Hi Paul,

I've finished my  (13mm) thick butterfly throttles and I'm trying to
decide if an over the top variable induction pipe (runner) system
will have any merit. Near sealevel yes,  but what about up high?

Does air pressure within the airbox affect the optimum length?

Doug in Japan

Frequency = speed-of-sound/wavelength

An alteration in either speed or wavelength will result in an
alteration of the natural frequency.

You can calculate it from this chart.

Why 13 MM ?

Paul Lamar

Paul,

Thanks. I recently found out that the total volume of the air box
and ducts, filter etc. is important. Especially for a turbo charged
engine. Too little and the air resistance goes up so the engine is
starved. Too much and the response time is lowered, or the engine
bogs. For aircraft I would imagine it is better to err on the side
of being to big.

Here is a handy calculator I discovered for the speed of sound calculations.
http://www.sengpielaudio.com/calculator-waves.htm     For simpler
calculation based on temp. only try here.
http://www.sengpielaudio.com/calculator-speedsound.htm  I used this
to determine that at cooler temperatures (up high) the tuned length

As for why the 13mm thick throttle, the short answer is that number
is the minimal thickness that would work without throttle plate
interference. The throttle plate as designed is actually slightly
elliptical. Edges are slightly beveled to reduce air resistance.
I'll fine tune the shape once I put it on the flow bench. Long
answer: Having the throttle directly on the housing and having the
throttle plate swing down inside the inner sleeve is about as close
to the intake port as I could get it in the intake size I wanted. I
explored several variations of slide throttles but was unhappy with
the large amount of real estate it required.

 In the attached pictures:  These pictures are taken before the
parts where polished, painted, and in the case of the throttle,
welded. This throttle shown goes on the PSRU side, the accessory
side throttle is reversed. Thus a coupler join the throttle shaft
together over the center housing. You can see that throttle plate
when closed reaches a smidgen below the throttle plate step bore.
This bore interfaces with a protrusion on the runner collar so the
positioning is correct. (left of picture). Naturally gasket material
will be used. The collar will have the FRP runners bonded to it when
I figure out how to cast them accurately. Probably use the wash out internal
mold idea. The tube on the right is the double O-ring sleeve that
fits within the intake housing bore. Notice the taper on the top
inside.  This is so the  throttle plate clears the edges when it
opens into the 2" ID sleeve. The throttle and the intake runners are
slightly larger in ID than the intake sleeve.  53mm verses 51mm.
This was done to compensate for the cross sectional area loss the
throttle plate creates when fully open. The throttle plate support
shafts were designed in a manner to minimize the cross sectional
area when open.  The central hole will most likely be enlarged so
that the engine may idle from the air entering there. This idling
hole may be a bad idea as it isn't found in traditional plate throttles.

A construction challenge:  The stainless shaft and throttle plate
had to be TIG welded in situ. With a jig and the skill of my
friend's (small dextrous hands), he was able to do a fine job.
Bearings are a hard teflon material, called BEAREE from NTN Bearing
company. Other pictures show the throttle plate in various
positions. Four M5 size studs screwed and sealed into the rotor
housing retain the throttle, the insert sleeve as well as the intake
runners.

Doug in Japan

13 MM is over a half inch thick. Surely your butterfly is not 1/2
inch thick.

When I gave a lecture at the World Motor Sports symposium in Oxford
to the top F1 race car engineers there was a guy from Porsche that
gave a lecture on butterfly valves among other things. Here are a couple
of pictures. I also have an animation but it is 4 meg. You should
have used our low cost and easy to make slide throttle.  I just
finished a turbo engine with slide throttle for a guy in Saipan.

Every wart in the intake manifold comes right out of your pocket in precious
gasoline burn and range.

What were you thinking? :)

Paul Lamar


Variable length intake as per the Le Mans engine is for a broad torque range
in automotive use. For aircraft, it is just more weight, as you will run at a
fairly narrow and consistent RPM range. The throttle plates close to the rotor
housing is also automotive derivative for throttle response. Again not
necessary for aircraft. For my money, I would use a p-port with a similar
aftercooler set-up like Paul shows in his attachments with the single slide
throttle between the turbo and aftercooler.
Between design time, machining and the welding; you have a lot invested. I
hope it works for you.

Dale Davies