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#121
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Sorry for the tone but it is incredible to me that anyone thinks that
changing oil protects against structural failure of a crankshaft or connecting rod. Yes changing the oil makes the bearings, gears, cam/lifters and all other rubbing/sliding parts last longer but it does not affect cracking one bit. Mike MU-2 "Tom S." wrote in message ... "Mike Rapoport" wrote in message link.net... Presumably you have never worked on an engine at all.. Please describe how changing engine oil keeps a connecting rod from breaking in half. Please lose the patronizing tone that you came into this discussion with, then I'll continue with my QUESTION. (No wonder that one guy said he came into the group, then left after seeing the abuse some dole out.) |
#122
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"Mike Rapoport" writes:
But do you agree that components that require maintenance (propeller, cylinders, engine mounts, ...) can cause/accelerate crankshaft failures? I suppose that I agree to a limited extent, but virtually all crankshaft/connecting rod failures are caused by a flaw/fault in design/manufacture or installation. Once the crank or connecting rod is installed, nothing is done to it and it is unseen until overhaul time. A failure of either of these components is not going to put much, if any, metal into the oil until the bitter end either.. I was thinking less of metal in the oil than the forces exerted on the crankshaft. An out-of-balance prop or even a faulty spark plug can cause out-of-spec. impluses to be exerted on the crankshaft. I sure don't know how significant that is likely to be though. ('course you can consider the stories of pilots taking off after prop. strikes as an extreme.) --kyler |
#123
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#125
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Kyler
Another true (War) story. T-28A 7 cyl 900 HP engine. (128+ HP per cyl) 2 blade Aero-Products prop (big wide paddle blades to absorb HP) Prop shaft cut with a square corner where it transitioned to throw. At original cruise rpm viborations/stresses caused prop shaft to break off and prop depart plane. Result - dead stick with prop missing. Fixes tried. 1. Tried 3 blade prop which reduced stress on crank - worked but cost too much to throw away the relatively new 2 blade props and get new 3 blade props. 2. Dissambled engine and under cut (rounded) square corner betweem shaft and throw. More failures. 3. Set up a restricted rpm range that could be transitioned but not fly steady state in. 4. Raised cruise rpm 150 rpm changing stress on crank. These two worked but reduced range and duraation a lot. Had to refuel after every training mission vs flying two missions on one load of fuel. Looks like this true life story supports both sides of the argument? Big John On Mon, 01 Dec 2003 20:09:35 GMT, Kyler Laird wrote: "Mike Rapoport" writes: But do you agree that components that require maintenance (propeller, cylinders, engine mounts, ...) can cause/accelerate crankshaft failures? I suppose that I agree to a limited extent, but virtually all crankshaft/connecting rod failures are caused by a flaw/fault in design/manufacture or installation. Once the crank or connecting rod is installed, nothing is done to it and it is unseen until overhaul time. A failure of either of these components is not going to put much, if any, metal into the oil until the bitter end either.. I was thinking less of metal in the oil than the forces exerted on the crankshaft. An out-of-balance prop or even a faulty spark plug can cause out-of-spec. impluses to be exerted on the crankshaft. I sure don't know how significant that is likely to be though. ('course you can consider the stories of pilots taking off after prop. strikes as an extreme.) --kyler |
#126
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#127
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(Michael) wrote in message . com...
It's very frustrating as an instructor not to be able to give your student solid estimates on which risks are truly significant, but the alternative (reaching firm conclusions from nonexistent numbers) is far worse. I agree about the frustration. I disagree that I was in any way trying to reach firm conclusions; just trying to offer some sense of the scope of the potential problem, be it engine failures or stall/spins. And I do think it is fair in the case of the stall/spin, for example, to say that the last maneuver performed by nearly one out of four pilots who's aviation career has ended in death and who also ended up in the NTSB database was a stall/spin. This does provide some context about the stall/spin risk, especially in the accident process leading to generation of an NTSB report. As a flight instructor charged with the task of educating pilots and (hopefully) offering them guidance in terms of how often to practice certain procedures/maneuvers on their own, what frequency do you recommend in this regard, and on what is that recommendation based? Whatever is required to maintain proficiency. If during your recurrent training cycle you handle the engine failure competently (meaning accomplish the task smoothly and with the successful outcome never seriously in doubt) then you are maintaining proficiency. Otherwise you are not. But what about in between the recurrent training cycle? Do you make any recommendations to your students at all in this regard? What to work on, how to work on it, what frequency to practice? And in terms of "smoothly with the successful outcome never seriously in doubt" -- do you apply Practical Test Standards to the tasks -- which are minimum acceptable standards, i.e.: training to the lowest common denominator -- or do you challenge your students to be better than the average, the minimum standard? And if you challenge them to take their flying to the next level, I would assume that would be based on your own experience, both personally and as an instructor dealing with the problems, errors, and misunderstandings your students commonly have when they fly with you, no? And I would bet that sans any hard scientific data to support your anecdotal experience, you could tell me with reasonable certainty where the problem areas will be, specifically what the errors will be, etc. that you will encounter with the majority of your students under certain tasks. Specific numbers are very much a function of the airplane and pilot proficiency, and one size does not fit all. For the majority of GA pilots flying GA airplanes, I have not found that to be the case at all. The problems I deal with with my students all fall within a pretty well-defined envelope across the board, across light, single-engine, GA airplanes. In fact, I would say I've found it much more difficult for higher time pilots to break their bad habits simply because the habits have been ingrained for far too long. The typical profile of the pilot I fly with is a pilot who is active in general aviation, active in the ratings process, active in the pursuit of knowledge, experience, safety, and who has 100 to 600 hours total time. These pilots come from all over the U.S., from all kinds of flight schools, flying all kinds of light, single-engine airplanes. And I often fly with them in the equipment they are used to flying. Anything from the Cirrus SR20/22, to the J-3 Cub, to the C-206 Amphib, to the Pitts, Pipers, Cessnas, RV's, Zlins, even rarer airplanes like the Aero Subaru and the FAA Bravo. In that sense, the pilots I deal with are likely above the average in terms of their approach to flying and flight safety -- that's why they are training with me. That and the realization that the primary flight training process often leaves a lot to be desired in terms of dealing with many different safety issues, not to mention the pure art of flying the airplane. In fact, typical pilots under duress will invariably only be able to perform as well as their most basic skill set allows. Define most basic skill set. Keep in mind that for some, this will include night partial panel flying. For others, it may be substantially more limited. And those skills that are the most practiced, the most familiar, the most "natural" to the pilot are the ones that will largely determine the outcome. Again, this is based on my anecdotal experience instructing 1,000's of pilots while they are placed under duress during emergency maneuver training -- typical pilots from across the country who are representative "products" of our national flight training system. I'm not convinced that's true. I suspect that the pilots who voluntarily get emergency maneuvers training are the same pilots who doubt their ability to handle emergencies. Such doubts are usually justified. See above about the typical pilot profile of those I fly with -- they are likely above average and at least recognize and deal with any issues they may have. But for each one of the pilots who takes spin, EMT, or aerobatic training for safety reasons, there may be scores of others who have no clue, or who have simply given up and left aviation altogether because of unaddresses issues/fears that could have been dealt with. I don't believe a stall-spin involves a typical pilot at all. The numbers and the anecdotal experience of professional spin/aerobatic flight instructors are totally at odds with your belief. So how many inadvertent stall-spins do they get to see under normal conditions? I'm not sure I understand the question... The typical pilot is trained by the typical flight instructor, who himself/herself has a marginal understanding of, and marginal practical experience with, anything related to stalls and spins and therefore, is incapable of adequately providing stall/spin awareness training to their students. That's probably true, but on the other hand most modern airplanes have to be pretty severely mishandled to cause an inadvertent spin. Not true -- I routinely demonstrate one variant of the classic skidded turn base-to-final at altitude with students, and in every single spins-approved airplane I've ever tried this in, I've been successful entering a spin from a left turn, with 1200-1800 rpm, without any aileron, with less than full rudder and elevator inputs, and with the ball less than 1/2 ball width out of center. This has been true even in spins-approved airplanes that either would not, or were very reluctant to, perform a left spin entered normally. See also "Rudder and Elevator Effects on the Incipient Spin Characteristics of a Typical General Aviation Training Aircraft." AIAA Paper 93-0016. Reno, NV: January, 1993, by Patrick Veillette. And pilots with fewer than either 500 hours total time, or 100 hours in type, are more likely to encounter an inadvertent stall/spin than to have a genuine engine failure. Why do you keep going back to the patently unprovable? All we know is that they are more likely to have an accident caused by stall-spin rather than engine failure. This tells us nothing about the likelihood of encountering either hazard. Thos enumbers are from an NTSB study. I'm notmaking them up. Perhaps you'd be happier if I prefaced with "Pilots who make it into the NTSB database share these characteristics..." Now let's consider something else. A pilot who flies 200 hours a year is 10 times more likely to have an engine failure than one who flies 20 hours a year, since engine failure is not under his control. Are you seriously suggesting that a pilot who flies 200 hours a year is 10 times more likely to inadvertently spin than one who flies 20 hours a year? I would argue that he is LESS likely to inadvertently spin, since the higher level of proficiency that is a nearly inevitable result of flying a lot and often will make him less likely to miss the rather obvious clues. You admitted yourself, all flight time is not equal. In that regard, I would say the pilot who flies 200 hours a year of white-knuckled X-country, averaging one power-on landing every 2 hours, who is deathly afraid of stalls to begin with and has never spun, and flies by the adage "maintain lots of extra flying speed just in case" is far more likely to encounter an inadvertent stall/spin in a stall/spin critical situation than a pilot who flies 20 hours a year in his Pitts, 30 minutes at a shot, performing advanced aerobatic maneuvers and averaging 4 gliding landings per hour (my former Pitts partner did just this last year). I'd bet on the survival of this Pitts pilot over the other one in a similar stall/spin critical scenario. Perhaps a better gage of a pilot's ability to deal with stall/spin critical operations is not flight time, but rather the number of landings per hour. After all, one trip around the pattern exercises many, many critical piloting skills. It would be interesting perhaps to do a study with this as the hypothesis -- would this interest you??? Rich http://www.richstowell.com |
#128
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