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Pazmany PL4



 
 
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  #21  
Old February 26th 08, 06:13 PM posted to rec.aviation.homebuilt
JohnO
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Posts: 120
Default 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  
Old February 26th 08, 09:02 PM posted to rec.aviation.homebuilt
flash
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Posts: 67
Default 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  
Old February 27th 08, 12:03 AM posted to rec.aviation.homebuilt
Morgans[_2_]
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Posts: 3,924
Default 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  
Old February 27th 08, 12:18 AM posted to rec.aviation.homebuilt
[email protected]
external usenet poster
 
Posts: 472
Default 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  
Old February 27th 08, 02:22 AM posted to rec.aviation.homebuilt
Peter Dohm
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Posts: 1,754
Default 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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