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Those aircraft all suck! That third dimension hardly counts when you have to watch the world whizzing by at 100 knots to get it. (F-35B will get a partial pass.) Click here for the full 1024x768 image. Sikorsky AH-60L "Battlehawk", for when you can't afford an Apache  Click here for the full 800x504 image. Sikorsky S-67 Blackhawk, the lesserknown Sikorsky Blackhawk  Click here for the full 1400x612 image. AH-56 Cheyenne, world's fastest compound helicopter to this day. Very early "rigid rotor"  Click here for the full 1600x1212 image. Kaman K-1200 K-MAX, a flying eggbeater  Click here for the full 1024x768 image. Boeing A-160T Hummingbird, a flying fuel tank  Click here for the full 1200x750 image. Mi-24, the modern Shturmovik  Click here for the full 1024x768 image. Ka-50, great gunship airframe, bizarre single seat arrangement  Click here for the full 1024x768 image. Mil V-12 (the world's largest helicopter)  Click here for the full 1200x782 image. Mi-26, the world's largest practical helicopter These guys have big engines, big gearboxes, and all sorts of mechanical crap. They're loud and utterly utilitarian. AI should love this poo poo. Tetraptous fucked around with this message at 02:07 on Mar 9, 2010 |
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Mar 9, 2010 02:03
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Some Guy From NY posted:I love the Sikorskiy Blackhawk. It seems like an amazing helicopter. Bad timing, more than anything. The prototype crashed well after the Army had already rejected the proposal - Sikorsky was trying to drum up export sales for their self-funded design. That video was similarly produced for export sales. No doubt it was a good ship, but after the AH-56 Cheyenne program delays the Army was looking for a low risk option and even the S-67, less advanced than the original S-66 (it had a swiveling tail rotor), was consider too risky. The drag brakes were a fantastic feature for a gunship though - they'd have enabled the vehicle to adjust the fuselage trim independently of rotor trim which would be helpful in strafing runs, but also in reducing noise in certain circumstances (though I don't know if Sikorsky was aware of the latter at the time). The S-67 was also pretty drat big, compounded by the fact that wings add a substantial download penalty during hover. Anyway, with Vietnam winding down the Army was content to make due with a less radical step forward. Even today, we don't have a helicopter airframe half as capable as the AH-56. Obviously, our avionics and weapon systems are much improved, but in terms of pure performance the rotorcraft industry is basically where it was 30 years ago.
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Mar 9, 2010 03:09
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Beerios posted:Most pictures really don't do the Mi-26 justice. Here's a better illustration of just how huge it really is - that little thing underneath that it's carrying is a loving Chinook. True enough. Standing next to one, you realize the airframe is more like a small airliner than a normal helicopter. The tail rotor is similar in size to the main rotor of many light utility helicopters.
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Mar 10, 2010 05:23
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Granted, the XB-70 was a nuclear bomber (or at least, was supposed to be), went Mach 3, and had a vaugely F-15ish twin vertical - certainly not a Navy plane, but maybe that's where the confusion comes from? The XB-70 at Wright-Patt is really something to behold, and it's hard to conceive of it's shear size without seeing it in person. A much more impressive aircraft, IMO, than the A-12/SR-71. I recommend the museum there heartily, the XB-70 alone is worth the trip but they have tons of other great stuff too.  Click here for the full 1348x1092 image.
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Mar 22, 2010 23:36
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JnnyThndrs posted:I lived on the Sunnyvale/Mt. View border for ten years, not far from Moffet Field and you could hear those P3 Orions about a hundred miles away in the middle of the night, they'd just kinda drone away FOREVER before they actually landed there. I got used to it, the noise was sorta comforting. Let it also be known that NASA Ames (at Moffett) has the world's largest wind tunnel - well, it's actually the world's two largest wind tunnels in one package.  Click here for the full 1896x1397 image.  (Look for the people standing in front of the fan section).   SMART rotor (basically an MD-902) in the 40x80 foot closed-loop acoustically treated section.   F/A-18 in the 80x120 foot open loop section. One of the few wind tunnels in the world large enough to test full scale aircraft. When it was built around WWII, it was just right for testing the aircraft of the day. These days, the tunnel is really best suited to testing rotorcraft, but the (actual) F/A-18 above shows that it's useful in fixed wing high AoA tests, too. Tetraptous fucked around with this message at 05:21 on Mar 25, 2010 |
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Mar 25, 2010 05:18
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D C posted:Much love for the AStar. Don't see too many other 3-bladed helicopters these days, but it's quite economical for an articulated rotor helicopter with very good performance for the price. My only complaint is the blades go the wrong way round, like most other French and Russian helicopters.
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Mar 26, 2010 02:04
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Flying boat? VTOL? Kaman K-16B Tilt-wing. Project was cancelled before it flew.  Click here for the full 1479x999 image.
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Mar 26, 2010 19:28
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    Tetraptous fucked around with this message at 02:06 on Mar 31, 2010 |
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Mar 31, 2010 02:03
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The Micheal Yon article they're from is misleading, and blames it on static electricity. The truth is simpler - during brownout conditions, sand can strike the titanium abrasion strips that coat the leading edge of the rotor and cause it to spark. Although these images are somewhat augmented, it can be a real problem at night during insertion operations because it can reveal the location of the helicopter to the enemy.
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Mar 31, 2010 02:18
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Boomerjinks posted:WB-57, basically the US bought the licensing to produce the British Canberra bomber, it sucked for what we wanted so we gunned it up, made it's engines start with a pyrotechnic charge, and then started using it for high-altitude weather monitoring, reconnaissance, and space program observation. I was working a flight test program when one of these had engine trouble after a shuttle launch and had to come down at Moffett Field for repairs. Those guys took over our hanger, but were able to source an engine, replace it, test it, and head off back to JSC in about 48 hours. Seriously, the quickest NASA operation I've ever seen. I remember when I saw that thing roll up, I was scratching my head for a bit trying to figure out what sort of aircraft it was. They've got a pretty nifty website, including a copy of the ops. manual.
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Apr 6, 2010 23:49
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ApathyGifted posted:Helicopter people: Net rotor forces are approximately perpendicular to the rotor tip path plane, so we need to tilt the rotor tip path plane, e.g. through flapping, to control the helicopter. The 90 degree advance on the cyclic controls is because for a rotor with zero hinge offset (e.g. a teetering rotor), the blade flapping response to changes in loading will be delayed by 90 degrees. One way to view this is that the rotor's rotating flap natural frequency is exactly 1/rev, and so this type of rotor is in resonance. However, changes to the flapping hinge will increase the rotating flap natural frequency, and move the rotor flap response away from the resonance. For a typical full-size articulated rotor, the hinge offset is on the order of 5% R, and the required advance will be slightly less than 90 degrees. For a hingeless rotor, the effective hinge offset (resulting from the stiffness of the blade root flexure) may be much higher, and correspondingly less advance of the controls will be required (on the order of 75 degrees). To calculate the exact advance required, you need to know the blade flapping moment of inertia and the effective hinge offset; you will also need to know the blade root stiffness for a hingeless rotor. Things are a bit different if the rotor is designed with pitch-flap coupling (or a "delta-3" hinge), such as a tail rotor, or via a stabilizer bar, which can result in considerable increase in rotating flap natural frequencies and hence significant decrease in the amount of cyclic advance required. All that said, what's the difference between a single, isolated rotor and a coaxial rotor? Other than the fact that they spin in opposite directions, there is none. The cyclic advance is wholly dependent on the flapping hinge of the rotor and any pitch-flap coupling introduced through delta-3 or other mechanical devices (which are not generally used for full-size helicopter main rotors). The math behind all of this is available in a few texts, and is usually a part of what we call "helicopter dynamics." Stepniewski wrote a great (and FREE!) book on helicopter aerodynamics, which is quite readable and includes a brief treatment of blade flapping dynamics on page 10 that you can find here. Wayne Johnson's Helicopter Theory goes into much more detail on dynamics, including things like delta-3, and is quite affordable in the Dover edition, but I think it's a better reference than a book to learn from. Leishman's Principles of Helicopter Aerodynamics is a great book to learn from, and there is a recent up-to-date edition, but it is expensive! Ray Prouty's Helicopter Performance, Stability, and Control is also very good, but expensive and now hard to find. At the risk of outing myself on the forums, I did my PhD on a narrow niche of helicopter aerodynamics, and do research in that area for a living. I'm not an expert in dynamics, but I do know a little of everything about helicopter theory and I'm happy to answer any technical questions about helicopters in this thread.
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Mar 24, 2016 04:10
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holocaust bloopers posted:You have a cool PhD and job. I have a personal soft spot for the Bell 206, since I've spend a lot of time working in and around them. My favorite helicopter otherwise changes depending on what I'm thinking about at the time. Right now, I am trying to learn more about Sikorsky's first Blackhawk, the S-67, see here in video. After the ambitious AH-56 Cheyenne was cancelled, Sikorsky developed the S-67 using internal funds as a less risky, but still high performance, alternative. Sikorsky would later convert it to a fantail configuration. The Army never developed a specific requirement for a vehicle like the S-67, and Sikorsky wasn't able to convince them to buy before crashing the only vehicle at Farnborough. Eventually, the Army came up with the AAH requirement, which was even less ambitious and would result in the ugly and slow AH-64 we know and love today. The Constellation is a fine looking airplane. It's not on my list of beauties, but I don't know why some in this thread seem to be repulsed by it!
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Mar 24, 2016 05:10
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Luneshot posted:What lunatic came up with the idea of helicopters in the first place and how did the entire rest of human society not respond with "you're loving nuts and this is an affront to the very concept of aerodynamics" The history is pretty interesting, and unlike with manned aircraft, it's pretty hard to say for certain who built the first machine that counts as a flying helicopter. I think the prize for the first practical helicopter actually has to go to the Germans, with the Fw-61, as famously flown by Hanna Reitsch. Maybe I will do an effort post on the subject sometime soon.
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Mar 24, 2016 05:17
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holocaust bloopers posted:How does noise dampening work for rotors? I'm not sure exactly what you mean... but, for noise we usually think of two different types, interior and exterior. For interior noise, the traditional solution is to add sound absorbing liners to the cabin, but these are heavy and so you'll usually only see effective ones on helicopters configured for executive transport and the like. It's an option for military helicopters, too--I know the H-60 can be fitted with a liner, but it can't be used with the doors open in flight--which means it is rarely installed in the first place. Designers will also be careful to avoid having panels resonate at the forcing frequencies of the rotor, since they can cause noise in the cabin. (Interesting side note: if you work through the math, a rotor only passes through vibrations at frequencies that are harmonics of N/rev for vertical vibrations and N+1/rev and N-1/rev for lateral vibrations, where N is the number of blades. All other frequencies are filtered out. This is a major reason for why helicopters with more blades have lower vibratory loads!) Transmission noise and vibration is also important for interior noise, so a lot of effort goes in to designing quiet gear-engagements. You can use helical gears for most applications, which reduce noise, but the main rotor gearbox is normally a planetary gear system which cannot support the thrust loads of a helical drive. (I suppose you could use a herringbone or double-helix type gear, but I've never heard of it being done in practice.) More recently, helicopters are being designed with active noise and vibration suppression systems, which cancel out structural vibrations and reduce acoustic transmission through the structure. Exterior noise is more in my wheelhouse; here we are primarily concerned about the aerodynamic noise generated by the rotors. Broadly speaking, this noise is generate through two mechanisms: thickness noise, which is caused by the physical volume of air being displaced by the rotor blades every blade passage, and loading noise, which is caused by the pressures exerted by the rotor on the air (remember Newton 3rd law--if aerodynamic forces are applied to the rotor blades to support the helicopter, the blades must be pushing back on the air!). Thickness noise radiates primarily in the plane of the rotor in the direction of travel (so, out in front of the helicopter), and for that reason is important for aural detection. As the Mach number on the advancing tip increases, locally supersonic pockets can form around the blades, dramatically amplifying the effective fluid displacement caused by the blade volume. When this happens, we call it high speed impulsive noise, and it's what is responsible for the characteristic popping sound of the Vietnam era UH-1 helicopter which had a very high tip speed by modern standards. Thickness noise can be reduced by reducing blade thickness (duh!) and chord near the tip, and more effectively, through reductions in tip speed. But tip speed reductions come at a big cost--lifting capability of the rotor decreases, which means the blade chord must be increased to compensate. Also, the power required to support the helicopter doesn't change much as tip speed goes down, and just like a car engine, as RPM decreases torque must increase for the same power. As when torque increases, the transmission and shafts have to get that much bigger to support the load. Lastly, autorotative safety margins decay as tip speeds go down, since the rotor no longer "stores" as much kinetic energy. So far, manufacturers haven't been willing to suffer much of a performance/weight penalty in order to reduce noise; since at the end of the day, their customers aren't willing to pay much for the latter. For loading noise, we can also subdivide into a couple of categories. Lower harmonic loading noise is caused by the steady and lower harmonic airloads required to support the helicopter that are generated by the blades--like thickness noise, it's mostly low frequency, although most of the energy goes out of the rotor plane (and generally towards the ground). There's not too much you can do to reduce these airloads, since they are required to lift the helicopter! Reducing disk loading by increasing rotor radius will have a modest effect on this noise. Reducing tip speed will have a more powerful effect, but still less so than for thickness noise. A special case of loading noise is called blade-vortex interaction noise. Just like an airplane wing, the rotor blades shed a tip vortex. However, what's unique to helicopters is that vortices shed from the blades near the front of the rotor disk will convect rearwards as the helicopter travels forward, and can pass close by the blades near the rear of the rotor disk. When this happens, the vortex causes a small but rapid change in the angle of attack of the blades causing a corresponding change in airloads. This can result in vibrations and a very powerful impulsive noise. In normal level flight, the rotor wake is well below the rear of the rotor disk, but during descents or maneuvers, the wake can come up into the rotor and create the higher frequency and more annoying "wop-wop-wop" sound you've heard if you've seen helicopter flying around near you. The best way to mitigate this noise source is to avoid flight conditions where it can occur; and there's a lot of work in low noise flight operations to this end. From a design viewpoint, you can make changes to the blade planform to reduce this noise (see the Blue Edge blade for a flying example) and use active control techniques to attempt to locally increase the separation between the vorticies and blades, but to be honest, the demonstrated reductions are pretty modest. Even lowering tip speed is not that effective for this noise source. That's probably more than you cared to know; long story short, noise reduction ain't easy. We're still looking for the magic bullet. Nerobro posted:I need to read mister PHd's post. So, I only have a cheapo 3-channel coax helicopter sitting in front of me, but I notice that has both a stabilizer bar and an incredibly large amount of delta-3 coupling for the upper rotor. i.e., if I flap the rotor up, the blades pitch down automatically. That makes a huge difference and will massively reduce the swashplate "advance" required, but its not at all like a "real" coax helicopter. Delta-3 is almost never combined with cyclic pitch control because it reduces responsiveness and is bad for edgewise (forward flight) perfomance--but I think it may be common on RC helos without much active stability control through gyros, since they're so squirrelly. But I admit that I haven't studied the little guys so much. vessbot posted:
You are absolutely correct! The mechanically simple solution is superior to the tiny gain in control performance you'd get from having fully de-coupled swashplates for both rotors. Tetraptous fucked around with this message at 17:51 on Mar 24, 2016 |
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Mar 24, 2016 17:02
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holocaust bloopers posted:Yep, that's what I was asking about : silencing the rotors externally for stealth purposes. Then you might enjoy this article about a low noise helicopter developed to quietly place a wiretap on top of a tall pole for the CIA during Vietnam. Not mentioned in the article, but some old timers who were around in those days tell me that Hughes' primary motivation was to get money from the government to design and test a new, higher performance 5-bladed rotor, which would eventually form the basis of the Hughes 500D. The improved lifting performance was exploited to drop RPM for this project, but there were still severe performance penalties.  This is one of the machines after it was turned over to the Army for additional testing (much of the data is public, and can be found listed under the Hughes "Quiet Helicopter Program"). Note the 5-bladed main rotor, 4-bladed "scissor" tail rotor, and huge engine muffler. The main and tail rotor designs are still in use for some of the spec. ops. H-6 "Little Bird" variants, although at full rotor RPM for performance. It's still one of the quietest helicopters ever made, and shows what you can do if noise is a priority. Tetraptous fucked around with this message at 19:27 on Mar 24, 2016 |
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Mar 24, 2016 19:21
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ehnus posted:I remember being overflown by a MD NOTAR (Explorer?) once and was amazed at how quiet it was. It didn't sound like a helicopter at all, more like a sewing machine passing overhead than anything. Yeah, the Explorer is one of the quietest helicopters that size. The tail rotor contributes to a lot of the noise in the frequency bands we hear well at closer ranges, so eliminating it does a lot for noise reduction. Unfortunately, the commercial success (or rather, lack thereof) of MD Helicopters shows that low noise alone isn't going to get you many sales. Interestingly enough, the K-1200 K-MAX is also one of the quietest helicopters of its size, both because of the lack of a tail rotor and because the intermeshing rotor configuration allows for a very low disk loading and correspondingly low rotor tip speeds. The single-place cockpit (so small, some of the instruments are mounted outside the glass!) hasn't been that attractive, and production was shut down for many years. An engineer at Kaman once told me a story of a pilot trying to find space to put his overnight bag in the small cockpit, eventually jamming it between the windscreen and the instrument panel, and then having it come loose during flight and get stuckunder the pedals--fortunately, he was able to grab it while spinning around and pin it behind his head and the seat for the rest of the very uncomfortable flight. It's a neat machine though, and fortunately military interest in the unmanned K-MAX has given them reason to restart the line after a 12 year shutdown, with the first new build helicopters coming off the line in 2017.  EDIT: Nerobro posted:That off angle cross tail is also used on the apache. And the Mi-28. 
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Mar 24, 2016 22:05
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So, the big issue is that helicopter main rotor blades have an aspect ratio of around 18, and because they are in edgewise flight the loading is pathologically unsteady. Compared to airplane wings, helicopter rotor blades flap around like wet noodles. This means that introducing significant sweep becomes an aeroelasticity nightmare. Modern helicopters do have sweep and exotic shapes in the tip region, for example look at the H-60M blades or the BERP rotor. But scimitar shaped blades are simply not feasible, even though they would be good for aerodynamics and acoustics, given infinitely rigid blades.  BERP IV
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Mar 25, 2016 02:35
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Cat Mattress posted:Does it count as exotic? The Airbus H160 has odd-looking blade tips. Yup, those are essentially the aforementioned Blue Edge blades. One of the primary purposes of that tip shape is to spread out the effect of a blade-vortex interaction over time, so as to reduce the intensity of BVI. The tip sweep also helps reduce compressability effects at high speed and has a slight amount of anhedral, which lowers the position of the tip vortices by a small amount, offering a small benefit to hover performance. There is probably also some aeroelastic tailoring, too--for instance, the twist of the H-60 rotor blade is highly non-linear, and changes dramatically at the very tip--this was cleverly designed so as to give the rotor a high overall twist in hover, where twist is helpful, but effective relieve that twist through aeroelastic tailoring in forward flight, where twist is harmful.
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Mar 25, 2016 10:18
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Nerobro posted:It IS fatigue city. That's a reason why composite blades were/are such and important thing. On big helis there's some really advanced systems for keeping track of blade integrity. Some blades are pressureized, and there's a pressure guage that you can check before each flight. (like the red/green valve stems you can get for your car tires) IIRC one the really big ones to get an active monitor of the blades they use that sytem with a radioactive slug on the indicator. If a radiation detector goes off... you land it. Now. http://www.google.com.sv/patents/US4010708 Even commercial helicopters have pretty short overhaul intervals. For instance, the Bell 206 main rotor blades have lifespans on the order of 1400-3600 hours. At a cost of around $30k per blade, and two blades per helicopter, you're spending $15-20/hr. just on main rotor blade parts costs. Add in all the other parts and salaries for your A&Ps, etc, and you're looking at a few hundred an hour on maintenance alone. That's a pretty simple helicopter too--costs pretty much just go up from there. Probably the biggest cost savings that's come with composites is in the adoption of hingeless and even bearingless rotor systems. Here's a neat 3D animation I found of the hingeless, though not bearingless, rotor system used in the AS350. Instead of having mechanical hinges that need constant inspection, lubrication, and replacement, modern helicopters have composite flexures that allow for blade motion and reduce fatigue. Moreover, lead-lag dampers (which are critical for preventing ground resonance, as seen in this classic video) have been widely replaced with single-piece elastomeric dampers on newer helicopters. The older hydraulic dampers required constant checking of fluid levels and function, and were a significant maintenance expense.
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Mar 25, 2016 10:37
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Phanatic posted:Ground resonance is a phenomenon that occurs as a result of having a fully-articulated rotor system; if you don't let your blade lead/lag, you don't need lag dampers. Great post, but a small nitpick. Soft-in-plane hingeless rotors (which almost all new hingeless rotors are) are still susceptible to ground resonance, since they do permit lead-lag motion, and they will have elastomeric damping of some sort. For example, here's a drawing showing a typical Bell type hingeless rotor (with a cloverplate or stacked yokes) highlighting the elastomeric dampers.  And here's a photo of the stacked hub of the soft-in-plane hingeless Bell 412.  You are correct about stiff-in-plane rotors, such as teetering rotors that can permit collective lead-lag but inhibit scissoring motion, and earlier "rigid" hubs like the titanium Bölkow-style hub used on the Bo-105 and descendants, shown below.  A stiff rotor like the Bo-105 has a high effective hinge offset, that allows the rotor to transfer large moments through the rotor shaft, resulting in a very maneuverable machine. (Hence, why folks like Chuck Aaron fly these things!) But, also allows for efficient transmission of vibrations from the rotating frame into the non-rotating (i.e. fuselage) frame--which is bad for ride comfort and component life. EDIT: I should credit this great site with many pictures of rotor heads. Tetraptous fucked around with this message at 20:58 on Mar 25, 2016 |
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Mar 25, 2016 20:50
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After the warm reception my previous helicopter posts received, I promised you all an effort-post about the development of the helicopter. I've been busy the last couple of weeks doing the writing about helicopters that I get paid for, but those papers are now behind me and the wife is out of town, so I figured I'd finally get around to this: The Early History of the Helicopter, Part I While I won't say there is no longer any controversy, for the most part, it is now widely recognized around the world that the Wright 1903 flyer was the first heavier-than-air powered aircraft. In developing it, the Wright brother achieved the first sustained, stable, and controllable flight of a man-carrying aircraft. By the end of this story, I want you to realize that the same sort of clarity has never been reached about who made the first "true" helicopter! Helicopter Prehistory Some of the basic principles of the helicopter rotor have been known for a very long time, perhaps even pre-dating the concept of a fixed-wing airplane, though I will not dwell on them here. To give a brief summary of the highlights, as early as 400 BCE the Chinese had invented the "bamboo dragonfly" or "Chinese flying top," a toy you may be famililar with today consisting of a wooden stick with a rotor on one end that can be rolled between the hands until it lifts off into the air. The ancient Greeks played around with similar ideas. Much later da Vinci would revisit the idea of applying an Archemedes like screw to the air in his famous (though utterly impractical) helicopter. Skipping ahead another three hundred years, Sir George Cayley, perhaps the father of the science of flight looked into rotating wings, both as a practical means to study the airdynamics of wings before airfoils, and by 1843 proposing a vertical takeoff "aerial carriage," shown here:  The First Steps From this point, up until the first successes with the airplane, a number of people experiment with model helicopters powered by steam, gunpowder, and early combustion engines. Some success is achieved, with several models making uncontrolled leaps tens of feet into the air. One of the first claimants to the development of the first helicopter is Louis Bréguet, who you may already know for developing one of the earliest successful fixed wing aircraft, the Type I, for pioneering all-metal aircraft construction, for starting the famous Bréguet Aviation company that would build some of the best aircraft in WWI for France, for the Bréguet range equation, or for founding one of the earliest French airlines that would eventually become a part of Air France. Before any of that, Bréguet, with the help of his brother Jaques and advice from physiologist and early aeronautics researcher Charles Richet, would design and contruct the man-carrying Breguet-Richet Gyroplane No. I.  The Gyroplane had four 8m diameter rotors, each with four bi-plane like rotating wings, connected through steel trusses to the "pilot's" seat in the center. That's 32 rotor blades, if you're counting! It weighed 500 kg without the "pilot," and was powered by a 40 hp Antoinette engine. I write "pilot" in scare quotes, because the poor man in the center of the machine lacked any real means of control! In September of 1907 several "flights" of the Gyroplane would be conducted, obtaining altitudes as hight as 1.5m above the ground. Photographs of these events show four assistants, one holding each of the trusses, ostensibly to hold down and stabilize the otherwise uncontrollable helicopter. However, French helicopter historian Jean Boulet claims these assistant would later confess that they were in fact lifting the machine into the air! In any case, the claim that the Gyroplane constitutes the first helicopter is dubious, at best. A contempory contender for the first helicopter is Paul Cornu, from Liseux, France. His family was engaged in the business of building bicycles and motorcycles. Clearly this was good training for a would-be aerospace engineer, much like the Wright Brothers and Glen Curtiss. Paul Cornu, like his father, was a serial inventor, inventing a temperature-controlled incubator, a steam-powered clock, several motorcycles, a new kind of rotary engine, steam powered bikes and trikes, and even a small twin-engined car. In 1903, the 50,000 franc Grand Prize of Aviation was established for the first aircraft to fly a 1km circuit in France--by 1905 this prize remained unclaimed, even though the Wright Brothers in America had long since surpassed its requirements. Cornu decided make an attempt at it with help from his brother and father. He decided to pursue a helicopter design; while this may seem crazy to us today, you must realize that at the time, while fixed-wing aircraft were having some successes, it was not at all clear that this was the easiest path to sustained and practical flight. The Cornus took a very methodical approach to developing their flying machine, building and testing a series of increasingly large and complex models. Most importantly, Cornu considered very carefully the problem of control of the helicopter, experimenting and patenting a system of vanes mounted below the rotor to deflect the airstream for control. In 1907 the Cornus would build their man-carrying helicopter. The machine had an 8-cylinder 24 hp Antoinette engine, which drove two tandem rotors through a system of belts and pulleys. Each rotor had two blades, with two vanes mounted underneath for slipsteam control. In addition, the collective pitch of the rotors could be varied individually to provide longitudinal control. The pilot sat perilously close to the engine mounted between the two rotors, with a series of levers for controlling the aircraft. The vehicle was supported on the ground with a four-wheel undercarriage.   Cornu began a series of tests of the machine in September of 1907, first unmanned and later with himself as the pilot. By December, Cornu reports success lifting off with himself at the controls. In 1908, on a gusty day, the machine is reported to lift off so violently that Cornu's brother must leap onto it to restrain it. However, there are no reports of independent witnesses stating that the machine has sustained flight. On the few occasions Cornu manages to assemble a crowd, he fails to take off. J. Gordon Leishman wrote a very nice paper on the history of this machine, which seems to be availible here (PDF). He also models the performance of Cornu's machine; his analysis suggests that even under ideal circumstances, the Cornu helicopter was probably not capable of flight. However, his machine was much closer to success than Bréguet Gyroplane No.1. Bréguet would keep at it over the next year, developing the Gyroplane No.2. Gyroplane No.2 increased power to 55 hp with an 8-cylinder Renault engine. This engine drove two rotors, again with four bi-plane like rotating wings, which were tilted forward and sandwiched between a larger set of fixed wings. Behind these was a conventional empennage for control during forward flight. The aircraft had tricycle-type landing gear.  This strange aircraft would fly sometime in July of 1908, supposedly flying several times with good controlability and reaching a height of 4.5m of the ground. What we do know for certain is that the aircraft lifted off the ground well enough to be heavily damaged on its last landing! Bréguet would rebuild this into the slightly simpler Gyroplane No.2bis. This drove two two-bladed rotors, now set between two biplane wings. Two outrigger gear were added to the aft wing, in addition to the tricycle set. This contraption was flown in April 1909--I can find no record of its performance, but do know that the aircraft was destroyed in May when a big storm wrecked Bréguet's shop.  Here's a short video of the Gyroplane No. 2bis in "action": https://www.youtube.com/watch?v=bd9kQ9IMIQc Although, Bréguet achieved some success here, the aircraft was not really capable of vertical flight and so can't really be counted as a helicopter. However, this will not be the last we hear of Bréguet! So far, I've only spoken about machines that have at least attempted to carry a man aloft, but I'll make an exception here, and talk about another contemporary of Cornu and Bréguet who developed a couple of unpiloted helicopters around this time. Igor Sikorsky was born in Kiev, Ukraine in 1889, then a part of the Russian Empire. As a young boy, he drove into every mechanical device he could lay his hands on, building small toys and even an electric motor. His parents gave up the back room of their house for him to use as a workshop. At 12 years old, Sikorsky would build a tiny rubber-band-powered counter-rotating helicopter. In 1903 he would join the Imperial Naval Academy in St. Peterberg, but spurred on by reports of early aviation pioneers like the Wrights, he would quit in 1906 to tinker at home and work on several projects, including a steam-powered motorcycle (this is becoming a bit of a theme!). In 1908 he came across a foreign newspaper article describing Wilbur Wright's demonstrations in Paris, with photographs of the new flying machine. In 1909, at age 19, his sister gave him funds to travel to Paris, where he studied the many new aircraft there and met with aviation pioneers like Bleroit. Here, Sikorsky bought a new 25 hp Anzani aircraft engine and took it home with him intent on building a helicopter. Like the rubber-band powered toy he'd built before, this machine, the Sikorsky H-1, would feature two two-bladed counter-rotating rotors.   Sikorsky would quickly realize that 25 hp was insufficient to carry the 350 hp machine aloft. He would continue working, eventually developing the H-2,using the same engine and a similar coaxial design, but with three bladed rotors, collective pitch control, and a lighter overall weight.  This helicopter would make several very short hops, but a lack of power and severe vibration would convince Sikorsky to give up on helicopters, and turn his attention to fixed-wing aircraft, with which he had much success. Oh well, it was another good attempt, but I suppose this is the last we'll hear of this guy. Another Russian helicopter pioneer working at the same time was Boris Yuriev. Yuriev was a student at the Moscow Technical Insitute under the great scientist and fluid mechanisist Nikolay Zhukovsky (Who the more mathematical among you may recognize from the Joukowsky Transformation or the Kutta-Joukowsky theory of lift). In 1909 he developed plans for a coaxial machine, like Sikorsky's, but larger and more complex with a 90 hp Gnôme rotary engine, two rotors of dissimilar diameters, and an additional propeller on a boom for directional control, and a recovery parachute in case of engine failure. The machine was to weigh nearly 700 lbs. It's not clear to me if it were ever built and I cannot find any photographs. Yuriev conducted a number of experimental studies on the drag of rotors, concluding that more power and less weight was required. He came up with a new design, which weighted only 450 lb, with a single main rotor and a tail rotor at the end of a tail boom for directional control--i.e., the modern conventional helicopter. He estimated that this design would require a 50 hp engine--however, only a 25 hp Anzani engine was availible to him through the Moscow Aero Club. Nevertheless, he commenced construction of a prototype. In 1911 he filed a patent for the swashplate, controlling the cyclic pitch of the rotor to provide control of the vehicle. The vehicle was completed in 1912--however, pitch control was absent on the final helicopter in order to save weight. The helicopter was ground tested, but Yuriev was correct in his estimation of the required power, and the vehicle never made it into the air. However, Yuriev had developed some of the key ingredients for the modern helicopter.  Next we have Jacob Ellehammer, born 1871 in Bakkebřlle, Denmark. Ellehammer apprenticed as a watchmaker, but after his apprenticeship ended moved to Copenhagen, where he would soon found his own company and invent an astounding array of devices, eventually having 411 patents to his name. Many of his inventions would involve the internal combustion engine. Now, this may come as a shock to you, but he invented a motorcycle in 1904. In 1906 he would be the first European to fly an airplane powered by an engine. By 1912, he decided to turn his attentions to the problem of the helicopter. Ellehammer devised a coaxial machine with six short blades attached to a circular hub of 20' diameter forming each rotor. The upper disc was just an open ring, but the lower disc was covered in fabric with the (dubious) intent that it could be used as a parachute to float to safety in the event of an engine failure. Of particular importance, the blades of Ellehamer's helicopter could have their pitch varied cyclically for control. In addition, the pilot could move his seat fore and aft, left and right, shifting his weight for additional control authority.  Ellehamer's helicopter was also not capable of sustained flight, but it under ground effect it could hop into the air. The above picture, in 1914, is unique in that it's the first photographic evidence of a helicopter flying aloft. Suck on that, Cornu! The Some Success, at Last WWI prompted the development of some of the first aircraft for practical application, and the helicopter was no exception. A lieutenant in the Austrian Army's observation balloon corp named Stefan von Petróczy was frustrated by the vulnerability of the hydrogen-filled balloons then in service for artillery spotting and observation. Enemy aircraft had been very successful at shooting down these balloons during the long and slow process of reeling them back down to the ground. Petróczy sought new kind of tethered vehicle that would be less visible to flying aircraft and could be quickly returned to the ground when they approached. The task was assigned to the already well-known student of Ludwig Prandlt, Theodore von Kármán, who was called up in the draft like anyone else, and engineer Wilhelm urovec. By August 1917 Kármán and urovec had succeeded in model-scale tests up to 15m and had designed a full-scale version of the helicopter, at the time called the Schraubenfesselflieger, or rotor-driven tethered aircraft. After the war, it was called the Petróczy-Kármán-urovec PKZ-1. Just like today, the boss gets top billing despite doing no actual work. The PKZ-1 was supported by 4 rotors, two on each side of the observer's seat. The rotors were powered by a massive 190 hp Austro-Daimler electric motor weighing 195 kg, but overall weight was still kept below 650 kg because power was supplied from much heavier engines on the ground through an aluminium cable, eventually intended to reach 800m in length. No control was provided on board the vehicle--instead, three tethers would be operated by men on the ground to keep the vehicle stable. In November 1917 urovec would move on to another design, leaving Kármán to oversee the remaining work.  Flight trials began March 1918. Hover tests were successful, reaching heights of 6m, but the overloaded copper windings of the motor (predictably) burned out during the forth flight. By now, urovec had made some progress on his other helicopter project, and the PKZ-1 was abandoned. urovec's other project would be called the PKZ-2, despite having little to nothing to do with either Petróczy or Kármán. urovec would later accuse Kármán of trying to claim primary credit for the machine after the war. PKZ-2 was a coaxial design with two fixed-pitch two-bladed contra-rotating rotors. It was powered by three Gnôme rotary engines of 100 hp (later upgrade to 120 hp), each mounted on an arm cantilevered out to the sides of the vehicle. The observer had a commanding view from a terrifying looking crow's nest above the rotors.  Tests with the 300 hp variant began in April 1918, with flight times of up to an hour and hovering heights of 1.2m above ground. After the engines were upgraded to a total of 360 hp, heights of 50m were obtained in May. I don't think anyone was ever fool enough to fly in the machine; as the height increased and the weight of the tethers increased, the vehicle had more trouble sustaining flight and stability became a bigger issue. urovec was unable to solve these problems before the war was over, ending this line of development. Although finally achieving sustained hover in a vehicle (at least designed) for man carrying, the PKZ series were uncontrolled and tethered to the ground--hardly qualifying as a true helicopter in most minds. Father and son team, Émile and Henry Berliner, are little known, but a very important next stop on road to the first true helicopter. Émile was born in Hanover in 1851, immigrating to Washington DC in 1870 to escape the draft during the Franco-Prussian war. He is perhaps most famous for his work in developing the gramophone. However, as early as 1907 he began work on the development of the helicopter. It is reported that he constructed a man-carrying coaxial helicopter in 1908 with John Williams, using two 36 hp engines, however the vehicle does not seem to have achieved unsupported flight. Information about this vehicle is scant, and I don't have much else to say about it. However, this endeavor did lead Berliner to pursue the development of lightweight rotary aviation engines, forming the Gyro Motor Company in 1909 and eventually developing engines producing as much as 110 hp by 1914. However, the contemporary Gnôme rotary engines proved more popular in the European market, where most aviation activity was occuring at the time, and the engine company did not survive the introduction of newer designs following WWI. More importantly, though, Berliner's experimentation with rotors on rolling carts led him to the discovery of translational lift, which reduces the power to keep a helicopter aloft as the forward (edgewise) speed increases. Émile would exploit this concept in his next attempt. In 1914, Émile's son, Henry, quits his job as an aerial photographer with the US Army and joins his father in the development of a new flying machine. After some unsuccessful experimentation with yet another coaxial machine in 1919, the Berliners switch their focus to a new kind of helicopter in the early 1920s. The Berliners took the fuselage of a Nieuport 23 biplane, removed the wings, and replaced them with outriggers supporting two two-bladed propellers. These two propellers could be tilted forward and backwards for directional control. The propellers were not mere airplane propellers, but carefully designed with aerodynamic properties suitable for edgewise flight. Below these propellers were vanes providing roll control through slipstream deflection. Lateral control was obtained through different braking of the two rotor shafts, adjusting RPM. A smaller variable-pitch propeller was mounted near the tail to provide pitch control. The conventional empennage of the Nieuport was retained, including elevator and rudder, for better control at high speed. The vehicle was powered by a 210 hp Bently engine. The Berliners would make several short flights out of the airport in College Park, Maryland. The lateral control through braking was found to work poorly in the first few attempts at hovering,  Representatives of the US military observed flights of the No.4 revision in June 1922, noting that it flew to heights of 10' at speeds of up to 15 mph for over a minute. Control of the machine was still very limited; nonetheless, the it safely performed a vertical takeoff, flew in forward flight, then landed; a world first. Does this machine qualify as the first helicopter? Maybe, but the vehicle was barely controllable and more importantly, many will argue that a true helicopter has the capability to autorotate to a safe landing in the event of an engine failure. The Berliners were clearly concerned about this too, as they looked forward to higher flying aircraft. Their solution to the problem of engine failure mid-flight was to add triplane wings back to the No.5 aircraft, making it a hybrid between a helicopter and a fixed wing plane (somewhat like the Gyroplane No. 2). The same propellers were retained in the new design. Of course, this still doesn't help during engine failure from hover!  This variant would fly for longer durations, reaching heights 15' above ground and speeds on the order of 30-40 mph. Astonishingly, the No.5 has actually survived to this day, and can be viewed at the College Park Aviation Museum, located at the College Park airport.  Émile would have a nervous breakdown in 1924, and retire from aviation pursuits, but his son Henry would continue, eventually founding the Engineering Research Corporation (ERCO). After WII ERCO would develop the Ercoupe, designed by Fred Weick, which was intended to be a safe stall-proof/spin-proof airplane fit for anyone to fly. The College Park aviation museum also has an early Ercoupe on display. On a personal note, the last time I visited, a very nice old lady working at the museum struck up a conversation with me. Turns out, she was Fred Weick's daughter, and had a lot of interesting things to say about his very successful career at NASA Langley, ERCO, Texas A&M, and Piper. I recommend visiting this little-known museum if you're ever in the DC area! Next up is the story of Étienne hmichen, a French engineer from Châlons-en-Champagne. Like many others, he was an accomplished inventor, developing the first electric stroboscope and an early high speed camera. He would work at Peugot before going off on his own to build a flying machine. His first "helicopter" was flown as early as 1920, and feature two belt driven rotors driven by a 25hp engine connected by a truss in tandem, much like Cornu's earlier design. hmichen quickly learned that his helicopter did not have nearly the power required to lift off of the ground, but he didn't let that stop him! hmichen attached a large cylindrical hydrogen balloon to the top of the vehicle, providing enough lift to get it off the ground.  Following this contraption, hmichen had developed an elaborately over-engineered quad-rotor machine called the No.2. It was powered by a yet another Gnôme rotary, outputting a much more impressive 180 hp. The general layout of the four main lifting rotors was much like Gyroplane No.1. However, eight additional small propellers oriented every which way were fitted to the craft: five thrusting vertically for stabilization, another at the nose for steering, and yet two more to push the thing into forward flight.  The No.2 would perform some brief "hops" in November of 1922. By 1923 hmichen would sustain flight for several minutes. In April of 1924, hmichen would go further, achieving the helicopter distance record of 360m. By May he would fly a 1km circuit over nearly 8 minutes of flight time. hmichen would experiment with various rotor configurations in the following decade, even returning to balloons, but never again achieving the record-breaking successes of his No. 2. Another contemporary, George de Bothezat, would construct a simpler helicopter in 1922 with his assistant Ivan Jerome. de Bothezat was born in Bessarabia to a wealthy family, received his doctorate at the Sorbonne on the topic of aircraft stability, supported flight research in the Imperial Air Force during WWI, and then fled to the US in May 1918 to escape the Bolsheviks during the Russian Civil War. de Bothezat, ever humble, would call himself "the world's greatest scientist and outstanding mathematician." Soon after arriving, he was hired by the NACA. In 1921, the US Army hired de Bothezat to construct a helicopter. de Bothezat and Jerome rapidly constructed a massive quad-copter, without doing any model scale experimentation beforehand. de Bothezat would power the helicopter with the same type of 180 hp Gnôme rotary engine used by hmichen's No.2. Each of the four main rotors would have six blades. The rotors each had collective pitch control. In addition, two small propellers were used to provide directional control. Three additional propellers were equipped above the large rotary engine simply to provide cooling airflow. The aircraft would be dubbed "the flying octopus."  In December 1922, not long after hmichen's first successful flight of the No.2, the de Bothezat helicopter would lift into the air, hovering a full 6' above the ground. The machine was remarkably stable--but essentially, uncontrollable. Any forward velocity obtained was simply due to the wind in the air! Nevertheless, over 100 flights would be made with the machine, flying for several minutes, carrying as many a four passengers and achieving heights above ground of 30'. The Army would finally give up the project in 1924, as much for the obvious impracticality of the machine as for the poor disposition of its inventor. Argentinian-born marquis Raúl Pescara would make the next major advance. Pescara would dabble unsuccessfully with several coaxial helicopter designs as early as 1919, but the real innovation would come from his Model 3 helicopter constructed in 1923 for the French. Pescara's machines had two coaxial rotors, each with six biplane like rotary wings. But what made the Model 3 unique was that cyclic and collective pitch control could be achieved through warping of the wings, introducing for the first time the practical application of modern helicopter controls. Directional control was achieved in the same way as for a modern coaxial helicopter, via different collective on the two rotors.  And here's a nice film about Pescara from 1922: https://www.youtube.com/watch?v=V0DJcKAJ4BA Pescara would attempt the distance record in September of 1923, flying nearly 1km before crashing. By May of 1924, Pescara would fly an improved version of the machine to a distance of 736m at speeds of 8 mph, handily beating the record set by hmichen just that April. Uniquely, Pescara understood and appreciated the life-saving value of autorotation, and designed his helicopters with this in mind. However, Pescara never actually flew high enough to safely conduct an unpowered descent. Pescara continued his work, developing more powerful helicopters, but with little lasting success. More to Come! Next up, we'll talk about perhaps the most important man in the practical history of the helicopter--a man who would never make a helicopter himself. In the 1930s, we start to see lightweight and powerful aviation engines come into being and systematic development of the aerodynamic theory of helicopters enabling aviation pioneers across the world to make huge leaps in the performance of these machines. In the run up to WWII, some nations invest heavily in helicopters on the back of these successes--others still set the area aside completely until the war is done. Lastly, we'll start to talk about the very first practical helicopters, having the utility necessary to warrant serial production. This post took a bit longer to put together than I anticipated, so it might be a bit until I finish the next part. Thus far it's a pretty comprehensive look at helicopter developments from 1900-1930. In fact, I know of nothing else quite like it. I would like to acknowledge some of the books in my personal collection that I leaned on in compiling this information. Principles of Helicopter Aerodynamics by J. Gordon Leishman (author of the Cornu paper mentioned above, and several others like it). This is a helicopter aerodynamics text, and a very good one at that, but Leishman is also a history nut and has composed a great outline of helicopter developments in the first chapter of his book. More than any other source, I relied on this to fit most of the above into a general progression. I skipped some developments covered in the book (and included others that are absent), so I recommend it hardily. I also relied on several papers he wrote for the History Committee of the American Helicopter Society and for AHS's Vertiflite magazine. Soviet Helicopters by John Everett-Heath is quite fascinating and provides an excellent description of early Russian helicopter development before launching into Soviet helicopter developments through the 1980s. This book first turned me on to helicopters when I found it in a library book sale back in high school. The Sikorsky Legacy by Segei Sikorsky, son of Igor Sikorsky. The book gives a brief, but unique look at some of Igor Sikorsky's early helicopter developments in Russia, which are not well sourced elsewhere. Sergei does quite a bit a public speaking about his father, and is a very approachable guy. If you ever have the opportunity to see him lecture, I recommend you take advantage of it. I also leaned on aviastar.org and Wikipedia to gain some clarity; but other than the photographs I used above, I found many conflicts with these sources when compared to other, er, more trustworthy ones! As always, please ask any questions--if I don't know the answer, I will do my best to find out. Tetraptous fucked around with this message at 16:21 on Apr 10, 2016 |
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Apr 10, 2016 06:22
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Fredrick posted:Tetraptous, please never stop. That was great! I don't have that much more information about Yuriev (Yuryev). At first, I don't think he was much known outside Russia, and in the early 1900s, maybe not even known outside Moscow. However, once the helicopter was shown to be practical in the 40s and 50s, I think Soviet historians began to write histories framing him as the father of the modern helicopter. By 1959, I can find an article in Flight magazine briefly mentioning Yuriev, but in general, he is absent from the English language history until recently. What is pretty clear is that Yuriev was frustrated with the Czarist government, who clearly had no interest in supporting aviation in Russia, and were perhaps even a little afraid of it. John Everett-Heath quotes a member of the Duma at this time stating "Before the man in the street is allowed to fly, one must teach the police how to fly." Yuriev would see the revolution through, and once the Russian Civil War settled down was quite happy with the improved support for aviation research provided by the Communists. He become an important leader in the Central Aero-Hydrodynamics Institute (TsAGI), essentially forming and running their helicopter research program, which I will get to later. Another researcher working under him, Mikhail Mil, would eventually go on to achieve a similar level of success in the USSR as Sikorsky would in the US. So here's where I start to speculate a bit: Western sources seem to indicate that Yuriev and Sikorsky had not contact; but Soviet sources claim that Sikorsky was mentored by Yuriev, and essentially stole his ideas when he fled to the US to escape the Bolesheviks. I can't actually find any substantial overlap in their biographies where they were ever in the same place in the same time, and Sikorsky had probably already set helicopters aside by the time Yuriev's major early achievements were made. Nonetheless, Sikorsky was clearly very interested in aviation, and surely would have been aware of any such developments to the helicopter happening in his own country. By the time Sikorsky would finally get back to the helicopter, so much other technical development had occurred, far surpassing Yuriev's first achievements that it's hard to attribute much of Sikorsky's success to Yuriev. I think by the 50s and 60s, the Soviets were attempting to minimize the importance of helicopter pioneers outside the Soviet Union when they first set out the write the history of this machine. Likewise, I think contemporary American writers tended to talk up the importance of Sikorsky and his VS-300, without giving fair credit to the many helicopter pioneers, mostly outside of the US, who did great things before him. By the end of this story, I hope it will be clear that the VS-300 was just one of many helicopter firsts, but not clearly the first helicopter. In any case, I think the story has started to become more complete since historians are no longer fighting the propaganda front of the Cold War. The history of early helicopter developments in Europe is much more widely acknowledged than it once was; however, English language sources for the history of aviation developments in Czarist Russia are still extremely limited, and colored heavily by the views of those who chose to leave Russia, ignoring much of those who chose or had to stay (like Yuriev). Tetraptous fucked around with this message at 16:19 on Apr 10, 2016 |
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Apr 10, 2016 16:10
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Cat Mattress posted:hmichen, or Oemichen when you can't do the fancy ligature. Thanks--it is corrected! That was the result of a poorly-planned find and replace as I went went back through trying to add the appropriate accent marks to all the European names. Tetraptous fucked around with this message at 16:19 on Apr 10, 2016 |
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Apr 10, 2016 16:13
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helno posted:What is your opinion on the safety and reliability of typical helicopters vs comparable fixed wing aircraft. Going by the statistics, helicopters are much worse! However, there's a little more to the story: when you compare kinds of operations performed by aircraft, you find that helicopters are used to perform a lot of inherently risky jobs, usually ones that fixed-wing aircraft simply can't do. The stuff a lot of "working" helicopters do, like power line maintenance, heli-logging, dropping rappelers into wildfires, EMS landings into confined or uneven terrain, servicing off-shore oil platforms, etc, is inherently dangerous. When you compare helicopters and aircraft performing the same missions to each other (where possible), like crop dusting, electronic news gathering, passenger/tourist transport, the accident rates are actually very similar. However, it's certainly true that helicopters are much more complex than fixed-wing aircraft of the same payload; to get "equivalent" safety, the helicopter requires much more maintenance, and that translates to higher costs. At any rate, I feel pretty safe flying in a well-maintained helicopter. In some ways, helicopters even have some advantages: a helicopter can safely fly and land under VFR with much lower visibility, since the pilot can fly very close to the ground and very slowly. Likewise, in the event of a power failure, while the helicopter can't autorotate as far as an airplane can fly, it doesn't need much room to land and so the pilot has many more options. helno posted:What are your thoughts on the Volocopter concept? basically a very large multirotor with many diverse and redundant fixed pitch props. I have yet to be convinced that "distributed electric propulsion" has any meaningful advantage over conventional aircraft, whether fixed or rotary wing. Addressing the Volocopter in particular, I have several concerns:
One positive merit I can think of is that the design does allow you to tailor the inflow distribution over the "disk", so there is less download from the rotors on the fuselage in hover. That could translate to a 5-10% gain in efficiency. holocaust bloopers posted:Hey Tetraptous, does the width of a rotor blade matter, or is there generally a sweet spot in terms of size? So, there's two things to consider. Disk loading, as um excuse me, mentioned, has a strong impact on the induced power required by the rotor--the bigger the disk, the more efficient the helicopter (at least in hover). The proportion of the disk which is "filled in" by blade area is called the rotor solidity. Increased solidity means my average blade lift coefficients are lower, so you have more margin available to pull thrust before stalling the rotor--you'll notice that attack helicopters tend to have a higher solidity--and ability to maintain lift in hotter and higher altitude conditions. On the other hand, higher solidity means greater profile power; although, as mentioned previously, for the same solidity, it's more profile power efficient to concentrate the blade area into fewer wider chord blades than lots of skinny blades. On the other hand, more blades mean less vibration and less mechanical wear. These days, two bladed rotor systems are out of favor for all but the smallest machines. One last thing the matters in rotor blade sizing is the inertia of the rotor system. While you always want the weight to be low, the rotor blades themselves are a bit of a special case. In order to give the pilot a lot of margin to perform a safe autorotation, you want to be able to store a lot of kinetic energy in the rotor system without overspeeding it. The pilot can use this stored energy to arrest his descent during the final flare to landing, allowing the rotor RPM to droop just before setting down. This means that the moment of inertia of the rotor system should be kept fairly high, which is most easily obtained by making the blades reasonably massive. There are several definitions of an "autorotative index," used in the design of helicopters, which usually combine the disk loading (lower is better) and the inertia (higher is better) in some way, so as to come up with a quantitative rating for autorotative performance. Anyway, I had the pleasure of learning a bit about helicopter design from Marat Tishchenko, who sadly passed last year. He was chief designer of the Mil OKB, being head of aerodynamics before that under Mil himself, and essentially led the Mi-24, V-12, and Mi-26 projects. He always said that the best aspect ratio for a rotor blade for a transport helicopter was somewhere around 16. And sure enough, if you run the numbers for just about any transport mission using any one of the helicopter sizing methods out there, something around there will spit out as optimal. Check most transport/utility helicopters in production today, and you'll find they're all around there, too. I couldn't articulate for you exactly why that's the right number, and neither could Tishchenko, but he had a fantastic intuition for what would make a good helicopter. Tetraptous fucked around with this message at 07:23 on Apr 13, 2016 |
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Apr 13, 2016 07:13
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HawkHill posted:Tetraptous, thanks for the very interesting post. Thanks! Brennan's helicopter is also very interesting--I researched him, as well as some other early helicopter pioneers, but decided to omit them in my post as the length increased. I tried to focus on people with claims to the first helicopter, those who developed key technologies that led to the modern helicopter, and some others, like Sikorsky, who are of particular historical interest. Working on Part II now, which will cover some of the major advances in helicopter technology from the late 20s and 30s. I think there will also be a separate Part III, focusing on developments around the WWII era. Tetraptous fucked around with this message at 00:16 on Apr 21, 2016 |
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Apr 21, 2016 00:13
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Enourmo posted:Man and Smarter Every Day just did a video on autorotations as a rebuttal to a Neil DeGrasse Tyson tweet. That's one you can't recover from. This is a great video; I'm convinced that the primary cause of people's objections to helicopter operations is a perceived lack of safety, mostly because they don't understand that a helicopter can make a safe landing without power. It's also wonderful to see a full auto to the ground--only a few instructors do that. The Robinson cyclic stick always seems weird to me, even in video, and it's one of only a couple helicopters I've had the chance to pilot myself. Still, a clever way to keep cost down. Frank Robinson has come closer to the dream of a true "Personal Air Vehicle" than anyone else.
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Apr 29, 2016 23:18
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Wow, that is an incredible story--almost impossible to believe they got that aircraft down safely. The first Hiller H-12 was built in 1948; Hiller still exists and has been supporting those that are still flying with new parts since that time. Amazingly, they were in talks to re-start production in China for the Chinese market as late as 2011; they still have a website up, but I don't know if there's been any progress since.
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May 2, 2016 05:35
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The better to ground loop with!
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Jun 5, 2016 22:43
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babyeatingpsychopath posted:Does the MD-500 have a rigid rotor head that would preclude the guy from getting lunched while under the rotor disc? I realize the helicopter is still 5-6' off the ground at the beginning of the clip, but at "skids in grass" level, how far down does the tip path bend during those kind of maneuvers? The 500 does have a bearingless rotor system, but it's not so stiff as to work much differently than an articulated rotor would. However, the rotor flapping is surprisingly small when the rotor is loaded (e.g. lifting the helicopter). I've done a few flight tests where we've done direct measurements of rotor flapping during maneuvers, and the change in TPP orientation relative to the shaft is typically very small (like a degree or two) for all positive load factor maneuvers where the rotor is hingeless, articulated, or even teetering. For this reason, I usually don't even try to get these measurements anymore since I can calculate the TPP orientation and angle of attack well enough for just about any helicopter with instruments in the non-rotating frame. Where you get in trouble is when the rotor becomes unloaded, for instance when in contact with the ground or during low or negative-gee maneuvers. This is usually where you'll see bad things like mast bumping, tail boom strikes, or blades flapping down and hitting people on the ground.
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Jun 30, 2016 09:17
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C.M. Kruger posted:
As an undergrad, I had a professor who, earlier in his career at Calspan, was involved in the development of the NC-141H's spiritual successor, the NF-16D VISTA. VISTA had a set of programmable flight computers which could independently actuate the various control surfaces of the aircraft. The primary use of the aircraft was to provide handling qualities feedback early on in the development of flight control systems for then-next-generation NATO combat aircraft like the F-22, the Eurofighter Typhoon, and others. The flight control computer would simulate the dynamics of the proposed aircraft plus that aircraft's own control system. As the test pilot in the front seat provided feedback on the handling qualities of the simulated aircraft, an engineer in the rear seat could actually adjust the control constants in flight for the simulated flight control system to "tune" the performance of the aircraft until the pilot was happy with the results. VISTA was used for a number of other research purposes, testing robust control techniques to handle failures of control surfaces gracefully, adaptive "learning" control systems which would discover the flight dynamics of the plane as the pilot flew it, and eventually being adapted to study thrust vectoring. Altogether, a very neat machine. 
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Aug 5, 2016 13:32
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Luneshot posted:Identification question: This helicopter with a long horizontal boom has been making straight passes every thirty minutes or so over my neighborhood for the past couple days. My best guess is that it's one of two possibilities: crop spraying (but I live in a suburban area, there are no crops around here). My other thought is some sort of radar mapping or synthetic aperture radar, and that seems more likely to me. That's definitely a spray rig; but who knows what they're doing. Probably spraying something, but I once worked on a flight test program where we modified a similar Simplex spray rig to hold sensors on the spray boom. We left the tank/pump in place since the configuration already had an approved STC and it was less work just to leave it there. We were flying over an airfield in the Bay Area and a number of people called the police with concerns ranging from terrorist chemical attack to some (not so) secret government mind control program.
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Aug 25, 2016 04:26
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Suicide Watch posted:https://www.wired.com/2016/09/air-force-stash-f-22s-us-nasa-yeah-sure-got-room/ The Wired article acts like this was an unusual request, but Langley Air Force Base has been rolling aircraft into the NASA Langley hanger for years when a big storm / hurricane is going to hit. May as well, the hanger is huge and usually just houses a handful of GA aircraft and sometimes an OV-10 or two. Years back, NASA decided to move the bulk of its flight research aircraft to Dryden (now Armstrong), which I think was a huge mistake; there's a huge, but hard to quantify, benefit for researchers to be able to crawl around the aircraft they're studying and meet face-to-face with the pilots and maintenance and operations personnel on the regular. The newest generation of aeronautical research engineers has never been in and around these aircraft, so they don't really know how they're used and what they can do. 
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Sep 9, 2016 06:37
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brains posted:i'm glad we settled with that single engine naval strike fighter with no reservations because modern engines are just so reliable these days. With two engines, it would've been twice as likely to have burnt to a crisp! Seriously, though, it was my understanding that the primary reason the F/A-18 has two engines is to reduce the inertia of the rotating sections of the engines to meet the Navy's requirements for throttle response during carrier landings, not really for OEI capability, limited as it is in a tactical fighter.
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Sep 24, 2016 22:38
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It is possible to reduce (but not eliminate) the acoustic effects of sonic booms by shaping the fuselage. NASA and DARPA had the Shaped Sonic Boom Demonstrator program a decade or so ago, which modified an F-5 with a bulbous nose.  This shaping causes the energy from the boom to be more distributed over time/space in the far field, resulting in the peaks of the typical N-wave to be rounded off--there's still a lot of low frequency energy left, but the parts of the boom that bother people are somewhat attenuated. The renewed push for SSTs relies on people convincing FAA/ICAO that modern vehicles can be designed to have low booms that will be accepted by the community, and to allow the ban on supersonic flight to be replaced with some sort of noise certification. I'm personally of the opinion that such shaping will only be marginally effective--moreover, I think that even if you can effectively reduce the perceived level of booms, people still won't accept it due to a) environmental concerns about the increased fuel burn b) worries about booms causing damage to people's health, livestock, and structures and c) the perception that these vehicles are not useful, except for the very wealthy, since the first examples will be especially expensive business jets. Even worse, though, is that the economics of these aircraft don't make a lot of sense in an era where airliners are filling every seat and flying even slower than before to save every last penny. There's an argument to be made for an SST that can travel faster than Mach 3, where fuel per pound per mile can actually get pretty low due to a high propulsive efficiency, but airliners in the Mach 1-3 range could never be cost competitive with subsonic aircraft. As for boom.aero, I think it's a ridiculous endeavor, bordering on the fraudulent. They simply don't have the resources to build, but more importantly certify, anything like the 1/2-size Concorde they've been pushing. Companies like Boeing and Airbus nearly bankrupt themselves developing new subsonic airliners and getting them to production. You can look at boom.aero's about page to see their best people; they have a couple people who know a thing or two, but nothing special compared to the rest of the traditional aerospace industry. Nothing like the advance concept divisions of the big companies, or even smaller ones like Cessna and Gulfstream. What fairy dust do they have that the rest don't? I see boom.aero, and the rest of the new generation of aerospace startups--pushing the likes of cheap SSTs, electric aircraft, and poorly conceived VTOL configurations--as bilking Silicon Valley "venture capitalists" with tech backgrounds into supplying dumb money so they can play at being Burt Rutan for a couple of years. Aerospace isn't software; it's a highly regulated industry with huge capital expenditures and necessarily long development times.
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Nov 22, 2016 07:33
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bennyfactor posted:Wait, are the pinstripes on the side of the jet literally the chart of its sonic boom performance? I've looked at pictures of that funny jet for years and just now realized it. Yes they are! The red N-wave pinstripe is the pressure time history you'll measure using a microphone for any conventional pointy nosed supersonic airplane. The black "flat top" N-wave pinstripe is what they hopes to get with the bulbous shaping--this obviously increases the wave drag, but if your choice is higher drag or not flying at all, the drag isn't so bad. They had a pretty good idea that it would work prior to the experiment, hence the fancy pinstriping. The original plan was just to fly the different F-5 variants that have different length pointy radomes--but they quickly realized that wouldn't show much of an effect, since the shaping is much more important than the length. Apparently the F-5 has an easily swapped out nose, though, so they decided to stick with that choice of airframe. Tetraptous fucked around with this message at 22:57 on Nov 22, 2016 |
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Nov 22, 2016 22:54
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I once did a flight test at Eglin off the range containing what's left of the small runway the Doolittle raid was developed on. It was cool to be there, but there's not much to see other than an X'd out runway in the middle of what Floridians call "the woods." Other than the Armaments museum and the naval air museum at Pensacola, I can't think of anything else worth seeing. If you're near the base, the French Quarter serves great Cajun food. I go there regularly, so I'm also interested in things to see if I'm missing something cool.
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Nov 23, 2016 16:14
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MrChips posted:Wow that guy is colossally stupid. Agreed. I'm intimately familiar with one specific aspect of type certification, and in that case industry is already running their own test programs to show that they meet the requirements. FAA, or any of the other civil airworthiness authorities, have the right to send engineers or pilots of their own to participate in or observe the various tests, but this right is rarely invoked, and the organizations under ICAO also generally accept each other's findings and work together to make sure that they aren't imposing redundant requirements on industry. While I can only speak to one area with certainty, it's my understanding that the other cert requirements work the same way, and government is actively participating in only a tiny sliver of the required tests, and even only observes a minority of them. In all cases, these happen on industry's schedule and on their test plans. I don't really see how a cost savings can be achieved by getting rid of what little government oversight there is while still maintaining the same requirements, unless your cost savings plan is that industry will cheat like hell. There might be a case that the requirements should be relaxed--air travel is way safer than other modes of transportation, and we pay for that--but, humans are bad at weighing the risk of low probability, high consequence events like airliner crashes and I don't think public opinion would allow for a less safe aviation industry. I also read this guy's "paper" on sonic booms, and it's very poorly researched. For one, dBA is a terrible metric to use for sonic booms, and a 90 dBA boom from a large transport would be totally unacceptable to just about everyone. Coming up with a good acceptance criteria has been very hard, and it's not clear there even is one. There are decades of research on this topic, much of it available using a quick Google search, so there's no excuse making an argument based on such faulty data. Let's not even get into the economic inplausibility of point to point travel everywhere and loving hypersonic commercial aviation anytime soon! I think the only good point he had was that the ban on foreign airlines running domestic routes is stupid--that probably true, so long as you're careful that subsidized foreign flag carriers aren't trying to run domestic routes below actual cost.
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Dec 11, 2016 00:06
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Sperglord posted:The line about hypersonic aviation was the clearest sign he has no idea about what he talks about. Sonic booms are "N-wave" events, that contain lots of low frequency energy. In general, the A-weighted sound pressure level (dBA) doesn't do a great job at reflecting what bothers people most. From my reading of the research, the perceived noise level (PNdB) is a lot more closely correlated to actual annoyance, but still lacks the contributions to annoyance of rattle and vibrations caused by the low frequency boom, especially when people are inside structures (e.g. their homes). You're also sort of right that the boom is a short-duration event, and most of these metrics are designed for longer duration--and are usually integrated over time to show a cumulative effect in a way that we're not sure works well for booms. In any case, though, 90 dBA is really loud; we generally consider something more like 65 dBA to be an acceptable level in a suburban environment, but people's annoyance is strongly related to the kind of noise it is. Someone in Iowa might accept their neighbor mowing their lawn, because they also mow their lawn, but they won't accept the boom from some rich jerk's SSBJ while he flies from NY to LA. And unlike conventional airport noise, booms affect everyone along the flight path, so there will be a lot of people in so called "flyover country" who will be affected by booms but will see little benefit to themselves. As for the overpressure of the sonic boom, it's not at all constant above Mach 1.2--in fact, it generally increases with the square of the Mach number, and will be more powerful the larger the aircraft and the higher the Mach. The overpressure will attenuate with altitude, though, so a high speed overflight might not be so bad if you're flying at SR-71 altitudes.
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Dec 11, 2016 06:17
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ApathyGifted posted:I still don't understand how open fans are more efficient. Shouldn't the fan on a traditional turbofan basically act like a ducted fan, with the associated decrease in tip losses? On a simple level, a duct essentially allows a smaller rotor to generate more static thrust for the same power by creating a low pressure area on the duct lip that augments the thrust and allows the fan to act as thought it were larger. This allows a smaller, and lighter, engine to provide the same takeoff thrust as a larger and heavier unducted fan. The duct also provides additional benefits for blade containment, noise abatement, and engine packaging. However, this thrust augmentation is offset by skin friction drag, both inside the duct, but also outside the duct when in cruise. Moreover, during cruise the thrust required is lower and less of a pressure reduction is achieved on the duct lip during forward flight than in a static condition, reducing the benefit of ducting. At cruise speeds, the duct causes a reduction in performance due to the additional drag and reduced thrust augmentation, especially when compared to an open rotor of the same total diameter or weight. Since most of the flight is spent in cruise, power reductions here are much more important for fuel economy than during takeoff. Of course, the engines are sized for takeoff, and you still have to carry all that weight around in flight. In addition to the extra mass flow, one other benefit a coaxial open rotor sees that a coaxial helicopter doesn't really is swirl loss recovery--in a ducted fan, this is partially accomplished using stators. One of the biggest barriers to open rotors is noise. Acoustic liners install in the fan ducts are remarkably effective at knocking out the fan tones generated in the duct. Open rotors don't have these liners, and for aerodynamic and structural reasons, they have fewer blades and spin at lower RPM, which results in a lower frequency noise that is harder to block with the fuselage, is more likely vibrate the airframe causing acoustic re-radiation from panels in the fuselage, and is potentially more annoying to the passengers. The airframers get interested in open rotors every time fuel prices soar, but once Jet A is cheap again, the development work stops.
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Jan 2, 2017 21:44
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BIG HEADLINE posted:Somehow I have to think that was just some random Ahmed's 'hobby project.' Now I'm imagining some Syrian dentist arguing with the Islamic State Aviation Administration's inspector: "You show me in the Quran where is says this isn't an acceptable way to drain a static pressure line!"
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Jan 20, 2017 14:42
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