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Carter Copter Breaks Mu-1 Barrier 368

tyler_larson writes "Just over a week ago, Jay Carter's CarterCopter managed to break a significant rotorcraft barrier, traveling at a mu ratio of 1. This 1-to-1 ratio (sometimes called the mu-1 barrier) represents a condition where the forward speed of the craft is the same as the speed of the tip of the rotor. This means that at a certain point, the tip of the retreating blade is "standing still" relative to the wind and producing no lift, while the rest of the blade is actually moving backwards through the air. Such a condition is normally impossible for a rotorcraft, and so the forward speed of a helicopter is limited by the the speed of the rotors. This accomplishment by the CarterCopter, which some insisted couldn't be done, proves that this new craft is not subject to that limitation."
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Carter Copter Breaks Mu-1 Barrier

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  • So... (Score:5, Funny)

    by Arghdee ( 813921 ) * on Tuesday June 28, 2005 @06:21AM (#12929793)
    The whole thing is moving forward while parts of it are moving backward or standing still at the same time?

    Sounds suspiciously like a certain operating system :D
  • by Anonymous Coward on Tuesday June 28, 2005 @06:22AM (#12929797)
    Q: How fast can a helicoptor travel?
    A: Mu []
    • Q: How fast can a helicoptor travel? A: An African Helicopter or a European Helicopter?
    • Re:Riddle me this (Score:2, Informative)

      by Foolomon ( 855512 ) is a tad incorrect. The correct Chinese (Mandarin) is "mei you" (pronounced "may yo" with the "y" at the end of the first word hanging a bit).

      Literally, it translates to "don't have."

      The equivalent in Cantonese (which, until the 1949 Revolution was the official language) is "m'o" where the "m" is overpronounced a bit. This may be the version that escaped into Japan, but I doubt it since the Japanese assimilated Chinese many centuries ago when, I imagine, China was still a collection of feudal p
  • Heli-plane? (Score:5, Interesting)

    by Anonymous Coward on Tuesday June 28, 2005 @06:29AM (#12929818)
    Hmmm, it looks lie it blurs the line between a helicopter and an airplane. That thing has pretty darn large wings. I guess the big deal is really having the rotors not "get in the way" traveling at that speed, since the wings really are providing most if not all the lift? What happened to those experimental copters that you could actually just shut down the rotors and have them be fixed during forward flight?
    • V22 Osprey? (Score:2, Informative)

      What happened to those experimental copters that you could actually just shut down the rotors and have them be fixed during forward flight?

      Hmm... are you referring to the V22 Osprey []?

      • Sikorsky X-Wing (Score:5, Informative)

        by Savage-Rabbit ( 308260 ) on Tuesday June 28, 2005 @07:08AM (#12929945)
        Hmm... are you referring to the V22 Osprey?

        From the sound of it he is referring to the Sikorsky X-Wing [] The idea was to build a conventional helicopter that had rotors who generated lift no matter how they were oriented by using compressed air that was bled over the rotor surfaces to create lift. I am no aerodynamicist but I think this concept is called a boundary layer control system (like blown flaps). The X-Wing would thus be able to take off like a Helo but could fix the rotors in place and have them act like conventional wings for high speed flight. The X-Wing was abandoned in favor of the V-22 which is a more elegant if troubled [] solution. I rather liked the X-Wing though it was the closest engineers ever got to creating a real world AirWolf [].
        • Looking at pictures of both i find "more elegant" to be a bit of a stretch. Where the Sikorsky looks semi-nice, the V22 looks positively ugly.

          Just my opinion :-)
    • Re:Heli-plane? (Score:5, Informative)

      by Anonymous Coward on Tuesday June 28, 2005 @06:47AM (#12929872)
      From the FAQ;

      How can the CarterCopter fly so fast and efficiently? Shouldn't the rotor slow it down?

      The CarterCopter is a hybrid between an airplane and a rotorcraft. A rotor is a very efficient device for providing lift at low speeds, but its drag increases rapidly as the aircraft goes faster if it must continue to support the aircraft. In the CarterCopter, as the aircraft speeds up and the wings begin producing more of the lift, the rotor produces less lift and can slow down given the correct control input. The reduction of rotor lift and lower rpm significantly decrease the rotor drag (in fact, a three fold reduction in rpm results in approximately a 27 fold reduction in rotational drag- drag required to just spin the rotor). The rotor drag at very low rpms and low lift basically becomes a function of its area (which is relatively small compared to an airplane wing of similar gross weight) and the forward speed of the aircraft.

      Wings are very efficient at high speed, but can't provide enough lift as the aircraft slows down. In most aircraft, the wings are sized significantly larger than they need to be in cruise flight so that the pilot can fly slower for landing. Most airplanes also have some type of high lift device, such as flaps, which further decrease the minimum flight speed of the aircraft, but add weight and complexity to the wing. The CarterCopter has a very simple wing, sized much smaller than a conventional aircraft of similar size, because the wing only needs to support the aircraft at high speeds.
    • Actually it is what is called a compound helicopter. But the Carter Copter isn't a helicopter at all. It is an autogyro. It can not hover and can only take vertically using a hope method. They power up the rotor on the ground and use the stored energy like a flywheel to jump straight up.
      While this is pretty cool this test flight was at a speed that current helicopters can reach. It is still an interesting R&D project. I will be interested in how things shake out. There claim of a 500 mph cruse has yet t
  • mu and swimmers (Score:2, Interesting)

    by BigMike ( 122378 )
    I was actually surprised to hear about the mu limitation concept. Swimmers for examle might actually swim faster than their handspeed through the water - an efficient swimmer miht actually take his and out of the water at a point AHEAD of where the same hand entered the water.
    • Re:mu and swimmers (Score:5, Insightful)

      by tanveer1979 ( 530624 ) on Tuesday June 28, 2005 @06:41AM (#12929855) Homepage Journal
      Its because they use their legs.
      • In other news: Ice Yacht's often go faster then the actual windspeed.
      • Not necessarily. If you push back highly effectively for the first part of the stroke then the latter part of the stroke (with the hand folded) can be highly inefficient - even negative.

        So, it's because the hands aren't paddlewheels - they have variable profile in aeronautics terms.

      • I seem to remember hearing that very little power is generated by the legs, with the exception of when they are used in conjunction with the rest of the body in a dolphin kick style. That's (one reason) why you don't see short stocky swimmers; because wingspan is much more important. Kicking is basically just used to keep the lower half of the body aloft.
        • That really depends on the stroke. Breastroke is a whole lot of kick, alas its also a slow stroke then the crawl. But kicking does provide a reasonable amount of power, otherwise you'd never get anywhere with a kickboard.

          As for the dolplin kick, its really one of the weakest kicks out there, and one of the hardest. Its use with the butterfly has more to do with the execution of the stroke than anything else, no other kick would really work since timing is so key to doing the butterfly.
          • Re:mu and swimmers (Score:3, Informative)

            by Peyna ( 14792 )
            As a former swimmer myself, I can tell you that a dolphin kick is much faster through the water than a standard kick. This is why a few years ago the rules were changed to allow a dolphin kick underwater off of the start and off of the wall on turns for all except breaststroke.

            If you watch the olympics you will see they almost all use a dolphin kick off the start and wall. This isn't because they want to go slower.
    • You can do the same thing while swimming really slow; it's called "floating".
    • Depending on the stroke this is no big accomplishment. First, as a sibling post points out, swimmers also use their legs (and most of their body, especially for a butterfly stroke). Second, their is the distinct possibility of a pause at the end of the stroke, especially in swimmers going for efficiency rather than speed (gliding). This isn't breaking the mu limitation, but rather about using more of your body. I think the mu limitation only applies to (in choppers) vehicles with no other means of propu
      • Re:mu and swimmers (Score:3, Informative)

        by petecarlson ( 457202 )
        mu is not about propulsion but rather about lift on the retreating blade side. The whole discussion about swiming has nothing to do with the reality of the topic.

    • Re:mu and swimmers (Score:4, Interesting)

      by Fringex ( 711655 ) on Tuesday June 28, 2005 @09:41AM (#12930717)
      Swimmer here.

      This doesn't really apply as one poaster pointed out that simply gliding through the water will allow you to have your hand exit where it entered. Infact you can have it exit beyond where it entered with simple glide. The problem is you slow down.

      Hard to say if it the slow down is avoidable but I am sure through some testing you can find out. Depends what application you are putting it in. Sprinting will never be the case since that is a mroe chaotic means of racing but distance swimmers might have more luck with this.

      As for kicking it does supply power, more than you would like to think. If kicking supplied next to no power you wouldn't see swimmers kicking as often as they do. A slight kick keeps your feet aloft. Rapid kicking actgually gives you fair forward propulsion.

      The best example I can give you is to try and find the video of Jeff Rouse in the 1996 Olympics. At the flip turn his dolphin kick alone allowed him to increase is lead by over a body length and a half if I remember correctly. He was the last one to surface but increased his lead massively.

      Kicking alone can be impressive especially underwater. In texas they had a rule that you had to surface before the second set of flags. I watched a couple guys from a competing team nearly get DQ'd because of them kicking 3/4's the length of the pool. They also won mind you.
  • For the purposes of this, do they measure air speed or ground speed? If it's really one of those things considered to be "impossible", could it just have been a heavy head wind?
    • They mesure airspead. Groundspead is totally irrelivant.
      • They mesure airspead. Groundspead is totally irrelivant.

        Yup. Groundspeed is only relevant to the persons inside the aircraft who are in a hurry to get from point A to point B in some amount of time. To the aircraft itself, any aircraft, the only speed it knows about is airspeed. By definition, mu is a ratio based purely on airspeed.

        BTW, I've seen the CarterCopter up close and personal once... even got to touch it, but they wouldn't let me sit inside for a photo :-/. It's quite an amazing machine.
  • they cheated (Score:5, Insightful)

    by Anonymous Coward on Tuesday June 28, 2005 @06:33AM (#12929833)
    I fly radio controlled helicopters all the time and worked for Bell for quite some time. Although this is a great accomplishment, it doesn't really break the mu-1 barrier because it is a hybrid between a helicopter and an fixed wing airplane. This is like saying "fixed wing aircraft don't need a runway" when the harrier came out. Regardless, mu-1 will always be here for the purists.
    • by Anonymous Coward on Tuesday June 28, 2005 @06:41AM (#12929861)
      the carter copter cannot hover and it is relying on a prop on the back to provide the thrust needed for forward flight. what they have achieved is limiting the flutter associated with the approach of mu = .75. So yes, the parent is right, this is no better than a harrier with a rotor instead of motorized engine exhausts.
      • by Council ( 514577 ) <[rmunroe] [at] []> on Tuesday June 28, 2005 @06:47AM (#12929874) Homepage
        what they have achieved is limiting the flutter associated with the approach of mu = .75
        Yeah. From TFA:
        the CarterCopter, which some insisted couldn't be done, proves that this new craft is not subject to that limitation."

        So they're not saying "this breaks the helicopter record" so much as "these new copter thingies are really cool."
        • Yeah. Or to word it differently:

          Look! This thing that is not a helicopter is not subject to the limitations of helicopters!

          Next they're going to tell me that these newfangled horseless carriages can do things my bicycle can't.
          • The CarterCopter never claimed to be a helicopter... only a rotorcraft. (Gyroplanes and helicopters are both types of "rotorcraft"... FAA's definition) The CarterCopter folks only wanted to be the first "rotorcraft" to break 1.0 mu. Still, it's pretty neat what they've accomplished with their applied engineering and they've acually built and flown their machine unlike many other hyped up experimental flying machine concepts such as Moller's Skycar.
  • by rossdee ( 243626 ) on Tuesday June 28, 2005 @06:40AM (#12929854)
    They cheated! It has wings.

    One other way of dealing with the asymetric lift in high speed rotorcraft is to use 2 contra rotating rotors, for example the russian Kamov helicopters.
    • by CvD ( 94050 ) * on Tuesday June 28, 2005 @07:17AM (#12929984) Homepage Journal
      I'm curious: how does it work in regular helicopters anyways? The left side will always have more lift than the right side during forward flight (assuming clockwise rotation). How is this compensated for? I would imagine it slanting/leaning to one side if it wasn't compensated.
      • by MadCow42 ( 243108 ) on Tuesday June 28, 2005 @07:40AM (#12930074) Homepage
        The angle of attack of one blade is different than the other... on advance the angle/lift is lowered, and on retreat is is increased. So, the lift generated is the same although the relative wind speeds are different.

        This means that the blade angle is adjusted continually as the blade rotates - that's the main reason why you see such a complicated coupling at the hub of a helicopter blade.

      • by lauwersw ( 727284 ) on Tuesday June 28, 2005 @07:44AM (#12930092)
        As far as I know there are some tilting mechanisms built in to the rotor, so that each time the rotor goes backwards, it is tilted a bit more, giving it more lift. At the side going forwards, the tilt is lowered. When you balance this carefully, you should get equal lift at both sides. Complex but it works, still causing lots of shaking. That's why copters need much more maintenance than planes.
      • Full explanation... (Score:5, Informative)

        by Gadgetfreak ( 97865 ) on Tuesday June 28, 2005 @12:37PM (#12932643)
        I'm a MechE who did an internship at Sikorsky 3 years ago. They had an "Intro to rotorcraft" pamphlet which was rather enlightening.

        What gets me the most is that fundamentally, it's an unstable flying machine. But each corrective measure yeilds a slightly lesser instability, which requires further adjustments.

        Yes, each blade changes pitch during rotation. Advancing blade flattens out, while the retreating blade increases pitch. This keeps the copter level.

        To generate more or less lift for altitude adjustment, there is a "collective" pitch increase or decrease in addition to the cyclic pitch adjustment.

        But what I didn't understand overall was that the rotor blades do not rotate in a flat plane. They rotate in a wide "cone" whose central axis indicates the overall main rotor force vector. By changing the shape of the cone, you change the direction of the force. This is done by "flapping" each rotor blade, like a bird wing, with respect to the central hub. So, for a helicopter moving forward, a given rotor blade will swing up on the back half of it's rotation, and drop back down for the forward half of the cone. The inclined angle allows the blade's aerodynamic lift to provide a forward component of thrust. This "cone" is adjusted for whichever direction the pilot whishes to move.

        The tail rotor, as most people know, provides the counter rotating force from the main rotor. But it also provides a sideways thrust, so without correction, the entire helicopter would drift sideways. So to correct for this, the main rotor blades always flap slightly on one side to counteract this effect and keep the helicopter stationary.

        Rotor blades not only change pitch and flap, but they also lead and lag freely. The angle between blades as viewed from above is not always equal. The main reason is that not only do you have stall speed problems on the retreating blade, but you've got shock wave problems on the advancing blade.

        It's all a tricky balancing act.
    • If it matters, the wings provide only a trivial amount of lift at low airspeeds. Most of the lift is provided by the rotor (which is unpowered, making it quite different than a helicopter).
  • Wait, what? (Score:3, Interesting)

    by Council ( 514577 ) <[rmunroe] [at] []> on Tuesday June 28, 2005 @06:41AM (#12929858) Homepage
    This means that at a certain point, the tip of the retreating blade is "standing still" relative to the wind and producing no lift, while the rest of the blade is actually moving backwards through the air.

    The site is dashslotted so I can't see any diagrams, but I'm having trouble picturing this. "the tip of the retreating blade is 'standing still'" made sense, but how on earth would the rest of the blade be "actually moving backward through the air"? The retreating tip stands still, but then the rest of the blade can only be moving more forward than that.

    What am I missing?
    • Re:Wait, what? (Score:2, Informative)

      by tom17 ( 659054 )
      Terminology, there are 2 versions of "backwards" here... One is backwards for the helicopter, the other is backwards for the blade itself.

      In normal flight, the retreating blade is going backwards when its going forwards (hence retreating)

      So with this, the tip is still and the rotor is still travelling forwards with the helicopter, but backwards relative to itself and its aerofoil.
      • the rotor is still travelling forwards with the helicopter, but backwards relative to itself and its aerofoil.

        Wait, I'm still confused.

        What does "travelling backwards relative to itself" mean? And okay, backwards relative to the airfoil makes sense, but isn't that what it's doing anyway, always, on that side? Why would they say "the tip is standing still and other parts are moving backward" if they're talking about relative to the airfoil? The tip must also be moving backward relative to the airfoil.

    • Re:Wait, what? (Score:5, Informative)

      by armb ( 5151 ) on Tuesday June 28, 2005 @06:54AM (#12929899) Homepage
      It's backwards in that air is flowing from what would normally be the back edge of the airfoil section. It's the retreating blade so the back of the wing is towards the front of the aircraft - so moving forwards overall means moving backwards compared to its usual direction through the air.
      The diagrams worked for me just now.
    • I think that they phrased things poorly. I think what the poster meant was:

      1: The airspeed of the blade increases as you get closer to the blade tip and further away from the rotor hub.

      2: The tip of the blade has a 0 airspeed ( is "standing still" relative to the wind).

      3: Given 1 and 2, the rest of the blade must have a negative airspeed. Or, maybe a better way of saying it is that the trailing edge of the blade is actually meeting the air, not the leading edge. From the way they worded what they

      • Isn't this somewhat like the speed of light 'barrier'? Flying at mu-1 is a problem, but flying beyond mu-1 shouldn't be, right?

        Why not just fly really high, then drop like a stone and slowly level out. Then reverse the angle of the retreating blade, instead of increasing the angle, and you'll start getting lift on both sides of the rotor. The faster you go, the more lift on the retreating blade, and the difference in lift can be compensated for just like now. The blades need only be comstructed symmetricall

        • Well, there are a few other considerations, too. One of the things that limits pure helicopters to a maximum forward airspeed these days of around 200-250 knots is the tip speed on the advancing (not retreating) blade or blades.

          Remember that, just as the airspeed of the retreating blade tip is slower than that of the airframe, the airspeed of the advancing blade is faster than that of the airframe. In addition to the asymmetric lift problems of approaching mu-1, you also have a problem with transsonic a

    • Re:Wait, what? (Score:3, Interesting)

      by jcims ( 316827 )
      They aren't saying that the rest of the rotor is going backwards relative to the velocity of the aircraft. They are saying that the airflow over the rotor wing itself is reversed, because the forward velocity of the aircraft is greater than the retreating velocity of the blade itself.

      To illustrate it by an extreme example: If you just stopped the rotors completely at a position where they are perpindicular to the flight path, the wing on the 'retreating' side would be going forwards (of course), but the
  • by Gopal.V ( 532678 ) on Tuesday June 28, 2005 @06:49AM (#12929880) Homepage Journal
    I think the point is that the wing goes around . So the forward velocity varies depending on what angle the rotor is at that point. It also should be remembered that the wing tips move both ways (forward and backward). The whole point of that being - it will hop from side to side when it touches mu-1 (no, I am not a physics professor). These guys have been near mu-1 for about ~20 seconds.

    Also I think the mu-1 ratio has always dealt with the fact that most modern helicopters deal with rigid wings and the lift generated is from around 3/4th distance from the central point. I don't know if that's going to hold for the future (just like moore's law when quantum computers come... sheesh ).

    Insult me if I'm wrong. And TFA is slashdotted already . Can't more people use greasemonkey cacher [] ?.
  • by Monte ( 48723 ) on Tuesday June 28, 2005 @07:01AM (#12929925)
    ...all four hooves are off the ground at once!

    I've got pictures to prove it!
  • Helicopters (Score:3, Interesting)

    by mac123 ( 25118 ) on Tuesday June 28, 2005 @07:05AM (#12929935)
    I've heard a (traditional airplane) pilot who took a few helicopter lessons refer to it as "ten thousand components doing their best to come apart".
    • Re:Helicopters (Score:3, Interesting)

      by Linker3000 ( 626634 )
      I worked for a defence contractor in the UK involved in helicopter work. We had an engine specialist on site from one of the major helicopter manufacturers and he stated that he would never fly in a helicopter because it was too much of a risk!
    • a lot of fixed wing pilots aren't fans of Helicopters. My ground school instructor insisted Helicopters couldn't actualy fly, but they were so ugly the ground repelled them.

  • I've traveled twice in an ex-Soviet military helicopter. The second time, only because the alternative if I wanted to get back was even worse.
    I understand these are pretty reliable as helicopters go. And twice was enough to last me the rest of my life. So my reaction to this achievement is, perhaps unadventurously, Dangerous, ludicrously expensive and environmentally unfriendly form of travel made even more excitingly dangerous,ludicrously expensive and environmentally unfriendly. Wow.
  • Owned by Fanwing [] for quite some time now.
  • if they just make the wings on the side a LITTLE bigger.

  • by tomhudson ( 43916 ) <`barbara.hudson' ...'> on Tuesday June 28, 2005 @07:42AM (#12930080) Journal
    Okay, there's a rotational speed where the blade is standing still relative to the airflow for part of the cycle, but if you INCREASE the rotational speed beyond that point, the blade is moving faster than the airflow even on the "return", so it is again providing lift. Plus, the blade is only exactly perpendicular to the airflow only at two points.
    Mu, Mu,
    In the air,
    Was never a barrier,
    So I don't care.
    burma Shave
    Try a thought experiment with a blade with a tip velocity of 100 kph.
    Now give the craft a forward velocity of 100 kph.
    Sure, now the blade on the return side is stagnant (unmoving) relative to the airflow, but only at exactly 1 point. At all other angles, its not.
    Now, to get rid of even that one point, increase the tip rotational speed to 200 kph

    The blade is now providing lift even at that point because it is still moving at 100 kph relative to the local airflow.

    • Of course, you can (we just need materials that will allow it) also just tilt the blade so the leading edge becomes the trailing edge on the return (back) trip. Or put the whole thing in a thin, circular mini-duct the thickness of the blades, so the forward airflow doesn't come into consideration.

      You'd still need some other way to provide forward propulsion, though, but you'd get lift okay with any rotational speed you cared to design for.

    • 1) the rest of the blade is moving backward through the air (relative to the blade not the vehicle). See other responses to similar statements above.

      2) Increasing the blade speed is only possible until its air speed = mach 1 and then things shake apart. Lots of helicopters can go over 100MPH, it's getting to 350MPH (mach 0.5) that's a problem. You have forward motion of 350mph and with a "stationary" blade tip on one side you get 700MPH blade tip on the other side. Then you're done.

      Even fixed wing airc

      • there have been supersonic propellers developed that have a speed over their entire surface that's supersonic [] - not just the tips.

        In this paper a propeller having all sections operating at supersonic speeds is designated a supersonic propeller regardless of flight speed.

        And this was back in 1953!

        Also, as I pointed out, the tip is only stationary when it is exactly perpendicular to the airflow - otherwise, there is also a "sideways" component. Plus, there's no reason (and some research has been done on

  • Unfortunately, this doesnt help me with my helicopter flying ability in battlefield 2: I still keep doing the same thing:

    "Hey, you guys in my copter, I'm pretty sure this thing can break the mu-1 barrier! See, check it...."

    For some reason, I get a ton of "You have Teamkilled some guys" messages, then a little later, I'm back at the server browser. I think Battlefield 2 is dumping me whenever I get close to the mu-1 barrier.

    Next time, I think I'll try the apache...
  • But.... (Score:5, Funny)

    by Professeur Shadoko ( 230027 ) on Tuesday June 28, 2005 @08:13AM (#12930191)
    So many airspeed questions...
    but is it an european or an african helicopter ?
  • was said to be impossible too, but it happened...somehow [].
  • Impossible? (Score:2, Interesting)

    by Chris Snook ( 872473 )
    It used to be considered impossible to sail a boat upwind, too. The world of fluid dynamics is full of weird cheats, so the word "impossible" really shouldn't be used in describing yet-unacheived feats in the field.
  • I suspect the wings on that "helicopter" provided the lift during "mu-1" flight instead of the rotors.
  • "It's not that helicopters actually fly. It's just that they're so ugly, the earth naturally repels them."

    -- Any jet jockey

    Instead of defeating the Mu-barrier (retreating blade stall), it would impress me more if they could overcome compression effects when the forward-moving blade gets close to the speed of sound.
  • Page is down for me, but for those curious there are more funny things you won't believe they can fly [] (German text, but some pics). I saw one of these 2 weeks ago, looks _very_ strange how they fly. The top rotor is not driven by an engine, only the rotor on the rear. The top rotor is then rotated by the wind, giving lift to the aircraft.
  • by ztkl40a ( 577654 ) on Tuesday June 28, 2005 @11:09AM (#12931638) Homepage

    I'm one of the engineers for Carter Aviation Technologies. I'm also the webmaster. I've been reading through a bunch of the comments above, and thought that I'd just comment on a few of them. I know I'm not keeping all of the threads together, and that this post is rather long, but I have a lot of work to do today, and don't have time to keep track of a lot of threads. This will be my only post. If you want to specifically ask me anything, my e-mail address is

    The significance of mu-1 is that it allows you to slow down the rotor blade to reduce rotational drag, and keep the advancing blade from going so fast as to get into compressibility effects (close to the speed of sound). This lets you fly a whole lot faster on less power. The reason we don't just stop the blades is explained in our FAQ. But basically, keeping the rotor spinning gives you centrifugal force to help support the blade. If you stop the rotor, it becomes a wing, and then needs all of the same structural requirements of a wing, which adds a lot of weight. For high speed subsonic flight, the added weight more than offsets the drag savings.

    The CarterCopter was only a technology demonstrator, meant to prove the high speed portion of the flight. For that regime, we plan for the rotor to be in autorotation, so we designed our prototype as a gyroplane. We figured, why add all the extra components to our demonstrator when hovering flight with a rotor is already a well understood concept? Future production versions probably will have true helicopter capabilities, but the rotor will still be in autorotation at high speed. That's not to say that a gyroplane isn't practical. Most uses of helicopters are for their vertical takeoff and landing ability, not their hovering. Only specialized missions, like search and rescue, require hover. As was demonstrated back in the 30's and 40's, autogyros are capable of "jump" takeoffs by prerotating the rotor prior to takeoff, and can easily perform zero roll landings.

    When we say that the retreating blade has reverse flow, we are looking at it from the frame of reference of the rotor blade. With no forward speed, air flows over the rotor blade from leading edge to trailing edge. As you start moving forward, inboard portions of the retreating blade see airflow from trailing edge to leading edge. At mu-1, all airflow inboard of the tip is from trailing edge to leading edge, which makes the blade unstable. So we've devised and demonstrated a way to keep the blade stable with total "reverse" flow on the retreating blade.

    I saw someone mention world speed records of helicopters. The thing to remember is that speed records aren't always set by efficient machines, which is what we're trying to accomplish. The official record was the British Westland Lynx, at 249 mph. The unofficial highest speed I've heard of is a heavily modified Bell Huey. It was so inefficient that it could only fly at high speed for about 15 minutes before running out of fuel. It's top speed was somewhere around 315 mph. But, what we've accomplished is efficient high speed flight. We think that future versions (jet powered) will be able to fly at 300-400 mph.

    Finally, regarding the website, I apologize for the site going down this morning. We were not expecting to be on /. and get a lot of traffic. A couple months ago, we were on 60 Minutes, and the producers told us to expect millions of hits. I did a lot of work, temporarily moving the site to a different server, and we got jack sh_t for traffic. Now, all of a sudden, we get on /. and I get caught with my pants down. But what're ya gonna do?

"The only way I can lose this election is if I'm caught in bed with a dead girl or a live boy." -- Louisiana governor Edwin Edwards