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#12
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With our Mooney F model at best glide speed when I pull the prop control all
the way back (max pitch), it saves me about 300 fpm while maintaining best glide. With a minimum pitch, the blades are one big braking force. "Dale" wrote in message ... In article , wrote: Whether or not the engine is "running" if the rpm is below this range, moving the prop control has no effect on the pitch of the prop. That's what I thought until I tried it on my 182. Idle power, trimmed stable 80 mph glide with the prop control all the way forward. Pulled the blue knob back and watched the airspeed increase about 5MPH...pushed the blue knob in and I slowed again. -- Dale L. Falk There is nothing - absolutely nothing - half so much worth doing as simply messing around with airplanes. http://home.gci.net/~sncdfalk/flying.html |
#13
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I don't buy that. I can play with the prop at IDLE and zero knots and
get it to change RPM. My run-up is done at 1700 and the prop oil wash exercise has a big effect. Ed On Mon, 12 Apr 2004 18:06:09 -0400, wrote: On Mon, 12 Apr 2004 05:06:12 GMT, Ed wrote: snip In idle, with the prop at flat pitch, it feels too draggy and comes down like a rock. With it at high pitch, it seems to have too optimistic a glide ratio. What's the happy medium? I'm a little confused by this portion of your question, and a couple of the replies. I have never actually messed around a bunch with airspeed/descent rate/idle engine/prop rpm, but am pretty familiar with how a typical pressure-to-increase pitch constant-speed prop/governor works. Somewhere around 1600-1800 rpm, the prop governor ceases to output enuff pressure to change/maintain the propeller pitch, and the propeller goes to flat pitch. I've seen it on a gov bench, and on approach-to-land. Whether or not the engine is "running" if the rpm is below this range, moving the prop control has no effect on the pitch of the prop. TC snip |
#14
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I just want to clear this up. My home field (O17) - and just about
all those around it for 50nm are heavily wooded and surrounded by pines reaching up about 50'. Some of you guys are men to faith, obviously. I however, am not and prefer to try to perfect the simulation rather than log glider time. My goal is simply to set it up so the configuration for best glide or min sink (depending on distance to the runway) so as to get a feel for expected glide performance. Thanks for all the various suggestions. It convinces me there is not any one procedure past what the POH says about getting the motor started again and then technique becomes the rule. Ed (N119NC) On Mon, 12 Apr 2004 16:21:39 -0700, "C J Campbell" wrote: "Ed" wrote in message .. . I'm fairly new to GA after a 19 year break flying jets. I routinely fly a single engine experimental with a constant speed prop mounted on a Lycoming IO-360. 2 QUESTIONS: 1. What's the proper setup to simulate the way the plane would glide in case of an engine failure? I'm looking for pitch and possibly a manifold pressure number here. Unfortunately, it will be with the engine at idle at flat pitch. I will explain why below. 2. It that motor quits, will it still rotate through the flying airspeed envelope or can I expect it to stop rotation (assuming it's not frozen due to a mechanical failure)? In idle, with the prop at flat pitch, it feels too draggy and comes down like a rock. With it at high pitch, it seems to have too optimistic a glide ratio. What's the happy medium? The prop pitch is maintained by oil pressure. Most single engine piston installations set up the constant speed prop so that it will go to flat pitch if oil pressure is lost (the exact opposite of turboprops and piston twins). This is supposed to maximize your chances of restarting the engine, but you pay for it with glide range. The propeller will continue to windmill and create a lot of drag, but with the engine out you have little choice -- your oil pressure will be zero. It makes sense when you consider that most 'engine failures' are caused by fuel mismanagement. All you have to do is switch tanks and with the windmilling prop your engine will start right up again. You can make the propeller quit rotating by flying very slowly, but that will not improve your glide. Turboprops and piston twins set the prop to feather if oil pressure is lost. These propellers will stop rotating almost immediately. I don't live near a dry lake bed or I'd just shut it down and find out. I have the proper airspeeds for max range and min sink out of the POH but it does not quote any type of glide ratio. You could just stay in the pattern and shut it down. It should start right up again just by giving it some fuel. |
#15
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In article . net, Dave S wrote:
One caveat.. this works fine as long as the prop continues to windmill.. if it DOESNT... they you have just turned a training situation into what may be a bonafide emergency. I believe Highflyer has a story about that in a Taylorcraft...which lacked an electric starter, and the prop had stopped turning. Slope soaring saved the day. -- Dylan Smith, Castletown, Isle of Man Flying: http://www.dylansmith.net Frontier Elite Universe: http://www.alioth.net "Maintain thine airspeed, lest the ground come up and smite thee" |
#16
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On Tue, 13 Apr 2004 05:49:10 GMT, "Roy Epperson"
wrote: With our Mooney F model at best glide speed when I pull the prop control all the way back (max pitch), it saves me about 300 fpm while maintaining best glide. With a minimum pitch, the blades are one big braking force. I'll gladly take your collective word for it from in-flight observations. Mine were limited to shoving the prop ahead turning final (in every complex aircraft I've ever flown in) at approx 1200-1400 rpm (prop control previously set to 2300 in cruise) with no change in engine rpm/prop noise noted. Have pulled mis-rigged PT6A props to "flat" on short final a couple of times, have the stained shorts to prove it. Before I posted, I called my gov shop buddy to make sure his views coincided with what I remembered from hanging around in his shop. He related same, that the gov bench doesn't indicate useable gov pressure until around 1500-1600 rpm. As I recall, on most engines, the gov drive turns at about 90% of the indicated rpm. I stuff I work on now has a fixed-pitch first stage "prop", and I ain't allowed to drive it, so I can't add anything further. Regards; TC |
#17
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wrote in message
... Mine were limited to shoving the prop ahead turning final (in every complex aircraft I've ever flown in) at approx 1200-1400 rpm (prop control previously set to 2300 in cruise) with no change in engine rpm/prop noise noted. That's a completely different situation. At that power setting, the engine didn't have enough power to drive the prop at the selected RPM (2300), and so the blades were already at flat pitch. Selecting high RPM would have had no effect, since the governor was already trying to increase RPM, to its limits (maximum flat pitch). Next time, pull the prop to *minimum* RPM and see your glide angle decrease. Have pulled mis-rigged PT6A props to "flat" on short final a couple of times, have the stained shorts to prove it. Not sure how that statement fits in to the discussion, but the PT6 governors work differently from those found on most piston-engine singles. Before I posted, I called my gov shop buddy to make sure his views coincided with what I remembered from hanging around in his shop. He related same, that the gov bench doesn't indicate useable gov pressure until around 1500-1600 rpm. You mentioned "gov pressure" in an earlier post, and I still don't understand what you mean. The force to change the prop blade angle comes from springs and oil pressure, not the governor itself. All the governor does is adjust oil valves to control how the oil moves through the pitch change mechanism. In any case, as with the others, I've had no trouble at all reducing the blade pitch even in low-RPM, idle-power situations. I have no reason to expect I'd have any trouble in an actual engine failure, assuming the engine continued to windmill and run the oil pump. Pete |
#18
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On Tue, 13 Apr 2004 16:15:11 -0700, "Peter Duniho"
wrote: snip Next time, pull the prop to *minimum* RPM and see your glide angle decrease. It'll likely be years, I don't do GA anymore. Have pulled mis-rigged PT6A props to "flat" on short final a couple of times, have the stained shorts to prove it. Not sure how that statement fits in to the discussion, but the PT6 governors work differently from those found on most piston-engine singles. Doesn't have anything to do with it, this is Usenet. You really owe to yourself to try it once, though. It's similiar to tromping on a non-ABS brake pedal at 40 mph. Gets your attention at 75 feet AGL with the nose down coming-over-the-fence. Before I posted, I called my gov shop buddy to make sure his views coincided with what I remembered from hanging around in his shop. He related same, that the gov bench doesn't indicate useable gov pressure until around 1500-1600 rpm. You mentioned "gov pressure" in an earlier post, and I still don't understand what you mean. The force to change the prop blade angle comes from springs and oil pressure, not the governor itself. All the governor does is adjust oil valves to control how the oil moves through the pitch change mechanism. The base of a governor is another oil pump, stepping up engine oil pressure to over 175 psi. Maximum pressure is limited by a spring-loaded pop-off valve, just like the engine oil pump. http://www.mccauley.textron.com/prop...g03govern.html was the best picture I could find of it in a 30 second Google. In any case, as with the others, I've had no trouble at all reducing the blade pitch even in low-RPM, idle-power situations. I have no reason to expect I'd have any trouble in an actual engine failure, assuming the engine continued to windmill and run the oil pump. Agreed, like I indicated in another post, the oil pump/governor doesn't care what's turning it. TC |
#19
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wrote in message
... Not sure how that statement fits in to the discussion, but the PT6 governors work differently from those found on most piston-engine singles. Doesn't have anything to do with it, this is Usenet. Okay...just thought I'd ask. The base of a governor is another oil pump, stepping up engine oil pressure to over 175 psi. Maximum pressure is limited by a spring-loaded pop-off valve, just like the engine oil pump. Yes, but as far as I know, that pump will work just as well as the engine pump. Also, even if for some reason that pump failed, my understanding is that it would simply reduce the responsiveness of the governor. It wouldn't cause it to stop working altogether. The engine-supplied oil pressure would be sufficient. Agreed, like I indicated in another post, the oil pump/governor doesn't care what's turning it. Well, color me confused then. I thought we started this thread with you suggesting that if the engine has failed, resulting in low RPM, you wouldn't be able to get the prop to the coarse pitch setting. But, if you agree with what I said, so much the better. Pete |
#20
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"Peter Duniho" wrote in message ...
wrote in message ... Not sure how that statement fits in to the discussion, but the PT6 governors work differently from those found on most piston-engine singles. Doesn't have anything to do with it, this is Usenet. Okay...just thought I'd ask. Not a problem. The base of a governor is another oil pump, stepping up engine oil pressure to over 175 psi. Maximum pressure is limited by a spring-loaded pop-off valve, just like the engine oil pump. Yes, but as far as I know, that pump will work just as well as the engine pump. Also, even if for some reason that pump failed, my understanding is that it would simply reduce the responsiveness of the governor. It wouldn't cause it to stop working altogether. The engine-supplied oil pressure would be sufficient. I really would like to spend 24 hours in your world. Having spent 20+ years living in aviation, I'm still learning. IMHO it becomes quite obvious from reading your posts that airplane ownership has somehow mysteriously given you insight that mere mortals such as myself are sorely lacking. Where did you obtain the basis for this theory? I somehow doubt that you've ever had to troubleshoot/repair a prop/governor gripe. If you had, and had done your homework, you would have learned that one of the first steps in troubleshooting is verifying adequate oil pressure (also a crude method of determining adequate oil volume) to the prop governor. Please bear in mind, in a lot of engine designs, the prop governor is located at the tail end of the oil system, with a lot of built-in leaks between the engine oil pump and the governor pad. I find it rather funny that while the prop/governor will not function properly without approximately 30-40 psi to "step-up" to over 175 psi, you have determined that the governor oil pump (which initially you apparently doubted even existed) is not a necessary piece of the puzzle. Speaking from direct observation, at higher power settings, reduced/insufficient governor pressure delivered to the propeller dome can limit the ability to reduce engine rpm in a pressure-to-increase pitch system, and failure to obtain maximum rpm in a pressure-to-decrease system. Again, from direct observation, this can be caused by insufficient oil supply to the gov pad (see above), excessive rotor-to-housing clearance/physical gov oil pump damage, a fault in the oil pressure relief valve, or in extreme cases, excessive clearances/oil loss between the main crankshaft bearing and the crankshaft. Agreed, like I indicated in another post, the oil pump/governor doesn't care what's turning it. Well, color me confused then. I thought we started this thread with you suggesting that if the engine has failed, resulting in low RPM, you wouldn't be able to get the prop to the coarse pitch setting. That's entirely correct. I described my personal experiences in-flight, related that they were somewhat limited to the subject, and that I needed clarification. I also contacted two professional GA pilots, and a guy that has been repairing/overhauling prop governors for 20 years prior to posting. After reading subsequent replies, I freely admitted that I was wrong. Now I can factor that information into my personal database for future reference. Seeking new knowledge/other experiences was one of the primary reasons I climbed into the stinking swamp of GA on the internet to begin with. The other primary reason was to share my experiences and knowledge with no intention of financial gain. Over the years in these forums, my chosen profession has been repeatedly attacked, my personal experience and intent questioned. After spirited credentialled discourse with apparently clueless twits, surprisingly enuff I began to receive private communications from lurkers (and posters) who wanted me to maintain their aircraft. As this was never my intention, I had to become the anonymous self-proclaimed hairy mole on the ass that is rec.aviation. You see, I learned a long, long time ago that arguing on the Internet is like getting a gold medal in the Special Olympics. You (figure of speech, by no means a personal attack)may have "won", but you (along with all the other contestants) are still mentally-challenged. But, if you agree with what I said, so much the better. I share your joy; TC |
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