B: RE: RE: RE: High speed descents

[James Averett]

Don't the forces on the rod bearings reverse every revolution on a four cycle
engine (normal aspiration) anyway?  During the intake stroke the piston is being
pulled down the cylinder, while during the power stroke the piston is pushing
the rod.  Am I missing something?

Jim Averett
J35 IO550
TS36
Texas Hill Country


-----Original Message-----
From: beech-owners-bounces at beechcraft.org
[mailto:beech-owners-bounces at beechcraft.org] On Behalf Of Frisch, Josef C.
Sent: Monday, July 09, 2007 11:41 AM
To: beech-owners at beechcraft.org
Subject: B: RE: RE: High speed descents

Temps were mid 300s. (hottest maybe 360). I'm not too concerned about shock
cooling as such, but I thought at too low a power setting the forces on the
pistons reversed (inertial forces become > gas pressure forces) which could lead
to bearing problems - but maybe that is an OWT. Assuming you don't cool too
dramatically quickly, can you reduce power to idle in a fast descent?

--- Joe Frisch




-----Original Message-----
From: beech-owners-bounces at beechcraft.org
[mailto:beech-owners-bounces at beechcraft.org] On Behalf Of Ed Livermore
Sent: Monday, July 09, 2007 9:34 AM
To: beech-owners at beechcraft.org
Subject: B: RE: High speed descents

Joe: What temp was your most hot cylinder prior to descent? If it was in the
mid 300s or lower, I doubt there was any danger of shock cooling. My
understanding of that peril is that the hottest cylinders should be more
than 400 degrees before it becomes a real risk. As they say in Ada, it's
hard to shock cool what was never hot to begin with.

ed

-----Original Message-----
From: beech-owners-bounces at beechcraft.org
[mailto:beech-owners-bounces at beechcraft.org] On Behalf Of Frisch, Josef C.
Sent: Monday, July 09, 2007 12:29 PM
To: beech-owners at beechcraft.org
Subject: B: High speed descents

Flying into San Jose yesterday visual approach straight in, at about 6000'.
ATC had kept me high (well above the ILS glide slope) before clearing me for
the visual to 29, maintain best forward speed.  I did my usual of reducing
the power quite a bit (21" 2100, 8gpm LOP), descending in the middle of the
yellow arc (about 175 IAS - it was smooth air), then at about 2000', level
off, reduce power some more (15", 2300, now ROP - ready for landing), gear
and flaps out, descend like a greased safe to the runway. 

It worked, and I don't think was particularly hard on the plane, but the
passengers kissing the ground after we landed might be a hint that it wasn't
exactly an elegant approach. (with gear and flaps out, low power and 100
kits, the Bonanza descends on a glide slope the space shuttle would have
difficulty matching). 

What do people recommend for this sort of situation. I could put the gear
down early - but that limits me to gear speed (143kts in my plane), and I'd
need to keep in quite a bit of power even for that speed. I could have
reduced power more in the fast descent - but I don't know how low in power I
can go without over-cooling the engine. 


Of course I can just tell ATC that at this descent angle my best forward
speed is 135 kits (comfortable in the steep descent with gear out), but I do
like to help them out as much as I can. 


--- Joe Frisch


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