Hi Bill, Try this explanation:1. Torque is a direct result
of the
combustion
chamber's volumetric efficiency (rotary or piston
engine). When this
efficiency peaks; torque peaks.

2. The V.E. is mainly governed by the intake system. In
the intake pipe
the rush of air resonates, that is each time the
combustion chamber
intake closes (whether rotary, 2cycle piston or 4cycle
piston) the
air rush stops (sometimes even reverses).

3. This very brief stop sends an energy pulse back up the
pipe toward the
open inlet.

4. # 2,and 3 change with RPM.

5. A perfect length intake pipe for a GIVEN RPM will
contain that energy
and
revert it to push the next charge TOWARD the combustion
chamber.
This is "resonating."

6. This is important: Look at #5 again. The pipe length
that works
perfectly at XXX RPM is not the correct length for YYY
rpm. So, what to
do
Adjustable length intake pipes have been used on racing
engines but
are too cumbersome for aircraft use. So the next best
choice is to
pick an RPM that the engine likes and tune the intake to
operate
there and accept less V.E. at RPM's above and below
that engine
speed.
The aircraft piston engine (big bore/big stroke = lots of
mass moving back and forth large distances) is happiest
at about
2500 RPM and the intake is designed around that.
NASCAR engines
(big bore/ short stroke = lightweight mass moving back
and forth
short distances) are happiest around 8000 RPM and their
intake is
designed around that (put a NASCAR intake manifold on
your family
ride and you will be terribly disappointed)
The rotary engine
(lots of mass but NO DIRECTIONAL CHANGE) is happiest
around
6000 RPM (rotor speed is around 2000 RPM, bearing loads
are
lightest, V.E. is pretty good, vibration is quite low,
power
output vs. engine wear is very good).

So with an engine that
wants to run forever at 6000 RPM that's where
aircraft conversions
are run and the intakes are designed for that speed. To
get back
to a proper propeller speed requires a +/- 40% reduction
box.

Seems like a hell of a penalty until you look at the
whole picture.
Even with the added weight, the power to weight ratio for
a P-Ported
rotary easily surpasses today's standard aircraft
engine.

If you've
ever shock cooled your Lycoming, your repair bill
exceeded the cost
of TWO COMPLETE rotaries. Can't happen with liquid
cooling. Have you
priced a Continental exhaust valve lately Rotaries have
no exhaust
valves. This is only some of why we're here. Stay
with the newsletter,
there are nuggets of valueable info here.

Hope this
affords some more
understanding.
Dave M

I agree with most everything you said Dave - except for
the bit about
aircraft engine intakes being tuned for 2500rpm.I
don't think
they're tuned at all except for easy packaging.Regardless of the
engine type, tuning for 2500rpm will require _long_
runners.

This
site is interesting:
http://www.wallaceracing.com/runnertorquecalc.php
This page has a model for calculating runner specifics.2700 rpm and
360 cu-in in four cylinders (a Lycoming) gives runners 31
inches long.

A similar length pipe would be required for the exhaust.Most
aircraft don't have room for such long runners.The
F1 racers are
probably the closest - with headers-collectors on some of
the O-200's.

They're quite long (24" - a guess), but the
engines turn ~4000 rpm.
Headers optimized to work at the stock 2750 rpm red line
would be
significantly longer.The F1 rules don't allow
diddling with the
intake configuration - otherwise you'd see long intake
spiders too.

The model doesn't really appear to be set up for a
Wankel rotary.A
160 cu-in two rotor (13b) at 6000 rpm calculates to a
14" runner,
which experience has shown is too short.There's
probably something
about the multiple rotor faces sharing the same runner,
and that the
rotor turns at 1/3 of the e-shaft speed that comes into
play - I don't
have that all figured out...It seems like the calculated
runner
length is about 1/2 what it should be.


I would add to #2 above that the reason the intake is so
important to
VE is that on a naturally aspirated engine, only
atmospheric pressure
is available for cylinder filling.I think things look
different if
you have forced induction.

Regards,
Matt-

Matt,
A tuned intake is a function of velocity which in turn is a
function of
intake diameter and length and RPM.
If you have a set diameter and RPM you can work out the
rest.
George (down under)

Or you can just copy this.
Paul Lamar


This discussion is a little over my head (and I currently have the flue)
but I wounder what effect a device such as a standpipe commonly used in
plumbing water systems would have on the resonance of the intakeAs the
intake port is closed, excess air would in part, be diverted into the
stand pipe.As the port opens, it would add to the air going into the
chamber.

For those of you who are not versed in plumbing 101, a stand pipe
is an additional vertical pipe with one end caped and the other
is attached to the water line in the proximity of a valve.It prevents
what is called a hammer noise in the Water line when the valve is
closed quickly diverting the water flow and compressing the air
in the standpipe.

Joel

I'm taking three aspirin, so call me in the morning.

Joel,
The standpipe idea is used on single cylinder dirt bikes. They
came up with the idea of calling it a"Boost Bottle."
Laughable name but the idea is the same. Not sure if it
will help a rotary as the pulses are much closer together,
but the idea has been used before.
Bill Jepson

Its is really a Helmholtz resonator.
Look it up on google.

http://www.dinamoto.it/DINAMOTO/on-line%20papers/risuonatore/risuonatore.html

Late model Porsche engines use the principle.

Paul Lamar

Bill,
Is it true that the optimum inlet speed  fro max VE is between 200 mph and
300 mph  - and in exceeding 600 mph the inlet tube is so full of  pulses it
acts to restrict flow?
George (down under)