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#21
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PSRU design advantages
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$%H.11944@clgrps13... This is probably going to open old wounds. What I would like is experienced input on the advantages, for economic, efficiency and longevity etc. of different types of redrives. I am leaning towards a cog-belt reducer in a 6 cylinder, liquid cooled, configuration driving a long drive shaft to the prop. The collective experience is zilch = nada = squat = undefined. THAT is what everybody had been trying to tell you. Wait a second. Look around the airport. How many shaft driven propellers do you see? Have you ever seen? If you are heart set on doing it, I sincerely wish you luck. But I can't offer any further advice - 'cuz they ain't none... Richard |
#22
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PSRU design advantages
Richard Lamb wrote:
ADK wrote: IF you had to design a PSRU, to drive a pusher propellor via shaft, what would your experience dictate? Thinking along the lines of a gearbelt, chain or gear. Please, I would appreciate the collective experience available on this group. I have decided on the aircraft, but want to make it the most reliable and safest it can be. "ADK" wrote in message news:X6TXf.28774$%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 |
#23
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PSRU design advantages
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. "ADK" wrote in message news:3pGYf.26105$Ph4.10950@edtnps90... IF you had to design a PSRU, to drive a pusher propellor via shaft, what would your experience dictate? Thinking along the lines of a gearbelt, chain or gear. Please, I would appreciate the collective experience available on this group. I have decided on the aircraft, but want to make it the most reliable and safest it can be. "ADK" wrote in message news:X6TXf.28774$%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. |
#24
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PSRU design advantages
My friends who flew the P-39, always said they worried about the drive shaft running between their legs, breaking loose ) Big John `````````````````````````````````````````````````` `````````` On Wed, 05 Apr 2006 13:23:05 GMT, 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$%H.11944@clgrps13... This is probably going to open old wounds. What I would like is experienced input on the advantages, for economic, efficiency and longevity etc. of different types of redrives. I am leaning towards a cog-belt reducer in a 6 cylinder, liquid cooled, configuration driving a long drive shaft to the prop. The collective experience is zilch = nada = squat = undefined. THAT is what everybody had been trying to tell you. Wait a second. Look around the airport. How many shaft driven propellers do you see? Have you ever seen? If you are heart set on doing it, I sincerely wish you luck. But I can't offer any further advice - 'cuz they ain't none... Richard Richard, Didn't the military do this once?? Seems there was the P-39 Aircobra, shaft driven from a rear mounted engine?? Are the gray cells working that far back?? Not that it would be applicable to an experimental, but at least It was once done? George |
#25
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PSRU design advantages
Big John wrote:
My friends who flew the P-39, always said they worried about the drive shaft running between their legs, breaking loose ) Big John `````````````````````````````````````````````````` `````````` On Wed, 05 Apr 2006 13:23:05 GMT, George wrote: Richard Lamb wrote: ADK wrote: IF you had to design a PSRU, to drive a pusher propellor via shaft, what would your experience dictate? Thinking along the lines of a gearbelt, chain or gear. Please, I would appreciate the collective experience available on this group. I have decided on the aircraft, but want to make it the most reliable and safest it can be. "ADK" wrote in message news:X6TXf.28774$%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 Sounds like a legitimate concern to me |
#26
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PSRU design advantages
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. "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 The P-39/P-63 examples can't probably be compared directly with this matter in question. These designs both have a large reduction gear casing in front of the plane. The support structure for this PSRU looks very firm. Perhaps the safety cage type center fuselage structure has something to do with the lack of severe resonance problems? Any known resonance problems with these aircrafts? JP I find myself wondering if, even though the P-39/63 can't be directly applicable to experimental class aircraft, isn't there a lesson to be learned here. The primary shart turns at engine speed, the PSRU is located remotely and the propeller is not transmitting torsional resonant frequency pulses to the shaft. At least not directly. Would a pulse absorbing coupling, such as Molt used, totally eliminate the resonant frequencies in the shaft?? Since the OP was thinking of a remote mounted engine and a long shaft, is this worth considering, since he seems bent on exploring this possibility?? Just my mental ruminatings. YMMV |
#27
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PSRU design advantages
"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 |
#28
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PSRU design advantages
On Wed, 05 Apr 2006 13:56:26 GMT, George wrote:
Big John wrote: My friends who flew the P-39, always said they worried about the drive shaft running between their legs, breaking loose ) Big John `````````````````````````````````````````````````` `````````` On Wed, 05 Apr 2006 13:23:05 GMT, 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 Sounds like a legitimate concern to me If it EVER did, it was a legitimate concern. Did they have quill shaft failures??? *** Free account sponsored by SecureIX.com *** *** Encrypt your Internet usage with a free VPN account from http://www.SecureIX.com *** |
#29
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PSRU design advantages
"Peter Dohm" wrote in message ... "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 You're right. I forgot that there were some successful 9 cyl geared engines. The radials used planetary gears in the nosecase. I like planetaries since there's a lot of tooth engagement to carry the power yet they tend to be compact and light. 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. Bill D |
#30
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PSRU design advantages
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. |
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