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#31
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PSRU design advantages
"George" wrote in message m... JP wrote: "George" kirjoitti gy.com... Richard Lamb wrote: ADK wrote: IF you had to design a PSRU, to drive a pusher propellor via shaft, what would your experience dictate? Thinking along the lines of a gearbelt, chain or gear. Please, I would appreciate the collective experience available on this group. I have decided on the aircraft, but want to make it the most reliable and safest it can be. http://www.prime-mover.org/Engines/T.../contact1.html |
#32
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PSRU design advantages
".Blueskies." wrote http://www.prime-mover.org/Engines/T.../contact1.html Thanks, so much, for posting that link. It was the one the OP needed to read, but I did not remember enough about it, to find it. It is now on my hard drive. To the OP; did this scare you enough? My best advise? Change the design, so it does not involve a long driveshaft. It is doubtful (from reading your questions) that you have the expertise to solve a problem of that magnitude. It is doubtful that you even know anyone capable of solving such a problem. Even if you or someone you know has enough "mojo" to solve the problem, you probably will spend a fortune getting the application to be safe and reliable. Remember, it kicked Burt Rutan's arse. That is really saying something! -- Jim in NC |
#33
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PSRU design advantages
"Bill Daniels" bildan@comcast-dot-net wrote I suppose...you could use a hydro drive. Turn a pump with the engine and use a hydraulic motor to turn the prop. Some type of pressure regulator could smooth the pressure to the prop motor. Might work for a really slow turning prop. One word. HEAVY ! ! ! -- Jim in NC |
#34
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PSRU design advantages
George wrote:
Richard Lamb wrote: ADK wrote: IF you had to design a PSRU, to drive a pusher propellor via shaft, what would your experience dictate? Thinking along the lines of a gearbelt, chain or gear. Please, I would appreciate the collective experience available on this group. I have decided on the aircraft, but want to make it the most reliable and safest it can be. "ADK" wrote in message news:X6TXf.28774$%H.11944@clgrps13... This is probably going to open old wounds. What I would like is experienced input on the advantages, for economic, efficiency and longevity etc. of different types of redrives. I am leaning towards a cog-belt reducer in a 6 cylinder, liquid cooled, configuration driving a long drive shaft to the prop. The collective experience is zilch = nada = squat = undefined. THAT is what everybody had been trying to tell you. Wait a second. Look around the airport. How many shaft driven propellers do you see? Have you ever seen? If you are heart set on doing it, I sincerely wish you luck. But I can't offer any further advice - 'cuz they ain't none... Richard Richard, Didn't the military do this once?? Seems there was the P-39 Aircobra, shaft driven from a rear mounted engine?? Are the gray cells working that far back?? Not that it would be applicable to an experimental, but at least It was once done? George Wasn't the gub'ment, George, but Bell Aircraft. P-39 not only had a drive shaft but a cannon firing thru the psru gearbox. layout of engine, gearbox and cannon at: http://www.home.earthlink.net/~tp-1/p392.jpg So it *can* be done. (The cannon firing thru the prop! ) I was curious to see if Bell had reduced the shaft RPM between the engine and gearbox, but it looks like 1:1 there. That might have been of interest to the OP, since his setup will likely drive the shaft at prop rpm (after the psru). Gonna take one tough (probably spelled h.e.a.v.y) shaft for that service... Are there any others? Richard |
#35
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PSRU design advantages
Actually I do work in aviation. I am an aviation machinist and aircraft
mechanic, I also work on Allison turbines (hercs and convairs) that drive a gearbox via a shaft. My experience is mostly helicopters but being a fixed wing pilot I want to have my own plane for cross country flights. I don't believe any one person can ever learn everything there is to know about a subject and therefore I am was soliciting usefull information on this subject. Thank you! "Richard Lamb" wrote in message .net... ADK wrote: IF you had to design a PSRU, to drive a pusher propellor via shaft, what would your experience dictate? Thinking along the lines of a gearbelt, chain or gear. Please, I would appreciate the collective experience available on this group. I have decided on the aircraft, but want to make it the most reliable and safest it can be. "ADK" wrote in message news:X6TXf.28774$%H.11944@clgrps13... This is probably going to open old wounds. What I would like is experienced input on the advantages, for economic, efficiency and longevity etc. of different types of redrives. I am leaning towards a cog-belt reducer in a 6 cylinder, liquid cooled, configuration driving a long drive shaft to the prop. The collective experience is zilch = nada = squat = undefined. THAT is what everybody had been trying to tell you. Wait a second. Look around the airport. How many shaft driven propellers do you see? Have you ever seen? If you are heart set on doing it, I sincerely wish you luck. But I can't offer any further advice - 'cuz they ain't none... Richard |
#36
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PSRU design advantages
The 9 cylinder 1820 and 1840 CID radials used on B-17's were geared approximately 16:9. However, your point is well taken, and I also am unable to name any 4 or 6 cylinder engines that have stood the test of time with reduction drives. Continental GO-300 (Cessna 175). Lycoming GO-435 (Navion). -- Geoff The Sea Hawk at Wow Way d0t Com remove spaces and make the obvious substitutions to reply by mail Spell checking is left as an excercise for the reader. |
#37
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PSRU design advantages
Peter Dohm wrote:
"Bill Daniels" bildan@comcast-dot-net wrote in message ... The basics: Piston engines produce more power per pound if they rev higher. (HP = RPM x torque/5252) Propellers are MUCH more efficient if they turn slow. This begs for a PSRU. BUT, a PSRU adds weight, cost and complexity. Resonances, particularly torsional resonances are a real problem. Lots of examples of PSRU's on 12, 14 and 18 cyinder engines Few workable examples with fewer cylinders suggesting PSRU's don't like power pulses. If a shaft has a strong resonant fundamental, don't excite it or lower the fundamental below the input frequency. Tuning a PSRU/shaft/propeller system is like tuning a piano - it's an art not a science. The 9 cylinder 1820 and 1840 CID radials used on B-17's were geared approximately 16:9. However, your point is well taken, and I also am unable to name any 4 or 6 cylinder engines that have stood the test of time with reduction drives. I also believe that tuning any drive system, including a PSRU, is a science--when fully understood. And therein lies the rub: There's plenty left to learn--especially if it must also be light. So, in practice, you are right--it is still an art. :-( Peter Rotax - the 912/914 Jabaru - (but the 6 cylinder will be a better seller - IMHO) Believe it or not, a few VW's with belts. And a couple of Subes with Rotax B boxes scabbed on. The one that DIDN'T work was the Geo Metro 3-banger (broke the crank). But that issue was already known - don't cut off any flywheel on 3 holers. With the full flywheel, the 3 cylinder runs fine. Richard |
#38
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PSRU design advantages
Ian Stirling wrote:
Peter Dohm wrote: snip The 9 cylinder 1820 and 1840 CID radials used on B-17's were geared approximately 16:9. However, your point is well taken, and I also am unable to name any 4 or 6 cylinder engines that have stood the test of time with reduction drives. I also believe that tuning any drive system, including a PSRU, is a science--when fully understood. And therein lies the rub: There's plenty left to learn--especially if it must also be light. So, in practice, you are right--it is still an art. :-( I suspect that electronics help. Instrumenting the shaft, to measure resonances in real time is no longer prohibitively expensive. I suspect a belt PSRU - if properly configured could act to decouple the prop from the engine/shaft somewhat. Add one or more rotational vibrational dampers - fill the shaft with oil? And trim. Best tool available to the amateur is a variable speed strobe - Party Light! That way you can actually look and SEE what's happening. Richard |
#39
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PSRU design advantages
There is nothing that eliminates a long shaft from the design of a
PSRU. Nonbelievers might be advised to consider ship propulsion; long shafts, low cylinder counts, propellers operating in uneven flow, often via a gearbox. Sound familiar? The important issue is torsional stiffness of the shaft, not length. A long shaft can be torsionally stiff or soft, depending on diameter and material. The engineering process will tailor torsional stiffness of the shaft (along with a number of other factors) to adjust natural frequency. The information you need is found in engineering texts, not on RAH. The subject can be complicated, but there are no unknowns. You will find most of the torsional vibration classics listed in the bibliography of Taylor's "Internal Combustion....". Some texts, like Wilson's "Practical Solution.." (the ultimate reference) will be difficult to locate. Try a large university library. The best readily available text (sort of the ultimate primer on all matters vibrational) is JP DenHartog's "Mechanical Vibrations". You can buy it for less than $15 at Amazon. Here is a short list: CF Taylor, "The Internal-Combustion Engine in Theory and Practice", 1966 (vol. 1), 1968 (vol. 2), MIT Press W Ker Wilson, "Practical Solution of Torsional Vibration Problems", 3rd Ed, 5 Vols., 1956, 0412091100, Chapman & Hall JP Den Hartog, "Mechanical Vibrations", 1956, 070163898, McGraw-Hill My compliments to Mr. Christley, whose comment (re frequency) was a sole beacon of accuracy. Dan Horton |
#40
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PSRU design advantages
-----------snip------------
Wasn't the gub'ment, George, but Bell Aircraft. P-39 not only had a drive shaft but a cannon firing thru the psru gearbox. layout of engine, gearbox and cannon at: http://www.home.earthlink.net/~tp-1/p392.jpg So it *can* be done. (The cannon firing thru the prop! ) -------------snip----------- IIRC, the Messerschmidt ME-109 (a/k/a BF-109) was similar--except that the long driveshaft was omitted, the engine was in the "normal" location, and the canon was located in the valley area of the engine. Peter |
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