brian
Joined: 02 Jan 2006
Posts: 643
Location: Sacramento, California, USA
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 Posted: Fri Apr 07, 2006 5:40 am Post subject: Firewall fuel shut-off (was: glide ratios |
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Jerry Painter wrote:
| Quote: | I agree that flipping the mag switch on and off is probably not a good idea.
Imagine the inertia of the huge prop on a 4360, or even on a CJ or -52, and
the loads from instantaneous full power torque reversals. I remember seeing
pictures several years ago of a CJ that had a sudden in-flight engine
stoppage. The crankshaft was twisted a whole bunch by the prop inertia
(though it remained attached--splined shaft, YMMV, esp w/flanged shaft).
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But that is not what we are talking about here. You are not getting a
sudden stoppage of all the moving mass in the engine and prop. They
continue to turn normally and none of that rotating momentum is
transferred to the airframe as it would be if the engine seized. All you
get is application and removal of the normal engine operating torque,
something you get whenever you move the throttle from closed to open and
back again. It just happens a little more quickly. If it causes damage
to your airplane then you were living on borrowed time anyway.
Ever stomped the throttle in your car to the floor suddenly or
completely removed your foot from the throttle suddenly? Same thing. It
doesn't break your car and it won't break your airplane either.
| Quote: | WWI rotary engines were low-horsepower, low-compression and though they had
lots of engine rotating mass, also very low propeller mass and the
crankshaft was firmly attached to the firewall, so no great opposing forces
to be absorbed like a "normal" airplane engine.
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The rotating mass of the Gnome rotary even with a "low-mass" prop (I bet
that huge wooden club probably massed as much as our current crop of
props) is *HUGE* compared to our engines as the entire case is rotating
along with the prop, pistons, rods, cylinders, heads, valve train,
exhaust, etc. Only the crank remains stationary. That thing had
*enormous* rotating mass. That they could turn the mags on and off with
impunity tells you that this approach is not likely to break your
airplane or engine.
| Quote: | My guess is the reason we shut down with ignition (esp HS-6/A) and full
throttle advance is that pulling the mixture won't shut the fuel off
sufficiently to obtain clean shutdown--a function of carburetor design. A
little residual fuel could result in dieseling, kickback and engine damage.
Again, what works for one engine, even with similar systems, may not work
for another.
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There is no idle cut-off circuit in the Chinese pressure carb. The
mixture control is not intended to shut the engine off. ICO is actually
an additional valve that completely turns off the flow of fuel to the
engine.
--
Brian Lloyd 361 Catterline Way
brian-yak at lloyd dot com Folsom, CA 95630
+1.916.367.2131 (voice) +1.270.912.0788 (fax)
I fly because it releases my mind from the tyranny of petty things . . .
- Antoine de Saint-Exupery
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_________________
Brian Lloyd
brian-yak at lloyd dot com
+1.916.367.2131 (voice) +1.270.912.0788 (fax)
I fly because it releases my mind from the tyranny of petty things . . .
- Antoine de Saint-Exupery |
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