Why helicopters fly by themselves..
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Why helicopters fly by themselves..
I recalled this story when there was a debate in a FW forum about the story of the helicopter that took of by itself and I mentioned that it was fully plausible with a governor equipped heli where the collective lock was off or malfuntioning. It was in a Swedish flying magazine in the early 90's and is sobering reading.
Here was my response in the FW forum:
I might just as an aside mention that the reason the collective/blades go up is due to safety. If the collective pitch rod, horn or nut should fail, you want the blades to default to max alfa/lift. Yes the helicopter will climb at max until it can climb no more (density altitude), but at least it won't crash. And you could in an emergency reduce rpm to get down, perhaps.
There's a harrowing story about this very scenario in the north of Sweden (snow, mountains, forests - think Alaska) some years ago.
The pilot is doing inspection in a small Hughes 300C (two place, and the premier training heli before the R22 came along) and with him is a non-pilot. They're in the mountains. It's freezing. The pitch nut fails and the blades defaults to high alfa and the heli starts to climb. But not very much as the density altitude is pretty high. Now, the pilot has two options: Wait until it runs out of gas and fall like a brick (no autorotaion possible) to certain death, or try to reduce rpm to get down. But due to the density altitude the blades are close to stall already and the cyclic controls are sloppy up high and reducing rotor rpm could risk stalling the rotor completely and make control impossible with no recovery possible.
Now mountains are approaching and they're running out of time. The pilot instructs the passenger (who had some experience riding in heli's) to step out on the skid and try to pull down on the pitch horn manually. On the Hughes 300 you can just about reach the rotor hub if you hang out through the door. It's freezing, slippery and dangerous and he can't do it with a glove. Imagine sticking your fingers up into a rotor hub and try to pull down on a metal horn with your bare fingers in minus 30 degrees! After many failed attempts they manage to be able to somewhat control the height, with the pilot doing finger commands - "UP!", "DOWN!".
They finally managed to land the heli and walked away from it, but I think the passenger froze his fingers off and had to get some removed. True harrowing story.
Here was my response in the FW forum:
I might just as an aside mention that the reason the collective/blades go up is due to safety. If the collective pitch rod, horn or nut should fail, you want the blades to default to max alfa/lift. Yes the helicopter will climb at max until it can climb no more (density altitude), but at least it won't crash. And you could in an emergency reduce rpm to get down, perhaps.
There's a harrowing story about this very scenario in the north of Sweden (snow, mountains, forests - think Alaska) some years ago.
The pilot is doing inspection in a small Hughes 300C (two place, and the premier training heli before the R22 came along) and with him is a non-pilot. They're in the mountains. It's freezing. The pitch nut fails and the blades defaults to high alfa and the heli starts to climb. But not very much as the density altitude is pretty high. Now, the pilot has two options: Wait until it runs out of gas and fall like a brick (no autorotaion possible) to certain death, or try to reduce rpm to get down. But due to the density altitude the blades are close to stall already and the cyclic controls are sloppy up high and reducing rotor rpm could risk stalling the rotor completely and make control impossible with no recovery possible.
Now mountains are approaching and they're running out of time. The pilot instructs the passenger (who had some experience riding in heli's) to step out on the skid and try to pull down on the pitch horn manually. On the Hughes 300 you can just about reach the rotor hub if you hang out through the door. It's freezing, slippery and dangerous and he can't do it with a glove. Imagine sticking your fingers up into a rotor hub and try to pull down on a metal horn with your bare fingers in minus 30 degrees! After many failed attempts they manage to be able to somewhat control the height, with the pilot doing finger commands - "UP!", "DOWN!".
They finally managed to land the heli and walked away from it, but I think the passenger froze his fingers off and had to get some removed. True harrowing story.
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Harrowing indeed.
I read a similar story which I believe happened in the states but this involved a Bell 47 or something similar, only here they inserted a swissarmy knife IIRC and regained control.
I read a similar story which I believe happened in the states but this involved a Bell 47 or something similar, only here they inserted a swissarmy knife IIRC and regained control.
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If the collective pitch rod, horn or nut should fail, you want the blades to default to max alfa/lift. Yes the helicopter will climb at max until it can climb no more (density altitude), but at least it won't crash. And you could in an emergency reduce rpm to get down, perhaps.
I know of a Bell 412 which was almost new, flying offshore, that lost all "communication" between the pilots collective and the pitch change links, it was due to a failed bolt on the swashplate scissor, the 4 rotor blades went where the aerodynamic loads and the elstomeric bearings took them to, and it wasn't to "max alfa/lift", it was just close to flat pitch, the pilot flew close to the water with cyclic, lowered RPM's using thottle and ditched, everyone got out and when the boat came to pick up the Bell 412 it hit it and it sunk it.
Then we had the crash between two Bell 206's one of them went underneath the other and ripped the skids off the top one, in the process it completely broke both pitch change rods, the blades simply "defaulted" to something like "flat pitch", and the helicopter oscilated and sunk into trees, it's occupants survived.
I had also heard the story you mentioned, but I think it had take place in a Bell 47 or Hiller, and they used a swiss knife to stick it where the bolt used to be.
In aviation we sometimes hear apochryphal stories that sound amazing. Skeptical me, I don't take them as fact unless it's a first-person report. In the case of one of these tales, we may be in luck.
To wit: Go HERE
EDIT: Ahh, since we can't post links to the Spot of blogs, do a search for a blog called "Tailspin Tales," and look for the post entitled "Saved By A Leatherman Pocket Tool," (December, 2008). You can read all about it.
In the event of a break in the control linkage, having the pitch of the main rotor go to "full" would not be a good thing in either a piston or turbine-powered helicopter.
To wit: Go HERE
EDIT: Ahh, since we can't post links to the Spot of blogs, do a search for a blog called "Tailspin Tales," and look for the post entitled "Saved By A Leatherman Pocket Tool," (December, 2008). You can read all about it.
In the event of a break in the control linkage, having the pitch of the main rotor go to "full" would not be a good thing in either a piston or turbine-powered helicopter.
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They might not go to full alfa, but at least have a positive pitch.
I swear I read this in a Swedish magazine, however, that could have been fabricated or second hand of course.
I swear I read this in a Swedish magazine, however, that could have been fabricated or second hand of course.
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There are three control rods to the swash on a 300, they move collectively down for positive pitch. There is a mechanical mixer at the front of the trans housing that enables all 3 rods to move with the collective. If you were to grab ONE at the swash you would be making a cyclic input, but without the 1.5-2 foot lever arm of the cyclic or collective handle you would need to be Heman to get it to budge!
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I can report with unhappy certainty that at least the MD500D (I used to fly), but very probably all other helicopters, have a very short flying life left when any part of the rotating flight control system is no longer connected. This happened to the aforemetioned MD500D, due to a jammed and sheared swashplate, and the flight lasted only seconds more. There are just too many forces at work for aerodynamic trailing of the blade itself to keep it doing anything useful. There is certainly no "back up system" to assure this....
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I don't think I would like to count on any of them flying themselves, but I vaguely remember the one mentioned, I thought it was a Hiller. 12e.
I have paid particular attention to this area of the flight control systems ever since - way back when I had about 400 hours or less - i had landed for fuel, in a hurry. Looked up at the swash plate and lo, there in the fore &aft position on the swash plate was the bolt, with no nut and already about 1/2 inch out.
I don't remember much from the next few minutes, except I just shut down and had a coffee from the stock camp cook who was close by. Then I drove back to the station and fossicked around for a nut, bolt and split pins from the heilcopter spare bits, returned and got flying again. The head stockman was dirty because I had left him in a bad posi with uncontrolled cattle, but me I was still very pale for sometime. That night I rang the ginger beer. who came down the next day.
I don't know whether it it was because of that or about the same time for other reasons there was an AD specifying certain hardness of all of those control bolts.
Since then I always paid a lot of attention also on all machine flight tests to having the blades set up so well that when one was flying one could take the hand off the collective at any time and it should stay there, also making sure that the blades were not liable to flick up or down because they were swept just a teensy bit forward. The up or down forces always come from aft or forward cyclic inputs or wind gusts imitating that.
Some robbie heads were very difficult to get into line, but I have never tried these stunts with articulated heads.
Another one of the reasons why one doesn't fly too far away from the firma terror.
I have paid particular attention to this area of the flight control systems ever since - way back when I had about 400 hours or less - i had landed for fuel, in a hurry. Looked up at the swash plate and lo, there in the fore &aft position on the swash plate was the bolt, with no nut and already about 1/2 inch out.
I don't remember much from the next few minutes, except I just shut down and had a coffee from the stock camp cook who was close by. Then I drove back to the station and fossicked around for a nut, bolt and split pins from the heilcopter spare bits, returned and got flying again. The head stockman was dirty because I had left him in a bad posi with uncontrolled cattle, but me I was still very pale for sometime. That night I rang the ginger beer. who came down the next day.
I don't know whether it it was because of that or about the same time for other reasons there was an AD specifying certain hardness of all of those control bolts.
Since then I always paid a lot of attention also on all machine flight tests to having the blades set up so well that when one was flying one could take the hand off the collective at any time and it should stay there, also making sure that the blades were not liable to flick up or down because they were swept just a teensy bit forward. The up or down forces always come from aft or forward cyclic inputs or wind gusts imitating that.
Some robbie heads were very difficult to get into line, but I have never tried these stunts with articulated heads.
Another one of the reasons why one doesn't fly too far away from the firma terror.
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Though I have never flown one, I think the Hiller 12E was something of an exception, in that the blades were conected to a fly bar with gyroscopic and aerodynamic properties. Perhaps there could have been a tolerance for a flight control to swashplate/fly bar control loss, but I very much doubt that a flybar to blade control loss would not result in immediate loss of control.
Though blades generally do have their feather axis pivot point forward of their center of lift, there are many other factors which would prevent a blade from seeking its own trailing pitch position based upon aerodynamic forces alone.
Though blades generally do have their feather axis pivot point forward of their center of lift, there are many other factors which would prevent a blade from seeking its own trailing pitch position based upon aerodynamic forces alone.
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tet from the kite
We must swap Hiller stories some time!
Mine broke bolts, and it tore bolts out of the tailboom too at the universal joint bearing. It sheared its alternator drives and fried its ludicrous nicad battery.
And it did try to fly itself: straight down.
I never did work out why it would suddenly go into a giant negative G bunt. Not once. Several times. I even wrote to Ray Prouty about this. He could not help me. I wrote to CASA. My boss sacked me for that.
But about a year ago, on this very forum, one of the participating engineers (eric ferret?), suggested a brinnelled bearing.
And I am sure that that was the answer. pilot moves the collective down: nothing happens: pilot moves the collective down further: still nothing: a ball (or roller) bearing has become trapped in a brinnelled groove in a blade grip bearing.
So again: pilot moves the lever down. NOW the force is sufficient for the ball (maybe roller) out leap out of the groove and furnish a MAJOR pitch reduction!
Result: giant nose over and dive at the ground. Result: negative G bunt and instant engine and rotor overspeed.
And I never will forget the sight of that geologist's pick rotating over and over in the air coming towards me, before wandering back and taking a chunk out of the windscreen.
And yet I was fond of that treacherous old heli. It was like a goat, or maybe a magpie. Devious and nasty; yes, but always doing something interesting.
thekite
Mine broke bolts, and it tore bolts out of the tailboom too at the universal joint bearing. It sheared its alternator drives and fried its ludicrous nicad battery.
And it did try to fly itself: straight down.
I never did work out why it would suddenly go into a giant negative G bunt. Not once. Several times. I even wrote to Ray Prouty about this. He could not help me. I wrote to CASA. My boss sacked me for that.
But about a year ago, on this very forum, one of the participating engineers (eric ferret?), suggested a brinnelled bearing.
And I am sure that that was the answer. pilot moves the collective down: nothing happens: pilot moves the collective down further: still nothing: a ball (or roller) bearing has become trapped in a brinnelled groove in a blade grip bearing.
So again: pilot moves the lever down. NOW the force is sufficient for the ball (maybe roller) out leap out of the groove and furnish a MAJOR pitch reduction!
Result: giant nose over and dive at the ground. Result: negative G bunt and instant engine and rotor overspeed.
And I never will forget the sight of that geologist's pick rotating over and over in the air coming towards me, before wandering back and taking a chunk out of the windscreen.
And yet I was fond of that treacherous old heli. It was like a goat, or maybe a magpie. Devious and nasty; yes, but always doing something interesting.
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thekite:
Just curious to know if a full and free controls check on the ground with the rotors stopped detected anything unusual with the flight controls?
Just curious to know if a full and free controls check on the ground with the rotors stopped detected anything unusual with the flight controls?
.................................. to burst the pilots ego! See - we don't need you after all!
kite,
That would be the dreaded "collective hump" (in more ways than one) S/S blades?
The trick with the fried ni-cad was to remove it and place by the door (door off of course). If it got too nasty you could just kick it out the door. You had to be careful if you were a little guy and did this with jerry cans in the boot. The resultant aft C of G after you booted the battery out was something to contend with!
kite,
That would be the dreaded "collective hump" (in more ways than one) S/S blades?
The trick with the fried ni-cad was to remove it and place by the door (door off of course). If it got too nasty you could just kick it out the door. You had to be careful if you were a little guy and did this with jerry cans in the boot. The resultant aft C of G after you booted the battery out was something to contend with!
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Well kite maybe you would remember the guy who used to live in KUNUNURRA, who managed to lose a paddle one day, not me, but it was a very funny story afterwards, knuckles skinned on the instrument panel etc. still alive and kicking. Yep he reckoned that one flew itself to the ground.
He also was going to be a rich mega star by taking over the dealership of the benson.
He has a very funny series of photgraphs, starting with the brand new box and finishing with bits all over the ground.
He tells it with such a laconic dry humour that one cannot help but laugh. if you know him he will tell a rather funny story about yours truly also. which wasn't at the time of course, at all extremely funny.
He also was going to be a rich mega star by taking over the dealership of the benson.
He has a very funny series of photgraphs, starting with the brand new box and finishing with bits all over the ground.
He tells it with such a laconic dry humour that one cannot help but laugh. if you know him he will tell a rather funny story about yours truly also. which wasn't at the time of course, at all extremely funny.
