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Carter Copter Breaks Mu-1 Barrier
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."
Hmm... are you referring to the V22 Osprey?
The owls are not what they seem
http://www.mirrordot.com/stories/bf0f11195820e13dd 7a4abf6e87b3b74/index.html mirror
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.
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.
If a rotor on a moving craft moves quickly enough that the tip-speed is equal to the speed of the craft, then the tip of the rotor will stand still, relative to the surrounding air on its way backwards.
But all other parts of the rotor move *slower* than the tip, so no part of the rotor will move backwards relative to the surrounding air. That's just bullshit.
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.
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.
rant
The tip of the rotor stays still in the air. The rest of the rotor is swinging toward the rear of the aircraft more slowly than the tip, and therefore moving forward in the air.
However, it is _facing_ backward, as this is the retreating blade of the rotor we're talking about. The air therefore pushes against the _trailing_ edge of the rotor blade (except at the tip, which experiences an eerie calm). In a regular helicopter, the air only ever pushes against the _leading_ edge of the blade.
Thus, the blade moves backward relative to the surrounding air, though it is still travelling in the direction that is forwards for the helicopter.
Now, wash your mouth out with soap. You could have just said 'I don't understand' rather than making with the rudeness and attitude. WTF is up with American public schools??
Whence? Hence. Whither? Thither.
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.
Only to idiots, are orders laws.
-- Henning von Tresckow
Quidquid latine dictum sit, altum videtur
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.
MadCow.
I used to have a sig, but I set it free and it never came back.
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.
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.
We are talking about Relative motion here.
You and the blurb are wrong, the grandparent is right. There are three frames of reference here, the helicopter, the air, and the wingtip.
From the helicopter's reference, the blade is spinning around a fixed point, so that at one extreme the edge of the blade is traveling forwards at speed x, and at one extreme is traveling backwards at speed -x. The air is rushing towards the helicopter at speed -x.
Now, from the air's reference, the helicopter is moving forwards at speed x. The point the blade is spinning around is also moving at speed x, so at one extreme the speed of the blade tip relative to the air is x + -x = 0, and at the other it is x + x = 2x.
Now, lastly, from the tips perspective. It sees itself as stationary, the helicopter as rotating around it with a speed of -x, and air meeting it with a speed between 0 (at one extreme) and 2x (at the other extreme).
If the helicopter were standing still, then the blade would always see the air coming towards it at x. On the other hand, if the blade were standing still and helicopter moving, then the blade would see the wind coming towards it at speed x at one extreme, and speed -x (from behind) at the other extreme. In other words, it is only when the rotor speed goes _below_ the airspeed that air starts rushing over the rotor in the "wrong direction".
So the different conditions are:
Rotor speed > Air speed: Tips sometimes flow backwards compared to the air, sometime forwards. Tips always see air flow from in front.
Rotor speed = Air speed: Tips sometimes stand still compared to the air, the rest of the time go forwards. Tips see air coming from in front, expect at the extreme where the air is not moving relative to them.
Rotor speed Air speed: Tips are always moving foward compared to the air. The tips see that air as coming alternatively from in front, and behind.
They mesure airspead. Groundspead is totally irrelivant.
:-/. It's quite an amazing machine.
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
When you think of a helicopter travelling at a normal speed, you'd correctly think that the blades are always slicing 'into' the wind, which is why helicoptors produce so much lift (and why they can hover).
Okay, now imagine the rotor is going really slow. Like 1 revolution per second. Now imagine the helicopter is travelling really fast. On the right hand side of the plane, the blade will still always slice into the wind. But on the left hand side (as the blade retreats), the blade is going slow, but the copter is going fast, so it's airflow is actually backwards over the blade. The airflow is still going from the helicopter's front to its tail, but the blade is facing the wrong way, and if you don't 'flip' the rotor, it will not provide any lift (helicopters flip the blade, autogyros, which is what the CarterCopter is, doesn't). This is mu > 1. And if you imagine a slow rotor/fast copter scenario, you can see why this has never been achieved before.
At mu = 1, it's just at the point between the two scenarios - where the speed of the tip of the rotor is 0 mph (reference to the ground, not the aircraft). So while the inner chord of the blade is going more slowly in the backwards direction, this menas they're going faster in the positive direction. Couple that with the fact they're facing backwards, and indeed the blade is actually moving backwards through the air
Catb.org 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 provinces replete with a smorgasboard of dialects.
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The 1965 ringtail compound helicopter
Now, if the rotor really is unpowered, the damned things not capable of vertical takeoff anyway, its not really a helicopter, and so can't break any helicopter records anyway.
My other car is a Popemobile
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.
What?
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.
CP
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 jrlewis_at_wf.net.
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?
No, it may look like an autogyro, but it's not. Autogyros and Autogiros have unpowered rotors, however, the CarterCopter has a fully powered rotor.
That was the turning point of my life--I went from negative zero to positive zero.
"The correct Chinese (Mandarin) is "mei you" (pronounced "may yo" with the "y" at the end of the first word hanging a bit)."
That is actually a tad incorrect too. In Mandarin
mei you doesn't only translate to "don't have" it can also mean "without" there is a small difference.
Mu is more likely to be a distortion of the Chinese "Wu" e.g. "Wu Suo Wei" = doesn't matter.
And the Taoist "Wu Wei" - No action / action without action.
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.
"No fair, you changed the outcome by measuring it!" - Professor Hubert J. Farnsworth
The difference is, the Hokum has two counter rotating main roters, so while one is stalling on the left, the other is generating lift, and the same on the right.
. gif
This also prevents the Hokum from falling out of the sky when the blade tips become super sonic which also causes the blade to lose lift.
This is why the Hokum has such a high top speed, not because of brute force, but because of good design.
http://www.inetres.com/gp/military/ar/rotor/Ka-50
You forgot to mention that it crashed on a subsequent flight and sustained considerable damage.
Basically, to land using autorotation, the pilot uses his controls to angel the rotor blades such that he is not trying to have the rotor produce lift, but allows the airflow from the helicopter's downward fall to keep the rotor blade spinning at high speed.
At the proper distance from the ground, the pilot adjusts the controls so that the rotor starts to produce lift and slows its spinning - transfering the kenetic energy of its spinning motion into lift.
The timing of this has to be correct - if the pilot applies lift to soon, the verticle descent will be slowed, but the velocity of the rotor's spinning motion will diminish to the point where no lift is being produced while the helicopter is still in the air - meaning the chopper will start accelerating downward again with no real way to recover. If the pilot waits to long, the verticle descent of the helicopter cannot be slowed down in time and the helicopter will plow into the ground.
Understanding is a three edged sword. - Ambassador Kosh Naranek, Babylon 5