What's new
Van's Air Force

Don't miss anything! Register now for full access to the definitive RV support community.

Cowling Crack Help

Hi guys,

Non-builder here looking for some guidance on what to do about some cracking along the lower cowl/scoop on my RV8. These forums have been a wealth of information for me.

Cracked started as a small line in the cowl, and is now growing and present on both sides.

No cracks on the inside of the cowl that I can see.

Is this an "inject with glue" kind of fix, or is it going to require something more invasive?

Searched and searched but couldn't find any posts relating to cracks around the scoop. I dont believe the actual scoop is separating. I had someone tell me it was a bondo that the builder had used to smooth out the curvature of the scoop to cowl.

Pics attached showing both sides. Smaller crack is forming on the left while larger is on the right.

Thanks!
 

Attachments

  • MVIMG_20201217_164223.jpg
    MVIMG_20201217_164223.jpg
    100.5 KB · Views: 516
  • MVIMG_20201217_164239.jpg
    MVIMG_20201217_164239.jpg
    106.7 KB · Views: 473
  • MVIMG_20201217_164307.jpg
    MVIMG_20201217_164307.jpg
    54.4 KB · Views: 450
  • MVIMG_20201217_164502.jpg
    MVIMG_20201217_164502.jpg
    103 KB · Views: 453
  • MVIMG_20201217_164508.jpg
    MVIMG_20201217_164508.jpg
    140.8 KB · Views: 507
Working with fiberglass isn't hard, it is a lot more forgiving than working with metal, except for the sanding dust and messy epoxy.

I would sand off the exterior paint down to the fiber, layup more fiberglass and epoxy and repaint. You can buy the fibeglass and epoxy from any local boating supply.
 
Is this an "inject with glue" kind of fix, or is it going to require something more invasive?

More invasive. Minimum repair is remove the paint, remove the separated material, rebuild as appropriate, refinish.

I don't believe the actual scoop is separating. I had someone tell me it was a bondo that the builder had used to smooth out the curvature of the scoop to cowl.

Possible. Hard to say for sure without removing paint, although a close look up behind the separated material would probably tell the tale.

The cowl is subject to pressure from the inside, which attempts to inflate its more-or-less rectangular profile into a circular shape.
.
 

Attachments

  • Cowl Pressure Shape.jpg
    Cowl Pressure Shape.jpg
    17.1 KB · Views: 281
seems like it is pulling loose at the aft end also. it may be beneficial if the cowl would fit the aft attachments in a stress free condition. any stress on the cowl fasteners with vibration will cause it to wear thru. if you don't wish to recontour the cowl to be stress free you may add an alum doubler plate strip on the outside of the cowl at the fastener location to reduce the fastener pull thru and give more life.
 
Last edited:
Yep, I'm with Dan and Phat, not that they need my endorsement, but the only way to fix this is the right way.

Grind it down to eliminate the de-bonded area and lay up strips for strength, micro to smooth and buff to perfection. Paint in there somewhere.

That scoop provides the only longitudinal stiffness in the cowl, so all the pressure along the length results in additional loads in area resulting from the inflation Dan mentions.

Is that scoop added or original? Photos from the inside may be helpful for understanding but won't change the recommendation. We all assume you are well versed in fiberglass, so if not, don't feel shy about questions.
 
Don't use anything filler other than epoxy and micro balloons I.e. don't use bonding. Find an RV or Composite home builder in your area. A LongEZ guy could fix this in his sleep. Also if it turns out that you need some glass beef up, which is possible, when you lay it up put the cowl back on the airplane while it cures so it maintains the correct shape.
 
Stop Drilling in FG

I did some cowl work last year that cracked in a similar location and found stop drilling in FG to be completely ineffective unfortunately.

A flapper wheel on the dremel has turned to be the quickest way to remove paint with the least damage.

The trailing edge my bonding of the scoop failed. At the time I tried to avoid taking the bottom piano hinge off during the repair which left a weak spot. So, biting the bullet now.

Cleaned it up, thinned the connection point for a pseudo scarf, re-bonded with flox and then building layers back up. Also some of my previous work was too thin. I built up layers to get it all to an approximate .010 in.

I have zero experience in FG and it's been both frustrating and rewarding to figure it out on a flying plane; the old posts here have been a huge help.
 

Attachments

  • PXL_20210103_023538094.jpg
    PXL_20210103_023538094.jpg
    180.3 KB · Views: 305
Cracked fiberglass

Having made repairs to cracked fiberglass on both boats and cowlings, with good long term success, suggest the following method.
Sand back from the crack approximately an 1 - 1.5" with an aggressive grit of sandpaper, 80 grit being adequate.
Your repair needs to have a good mechanical bond to attach to. Focus your most aggressive sanding on the back side of the repair. The goal is to sand a bit of a pocket on back side of the crack, to receive several layers of bi-directional fiberglass cloth.
After sanding a slight depression that straddles both sides and the full length of your crack (ok... the planes crack) prepare the fiberglass cloth filler strips. Don't forget to clean your sanding job squeaky clean and wiped with acetone.
Cut strips of fiberglass cloth to fill the depressions you have just sanded. Three or 4 layers of cloth strips should be adequate on the back side. The first layer onto your repair will be approximately .25 - .375" wide, the next layer onto the repair will be overlapping and slightly wider than the first layer and perhaps .5" wide. The goal is to build thickness (strength) and achieve maximum bond area with overlapping layers of cloth.
On the outside of the repair if appearance is important, same approach as the back side, but don't use as many layers of fiberglass cloth. Your fiberglass layup on the pretty side needs to be built up to slightly shy of the finished surface.
Rather than using fiberglass resin for the repair, I strongly recommend using epoxy resin instead. I have discovered that when using fiberglass resin that a microscopic crack can develop around the perimeter of the repair and likely a result of the heating from exothermic reaction, then subsequent cooling.
Keep in mind the strength of your repair is in the cloth, not the resin. Only use the amount of resin required to wet your cloth, using a squeegee to remove any excess resin.
After your layup has setup, scuff the the side that you will be painting with 80 grit sand paper again. Mix up a very small (.5 ounce?) batch of epoxy and mix in some micro balloons. Keep adding micro balloons until you have a slurry about the consistency of peanut butter.
Apply this epoxy filler paste slightly proud to your repair, then sand flush. Keep applying and sanding until it blends/fairs perfectly with the surrounding profiles. When your filling and fairing creates a perfect match with the surrounding profiles, it will have been sanded to at least 220 grit, or even better 320 grit.
It isn't quick and easy to make a good and long term repair to cracked fiberglass. A quick repair means you will be doing it again. Very carefully masking around the area to be repaired is always a good plan. Apologies for the winded reply...
Hope this helps, Cheers!
 
There are great books available on glassing and repairs...if you're on a budge there are plans for the still Long Ez floating around on the internet to download...very good general construction techniques in there.
 
Richard's repair approach is spot on. The basic repair done on boats everywhere!

Just keep in mind that thick layups are heavy. Keep your repair small (within strength guidelines) and epoxy to a minimum. Usually the weight is well worth the strength of the repair.
 
Back
Top