I wonder what this test proves? That you can tie a helicopter down, put it on full power and disintegrate it? WTF!?
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They do this all the time in the automotive industry. You put the motor in the dynamometer, run the engine until it breaks, then you re-engineer the part so it doesn’t break, rinse and repeat. After you do that for a couple of years you have an engine that lasts a good long time.
Cool. Mythbusters would love to test this thing!
Although GregA may be right, i think that this is a demonstration to show how important it is to keep helicopter blades perfectly balanced. Even something as small as a lawnmower or a CD drive on your computer with an uneven spinning part will eventually break itself to pieces.
2,
they aint done that in ALONG time for car engines..
I believe this was one of the old style Shnooks (sp?), made by in the Vietnam war era. I’m sure this footage is part of the propaganda campaign to get them all replaced with newer, more expensive troop carriers. Like the Ospry. Yeah… this old workhouse finally fell to pieces after decades of faithful service, and slipshod maintenance (at least at the very end it was). This just proves that you break something if you really, really, REALLY try to break it. Gee, it failed to pull up the concrete it was tethered to! I wonder if they loosened up any body bolts and rivits, just before testing? They would never subject a new prototype to this kind of abusive testing, Your tax dollars at work alright. Proving to Congress that they were right to order an all new fleet of aircraft, rather than improve a little on these babies. And make some new ones. Why does every new war toy have to be radial departure from its predescessor? Don’t they ever hit a sweet spot in aircraft design?
It’s called a ground harmonics test. LIkely, this aircraft was a fatigue test article that already had a full lifetime’s worth of abuse in the fatigue test rig. The airframe’s lifespan was already maxed out and would never fly again anyway. This is a test to determine where the aircraft would fail at max stress levels. Afterward, the aircraft would be examined to determine what failed first. This is a drastic test that cost very little and does not “waste” aircraft. It makes all others that safer by letting airframe inspectors know what to look for in active duty aircraft.
#4
When you said
“Although GregA may be right”
I think I heard several people scream.
Mark 7 is probably right to an extent.
My guess is that it’s an old helo being used to experiment with “ground effects”, where basically the downwash from the blade hits the ground and bounces back up, hitting the blade and starting to cause uneven lift, eventually unbalancing the whole system. It is still a fairly poorly understood phenomenon, but it has brought down many helos in low hover, and was the main cause for most of the accidents with the V-22 Osprey.
Basically it is like having the helo blade fly through mini air-pockets over and over and over, increasing the oscillation with every pass.
@#5 ECA
I beg to disagree. I worked for BMW for nearly 10years and happen to know that they still do this as part of their development process. Not only do they run the engines at redline for hundreds of hours but they also have a full dyno rig that actually simulates every corner and bump of the NĂĽrburgring and tests the whole drivetrain not just the motor.
Actually, it looks to me like a form of Ground Resonance test.
Tom
It looks like a character in the Wallace and Grommit series!!
I was just surprised that it didn’t “fly apart” more than it did, especially the rotor-blades.
Is this one of the piston-engine helicopters?
Tom, you are right. I used the wrong term. It’s called a “ground resonance” test, not “ground harmonics”. I meant the same thing, though. It has to do with the resonance that the pulses of downdrafts from the blades react with the ground and the aircraft. It can end up with a feedback loop that does nasty things. Here is another view of the same test:
http://tinyurl.com/2gbrpt
As for the V-22, the issue that caused the big crash that killed a load of Marines was a pilot that exceeded all prescribed flight parameters and descended far too fast. The aircraft entered what is called “vortex ring state” and it is not related to ground resonance. I have heard of no problems with ground resonance with the V-22. The early V-22 crash where the aircraft flipped over was due to a mechanic that incorrectly wired up the flight control computer. Some people thought it was ground resonance but that was false.
Basically, all rotorcraft can enter vortex ring state. It is when the rotorcraft descends faster than the air it is pushing down with the rotor. At that point, the rotor stalls. It is just that the peculiarities of VRS with the V-22 were not fully explored. Pilots are trained to stay out of it and there are procedures to get out of it if it inadvertently occurs.
If the pilot had not exceeded the flight envelope then the crash would never have happened. At the rate he was descending, VRS occurred so quickly and violently that either there was not enough time to react or the pilot did nothing and screwed the pooch.
Mike, this is the Boeing Vertol CH-47, a twin turbine aircraft. No piston engines on that puppy. Actually, I can’t think of a single piston engine rotorcraft currently in use by the U.S. military. They’re all turbo-shafts.
I think a video of a 777 test can help explain why these types of events/tests happen.
Ok, I retrack my prior paranoid rant. There could be such a fatique test. Though unless they’re planning to keep this model in production, I can’t see the purpose of it. Is this old test footage that we’re only now seeing,
from when its ground harmonics was unknown?
As for the V-22 Osprey. I’m not an aerodynamics expert. But having the rotors out on the wings, instead of inline with the fuselage, struck me as inherently NUTS! The inline rotor config, like that of the CH47 Chinook,
proved a two rotor system was stable. But the V22’s right angle to fuselage config is scarely unstable at liftoff and touchdown. And I believe they’re trying to overcome too much lateral instability that’s inherent in that design. It would take a great detail of coordinated rotor speed and pitch control by a computer system to compensate. It will never be done manually. The problem is then, making gyro devices responsive enough to detect the wing waggle. But they’re a lot of mass to stablize for, and it’s not that simple. Plus the idea of rotating a massive engine 90 degrees, while its spining at high speeds. Rather than only tilting rotor blades a few degrees, also strikes me as NUTS!
The gyroscopic stress on the main engine parts must be enormous. Anything that big and power doesn’t want to be flipped over. And ignoring the laws of physics and motion, and just brute forcing it over, just transfer the stress to some other part of the system. I’m surprised the engine mounts don’t rip the wings apart. I think the V22 will be a very long time in development, trying to design out all these problems.
But then, I’m not an aerodynamics expert. What the hell do I know!
Glenn E.
Like virtually all new aircraft, the computers are in control. Flying the V-22 without computers would be difficult but not impossible. Mainly, the transition is the tough part. The computers handle everything, however, and makes it very simple to fly (there isn’t even a collective stick since the computers handle it everything).
This doesn’t make the V-22 flawed. Heck, the F-16 CANNOT be flown without computers. You don’t think it is “nuts”, do you? If you lose the computers on the F-16, it will tumble in less than three seconds. The F-22 and F-35 are equally unstable without computers. The VTOL version of the F-35 would be virtually unflyable without them. Currently, the Harrier VTOL is the most difficult to fly and dangerous aircraft ever fielded because it is all flown by “seat of the pants”. The F-35 will achieve the same feat effortlessly. Even the Space Shuttle has seven flight control computers. It, too, would be a disaster waiting to happen without them.
As for the engines flying off the wing, not likely. Gyroscopic effects are all accounted for. The engineering is sound and proven.
It may seem nuts to you but I am sure that people thought the Wright Brothers were nuts, too. It all has to do with vision, identifying obstacles, and using technology and engineering to make it once nutty ideas into commonplace everyday realities.
As for the development of the V-22, yes, it continues, just like development continues on all aircraft currently in production. There is nothing in the V-22 that has not or cannot be overcome. As a matter of fact, the V-22’s are combat ready and are going to Iraq in the fall. Soon, they will be combat proven. It is truly an amazing tool and even greater engineering achievement. It is revolutionary.
#14 – Hey Mark, that was the same test only shot from the right profile. The aircraft fell to pieces exactly the same way and same time (smoke and all) as in the Dvorak blog. It looked to me as if the rear gear box burned out its bearings from too much rotor waggle. And when it seized up, it ripped free of it mountings and torn free, taking the rear cowling and rotor blades with it. I’m not familar with the internal design. But I’d guess that the engine is back there too, and the foward rotor is connect to it by a drive shaft that runs along the ceiling. The front bearings didn’t seize up because it’s designed to take more movement. That’s why the V22 lilting rotor/engine design scares me. Can it be strengthed to take rates of tilt fast enough to make VTOL manuevers in combat situations? I quess it can going dead slow. But that tends to leave the crew a “sitting” (or hovering) target, waiting for the engines to precess within safe rate specs.
Man, you guys are thick. Quite obviously it was a helicopter that was illegally parked and got the ‘clamp’, and the pilot decided that instead of having the clamp removed he was going to try and fly off with the clamps still in place.
Its a warning to illegal helicopter piloits that the the days of willy-nilly helicopter parking are over!
ha! #19 nailed it 🙂
but very interesting to watch.
I just wonder how valuable the results were. It obviously died form resonance which is much different when tied down hard to a low hover scenario. Well, maybe the rear gearbox went because of overtorque.. who knows.
Just proves my point: helicopters can’t fly, they’re too ugly. They just have chosen to ignore the fact and go ahead anyway… most of them…
pj
Ya let’s run our harmonics tests while actually in the air, because you know us heli pilots looove doing that.
Read a little W.J. Wagtendonk “Principles of helicopter flight” it gives a good explanation. Multiple things may cause ground resonance.
I guess you guys in the states have an excess of military personell now do you. Getting shot at isn’t enough? You want them to die testing helicopters as well.
#6- Shnooks?
Chinooks.
#21: I think you took that just a tad too serious…
pj
I figured that some of our intelligent, well-read readers would know what this test was all about. Good info guys.
#1 & #6 got it right.
This is one of a reliability, stress, or MTBF test. The remains will be examined to determine what failed, why it failed, and what were the consequences of the failure. That information will be used to predict other potential failures in aircraft still flying, inspection techniques and criteria, inspection scheduling, and design information for refurbishing and for next generation aircraft. A cable is visible leading from the nose which most likely carries several sensor’s information.
If this was a vortex test then they would have used smoke streamers to demonstrate air flow. At the start of the video, all goes well. A few seconds in there appears to be a vibration beginning; something broke in the rear transmission.
It shows what happens if we let the terrorists get access to ropes and cables.
#27, Elwood,
That was my other explanation.
Glenn E. – I stated that it was the same test from a different angle in post 14. I thought people might like to see the side view.
The engines are in the two pods on either side of the rear cowling. Yes, the two engines power both rotors through a series of gearboxes and driveshafts, one of which runs the length of the cabin. As for seized bearings, I don’t know where you are getting that.
I don’t see any signs of anything seizing. The smoke could just be just a sign of a flame out as the test administrators tried to perform an engine shutdown which allowed unspent fuel to puff out the back of the nacelles. That’s just speculation, though.
As for the V-22: “Can it be strengthed to take rates of tilt fast enough to make VTOL manuevers in combat situations?” – It was designed to do this from day one with 12 second conversions from helo to airplane modes. There is no need to further strengthen it. Not unless you want to do barrel rolls at fifty feet from a hovering position or something crazy like that. Exactly what combat maneuvers do you expect it to do, anyway? If you want infinite maneuverability and acceleration then I guess we need to go get the guys at Area 51 and ask them to build our next VTOL troop carriers out of old flying saucers. As racers say, “Speed costs money. How fast do you wanna go?”
Sagrilarus – The V-22 does not have rotor blades like a conventional helicopter which normally have a constant cross-section from hub to tip. The V-22 blades have a progressive cross-section so that the section near the hub has more “bite” and pushes air at near constant rates down the entire blade length despite the changes in radius and subsequent reduced relative velocity. The V-22 rotor blade is much more efficient than you give it credit for. It creates gobs of airflow over the entire blade length, not just at the tip. See the following picture:
http://op-for.com/v-22.jpg
As for the transition from helo mode to airplane mode, it takes less than 12 seconds. From a hover, it can out accelerate any rotorcraft around to 100 knots and that is just where the helo poops out and the V-22 starts really moving. So maybe a helicopter can jink better than the v-22, I guess. Personally, I just want to exit the danger zone as quickly as possible. Speed is the key to both surprise and survivability. It is about minimizing exposure to threats, not dodging bullets once the bad guys wake up and grab their guns.
Finally, the V-22 can carry troops twice as far and twice as fast as the old helicopters it will replace. The V-22 can carry 24 battle ready troops 250 nm at 225 knots and then return to base without refueling. That is flatly impossible in a CH-46 or CH-47. What more do you want? Do you want a VTOL C-130? If so, Bell-Boeing is doing preliminary work on the QTR right now:
http://tinyurl.com/yu2l4k
#22: the QTR:
huh, a staggered tandem propeller… good fun with the thrust interference in forward mode. Bit like a push/pull really, which is always interesting because the rear prop will generally work in the propstream of his front buddy. It will therefore work with a generally higher airspeed, thus steeper blades. Now tilt that to create horizontal life…. good fun.
It looks like they’re staggered, but if they’re not staggered by more than one prop diameter, the rear one will still see some very difficult terrain there…
Looks like a fun concept to watch out for. Loads of aerodynamic challenges.
pj
this was a ground resonance test but its NOT cause by pockets of are.. the blades are at flate pitch in this test.. it can happen to any helicopter (usualy one with wheels) an oscellation starts and is small but if it hits just the right frequency this can happen. the way to get out of it is to lift off the ground for a seccond and then set it back down. the aircraft HAS to be touching the ground for this to happen.