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Sam,
Things are a bit busy here - 2 funerals, and now
out-of-state company coupled with next week's vacation.
I believe Tracy's design works because his bells
are within 3/4 inch of the plenum box wall. I believe he is getting a
reflected compression wave off the wall that reenters
the intake pipe it came out of. I have not done the math but I believe the
total intake lenght from rotor face to wall and back
should be the same as the length sound would travel during the time period
starting when the rotor closes the intake port and ending when the next intake
cycle is about 3/4 closed.
An example would be as follows:
Shaft rpm = 6300 rpm
Rotor rpm = 2100 rpm, 360 deg/rev X 2100 =
756000deg/minute.or 75600/60 = 12600 deg/sec.
The rotor turnes 1/3 of a rotation going from
intake closed to next intake closed. ( on the same rotor).
1/3 X360 = 120 deg of rotation.
120 deg/12600deg/sec = 0.0095238sec.
But I want the reflected wave to get there about
3/4 thurough the intake cycle. We need to back up the intake angel 1/4 of
the total time the intake is open.
I don't have the intake degrees here but assume it
is 60 deg.
1/4 X 60 deg = 15 deg.
120 deg - 15 deg = 105 deg of rotation for the wave
to leave the rotor face, go through the tube, bounce off the far wall and return
to the rotor arriving when the intake is 3/4 through the intake
cycle.
Using 105 deg/12600deg/sec = 0.00833
sec.
Using 1100 fps as the speed of sound -
1100fps X 12 in/ft = 13200 in/sec.
The total intake length would be 13200 X
.00833 / 2 = 55 inches.
If you use the 3 rd. bounce of the compression wave
off the plenum wall the intake would need to be 1/3 X 54 or 13.74 inches
long.(most of the car engines that used tuned intakes used the 3 rd. bounce from
what I've read)
If the speed of sound is 1100 f/sec.
----- Original Message -----
Sent: Tuesday, July 20, 2010 11:03
AM
Subject: Intake
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I have been up in Michigan for awhile on vacation and the sad thing
is I had to drive. Last weekend I spent hours staring at the plane and
taking measurements trying to figure out how to duplicate Tracy's
Intake design and how to fit it in our cowling. Tracy mentioned that he
has a total runner length of 11.25 including what's in the block. Block
length is close to 3", am I reading this correctly? What is driving this
design is the lack of space in the forward most intake port. To reach
the length of 11.25 we're looking at 8.25" of tubing from the block. I
have tried various radius tubing only to find out that it
will hit the cowling somewhere in the design. If I end up with a
straight tube design I can fit a 7.5" tube and leave enough room for a
.75 distance between the bell mouth and plenum box. This will leave a
total of .75" to 1" short of 11.25", what effect it will have? I don't
know. Had you had a chance to verify Tracy's design yet? I plan on
machining the intake plate this weekend and fitting the tubing. I
appreciate you trying to reach me but it seems we can never get in touch
with one another, I'll try to call you later to see what you have come
up with, take care.
Sam |
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