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Broken Exhaust Stack - Forced Landing
From CP73, Page 5, (October, 1992)
I'm writing this letter in the interest of safety for all
canard-pusher type designs. Please feel free to edit or paraphrase it at will; I just want
to help others avoid the scare that I had.
As a little background, I bought my Long-EZ about two and a half years ago with 400 hours on the airframe. Since then, I have put almost 300 more hours on it, including a trip around the borders of the US last summer. I love my plane, but my only regret is that I did not have the honor of building her myself.
Last week, after doing an oil change, I took off into a quiet Friday evening sky at my home field for a test flight. I climbed to 8,000 feet, where I spent about 15 minutes watching the sun set, after which I started my descent.
Suddenly, there was a loud bang, followed by violent vibrations. I immediately pulled the throttle to idle and shut off the mags as I pulled the nose up. The prop stopped quickly, and I was able to see in my rear-view mirror (a small convex mirror inside the canopy for looking at my passenger) that something had hit my B&T prop and that it was badly broken.
I decided to keep the engine off and glide back to my home field. Fortunately, I was at about 5,000 feet and only 10 miles from my airstrip, a milelong asphalt runway. This would have been possible in any plane, but was an easy task in the Long-EZ with its great engine-out performance. announced my problem on unicom and the FBO operator monitored my descent.
As I touched down on the runway, I was amazed as to how dark it was, for I'd forgotten that sunset at 8,000 feet occurs quite a while after it had on the ground at sea level. I rolled out without any problems and got out to inspect the damage and determine the cause.
It was immediately obvious that my right exhaust stack had broken inside the heat muff box and that was what had damaged my propeller. The damage to the prop consisted of complete loss of the plastic rain edge, a gouge out of the leading edge of the blade measuring about I inch by six long, and a 5 inch longitudinal crack propagating from the impact point towards the hub.
After pulling the cowlings and exhaust stack, I was able to determine that the cause of the problem had been entirely the result of the builder NOT FOLLOWING THE PLANS and my A&P mechanic and I missing a problem in the recent annual inspection (5.5 flight hours prior).
The heat muff and been built as per the plans except that it had not been welded directly to the exhaust stack. Instead, it had been built to be a snug fit. The problem with this was that this design allowed it to vibrate, albeit in very small movements, and this slowly ground away at the wall of the exhaust stack. The groove was deepest on the inside wall of the muff. After almost 700 hours of use, the walls of the stack were paper thin and finally gave way, allowing a half-foot long section of the exhaust stack to separate and hit my prop.
Believe it nor not, this failure may have saved me from an even greater danger - that posed by carbon monoxide poisoning from exhaust gases leaking into my cabin air system.
1. With the engine off, I'm glad I have a Long-EZ, as she has a great glide ratio and handles like a dream.
2. I was glad that I had practiced simulated engine failures just the flight before; the practice really helps out.
3. Build your planes as per the plans. If you do buy a used RAF design, go over each and every step in the plans (which should be included as a condition of sale) to find where an error or oversight might have occurred.
4. Pay special attention to the dangers of very small vibrations; small movements over long periods of time can grind through very strong metals.
I hope that this information is of help. If there are any of
you out there thinking of buying a used EZ, please call me. The designs are great, but, as
experience has taught me, used homebuilts have an unusual number and kinds of pitfalls.
Have a great day flying, and thanks to the folks at RAF for their continuing support.