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#21
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Pazmany PL4
On Feb 26, 2:46*pm, (Drew Dalgleish)
wrote: On Tue, 26 Feb 2008 03:00:47 -0800 (PST), JohnO wrote: On Feb 26, 8:23=A0am, cavelamb himself wrote: Beryl wrote: wrote: On Feb 25, 10:58 pm, flybynightkarmarepair wrote: I've since heard from Veeduber (who knew Pazmany, and flew out of the same airport as the prototype) that you could smell the first ship before you could see it, as it burned, errr flew off the first 40 hours with the belts constantly slipping. ------------------------------------------------------------------ Well... mebbe it wasn't quite that bad... :-) =A0But with multiple vee belts it's impossible to keep ALL of them at the same tension. =A0The loosest of them would slip and there was a definite pong of hot rubber after every flight. Eh? I can't visualize it. Either all, or none, slip. Nope. =A0That's not how it works, Beryl. Oh, maybe if all the belts really were teh exact same size. Or if the pulleys were really exactly parallel. In the real world neither of thoese little details ever work out - quite that exactly. The biggest one slips. How can you tell which is the biggest one? Easy. It's the one that slips! As tehy say, YMMV... Richard- Hide quoted text - - Show quoted text - Caveman, you cannot have one belt slipping and not the others. Think about it - the pulleys on each shaft are all the same size and rotating at the same speed. You can only have slip if one pulley is rotating at a different speed to the other. If one slips they *must* all slip. The longest one slips on both pulleys.- Hide quoted text - - Show quoted text - Are these belts zero stretch? If they are then I'd agree with you. The only zero stretch belts I am familiar with are kevlar reinforced toothed belts running on cogs. As long as the belts in the original question are stretched so that the longest one is now the same length as the shortest one there can be no slip. |
#22
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Pazmany PL4
Peter,
It really doesn't matter WHERE in the lineup the longest belt is. You can have two, or "very many", and absolutely none of them will be the exact same length. One WILL be longer than all the others, and (by very keen observation it will be also found) one of them will be shorter than all the others. Always, one will carry more torque, horsepower, heat, friction, wear (or your malady of choice) than others and share the rest of the difficulties among its companions, and will lead to premature failure of one belt or another. Those difficulties, along with uneven stretch pattern among the individual belts - thus making it hard to maintain proper tension on each and every belt in the setup, is what gave rise to the new style of belts and pulleys. Even pulleys that are quite carefully manufactured will still have the grooves nearly exactly same angle and depth and diameter- but never exactly. It is actually kind of like shooting fish in a barrel with a shotgun. You have just got to wait and see what comes to view after all the smoke clears. The plane and installation in question did not take advantage of the "poly-V" single belt with multiple grooves - much like the serpentine alternator belt on your 1980 F-150. And the "cog" type belt, as in timing belts and synchronized drives was not an option then, either. Multiple vee-belts were a compromise solution, and the difficulties associated with that solution were what came along with the perceived benefits, like rpm, power, weight, cost. Flash "Peter Dohm" wrote in message . .. "Beryl" wrote in message ... wrote: On Feb 25, 10:58 pm, flybynightkarmarepair wrote: I've since heard from Veeduber (who knew Pazmany, and flew out of the same airport as the prototype) that you could smell the first ship before you could see it, as it burned, errr flew off the first 40 hours with the belts constantly slipping. ------------------------------------------------------------------ Well... mebbe it wasn't quite that bad... :-) But with multiple vee belts it's impossible to keep ALL of them at the same tension. The loosest of them would slip and there was a definite pong of hot rubber after every flight. Eh? I can't visualize it. Either all, or none, slip. I must admit that I am having a little trouble visualizing this one as well--unless that loosest belt was either the farthest from the engine or the farthest from the prop. In those cases, I have no trouble at all. Peter |
#23
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Pazmany PL4
"Drew Dalgleish" wrote The longest one slips on both pulleys. Think about it for a moment... If one belt is a little longer, it would not be able to carry as much power, because it is not as tight as the others. The others tight belts will carry nearly all of the power, up until the point where they can not carry all of the power. Then the tight ones will start to slip. If the long belt is not able to carry power, but the short tight ones can carry all of the power being produced, then there will be no slippage. It is counter intuitive, but that is the situation. If there are 4 belts, and three can carry all of the HP, and the 4th one is loose, it will not slip. It will not be carrying any power, though. If all 4 belts have to be pulling equal load to be able to carry all the HP being produced, and one belt is loose, then the tight 3 will slip, because the 4th loose belt can not carry its share, and is slipping. In my experience of multi V-belt farm type equipment, if you start with 4 new identical belts, and they are a well matched set of identical lengths, they all will pull evenly. If one is loose, they will slip like I said above, and will often times stretch to be more closely matched and start pulling more evenly, if there is enough tension to pull them back tight, and you do not completely glaze the belts from the initial slipping. I bet the multiple V-belt reduction unit is running at a very high percentage of maximum HP recommended by the belt manufacturer. It would be more likely to smell like burned belts than most farm type applications, where the loads are kept more conservative by just adding more belts. -- Jim in NC |
#24
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Pazmany PL4
On Feb 26, 12:02 pm, "flash" wrote:
....... What he said. Plus the fact #4 ovaled out quick like a bunny as the asymmetric load was increased (ie, trying to offset the belt slippage) ... which also wore out the lower pulley. The craziest part was that Walt Mooney had similar problems with the Crosley (sp?) powered Mite... and he was standing right there :-) -R.S.Hoover |
#25
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Pazmany PL4
"Morgans" wrote in message
... "Drew Dalgleish" wrote The longest one slips on both pulleys. Think about it for a moment... If one belt is a little longer, it would not be able to carry as much power, because it is not as tight as the others. The others tight belts will carry nearly all of the power, up until the point where they can not carry all of the power. Then the tight ones will start to slip. If the long belt is not able to carry power, but the short tight ones can carry all of the power being produced, then there will be no slippage. It is counter intuitive, but that is the situation. If there are 4 belts, and three can carry all of the HP, and the 4th one is loose, it will not slip. It will not be carrying any power, though. If all 4 belts have to be pulling equal load to be able to carry all the HP being produced, and one belt is loose, then the tight 3 will slip, because the 4th loose belt can not carry its share, and is slipping. In my experience of multi V-belt farm type equipment, if you start with 4 new identical belts, and they are a well matched set of identical lengths, they all will pull evenly. If one is loose, they will slip like I said above, and will often times stretch to be more closely matched and start pulling more evenly, if there is enough tension to pull them back tight, and you do not completely glaze the belts from the initial slipping. I bet the multiple V-belt reduction unit is running at a very high percentage of maximum HP recommended by the belt manufacturer. It would be more likely to smell like burned belts than most farm type applications, where the loads are kept more conservative by just adding more belts. -- Jim in NC Thanks Jim, That is all in keeping with what I had always understood, and also makes a great point about conservative versus optomistic designs. Peter |
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