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Cowl woes

BruceMe

Well Known Member
So the cowl on the RV-6 I bought got smashed when it rolled over. Now I need to make some decisions. And rather than post them here and ask for opinions and do what I was going to do anyway. I'll put my plan out there for you all take turns shooting it out of the sky; how's that sound?

20160530_165753.jpg


First... This cowl weighs A TON! Like 2x a normal RV cowl easily. I think an owner tried to make it fire resistant and slathered on RTV or something. So I'll be hard at work removing layers of something there on the bottom

Second... It has a cowl flap. That's gone. I'm glassing over it and removing all hardware.

Third... I'm going to cut out the old scoop and insert one I had from my RV-4 that I never used (I went with stock). It's not going to be the right shape towards the back, but I think it starts out right and I can fill in the rest.

20160530_165807.jpg


Ok... Fire away
 
Buy a new one.

I suspect you not a fiberglass guy, otherwise you wouldn't ask the forums opinion. So rebuilding that would be a big challenge. There are enough patients testing procedures it the RV without taking on something like this unnecessarily.

I sent one to the dump yesterday that was in better shape. If dough is an issue maybe post a want ad for a damaged but buildable cowl.

Just so you get your full 2 cents worth, If that really is RTV silicone inside the cowl you won't get any resin to stick to the repair areas. Even grinding it off will leave some residual in the pores.

You asked...😎
 
Well, here is my 2 cents.

From the photos it looks like someone used epoxy to work the area around the cowl flap------the brown stuff-----and it did not stick.

From the way you describe the weight, the fact it does not appear to have any honeycomb and the lack of bonding of the brown stuff--------I suspect you may have a polyester cowl, not epoxy. I believe Vans used polyester resin for the fiberglass in the early kits.

The repair work is really not that bad, just time consuming.

You need to determine if the cowl is polyester or epoxy first off, find someone who knows the difference. Use the correct material or it is not going to adhere correctly.

For the scoop, you might think about useing camlock type fasteners to attach it. The scoop on my 10 is done that way, and it is really nice to access a large part of the engine bottom without having to pull the cowl.

A word of caution about polyester-----(if that is what it is??) The hardener is nasty stuff. Methyl ethyl ketone peroxide as I recall, https://en.wikipedia.org/wiki/Methyl_ethyl_ketone_peroxide and it will eat skin and eyeballs. The resin working time is pretty short compared to epoxy.
 
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I picked this up short money and I have pocket room to make it right. It just takes so _LONG_ to fit a new cowl too ya know! But I'm starting to think about Mr James. A grand is for a great cowl is starting to sound better.
 
:mad: That is so _NOT_ how my RV-4 cowl went. :mad: A month of trim and guess and then months and months of blisters gaaah! :eek:

Someone save me
 
You can fit a new cowl in an afternoon.

An afternoon...on Venus maybe (its day is actually longer than its year).

It's the details that take the time. I felt like I made pretty accurate cuts, but there was lots of sanding and refitting to get the edge gaps just so, an iterative process that took the better part of a week. And then there's the hinges, the fiberglass intake tube, etc., etc.

I like Mike's idea of cam-locking a new intake snout in place. Pete McCoy did his this way too, and it looks fine. Change it up with a P40-style shark mouth when the mood strikes! :) Plus, your upper cowl looks usable, and the hinge work is all done. And you're saving all the time of prepping and pinhole-filling a new cowl, which could be several afternoons by itself.

On the other hand, those Sam James Cowls look great!!!
 
Yes it's repairable. Is it worth it?? Debatable.

Look at it this way, you have already stated that it is heavy, and to carry out the repairs will require grinding and adding layers of material to reinforce the damaged areas. I would suspect that once you start the grinding process you will find even more damage or signs of stress in the form of fine cracks and crushed resin in the laminate. This also need to be repaired. By the time you do this and complete the inevitable filling and fairing to achieve a smooth finish you will probably have added even more weight.

I would suggest it is 50/50 either way for repair verses new. Depends how skilled and keen you are for the challenge. If it was me (and it's not!) I would be inclined to bin it and go for a new cowl (and I'm in the composites industry).

My opinion, worth what you paid for it.

Clive Whittfield
Auckland
New Zealand
 
You need to determine if the cowl is polyester or epoxy first off, find someone who knows the difference. Use the correct material or it is not going to adhere correctly.

Mike and O/P,

While polyester resin has poor bonding when applied to cured epoxy resin and should be avoided, the opposite is not true. Epoxy bonds very well to cured polyester resin; in fact far better than poyster resin bond to cured polyester resin. West Epoxy is marketed by West Marine primarily to the Marine industry (just about every fiberglass boat produced used polyester resin). In that area, I would speculate that over 80% of the epoxy sold is for Polyster-based F/G repair or skim coating.

Larry
 
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It just takes so _LONG_ to fit a new cowl too ya know!

Have you ever faired complex curves? Looking at what you have to repair and assuming you are somewhat new to finish work (not implying this is the case), I don't see how you can consider a new cowl to take longer to complete. If the interior is coated with RTV, nothing can be done until that is removed and scrubbed, and scrubbed, and scrubbed....

EDIT: I just realized that you will be grafting on a new air scoop and therefore my comments about fairing don't really apply.

Larry
 
How long... really?

I've owned an RV-3 then -4 since '97. I've done a lot of cowl work I don't lothe it, I don't fear it, but I respect it. It's just what ultimately makes a finished RV.

That said, how long would it honestly take to fit and finish (less paint) a James cowl designed for my configuration with induction, etc?

My guess (feel free to back this up with experience anyone)... two weekends, but only because these cowls are molded to fit my airplane (RV-6) and this configuration (O-320 fixed pitch & 4" extension). If any of that isn't true... double or triple.

Now that said, I think I can fix this cowl and trust me... I can make it lighter stronger and prettier than it was. And it fits today. That would probably take me about two days spread out over a couple weekend because of cure times.

So I guess I'm answering my own questions here. Better get some fresh epoxy.
 
cowling

I would go with a new cowling some one on this forum probably has one for sale.If you repair go with epoxy as it can be used on polyester,but polyester can not be applied to epoxy.
Bob
 
What about repairing this? Suggestions

This is off my new to me RV3. I removed the pop rivets and found the holes are .200 to .160 oval. I did not like it structurally or aesthetically. I am looking for suggestions on how to repair. A ex-Convair employee friend of mine, suggested expoxing in the holes, redrilling in a new location and attaching with soft rivets. Photos are on my Flickr account if the link doesn't work.

https://www.flickr.com/photos/24686554@N02/albums/72157670220477361
 
This is off my new to me RV3. I removed the pop rivets and found the holes are .200 to .160 oval. I did not like it structurally or aesthetically. I am looking for suggestions on how to repair. A ex-Convair employee friend of mine, suggested expoxing in the holes, redrilling in a new location and attaching with soft rivets. Photos are on my Flickr account if the link doesn't work.

https://www.flickr.com/photos/24686554@N02/albums/72157670220477361

That suggestion sounds like a good path. Epoxy with flox is a strong hole filler. Just drill them to expose fresh material. I put a piece of packing tape on one side and squeeze a little extra in, then sand both sides smooth. I like the slower setting epoxy rather than the fast (west or others) YMMV.
 
Wouldn't fitting the new be relatively easy if in possession of the old?

Transfer strips taken from the old and used to locate holes in the new could be widened to allow determining trim lines.

( Hint: There is a "science" to transfer strips that increases accuracy by orders of magnitude)

FWIW

mjb
 
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In my experience epoxy adheres well to polyester if properly prepaired, but not vice versa. If you have more time than $$ go for the repair. It might not work, or you might not be happy with the result, but all you have lost is your time. The material cosy is low.

The most important thing when doing a repair like this is to find a way to maintain alignment with any fasteners or holes that interface with the airframe. Invariably if you cut out a chunk and feather in a new piece the cowl will change shape slightly and the fit will change. And that will give you fits!

My 3 cents ($Cdn)
 
To the guys who suggest this is not worth repairing I totally see where they are coming from. Some people buy a broken plane hoping to trade sweat for $$. If they have a good eye for judging what is needed and bargain accordingly, they have the tools and skills and determination, they may win. Or if they don't have those things they might get hosed. Also some guys like the challenge of rescuing a wreck. So there is, as I am sure you realize, as many answers as people you ask and it depends on who is doing the work. Myself I would take a crack at it and see how it goes. You can always bail. But a new cowl is, for a Cannuck, $2k delivered. That is a big tick in the "repair" column! I can do a lot of sanding for $2k. Good luck.
 
advice and opinion...

First, this thread goes a few months back, I should let you all know that I opted to use the cowl I have, but put a new scoop on it.

Other than buying a new scoop and chopping out the old one, I honestly haven't done much , but here's my blog post on what I've done so far

Photos are there. I know early on folks where saying I should replace it. I'm glad I didn't, this should save at least a month of awful glass work and lots of headache. I'm glad I went this way. I'll be sure to post to this thread when I'm all done with all the gory details.
 
This is off my new to me RV3. I removed the pop rivets and found the holes are .200 to .160 oval. I did not like it structurally or aesthetically. I am looking for suggestions on how to repair. A ex-Convair employee friend of mine, suggested expoxing in the holes, redrilling in a new location and attaching with soft rivets. Photos are on my Flickr account if the link doesn't work.

https://www.flickr.com/photos/24686554@N02/albums/72157670220477361

Yeah... I see the ugliest. I've done something like this in the past to my RV-3 cowl back in 1997, it worked great. Fill, sand, re-drill, paint and forget it. Will look fabulous and you'll never know it was ugly.
 
Removing the rivets and cleaning up the mess

Thanks for everyone's response. I was also tempted to install some Dzus fasteners but will probably go with the extruded hinge. Pazmany Co. donated his business remains to our EAA chapter so I have plenty of hinge material.

Now to get itchy.
 
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