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- Pridružio: 23 Okt 2010
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djordje ::МиГ 29 ОВТ, погледајте хоризонталне стабилизаторе? Невероватно и занимљиво!
Збиља би било занимљиво сазнати вредности диференцијалног отклона хоризонталаца на овој машини и режиме рада диф. отклона хор.стабилизатора?
Tematika je vrlo interesantna, ali mislim da cemo ostati samo u sveri nagadjanja bez konkretnih podataka od strane proizvodjaca, sto opet sa svoje strane i nije tako lose jer predstavlja jos jedan izazov za resavanje putem razmisljanja i logickog povezivanja.
Tom prilikom u obzir trebamo da uzmemo par stvari!
Aerodinamika kod Miga 29M (koji je koristen za ispitivanje TVC) je promenjenja i prvi put je koristen FBW zbog "relaksirane" staticke stabilnosti.
Jasno je da primena TVC kod M modela dovodi do promene (reprogramiranja) FCS sistema, ali tu moramo da uzmemo u obzir normalan rezim leta bez upotrebe TVC i rezim leta kada se koristi TVC.
Moja je pretpostavka da je sistem upravljanja u rezimu bez TVC gotovo identican radu FCS sistema kod obicnog Mig-29M (neznatne promene su moguce zbog minimalnog povecanja tezine mlaznica)
Prve verzije M modela su koristile analogni FBW, dok potonje kao sto je recimo Mig-35 ili Mig-29K koriste digitalni FBW i FCS
Citat:New 3-chennal fly-by-wire KSU-961 system with 4-time signal doubling. It's made on the basis of MiG-29K/KUB's FBW KSU-941 system and provides controllability of flying in all modes including super- maneuvering on over-critical AoA too.
Evo sada nekih interesantnih podataka vezano za Mig-29M
Citat:The MiG-29M Fulcrum E has a new fuselage structure, internal equipment, new wings, distinctively larger tail-planes with saw-tooth leading edge, and fins. The improved aerodynamic configuration is characterized by a repositioned, enlarged, and sharper wing-leading-edge-extensions that provide double the lift of earlier MiG-29's for increased handling at low speeds, a fallout of the shipboard requirements. Lower effective wing loading is also obtained, although leading edge slats still program full-up or full-down according to AOA thresholds and cockpit switch positions.
Vidimo da se radi o obimnom aerodinamickom redizajnu.
Interesantan je podatak vezan za povecanje uzgona strejka (lerx) i smanjenju "wing loading"-a, sto je takodje jedan od razloga pomeranja aerodinamickog centra unapred, cime je dobijen staticki nestabilan avion.
Vidimo da je funkcija predkrilaca ostala nepromenjena.
Citat:There is a welded aluminum-lithium center section wing-box backed-up by thicker welded steel in front of the main landing gear (MLG) which appears to be for a beef-up of the structure and the landing gear. But the use of the lithium-aluminum welded alloys in the forward fuselage allows for needed weight reductions and added fuel volume.
Smanjenjem tezine u prednjoj zoni trupa je centar mase pomeren unazad, sto je takodje doprinelo stvaranju nestabilne platforme, odnosno omogucilo je primenu vestacke stabilnosti, koja je dovela do poboljsanja manevarskih sposobnosti i agilnosti aciona.
Ovo nije ni malo lak zadatak tim pre sto je vrlo tesko i nezahvalno od staticki stabilne platforme napraviti uspesnu nestabilnu platformu uzimajuci u obzir njene "nasledjene" aerodinamicke i staticke karakteristike.
Citat:Honeycomb composite materials are also widely used. The chaff and flare dispensers have been relocated from the top of the wing to an integral housing under a panel on the upper side of the fuselage.
The airframe has a more tapered radome with a nose lengthened around 7.5 in (20 cm), a wider and longer dorsal spine, a longer canopy, a slightly changed wing position (aft) more rounded wing tip trailing edges, and a new ramp without suck-air louvers on top. The FOD doors that used these vents have been removed in favor of a more effective screen system in the duct itself, similar to the Su-27 and first seen on the Naval MiG-29K. The inlet redesign also increased mass flow at takeoff. The landing rollout distance has been decreased by modifications in the air brakes and brake parachute as well as a strengthened undercarriage. The effects on range/payload by eliminating of the upper air ducts and the sacrificing of trim and longitudinal stability have been compensated for by the fly-by-wire control system. Large easy-to-remove hatches give unobstructed access to the equipment.
Citat:There is an even longer/wider dorsal spine, a reduced gun load to 150 rounds (30mm), increased span ailerons, bulged wingtips with fore/aft ECM antennas, eight underwing hardpoints, larger airbrake above the fuselage, and full provisions for precision guided munitions and advanced BVR weapons. Twin vertical tails are properly positioned to enhance high "AOA" stability.
The MiG-29M is the first Fulcrum with a full quadruplex fly-by-wire flight control system that, according to Waldenberg, combines both analog and digital devices incorporating multiple redundancies and utilizes relaxed static stability. Maneuvering performance has been maintained but there has been a substantial increase in permissible angle-of-attack (AOA) over the present 30° and acceptable G-loading. He also mentioned his continuing distrust in full-digital systems, taking note of JAS-39 Gripen and F-22 crashes. The SOS-3 stall/limiter system allows for unrestricted use of high AOA which is automatically combined with a roll/yaw limiter a graduated 17 kg. (38 lbs.) stick-force inducer. There are no control limits imposed where G-limits do not exist, thus allowing for slow speed scissors and tail slides. Spins are impossible to enter unless the limiter is turned off. Engines are considered unrestricted (100% efficient anti-surge system) throughout the operation envelope and on the edges exhibiting record accel rates from idle to max thrust with any weapons being employed. Takeoff T/W has been maintained at 1:1.
Vidimo da je izlazak na kriticne napadne uglove, iznad onih na koje je izlazio bazni Mig-29, sada moguc, sto sa svoje strane moze da implicira drasticnije otklone horizontalnog repa, pogotovo pri valjanju na vecim napadnim uglovima kako bi se povecala kontrola na tim ekstremnim rezimima.
Dimenzije h. repa (povrsina) je takodje znacajno povecanja sto znaci da se od njih zahtevala veca efikasnost, a takodje se na taj nacin povecao i ukupni uzgon aviona, jer je sada Mig-29M nestabilna platforma kod koje rep (recimo u krstarecem rezimu) vrsi pozitivno trimovanje cime se povecava uzgon aviona.
Sve ovo vazi (naravno pod pretpostavkom da sam u pravu  ) za rezime koji ne ulaze u POST STALL oblast ili kada nije ukljucen TVC, jer znamo da on kod OVT modela ucestvuje i u klasicnom manevrisanju (smanjenje "trim drag"-a, povecanje uzgona itd.)
Ukljucivanjem TVC stvar se menja i FCS i FBW prelaze u drugi "rezim".
Dacu jedan primer
Na ovoj slici mozemo da zapazimo da je otklon h. repa gotovo identican iako avion izvrsava valjanje.
Primecujemo da u manevru valjanja ucestvuju eleroni i TVC.
Sta se time dobilo?
Pa po nekoj logici rep u tom slucaju ostaje rasterecen, odnosno moze da se iskoristi za kontrolu aviona po dubini ili moze da se iskoristi za generisanje uzgona ako nije neophodan izlazak na velike napadne uglove u trenutku valjanja.
Upotpunjavanje elerona, odnosno povecavanje kontrole valjanja na svim rezimima izvrsava TVC (cime je moguce i smanjenje otpora vazduha), jer h. rep ne mora biti diferencijalno otklonjen kao sto je to slucaj kod obicne dvadeset devetke.
Ali ono sto je interesantno jeste da se u rezimu kada se ne koristi TVC , kod recimo Miga 35 koristi diferencijalni otklon h. repa prilikom valjanja kao kod obicne dvadeset devetke.
Skrenuo bi paznju na jos jednu stvar!
Na ovoj slici je primetan drugaciji otklon h. repa prilikom poletanja kod OVT, iako su predkrilca i stajni trap spusteni.
Komentarisali smo kako mozda nema slicnosti izmedju nacina na koji funkcionise sistem upravljanja kod OVT modela i kod obicne dvadeset devetke, ali ove fotke pokazuje da neka paralela postoji (kada se ne koristi TVC)i da je drugaciji (diferencijalan) otklon moguc i kod obicne dvadeset devetke iako su predkrilca i stajni trap izvuceni.
Dakle ovde se radi o obicnom dvosedu, a ne o OVT modelu, a ova fotografija neosporno dokazuje da je drugaciji otklon repa moguc.
Sto se tice sadejstva upravljackih povrsina i TVC kod OVT modela kod ekstremnih POST STALL manevara, nesto sam pisao o tome na drugim temama, a da bi sto preciznije ustanovili kako sve to funkcionise u letu (tu pogotovo mislim na h. rep), neophodno je da imamo snimak visoke rezolucije i sve dobro propratimo.
Pozdrav 
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