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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 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.
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.
Its because they use their legs.
My Aurora : http://www.youtube.com/watch?v=o91ZsGwJYyg
FB : https://www.facebook.com/TanveersPhotography
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.
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.
...all four hooves are off the ground at once!
I've got pictures to prove it!
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.
if they just make the wings on the side a LITTLE bigger.
"He's a real midnight golfer"
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 airflow over it would be reversed, or 'backwards', because the trailing edge of the airfoil would be the 'leading edge'.
All helicopters experience some mu, the point about mu-1 is that the entire retreating blade is subject to non-positive airspeed, and thus provides non-positive lift. In this case, rather than speeding up to mu-1, what they did was attain a velocity where the 'winglets' were providing sufficient lift to keept the craft airborne, and then carefully slowed the rotors to speed required for mu-1. Agreed it's a bit of a 'cheat', but i think it's a very impressive aircraft nontheless.
I would have to imagine that it would be possible to create a non-hybrid helicopter that could exceed mu-1 by rapidly changing the shape of the airfoil (not just the angle of attack, which is done now) as it rotates. This would require some pretty advanced materials to put up with the stress, but i don't see why it is 'impossible'.
So many airspeed questions...
but is it an european or an african helicopter ?
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.
See http://www.bris.ac.uk/researchreview/2003/11138152 75 for more info.
Karma: Chameleon - mostly influenced by bad '80s New Wave music
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