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cjpilot710(at)aol.com
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 Posted: Sat May 03, 2008 6:17 pm Post subject: "Over Square, back loading, detuning, underboost-etc. |
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There has been several things mentioned here about the necessity or not of staying "over square". Some are not quite sure at what is happening. I have "lived" with this a good many years and I know that big radials will not last long if you treat them poorly. In fact one of the reasons the bombers I fly stay "in business" is because of the way we fly the engines. Averaging around 300 plus hours a year per airplane - that's equates to about 600 takeoff and landings a year per airplane. If we flew them the way the USAAF did, we'd be changing engines every couple of months. Usually we change one engine per year per airplane. Here is how the problem was written up in Warbird Notes #3 in March 1994, by R.L. Sohn. It is probably the best explanation I've ever seen written.
"Now the cause which we want discuss in this bulletin. This happens when the pilot pulls the throttle back to a very low MP. --------- Under normal conditions the master rod thrust bearing is loaded against the crankshaft from multiplicity of direction as all the pistons progress through their assigned firing order. Remember that all the other connecting rods are linked to this one master rod and the pressures on this master rod journal are the constantly changing resultant of all the pressures exerted by these pistons. The crankshaft is drilled on the thrust side allowing oil access to this area when under power. The heat is carried away with the oil flow. No oil hole is drilled on the anti-thrust side, it's not considered necessary since the hole the thrust side provides constant lubrication from pressurized oil flowing around the bearing. If this series of alternating forces is severely disturbed by a large reduction in MP then the propeller in effect is turning the engine. It might be helpful here to visualize the unloaded pistons trying to throw themselves out the top of the cylinders. In this case the load is continuously applied to this one (anti-thrust side) area of the master rod journal where no oil hole is located. In short order this "squeeze play" situation causes oil (lubrication and cooling ) starvation resulting in failure to dissipate the frictional heat. This rapidly progresses from overheating to self destruction. In some cases during tear down the bleed holes have been found wiped full of silver metal from the multi-layered plating of the master rod bearing"
The Wright can stand up a little better the Pratts because the they have more master rod bearing area. The journal diameter of the 1820 is about 3 1/4" as compared to the 1830's 2 5/8". Both have virtually the same displacement.
Comparing the M-14? There no doubt that the forces and situation is the same. However I do not know the oiling of the M-14. Jill could elucidate better than I on that. I think if you compare engine size to horsepower (I don't how to arthritically do that) I believe you'd find the M-14 is "beefier" for its HP. I know that I fly my M14 the same way I do the Pratts and Wrights.
Jim "Pappy" Goolsby
Wondering what's for Dinner Tonight? Get new twists on family favorites at AOL Food.
[quote][b]
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viperdoc(at)mindspring.co
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| Posted: Sat May 03, 2008 7:50 pm Post subject: "Over Square, back loading, detuning, underboost-etc. |
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Pappy,
Thanks. So my theory according to this excerpt was correct in feeling comfortable in pulling the MAP to idle with the %RPM pushed up.
Now I understand better what is really going on at the Master Rod main bearing.
Doc
From: owner-yak-list-server(at)matronics.com [mailto:owner-yak-list-server(at)matronics.com] On Behalf Of cjpilot710(at)aol.com
Sent: Saturday, May 03, 2008 9:14 PM
To: yak-list(at)matronics.com
Subject: "Over Square, back loading, detuning, underboost-etc.
There has been several things mentioned here about the necessity or not of staying "over square". Some are not quite sure at what is happening. I have "lived" with this a good many years and I know that big radials will not last long if you treat them poorly. In fact one of the reasons the bombers I fly stay "in business" is because of the way we fly the engines. Averaging around 300 plus hours a year per airplane - that's equates to about 600 takeoff and landings a year per airplane. If we flew them the way the USAAF did, we'd be changing engines every couple of months. Usually we change one engine per year per airplane. Here is how the problem was written up in Warbird Notes #3 in March 1994, by R.L. Sohn. It is probably the best explanation I've ever seen written.
"Now the cause which we want discuss in this bulletin. This happens when the pilot pulls the throttle back to a very low MP. --------- Under normal conditions the master rod thrust bearing is loaded against the crankshaft from multiplicity of direction as all the pistons progress through their assigned firing order. Remember that all the other connecting rods are linked to this one master rod and the pressures on this master rod journal are the constantly changing resultant of all the pressures exerted by these pistons. The crankshaft is drilled on the thrust side allowing oil access to this area when under power. The heat is carried away with the oil flow. No oil hole is drilled on the anti-thrust side, it's not considered necessary since the hole the thrust side provides constant lubrication from pressurized oil flowing around the bearing. If this series of alternating forces is severely disturbed by a large reduction in MP then the propeller in effect is turning the engine. It might be helpful here to visualize the unloaded pistons trying to throw themselves out the top of the cylinders. In this case the load is continuously applied to this one (anti-thrust side) area of the master rod journal where no oil hole is located. In short order this "squeeze play" situation causes oil (lubrication and cooling ) starvation resulting in failure to dissipate the frictional heat. This rapidly progresses from overheating to self destruction. In some cases during tear down the bleed holes have been found wiped full of silver metal from the multi-layered plating of the master rod bearing"
The Wright can stand up a little better the Pratts because the they have more master rod bearing area. The journal diameter of the 1820 is about 3 1/4" as compared to the 1830's 2 5/8". Both have virtually the same displacement.
Comparing the M-14? There no doubt that the forces and situation is the same. However I do not know the oiling of the M-14. Jill could elucidate better than I on that. I think if you compare engine size to horsepower (I don't how to arthritically do that) I believe you'd find the M-14 is "beefier" for its HP. I know that I fly my M14 the same way I do the Pratts and Wrights.
Jim "Pappy" Goolsby
Wondering what's for Dinner Tonight? Get new twists on family favorites at AOL Food.
| Quote: | | http://www.matronics.com/Navigator?Yak-List |
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[quote][b]
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jack
Joined: 01 Nov 2007
Posts: 10
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| Posted: Sat May 03, 2008 8:19 pm Post subject: "Over Square, back loading, detuning, underboost-etc. |
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--- On Sat, 5/3/08, Roger Kemp M.D. <viperdoc(at)mindspring.com> wrote:
| Quote: | > ... Now I understand better <<
|
Randy Sohn is surely one of the masters of the radial world, indeed, one of the masters of the legacy aviation world.
There may be some reading this list who don't know his name. He's had a good bit to say about flying and it can be a good idea to search out his comment.
best ...
jack
| Quote: | From: Roger Kemp M.D. <viperdoc(at)mindspring.com>
Subject: RE: "Over Square, back loading, detuning, underboost-etc.
To: yak-list(at)matronics.com
Date: Saturday, May 3, 2008, 11:47 PM
Pappy,
Thanks. So my theory according to this excerpt was correct
in feeling
comfortable in pulling the MAP to idle with the %RPM pushed
up.
Now I understand better what is really going on at the
Master Rod main
bearing.
Doc
From: owner-yak-list-server(at)matronics.com
[mailto:owner-yak-list-server(at)matronics.com] On Behalf Of
cjpilot710(at)aol.com
Sent: Saturday, May 03, 2008 9:14 PM
To: yak-list(at)matronics.com
Subject: "Over Square, back loading,
detuning, underboost-etc.
There has been several things mentioned here about the
necessity or not of
staying "over square". Some are not quite sure
at what is happening. I
have "lived" with this a good many years and I
know that big radials will
not last long if you treat them poorly. In fact one of the
reasons the
bombers I fly stay "in business" is because of
the way we fly the engines.
Averaging around 300 plus hours a year per airplane -
that's equates to
about 600 takeoff and landings a year per airplane. If we
flew them the way
the USAAF did, we'd be changing engines every couple of
months. Usually we
change one engine per year per airplane. Here is how the
problem was
written up in Warbird Notes #3 in March 1994, by R.L. Sohn.
It is probably
the best explanation I've ever seen written.
"Now the cause which we want discuss in this bulletin.
This happens when
the pilot pulls the throttle back to a very low MP.
--------- Under normal
conditions the master rod thrust bearing is loaded against
the crankshaft
from multiplicity of direction as all the pistons progress
through their
assigned firing order. Remember that all the other
connecting rods are
linked to this one master rod and the pressures on this
master rod journal
are the constantly changing resultant of all the pressures
exerted by these
pistons. The crankshaft is drilled on the thrust side
allowing oil access
to this area when under power. The heat is carried away
with the oil flow.
No oil hole is drilled on the anti-thrust side, it's
not considered
necessary since the hole the thrust side provides constant
lubrication from
pressurized oil flowing around the bearing. If this series
of alternating
forces is severely disturbed by a large reduction in MP
then the propeller
in effect is turning the engine. It might be helpful here
to visualize the
unloaded pistons trying to throw themselves out the top of
the cylinders.
In this case the load is continuously applied to this one
(anti-thrust side)
area of the master rod journal where no oil hole is
located. In short order
this "squeeze play" situation causes oil
(lubrication and cooling )
starvation resulting in failure to dissipate the frictional
heat. This
rapidly progresses from overheating to self destruction.
In some cases
during tear down the bleed holes have been found wiped full
of silver metal
from the multi-layered plating of the master rod
bearing"
The Wright can stand up a little better the Pratts because
the they have
more master rod bearing area. The journal diameter of the
1820 is about 3
1/4" as compared to the 1830's 2 5/8". Both
have virtually the same
displacement.
Comparing the M-14? There no doubt that the forces and
situation is the
same. However I do not know the oiling of the M-14. Jill
could elucidate
better than I on that. I think if you compare engine size
to horsepower (I
don't how to arthritically do that) I believe you'd
find the M-14 is
"beefier" for its HP. I know that I fly my M14
the same way I do the Pratts
and Wrights.
Jim "Pappy" Goolsby
_____
Wondering what's for Dinner Tonight? Get new
<http://food.aol.com/dinner-tonight?NCID=aolfod00030000000001>
twists on
family favorites at AOL Food.
|
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know-it-all with Yahoo! Mobile. Try it now. http://mobile.yahoo.com/;_ylt=Ahu06i62sR8HDtDypao8Wcj9tAcJ
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Rob Rowe
Joined: 10 Jan 2006
Posts: 124
Location: Berkshire, UK
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| Posted: Sun May 04, 2008 8:35 am Post subject: Re: |
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FYI - extracted the following master connecting rod lubrication description from the M14P manual ...
“The crank-pin has a radial hole to supply oil from the crankshaft rear to its front section and two radial holes to feed oil to the master connecting rod bushing which are at an angle of 60° from the axis of symmetry in the direction of crankshaft rotation”
... and compiled the attached JPG file composite of the associated schematic diagrams from the same source (which won't be distributed with the daily digest email but can be found at ... http://forums.matronics.com/viewtopic.php?t=43148 )
I'll leave it to the engineers amongst you to determine the significance of this description.
Rob R.
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mark.bitterlich(at)navy.m
Guest
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| Posted: Mon May 05, 2008 1:05 pm Post subject: "Over Square, back loading, detuning, underboost-etc. |
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Jim, just a comment. I am not disagreeing with anything you have said
or the quotes from others with far more round engine time than my own.
That said, the M-14 has been flying in Unlimited Aerobatic Competition
for years. I happen to have the privilege of working with (and on) the
M-14 engines mounted in a few of the most heavily and most outrageously
flown aircraft in this country. In most every M-14 engine I have had
experience with, the failure items usually consist of front engine seals
(gone bad from extreme loading in gyroscopic maneuvers... Looks like a
prop seal, but isn't!) some cracked piston rings, a lot of #2 cylinder
low compression gripes, many mag gripes, bent rods from oil in the
cylinders, but not one ... Not one single occasion of bad internal
bearings or any kind of silver in the screens. These engines are
usually flown with two power settings. WFO, and yanked to zero. The
only "normal" engine use is flying to and from the locations of the
competitions or air shows. Possibly we are not into the range of total
operating hours to see this kind of wear and failure yet? Most of the
aerobatic guys I know change engines at around 1000 hours even if they
are running OK.
Point is, I understand and concur with every word you have said, and
like yourself, I am wondering if there is anything different or special
about the M-14, because it sure is not failing like the American made
round engines would if treated the same way. Further, I believe that
the M-14 weighs less than any other American made engine for the
horsepower it produces. It is also 'geared' and turns higher RPM than
most made American Radials too.
I believe someone ought to contact Russian Master Mechanic Vladimir
Yastremski and ask him about this issue. I honestly believe he would
know even more than Jill or George about the matter.
Just a thought.
Mark Bitterlich
--
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