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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."
The whole thing is moving forward while parts of it are moving backward or standing still at the same time?
:D
Sounds suspiciously like a certain operating system
Q: How fast can a helicoptor travel?
A: Mu
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?
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.
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.
Hmm... are you referring to the V22 Osprey?
The owls are not what they seem
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.
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?
xkcd.com - a webcomic of mathematics, love, and language.
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.
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 ?.Quidquid latine dictum sit, altum videtur
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.
We are talking about Relative motion here. Imagine me running west for an hour. Ideally I have run about 10 kms in that hour - but from the perspective of someone stationary in orbit (I mean someone stationary with respect to earth's gravity centre) - you have moved around 800 kms (depending on where the observer is, calculate tangents and multiply by cosine of your lattitude to get correct answer).
Anyway, the fact here is that - the relative velocity of the tip of the wing with respect to the air around it is Zero. Zero air speed over the wing == zero lift and down comes the copter.But the speed of the wing parts nearer to axle is lesser - but since this is the retreating part of the wing - it does go forward with reference to the air speed (ie it's air speed is positive). Since we always assumed that the air speed of the retreating wing is always negative (ie it moves backwards) , this essentially puts extra stresses on the wing planes.
Ah !!Quidquid latine dictum sit, altum videtur
...all four hooves are off the ground at once!
I've got pictures to prove it!
I'm not sure if this means that if you walk the street slowly twirling a pen then you would be breaking the mu barrier too - but try it, you might get famous ;)
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".
Knights do not say mu. Kittens say mu.
"Oh drat these computers, they're so naughty and so complex, I could pinch them." --Marvin the Martian
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
Q. Does a cow have a buddha nature?
A. Mu.
Aide-toi, le Ciel t'aidera - Jeanne D'Arc.
Quidquid latine dictum sit, altum videtur
if they just make the wings on the side a LITTLE bigger.
"He's a real midnight golfer"
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.
So many airspeed questions...
but is it an european or an african helicopter ?
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
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.
There's no failure quite as dissatisfying as a complete and total solution to the wrong problem.
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
"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.
Don't see what the big deal is. As I recall, Airwolf could do that all the way back in 1985.
Kittens say mu.
Especially Greek kittens.
"I'm not impatient. I just hate waiting." - My Dad
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?
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
You forgot to mention that it crashed on a subsequent flight and sustained considerable damage.