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From: William R. Bayne [mailto:[EMAIL PROTECTED]
Sent: Sunday, December 04, 2005 5:07 PM
To: Ed Burkhead
Cc: Jerry Eichenberger
Subject: WRB Re: [COUPERS-TECH] C-85 approaching TBO time
RLYTECH
On Dec 4, 2005, at 11:16 AM, Jerry Eichenberger wrote:
I would vote to overhaul it. I have some personal experience to share withHi Jerry,
you:
About 30 years ago I owned...a Bonanza...with 5 other fellows...at TBO - everything with the engine was great - no oil
burning issues, great compression, ran like a fine watch, and oil analysis
showed no unusual metal.
We voted to, and did, run it another 100 hours. At that point, the group,
except for me, wanted to go another 100 hours. I put my foot down, and said
to either overhaul it or buy me out. We overhauled it.
The crankshaft had a crack, 270 degrees around the circumference, at the
number 5 main journal.
No amount of oil analysis, compression checks, or boroscoping will ever find
cracks, be they in the crank, oil pump drive gears and shafts, camshaft,
prop flange, or a few other parts that can cause a sudden and catastrophic
engine failure.
What you say in the paragraph immediately above is obviously true, but is it a "whole truth" upon which a decision of such major potential expense should be made? Sudden and catastrophic engine failures these days are rare, and even more so on the little low-compression Continental engines. I question if they are statistically significant. Consider the many people who agonize over being struck by lightning (extremely rare, statistically), yet get into a car without a thought (in which deaths are so common as to not always even make the local news. Their concern is out of touch with facts representing reality.
I agree most cracks are found at overhaul time (Magnaflux or Zyglo inspections) or after failure of the part (poshumously).
On the other hand, I believe the stresses a Bonanza crank is subject to (considering the higher compression ratio, higher output per cu. inch, and debilitating effects of such an engine by shock cooling, poor leaning practices, and generally higher expectations on the part of pilots) make any comparison with our low-compression stone-age fours one of apples and oranges.
The Ercoupe fleet has, on average, far fewer hours per engine and airframe than Bonanzas, Cessnas, etc. I would even go so far as to speculate that the great majority presently active either have the original crank (without cracks), or a crank that has been reground (from original manufacture, also without cracks).
Engines have a TBO for a good reason. And, remember that TBO is usually
based on the airplane's flying about 300 hours per year. Since very few
privately owned airplanes fly even 100 hours per year, the ravages of time
affect those engines just as much, if not more so, than hours alone.
The idea of TBO is one of "one size fits all". With any such "average" (which, in this case tends to be an understandably conservative one) there are the "if it ain't broke, don't fix it!" ones, those that are clearly overdue (that some may wonder how they made it this far) and those that failed before TBO. The "ravages of time" are seals and hoses becoming less flexible, tires weather checking, etc. An overhaul is not necessary to fix such things.
If my recollection is correct, Continental also has a "time since overhaul" recommendation independent of operational hours. It should go without saying that if an engine is overhauled at 600SMOH since an overhaul in 1951, it is highly unlikely any of the "hard" wearing parts would require replacement. Rehoning of cylinder walls with a set of new rings and engine gaskets and hoses might comprise most of the cost of such an overhaul on a mechanic-owned engine.
In my 40 years of flying, I've suffered 3, total, engine failures of a
mechanical nature. I don't want a fourth, especially in an Ercoupe.
Why do I say "especially in an Ercoupe"? For two reasons:
1. While one can adjust glide angle in a Coupe using airspeed, we do have
to admit that with no flaps, and no ability to slip, modulating glide angle
is more difficult that in an airplane with flaps, or one that can be slipped
effectively; therefore, you better plan your engine out approach very
carefully, and do it right the first time; and
I respectfully disagree. If one modulates one's glide angle by setting up an intentionally slower glide speed with a known greater rate of descent, and/or performs "S-turns" in lieu of using flaps or "slipping", the result is the same. It is the responsibility of the owner/pilot to become completely and competently familiar with the flight characteristics (and options thereby) of their aircraft over time. An emergency is NOT the time to confront such limitations for the first time. One should KNOW their best glide speed, descent FPM at that speed, and slowest safe without power and descent FPM at that speed whether by memory or by posting. One should KNOW how many feet they lose in making a 90-degree turn in a glide at both glide speeds, and what the "pilot picture" is during such an approach from prior practice repeated from time to time. Do these things and you are unlikely ever to make the evening news even after experiencing an emergency you were reasonably prepared to competently handle.
2. With a header tank always full of fuel, Ercoupes don't have the world's
best accident record relating to fires after a crash, especially if the
airplane ends up inverted and you can't get out of it.
Once again, think this through. If the pilot can make the arrival at minimum speed with less than a 600 FPM descent on reasonably level terrain with no less than ten feet between the trees chosen to slow the plane ;<) the nose tank cannot rupture. As pilots, we are responsible to always have a reachable landing spot picked out when aloft; even if some aren't very desirable (such as over water). It's one reason to fly cross-country higher (as opposed to lower). Altitude = more options. If you select a too-soft field and the nose strut digs in and flips you, it is by no means a "given" that there will be a fire. The great majority of such incidents did not.
On the other hand, if one is not prepared, not competent, panics, or makes poor decisions, yes. Contact with terrain at a speed and angle sufficient to rupture the nose tank have resulted in fires. Again, most of the time they don't, and of those that do, the occupants are successful in exiting the aircraft. If I didn't believe the risk of an emergency landing post-arrival fire to be a manageable one, I wouldn't fly a coupe.
Regards,
William R. Bayne
<____|-(o)-)____>
(Copyright 2004)
So, I'll spend the money and overhaul at or before TBO.
Jerry E.
-----Original Message-----
From: Ulrich Hertig [mailto:[EMAIL PROTECTED]
Sent: Sunday, December 04, 2005 3:09 AM
To: [email protected]
Subject: [COUPERS-TECH] C-85 approaching TBO time
Dear Coupers,
right now I have a chance to buy a Coupe which seems
to be in excellent condition but the engine has almost
1800 hrs. All 4 cylinders have been replaced during
the last 150 hrs. The seller says the engine runs
fine, uses hardly any oil and has a high oil pressure
indication so there is nothing to worry about.
Now is it advisable to run an engine beyond its TBO
time? And how about the other parts in the engine like
crankshaft, bearings etc.? Do I have a higher risk to
encounter major problems?
I'd be most grateful if anybody has experience on this
subject and could advise me.
Many thanks.
Ulrich 'Rick' Hertig
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