Eventually, the airframe was strengthened and the control system was modified to prevent overstressing the aircraft.<ref name="bliznyuk2000" />{{rp|at=Ch. 3.14.}}