I just spent some time looking on the internet for negative comments
about JB Weld. I did not find any. One testimonial, a guy repaired
a gouged cylinder wall and ran the engine for several hundred
hours. Tear down showed no change or deterioration in the JB
Weld. Also, JB weld claims the product is good to 500 degrees.
Based on what I have learned today, I think my skepticism about JB
Weld was misplaced. Jerry
Jerry,
If your considering manufacturing P-ports, you might consider a slightly
tapered shrink fit of the tube within the housing with some high temp
epoxy
to take up and imperfections in the machining.i.e. heat-up the housing
and
freeze the tube - his would take some experimentation to find the most
suitable size whereby you can still get the tube inside the housing and
this
would all need to be done on a CNC for the accuracy needed.
This would be the most ideal method of sealing, but how practical it
would
be I'm unsure!
Just a suggestion, as it's something I'm considering..
George ( down under)
Hi George;
I did my Pports as you are suggesting with the inserts all the way
through with
match tapered (smaller towards the inside of the housing) insert and
bored hole
and an interference (hot rotor-cold insert) press fit with epoxy on the
prepared insert
bored hole.
One advantage is that it should never fall into the engine.
One disadvantage is that the 2" ID is rounded to 2.125" on the rotor
surface - I am
not too concerned about the slightly reduced apex seal support as the
edges are
beveled to soften the apex seal landing back onto the rotor surface.
This measuring and fitting took significantly longer by hand using a
basic mill, lathe,
digitial calipers and sandpaper...and lots of measurements.
The interference can be figured out easily enough looking up the
material and
temperature differential you plan to use between the housings and
inserts.
One press fit did take a little more convincing with a mallet and wood
block ;)
I machined the inserts as well, finding the correct sized tubing could
save a lot of work.
Without starting an epoxy war...
One of my biggest concerns is the ability of any epoxy to bond to
aluminum with less than Boeing processes.
Any bond can fail for a variety of reasons - poor surface prep, surface
contamination, poor epoxy prep,
differential thermal expansion at temp, chemical resistance, vibration,
thermal stability at higher temp (say 300F),
epoxy cure shrinkage, and for northern residents - differential thermal
shrinkage over the winter months.
In any case, some sort of mechanical assistance/backup to the epoxy is
not a bad idea - threading, brazing,
welding, press fit, pins, extra mechanical bond area (grooves, etc...)
to insure the insert does not fall into the
engine catastrophically without warning. A leak would be annoying, but
hopefully less dramatic and with warnings...
Take a look at an interesting article by Bill Husa regarding bonding:
http://www.oriontechnologies.net/Documents/bonding.pdf
To summarize - sanding the aluminum surface with epoxy already on the
surface may help adhesion by removing
and preventing the oxide layer from reforming.
Cheers
Cary
Cary,
I was thinking of a slight taper on both ends with the tube being
mechanically locked into position and the thin high temp epoxy only being
a
( surface imperfections) void filler, in the tapers and of course the
water
cavity.
This would be extremely difficult to do as your measurements would need to
be exact AND you would get only one go at it.
The benefit would be that you would never have to worry about the tube
moving either way.
I have looked at the threaded inserts, as done by X-Treme Rotaries, but
others suggested that it wasn't optimum.
Is nothing ever easy!!
George ( down under)
Anodizing or etching improves the bond but IMHO it is not necessary.
However some very small groves on the OD of the tubing
about .020 inches deep would also lock it into the housing.
If one were worried about the bond use some JB weld to
bond three pieces of .065 thick aluminum together that
have roughly two square inches of contact area. Say two inches
long by 1 inches wide. Say something like this.
Hole
__________________
^ ___________________
__________________ ^
^ -------------- Hole
Hole
You need three pieces to load the bond in pure shear to emulated
the pure shear the tube would experience in the bored housing.
Two pieces would cause a peeling action due to out of axis
loads.
Then use this and an engine hoist to pick up something heavy.
My guess is the aluminum will fail before the bond shears.
Paul Lamar ...No rotor no motor.
Paul,
I'm sure the JB weld is good as suggested, it's the temp cycles i.e.
expansion and contraction that I worry about. It has been suggested to me
that any P-port which depended upon bonding of the materials alone, will
eventually leak. It was suggested that a mechanical tapered lock as I have
explained would be the optimum solution. However this may be extremely
difficult given the limited space in question - might even be impossible.
The only way I can see it being successfully done is with CNC.
I'm not saying that what you propose or what Jerry is doing isn't good
enough, it may well be sufficient for our purpose - it's just you hear so
many things from the experience racing crowd. Perhaps I'm overly concerned,
which is one of my idiosyncrasies.
George ( down under)
If you are concerned just tig tack weld it in.
Paul Lamar
Paul,
George hit the nail right on the head. The issue isn't will the insert move
or how strong the holding force of the epoxy is. The issue is will the
epoxy adhere to all surfaces well enough to make a waterproof sealing that
will last under the rigors an aircraft endures.
A press fit makes sense and if done like Cary suggested will seal. A flange
welded onto the outer part of the insert held down to the housing with a
several screws ala Everett Hatch makes sense as well. I wonder if he had
any O rings or gasket material under the plate as well.
A screw in fitting should be easy to thread seal as well. Does Mazdatrix tap
the inner liner only? If the inner and outer part of the pipe had proper
seals then JB Weld would not be an issue or even be needed.
I see the light on the hole shape as Aubrey rightly pointed out, aviation
needs would dictate a shape that is easiest on the seals. Thanks for
pointing that out.
More importantly concerning all the recent discussion is unless we know and
use the R26B's port timing, port shape, manifold ID sizes, and lengths,
slide throttle hole shape, third plug etc. then the quest "to copy the
Lemans engine exactly" is counter productive and their data is only ballpark
for us. Or we try to find our own way that fits aviation needs. In that
case Everett Hatch or Mistral Corp. is the role model we need to be
emulating not a Lemans engine.
Perhaps it finally dawned on me that the Lemans winning car didn't need to
fly more than a few inches AGL:)
Respectively yours
DougFir
You are now talking big bucks for a mill that can thread internal
holes. Not something you can do on a lathe. The simple system
will work fine if you pressure test the p-port tube before
you assemble the engine. However this is a free country
spend as much money as you like :)
"In that case Everett Hatch or Mistral Corp. is the role model
we need to be emulating not a Lemans engine."
Fine if you want to limit the HP to 200 HP in the case of Mistral
and 215 HP in the case of Power Sport. With slightly worse BSFC
I might add.
Intake systems are high speed aerodynamic devices. Why add drag?
Would you purposely add drag to your airplane for no reason?
Would you get lower MPG on your airplane if you added drag?
Paul Lamar ...No rotor no motor.
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