- Dec 26, 2021
- Reaction score
- Kawerau, New Zealand
here is a possible sleeved folding scheme, where the tail cone is a convergent annulus around the centre cone.Hi Owen,
Yes, I have been thinking about something like an Archimedian screw - with variable pitch as the passage progresses along the pipe.
First I need to understand - what length and diameter of header pipe are you planning? Do you have a design of expansion box already worked out?
If not, this guide seems straightforward to design one.
As gases do not really appreciate cones and tubes, just flat planes that they reflect off, the "spiral" tube should be pretty much OK as would a rectangular tube. In simple terms, the mean diameter of a spiral tube would be akin to the length of the middle of the spiral chamber - that is really just a rectangular tube wrapped into a spiral. But as the cross-section needs to change, the change of pitch of the screw alters the length of one side of the rectangle - thus increasing or reducing the CSA, and simulating the expanding and reducing cones of a twin-cone expansion box.
So I understand you are planning on a 60cc, engine, 6300rpm as the tuned speed. (I may get this completely wrong, but please bear with me?).
we can calculate closely the pipe length. The formula for determining the length is:
Lt = (Eo x Vs) / N English OR (83.3(Eo x Vs)) / N Metric
Lt = tuned pipe length, in inches OR millimeters
Eo = exhaust open period, in degrees
Vs = wave speed (1700 ft/sec OR 518.16 Meters/sec at sea level)
N = crankshaft speed, in RPM
83.3 x (120 x 518.16)/6300 = 822.1mm.
I see the side view shows a much shallower convergent angle for the length, even though the annulus starting
area should be very close at 1/2 r wide.
A fairly long slotted or perforated area is needed for the transfer to the muffler stage.
How do you think this would work?
Will it actually reflect the main sonic pulse?
I will calculate some actual lengths.
Thanks for the google search-I downloaded or copied lots of images from this.
If I can keep the centre cone to 72 mm, then the overall diameter will be 110 mm., which is probably OK.
Thinking about return pulses- unless 45 degree cones are used, the return pulses will bounce around quite a bit.
***************** TP60 engine mods are coming along well.
I will turn the barrel and piston around again, to make the Cool-side the combustion thrust side.
The ring land above the exhaust is overloading, and wiping aluminium above the exhaust.
This may be caused by insufficient piston support beside the exhaust, or piston rocking.
Fixing the cold side should reduce rocking.
It will be interesting to see how the inserts stand up, and whether J-B can be used as a piston skirt coating.
The alternate Devcon etc "plastic metal" options seem to be only rated to 120 degrees, vs around 200 degrees C for J-B.
J-B seems to have a gritty surface texture.
It doesn't seem to erode piston rings though.