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#11
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a VERY close call/ armchair pilots
On Feb 24, 12:31 pm, "B4RT" wrote:
"Nick" wrote in message ... Thought you guys might be interested http://www.videosift.com/video/Helic...s-A-Close-Call But why wouldn't he have kept some negative collective to keep it nailed to the deck?.... how far would the tips 'dished' down?.....not enough to cause the crew more worries than they already had?? It seemed very light on the skids on the previous couple of swells?? Negative collective? .....ROTFLMFAO! Boy I dont think I have that option on mine. Heh! The only heli's I've seen that can do negative are the R/C ones - they can fly upside down! My armchair analysis is that the helicopter appeared to have a forward CG and the deck was pitching as much as 15 degrees and rolling about 7 or 8. I don't think the pilot really ever "wanted" to take off. It looked to me like the deck pitched forward a whole lot and he thought the helicopter would nose over if he didn't take off. The deck angle was pitched very far forward at the moment of the tail strike, and the camera gives the illusion that the helicopter was at far less level pitch that it was. I'm thinking that the pilot was taking the lesser of two evils and got bit by one of them. Its clear to me that he was pretty skilled because doing a totally successful hovering auto to that platform like that couldn't be done by an unskilled pilot. The only bad piloting in this incident appears to have happened way before the engine started when someone decided that it was ok to take off in seas like that. Bart |
#12
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a VERY close call/ armchair pilots
On Feb 24, 12:31 pm, "B4RT" wrote:
"Nick" wrote in message ... Thought you guys might be interested http://www.videosift.com/video/Helic...s-A-Close-Call But why wouldn't he have kept some negative collective to keep it nailed to the deck?.... how far would the tips 'dished' down?.....not enough to cause the crew more worries than they already had?? It seemed very light on the skids on the previous couple of swells?? Negative collective? .....ROTFLMFAO! Boy I dont think I have that option on mine. My armchair analysis is that the helicopter appeared to have a forward CG Why would that be? and the deck was pitching as much as 15 degrees and rolling about 7 or 8. I don't think the pilot really ever "wanted" to take off. It looked to me like the deck pitched forward a whole lot and he thought the helicopter would nose over if he didn't take off. The deck angle was pitched very far I don't think the problem was the angle of the deck - more that it's acceleration down cancelled some gravity - a little POSITIVE collective could have been enough to lift off. Seems like he had a lot of forward cyclic as well though. forward at the moment of the tail strike, and the camera gives the illusion that the helicopter was at far less level pitch that it was. I'm thinking that the pilot was taking the lesser of two evils and got bit by one of them. Its clear to me that he was pretty skilled because doing a totally successful hovering auto to that platform like that couldn't be done by an unskilled pilot. The only bad piloting in this incident appears to have happened way before the engine started when someone decided that it was ok to take off in seas like that. Bart |
#13
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a VERY close call/ armchair pilots
"JohnO" wrote in message s.com... My armchair analysis is that the helicopter appeared to have a forward CG Why would that be? I dont know, maybe there were two fattys on board with the pilot. I've flown an Enstrom and don't recall it being nose heavy, but each time the ship pitched forward I thought I noticed it get light on the aft section of the skids. and the deck was pitching as much as 15 degrees and rolling about 7 or 8. I don't think the pilot really ever "wanted" to take off. It looked to me like the deck pitched forward a whole lot and he thought the helicopter would nose over if he didn't take off. The deck angle was pitched very far I don't think the problem was the angle of the deck - more that it's acceleration down cancelled some gravity - a little POSITIVE collective could have been enough to lift off. Seems like he had a lot of forward cyclic as well though. Nah... I don't think so. Boats dont go up and down in seas like that with negative G's that significant. Enstrom pilots don't tend to spend a lot of time getting light on the skids either because of the damn oleo struts and ground resonance tendancy of that machine. That guy flying was no amateur, he was locked and loaded when he chopped the throttle and did that auto. There's several HUGE differences in the flight dynamics of RC heli's and real ones. RC's tend to have very low CG's, this makes them more stable. RC's have an assload more collective juice than the big things, you don't come off the helipad in a real one without really intending to do it. The static and dynamic relative rotor mass of a an RC is very small, you can move the cyclic much more quickly in an RC and have it take effect without lag. The big spinny gyrosope thingy on top doesnt wan't to change that quickly on a big helicopter. These differences can make it hard to extrapolate the operation of a big one from experiences with a small one. Just imagine trying to drive a semi truck in the same manner you'd drive a Porche. Bart |
#14
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a VERY close call/ armchair pilots
Negative collective? .....ROTFLMFAO! Boy I dont think I have that option
on mine. What is the pitch range on this helicopter?......anyone?......I 'fly' RC, but it'd be interesting to know that negative pitch as not possible.....does that go for all full size helis? So the fact that the machine appeared light on its skids could not have been corrected?....or minimised? "B4RT" wrote in message ... "Nick" wrote in message ... Thought you guys might be interested http://www.videosift.com/video/Helic...s-A-Close-Call But why wouldn't he have kept some negative collective to keep it nailed to the deck?.... how far would the tips 'dished' down?.....not enough to cause the crew more worries than they already had?? It seemed very light on the skids on the previous couple of swells?? Negative collective? .....ROTFLMFAO! Boy I dont think I have that option on mine. My armchair analysis is that the helicopter appeared to have a forward CG and the deck was pitching as much as 15 degrees and rolling about 7 or 8. I don't think the pilot really ever "wanted" to take off. It looked to me like the deck pitched forward a whole lot and he thought the helicopter would nose over if he didn't take off. The deck angle was pitched very far forward at the moment of the tail strike, and the camera gives the illusion that the helicopter was at far less level pitch that it was. I'm thinking that the pilot was taking the lesser of two evils and got bit by one of them. Its clear to me that he was pretty skilled because doing a totally successful hovering auto to that platform like that couldn't be done by an unskilled pilot. The only bad piloting in this incident appears to have happened way before the engine started when someone decided that it was ok to take off in seas like that. Bart |
#15
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a VERY close call/ armchair pilots
On Feb 25, 2:13 am, "B4RT" wrote:
"JohnO" wrote in message s.com... My armchair analysis is that the helicopter appeared to have a forward CG Why would that be? I dont know, maybe there were two fattys on board with the pilot. I've flown an Enstrom and don't recall it being nose heavy, but each time the ship pitched forward I thought I noticed it get light on the aft section of the skids. and the deck was pitching as much as 15 degrees and rolling about 7 or 8. I don't think the pilot really ever "wanted" to take off. It looked to me like the deck pitched forward a whole lot and he thought the helicopter would nose over if he didn't take off. The deck angle was pitched very far I don't think the problem was the angle of the deck - more that it's acceleration down cancelled some gravity - a little POSITIVE collective could have been enough to lift off. Seems like he had a lot of forward cyclic as well though. Nah... I don't think so. Boats dont go up and down in seas like that with negative G's that significant. Definitely not true. Ever watch thet tv show 'Deadliest Catch' where they embed a camera guys on crab boats in the Bering Sea? One of the things they do to pass the time between getting cold and wet is to jump up just as the boat plunges into a swell. They float like astronauts for a moment. I've never done that but have certainly been on the deck of a boat many times and felt very much unweighted as the boat plunges into a trough. I assume it would be normal practice for a vessel to steam into the wind when carrying out aircraft operations and this gives the fastest drops into the swell. Enstrom pilots don't tend to spend a lot of time getting light on the skids either because of the damn oleo struts and ground resonance tendancy of that machine. That guy flying was no amateur, he was locked and loaded when he chopped the throttle and did that auto. He sure did that beautifully. But even pros sometimes get sloppy for a moment on rare occasions. It's not out of the question that he slipped up, but then his training and experience snapped in to save the day. There's several HUGE differences in the flight dynamics of RC heli's and real ones. RC's tend to have very low CG's, this makes them more stable. RC's have an assload more collective juice than the big things, you don't come off the helipad in a real one without really intending to do it. The static and dynamic relative rotor mass of a an RC is very small, you can move the cyclic much more quickly in an RC and have it take effect without lag. The big spinny gyrosope thingy on top doesnt wan't to change that quickly on a big helicopter. These differences can make it hard to extrapolate the operation of a big one from experiences with a small one. Just imagine trying to drive a semi truck in the same manner you'd drive a Porche. Bart |
#16
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a VERY close call/ armchair pilots
Negative collective? .....ROTFLMFAO! Boy I dont think I have that option
on mine. What is the pitch range on this helicopter?......anyone?......I 'fly' RC, but it'd be interesting to know that negative pitch as not possible.....does that go for all full size helis? I know of only one big helicopter that ever had negative pitch (-3°). It is a military American one; can't recall the type. The reason for that is that it should be able to do a very quick vertical descent while hovering just over tree tops. For all other helicopters it were pretty useless but would cost a lot because the control rigging would need far more travel. There is no civilian helo with negative pitch, not even 0°. The minimum pitch might be as high as +4°. |
#17
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a VERY close call/ armchair pilots
"Steve L." wrote in message news Negative collective? .....ROTFLMFAO! Boy I dont think I have that option on mine. What is the pitch range on this helicopter?......anyone?......I 'fly' RC, but it'd be interesting to know that negative pitch as not possible.....does that go for all full size helis? I know of only one big helicopter that ever had negative pitch (-3°). It is a military American one; can't recall the type. The reason for that is that it should be able to do a very quick vertical descent while hovering just over tree tops. For all other helicopters it were pretty useless but would cost a lot because the control rigging would need far more travel. There is no civilian helo with negative pitch, not even 0°. The minimum pitch might be as high as +4°. Thanks for the reply. But what happens during autorotation to keep the headspeed up? ......headspeed will surely decay very quickly at +4degrees? |
#18
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a VERY close call/ armchair pilots
"Nick" wrote in message
... "Steve L." wrote in message news Negative collective? .....ROTFLMFAO! Boy I dont think I have that option on mine. What is the pitch range on this helicopter?......anyone?......I 'fly' RC, but it'd be interesting to know that negative pitch as not possible.....does that go for all full size helis? I know of only one big helicopter that ever had negative pitch (-3°). It is a military American one; can't recall the type. The reason for that is that it should be able to do a very quick vertical descent while hovering just over tree tops. For all other helicopters it were pretty useless but would cost a lot because the control rigging would need far more travel. There is no civilian helo with negative pitch, not even 0°. The minimum pitch might be as high as +4°. Thanks for the reply. But what happens during autorotation to keep the headspeed up? ......headspeed will surely decay very quickly at +4degrees? I fly RC helicopters too and have "very" limited experience in the full size counterparts. What most RCer's don't understand is that you don't need negative pitch to autorotate. What RCer's refer to as "negative" collective is simply an measurement of blade incidence. It has nothing to do with the rotor blades aerodynamic angle of attack (AOA). Nick, even if you're running your model with a -5 at full down setup, the blades are still flying a positive AOA in the auto at that setting. Granted, it'll be dropping like a rock in that mode but the blades are still seeing a positive AOA. I've played around with autos on my RC birds and, with a bit of a breeze, have made sustained autorotative approaches and a safe landing with the collective as high as +3 degrees. Granted, I wasn't carrying a lot of rotor rpm on the descent so the collective "pull" at the bottom was a bit critical but it's definitely doable. The full size birds, as Steve L pointed out, rarely if ever go into the negative incidence range. First, because the simply don't need to and more importantly, because they are "much" more critical about maintaining a specific rotor rpm. If they dropped into a negatie incidence range, they'd overspeed the rotor with obvious results. The big guys simply can't stand the rpm swings that our models do in their stride. FWIW! Fly Safe, Steve R. |
#19
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a VERY close call/ armchair pilots
I didn't measure it, but from the look of it the blade pitch at the tip of
the main rotor of my jetranger when its at 90 degrees to the right (the most negative pitch point) and the collective full down is roughly 0 degrees, it might even be a shade negative. Bart "The OTHER Kevin in San Diego" skiddz "AT" adelphia "DOT" net wrote in message ... On Sat, 24 Feb 2007 15:06:40 -0800, Steve L. wrote: I know of only one big helicopter that ever had negative pitch (-3°). It is a military American one; can't recall the type. The reason for that is that it should be able to do a very quick vertical descent while hovering just over tree tops. A&P buddy of mine who was in the Marines told me the CH-53 can do about -3 degrees collective. Not sure of the reasoning behind it.. For all other helicopters it were pretty useless but would cost a lot because the control rigging would need far more travel. There is no civilian helo with negative pitch, not even 0°. The minimum pitch might be as high as +4°. The negative twist in the blades might get parts of the blade into negative pitch in an auto (or even a rapid power descent) but I don't know if the AoA ever goes negative... |
#20
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a VERY close call/ armchair pilots
B4RT wrote: I didn't measure it, but from the look of it the blade pitch at the tip of the main rotor of my jetranger when its at 90 degrees to the right (the most negative pitch point) and the collective full down is roughly 0 degrees, it might even be a shade negative. Was that with the cyclic neutral? If so, it would be interesting to have someone in the ship apply full down collective and full back cyclic while you looked at it. Don W. |
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