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Power-off glide?

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What avbug said and the others for power on approaches. Practicing for power off glide/approaches is fine but not as a normal everyday approach especially in higher power/tubocharged aircraft. If you are nervous about single-engine aircraft there is always twins.
 
TDturbo,
My major beef with that article is that the author repeatedly refers to his "gut feelings". In reality, he is just making a guess. He states he has no evidence, just theory. Let's look at another "guess". I fly 182s out of a small dropzone in northern Wisconsin. It wasn't unusual this winter to see temps around minus 20 degrees fahrenheit at 11,000MSL. On climb out I had CHTs around 400 degrees fahrenheit. Common practice is to allow no more than a 25 degree drop in CHTs per minute while descending. Imagine if I were to go to flight idle immediately and went into a descent with IAS around 160kts...the CHTs would drop like a rock (or skydiver even...). The front of the cylinder exposed to the relative wind is experiencing a much more rapid cooling than the rear of that same cylinder. The difference in contraction rates distorts the cylinder. It may not be much...but over time it would seem to matter a lot. This last winter with me flying...no jugs had to be replaced. Last year 3 jugs were replaced. The only major difference being that last year's pilot treated the airplane like a 2 dollar....(fill in the blank). The engine in the plane has over 2500 hours since overhaul. TBO is an arbitrary number set by the manufacturer. It does indeed not mean anything. You can use an engine past TBO all you want as long as it can pass an annual/100 hour. I think TGTBO should be the term (total guess time between overhaul). Just my opinion and a barbecue chicken san'wich.
 
AVBUG

I'm just curious. Does your background include extensive experience with large "round" engines?
 
If you have a 2000 TBO engine and your replacing the top end every 500 hrs thats normal? TBO gives you a baseline on what you SHOULD see out of the engine and IS an important number to judge engine treatment. If your engines consistantly need overhall before TBO, your doing something wrong. It maybe an arbitrary #, but it gives you an idea on what the engine life should be, thats all I'm saying.


AWAcoff,
Your preaching to the choir here, I never advocated chopping power from cruise in subzero temps to practice power off landings; I just believe you should stay current doing them in small planes weather permitting. As far as shock cooling in small engines, I don't buy it, that is only one of hundreds of articles debunking that wives tale. Sure, shock cooling a hot running big turbo is unwise, but the initial intent of the threads author pertained to training aircraft, hence the observation.
 
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Surplus,

It does; it includes time spent flying them, and working on them as a mechanic. It also includes time spent working as a mechanic on turboprop engines, and turbojet engines, and even a short time as Director of Maintenance. I will never claim to be an expert, or even very knowledgable on most subjects.

On the subject of shock cooling, there have been some very good articles written each way. My favorite were written by Kas Thomas, who used to write for TBO advisor. I have several of his books right next to me. (Worth reading for those operating piston engines, incidentally; Fly the Engine, is a good one). He published a very convincing article years ago that seemed to disprove shock cooling, and then years later he published an equally convincing article that proved it.

I performed maintenance for a company one season that flew 30 piston airplanes. During five months, I changed 28 cylinders; cracked between the valves in the head, as a result of shock cooling. I'll grant that we felt part of the cause was due to some changes in Metalurgy that Continental had effected in their cylinder construction; the cylinders were without question more susceptible to damage, but the fact was it wasn't the metal that caused the cracking; it was the pilots.

I believe in the dangers overboost because I've changed enough cylinders on my own airplanes when the heads came off...after years of exposure. I believe in the dangers of shock cooling because of experience. That's not to say many more years of experience with diving airplanes at idle and seeing no damage couldn't convince me otherwise...but it's not a risk I'm willing to take, and it would take a lot of years to undo my belief in what I've seen to date.

On any given flight, I had 14 times the number of cylinders to deal with during the course of that flight, than most light airplanes today. It only took one to wreak havoc, and I was also responsible for maintaining those cylinders, and the rest of the airplane. I took them very seriously, and I got a LOT of exposure to the potential hazards that those engines might encounter. Shock cooling is real, as are the other hazards mentioned.

TBO is a misunderstood subject. TBO is a number. It doesn't change, except by ammendment. It's only purpose is a guideline, except for operators under Part 135. It is not a mandatory interval. It represents nothing but a best fair guess as to a general time that an overhaul *might* be recommended. Shock cooling doesn't affect TBO. Running sulfuric acid in the engine doesn't affect TBO. Shooting the engine with a .50 BMG round doesn't affect TBO. It stays the same.

An engine might not last until the recommended TBO. That still doesn't change the nature of TBO. It's an arbitrary number which is established at the time of manufactur, and is subject to ammendment. The amount of time an engine actualy goes before it's owner elects to have it overhauled has no bearing on TBO. Once an engine is overhauled, TBO no longer applies; it's based on a factory engine, first-run. For example, an engine with a 2,400 hour TBO gets overhauled at 1,800 hours. How many more hours does it have? Who knows?

Under part 91, engines are operated on-condition. An engine may be operated beyond TBO safely for many hundreds of hours, or it may require overhaul after only several hundred hours. There are many degrees of overhaul. An engine which has experienced several top overhauls, or cylinder changes during the course of it's life prior to "TBO" isn't working toward TBO any more...because it no longer applies. It didn't make it. This is very common. The engine is operated on-condition. The only time that TBO becomes mandatory is under 135, when an exemption is required to operate the engine beyond TBO.

I have worked for operators that were responsible for extending TBO by 300-400 hours, by submitting the data from our programs to the manufacturer. Accordingly, we were able to operate aircraft far beyond the origional TBO, while flying under 135. One employer single handedly extended TBO on a common piston recip by 400 hours, 50 hours at a time. We did complete teardowns, split the case, and everything. Lots of documentation and testing. Then we rebuilt the engines and moved on.

An engine may not make it to "TBO", but it doesn't change TBO. what prevents an engine from getting there may be a number of factors involving mechanical defects and operating conditions, but by and large the biggest single factor is the pilot. Metal remembers; any stresses placed on a metal part are there for the life of the part. Stress is cumulative. You may do power off descents and rapid changes until the cows come home and see no damage. However, the stresses are there, much like bending the tab on a pop can back and forth many times. Sooner or later something will give. Is it the last 50 renters that abused the airplane to this point, before you take it, or the next one? Will it be you?

Treat those engines like your life depends on them. They're your best friend. Treat them like your life depends on it, because...it does!
 
Power-off landings

Back to the original idea: power-off landings.

I've had some instructors who expoused this idea mentioned earlier that every approach should be set up so that if you should lose power at any time, you should be able to complete the landing.

I understand this business about the back-side of the power curve etc., but still not sure if I get it. If I were to suddenly lose power completely, wouldn't my rate of descent increase? Or does the back side of power curve mean that I extend my glide path. Does this require a different airspeed from the approach speed?

Thanks for helping clear this up.
 
TD,

What make/model engine are you flying that's only getting 500 hours? What kind of overhaul is being performed? What type of aircraft, and what kind of operation? What experience level for the pilots?
 
Good post avbug,

I think were getting caught up in semantics instead of substance. I understand what you are saying and feel we are on the same page.
 
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avbug,

I was using the 500 hrs an example of a common TBO for a small plane. If you're not making it to TBO and replacing major components at 500hrs on a 2000hr TBO engine, somethings wrong. When I say shock cooling doesn't effect TBO in a normally aspirated small engine, I realize it doesn't change the factory given #, only the ability to reach that #, therefor effecting that engines TO BE OVERHAUL time. Like I said, semantics.
 
I think AvBug's point is that "making TBO" is not necessarily a good measurement of how well an engine is cared for. TBO is fairly arbitrary, and a well maintained and properly operated engine can make it well beyond TBO.
 

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