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Carter Copter Breaks Mu-1 Barrier
Posted by
timothy
on Tue Jun 28, 2005 05:18 AM
from the thwop-thwop-thwop-chunk-chunk-chunk dept.
from the thwop-thwop-thwop-chunk-chunk-chunk dept.
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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So... (Score:5, Funny)
Sounds suspiciously like a certain operating system
Re:So... (Score:5, Funny)
Parent
Re:So... (Score:3, Funny)
And some parts shake. That's what it's all about! [teach-nology.com]
OT: Whenever I hear mu... I think of (Score:3, Informative)
MU [wikipedia.org] - the only answer to Have you stopped beating your wife yet ?. And the cairo 1992 promises [byte.com] (notice the date and the first paragraph).
Riddle me this (Score:5, Funny)
A: Mu [catb.org]
Re:Riddle me this (Score:3, Funny)
Heli-plane? (Score:5, Interesting)
V22 Osprey? (Score:2, Informative)
Hmm... are you referring to the V22 Osprey [navy.mil]?
Sikorsky X-Wing (Score:5, Informative)
From the sound of it he is referring to the Sikorsky X-Wing [wikipedia.org] 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 [g2mil.com] solution. I rather liked the X-Wing though it was the closest engineers ever got to creating a real world AirWolf [nostalgiacentral.com].
Parent
Re:Heli-plane? (Score:5, Informative)
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.
Parent
Re:Heli-plane? (Score:3, Informative)
mu and swimmers (Score:2, Interesting)
Re:mu and swimmers (Score:5, Insightful)
Parent
Re:mu and swimmers (Score:3, Informative)
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.
Re:mu and swimmers (Score:4, Interesting)
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.
Parent
Re:mu and swimmers (Score:3, Informative)
CP
Measuring speed? (Score:2)
Re:Measuring speed? (Score:2)
Absolutely correct. (Score:3, Informative)
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
they cheated (Score:5, Insightful)
Further explaination... (Score:5, Informative)
Parent
Re:Further explaination... (Score:4, Insightful)
Parent
Its a bird, its a plane, its a helicopter... (Score:5, Insightful)
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.
Re:Its a bird, its a plane, its a helicopter... (Score:5, Interesting)
Parent
Re:Its a bird, its a plane, its a helicopter... (Score:5, Informative)
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.
Parent
Re:Its a bird, its a plane, its a helicopter... (Score:3, Interesting)
Re:Its a bird, its a plane, its a helicopter... (Score:5, Informative)
Parent
Full explanation... (Score:5, Informative)
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.
Parent
Wait, what? (Score:3, Interesting)
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)
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.
Re:Wait, what? (Score:5, Informative)
The diagrams worked for me just now.
Parent
Re:Wait, what? (Score:3, Insightful)
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
Re:Wait, what? (Score:3, Interesting)
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
Tip of the wing ... not the entire wing ! (Score:3, Insightful)
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 [uni-magdeburg.de] ?.And at a certain point in it's flight.... (Score:4, Funny)
I've got pictures to prove it!
Helicopters (Score:3, Interesting)
Re:Helicopters (Score:3, Interesting)
I bet they can get the rotor speed to 0 (Score:3, Funny)
How is this such a big deal? (Score:3, Informative)
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.
But.... (Score:5, Funny)
but is it an european or an african helicopter ?
Post from Carter Engineer (Score:4, Informative)
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?
Re:oh.. (Score:2, Informative)
Re:oh.. (Score:3, Funny)
Re:oh.. (Score:3, Funny)
Especially Greek kittens.
Allow me to explain (Score:5, Informative)
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??
Parent
Point of reference of movement.... (Score:3)
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
Re:Geometry lesson (Score:3, Informative)
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 pla
Re:Why did the cat fall off the roof? (Score:3, Funny)
Q. Does a cow have a buddha nature?
A. Mu.
Re:That's not that impressive (Score:4, Interesting)
See http://www.bris.ac.uk/researchreview/2003/11138152 75 [bris.ac.uk] for more info.
Parent
Re:That's not that impressive (Score:3, Interesting)
And yes, those blades have a LOT of inertia. I expect that they're probably one of the easiest helos even now to do a full auto on. If you look back at one of my previous posts [slashdot.org], I used to be an AH-64 crew chief lo these many years ago. They taught us a little bit about the areodynamics in school, but they really didn't