"lehanover@aol.com"
<lehanover@aol.com> to Rotary
Hide options  8:10 am (5 hours ago)
From: lehanover@aol.com <lehanover@aol.com> Mailed-By: lancaironline.net
Reply-To: Rotary motors in aircraft <flyrotary@lancaironline.net>
To: Rotary motors in aircraft <flyrotary@lancaironline.net>
Date: May 2, 2007 8:10 AM
Subject: [FlyRotary] Re: Throttle body size/ other "Paul" issues
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garbled?
When the TB is opened suddenly from idle or near idle, the the very
low pressure inside the manifold is replaced by a sudden inrush of
local air pressure. So should the local air moving through the
manifold not contain enough fuel to provide a viable fuel/air mixture,
the engine starts to die.

But, as you have noticed, the situation seems worse than that. Not
just a stumble.

At very low throttle openings, the available air for cylinder filling
is far below the actual displacement of the engine. So, the amount of
air available to compress before combustion is also very low, so, the
effective compression ratio at idle is likewise very  low.  Just fine
for running  smoothly at 700 RPM and little to no load.

So now we slam the throttle open, the inrush of air roars down the
runners and into the chambers with far less than an ideal mixture, and
what is the effect on cylinder filling for the next revolution?

Why it is outstanding. Maybe over 100%. And it is too lean to light.

So when you see that old guy in the Champ, who always kills the mags
and goes to full throttle at the same time, as he was told to do back
in 42,
what is he doing? He is going from a very low cylinder filling idle
with low effective compression ratio, with a carb that has no
accellerator pump,
or, very little accellerator pump, to great cylinder filling and a
high effective compression ratio and poor to well over lean mixture,
and pop pop. The engine stops in two blades with little to no fuel in
the cylinders.

And its the original engine, and it has good compression, and its no
use telling him otherwise, because he learned it that way, and that
way it will stay.

Same thing for the rotary. You come in a bit hot, with the power
(throttle all the way closed) off and in a beautifull forward slip,
and it is going well but a bit too well as it looks like touchdown
will be just a hair short of the numbers, with your moron friends
watching who will settle for nothing short of a great landing, you
snap out of the slip right on the centerline, and after waiting a bit
too long you pop open the throttle to extend just a bit, and you get
nothing at all. So then a bunch more throttle and nothing, and just as
the mains touch a bit too hard, the damn power comes on like a top
fuel dragster, and you fly down the centerline a hundred yards, to the
same landing you commited at the end of your first solo, 43 years ago.
(snip)

Sounds like we could use a TPS on our planes...