RV-4 Cowl Cracks

[bruceinusa]

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

[lr172]

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

[wilddog]

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.

[bruceinusa]

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.

[FinnFlyer]

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

[FinnFlyer]

Originally Posted by bruceinusa

Makes me feel like a wimp that over 10,000 Vans constructors have managed to do it just fine and without whining about it.

Who do you know that didn't whine about it?

Finn

[Larry DeCamp]

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.

[Kyle Boatright]

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.

[David Paule]

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

[Johnnybgoode]

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