Engine Gurus

Aztec Driver

Aztec Driver

Line Up and Wait
Joined
Mar 7, 2005
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Elizabethtown, PA
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Bryon
Ted, and others much more experienced than I on engine wear and tear.

I recently flew with a person for an "interview" for a new flying job. There procedures for engine management were far beyond my normal engine management lessons learned in the past. While they are not particularly dangerous, and they are somewhat understandable, they seem a bit extreme.

This is on a normally aspirated IO540.

The startup and run up procedures are normal, but takeoff is a bit on the long side. I usually take 3 seconds or so to go from idle to takeoff power in the planes that I fly. Smooth and slow, at least, that is how I considered it. It could be standing on the brakes for a short field, or a rolling takeoff, but it would still be approximately 3 seconds to get to full throttle. The procedure they would like me to employ takes considerably longer, reaching full throttle at or just before rotation speed on a rolling takeoff, or holding the brakes for a good 8 seconds of slow throttle increase.

Any real reason to go this slow? I understand it is less stress on the engine all at once, but to this extreme?

Descent and power reductions are a little better, but they would like a limit of 500 fpm and 1" mp per minute, which is reasonable. It does make one calculate way ahead of the norm, and hope ATC is flexible.

Shutdowns are made at or just above 1000 rpm, "to prevent plug fouling." "Running it idle for any length of time and then shutting it down leaves a lot of unburned fuel in the cylinders., causing plug fouling." This one I am dubious about, but ask for anyone else's input.

I will certainly run it as they require, but I would like to make sure these procedures make sense.
 
I think I'm going with Henning's answer. Pretending to baby the engine and simultaneously lowering their safety margin below what the manufacturer put in the book for takeoff seems like a really stupid combination. I bet the book numbers for takeoff distances weren't done under those conditions.
 
Sounds like an interesting approach to bringing on power. I have to bring on power slow in the 'kota 'cause it's got a funky wastegate. With a normally aspirated engine I wonder what they are thinking.

How is fuel trim set on the engine? Is it just set at idle and full power or is it checked at points in between? Full rich, full RPM, and partial throttle sounds like a weird place to be. Maybe it isn't weird, :dunno:
 
If you had really crappy fuel, so bad you had to limit acceleration, it would make sense.
 
Three issues...

1) Power Advance on takeoff. Is there any science behind their preferred technique? Or even logical reasoning?

2) Shock Cooling - I understand that one. Good luck with it in the real world.

3) There is some merit to idling >1,000 rpm prior to shutdown. It keeps the cylinder temps higher and minimizes lead fouling. But their idea of unburned fuel in the cylinders at shutdown is silly. How do you shut down the engines? By removing fuel. Their reasoning doesn't stand up to logic.
 
We used to take like 3 seconds on our 550s, I do the same on my personal stuff.

Decent, it's all about CHTs, 1 degree per 2 seconds max, I lean for decent to keep the temps up, stayed in the green till short final, always worked fine

Shutdown, idle then ICO for a N/A engine. Worked fine.
 
The only opinion that matters is that of the person who owns the plane and writes your check.

As an example, I was 18 with maybe 150hrs in a logbook when I moved from the C337 to the C421. The ops spec for us babies allowed 4 or 5 specific MP/RPM/Mixture combinations for us to use for all phases of flight, no exceptions.

I thought that was stupid, we were wasting fuel, losing speed, running at elevated temperatures, you name it for a given situation. But I kept my mouth shut and followed the rules. I stayed employed. And the engines in those 421's lasted and lasted.

Managers develop work rules in response to specific problems they have experienced. Who knows what your new boss's reason's are, but he gets to make the rules.
 
JHW said:
The only opinion that matters is that of the person who owns the plane and writes your check.

.
Click to expand...

There ya go.

You fly my planes you will make power settings and power reductions and decents as I train you.

On the ground you will be off the brakes for taxi. No brakes on landing, 7000+ feet is long enough to slow down.

Cylinders and brakes cost money. Use them up and you bonus is lower. Burn them up and you will be driving a truck...:lol::lol:
 
I think the power reduction 1"/min is an overkill on a NA IO-540. I personally use about an 8 second application of power runway permitting. In particular I am gentle with the throttle if the engine has not been up to cruise operating temperatures.It hurts when I hear the roar of a big engine thatjust had the throttle stuffed. Why do people do that? In my twinkie I found that having an engine cut out at full power and very low speed is a lot more exciting keeping straight than it is losing one at a higher speed.

Charlie Melot Zephyr Engines
 
and there was no discussion about leaning?....and running lean of peak?:goofy:
 
I definitely WILL run the machine to their specs. So you can stop those comments. It is their machine, after all.

I just thought it a little extreme.

No mention of riding brakes, but keeping the engines at around 1000 rpm constantly makes for an interesting taxi, especially if downhill. He frowned every time I brought the engines down below 1000 when I wanted to slow the taxi down and without riding the brakes. I would have thought he wouldn't want the brakes used like that either.

And, yes, we run lean. 1500 EGT running at 23/2300. GPH down around 26.

Nothing too dire or life threatening, I just wondered what others thought, preferably the folks with more engine experience. :D
 
Brake pads are cheap and easy to replace. You can change brake pads faster than cleaning plugs.
 
I also think the splash lubrication of the cam is reduced significantly under a 1000 rpm's. That might have something to do with it.
 
So if they are a commercial outfit, assuming part 135, can they go beyond TBO? or is that operational specific to whatever was approved? Why I'm asking is, I can see them being like that to get 4,000hrs out of the motor, but if you can't legally, why bother?
 
I'm not a guru - I run an IO-540 in an RV10.

I attended Lycoming's engine school and was told that cool running combustion chambers is what 'fouls' plugs with lead deposits. It's not excess fuel or unburnt fuel, but rather it's a temperature driven event. They mentioned tests where lead formations were observed increasing rapidly at specific temperatures.

They suggested that idling no lower than 1000rpms and keeping it well leaned all the way to shutdown would prevent lead fouling for the most part. I've done that over my engine's first 600 hours - so far so good except for an hour long conga line at Oshkosh. I find 1000rpms comfortable for taxi but twice the thrust on a twin might be a different matter.
 
mrkbbd said:
So if they are a commercial outfit, assuming part 135, can they go beyond TBO? or is that operational specific to whatever was approved? Why I'm asking is, I can see them being like that to get 4,000hrs out of the motor, but if you can't legally, why bother?
Click to expand...

In general, 135 will be tied to TBO and any other Service Bulletins. However, there are programs that when arranged allow you to go beyond TBO 'on condition'.
 
Henning said:
In general, 135 will be tied to TBO and any other Service Bulletins. However, there are programs that when arranged allow you to go beyond TBO 'on condition'.
Click to expand...

For my company we can go over TBO to take the plane where it needs to go for engine replacement.

In the bush I think we could go over TBO on the condition that the replacement engine is in transit, but only 10 hours over.
 
Zeldman said:
For my company we can go over TBO to take the plane where it needs to go for engine replacement.

In the bush I think we could go over TBO on the condition that the replacement engine is in transit, but only 10 hours over.
Click to expand...

I have heard of, not seen, operators getting 3000hrs.
 
Most of their procedures are taken from Lycoming Service Instructions.

The 1000 rpm's for 30-60 seconds before shut down is word for word from Lycoming as a way to prevent lead fouling from idling before shut down.
 
It sounds to me like they're paranoid about their engines. I don't see any merit from an engine perspective to the 8 second throttle advance. Holding the brakes while advancing power is hard on the props as well. From a short runway, you're obviously hurting your takeoff roll and that ultimately gives you fewer options. I can see Charlie's point regarding full power at low speed being "interesting" in a twin, and so runway permitting I don't see a problem there per se. But for the engines, don't see the point.

In 1,000 hours in the Aztec, I never once had a fouled plug. I don't even think I ever changed the plugs, either, just did the normal cleaning and gapping, and that was every 100 hours or so. I also never shut down the engines above 1,000 RPM. Came in at my normal 600ish RPM loping idle. Used whatever RPM was appropriate for taxiing. Do the same in the 310. Had one fouled plug in 700 hours, but those were on old plugs.

So my opinion, they're being quite extreme. But, as Jeff said, it's what the boss wants, no problem. When I was flying the Navajos I got told by the boss to run them ROP, and the boss liked 33"/2300 RPM for cruise. Fuel and MX bills weren't coming out of my wallet. :)
 
comanche pilot said:
I also think the splash lubrication of the cam is reduced significantly under a 1000 rpm's. That might have something to do with it.
Click to expand...

I was going to mention that. Not sure about that particular motor but I've seen it mentioned several times about mine.
 
rbridges said:
I was going to mention that. Not sure about that particular motor but I've seen it mentioned several times about mine.
Click to expand...

I'd not be worried about that aspect. Cam failures come from lack of lubrication during cold starts and from corrosion while sitting.
 
Ted DuPuis said:
I'd not be worried about that aspect. Cam failures come from lack of lubrication during cold starts and from corrosion while sitting.
Click to expand...
and from poor mfg process control.....leading to out of spec tappet hardness. :yikes:
 
Checkout_my_Six said:
and from poor process control.....leading to out of spec tappet hardness. :yikes:
Click to expand...

Also correct. I'm assuming a part made properly. If it's not, it ain't a gonna last anyway.
 
mrkbbd said:
So if they are a commercial outfit, assuming part 135, can they go beyond TBO? or is that operational specific to whatever was approved? Why I'm asking is, I can see them being like that to get 4,000hrs out of the motor, but if you can't legally, why bother?
Click to expand...

Part 91.
 
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