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poasttown(at)yahoo.com
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 Posted: Mon Mar 18, 2013 6:22 am Post subject: New Cowling |
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A few years ago I fabricated a new cowling for my Kitfox IV around my Jabiru 2200 installation. After many hours of work the cowling looks pretty good. However, because I needed to make some needed modifications to the cowling over time it is somewhat pieced together. I would like to fabricate a new cowling using the old cowling if possible but I don't want to destroy my current cowling in the process. This would allow me to continue to flying while I worked on the new cowling at a relaxed pace.
I'm looking for some possible resources to help me in the process. I can't remember if any of the workshops at Oshkosh addressed this issue or not. My last attempt at this involved using the old cowling along with foam and auto putty to get the desired shape. I then layed fiberglass over this cowling to make a mold which I used to make my current cowling. I am no expert in this area so any semi-expert or expert advice would be greatly appreciated.
Mike Chaney
1996 Kitfox IV, Jabiru 2200
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Guy Buchanan
Joined: 16 Jul 2006
Posts: 1204
Location: Ramona, CA
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| Posted: Mon Mar 18, 2013 9:27 am Post subject: New Cowling |
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On 3/18/2013 7:22 AM, Mike Chaney wrote: | Quote: | | I'm looking for some possible resources to help me in the process. I can't remember if any of the workshops at Oshkosh addressed this issue or not. My last attempt at this involved using the old cowling along with foam and auto putty to get the desired shape. I then layed fiberglass over this cowling to make a mold which I used to make my current cowling. I am no expert in this area so any semi-expert or expert advice would be greatly appreciated. |
I can't tell if you already did this, but if you like your current cowling you use it as a male plug and build a female mold over it, from which you can pull nice, non-piecemeal parts. You can even temporarily add to your current cowling temporarily for the purposes of making the mold, but of course it's much more difficult to subtract.
Here's a great description of how to make a mini-mold. A large part mainly differs in how you support both the male plug and the female mold. For a Kitfox cowl one problem is keeping the plug stable while you construct the mold. If you can construct the mold while the cowl's installed this might not be a problem. If not you will have to install some temporary bulkheads and stringers. The problem is that fiberglass attachments for your bulkheads shrink and change the shape of the plug so you want to first bond a "pad" to the inside of the cowl using a small, distributed amount of caulk or other soft adhesive. Once cured thoroughly you bond the bulkheads or stringers to these pads. The internal structure should provide just enough support to make a good plug. Don't forget to include some way to support the plug off the ground to free up the plug's edges.
The second problem is that you want the mold to be longer, at each edge, than the part, so you can trim the edges after you make the part. Again, making the mold with the cowl on the aircraft may facilitate this since you could fill all the joints and screw heads temporarily and make the mold over them, overlapping the part line by a couple of inches. You make the mold over the screws then come back and fill the screw indents in the mold very carefully. (You have to make sure you can remove the mold over the screw heads, though.) Another cool way to alleviate this problem is to make the mold so that the final cowl is made in one piece, as in the above mini-example. You then cut the resulting cowl in such a way as to enable you to use piano hinge to connect the two pieces. This results in a really cool, fastener-less design. (All RV and Lancair cowls are done this way.) You still have the problem of the other edges but this gets rid of the joint overlap problem. (You add shims between the molds pieces to give you enough additional material for a saw kerf and edge clean-up.)
As to the free edges you have to find a way to temporarily build up the existing cowl plug to extend the edges. I've recently done this by using 2" styrofoam insulation board from Home Depot with the facings stripped off. I bonded three together to make a 6" thick "bulkhead", then rough shaped them to the inside dimension of the cowl at the free edge, then cleaned and taped the inside of the cowl edge with aluminum tape, then bonded the bulkhead to the tape, then filled and faired the exterior of the styrofoam using art plaster to "mimic" an extension of the cowl. You then seal the plaster and apply release as you do for the part. You may be able to use the styrofoam as your stabilizing bulkheads required above.
When you make the mold you do so as in the example, with a part line "dam" or wall, but made from something really flat. Melamine board is good for this, since nearly all plywood is warped. (Melamine is particle board or MDF with a nice plastic coating on it. It's used for shelves and other kitchen stuff.) Unlike the example above the first layer of glass should be chopped strand mat. If you use anything woven it will print through the gelcoat and ruin the surface of the mold. The reason they didn't do it on the mini-part is because there's no chopped strand mat that will turn the corners they require on such a small part. (Which is to say you'll have equal problems if you try to get it to turn hard corners on your part.)
You will have to make your mold much thicker than the mini mold, above. (Plan for at least 1/8" total thickness, much thicker than your cowl.) and you'll have to add bulkheads to stabilize it, taking great care to pad the bulkheads so any shrinkage in the attachments doesn't "pull" the mold and distort it.
That's it in short form. There's much more to it in the details, of course, Unfortunately you can see your existing cowling will be laid-up for a while, (pun intended,) since you have to use it as a plug, but once the mold is made you can revert your cowling and get flying again while you make the new cowl. I don't have any more written resources but will advise you to look to the model aviation community. They do this type of fabrication a lot and there's a lot of chatter about it on the Internet. And some of their aircraft are nearly as large as a Kitfox! A quick Google "making fiberglass molds" revealed a lot of good information too, including some video tutorials.
Good luck!
Guy Buchanan
Ramona, CA
Kitfox IV-1200 / 912-S / Warp 3cs / 500 hrs. and grounded
Now a glider pilot, too.
[quote][b]
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Guy Buchanan
Deceased K-IV 1200
A glider pilot too. |
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lcfitt(at)sbcglobal.net
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| Posted: Mon Mar 18, 2013 9:45 am Post subject: New Cowling |
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Mike,
I think the trick is to use the original to make a master female mold, then a copy just as you did on your first cowl. The challenge can be made easier by using the proper release agents. I have found that simply waxing the original or mold will sometimes result in damage to either the original piece or the mold. Typically, I will use wax and then spray a coat of PVA mold release -
http://www.tapplastics.com/product/fiberglass/mold_releases/tap_pva_mold_release_liquid/67
You might find it locally. It is water based with an alcohol content that makes it flow well over the waxed surface. I usually use an old detail spray gun, but the gun should be cleaned after each use. I have also put it in a squeeze spray bottle (Windex). The tip needs to be rinsed as the stuff will dry and clog everything if left too long. If you will be using it periodically over several days, I would think removing the spray assembly and putting it in a bottle of water to keep it moist would eliminate that. The PVA film is easy to remove from the resin surfaces after separating by simply rinsing or wiping the parts with a damp cloth. Before other body work or paint the surface should also be scuff sanded. Another trick from the Lancair book is to use a lot of paper towles after the lay-up to absorb and remove excess resin from the lay up. It is surprising how much resin can be removed for a lighter cowl.
I would suspect your cowl might be out of service for less than a week and should come from the female master mold blemish free. I have used it on the surface of finished fabric to fabricate fairings and if carefully applied it doesn't harm the painted surface.. Another trick I learned when helping a guy with a Lancair to cover such things as Camloc receptacle holes and other holes is the typical 3M clear shipping tape. It is very thin and epoxy will not adhere to it. Small cut circles to cover such holes will prevent the resin and cloth from penetrating resulting in a separation nightmare and will leave a very slight blemish that can be easily corrected with Micro. In my case, I used it to "mask" around the fairing work area so stray drips can be lifted off without damage.
Lowell
I am currently working on fiberglass on a project and this is all pretty fresh. In fact, as I write this, I am about to run down to the local Tap store for some resin and other materials. I forgot where you are located - tap is pretty much a Northern California family operation with some stores in Oregon and Washington but other suppliers will handle PVA.
Lowell
From: Mike Chaney (poasttown(at)yahoo.com)
Sent: Monday, March 18, 2013 7:22 AM
To: kitfox (kitfox-list(at)matronics.com)
Subject: New Cowling
A few years ago I fabricated a new cowling for my Kitfox IV around my Jabiru 2200 installation. After many hours of work the cowling looks pretty good. However, because I needed to make some needed modifications to the cowling over time it is somewhat pieced together. I would like to fabricate a new cowling using the old cowling if possible but I don't want to destroy my current cowling in the process. This would allow me to continue to flying while I worked on the new cowling at a relaxed pace.
I'm looking for some possible resources to help me in the process. I can't remember if any of the workshops at Oshkosh addressed this issue or not. My last attempt at this involved using the old cowling along with foam and auto putty to get the desired shape. I then layed fiberglass over this cowling to make a mold which I used to make my current cowling. I am no expert in this area so any semi-expert or expert advice would be greatly appreciated.
Mike Chaney
1996 Kitfox IV, Jabiru 2200
[quote]
href="http://www.matronics.com/Navigator?Kitfox-List">http://www.matronhref="http://forums.matronics.com">http://forums.matronics.com
href="http://www.matronics.com/contribution">http://www.matronics.com/c
[b]
| | - The Matronics Kitfox-List Email Forum - | | | Use the List Feature Navigator to browse the many List utilities available such as the Email Subscriptions page, Archive Search & Download, 7-Day Browse, Chat, FAQ, Photoshare, and much more:
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Lynn Matteson
Joined: 10 Jan 2006
Posts: 2778
Location: Grass Lake, Michigan
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| Posted: Mon Mar 18, 2013 12:19 pm Post subject: New Cowling |
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In addition to what Guy and Lowell have said, there is another way to
go...see if Pete at USJabiru still sells the Skyfox cowl made for the
Kitfox IV and the Jabiru engine. That is what I bought back in 2005
when I ordered my engine. There is still a bit of work to do to make
the cowl-to-windshield transition compatible, but for about $600
(2005 dollars) it's already shaped, and fits the engine like a glove.
The Top half overlaps the bottom with a "joggle" and the fit is
pretty good, but will take some cleaning up with a file or sandpaper.
The air inlets are properly sized for the 2200 engine, and there is
an opening for the oil cooler air. See picture of my cowl during
fitting.
If you still want to make your own, there is a tape that Spruce
sells..."Fiberglass 101"... which is pretty good for less than $30,
and which explains the use of parting agents, dealing with sharp
corners, etc.
Lynn Matteson
Kitfox IV Speedster, taildragger
Jabiru 2200, #2062
Prince prop 64 x 30, P-tip
Electroair direct-fire ignition system
Rotec TBI-40 injection (sleeved to 36mm)
Status: flying with 1417 hrs... (since 3-27-2006)
On Mar 18, 2013, at 10:22 AM, Mike Chaney wrote:
| Quote: | A few years ago I fabricated a new cowling for my Kitfox IV around
my Jabiru 2200 installation. After many hours of work the cowling
looks pretty good. However, because I needed to make some needed
modifications to the cowling over time it is somewhat pieced
together. I would like to fabricate a new cowling using the old
cowling if possible but I don't want to destroy my current cowling
in the process. This would allow me to continue to flying while I
worked on the new cowling at a relaxed pace.
I'm looking for some possible resources to help me in the process.
I can't remember if any of the workshops at Oshkosh addressed this
issue or not. My last attempt at this involved using the old
cowling along with foam and auto putty to get the desired shape. I
then layed fiberglass over this cowling to make a mold which I used
to make my current cowling. I am no expert in this area so any
semi-expert or expert advice would be greatly appreciated.
Mike Chaney
1996 Kitfox IV, Jabiru 2200
www.matronics.com/contribution _-
============================================================
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| | - The Matronics Kitfox-List Email Forum - | | | Use the List Feature Navigator to browse the many List utilities available such as the Email Subscriptions page, Archive Search & Download, 7-Day Browse, Chat, FAQ, Photoshare, and much more:
http://www.matronics.com/Navigator?Kitfox-List |
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| Description: |
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7061 Time(s) |
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_________________
Lynn
Kitfox IV-Jabiru 2200
N369LM |
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Guy Buchanan
Joined: 16 Jul 2006
Posts: 1204
Location: Ramona, CA
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| Posted: Mon Mar 18, 2013 12:50 pm Post subject: New Cowling |
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On 3/18/2013 10:44 AM, Lowell Fitt wrote: | Quote: | | You might find it locally. It is water based with an alcohol content that makes it flow well over the waxed surface. I usually use an old detail spray gun, but the gun should be cleaned after each use. I have also put it in a squeeze spray bottle (Windex). |
These things are great for spraying PVA. When I was a pro the fab companies used them quite heavily.
Guy Buchanan
Ramona, CA
Kitfox IV-1200 / 912-S / Warp 3cs / 500 hrs. and grounded
Now a glider pilot, too.
[quote][b]
| | - The Matronics Kitfox-List Email Forum - | | | Use the List Feature Navigator to browse the many List utilities available such as the Email Subscriptions page, Archive Search & Download, 7-Day Browse, Chat, FAQ, Photoshare, and much more:
http://www.matronics.com/Navigator?Kitfox-List |
|
_________________
Guy Buchanan
Deceased K-IV 1200
A glider pilot too. |
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| Back to top |
|
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Lynn Matteson
Joined: 10 Jan 2006
Posts: 2778
Location: Grass Lake, Michigan
|
| Posted: Mon Mar 18, 2013 12:50 pm Post subject: New Cowling |
|
|
In addition to what Guy and Lowell have said, there is another way to
go...see if Pete at USJabiru still sells the Skyfox cowl made for the
Kitfox IV and the Jabiru engine. That is what I bought back in 2005
when I ordered my engine. There is still a bit of work to do to make
the cowl-to-windshield transition compatible, but for about $600
(2005 dollars) it's already shaped, and fits the engine like a glove.
The Top half overlaps the bottom with a "joggle" and the fit is
pretty good, but will take some cleaning up with a file or sandpaper.
The air inlets are properly sized for the 2200 engine, and there is
an opening for the oil cooler air. See picture of my cowl during
fitting.
If you still want to make your own, there is a tape that Spruce
sells..."Fiberglass 101"... which is pretty good for less than $30,
and which explains the use of parting agents, dealing with sharp
corners, etc.
Lynn Matteson
Kitfox IV Speedster, taildragger
Jabiru 2200, #2062
Prince prop 64 x 30, P-tip
Electroair direct-fire ignition system
Rotec TBI-40 injection (sleeved to 36mm)
Status: flying with 1417 hrs... (since 3-27-2006)
On Mar 18, 2013, at 10:22 AM, Mike Chaney wrote:
| Quote: | A few years ago I fabricated a new cowling for my Kitfox IV around
my Jabiru 2200 installation. After many hours of work the cowling
looks pretty good. However, because I needed to make some needed
modifications to the cowling over time it is somewhat pieced
together. I would like to fabricate a new cowling using the old
cowling if possible but I don't want to destroy my current cowling
in the process. This would allow me to continue to flying while I
worked on the new cowling at a relaxed pace.
I'm looking for some possible resources to help me in the process.
I can't remember if any of the workshops at Oshkosh addressed this
issue or not. My last attempt at this involved using the old
cowling along with foam and auto putty to get the desired shape. I
then layed fiberglass over this cowling to make a mold which I used
to make my current cowling. I am no expert in this area so any
semi-expert or expert advice would be greatly appreciated.
Mike Chaney
1996 Kitfox IV, Jabiru 2200
www.matronics.com/contribution _-
============================================================
|
| | - The Matronics Kitfox-List Email Forum - | | | Use the List Feature Navigator to browse the many List utilities available such as the Email Subscriptions page, Archive Search & Download, 7-Day Browse, Chat, FAQ, Photoshare, and much more:
http://www.matronics.com/Navigator?Kitfox-List |
|
| Description: |
|
| Filesize: |
410.42 KB |
| Viewed: |
7060 Time(s) |
|
_________________
Lynn
Kitfox IV-Jabiru 2200
N369LM |
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