Borut Podgoršek

Borut Podgoršek

Ponedeljek, 31 December 2007 10:37

Masa konstrukcije letal

Cilj konstruktorja letal je zgraditi konstrukcijo, ki bo uporabniku letala omogočala njegovo najučinkovitejšo uporabo preko celotne življenjske dobe. Pri tem mora upoštevati številne dejavnike, ki vplivajo na konstrukcijo letala (masa, korozija in utrujanje materiala, cena materiala, ...). Za uporabnika je najbolj pomemben dejavnik vsekakor masa letala v primerjavi z koristnim tovorom, ki ga letalo lahko prepelje. Masa konstrukcije potniških letal naj bi se gibala v območju med 25 in 30 % celotne mase letala. Delež koristnega (plačljivega) tovora naj bi se gibal okrog 20 % odvisno od tipa letala. Če bi na primer maso konstrukcije letala A310 zmanjšali za 400 kg bi lahko namesto te mase prepeljali štiri potnike več oziroma bi v enem letu porabili za 25.000 $ manj goriva. Neposredni stroški vzdrževanja letala bi bili tako mnogo manjši.

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Ponedeljek, 31 December 2007 10:35

Konstrukcija krila

Krilo mora biti oblikovano tako, da ustreza aerodinamičnim zahtevam, hkrati pa mora prenašati vse obremenitve, ki delujejo nanj. Na krilo delujejo normalne in tangencialne obremenitve (prečne sile, torzijski moment in upogibni moment). Prečno silo prenaša stojina, upogibni moment v vertikalni smeri prenašajo nosilci in torzijski moment prenaša oplata krila. Tangencialne obremenitve delujejo v pravokotni smeri glede na normalne obremenitve in so mnogo manjše od njih. Obremenitev konstrukcije celotnega letala je potrebno izračunati v vseh režimih letenja. S tem dobimo skrajne točke obremenitvene envelope znotraj katere je letenje s strani obremenjevanja konstrukcije varno.



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Z razvojem tehnologije se je spreminjal tudi pristop k konstrukciji krila in celotnega letala. V zgodnjih 50-ih so na nosilce krila in rebra pritrjevali relativno majhne in tanke plošče oplate, kar je bilo precej zamudno in drago. S tehnološkim razvojem so omogočili izdelavo večjih in ukrivljenih kosov oplate kar je skrajšalo čas gradnje in izboljšalo aerodinamično obliko. Nosilce in rebra krila so med seboj kovičili prav tako pa so na njih kovičili tudi oplato. Potrebna elastičnost krila je bila tako zagotovljena. V zadnjem času se uveljavlja nova tehnologija pritrjevanja oplate na konstrukcijo in sicer z laserjem.

Ponedeljek, 31 December 2007 10:26

Težava z nihanjem mase

Dolga puščičasta krila, ki so podvržena velikim aerodinamičnim silam se upogibajo in zvijajo. Gradiva iz katerih je konstrukcija narejena morajo biti zato dovolj elastična in hkrati trdna. Najbolj znan in moteč vpliv zunajih sil je nihanje in zvijanje krila – flutter. Flutter je pojav ko določena masa začne zaradi vztrajnostnih sil nihati. Nihanje lahko privede do porušitve komponente (krilo, zakrilce, ...) in posledično neizbežne katastrofe. Komponente so zato konstruiane tako, da ne pridejo v resonanco (nihanje se povečuje), kar bi se lahko zgodilo pri določeni hitrosti letal. Hitrost pri kateri bi lahko prišlo do pojava fluttra je običajno vsaj 30 % nad največjo hitrostjo letenja letala. Na ta način se izognemo prevelikemu in nevarnemu vplivu nihanja komponent. Znani so primeri, ko je letalu enostavno odpadel motor ali del krila.


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Ponedeljek, 31 December 2007 15:26

Položaj motorja

Položaj motorja vpliva na stabilnost letala, zato je zelo pmembno, kje je motor vgrajen. Danes sta nabolj značilni mesti za vgradnjo motorja pod krilom in na zadnjem delu (CRJ200, DC-9, ...) letala. Motorji so običajno v parih po eden ali dva na vsaki strani krila letala (A320, B737, A340, B747, ...). V preteklosti so imela nekatera letala tri motorje (DC-10, L-1011 tristar, B727, ...) od teh je bil tretji vgrajen v rep letala.

Prvo letalo na reakcijski pogon comet je imelo motorje vgrajene kar v krilo. V tem primeru mora biti krilo debelejše, kar pa povečuje upor. Danes so v potniških letalih v uporabi predvsem turboventilatorski motorji, ki imajo veliko obtočno razmerje zato vgradnja v rep ali v krilo ne pride več v poštev.

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Petek, 06 Julij 2007 15:20

Konstrukcije in konstrukcijska gradiva

Konstrukcije in konstrukcijaks gradiva potniških letal po drugi svetovni vojni

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Z uveljavitvijo reakcijskih motorjev v petdestih letih prejšnjega stoletja se je na področju letalskih konstrukcij marskiaj spremenilo. Sicer pravokotno in elipsasto krilo so zamenjali z puščičastim krilom, ki je omogočalo višje hitrosti letenja. Krila so bila tanjša in bolj vitka. Večji razpon kril pa je pomenil tudi večje obremenitve gradiv iz katerih so bili zgrajeni nosilci krila. Na eni strani so bile obremenitve višje zaradi daljše razpetine krila na drugi strani pa so se zaradi puščice krila pojavljale dodatne torzijske obremenitve v korenu krila, kamor se prenašajo vse obremenitve in kjer se te obremenitve seveda tudi seštevajo. Rezultat vsega tega so bile močnejše konstrukcije nosilnih delov, ki so prenašale te obremenitve in posledično tudi večja masa konstrukcije krila. Z razvojom novih tehnologij in predvsem novih gradiv so razvojni inženirji uspešno tekmovali z zniževanjem mase kril in celotne konstruukcije letala.

Težava z nihanjem mase
Konstrukcija krila
Položaj motorja
Masa konstrukcije letal
Staranje letal
Gradiva

 

Ponedeljek, 19 November 2018 08:10

S hrano proti stresu

Leta 2012 sem imel možnost leteti s 75 let starim letalom Polikarpov Po-2. Občutek je bil veličasten. Srčno verjamem, da se prvi potniki, ki so leteli na redni liniji med Londonom in Parizom leta 1919, niso počutili dosti drugače od mene.

Lani sta Slovenijo in Ministrstvo za obrambo obiskala astronavtka Sunita Williams ter general Frank Gorenc. Oba potomca Slovencev, ki so se izselili v ZDA, sta dokazala, da s pridnim delom in vztrajnostjo lahko uspeš. Decembra smo objavili intervju s Sunito Williams, tokrat pa smo pripravili intervju z generalom Frankom Gorencem, ki je avgusta lani postal poveljnik zračnih sil Nata in hkrati poveljnik ameriških zračnih sil v Evropi ter Afriki. (interview with Frenk Gorenc in English)

Ponedeljek, 16 Februar 2015 08:14

Tow tractors

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Modern airports allow passengers to pass rapidly through terminals and board aircraft via boarding bridges. In these cases the aircraft are parked with their noses right up against the airport building. In order to reach this position on arrival or return to the apron centreline, from where they can continue under their own power, on departure, aircraft are assisted by special aircraft tow vehicles that are known in technical jargon as “pushback tractors”. Tudi v slovenščini

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At Ljubljana Airport, which is also the home of Adria Airways, aircraft pushback operations are carried out by four vehicles that differ in terms of weight and engine power – and therefore the total weight they are capable of moving. The most powerful vehicle is a Schopf F300, which is capable of moving aircraft with a maximum take-off weight of up to 400 tonnes and costs half a million euros. It weighs an impressive 43 tonnes and its 173 kW engine can power it to a maximum speed of 30 km/h. The heaviest aircraft it has towed to date is an Antonov An-124, which has a fully laden weight of 400 tonnes. The ground handling service at Ljubljana Airport has 21 trained aircraft pushback operators who work in three teams. On average they carry out around 20 aircraft pushbacks each day: slightly fewer in winter and more (up to 25) in summer. They also look after those aircraft that need to be moved from the apron to hangars or other parking spaces.

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Once all passengers have boarded an aircraft, the loading of baggage, freight and mail has been completed and all ground handling vehicles have withdrawn to a safe distance, the captain or first officer requests the airport control tower for permission to start the engines and move the aircraft back from the terminal building. Pushback is carried out by a ground crew team consisting of a “ramp agent” and a tractor operator. The drawbar can be attached to the aircraft once passenger embarkation or disembarkation is complete and the steering bypass has been engaged, meaning that the aircraft's nose wheel is now controlled externally. The drawbar attachment and drawbar itself differ for different types of aircraft (aircraft type and weight, specific restrictions). After attaching the drawbar to the aircraft's nose gear, the operator attaches the other end to the towing tractor and, with the permission of the person in command of the aircraft, removes the chocks from the aircraft's wheels. He then waits for the signal from the ramp agent, who first checks that the area around the aircraft is clear and then talks to the pilot via the intercom. The tractor operator is advised by the operator in the ground handling service's technical centre that the aircraft is cleared to move and then waits for the signal from the ramp agent, who unclenches his fist to signal that the operation can begin. The tractor operator switches on rotating red warning lights, to show that the pushback operation is now under way. As soon as the aircraft is cleared to move from its position, the aircraft's crew switch on the anti-collision lights – flashing red lights on the aircraft's fuselage – which sends a clear message to everyone on the apron: “The aircraft is about to move. Keep your distance!” Pushback follows the planned curves of the taxiways. In the case of a non-standard pushback, Ground Movement Control (GMC) communicates with the tractor operator and gives instructions on where to move the aircraft.

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Usually pushback is from the parking position to the centreline of the apron, from where the aircraft can continue under its own power in accordance with GMC instructions. During the pushback operation the ramp agent controls the thrust of the aircraft's engines. When pushback has been completed, the ramp agent first uncouples the tractor from the drawbar. He then detaches the drawbar from the aircraft's nose gear and re-attaches it to the tractor, and restores control of the nose wheel to the aircraft's crew. The pushback tractor then moves out of the taxiway safety zone. This concludes the pushback operation. The duration of the operation depends on the complexity of the procedure but on average pushback takes between 3 and 6 minutes.

The movement of aircraft is carried out according to precisely defined instructions and procedures laid down by the responsible airport services, air traffic control and aircraft manufacturers. If this were not the case, there could be a risk of damage to the aircraft (the nose wheel) or airport equipment (such as the draw bar) or even a risk of collision with another aircraft or with a ground handling vehicle. According to pushback tractor operators, it is easier to move large aircraft because they are more stable and it is easier to see what is happening. Apparently they also handle better during pushback.

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Text and photographs: Borut Podgoršek

 

Ponedeljek, 20 Avgust 2018 08:04

Letališke službe

V tej rubriki predstavljamo letališke službe.

Vozila za vleko letal - Tow tractors

Zbirka Parka vojaške zgodovine je bogatejša za nov, dragocen eksponat –lovski bombnik F-84G Thunderjet (polna oznaka: Republic Aviation F-84G Thunderjet 10642 (serija F-84G-31RE, serijska številka 52-2910). Letalo, ki je eksponat Vojaškega muzeja Slovenske vojske, bo v naslednjih dneh sestavljeno in odslej na ogled obiskovalcem Parka.

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