Mounting cowl - RCCanada - Canada Radio Controlled Hobby Forum
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Old 05-23-2006, 06:51 AM   #1
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Mounting cowl

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Hi Guys just wondering how you mount the cowl to prevent it cracking.
I think I read somewhere using fuel tubing to absorb the vibration, but I can't find it now.

I am looking for the best way to prevent cracking and splitting, any ideas would help. I did a search but either I missed it or typed wrong info.
Thanks in advance.
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Old 05-23-2006, 07:40 AM   #2
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I've used 2 methods

1: Rubber grommets . Though you can get ones setup for helis or servos, you can actually go to CTC and puy them; depending what size you want. These assist in absorbing the vibrations that can crack a cowl.

2. Epoxy a block of thin light ply on the inside of the cowl where the holes go. Though probably my second best method, it does reduce the risk of the screw hole expanding and causing cracking.

I'm sure there are other methods, this is what I use.

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Old 05-23-2006, 08:01 AM   #3
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I've learned a couple things the hard way over the years. Heres what works for me.

Make sure the retaining screw is perfectly flush to the cowl. If there is any angle at all, the vibration of the motor will cause cracking.

Drill a mounting hole in your cowl using a high speed dremel or a fine file. A drill bit will leave rough edges that tend to crack.

I have been using round servo grommetts in the mounting holes. Go to your LHS and dig thru their box of servo supplies behind the counter.

Use a small flat washer under the head of your mounting screw to spread the load on the rubber grommet.
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Old 05-23-2006, 09:05 AM   #4
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In addition to all of the above, keep the mounting screws away from the edges of the cowl. The further away the better.

Ed S
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Old 05-23-2006, 10:36 AM   #5
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Hi Alan,

You could also drill a hole and add Nyrod tubine in the hole, make sure its flushed from inside and cowl and angiles are stright, i have used this methord and it worked for me, what type of cowl are you using, is it plastic or fiberglass?
Also try to drill hole away from the joining seam if possible to prevent cracking..
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Old 05-31-2006, 11:30 AM   #6
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What I have used in the past, that worked well for me, is to CA a small square (1/2" square) piece of fibreglass cloth or carbon fibre cloth to the inside of whatever you are attaching to the airframe. This can be done either before or after you drill the mounting holes. Using this method is quick and simple - it has never failed me. One caution, if you use carbon fibre cloth the dark colour may show through thinner plastic or fibreglass parts

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Old 05-31-2006, 02:08 PM   #7
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Has any one ever heard or tried the cowl ring method.You bolt a hard wood ring to the firewall and the outer portion of the ring is glued to the inside of the cowl.I would like to try it but I am not sure what glue is used to glue the fiberglass cowl to the wood.
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Old 05-31-2006, 02:22 PM   #8
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Originally Posted by bigguy
Has any one ever heard or tried the cowl ring method.You bolt a hard wood ring to the firewall and the outer portion of the ring is glued to the inside of the cowl.I would like to try it but I am not sure what glue is used to glue the fiberglass cowl to the wood.
Iv'e tried this method with a 1/5th scale Pica Waco. I used PFM to glue the wooden ring to the fibre glass cowl. In canada I believe PFM is called GOOP. There are many different kinds of GOOP but Iv'e been told they are all the same. Please others feel free to correct me if I have the product names confused.
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Old 05-31-2006, 05:44 PM   #9
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I have pretty much switched over to the cowl ring method.

The initial glue joint cowl to ring isnt important but the fit to the fuse is.

You can use goop or equivalent,30 min epoxy thickened with cornstartch,epoxy with some fibreglass chopped up and added etc etc

Mount the ring to the firewall and the cowl to the ring using a stick and some of the above glue methods ..........only a couple of dabs are needed.
Let them set up then remove the cowl and ring assembley from the fuse .
Then put a bead of whatever glue completely around the cowl ring joint.
I use a long allen key ,4/40 allan bolts,and blind nuts on the inside of the firewall to mount the cowl.
Have never had a cowl come loose ,crack ,or give any trouble whatsoever since using this method on all sizes of models up to 60cc IMAC gassers.
This is a particularly nice touch on scale models without the mounting screws showing with traditional mounting practices.
will get you the instruction manual for the GP Christen Eagle Bipe which uses this cowl mounting method........its on page 20.
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Old 06-01-2006, 04:48 AM   #10
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Try gluing an CA Hinge to the inside of the cowl where each screw hole will be and use a rubber grommet in the hole. I like to use machine screws into threaded inserts or "T"- nuts over using just wood screws into the hardwood block.
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