Делтапланеризъм > Делтапланеризъм
Aerobatics
krassihg:
Митак, няма крило дето да не може да се счупи...в края на краищата крилата са тестирани на плюс 6, минус 4 G, нали така? Ако преминеш над тези граници, крилото се чупи. Ако се зачетеш в коментарите, има доста добри обяснения. Един от тях казва че не е въпроса в това дали крилата са достатъчно здрави, а в това че със сегашните скоростни възможности на крилата е много лесно да се постигне претоварване над допустимото . И това е което някои пилоти не разбират или някакси не го съобразяват. Ако се набримчиш с над 120 км в час и изведнаж избуташ яко, много лесно ще постигнеш претоварване повече от 6 G. Затова един от тях обяснява че при лупинг никога не позволява на рамката да иде напред на ниво повече от брадичката му.
krassihg:
Pilot Bill appears to have pulled up hard, based on the bar position at what seems to be in the bottom third or half of the looping maneuver. The bar is upper chest, lower neck area. In my glider, this position is not reached until much later in the climb, nearing the top of the looping type maneuvers, where speed and thus loads are reduced. That's a best guess looking a the photo sequences, but again, I was not there.
Pilot Tom looks as if he lost energy/speed going over the top. The smoke trails break indicating too much angle of attack, possible stall effect, and then the glider appears to sideslip with negative loading on the wings. I would guess what happens next is a violent tumble.
One thing that is sometimes forgotten is how critically serious doing aerobatics actually is. There are pilots that make it seem so effortless, and so reasonably safe. This has always been the illusion created by proficiency. The fact is, aerobatic flying is very risky, and the consequences can be devastating. Only by analyzing everything to the finest detail over the many years that I have been flying has made me feel "comfortable" and confident with such maneuvers. But I never forget the seriousness of this kind of flying. My family and close friends understand that as well, that if anything were to ever happen to me as a result of hang gliding, that my long term perspective has always been to try to learn from missteps and try to prevent missteps in the future.
Another thing that is worthy of mention is that the modern gliders and harnesses allow a bit of fast-tracking into looping. Looping speed is attainable much easier these days. The other day a pilot was asking me how to do loops optimally. I said, you get optimal dive speed, pull up with the optimal speed (not too strongly, and not too slowly), and meter out the energy over the top optimally, then complete the maneuver with an optimal pull in for another maneuver or with an optimal pitch to conclude the sequence. He asks, yeah, so what is optimal? I say, i you don't know, you are no where near ready to loop. This guy was not even doing wingovers with any regularity, and didn't have any real grasp on nailing 110 degree wingovers, or 150 degrees, or so on. Wanted to go straight to loops while skipping all that progressive work up in bank angle that old timers ha to work through more gradually as gliders progressed in design capability. I was purposely vague in order to feel out what the real question was, and as suspected, this particular pilot was looking to fast track to loops without working his way up to them progressively. It's possible to do that with modern topless gliders and big enough balls. So, it is possible to see less seasoned aero pilots everywhere, going way steep. It's something that the old timers can keep in mind when conversing with newer aero pilots I think.
My deepest sympathies for the family and friends of Tom, and best wishes for Bill's recovery. Aero is big time risk, and big time consequences. The only way I can justify it for myself is to be as pick and as anal and as analytical about it as I can, so that I can reduce the risk as much as humanly possible.
krassihg:
Good points. I'd like to add a few points of my own to these. I noticed the same things in the photos, that Tom looked to be pushed out pretty much fully, all the way, unless the angle of the photos misrepresented his arms. But the smoke trails also told me that he was not with all that much speed, and speed versus flying is a bit different thing. The smoke indicates turbulence right near the end of the arc, turbulence associated with a stall, also an indication of being pushed out too far. In general, two things make you run out of flying speed when doing aerobatics; climbing away from gravity and or pushing out. Combine both and energy drains away doubly fast. One might thing that a low bank aerobatic maneuver like a 90 degree wingover should be safe and easy to do, but keeping in mind what eats up speed and energy a pilot can still find themselves at this low bank, seemingly safe 90 degree or just beyond with no speed and be in a way worse situation that were one losing speed at 150 degrees of bank.
Something I learned from the WW boys a LONG time ago has served me quite well. That stall is not a function of airspeed, but a function of angle of attack. I remember Mike Meier writing that, and it has stuck with me forever. Angle of attack. Push out too far, and you stall. Push out and you also slow down, but it is the pushing out too far, raising the angle of attack higher than stall angle that is the real critical thing to remember. Tufts on the wing allow us to see and understand where that stall angle is reached relative to bar position. Knowing where the bar is relative to my chest, or neck, or face when stall angle is achieved, I know where never to put the bar during maneuvers. If I find out in still air, level flight, slow speed, that the tufts tickle or reverse when I put the bar 6 inches in front of my face, then I know never to put the bar that far when doing aerobatics, or when thermaling in rougher air. Stalling decreases sink rate performance too, so avoiding stalls is good practice all around. Tufts give us the information we need to understand a LOT of things associated with a wide variety of flying styles and preferences.
I don't have a T2C, but I do have a T2, and before that several other conventional topless gliders. Something I had to learn right away with them is that with the VG on (for aerobatics), the position of the basetube shifts back relative to no VG. Nearly ALL my aerobatic maneuvers thus needed to be adjusted in my mind and in my muscle memory so that I adjusted for this more rearward bar position. It was fairly challenging to change years and years worth of muscle memory so that I was not pushing out too far in my maneuvers. This really started with the Laminar I got in 2002, but it is still the same with the T2.
When I do wingovers or loops, I go by feel of the glider primarily, and the bar position is secondary for the most part. But adapting to a new glider and a new bar position characteristic of that new glider, is something that has to be reconciled with the feel and response. Over time. If there are differences, it takes time to adjust. Looking at the photos of Tom, he really appears to be pushed out fully, which with my arms would be something like a foot or a foot and a half PAST stall angle of attack. That is what can drastically eliminate flying speed and even roll response. Pushing out too far in an aerobatic maneuver, even one at 90 degrees of bank, is a terrible idea. Forget the aft CG idea for a minute, and consider that pushing out is comparable to putting on the brakes, slowing the glider quickly, and forcing it into a stall. With modern topless gliders, with VG on and very little twist, when stall happens in can spread rapidly from root to tips, a full span stall, which when at 90 degrees or beyond in bank, means even better braking than when flaring to land. The glider is unloaded, zero G positive, and so there is no pilot weight to created washout beyond what the sprogs produce. So it's one of the worst possible scenarios, pushing out too far when vertical or just past vertical.
I thought something similar when I saw the photos of Bill. Not regarding losing speed, but bar position and that it looked to be much further forward for where the glider was in the maneuver. In my own glider, and in previous gliders even, bar position never reached the neck area until near the apex of a loop. With the modern topless gliders, it's possible to crest loops without the bar ever going past that position if the pilot has enough speed. So when I saw the bar at Bill's neck at what looked like just coming up from the bottom of the maneuver I thought holy cow, that looks like too much pitch for the bottom of a maneuver, and too much loading, and too little pitch reserve for the upper arc and the top. There are plenty of reference videos out now on Youtube that show clean, smooth, well executed loops and where the relative bar positions are for any particular point during the loop to show what I am talking about.
Every so often people talk about how many G's we pull in loops. I can't speak for other people's maneuvers or experiences very well, but I have a couple of G meters and I recently flew with my best one to check what I was pulling. It'd been several years since flying with them, and I was curious if the T2, being faster and cooler than my older kingposted gliders, would be pulling more or less load. What I found was what i found many times in the past; that the loops I do that feel consistent and comfortable to me are solid at 4 G's, consistently. I have pulled far more at times, but those are unusual situations. The typical loop I fly is right at 4 G's at the max load point. That's less than 800 pounds the glider carries for me. I can't remember off hand what the ultimate loads were for the HPII when I was really interested in clearly defining breaking strengths of my gliders, but it was something just over 1,900 pounds I think. If my T2 is anywhere near as strong as that glider, or even a bit less strong than it, then I am still pulling less than half the structural limits on the glider. That said, with lots of speed and improper management of that speed, it is easy to pass that ultimate load limit very quickly. Letting the bar out too fast is the primary method of overloading the glider, and G's ramp up VERY fast if one lets the bar out too fast in a loop.
At any rate, speed management and angle of attack management are so incredibly important for aerobatics, and while there are so many forgiving situations that people have gotten into, not understanding the very fine details of aerobatics, the subtleties, the concepts of speed, drag, angle of attack, technique, technique, technique, there are and will be those situations where forgiveness is not seen when one screws up. Even when one doesn't screw up, there are things beyond our control that can go wrong.
Aero is a blast, and sure, we like others to see and appreciate it with us. But one thing that is important is to get feedback from others, listen and learn. Take it all seriously. It's really bad to hear that someone has broken their glider, or worse yet, died as a result of pilot error when the pilot in question may have been lacking in information or judgment that may have been there for the taking. Ego may play into it, for sure. Being shy to point things out may also play a part in it. We all make our own decisions on how we fly, but as a pilot that had to learn aerobatics in a relative information vacuum, I now live for as much information as I can get, and share.
Aaron
krassihg:
Да, има такова крило, то е модел още от 1995-та, известно е с аеробатичните си качества, и дори сега може да се поръча ( не се прави серийно доколкото разбирам вече) . За подсилване, да, разбира се, всяко крило може да се подсили, но това води до увеличаване на теглото и по-твърда конструкция, така че всичко това си има последствия за перформанса на крилото.
Един аеробатичен Як-52 е разчетен на +7, -5 G....така че за Predator подсилен да издържа на +10 -6 ми се вижда малко нереално. От друга страна Predator е все пак с мачта, докато повечето нови крила са безмачтови, което значи че разчитат на здравината на карбоновата напречна греда, която бе въведена от Тевено на времето, като един опит да се намали съпротивлението, но с цената на ограничена здравина ( мисля че на времето първите карбонови напречки издържаха на -3 г). По същата причина не се препоръчва аеробатика за твърдите крила от типа на Атос. Просто конструкцията за да бъде приемливо лека, издържа до толкова че да покрие минималните изисквания.
2
F=mV / r
Това е формулата за смятане на центрофугалната сила ( всъщност се казва центрипетална сила, защото е насочена към центъра на въртене)Видно е че зависи от квадрата на скоростта, а е обратно пропорционална на радиуса на въртене, т.е. колкото по-стегнат завой се прави, толкова по-голяма е силата.
Когато това се сравни със силата при нормален полет, се получава претоварването.
А Джон Хеини е известен аеробатичен пилот и фотограф. Беше направил рекорд за брой последователни лупинги ( имаше конкуренция с Мич Макалиър, по прякор Лудия Мич ) нещо от сорта на 59 лупинга си спомням.
А, ето му страницата...
http://www.johnheiney.com/
а това е снимки на Predator...виждат се вортекс генераторчетата на челния ръб 4 на брой
http://www.upgliders.com/classifieds/p142_org/
krassihg:
Относно подсилването...ясно е че в един делтапланер има елементи натоварени на опън ( въжета да речем) , други на натиск ( мачта, странични тръби на рамка, напречка) , трети на огъване ( бедра-челни ръбове на крилото)и усукване. Както правилно отбелязваш Иво, няма смисъл да подсилваш прекалено едни елементи от конструкцията, ако да речем има един слаб елемент, който така или иначе първи ще поддаде при определени усилия.
Проблема е по-скоро в това, че крилото е меко, т.е. допускат се определени промени във формата на платното ( 3-измерно), но все пак кройката на платното е оптимизирана за точно определено огъване на бедрата да речем. Това значи че не можем да усилваме кой знае колко много напречката, ако имаме ограничени възможности да усилваме бедрата. А възможностите са ограничени поради факта че всяка добавена втулка или увеличена дебелина на стената на тръбата води до втвърдяване на тръбата и съответно по-малко огъване, и съответно непасване на извивката на бедрената тръба с извивката на кройката на платното.Навремето челните ръбове на крилата бяха прави, дори имаше дефлексори ( аутригери) за целта. После навлязоха моделите с контролирана извивка на челния ръб. Контролирана как? ами с подходяща дебелина на стената на тръбата и подходящ диаметър. А степента на огъването на тръбите се оказа много важно за управлението и стабилността на крилата...защото колкото повече се огъва челния ръб, толкова повече се увеличава тунелността и усукването на краищата и оттам стабилността на крилото.
Затова всеки уважаващ себе си производител на моторни крила ще ти каже че не е просто въпрос на подсилване на конструкцията на едно безмоторно крило, напротив...прави се специален разчет и се конструира моторно крило със съответно платно...правят се известни изключения от този принцип само когато става дума за свръхлеки колички, които са в рамките на полетното тегло на безмоторен планер ( примерно голям размер крило може да поеме количка плюс лек пилот), но дори и тогава производителите предупреждават че не поемат никакви ангажименти за моторизирани версии и че това са експерименти на отговорността на пилота, който има желание да ги прави.Защото самото присъствие на двигател внася цял куп нови усложнения от сорта на вибрации, по-високи скорости и по-високи диапазони на ъгли на атака и т.н. Затова аз лично съм песимист относно така наречените подсилвания на безмоторни крила, освен ако не се правят от производител, който има представа какво прави. В конкретния случай за аеробатични крила би могло да се усилва напречката, рамката и мачтата ( все елементи на натиск), могат да се усилят въжетата, но когато се стигне до челните ръбове, има граници до които може да се усилва, и те не са много високи...просто рискуваш да получиш толкова твърди бедра, че това ще влоши управлението и стабилността, както казах по-горе.
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