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AEROTUNELSKA ISPITIVANJA AERODINAMICKIH I BALISTICKIH KARAKTERISTIKA PROTIVOKLOPNE AVIO-BOMBE
Zoran D. Novakovic
Vojska Srbije, Vojnotehnicki institut, Beograd
e-mail: novakoviczoca@gmail.com
ORCID iD: ©http://orcid.org/0000-0002-7533-0149
DOI: 10.5937/vojtehg64-8352
OBLAST: masinstvo, balistika, aerodinamika VRSTA CLANKA: strucni clanak JEZIK CLANKA: srpski
Sazetak:
Aerotunelska ispitivanja protivoklopne avio-bombe (PTAB) se vrse se da bi se odredili aerodinamicki koeficijenti u rezimima podzvucnog i transonicnog strujanja. U istim rezimima strujanja ispituje se i vreme ar-miranja mehanizma upaljaca avio-bombe, koje direktno zavisi od uslova opstrujavanja protivoklopne avio-bombe. Krajnji cilj ispitivanja je definisa-nje pouzdane metode za odredivanje vremena armiranja upaljaca u aero-tunelu, cime se iskljucuju skupa letna ispitivanja. Za potvrdu metode predvidena je i verifikacija istih karakteristika protivoklopne avio-bombe u realnim letnim uslovima, nakon aerotunelskih ispitivanja.
Kljucne reci: vazduhoplovno naoruzanje, avio-bombe, upaljaci, vreme armiranja upaljaca, aerodinamika, aerotunelska ispitivanja.
Uvod
Sve veca efikasnost sistema PVO namece avionu koji napada cilj da, zbog svoje sopstvene bezbednosti, to izvede iz brisuceg leta (sa sto je moguce manje visine) i sto je moguce vecom brzinom napusti rejon ci-lja. To, sa druge strane, namece i dodatne zahteve pred vazduhoplovno naoruzanje, avio-bombe, koje u tom slucaju moraju biti kocene na svojoj balistickoj putanji, a njihov upaljac daljinski (vremenski) armiran, kako eksplozija avio-bombe kao slucajan - nezeljen dogadaj na putanji ili eks-plozija na cilju ne bi ugrozila sopstveni avion.
ZAHVALNICA: Autor se zahvaljuje kolegi dr Nikoli Zrnicu dipl. inz., bivsem ucesniku na ovom zadatku, na saradnji i nizu korisnih sugestija, narocito na deo teksta koji se odnosi na merenja u aero-tunelu i obradu rezultata ispitivanja.
Slika 1 - Graficki prikaz medusobnog rastojanja aviona i avio-bombe Рис. 1 - Графическое изображение расстояния между самолетом и авиабомбой Figure 1- Graphical illustration of a mutual position of an aircraft and an anti-armor bomb
Aerotunelska ispitivanja protivoklopne avio-bombe (PTAB) prethode letnim ispitivanjima sa ciljem da potvrde projektovane balisticke karakteri-stike i vreme armiranja upaljaca ili da se izvrse eventualne korekcije na svim uzorcima ovih avio-bombi pre skupih letnih ispitivanja prototipske partije iz domaceg razvoja. Prethodni proracuni balistickih putanja protivoklopne avio-bombe, sa projektovanim aerodinamickim koeficijentima, a sa usvojenom minimalnom visinom horizontalnog brisuceg leta, Hmin i di-japazonom brzina bombardovanja va=(6501-100) km/h, za dati tip leteli-ce, pokazuju medusobni polozaj aviona i avio-bombe na njenoj balistickoj putanji, sto je prikazano na sl. 1. Mehanizam za impulsno odbacivanje na avionu u trenutku t0=0, saopstava avio-bombama na izlasku iz potkrilne kasete pocetnu vertikalnu brzinu vy0, koje tom brzinom izlecu u horizon-talnu vazdusnu struju (brzina aviona va), cime se startuje okretanje vetru-ske mehanizma za armiranje upaljaca. Kada vetruska postigne odgova-rajuci broj obrtaja (granicnu ugaonu brzinu), tada se centrifugalni osigura-ci, razmesteni po obodu vetruske, razmicu i omogucavaju armiranje upaljaca. Krilca stabilizatora, nakon izletanja avio-bombe iz kasete, trenutno se otvaraju i stabilisu avio-bombu na njenoj balistickoj putanji.
Prihvatljiv trenutak kada upaljac treba da zavrsi armiranje je u intervalu vremena (t^ t2), mereno od trenutka pritiska bojevog dugmeta iz kabine pilota. Vreme ^ se odreduje se iz kriterijuma minimalnog bezbednog rastojanja - lkr aviona od avio-bombe, (Savezni sekretarijat za narodnu odbranu, 1988), a vreme t2 iz uslova pravovremenog armiranja upaljaca, tj. pre udara avio-bombe u prepreku, odnosno cilj. Upaljac protivoklopne avio-bombe je inercioni, sa prekidom inicijalnog lanca, daljinskim - vre-menskim armiranjem i samolikvidacijom. Trenutak kada upaljac treba da zavrsi armiranje t je zbirno vreme desavanja diktiranog niza dogadaja: vreme odrade releja instalacije na avionu nakon pritiska bojevog dugmeta - T1, vreme odrade mehanizma za impulsno izbacivanje avio-bombi -T2, vreme odrade mehanizma za armiranje - T3, vreme zauzimanja pozi-cije inercionog udarnika iznad detonatorske kapisle u upaljacu avio-bombe - T4. Vremena T1, T2, i T4 su reda velicine milisekunde, dok je vreme T3 reda velicine sekunde.
t=T1+T2+T3+T4, T3~T1, T3~T2, T3~T4, T3 - dominantno vreme,
Zbog drasticne razlike u redu velicina moze se u prvoj pribliznosti usvojiti da je:
t « T3, te(t1, t2).
Aerotunelska ispitivanja sprovode se na modelu protivoklopne avio-bombe, koji je aerodinamicki i geometrijski slican originalu i istovremeno prilagoden za dve vrste aerotunelskih ispitivanja:
1. Merenje aerodinamickih sila i momenata tenzometrijskom aero-va-gom na konfiguraciji modela bez vetruske mehanizma za armiranje (sl.3),
2. Merenje broja obrtaja n, odnosno vremena T3, od trenutka deblo-kiranja vetruske (tj. od trenutka kada je u aero-tunelu postignut zeljeni Mahov broj) do spadanja vetruske (sl.4).
Obe vrste aerotunelskih ispitivanja se sprovode se za karakteristicne vrednosti Mahovih brojeva 0,6, 0,7, 0,8 i 0,9 sto pokriva interval brzina (180-310) m/s aviona pri bombardovanju (Etkin, 1964).
Opis test modela
Model protivoklopne avio-bombe za aerotunelska ispitivanja je geome-trijski i aerodinamicki slican originalu, u razmeri 1:1. Model je prilagoden uslovima ispitivanja na repnom drzacu i prihvatu za ABLE MK XXV 1 aero-vagu (Anastasijevic, et al, 2001). Protivoklopna avio-bomba ima cilindricno telo sa ravnom ceonom povrsinom. Po obodu svog zadnjeg dela avio-bomba ima sest sklapajucih, simetricno rasporedenih krilaca koja cine stabilizator (2), sl.2, a iza cega se nalazi slobodno rotirajuca vetruska (1).
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Slika 2 - Test model PTAB (spoljni izgled): 1 - vetruska sa centrifugalnim osiguracima, 2 - stabilizator sa sklapajucim krilcima, 3 - telo bombe Рис. 2- Тестовая модель ПТАБ (внешний вид): 1 - крыльчатка с центребрежными предохранителями, 2 - стабилизатор со складывающимися лопастями, корпус бомбы Figure 2 - PTAB Test Model (exterior sideview): 1 - arming vane with centrifugal safety pins, 2 - stabilizer tail unit with folding fins, 3 - bomb body
Centrifugalni osiguraci, radijalno rasporedeni po obodu vetruske, razmicu se pri granicnom broju obrtaja kada se vetruska odvaja, te na taj nacin omogucava uspostavljanje inicijalnog lanca, odnosno armiranje upaljaca.
Nacin merenja i obrada podataka
Merenje aerodinamickih sila i momenata i vremena reakcije mehani-zma za armiranje je sprovedeno je u trisonicnom aero-tunelu T-38 Vojno-tehnickog instituta Vojske Srbije (Samardzic, et al, 2014). Aerodinamicke sile i momenti su mereni su ABLE-ovom tenzometrijskom sestokompo-nentnom aero-vagom na pravom stingu (sl.3), bez korekcije otpora baze modela. Osim aksijalne komponente vage merene su normalna kompo-nenta, bocna sila, moment propinjanja, moment skretanja i moment valja-nja, sto se uslovima testa nije trazilo, a sto je predstavljeno u obliku aerodinamickih koeficijenata u tabeli 1 i tabeli 2, u funkciji napadnog ugla.
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Slika 3 - Test model PTAB na pravom stingu Рис. 3 - Тестовая модель ПТАМ на прямой державке Figure 3 - PTAB test model on a straight sting
Merenje balistickih funkcionalnih karakteristika (T3, n) je sprovedeno je na lomljenom stingu (sl.4), sa uglom pregiba od 15 stepeni. Oba ekspe-rimenta obavljena su u transonicnom radnom delu aero-tunela T-38, pri br-zini strujanja koja priblizno odgovara Mahovim brojevima M=0,6^0,9. Pri-kupljanje podataka je obavljeno je sistemom za akviziciju TELEDYNE sa racunarom PDP 11/34. Obrada podataka izvrsena je standardnim soft-verskim paketom za obradu APS, racunarom VAX 11/780.
Slika 4 - Test model PTAB na lomljenom stingu Рис. 4 - Тестовая модель ПТАБ на кривой державке Figure 4 - PTAB test model on a broken sting
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Radi merenja broja obrtaja i vremena odvajanja vetruske, na telo avio-bombe ugradena je cevcica ciji se zavrsetak nalazi ispod rotirajuce vetruske, iznad koje prelecu grebenovi cetiri centrifugalna osiguraca. Cevcica registruje preletanje grebenova (rotaciju vetruske) kao ucesta-nost promene pritiska, odnosno registruje trenutak odvajanja vetruske kao skokovitu promenu srednje vrednosti pritiska preko posebnog dife-rencijalnog davaca pritiska PRT ugradenog u telo avio-bombe (sl. 5).
Davac je filtriran digitalnim filtrom od 1000 Hz zbog ocekivanog broja obrtaja ustanovljenog bez duvanja u aero-tunelu (3000 min-1). Za ostva-renu brzinu strujanja od 200 m/s, koja priblizno odgovara M=0,6, dobije-na je dominantna ucestanost f=190Hz, koja sa brojem grebenova vetruske N=4 daje broj obrtaja vetruske n:
n=f/N, tj. n=(190/4)x60=2850 min-1.
Slika 5 - Dijagram ucestanosti promene pritiska (I) - Airflow acceleration, (II) - T3 time, (III) - arming vane separation (fuze arming)
Рис. 5 - Диаграмма изменений давления (I) - Airflow acceleration, (II) - T3 time, (III) - arming vane separation (fuze arming)
Figure 5 - Diagram of Pressure Changing Frequency (I) - Airflow acceleration, (II) - T3 time, (III) - arming vane separation (fuze arming)
Rezultati ispitivanja
Merenja aerodinamickom vagom su pokazala su neocekivano veliki koeficient otpora ( Cx=4,41, Tabela 1), sto je posledica otpora krilaca stabilizator. Uloga krilaca stabilizatora je da uspore avio-bombu (smanje njenu brzinu i stabilisu je na putanji), odnosno zadrze je u odnosu na avion. Da bi se potvrdio uticaj otpora stabilizatora pristupilo se merenju aerodinamickih koeficijenata nakon demontiranja krilaca stabilizatora sa modela i ispitivanjem blunt body konfiguracije. Pri tome se dobio ocekiva-ni koeficijent otpora (Cx=0,79, Tabela 2), kao u referentnim aero-tunelima u svetu (Hoerner, 1965), (Finck, 1978).
Tabela 1 - Ispitivanje protivoklopne avio-bombe u aero-tunelu T38 Таблица 1 - Испытания противотанковой авиабомбы в аэродинамической трубе Т38 Table 1 - Wind tunnel testing of anti-armor bomb
Aero-tunel T-38 Wind Tunnel T-38
ISPITIVANJE PROTIVOKLOPNE AVIO-BOMBE U AERO-TUNELU T38 WIND TUNNEL TESTING OF ANTI-ARMOR BOMB
Ispitivanje PTAB01 PTAB01 Testing Duvanje broj: 2 Sequence number of blowing: 2 Datum 12. APR 00
Konfiguracija modela: kompletan model - Complete Model
i ALF A M Cx Cy Cz Cl Cm Cn
1 -0.12 0.603 4.4049 0.029 -0.015 -0.0031 0.0B3 -0.0950
2 1.92 0.603 4.353B 0.010 0.1B4 -0.0134 -1.1B1 -0.19B6
3 З.9б 0.604 4.3BB3 0.105 0.247 -0.0093 -1.B27 -0.001 B
4 б.97 0.603 4.4299 0.116 0.223 -0.015B -2.122 -0.04B4
б B.01 0.603 4.4B47 0.120 0.210 -0.0277 -2.305 -0.0743
б 10.05 0.603 4.549B 0.125 0.195 -0.02B6 -2.4BB -0.0695
i - indeks napadnog ugla (angle of attack index)
ALFA - napadni ugao (angle of attack)
M - Mahov broj (Mach number)
Cx - koeficijent sile otpora (drag force coefficient)
Cy - koeficijent bocne sile (side force coefficient)
Cz - koeficijent sile uzgona ( lift force coefficient)
Cl - koeficijent momenta valjanja (rolling moment coefficient)
Cm - koeficijent momenta propinjanja (pitching moment coefficient)
Cn - koeficijent momenta skretanja (yawing moment coefficient)
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Tabela 2 - Ispitivanje protivoklopne avio-bombe u aero-tunelu T38 Таблица 2 - Испытания противотанковой авиабомбы в аэродинамической трубе Т38 Table 2 - Wind tunnel T-38 testing of anti-armor bomb
Aerotunel T-3B
Wind Tunnel T-38
ISPITIVANJE PROTIVOKLOPNE AVIO-BOMBE U AERO-TUNELU T38
WIND TUNNEL TESTING OF ANTI-ARMOR BOMB
Ispitivanje PTAB01
PTAB01 Testing
Duvanje broj: 3
Sequence number of blowing: 3
Datum 12. APR. 00
Konfiguracija modela: cisto telo - Blunt Body Model
i ALF A M Cx Cy Cz Cl Cm Cn
1 -0.0B 0.29B 0.7723 0.047 0.023 0.0023 0.026 0.0150
2 1.94 0.29B 0.7753 0.052 0.015 0.0030 -0.013 0.0107
3 3.95 0.29B 0.7933 0.0B7 0.015 0.0036 -0.012 0.0172
4 б.9б 0.29B 0.B139 0.0B1 0.011 0.0044 0.023 0.0179
б 7.9б 0.29б 0.B515 0.049 0.043 0.045 0.041 0.0164
б 9.9б 0.29б 0.BB1B 0.037 0.0B4 0.0044 0.062 0.0167
i - indeks napadnog ugla (angle of attack index)
ALFA - napadni ugao (angle of attack)
M - Mahov broj (Mach number)
Cx - koeficijent sile otpora (drag force coefficient )
Cy - koeficijent bocne sile ( side force coefficient)
Cz - koeficijent sile uzgona (lift force coefficient)
Cl - koeficijent momenta valjanja (rolling moment coefficient)
Cm - koeficijent momenta propinanja (pitching moment coefficient)
Cn - koeficijent momenta skretanja (yawing moment coefficient)
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Slika 6 - Rekonstruisani test model PTAB (poprecni presek): 1 - vetruska, 1.1 - centrifugalni osiguraci, 2 - stabilizator sa sklapajucim krilcima, 3 - telo bombe, 4 - elektromagnet I, 5 - elektromagnet II, 6 - kotva, 7 - viljuska Рис. 6 - Реконструированная модель ПТАБ (поперечное сечение): 1 - крыльчатка, 1.1 - центробежные предохранители, 2- стабилизатор со складывающимися лопастями, 3 - корпус бомбы, 4 - электромагнит I, электромагнит II, съемник,
Figure 6 - Redesigned PTAB Test Model (cross-section): 1 - arming vane, 1.1 - centrifugal safety pins, 2 - stabilizer tail unit with folding fins, 3 - bomb body, 4 - electro-magnet I, 5 - electro-magnet II, 6 - lifter, 7 - locking fork 7 - вилка-предохранитель
Izmereno vreme T3 od 10s nije odgovaralo ocekivanom vremenu zbog dva razloga:
1. ubrzanje vazdusne struje do postizanja zeljenog Mahovog broja u aero-tunelu, odnosno rotiranje vetruske u tom periodu ne odgovara realnim uslovima upotrebe avio-bombe. U realnim uslovima, nakon izbacivanja avio-bombe iz potkrilne kasete aviona, vetruska trenutno upada u vazdusnu stru-ju koja odgovara brzini aviona (zeljeni Mahov broj u aero-tunelu),
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2. konstruktivna karakteristika mehanizma za armiranje ne dozvolja-va visekratnu upotrebu, sto se nije moglo izbeci u ispitivanjima, jer je jed-na te ista vetruska koriscena za vise duvanja.
Zbog toga se pristupilo rekonstrukciji modela i ponavljanju eksperi-menta, odnosno obezbeden je dovoljan broj uzoraka mehanizma za armiranje za svako duvanje ponaosob. Rekonstrukcija modela izvedena je tako da obezbedi mirovanje vetruske do trenutka postizanja zeljenog pri-tiska duvanja, tj. Mahovog broja u aero-tunelu. Kako je avio-bomba dela-borisana, to je njen unutrasnji prostor iskoriscen za smestaj elektromag-neta (I i II), (sl.6), koji pomocu svoje kotve (6) i viljuske (7), blokiraju/de-blokiraju okretanje vetruske (1). Elektromagnet I preko kotve i viljuske dr-zi blokiranu vetrusku za vreme ubrzavanja vazdusne struje u aero-tunelu do trenutka kada se postigne zeljeni Mahov broj. Tada elektromagnet I prestaje da deluje, a elektromagnet II povlaci kotvu, odnosno viljusku i deblokira vetrusku, tako da ona startuje sa obrtanjem pri zeljenom Maho-vom broju, a sto odgovara realnim uslovima upotrebe.
Zakljucak
Predstoji ponovno ispitivanje u aero-tunelu sa ovako rekonstruisanim modelom, kada ce za sva aerotunelska ispitivanja biti obezbeden dovoljan broj uzoraka novih mehanizama za armiranje. Krajnji cilj ovih ispitivanja je dobijanje krive zavisnosti broja obrtaja vetruske od brzine opstrujavanja avio-bombe (zeljenog Mahovog broja). Ako rezutati ispitivanja u aero-tunelu sa rekonstruisanim test-modelom avio-bombe budu potvráeni rezultatima letnih ispitivanja sa realnim avio-bombama, ovaj nacin ispitivanja u aero-tu-nelu moze se usvojiti kao pouzdana metoda za odredivanje vremena armi-ranja ove vrste upaljaca, Cime se zamenjuju skupa letna ispitivanja.
Literatura
Anastasijevic, Z., Marinkovski, D., & Samardzic, M. 2001. Merenje aerodinamickih derivativa stabilnosti u aerotunelima. Kumulativna naucnotehnicka informacija. Preuzeto sa http://www.vti/VANTIS/nti/nti/nti/01-3.htm
Etkin, B. 1964. Dinamika poleta.Moskva: Masinostroenie.
Finck, R.D.(1978). USAF Stability and Control Datacom, Final Report, AFWAL-TR-83-3048. April. Preuzeto sa
http://oai.dtic.mil/oai/oai?verb=getRecord&metadataPrefix=html&identifier=ADB072483.
Hoerner, S.F.(1965). FLUID-Dynamic Drag. Preuzeto sa http://www.greenbookee.net/hoerner-1965-fluid-dynamic-drag/
Samardzic, M., Anastasijevic, Z., Marinkovski, D., Curcic, D., & Isakovic, J. 2014. External Six-Component Strain Gauge Balance for Low Speed Wind Tunnels. Scientific Technical Review, 64(3), str. 40-46. Preuzeto sa www.vti.mod.gov.rs/ntp/lindex.htm.
Savezni sekretarijat za narodnu odbranu SFRJ. 1988. Borbena upotreba vazduho-plovnih sredstava pri dejstvu po ciljevima na kopnu i moru, knjiga I.
ИСПЫТАНИЯ АЭРОДИНАМИЧЕСКИХ И БАЛЛИСТИЧЕСКИХ ХАРАКТЕРИСТИК ПРОТИВОТАНКОВЫХ АВИАБОМБ В АЭРОДИНОМИЧЕСКОЙ ТРУБЕ
Зоран Дж. Новакович
ВСРС, Военно-технический институт, г. Белград
ОБЛАСТЬ: машиностроение, баллистика, аэродинамика ВИД СТАТЬИ: профессиональная статья ЯЗЫК СТАТЬИ: сербский
Резюме:
Испытания в аэродинамической трубе противотанковых авиабомб (ПТАБ) проводятся с целью определения аэродинамического коэффициента в режиме дозвукового и околозвукового течения.
В тех же режимах течения проходят и испытания необходимого времени для срабатывания механизма зажигания авиабомбы, которое зависит от условий обтекания противотанковой авиабомбы.
Конечной целью данных испытаний является разработка точных методов определения времени срабатывания механизма зажигания в аэродинамической трубе, так как их применение позволит существенно снизить расходы, за счет исключения дорогостоящих летных испытаний.
Проверка соответствия примененного метода и характеристик противотанковой авиабомбы будет проведена в реальных летных условиях, после проведения испытаний в аэродинамической трубе.
Ключевые слова: военно-воздушное вооружение; авиабомбы; механизм зажигания; время срабатывания механизма зажигания; аэродинамика; испытания в аэродинамической трубе.
WIND TUNNEL TESTING OF THE AERODYNAMIC AND BALLISTIC CHARACTERISTICS OF THE AIRCRAFT ANTI-ARMOR BOMB
Zoran B. Novakovic
Army of Serbia, Military Technical Institute, Belgrade
FIELD: Mechanical Engineering, Ballistics, Aerodynamics ARTICLE TYPE: Professional Paper ARTICLE LANGUAGE: Serbian
Abstract:
Wind tunnel testing of an aircraft anti-armor bomb (PTAB) is performed to determine its aerodynamic coefficients at subsonic and transonic flow regimes. In the same regimes, the fuze mechanism
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arming time is tested, directly depending on the local flow field around the anti-armor bomb. The objective of this investigation is to define a reliable method of determining the fuze mechanism arming time. A verification of the same characteristics of the anti-armor bomb in real flight conditions will be taken into consideration to approve the method after wind tunnel testing.
Introduction
Growing efficiency of air defense systems imposes on attacking aircraft to perform attacks at low altitude (at as low altitude as possible) and to leave the target area as fast as possible. This, in turn, imposes additional demands on aircraft weapons (bombs) which have to be slowed on their ballistic path with remote/temporal armed fuzes in order to avoid endangering aircraft by accidental bomb explosion on its ballistic path or bomb explosion on the target.
Wind tunnel testing of anti-armor bombs precedes flight testing in order to approve designed ballistic characteristics and fuze arming time or to make some potential corrections on all samples of anti-armor bombs of a nationally produced prototype lot, before expensive flight testing. Preceding bomb ballistic paths calculations that include the designed aerodynamic coefficients and the adopted aircraft low level flight minimum altitude - Hmin with a speed bombing range of va=(6501l100)km/h for the given type of aircraft show a mutual position of the aircraft and the anti-armor bomb (Fig. 1.). The impulse rejecting mechanism deliver to the bomb the orthogonal starting velocity vyo to the horizontal airstream (aircraft velocity vj. The bomb sweeps out from the container into the horizontal airstream which causes the rotation of the fuze arming mechanism vane, while body tail fins are deployed instantly to stabilize and slow the bomb along its ballistic path.
The fuze arming time measured from the instant when the pilot triggers the button is acceptable within the interval (t1, t2). The time t1 is determined by the criteria of the critical distance lkr, from the aircraft to the bomb (Savezni sekretarijat za..., 1988.) at the instant of fuze arming). The time t2 is determined from the condition of timely fuze arming, i. e. before the bomb impacts the target. The anti-armor bomb fuze is a percussion type of the fuze with initial chain interruption, remote-temporal arming and self destruction. The fuze arming time is a cumulative time of a defined chain of events (aircraft electrical installation relays the execution time-T1, impulse rejecting mechanism the execution time-T2, fuze arming mechanism the execution time-T3, fuze firing pin above percussion primer relocation the execution time -T4).
The Ti, T2, and T4 times are in miliseconds, while T3 is in seconds. Since there is a significant difference in time orders of magnitude, it could be adopted
t - T3.
The wind tunnel test model geometric and aerodynamic characteristics are similar to the original object. Also, the model is modified for two kinds of wind tunnel testing:
1. Tensometric sting-balance measuring of aerodynamic forces and moments of the test bomb model configuration without the arming vane mechanism, (Fig. 3),
2. T3 - time determination: The arming mechanism vane number of revolutions measured from the instant of the vane unlock (a moment when the wind tunnel achieves the desired Mach number) to the instant of the vane separation from the tail stabilizer tail unit, (Fig. 4).
Both tests are performed with characteristic Mach numbers: 0.6,
0.7, 0.8, and 0.9, which covers the interval of aircraft motion speed (180 310) m/s, (Etkin, 1964).
Test Model Description
The anti-armor bomb model with its own aerodynamic and geometric characteristics corresponds to the original, in scale 1:1. The bomb model is modified to be integrated with the ABLE MK XXV 1 sting-balance (Anastasijevic, et al, 2001.). The anti-armor bomb body is of a cylindrical shape with a front flat surface. The bomb tail unit comprises six radial folding fins located peripherally (Fig. 2), and the arming vane mechanism on the back side.
Four centrifugal safety pins radially located on the arming vane peripheral side are pulled out (at the critical number of revolutions when the arming vane is separated) to enable the initial chain set up
1.e. fuze arming.
Testing Description and Data Processing
The measuring of aerodynamic forces and moments as well as the arming mechanism execution time-T3 was performed in the Trisonic Wind Tunnel T-38 MTI SA. Aerodynamic forces and moments were measured on the ABLE tensiometric six-component sting-balance on a straight sting, (Fig. 3) without test model base drag correction (Samardzic, et al, 2014.). In addition to the axial force component of the sting-balance, other characteristics (vertical force component, lateral force, pitching moment, yawing moment, rolling moment) were measured, which was not a requirement of the test. All characteristics are presented in a form of aerodynamic coefficients as a function of the angle of attack, Table 1 and Table 2.
Measuring ballistic functional caracteristics (T3, n) was performed on a broken sting (Fig. 4) with a set-up angle of 15°. Both experiments were perfomed in the transonic working sector of the wind tunnel T-38 wind tunnel, with airflow speeds corresponding to Mach numbers from 0.6 to 0.9. Data collecting was accomplished by the TELEDYNE acquisition sistem. Data processing was performed using the APS data processing software package.
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The tubule is installed onto the bomb body in order to verify the arming vane number of revolutions and the arming vane separation time (T3). Its one end is located close to the rotating arming vane over which top four reefs of centrifugal safety pins are run. The tubule records the reefs run over (rotation of the arming vane) as a frequency of the air pressure changing, and records the instant of the arming vane separation as an abrupt change of an average pressure amount by means of a differential pressure transducer (PRT) installed into the bomb body (Fig. 5). Since the expected arming vane number of revolutions is 3000 r.p.m., the transducer signal is filtered by a 1000Hz digital filter. At a wind tunnel airflow speed of 200 m/s, with the equivalent Mach number of M=0.6, the dominant frequency f=190 Hz is obtained. Taking into consideration the number of arming vane reefs N=4, the number of arming vane revolutions is obtained:
n=2850 min-1 Test Results
The sting-balance measurements showed an unexpectedly large drag coefficient (Cx=4.41, Table 1), due to the deployed stabilizer fins. The role of stabilizer fins is to slow down the bomb (to decrease its speed and stabilize it on its balistic path), and to retard it with relation to the aircraft. In order to confirm the drag influence of stabilizer fins, measurements were repeated with the blunt body configuration after folding fins subassembly dismantling the folding fins subassembly. The result was the expected drag coefficient (Cx=0.79, Table 2) as the referent wind tunnels achieved world-wide, (Hoerner, 1965), (Finck, 1978).
The measured time of approximately 10s did not correspond to the expected arming mechanism reaction time for two reasons:
1. Airflow acceleration to the desired Mach number in the wind tunnel, i.e. arming vane rotation during this time does not correspond to the real usage of the anti-armor bomb. The arming mechanism vane falls into the aircraft speed horizontal airflow (the desired Mach number in the wind tunnel) instantly in the real flight conditions.
2. Arming vane mechanism design characteristic does not permit multiple usage, which could not be avoided in testing because one and the same mechanism was used many times.
For these reasons, the bomb test model and the experiment were redesigned. A sufficient number of samples of the arming mechanism vane were provided for each individual wind tunnel blowing. The bomb model redesign was perfomed in a way to prevent the arming mechanism vane from rotating until the blow pressure and the Mach number achieve desired values in the wind tunnel. Since the bomb body was discharged, the interior bomb body room was used to accommodate electro magnets I and II, (Fig. 6) which lock/unlock the arming mechanism vane by its lifter (6) and locking fork (7) . Electro magnet I locks the arming vane mechanism durring airflow
acceleration in the wind tunnel. At the instant of a wind tunnel airflow desired Mach number, Electro magnet I releases the locking fork while Electro magnet II pulls the locking fork back in order to unlock the arming vane mechanism. The arming mechanism vane starts to rotate at a desired Mach number (aircraft speed) which corresponds to real conditions of the anti-armor bomb usage.
Conclusion
New wind tunnel tests with a redesigned bomb test model are upcoming after providing an adequate number of arming mechanism vanes. The objective of these wind tunnel tests is obtaining a curve of the arming mechanism vane number of revolutions depending on the surrounding flow speed around the redesigned bomb test model. If the results of wind tunnel tests (with the redesigned bomb test model) are confirmed with the results of flight testing (with an actual anti-armor bomb), this wind tunnel testing could be accepted as a reliable method of fuze arming mechanism time determination of this kind of a bomb fuze. This wind tunnel testing will replace the expensive flight testing.
Key words: aircraft armament; bombs; fuzes; fuze arming time; aerodynamic coefficients; wind tunnel tests.
Datum prijema clanka / Дата получения работы / Paper received on: 26. 05. 2015. Datum dostavljanja ispravki rukopisa / Дата получения исправленной версии работы / Manuscript corrections submitted on: 12. 06. 2015.
Datum konacnog prihvatanja clanka za objavljivanje / Дата окончательного согласования работы / Paper accepted for publishing on: 14. 06. 2015.
© 2016 Autor. Objavio Vojnotehnicki glasnik / Military Technical Courier (www.vtg.mod.gov.rs, втг.мо.упр.срб). Ovo je clanak otvorenog pristupa i distribuira se u skladu sa Creative Commons licencom (http://creativecommons.org/licenses/by/3.0/rs/).
© 2016 Автор. Опубликовано в "Военно-технический вестник / Vojnotehnicki glasnik / Military Technical Courier" (www.vtg.mod.gov.rs, втг.мо.упр.срб). Данная статья в открытом доступе и распространяется в соответствии с лицензией "Creative Commons" (http://creativecommons.org/licenses/by/3.0/rs/).
© 2016 The Author. Published by Vojnotehnicki glasnik / Military Technical Courier (www.vtg.mod.gov.rs, втг.мо.упр.срб). This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution license (http://creativecommons.org/licenses/by/3.0/rs/).
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