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buddairbum(at)cox.net
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 Posted: Sun May 04, 2008 6:48 am Post subject: "Over Square, back loading, detuning, underboost-etc. |
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When it comes to big airplanes and radial engines, Randy is THE man. No one
in the universe has more experience both as a pilot of everything military
(radial and otherwise) and teaching people how to fly those. He's the
designated examiner for just about everything military that flies, including
(I believe) B-29's.
On 5/3/08 9:16 PM, "xiaobao" <aihuabao(at)yahoo.com> wrote:
| Quote: |
--- On Sat, 5/3/08, Roger Kemp M.D. <viperdoc(at)mindspring.com> wrote:
>> ... 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
> 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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