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#51
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Hi Cam...
You are absolutely correct. In the case of that particular Enstrom, the engine lost power and the clutch didn't disengage. So, the airflow upward through the rotor which should have been retaining the rotor's autorotation R.P.M..was expended trying to turn the engine due to the NOT disengaged clutch. The situation was bad anyway because they didn't have much altitude- maybe a couple of hunderd feet. |
#52
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Cheers Bob, Presuming they use a sprag type clutch, I'd imagine it would
have to be very badly worn to lock up in the driving state. Of the different types (sprag) I've seen, they seem inherently bullet proof buy there design. I'd love to see a fataly damaged one just to see how they wear. Cam..... |
#53
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On most helicopters that I have been in, testing the split (sprag clutch) is part of the power on preflight. It seems kind of odd that such a catastophic clutch failure would occur without warning in the preflight. Perhaps they skipped that step. Dennis H. "Cam" wrote: Cheers Bob, Presuming they use a sprag type clutch, I'd imagine it would have to be very badly worn to lock up in the driving state. Of the different types (sprag) I've seen, they seem inherently bullet proof buy there design. I'd love to see a fataly damaged one just to see how they wear. Dennis Hawkins n4mwd AT amsat DOT org (humans know what to do) "A RECESSION is when you know somebody who is out of work. A DEPRESSION is when YOU are out of work. A RECOVERY is when all the H-1B's are out of work." To find out what an H-1B is and how Congress is using them to put Americans out of work, visit the following web site and click on the "Exporting America" CNN news video: http://zazona.com/ShameH1B/MediaClips.htm |
#54
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"Sprag clutch" might have been more understandable. Presumably we are talking about a simultaneous sprag and engine failure. A locked sprag alone won't down a helicopter. The scorpion's main clutch engagement is mechanical rather than electrical. Should the sprag and engine fail simultaneously, the main engine clutch can be disengaged in less than one second. I don't know if this would be soon enough, but the 2 minutes that electric clutches take is most likely too long. Getting back to the scorpion. It would seem that nobody here has any concrete facts regarding any serious safety flaws other than the short landing gear. We (I) have discussed several items that could be designed better, but nothing was a serious safety issue. The older scorpion design is apparently high maintenance, but still safe. Dennis H. "Bob" wrote: When a "clutch" (freewheeling unit) locks up, your rotor stops turning. Bob Dennis Hawkins n4mwd AT amsat DOT org (humans know what to do) "A RECESSION is when you know somebody who is out of work. A DEPRESSION is when YOU are out of work. A RECOVERY is when all the H-1B's are out of work." To find out what an H-1B is and how Congress is using them to put Americans out of work, visit the following web site and click on the "Exporting America" CNN news video: http://zazona.com/ShameH1B/MediaClips.htm |
#56
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"Cam" wrote in message ... Cheers Bob, Presuming they use a sprag type clutch, I'd imagine it would have to be very badly worn to lock up in the driving state. Of the different types (sprag) I've seen, they seem inherently bullet proof buy there design. I'd love to see a fataly damaged one just to see how they wear. Cam..... I did a little research and found the NTSB report. Docket number NYC87MA024. It says the sprag clutch was under lubricated, was damaged internally, and had some incorrect parts fitted ( specifically short pawls ) and that it had "rolled over" in the opposite direction. I assume this means that the freewheel direction had reversed. There is also available an audio of the crash. Jane Dornacker was on air at the time. In the background, it seems the engine can be heard overspeeding, certainly revving freely with no load on it. Perhaps the engine didn't fail, the sprag clutch just let go ( hence engine sounds in the audio ) and in the panic he pulled pitch. The report says they were only at about 75 feet. Mark |
#57
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"Mark" wrote:
on it. Perhaps the engine didn't fail, the sprag clutch just let go ( hence engine sounds in the audio ) and in the panic he pulled pitch. The report says they were only at about 75 feet. That would make sense. By the time he realized that the running engine wasn't driving the rotors, it was too late. Dennis H. Dennis Hawkins n4mwd AT amsat DOT org (humans know what to do) "A RECESSION is when you know somebody who is out of work. A DEPRESSION is when YOU are out of work. A RECOVERY is when all the H-1B's are out of work." To find out what an H-1B is and how Congress is using them to put Americans out of work, visit the following web site and click on the "Exporting America" CNN news video: http://zazona.com/ShameH1B/MediaClips.htm |
#58
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"Bart" wrote in message
... Not true in many (most) turbines. wrote: On most helicopters that I have been in, testing the split (sprag clutch) is part of the power on preflight. It seems kind of odd that such a catastophic clutch failure would occur without warning in the preflight. Perhaps they skipped that step. I remember part of the Bell Jetranger preflight was to turn the blades by hand to 90/270, and you were supposed to turn them counter clockwise (the direction of normal rotation), I can't remember the reason why that particular direction was specified. Maybe so as to not spin the power turbine (and engine RGB) without proper lubrication, maybe it was to check for sprag clutch disengagement, maybe both reasons. As for testing the _engagement_ of the clutch on preflight, my first thought is that it is impractical. Even on a small ship like the Scorpion, the main rotor may normally experience several hundred pounds-feet of torque... For another data point, I can say that checking the freewheeling unit(s) is not a part of the H-60 preflight, the navalized version anyway. On a related anecdote, when one of my friends was a student pilot, he had a hard landing when the sprag clutch failed to reengage following a practice power recovery autorotation. It freewheeled just fine though, and it engaged fine up until before the auto. That is the only time I ever heard of such a thing happening. |
#59
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Actually, the preflight maneuver was to spin them clockwise 360 degs.
The reason you did that was to check for coke-ing of the turbine. Older C20-s had a problem with this, and by spinning the blades backwards you would also be spinning the turbine and you can hear and feel it. I've never heard of the opposite rotation being done, but im sure someone else will come up with a reason that it was. btw: spinning the turbine is still part of the postflight of the MD500, I was told that its because of the crazy engine angle. The reason for the 90 / 270 thing was to ensure that they were not still tied to the tailboom. One of the funniest/scary stories I heard was that during a maintenance run-up the pilot checked for the 90/270 blades, fired up the turbine, and then noticed (too late) that the mechanic had secured the blades to one of those large rolling toolboxes. The box rolled around and did some serious damage before the pilot could stop it. No one was hurt that I know of though. Bart Jim Carriere wrote: I remember part of the Bell Jetranger preflight was to turn the blades by hand to 90/270, and you were supposed to turn them counter clockwise (the direction of normal rotation), I can't remember the reason why that particular direction was specified. Maybe so as to not spin the power turbine (and engine RGB) without proper lubrication, maybe it was to check for sprag clutch disengagement, maybe both reasons. |
#60
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I suggest you contact B.J. regarding that cable head. I heard him tell one
guy not to fly the cable head. Also the pitch bearings in the Safari are nearly identical to the R-22 and even with grease did not experience failure during the first 75 hrs. I flew mine. I have converted the grips to oil and am using ATF which, I'm led to believe, is the same as the R-22. Some of the posters believe that only certified ships are safe. At the present time there has been only one fatality in the Safari and that was not attributed to the aircraft in any way. I'm sure that Robinson wishes he could say that R-22. BTW there are more than one Safari with over 1,000 hrs. accumulated. I previously owned a couple of Scorpions and did not get either into the air. I sold them to a guy who had an A&P working on them and I don't think they ever got them in an unchained hover. The last time I saw them try, the tail rotor drive belts were slipping and he couldn't stop the ship from trying to rotate. Only the chains stopped him. The other noticeable thing was the noise. The exhaust noise on the evinrude was painful some distance away. I don't know a good way to avoid hearing damage even with plugs and a headset. Stu Fields wrote in message ... The R22 is a fine helicopter. However, there are those that fly jet rangers that would call the R22 a "Death Trap". You suggested that the Scorpion is not safe. However, you did not specify 'why' you don't consider it safe. I don't mean to sound argumentative, but I need cold, hard facts and not general rumors that the ship is dangerous. What is specifically bad about the Scorpion? I realize that there are many unorthodox things being done, but is that really bad? Take the cable-in-shaft control head for example. The entire rotor head tilts on a U-Joint rather than cyclicly changining the pitch as does a traditional helicopter. You might look at that and wonder why BJ Shramm did it that way. Here is the answer. At the time, the patent on elastomeric bearings was still in effect. BJ could not use them. He elected to use traditional thrust roller bearings. The problem with using these bearings is that if they are under a load and are used cyclicly (rocking back and forth with every revolution), the grease rolls out of the way after a few minutes of operation and the bearings have to operate without lubrication. This results in a failure. To avoid this problem, BJ tilted the entire rotor head rather than changing the pitch cyclicly. In fact, the pitch on the blades only changes when the collective is moved and not the cyclic. This results in the grease being retained for a longer period of time. It still needs frequent regreasing, but at least you don't need a new set of bearings after each hour of flight. But getting back to the main point, I really do want to hear about specific problems with the Scorpion. I want to correct these problems as much as possible. Dennis H. (Ryan Ferguson) wrote: Man. Your messages about flight training and your experimental helicopter just give me cold chills. I'd have to agree with the others who've suggested that you give this another thought. Do you have kids? A family? It's not worth it, guy. Side note. Forget the Scorpion for meeting solo requirements. (You do realize you need an endorsement for that specific helicopter, right?) No sane instructor would sign you off to solo that thing. Lord have mercy. Dennis Hawkins n4mwd AT amsat DOT org (humans know what to do) "A RECESSION is when you know somebody who is out of work. A DEPRESSION is when YOU are out of work. A RECOVERY is when all the H-1B's are out of work." To find out what an H-1B is and how Congress is using them to put Americans out of work, visit the following web site and click on the "Exporting America" CNN news video: http://zazona.com/ShameH1B/MediaClips.htm |
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