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11-11-2013, 03:31 PM
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Join Date: Sep 2006
Location: Townsend, Montana
Posts: 3,179
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you may be correct Dan.
When I was chasing my phase 1 cooling. I sealed all the holes in the baffling with Red RTV. I also used the RTV to seal the front plenum to engine interface. I dropped temps about 15* that day. So don't know if it was the baffle holes or plenum lifting up.
I do now that it is sealed along the front now and I must cut it loose everything I pull the plenum cover and reseal when it goes back on. Good or bad I only do it a few times a year.
__________________
Retired Dam guy. Life is good.
Brian, N155BKsold but bought back.
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11-11-2013, 03:46 PM
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Join Date: Sep 2007
Location: Central IL
Posts: 5,516
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Quote:
Originally Posted by DanH
I notice you guys don't bother with fasteners across the front. It's difficult to imagine a good leak free fit along an unsecured edge when the lid is being pushed up by significant internal pressure.
At 180 knots and 3500 feet, even a James setup will load the plenum lid at 60 lbs per sq foot, the delta between plenum pressure and cowl pressure. You have 3 sq feet (or more), thus 180 lbs on a box lid with no fasteners across the whole front span...maybe 18"?
Need a familiar illustration? When we space fasteners 3" apart across the top center of a standard Vans cowl, out in front of the windshield, we can watch it bow up between them in flight. That's in response to lower cowl internal pressure, in this case about 20 lbs per sq ft. Sure, more area, but if the upper cowl has 3 times the area of a plenum (which can't be far from true), it is an apples-to-apples comparison.
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I will also be installing the SJ (long) cowl with the plenum cover. I understand what you are talking about there Dan, and will be keeping that in mind. Did you have any issues with your installation? How did you add attachment over this span? (I have many of your picts but don't remember this being illustrated)
__________________
Bill
RV-7
Lord Kelvin:
“I often say that when you can measure what you are speaking about,
and express it in numbers, you know something about it; but when you
cannot measure it, when you cannot express it in numbers, your knowledge
is of a meager and unsatisfactory kind.”
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11-11-2013, 05:25 PM
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Join Date: Dec 2005
Location: Mahomet, Illinois
Posts: 2,195
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Sealing the front of the plenum
My plenum followed the contour of the front of the engine case within about 1/4" on both sides of the case-split. I used some high temp (red silicone) weatherstrip I found at McMaster-Carr; sealed it up perfectly. Have never had a cooling issue from day 1. W'strip was cheap too. 
__________________
Terry Ruprecht
RV-9A Tip-up; IO-320 D2A
S. James cowl/plenum
(Dues paid thru Nov '18)
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11-11-2013, 05:59 PM
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Join Date: Jan 2005
Location: SC
Posts: 12,887
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One thing I didn't mention was that after using fiberglass to get the plenum to exactly match of the nose of my engine, I used high temp RTV to seal all around the plenum. This means the nose section, the sides along the aluminum plenum, in back, all around. I haven't noticed any indication that the high pressure air has moved past that seal.
__________________
Bill R.
RV-9 (Yes, it's a dragon tail)
O-360 w/ dual P-mags
Build the plane you want, not the plane others want you to build!
SC86 - Easley, SC
www.repucci.com/bill/baf.html
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11-12-2013, 06:39 AM
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Join Date: Oct 2005
Location: 08A
Posts: 9,500
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Quote:
Originally Posted by hydroguy2
...it is sealed along the front now and I must cut it loose everything I pull the plenum cover and reseal when it goes back on. Good or bad I only do it a few times a year.
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Whatever works. Given clean surfaces, I can believe a fat bead of cured silicone sealant will glue the edge to the case and withstand the load.
Quote:
Originally Posted by N941WR
..I used high temp RTV to seal all around the plenum. This means the nose section, the sides along the aluminum plenum, in back, all around. I haven't noticed any indication that the high pressure air has moved past that seal.
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Bill, yours is also glued to the case?
FWIW, you may not get much indication unless you go looking for it. Lots and lots of airplanes fly around with acceptable temperatures despite baffle leaks. However, eliminating all baffle leakage is the entire point of installing a plenum. Doing so allows the builder to take other steps and reduce total mass flow.
BTW, the stated pressure values are from measurement, not theory.
Quote:
Originally Posted by BillL
Did you have any issues with your installation? How did you add attachment over this span? (I have many of your picts but don't remember this being illustrated)
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The original install used a curved length of formed angle along the curved front bulkhead, one flange being riveted to the bulkhead and the other with nutplates for the lid. The pressure was enough to crack and fail that angle at each end, nearest the rubber inlet. This particular problem would not transfer to the James plenum, but it does illustrate the pressures.
The revision added a 90 degree flange to the lid, with fasteners in shear.
With the James plenum, it would be easy to add an attach point above the case split, in the middle of the unsupported span. Just need a small steel bracket attached to a case bolt, and one or more fasteners through the glass.

__________________
Dan Horton
RV-8 SS
Barrett IO-390
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11-12-2013, 06:57 AM
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Join Date: Jan 2005
Location: SC
Posts: 12,887
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Quote:
Originally Posted by DanH
...
Bill, yours is also glued to the case?
FWIW, you may not get much indication unless you go looking for it. Lots and lots of airplanes fly around with acceptable temperatures despite baffle leaks. However, eliminating all baffle leakage is the entire point of installing a plenum. Doing so allows the builder to take other steps and reduce total mass flow.
BTW, the stated pressure values are from measurement, not theory.
...
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Yes, mine is RTV'ed to the case and you are correct. You wouldn't notice it, unless you went looking for it.
I recently posted a thread about how I reduced my CHT's by plugging all the holes. However, one thing I didn't mention was that some of the RTV by the nose had let loose and there was a small dirt stain/trail from the plenum forward, indicating an air leak.
This will be something I now look for with each cowl removal.
The one thing I did not like about the Sam James plenum was that the fit around the nose was not very good and when I questioned Will James about it, he simply said, "Fill in the gap with RTV." That would have been over a 1/4" of RTV, which seemed unacceptable to me.
Quote:
Originally Posted by DanH
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Great idea!
__________________
Bill R.
RV-9 (Yes, it's a dragon tail)
O-360 w/ dual P-mags
Build the plane you want, not the plane others want you to build!
SC86 - Easley, SC
www.repucci.com/bill/baf.html
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11-12-2013, 07:00 AM
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Join Date: Sep 2007
Location: Central IL
Posts: 5,516
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Thanks, Dan, I did not realize which was the final configuration. I only had the earlier configuration pict with the vertical fasteners across the center and did not know you had further development. The feature of removal with only 1/4 tun fasteners seems very attractive for ease of inspection. It would seem silly for me to have quick release fasteners for the cowl, just to have the plenum glued in, although there is still some good advantage to that. While I loathe pondering too much in favor of building, my path is well invested now, so I may as well give it appropriate consideration.
__________________
Bill
RV-7
Lord Kelvin:
“I often say that when you can measure what you are speaking about,
and express it in numbers, you know something about it; but when you
cannot measure it, when you cannot express it in numbers, your knowledge
is of a meager and unsatisfactory kind.”
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11-12-2013, 07:05 AM
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Join Date: Dec 2005
Location: Mahomet, Illinois
Posts: 2,195
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Quote:
Originally Posted by N941WR
... the fit around the nose was not very good and when I questioned ... it, he simply said, "Fill in the gap with RTV." That would have been over a 1/4" of RTV, which seemed unacceptable to me.
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I felt the same way. That's why I searched out the hi-temp weatherstrip. That solution is working well; no signs of leakage or deterioration after a year and 110hrs.
__________________
Terry Ruprecht
RV-9A Tip-up; IO-320 D2A
S. James cowl/plenum
(Dues paid thru Nov '18)
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11-12-2013, 09:26 AM
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Join Date: Oct 2005
Location: 08A
Posts: 9,500
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Quote:
Originally Posted by N941WR
However, one thing I didn't mention was that some of the RTV by the nose had let loose and there was a small dirt stain/trail from the plenum forward, indicating an air leak.
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That's a good clue.
By all reports your 360-powered -9 is fast enough to generate significant plenum pressure.
Quote:
Originally Posted by BillL
The feature of removal with only 1/4 turn fasteners seems very attractive for ease of inspection. It would seem silly for me to have quick release fasteners for the cowl, just to have the plenum glued in, although there is still some good advantage to that.
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All the plenum lid fasteners are machine screws. The trouble with 1/4 turns is that the spring usually sets the maximum tension, at least if you want the heads flush. Given enough airspeed the edge of the plenum lid would lift up off the flange.
Quote:
Originally Posted by Rupester
That's why I searched out the hi-temp weatherstrip. That solution is working well; no signs of leakage or deterioration after a year and 110hrs.
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Do you have a photo for us Terry?
__________________
Dan Horton
RV-8 SS
Barrett IO-390
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11-12-2013, 09:12 PM
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Join Date: Mar 2005
Location: Olathe, KS
Posts: 374
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Dan,
I would be interested in seeing a close up of how the 90 degree flange at the front of the plenum attaches. There must be some really short baffle piece affixed to the case?
Thanks,
Scott
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