Get your popcorn ready...

[Blackhawk]

I lean aggressively during taxi. I didn't say that leaning aggressively during taxi caused burnt valves. What I said was that when a company changes something and has a problem go away, they tend to stick with it and its probably a good thing. Reading comprehension here man. I do know 207 operators that have said, "don't lean other than taxi," or "don't touch the mixture and stay below 1000'." Then they have the mixture adjusted to give about 18GPH at the cruise power setting. Nothing wrong with that if the company finds that its jug cracking / valve burning problem goes away in that particular kind of operation. An operation that has terrain to clear, and will have to frequently go above 1000' might have to adjust accordingly.

Again. I aggressively lean during taxi. I never said I didn't, and I've never heard of a company that said leaning was bad during taxi. But I do know of companies that have changed their policy on in flight leaning or stage cooling with good results. What companies do you know of that have told their pilots not to lean during taxi? Seriously. You want to talk about non-sequitor. Seriously though. Read what I wrote.

I read this part:
"This is not incorrect. Take all hangar talk with a boulder of salt. That said, when a company notices that they are burning through valves left and right, then changes a procedure, and suddenly the problem goes away, it might be an accurate diagnosis of a condition, or at least the technically incorrect logic behind whatever change they made had decent results."
This is my point. I guess I misunderstood what you wrote- it sounded like you were defending this premise and yes... I've heard this nonsense thrown around quite a bit.
When you change a condition and get a result you also need to make sure there is a correlation between the change and the result. Using the example of the burned valves. If a company changes their procedures and stops burning valves they need to also ensure they other conditions stayed the same. Were the cylinders with burned valves overhauled with the exact same valves and in the same way they were originally done? If not the cause may be a fault in the manufacture of the initial valves and using the procedure of leaning during taxi may be detrimental to valve longevity and may propagate false information and poor technique. This is how OWTs get born and propagated- someone in the field incorrectly correlates cause and effect. Again, I have nothing wrong with the operators in the field identifying and modifying procedures as they identify problems. They just need to make sure they correctly identify and correlate the cause and effect before they go monkeying with things.

 

[Chief Captain]

I'll admit to telling students that the MP shouldn't exceed the RPM, but I'm sure to tell them that it's ONLY a rule of thumb, and that the POH should be consulted when setting power. If I'm not mistaken, the Piper Arrow POH addresses this explicitly, and notes that it's incorrect, and the numbers in the performance section should be used.

 

[mshunter]

An old man I know who owns an A36 Bonanza never pulls the throttle off the firewall untill it's time to come down. He controls everything with the mixture and prop. His engine, last time I talked to him (about a year ago), had nearly 3000hrs on it. He had to replace a cylinder about three months after he bought it from it previous owner who had about 200hrs on an overhaul, and IIRC there was some sort of AD or SB about some cylinders on that engine cracking. But, it isn't making metal and compressions are good.

I think it's time to give him a call and see how he's doing.

 

[Hacker15e]

An old man I know who owns an A36 Bonanza never pulls the throttle off the firewall untill it's time to come down. He controls everything with the mixture and prop. His engine, last time I talked to him (about a year ago), had nearly 3000hrs on it. He had to replace a cylinder about three months after he bought it from it previous owner who had about 200hrs on an overhaul, and IIRC there was some sort of AD or SB about some cylinders on that engine cracking. But, it isn't making metal and compressions are good.

I think it's time to give him a call and see how he's doing.

Two words: "Beech Backward".

 

[Firebird2XC]

Actually, you can. Engineers only flight test the aircraft to certain, fairly arbitrary limits. The power plant, while being thoroughly tested may not have been tested in the type of operation that you use. Best bet is to find an operator who's been doing it for years and ask them. Consider this for example, I was doing a takeoff and a landing in the 206 and PA32 on average every 26 minutes if my log book is to be believed. I doubt Continental and Lycoming predicted that style of use in a cool, damp, salt rich environment.

Don't ask the engineer who tested the thing in california for 9 months. Ask the operator who did the operation in your region for 20 years. That guy is bound to know a bit about what makes the things last to TBO.

Those limits are the design operating specifications for the type. I know you fly in some different environments, but isn't there a point to remaining within those?

Operational experience in the field will round out what somebody figured in a lab every time, but using "field expedient" methods can be dangerous.
Not to mention- have you investigated what kind of operating conditions that power plant engineers tested their designs in? I think you're making assumptions.

 

[jynxyjoe]

Two words: "Beech Backward".

After flying the 310 a while I think Cessna has them beat.

 

[tgrayson]

Operational experience in the field will round out what somebody figured in a lab every time, but using "field expedient" methods can be dangerous.
Not to mention- have you investigated what kind of operating conditions that power plant engineers tested their designs in? I think you're making assumptions.

Agreed. Field experience only adds information if the data is gathered in a scientific manner and I doubt most operators are competent to do that. It's too easy for the untrained to interpret random fluctuations in the data as a trend with an identifiable cause.

 

[Blackhawk]

Agreed. Field experience only adds information if the data is gathered in a scientific manner and I doubt most operators are competent to do that. It's too easy for the untrained to interpret random fluctuations in the data as a trend with an identifiable cause.

Much clearer and succinct than what I tried to write.

 

[Mike H]

The "over square" rule of thumb (and that's all it is -- a ROT, which means it doesn't technically apply to all engines under all circumstances) comes from a time when big pistons ruled. With big pistons swinging big props, the inertia of the prop was as important a factor in the health/life of the engine as the inertia of all the pistons moving inside the engine.

Read up on "reciprocating loads" from Randy Sohn to get some background understanding of what drove the MP = RPM rule of thumb.

http://www.douglasdc3.com/sohn/3.htm

The argument can be made that these same forces are at work inside smaller pistons swinging smaller props, but as has been stated, manufacturer's operating specifications always trump ROTs.

If I read the article correctly, it seems to advocate reducing RPM along with MP- including on approach to landing? Interesting