Richard Konnen wrote:
Paul,
This may be an off question, do the length make a difference depending
on
the amount of draw ? What I mean is the amount of vacuum increases or
decreases with a combination throttle position and RPM, at least that has
been my understanding. With this in mind couldn't a vacuum and spring
operated system work instead of hydraulics?
Richard Konnen
I don't think so. Only in so far as the speed of sound changes with
air density. It mostly changes with temperature as I recall.
Aircraft engines run at wide open throttle 98% of the time anyway.
Paul Lamar
Dan Ruggirello wrote:
Paul, I think your answer is for the question "Will the standing wave
frequency change depending upon the air flow rate through the tube?"
But I think Richards question/idea was different. I believe the idea can
work with a vacuum diaphragm mechanism or using the flow forces acting on
the tube to change its length by compressing a spring with the correct
stiffness. It would take some trial and error, but once it is worked out, I
like it for a production idea. Nothing to adjust. The pilot already has
scads of other stuff to monitor.
Which flow forces? Do you mean the low pressure created as the air flows
over the bell and into the runner? If so that would tend to elongate the runner.
I am not sure that would be the signal you want. The optimum
length is not a function of air density or MAP and those signals would be.
The main signal you want is RPM regardless of the actual mass flow into
the runner or the MAP. What we are attempting to do here is optimize
volumetric efficiency at all mass air flow rates at specific RPMs.
The other problem with any kind of spring is the force applied
to the runner is not evenly distributed around the base of
the runner and therefore it would tend to cock the runner in its
housing. In the case of hydraulic pressure the force IS evenly distributed
around the base of the runner. It is not as trivial as it looks.
The advantages of the hydraulic actuation are somewhat subtle. PL
I thought of another idea as well that has the advantage of a stationary
tube inlet but it would need to make a 180 degree bend. The trombone slide.
It could use Paul's hydraulic cylinder idea or a vacuum actuated system.
Packaging could be tricky.
I guess while we are on this subject, what would be an optimum termination
for a NA system? If the tubes are the correct length, how would you avoid
making a dynamic chamber if you are using a single throttle body? Or would
you use multiple throttle bodies?
Dan--
The big difference between a plenum and a dynamic chamber is the
volume. If the volume is equal to or greater than the displacement
of an equivalent four cycle engine it is a plenum. Rule of thumb.
Interaction between rotors should be minimal. The 13B two rotor pumps roughly
the same amount of air as a 160 cubic inch four cycle piston engine.
Therefore the plenum should be 160 to 180 cubic inches.
The dynamic chamber is little larger than a section of the pipe.
Really it is just a T.
A single throttle body on an adequately large plenum should work but
perhaps not as well as a separate slide throttle for each runner as
used on the Lemans engine.
Paul Lamar
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