jynxyjoe
Queso King
That's recommended procedure isn't it?
Get your popcorn ready...
- Thread starter FDX8891
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That's recommended procedure isn't it?
Firebird2XC
Well-Known Member
I never said engineers made the rule I said engineers made the POH- which contains the tables and charts.
Hacker15e
Who am I? Where are my pants?
I'm glad you can speak for all engineers, everywhere.
drunkenbeagle
Gang Member
Can't anyone take a joke anymore?
But, I actually don't know any engineers that write manuals - we generally outline things for technical writers, who then pass it on to legal. Once, in a rare while, we are asked to review what they come up with. That's my experience, anyway.
Very helpful. Thanks Hacker.
What he said. Except, take it to 500. In other words, there is a point where it is bad for your engine. I don't know enough to know if detonation is the result, can't remember if I've read that or not. Maybe someone knows for certain? I'd love a good source on it to save somewhere for reference. Thanks.
Anyways, as long as you follow the engine limitations from the engine manual you're fine. You just need that manual and the Sea Level and Altitude Pressure chart.
What our college did was use the point of minimum allowable difference between MP and RPM on this chart and added about 500 RPM fudge factor. What this came to in our IO-360 engines was no more than 4 units difference.
1 unit = 100 RPM = 1 MP, so 24" MP and 2000 RPM is 4 units difference and would be safe to operate continuously at any altitude with ~500 RPM at even the most critical altitude for that particular setting.
Then again, we were always taught to fly with RPM lower than manifold pressure whenever possible for a few reasons:
- Less noise is nicer on the ears, incidentally reducing stress. According to wikipedia, loud noises can also cause premature ejaculation. I just learned that and wow am I glad they taught me to fly like this now!
- Less movement inside the engine means less engine wear.
- It is far better on gas!
Douglas
Old School KSUX
True! "Flying High Performance Singles and Twins" is a great book. I'm glad you read it.
---
The book isn't cheap, it isn't a page turner, but it will simply take the reader to the next level of piston/aircraft knowledge.
The first chapter is titled "The Air"
I had been teaching flying for two years and cockily started reading "The Air" but it knocked me on my butt in 10 pages.
jynxyjoe
Queso King
Pretty damn good book, have had it in the library for years.
ppragman
FLIPY FLAPS!
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.
jynxyjoe
Queso King
You're dangerous, pull the chute next time you Alaskan cowboy bee-bop.
I kinda lost my angry rant at the end there.
Blackhawk
Well-Known Member
Unfortunately, however, operators will often mistake a cause and effect and perpetuate myths that have no factual basis and make non sequitur assumptions/arguments. As an example I have sometimes heard a pilot state that leaning the mixture during taxi will burn a valve and they will site some person who leaned their mixture during taxi and a valve got toasted at some point. They mistakingly tie the leaning during taxi with the burned valve- the two are not related.
ppragman
FLIPY FLAPS!
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.
Take for example dreaded "shock cooling," I know of at least a half dozen operators off hand that stage cool their airplanes to prevent excessive reductions in CHT. The Continental and Lycoming manuals list a maximum change in CHT over a given period of time that is acceptable. The operators are in this case simply narrowing the allowable margin. Coupled with good preventative maintenance these techniques can depending on the implementation, be more conducive to engine longevity than the tolerances defined in the engine's operating manual. That doesn't mean that you shouldn't run "ovEr squreD" (OH TEH NOES!!!), and as always, you must consider the source. But operators are highly concerned with their bottom line, and given time may develop highly accurate ways of increasing engine life.
Blackhawk
Well-Known Member
Oh really now. Please explain to me the cause and effect. How is it that leaning agressively during taxi burns out a valve?? CHTs are well below 400 F. BHP is (or should be), well below 65%. Pressure within the cylinder is very low. So what is it that you know that engine experts such as Mike Busch don't know?
Burned out vavles have nothing to do with leaning during taxi; if anything agressively leaning during taxi helps to prolong valve life while taxiing with the mixture full rich is a detriment to valve life.
http://www.foxflying.com/engine_leaning.htm
http://www.avweb.com/news/airman/184502-1.html
http://www.swaircraftappraisals.com.../Operating Tips for Big-Bore Continentals.htm
You have just proved my point about pilots making non sequitur assumptions.
ppragman
FLIPY FLAPS!
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.
Who said anything about burning valves?
I don't think anyone said that all operator develop correct procedures. However, I'd put my money on at least a few currently exercised procedures being pioneered by operators and not engineers. Logic would tell me that this would be most likely in the places furthest from ideal conditions used for aircraft testing as they present opportunity. To fault all operator procedures because of examples like this, to me, seems like a non sequitur assumption.
drunkenbeagle
Gang Member
I don't think anyone said that all operator develop correct procedures. However, I'd put my money on at least a few currently exercised procedures being pioneered by operators and not engineers. Logic would tell me that this would be most likely in the places furthest from ideal conditions used for aircraft testing as they present opportunity. To fault all operator procedures because of examples like this, to me, seems like a non sequitur assumption.
I can assure you there are no procedures in the book for the glider towing operations I do. (the book covers dusting and spraying ops.).
So basically, we do what other operators have had success with.
ppragman
FLIPY FLAPS!
This.
I was always taught that the POH isn't regulatory anyway -- except the limitations section. I'm sure you've heard me preaching that in the past. Anyway, to think flight testing in ideal conditions provides good information for all conditions is simply silly.
So I think we are in agreement.
Blackhawk
Well-Known Member
I don't think anyone said that all operator develop correct procedures. However, I'd put my money on at least a few currently exercised procedures being pioneered by operators and not engineers. Logic would tell me that this would be most likely in the places furthest from ideal conditions used for aircraft testing as they present opportunity. To fault all operator procedures because of examples like this, to me, seems like a non sequitur assumption.
I don't deny that operators can identify problems and develop procedures in the field that engineers can't duplicate (I've been involved in doing this myself), but you need to be careful in your evaluation of procedures to ensure there is a relation to perceived cause and effect. The relation may be related, or may be random and related to something else. I used the example of leaning an engine during taxi on purpose as many pilots still claim they have burned valves doing this- but anyone who actually knows anything about how engines operate will tell you that this is not only impossible, but not leaning an engine during taxi will decrease the longevity of the valves. What happened is that pilots may have leaned during taxi. Unrelated to the leaning during taxi a valve got toasted somehow. The pilot incorrectly correlates the leaning during taxi to burning the valve and preaches this as gospel. This is born a procedure in the field based on poor understanding of systems and faulty logic in causes and effect.