Hairline cracks in top cowling

[PeytonM]

1989J, 2800 hrs.  I have three or four longitudinal hairline cracks, 4-6 inches in length, along the left side of the "bulge."  A MAPA Log article (2000) mentions an STC to add a rib, which suposedly fixes this once and for all.  I have already had a couple of repairs that failed, the most recent in less than six months!  Suggestions?  Who holds the STC?

[Piloto]

I had the same problem and fixed by applying a heavy coat of boat fiberglass resin underneath the cowling. It has been 7 years since and no cracks has shown anywhere. You can get the resin at most boat marine stores.

José

 

[johnggreen]

Peyton,

I agree with Jose' with a slight alteration.  I have owned two 8KCAB Decathlons.  The wheel pants are of very light construction and will crack without fail in just a few hours of flight time.  With my first Decathlon, which I bought with 800 hours total time, the wheel pants were totally covered with spider webbing.  I layered the inside with cloth and resined it in.  Repainted the pants and never had another crack.  With my second, which was almost new, I just pulled the pants when I bought the airplane and layered it as in the first set; not one crack after 200 hours of use which is when I sold the airplane, last year.

 

Do what Jose' says but don't use fiberglass resin, use epoxy which you can buy though West Marine products.  It is the same material that is used in aircraft construction and MANY TIMES the strenght of fiberglass resin.  Also, get the lightest fiberglass cloth you can which is also available through West Marine and put one layer of cloth on it.  It will add mere ounces and you will not believe the strength.  To get the visible cracks out will required removing paint and brushing on some pure resin with the sanding additive.  Check with a IA, but I don't believe you will run into any reg issues as long as the weight is minimal, which it will be.

Jgreen

[jwilkins]

My 231 cowl has a somewhat sloppy job of what looks like JB Weld reinforcing inside the cowl. It has worked to prevent more cracking but looks a bit amatuerish. Functional, but could have been done better.

It's been a few years since I've used them, but I give a strong second recommendation on the West System Epoxy. http://www.westsystem.com/ss/

Do yourself a favor and buy the West System pumps for metering the epoxy and hardener. It's worth it just for the mess it saves, and is more accurate than you will be trying to measure from the containers.

I fully recovered a woodstrip racing canoe (and made several repairs after finding rocks in the rapids). The wood strip canoe used the 4 oz fabric, but you might want to ask West if the carbon fiber would be better for the cowl reinforcement.

In my opinion the West System is the best source for Fiberglass Mesh / Epoxy fabrications and repair supplies. I know it is amazingly strong, bonds well to fiberglass (and wood), and would produce a professional looking reinforcement.

[jetdriven]

Previous owners used poleyester boat resin and fiberglass cloth on the top cowl, and it looks like shit. It also does not contribute much to stiffness becasue boat resin is softer than the epoxy and cloth your cowl is made from.   Cracks continue.

I would use epoxy and cloth, and use peel ply to get a smooth finish.

[Kwixdraw]

Check fiberglast.com .  Good products and info on proper use for various applications.

[PeytonM]

Shutdown, per POH: 1000-1200 RPM, already leaned during taxi.  Idle cutoff.