Konstrukcije in konstrukcijaks gradiva potniških letal po drugi svetovni vojni
Z uveljavitvijo reakcijskih motorjev v petdestih letih prejšnjega stoletja se je na področju letalskih konstrukcij marskiaj spremenilo. Sicer pravokotno in elipsasto krilo so zamenjali z puščičastim krilom, ki je omogočalo višje hitrosti letenja. Krila so bila tanjša in bolj vitka. Večji razpon kril pa je pomenil tudi večje 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 puščice 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 močnejše konstrukcije nosilnih delov, ki so prenašale te obremenitve in posledično tudi večja 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
V zadnjih petdesetih letih velja, da imajo bojna letala praviloma vitko konfiguracijo, težiščna točka je pomaknjena precej nazaj.
Za njihove dobre manevrske zmogljivosti je bistvenega naloga konstruktorjev zagotoviti čim boljšo prečno vzdolžno stabilnost pri letenju pod velikimi vpadnimi koti. Zagotoviti pri tem še odlično krmarljivost pa meji že kar na umetnost, zanesljivo pa vsaj na vrhunskost aerodinamične zasnove. Zahteva namreč natančno uravnoteženje statične in dinamične stabilnosti. Stabilnost leta novodobnih vitkih bojnih letal pod velikimi vpadnimi koti narekuje tok zračnih vrtincev na sprednjem delu, nosu letala ter tok zračnega vrtinčenja ob korenu kril ob trupu. Odtrganje zračnega toka pri vpadnem kotu med 30° in 40° namreč povzroči precejšnjo prečno vzdolžno nestabilnost. Za zmanjšanje prečnih motenj je rešitev v doseganju največjega vpadnega kota, saj se po vpadnem kotu 60° sežeta dva ločena toka zraka. Naslednji vpliv je giroskopski moment kot posledica rotacije motorjev, ki povzroča prečno nestabilnost, še posebej pri veliki kotni hitrosti gibanja po prečni osi.
Ena od značilnosti superkrmarljivih bojnih letal je znaten moment omahovanja nosu pri vpadnih kotih nad 60°. Do pojava pride, ker se središče vzgona krila pomakne nazaj zaradi odcepitve zračnega toka na krilu s približno četrtine tetive pri vpadnem kotu 20° do polovice tetive profila pri vpadnem kotu 80°. To središče vzgona je sedaj za težiščno točko in nastane sila, ki vleče letalo na nos, zato se dviganje nosu ustavi in letalo se ujame. Vzgon bi pri tem lahko dali v narekovaje, kajti pri vpadnem kotu 90° je edina sila, ki nasprotuje gravitaciji in drži letalo v zraku, potisna sila motorjev.
Poleg omenjenih aerodinamičnih rešitev, s katerimi se doseže superkrmarljivost, ponuja v bistvu boljšo rešitev, ali aerodinamičnost še izboljša, usmerjanje potiska. Najbolje v vseh oseh, čeprav je največ izkušenj le po vertikali.
V letošnjem letu je v času, ko se je bližala pomlad in, ko so se nad letališčem v Turiški vasi pri Slovenj Gradcu začeli zbirati kumulusi, ki so vabili k jadranju, odšel Ivan Smolčnik, pilot in publicist iz Mislinjske doline. Rad je letel in o tem je ostalo kar nekaj zgodb strnjenih v mapi, ki jih je pripravljal za izdajo svoje knjige, nekaj pa je objavljenih tudi na internetni strani Koroškega aerokluba. Vsaka zgodba je kot en trikotnik, ki je na svoji poti do zaključka tako turbolentna kot je lahko jadranje.
Nedavno sem imel možnost leteti s 75 let starim letalom Polikarpov Po-2. Občutek je bil veličasten. Srčno verjamem, da se prvi potniki, ki so leteli na redni liniji med Londonom in Parizom leta 1919, niso počutili dosti drugače 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 zračnih sil Nata in hkrati poveljnik ameriških zračnih sil v Evropi ter Afriki. (interview with Frenk Gorenc in English)
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
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.
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.
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.
Text and photographs: Borut Podgoršek
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.
Modest, unassuming, but extraordinary in all respects, Sunita Williams is one of the many descendants of Slovenians who went abroad to realise their dreams. However, the dreams of the parents have been fulfilled primarily by their children, Sunita being one of them. This year, she visited Slovenia for the second time. She also visited the Ministry of Defence. She presented her outstanding achievements, which are plenty, to Slovenians. Nobody was left indifferent.
Today, Sunita is the Director of Operations Russia in the Star City near Moscow. In that capacity, she runs an office which provides all the logistics for the US, European, Japanese and Canadian crewmembers training in Star City and who are preparing to go to space.
Tudi v slovenščini
How did work and book of Herman Potočnik Noordung The Problem of Space Travel - The Rocket Motor from 1928 influenced the development of space traveling and living in space?
I can’t exactly tell you from a historical perspective, but I am sure it was a huge influence on the first individuals who designed spacecraft. As a visionary, Noordung’s influence has been realized in many rocket and space ship designers plans.
You have been in Cultural Centre of European Space Technologies in Vitanje? In your opinion how can we bring space and living in space to ‘normal’ people and vice versa?
Certainly! Thru the center and the work that is going on with the International Space Station, we are hoping to share the visionary ideas and the actual scientic events that are occurring to help bring the concept of space and space travel into the household of all humans. Lots of work in this field is out there for the public and one goal would certainly be to get as many people involved to tap into their new and creative ideas.
How can this center contribute to conquer the space, the universe?
The center is a great place as a museum and a center for advanced thought. The atmosphere of the place allows people to open their minds like Noordung did. Creativity and imagination is the next step in advancement. In the words of Albert Einstein, knowledge is useless without an imagination.
Would you go to the Mars? And what would you miss most?
Sure I would go to Mars. With today’s technology it would be a long trip, and we have a lot of work to ensure the crews are safe from radiation and micro gravity induced issues on the human body. However, I think before long we will have the knowledge and technology to solve those problems. Advancements in propulsion will be needed to send people further out to the reaches of our solar system for sure. I think that might take a bit longer, but it WILL happen eventually. I think the things that we miss about earth and unique to earth – our air, wind, ocean, water, other living beings that we know. So, some memories of all these things of course would be important. Specifically family and a sense of connection with earth thru pictures or some media would be of high importance to me.
What are you doing at present?
As an experienced ISS, Shuttle and Soyuz crewmember, I am also part of many working groups that interact with our Russian counterparts, to include Soyuz technical support – launch, rendezvous and landing - , EVA (spacewalk), Crew equipment, clothing and food, training planning, etc. So every aspect of training and working with our Russian counterparts I seem to get involved in…funny, but it is overarching, and certainly fun, never boring.
Do you believe that there is another inhabited planet somewhere?
Absolutely. There are millions of stars in the universe that we know. Of course there has to be a star that is somewhat similar to our sun, which has planets that may possible be a distance that would sustain the atmospheric conditions to contain life. Maybe not exactly as we know it, but even here on earth we are discovering new species living in very different environments, like at the bottom of an ocean in what we considered toxic gases. So, more than likely yes.
Will Earth in 2100 still be the green planet or we will have to move?
That is a great question. I think only we can do as much as we can to sustain life here. Then of course there is always the possibility of us getting hit by some sort of asteroid that would change the landscape of the planet. Nature is by nature very balancing. When things get out of balance, it seems that generally our planet takes care of it. However very fast change from humans is tough for our planet to keep up with. I think we all must think about how we can conserve and help our planet as much as possible and possibly slow down dramatic changes that would change our atmosphere for example. If we as humans want to remain here.
What was your first impression when seeing the Earth from the space and feel the 0g?
Incredible. The planet is simply beautiful and alive and peaceful. I wonder at how lucky we are to be on this planet and how we as humans all should see this view and then I am sure we would all be nicer to each other.
What does it mean cancellation of Space shuttle program for future? Does NASA have near future plans to built new vehicle or you will rely on Russia and their transport capabilities?
NASA is building a new vehicle to hopefully take us out of low earth orbit. The space shuttle was an amazing vehicle and it was absolutely needed for us to build the International Space Station. However, we now would like to go further than low earth orbit – someplace that doesn’t necessarily have a runway to land on – like the moon or Mars. So we need a vehicle that can land under a parachute or with landing jets. We are working on that future vehicle which will safely transport people further and return them. It is the next good logical step in exploration. In the meantime, our Russian counterparts are helping us out by transporting humans to the ISS. We should have commercial providers, just like the airline industry which will soon take over that function of delivering people to low earth orbit alongside the Russians.
You have been launched also with Soyuz. What was the main difference compared to space shuttle launch?
Both are essentially the same. Except the shuttle uses solid rocket booster primarily for the first stage. The Soyuz uses all liquid engines in distinct stages for each propulsion to space. However, both rides are about the same amount of time, dictated by physics and both spacecraft are made to be the home to humans in space. They have different seats, but that is primarily for the landing phase of flight.
What do you think about privat companies like SpaceX, Orbital Science Corporation?
I think they are great. With them, there will be competition for the job to take humans to low earth orbit. With competition we will have a vehicle to do that job before long. There is a lot of young, new innovation with these new companies. I love their work ethic and their enthusiasm.
How would you rate Pipistrels achievements in NASA competitions? You visited Pipistrel.
Pipistrel is a wondering company. I love that their work is so innovative. They are really guiding the way of future general aviation. Their ideas and way of working is so clean, precise and elegant. This is the way our future will advance – thru technology that is good for our planet. I had a wonderful time visiting with the folks who work at Pipstrel, and I feel they are a family. They care about each other as well as their product. Cooperation, sharing ideas is the way of the future.
What does it mean to you the medal of merit which you got from the president of Republic of Slovenia?
The award and everything that it means was totally humbling. There are so many people and events which occurred to get me into space that I can only say that the award is really for all of them too. Of course my parents are a huge influence on me, so this award is really for them. I have had the opportunity to be taught by so many amazing people from elementary school to test pilot school. This award is for them. I have also worked alongside many international partners preparing for my spaceflights, this award is also for them. I just hope I am representing all of these people, their commitment, dedication and professionalism, to merit such a great honor.
What do you think about Slovenia and Slovenians?
Slovenia and Slovenians are awesome! I love the country. I feel at home there for both of those reasons. The people are as warm and inviting as the landscape. I love the natural feel of the country and pride that the people who live there take in keeping it that way. I think Slovenians really understand what the meaning of preserving our planet is. They love and appreciate nature and love to be part of it. I am very pleased to be from a place on the planet that epitomizes these ideas and ideals.
Author of the interview Borut Podgoršek and Sunita Williams on the left photo
Foto: NASA, UPRS, MORS, Reuters
On 20 November 2013, the International Space Station (ISS) celebrated the 15th anniversary of the launch of its first module to space. The station was jointly built by five space agencies. It is divided into the Russian and American parts, which are used by several countries. The ISS is used as a research laboratory carrying out experiments in biology, physics, meteorology and other sciences. Sunita Williams has been on the ISS twice and was the second woman to become commander of the ISS.
Skromna, neopazna, toda v vseh pogledih izjemna Sunita Williams je ena izmed mnogih potomcev Slovencev, ki so odšli v svet, da bi uresničili svoje sanje. No, sanje svojih staršev so uresničili predvsem njihovi otroci, med katerimi je tudi Sunita.
Letos je drugič obiskala Slovenijo, gostili pa smo jo tudi na Ministrstvu za obrambo. Svoje izjemne dosežke, ki jih je kar nekaj, je predstavila Slovencem, tudi Urši, Romani in Andreji. Nikogar ni pustila ravnodušnega. Danes je Sunita Williams vodja operacije Rusija v Zvezdnem mestu (Star City) pri Moskvi. V tej vlogi vodi urad, ki zagotavlja vso logistiko za ameriške, evropske, japonske in kanadske člane posadk, ki se usposabljajo v Zvezdnem mestu in pripravljajo za odhod v vesolje. Interview is also in English