Charlie: I designed my intake
plenum out of 125 mm (5 inch) irrigation pipe as a mould
and covered it (rolled) it with 8 layers of bidirectional
glass cloth.
The end cap on intake side for
the throttlebody is 8 mm fenolic sheet that is covered
with glass cloth to use as a hard point to bolt the TB
(throttlebody)The other end cap is roundshaped to optimize
waves "bouncing" inside the plenum.
The total volume of the intake
runners from the rotary surface to the bell mouths must be
calculated.
The volume of the intake plenum
must be 2,5 x intake volume if the intake runners.
I has p ported my 13B with 2 x
45 mm inside diameter runners.
For the best VE ( volumetric
efficiency) the "proof is in the poeding " to tunned the
length of the intake runners.
Don't know your setup , but for
p port 13B it is somewhere between 21 and 24 inch intake
runners.
Has build the plenum so that it
can bolt open to work and inspections inside.
I have build my own intake bell
mouth velocity stacks and covered it with carbon fiber
braided sleaves.
The whole plenum box can be
slide "up and down" on the runners to tunned it on run ups
for final testing for VE
Still building and no testing
has been done at this stage
Will post some photos for
comments, has to crop them on pc before mailing for size
tomorrow morning
As Lynn always say "I could be
wrong"
Le Roux
?
My '1st draft' (before the box) was a 6 " aluminum tube
(irrigation
tubing) that I re-contoured into a wavy contraption a little
closer to
flat where the bellmouths faced. 1/4" aluminum plate for the
ends. That
looked questionable, so I went worse. :-(?? I would expect a
round tube
with 1/4" end plates to handle the loads, but I haven't proven
it.
On intake size, most of the stuff I've read addressing both
induction
air and cooling talks about taking in every bit of the air
needed and no
more, because trying to take in more than needed either adds
drag as the
extra air flows through the plane's systems, or adds drag due to
spillage & turbulence around the lips of the intake.
Achieving that goal
is a pretty high bar, though, given the wide speed variations of
fast
a/c. Bernie Kerr (Hi Bernie, are you still watching?) used to
talk about
'external diffusion' (as opposed to internal diffusion, where
the air
enters the duct at system airspeed and slows within the duct),
which
apparently works well by slowing the air in front of the duct
and
minimizes spillage losses by optimizing the lip of the entrance.
Apparently has the additional advantage of making duct shape
less critical.
You can calculate the volume of air the engine ingests per
second, then
calculate the intake size required to take in that volume of air
per
second, all at expected operational speed. I suspect that's what
Tracy
did. I chose the easy (lazy) way out & sized the inlet the
same as? the
throttle body/total intake tube area, and am willing to accept
'external
diffusion' spillage at speed.
Or, like Lynn often says, I could be wrong. :-)
Charlie
On 9/12/2019 5:47 PM, Finn Lassen
finn.lassen@verizon.net wrote:
> Thanks Charlie,
>
> I was planning on using 1/4" plywood wrapped in fiberglass.
(Tracy had
> warned me.) I do have a length of 6" OD 0.035 SS pipe, but
what about
> the ends (or end opposite throttle body)?
> I can weld SS with my Henrob, but no success with aluminum.
Also the
> curve of the pipe would make me shorten the intake runners
a bit to
> make room around the bell mouths.
>
> I started reading the grapeape-inductionsystems.pdf paper
and realized
> that's going to take quite a bit of study and research.
Like what is
> the VE (Volumetric Efficiency) of a Renesis?
>
> Seems I start with the best intentions to design the
optimal
> installation and end up copping out and doing "looks about
right" or
> "what he did".
>
> Like, I have no clue how big my air intake opening should
be. Just the
> size of the throttle body? Tracy mentioned something about
the air
> intake should gradually open up to the size of the throttle
body. I
> should now have plenty of room in the left cheek for a
straight run
> from near the prop to the throttle body mounted on the
plenum (shoe box).
>
> Finn
>
> On 9/12/2019 5:26 PM, Charlie England
ceengland7@gmail.com
wrote:
>> Like most people's dad used to say, "Don't do as I do
(did); do as I
>> say." :-)
>>
>> Tracy looked at my box after it was built & pointed
out what I should
>> have considered: those big flat (thin) aluminum panels
won't survive
>> intake pressure waves. I knew better, but that part of
my mind had
>> gone on break during the entire construction of the
box. Car makers
>> don't waste aluminum making cast 1/4" thick plenums
just to get rid
>> of surplus aluminum. :-)
>>
>> That box is now lined with 1/4" plywood and fiberglass,
and weighs
>> far too much. I'm doubtful that it will be a flight
item.
>>
>> I'd suggest doing what Tracy did, & start with
plywood/fiberglass, or
>> use a 4"-6" round aluminum tube for the plenum. I can
probably dig up
>> some 6" if you want to try it, or check local
farm-market
>> publications down there for surplus irrigation pipe.
>>
>> I never did find any tube length/plenum sizing advice
for the rotary
>> that I trusted. Very few Renesis car guys ever touch
the stock
>> manifold, since it would be very difficult to improve
on Mazda's
>> design for a car.
>>
>> Charlie
>>
>> On 9/12/2019 12:02 PM, Finn Lassen
finn.lassen@verizon.net wrote:
>>> 6 1/2 years later I'm about to do the same and
would like to ask the
>>> same question before I make my "shoe box":
>>>
>>> "I'm curious about how others have adapted the
common Helmholtz
>>> intake tuning formulas to the rotary. Would anyone
care to 'show
>>> their (math) work'?"
>>>
>>> Rather than building it as big as possible, I'd
like to know if
>>> there is an optimal size.
>>>
>>> Finn
>>>
>>> Charlie's photo:
>>>
>>>
>>>
>>> On 2/17/2013 3:41 PM, Charlie England wrote:
>>>>
>>>> Now that everyone's awake again, I thought I'd
send a pic of my
>>>> intake progress (RV-7 Renesis with James Lyc
cowl). I played with a
>>>> couple of different materials for the bell
mouths. I tried gluing
>>>> up some 1/4" plexi from an old windshield, but
used super glue
>>>> instead of proper plexi cement (which I wasn't
able to find locally
>>>> in a hurry). The 1st try popped apart on the
lathe; the 2nd turned
>>>> out ok. Next effort was with 3/4" MDF (medium
density fiberboard).
>>>> That went well, until I put a little too much
side pressure on the
>>>> ring (homemade cutting tool) after undercutting
the center section.
>>>> Overall tube lengths will be ~11 3/4" block
surface to bell ends.
>>>> The plenum is *much* bigger than most tuning
sites recommend. I
>>>> figure that I can experiment with plenum size
by just stuffing it
>>>> with rigid foam to take up some volume, if
needed. Going the other
>>>> way wouldn't be so easy. :-)
>>>>
>>>> Since I don't have Mark's TIG skills, I thought
I'd ask what others
>>>> have used in joining thin wall tubing to 1/4"
aluminum plate.
>>>> Aluminum brazing rod? High temp epoxy? JB weld?
I do intend to add
>>>> bracing from the plate to the plenum assembly
to take some of the
>>>> cantilever & vibration stress off the
tubes.
>>>>
>>>> I'm using this length and concept because Tracy
has had great luck
>>>> with both HP & BSFC on his Renesis with a
similar configuration.
>>>> However, I'm curious about how others have
adapted the common
>>>> Helmholtz intake tuning formulas to the rotary.
Would anyone care
>>>> to 'show their (math) work'? Renesis users
would be better for me,
>>>> but any calcs would do. When I tried to adapt
the common formulas
>>>> to a rotary, I was getting 'interesting'
results, so I'd like to
>>>> know if I got lost somewhere while trying to
plug rotary 'valve'
>>>> timing into the formulas.
>>>>
>>>> Charlie
>>>> (Sorry for the sideways iphone pic; I guess you
can pretend that
>>>> you're looking down on it...)
>>>
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