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RV-4 Cowl Cracks

I have owned RV-4 N9547H (serial # 1654) for about 3 years. I did not build it but I love it. It has a carbureted O-320 engine. The upper engine cowl is repeatedly cracking (down to white fiber glass showing) at the front edge in the corner where the intake cheek turns up around the spinner hump. I have had it repaired 3 times over the past 3 years but each time the cracks come back quicker and worse than before. I am loathe to just keep spending money and down-time just repeating the previous repairs without getting to the root cause, (which might be as simple as: cowl old!) . The engine runs nice and smooth and I had a new Lonnie Prince fixed pitch prop installed (and dynamically balanced) 2 years ago. So I cant detect any unusual vibrations.

Would anyone say that the upper cowl is just plain worn out and needs replacing? The plane was completed in 2007. If so, do I have to replace the upper and lower cowls at the same time to ensure that they go together well? The bottom is in great shape. The existing upper cowl seems to fit very well at the moment: not too tight or too loose when you put it in place. I have shown the problem to Vic Syracuse at Falcon Field outside Atlanta and he could not see any reason to cause these cracks.

Any other theories on why this might be happening would be welcome. Also, how much fitting skill and time would be needed to install the upper cowl for a complete novice? Is this doable?

That's a lot of questions but as you can tell, I am a little worried about continuing to fly with this deteriorating cowl.

Thanks
Bruce.
(251) 214 5274
 
Hard to tell without a picture, but that area helps to hold the front of the cowl pieces together and was somewhat thin on mine. I would try adding some layers of glass to the back side to help reduce the movement that is likely causing the paint to crack. What was done in the previous "repairs?" Did they adding any glass layers or was it just a cosemetic fix?

Larry
 
I would also add layers on the inside. Be sure to remove oil and sand good first. Replacing the top cowl without experience could be challenging.
 
Yes, each time we have repaired it, we have "beefed" it up underneath as well as one top. Same result. I will try to post a picture soon.

Also, I found out today from Vans that my original cowl shipped in 1987. So it is probably the old gel coat type and may just be getting old and brittle. Could be time for new cowl.

And, yes , I am more than a little daunted about attempting to install a new cowl without any previous experience in this sort if thing. Makes me feel like a wimp that over 10,000 Vans constructors have managed to do it just fine and without whining about it.
 
Fix it!

Fitting the cowling and canopy are the two most time consuming and frustrating parts of building an RV-4. (compound curves)

Unless you feel the cowling is way too heavy, definitely sand down to glass fibers around the crack inside and then add multiple layers of fiberglass cloth using epoxy resin.

Also inspect the inside of both the cowling half for signs of parts rubbing on it. Also check the engine rubber mounts. Too soft? Try to see how much you can move the engine around by grabbing the prop (up/down, side-to-side). Vibration is not the only source of the engine moving around. G-forces too (including bumpy landings).

Finn
 
New Cowl ?

You can fly it UGLY during extensive beefing up and repair. Not true if you undertake the extensive project of fitting a whole new cowl.

Another issue with repeated failures to date could be resin compatibility. If the cowl is really old, Vans or Dan H may have a recommendation on resin choice for repair.
It is hard for me to understand how 4/5/6 layers of glass with proper resin and prep would continue to crack. I would predict a good repair would stop the problem, or the offending stress would be evident in a new (less robust) adjacent area. Food for thought.
 
If the subject cowl isn't a gelcoated cowl, ignore this comment, but my observation is that gelcoat gets old and eventually cracks.

If you do build a new cowl, that doesn't mean the airplane has to be down. You can start a new cowl, set it aside, reinstall and fly the old one, lather rinse repeat until the new one is finished.
 
Are the cracks gelcoat cracks or do they go down into the glass itself? Do they go down into the inside reinforcement?

For repairs of a recurring crack in the glass itelf, if you've already got a decent patch on the inside, perhaps it might be possible to sand away the original material and, using the patch as a male mold, build up a new area of the cowl. But I wouldn't try that without a thorough look at the cowl and assessment of the situation and materials.

Dave
 
Just guessing

But I'd say much of the hard part has already been done - you have a pattern for what fits your airplane. Get a new cowl, cut it in close to the existing cowl, and perform fitment trimming upon install. Should just take an hour or two... 😉

All this from someone who bought a flying -4 too, so maybe not the best advice...
Patrick
 
RV-4 Cowl cracks

I?ve chased this problem for years on my 20 year old RV-4 that I first flew in 1999. These early cowls were made with boat resin and gel coat and the older they get the crackier they get. The cracks are purely cosmetic but a real source of frustration.
A couple of years ago I wanted to repaint my custom flame job ( which had multiple cracks through them primarily around the spinner and air inlets ) so I pulled the cowl and sanded all back down to the gel coat and then kept going until the majority of the gel coat was gone. Latter We went so far and cut the front of the cowl off around the spinner and air inlets for our own performance up grades but now have new cracks at some of the transition areas. I haven?t been able to solve the problem so I?m resigned to the fact that Vans early cowl were just junk ! Walk the flight line at any RV gathering and all the 3?s and 4?s have the same cracking issues.
Permanent solution is an epoxy resin cowl in my opinion.
 
Yes, each time we have repaired it, we have "beefed" it up underneath as well as one top. Same result. I will try to post a picture soon.
.

You'll want to grind out the old repairs, as they have cracked as well. Try to grind down to the base cowl material, then re-do the patch. Be sure the patch extends far enough from the crack to get good support. Given that this is a problem area, I would taper the patch so that it is gets thicker as it nears the crack area.

Larry
 
I’ve chased this problem for years on my 20 year old RV-4 that I first flew in 1999. These early cowls were made with boat resin and gel coat and the older they get the crackier they get. The cracks are purely cosmetic but a real source of frustration.
A couple of years ago I wanted to repaint my custom flame job ( which had multiple cracks through them primarily around the spinner and air inlets ) so I pulled the cowl and sanded all back down to the gel coat and then kept going until the majority of the gel coat was gone. Latter We went so far and cut the front of the cowl off around the spinner and air inlets for our own performance up grades but now have new cracks at some of the transition areas. I haven’t been able to solve the problem so I’m resigned to the fact that Vans early cowl were just junk ! Walk the flight line at any RV gathering and all the 3’s and 4’s have the same cracking issues.
Permanent solution is an epoxy resin cowl in my opinion.

That makes sense. The polyester resins lose their liquid component over time and begin to crack, just like any plastic. Epoxy does not share this flaw and hence the go to material for longevity. An epoxy based patch should prevent future cracking, at least in the area of the patch. Future cracking could occur at the transition at the edge of the patch.

Larry
 
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Crack me up...

Bruce,
As mentioned above, the vinyl-ester early cowls like the one I received in 1989 in my RV4 finishing kit are crack prone for certain. Thirty years later the battle continues.
Over the years I used several different types of glass including Kevlar and various resins for repairs only to see new fissures appear seemingly overnight in new areas. Argh is an understatement...

You could buy a new Pre-Preg cowling, install all the hardware, hinges etc and prime/paint to match, or.....keep fighting cracks.

Your call :)
V/R
Smokey
 
Polyester vs Vinylester

Bruce,
As mentioned above, the vinyl-ester early cowls like the one I received in 1989 in my RV4 finishing kit are crack prone for certain. Thirty years later the battle continues.
Over the years I used several different types of glass including Kevlar and various resins for repairs only to see new fissures appear seemingly overnight in new areas. Argh is an understatement...

You could buy a new Pre-Preg cowling, install all the hardware, hinges etc and prime/paint to match, or.....keep fighting cracks.

Your call :)
V/R
Smokey

I?m pretty sure Vans early cowls were polyester resin same as most old boats. At least I?ve ground on both boats and Vans parts to make repairs and they sure smell the same. I have friends with Glasairs that use the vinylester resin system and it is far superior. I haven?t seen the cracking issues in their parts.
 
Gel-coat is hard colored resin they slather in the mold when they lay it up. This gives an even pinhole free surface. It is very hard and brittle and will crack over time. Heat, vibration, environmental conditions, age is the cause, but it is not a structural issue (unless you see cracks on the inner surface of the cowl).

Not even Van sells fiberglass parts with gel coat anymore. It is heavy and it cracks.... Yes 99% sure if it's an original RV-4 cowl is vinyl ester (or worse polyester but compatible with vinyl ester).

Cure = remove cowl and sand off ALL gel-coat, prime it, paint it. Enjoy crack free lighter cowl. (Sanding gel-coat by hand will take a long long time. Use power tools with care not to take off the glass plies. You don't have to get all of it off, just to where you start to see start to first ply though gel-coat. Thick gel coat which is what Van did was heavy and crack prone.)
 
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Great advice guys! I have so much fiber glass terminology now that I didn't know before! One question: if you stand off all the gel coat, do you have to replace it with some other layer of something to retain the strength of the cowl? Or do you just apply primer and paint?
 
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