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  #1  
Old 02-03-2017, 03:20 PM
KJBSouth's Avatar
KJBSouth KJBSouth is offline
 
Join Date: May 2014
Location: Spring Hill, Florida; Flushing, Michigan
Posts: 110
Default Plenum Tug-of-War

With the -7 build in Michigan while Dolly and I are in Florida, a project for the winter was to fabricate a fiberglass plenum lid, the oil fill door and some HDPE firewall and baffle wire pass through. I brought engine measurements (32"plus by 18"plus) and the top Vans cowl with us.

The oil door was fun, really. First try was two layers of 6 oz cloth cast onto the cowl over clear packing tape and Mother's Brazilian canauba auto wax. Two layers was too thin both in flexure and contour with the surrounding cowl surface. The second try at seven layers was stiff, but too thick. Like 'Goldilocks and the Three Bears' the third try at four layers was just right but will need some anti-flex reinforcing.

I purchased yards of cloth and West Systems epoxy at the new West Marine store located about a mile from here. It seems that from now on the WM stores will only carry smaller packages of cloth, not large rolls.

The outer surface of the RV-7 cowl received from Vans had pits reflecting the shape of the hexagonal cells in the sandwiched layer. After three thin screed layers of epoxy/microlite and two layers of rolled on clear epoxy the surface is ready for spray primer. Of course each layer was preceded by block sanding, but we don't like to think about that.

After all that I felt ready to tackle casting the plenum lid on the inside of the upper cowl. Clear packing tape and auto wax were again used for mold release. Six pieces of 6oz cloth were cut oversize (I only used five), along with a layer of 2mm Soric core material.



Blue sharpie lines on the cowl marked where the composite layers were to be placed. A single large piece of nylon sail cloth peel ply was laid over the waxed release tape and the blue lines traced. Epoxy was poured over the first layer of glass, and a bit on the second glass layer. Air was worked out with a plastic spatula. The third glass layer also required some epoxy. Then the Soric was placed and a 3" paint roller used to force contact and squeez excess epoxy to the edges. Corners of the Soric were lifted to verify epoxy was covering the bottom of this layer. The next two layers of glass and peel ply were applied in a similar manner.



The plenum lid easily popped from the mold after twelve hours. It was left for a day before our Tug-of-War and trimming loose cloth from the edges. The finish is beautiful. Weight at this point is 34.4oz. This is undoubtedly heavier than if the assembly had been vacuum bagged and resin infused. However, we can tolerate forward weight to offset the relatively light weight lithium battery and Catto prop.

__________________
Karl Bambas
1954 1st solo
1964 Mooney Statesman, 1979 C-172, 1948 Globe Swift (all sold)

RV-7 "Dream Weaver" N50KB
Empennage arrived 10/14
QB Wings & Fuselage arrived 06/15
Finish & FF kits arrived 11/15
Dual screen Garmin G3X instruments and harness delivered by Stein 01/16
First flight June 13th 2018

2021 Dues Paid
Builders Log
Family Blog
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  #2  
Old 02-03-2017, 04:53 PM
BillL BillL is offline
 
Join Date: Sep 2007
Location: Central IL
Posts: 6,326
Default Nice Work Karl!!

Quote:
Originally Posted by KJBSouth View Post
With the -7 build in Michigan while Dolly and I are in Florida, a project for the winter was to fabricate a fiberglass plenum lid, the oil fill door and some HDPE firewall and baffle wire pass through. I brought engine measurements (32"plus by 18"plus) and the top Vans cowl with us.

The oil door was fun, really. First try was two layers of 6 oz cloth cast onto the cowl over clear packing tape and Mother's Brazilian canauba auto wax. Two layers was too thin both in flexure and contour with the surrounding cowl surface. The second try at seven layers was stiff, but too thick. Like 'Goldilocks and the Three Bears' the third try at four layers was just right but will need some anti-flex reinforcing.

I purchased yards of cloth and West Systems epoxy at the new West Marine store located about a mile from here. It seems that from now on the WM stores will only carry smaller packages of cloth, not large rolls.

The outer surface of the RV-7 cowl received from Vans had pits reflecting the shape of the hexagonal cells in the sandwiched layer. After three thin screed layers of epoxy/microlite and two layers of rolled on clear epoxy the surface is ready for spray primer. Of course each layer was preceded by block sanding, but we don't like to think about that.

After all that I felt ready to tackle casting the plenum lid on the inside of the upper cowl. Clear packing tape and auto wax were again used for mold release. Six pieces of 6oz cloth were cut oversize (I only used five), along with a layer of 2mm Soric core material.

Blue sharpie lines on the cowl marked where the composite layers were to be placed. A single large piece of nylon sail cloth peel ply was laid over the waxed release tape and the blue lines traced. Epoxy was poured over the first layer of glass, and a bit on the second glass layer. Air was worked out with a plastic spatula. The third glass layer also required some epoxy. Then the Soric was placed and a 3" paint roller used to force contact and squeez excess epoxy to the edges. Corners of the Soric were lifted to verify epoxy was covering the bottom of this layer. The next two layers of glass and peel ply were applied in a similar manner.

The plenum lid easily popped from the mold after twelve hours. It was left for a day before our Tug-of-War and trimming loose cloth from the edges. The finish is beautiful. Weight at this point is 34.4oz. This is undoubtedly heavier than if the assembly had been vacuum bagged and resin infused. However, we can tolerate forward weight to offset the relatively light weight lithium battery and Catto prop.
You got me really laughing at that tug-of-war!! For this very reason, I now use a teflon coated peel ply from Aircraft Spruce. You can remember that for next time

BTW - - Don't be concerned about cutting the Soric sandwich parts. I tested some pieces to ensure it would not fail in shear - while it might be "theoretically" weaker, my test did not indicate that.

I can't wait to see the finished part.
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RV-7
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  #3  
Old 02-04-2017, 08:38 AM
Bob Martin's Avatar
Bob Martin Bob Martin is offline
 
Join Date: Jan 2005
Location: Charlottesville, Virginia
Posts: 1,279
Default Really nice work

Karl,
Excellent work on the plenum lid.
First I have seen the Soric core material used. What was your reasoning behind using it? I thought I read on the web it was used in vacuum bagging to allow the resin to spread better...but you clearly know how to move the resin around in your layup technique. Just curious.
Big question is how will you mount the lid to the baffling material??
Thanks for sharing the process and great pictures!
Loved the Tug of War.....
__________________
Bob Martin
RV-6, 0-360 Hartzell C/S, Tip up, 1200+TT
James extended cowl/plenum, induction, -8VS and Rudder. TSFlightline hoses. Oregon Aero leather seats.
D100-KMD150-660-TT ADI2- AS air/oil seperator. Vetterman exhaust with turndown tips.
Louisa, Virginia KLKU N94TB
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  #4  
Old 02-04-2017, 12:12 PM
BillL BillL is offline
 
Join Date: Sep 2007
Location: Central IL
Posts: 6,326
Default

Bob, the Soric is easy to wet, flexible to fit the contour, but does not soak up resin. It will provide some reinforcement separation for a stiffer part. Here is a one-core-one and a 2 layer test piece with the same weight on them. Note deflection.

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  #5  
Old 02-05-2017, 07:19 AM
KJBSouth's Avatar
KJBSouth KJBSouth is offline
 
Join Date: May 2014
Location: Spring Hill, Florida; Flushing, Michigan
Posts: 110
Default Reply

Bob

As Bill said, the Soric adds stiffness. It's like the shear web in an I-Beam. Light weight and very flexible, the Soric holds the fiberglass layers apart making the whole composite stiffer.

Attaching to metal baffles:
1. I'll cast three flat strips/sheets of four layer fiberglass
2. Clamp the sheets inside the side and rear baffles.
3. Lay the plenum lid over this and drill a few small holes down to the top edges of the fiberglass sheets.
4. Force epoxy/flox down through the holes to tack the lid to the back and sides.
5. Remove, trim the lid, glass the intersections and tack a thin aluminum strip that will later hold platenuts on the inside.
6. Reinstall, drill and cleco through baffles and plenum for mounting holes.
7. Remove, untack the aluminum strips and install platenuts. Reinstall, etc.
8. Scratch my head deciding how to transition from the plenum to the cowl air scoops.
__________________
Karl Bambas
1954 1st solo
1964 Mooney Statesman, 1979 C-172, 1948 Globe Swift (all sold)

RV-7 "Dream Weaver" N50KB
Empennage arrived 10/14
QB Wings & Fuselage arrived 06/15
Finish & FF kits arrived 11/15
Dual screen Garmin G3X instruments and harness delivered by Stein 01/16
First flight June 13th 2018

2021 Dues Paid
Builders Log
Family Blog
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  #6  
Old 02-05-2017, 09:03 AM
BillL BillL is offline
 
Join Date: Sep 2007
Location: Central IL
Posts: 6,326
Default Just a thought for you . . .

Karl, it would be nice to have the attachment to the baffles on the inside of the aluminum. You might consider assembling the baffles, trimming to generate cowl clearance, then remove them all, and turn upside down on the plenum cover and glass the inside corners.

The baffles sides are parallel. The back is straight and square to the sides, A rim of plywood could hold the dimensions for the process.

There is another thread with some very nice inlets. I will append this post with the link.

http://www.vansairforce.com/communit...plenum+attempt

And, Karl, you are welcome to my templates for the center baffle for my homebuilt plenum for the James cowl. Drop me an email.
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RV-7

Last edited by BillL : 02-05-2017 at 09:08 AM.
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  #7  
Old 02-05-2017, 09:45 AM
Bob Martin's Avatar
Bob Martin Bob Martin is offline
 
Join Date: Jan 2005
Location: Charlottesville, Virginia
Posts: 1,279
Default

Quote:
Originally Posted by KJBSouth View Post
Bob

As Bill said, the Soric adds stiffness. It's like the shear web in an I-Beam. Light weight and very flexible, the Soric holds the fiberglass layers apart making the whole composite stiffer.

Attaching to metal baffles:
1. I'll cast three flat strips/sheets of four layer fiberglass
2. Clamp the sheets inside the side and rear baffles.
3. Lay the plenum lid over this and drill a few small holes down to the top edges of the fiberglass sheets.
4. Force epoxy/flox down through the holes to tack the lid to the back and sides.
5. Remove, trim the lid, glass the intersections and tack a thin aluminum strip that will later hold platenuts on the inside.
6. Reinstall, drill and cleco through baffles and plenum for mounting holes.
7. Remove, untack the aluminum strips and install platenuts. Reinstall, etc.
8. Scratch my head deciding how to transition from the plenum to the cowl air scoops.
Thanks for the info on the Soric.......if I remember right Rutan did something like that with thin sheet of foam, to make it stronger. Soric sounds good at 2mils.
Karl, ponder the vertical joint some. Sliding the plenum vertically into the baffles makes it impossible to seal if it not a perfect fit. I installed an aluminum angle riveted to the top edge of the baffles and then layed up plenum lid over it and applied screws down from the top to secure. If I need to seal, a weather strip can be applied between the 2 mating surfaces.
Just a thought.
__________________
Bob Martin
RV-6, 0-360 Hartzell C/S, Tip up, 1200+TT
James extended cowl/plenum, induction, -8VS and Rudder. TSFlightline hoses. Oregon Aero leather seats.
D100-KMD150-660-TT ADI2- AS air/oil seperator. Vetterman exhaust with turndown tips.
Louisa, Virginia KLKU N94TB

Last edited by Bob Martin : 02-06-2017 at 07:19 AM. Reason: pic
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  #8  
Old 02-05-2017, 09:48 AM
Bob Martin's Avatar
Bob Martin Bob Martin is offline
 
Join Date: Jan 2005
Location: Charlottesville, Virginia
Posts: 1,279
Default Pictures

Quote:
Originally Posted by BillL View Post
Bob, the Soric is easy to wet, flexible to fit the contour, but does not soak up resin. It will provide some reinforcement separation for a stiffer part. Here is a one-core-one and a 2 layer test piece with the same weight on them. Note deflection.
Bill, Great Pictures....I will look into Soric more for future projects. Thanks for posting pictures.
__________________
Bob Martin
RV-6, 0-360 Hartzell C/S, Tip up, 1200+TT
James extended cowl/plenum, induction, -8VS and Rudder. TSFlightline hoses. Oregon Aero leather seats.
D100-KMD150-660-TT ADI2- AS air/oil seperator. Vetterman exhaust with turndown tips.
Louisa, Virginia KLKU N94TB
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