Ted
The pilot formerly known as Twin Engine Ted
- Joined
- Oct 9, 2007
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iFlyNothing
It has occurred to me that there are a number of common questions that come up regarding piston aircraft engines that people may benefit from having some basic understanding on. Below are my Top 10 Tips that have come from my experience operating piston engines for thousands of hours in a number of conditions.
1) Change your oil. You will walk over many dollars to pick up the penny that is extending an oil change. It doesn't need to be excessive. Whatever the manufacturer recommends for interval, change your oil then (this primarily varies with use of an oil screen vs. oil filter). Air-cooled engines have a number of hot spots and are harder on oil than water-cooled engines, and also have more biproducts of combustion slipping past the rings and into the oil due to looser clearances between the pistons and the cylinder walls. This is why air-cooled engines require more frequent oil changes than water-cooled. Make sure you use an oil that is acceptable for your engine. Continental starter adapters don't like the additive that is required by some Lycomings. Lycomings that require this additive genuinely need it.
2) Some engines are prone to detonation, and others are not. Typically, the turbocharged and high-power engines are the ones prone to detonation. The various (G)(TS)IO-520s, (TS)IO-550s, and (T)IO-540s rated at 300 hp or more are the most susceptible to detonation. Your 150 or 172 will not suffer detonation on 100LL unless there is something very, very wrong with it, or you've put in a Navajo engine (which would be impressive). The rule of operating at 65% power or below to pretty much eliminate the "red box" is accurate for most engines. Detonation is an event that has many factors involved (and beyond the scope of this thread). Some engines on 100LL do not have a red box at all. Again, this subject is more complex than the scope of this thread. Each airplane is different, and it is important to know your airplane.
3) There is nothing wrong with leaning your carbureted engine until it is rough and then richening it until it is smooth. This has worked well for millions of flight hours. It even works for some (but not all) fuel injected engines.
4) When you buy an engine monitor, don't panic at the numbers you see. Many calls to technical support are made because pilots install an engine monitor, and are suddenly convinced their engine is about to explode. Remember that it has run in the exact same plane without an engine monitor for decades and thousands of hours before you purchased this piece of equipment. CHTs and EGTs will be different, that is normal. They will vary with the condition of your cooling baffles, the inherent quality of the cooling system design (on many aircraft this is best described as "very poor", and would be graded a D- were it a class).
5) Lycoming recommends keeping your CHTs at or below 425F for climb and 400F for cruise. Continental recommends keeping your CHTs at or below 380F. I aim for 380F or below on the hottest cylinder regardless of Lycoming or Continental. Your engine will not explode if you get over these numbers. Extended operation above these numbers will reduce the life of your cylinders, but don't panic if, especially in the summer, you have trouble staying below these temperatures. In my aircraft, I will aim for 380F or below, running LOP. In the 380-400F range I'll keep a closer eye on it. By the time I hit 410F on the hottest cylinder, I will transition from LOP to ROP (if I don't have an engine that will allow me to run further LOP without roughness) to keep CHTs cold. Note that this is on the 310 and the Aztec - neither of which have optimal cooling, and both of which are naturally aspirated. If I were operating a turbocharged airplane, especially with Continental engines, I would be especially strict about the 380F, but exceeding that still won't cause the engine to explode.
6) LOP won't hurt your engine and ROP won't hurt your engine, provided each one is done properly. Millions of flight hours have been done both ways. The people who have longevity problems are the ones who treat the limits (CHT, EGT, and oil temperature) as goals.
7) Preheat your engine in the winter. It will thank you in the form of better longevity. You can do much more damage by doing a hard cold start on your engine than you can by running above 400F on your CHTs for a few hours. The electric pre-heaters that attach to your engine directly are preferable to the propane heaters, because they will heat the crankcase, crankshaft, oil, and bearings as well as simply the cylinders. All of these are important. A propane heater is still better than nothing.
8) If you have a high-powered engine, an engine monitor is a must, in my opinion. It becomes progressively less important as you have lower-powered engines, but I would put one in any plane I own. Once you have it, make sure you learn how to interpret the numbers that it provides you. I offer courses in this, both on the phone and in your airplane. There are several other good options as well. Any course (from someone who knows what they're talking about) you take will save you money in the long run.
9) With a few exceptions, operation above 75% power for extended periods is not going to provide you much besides high maintenance costs. Regardless of what the Beechcraft, Piper, Cessna, or Cirrus manual tells you: 79-86% power is not a proper cruise power point for longevity, especially on a turbocharged engine. The maintenance bills and engine life for people who agree or disagree with this point speak for themselves.
10) Your POH provides important guidance as far as acceptable power settings, especially on high-powered engines. These power settings may not all be optimal as far as speed and economy, but they are ones that have been considered appropriate because the engine did not suffer from any ill effects that would cause immediate, catastrophic damage. Operating outside of these settings makes you a test pilot. As an example, my Aztec limits you to 26" manifold pressure below 2300 RPM. This is due to propeller vibrations. The Navajo allows leaning to peak EGT (and therefore LOP) below something around 30"/2300 RPM (don't quote me on that). At 40"/2400 RPM, leaning is not permitted - full rich only. Failure to adhere to this limitation will likely very quickly turn your cylinders into piles of molten aluminum. Unless you have the documentation related to certification of your airframe's engine and propeller combination, you don't know if the limits they put in place are due to detonation, harmonics, or marketing, but I follow them anyway. The extra few knots I might gain in a turbocharged aircraft by increasing my MP past the top of the green arc won't make much of a difference anyway.
This is by no means all-inclusive, just a top 10.
1) Change your oil. You will walk over many dollars to pick up the penny that is extending an oil change. It doesn't need to be excessive. Whatever the manufacturer recommends for interval, change your oil then (this primarily varies with use of an oil screen vs. oil filter). Air-cooled engines have a number of hot spots and are harder on oil than water-cooled engines, and also have more biproducts of combustion slipping past the rings and into the oil due to looser clearances between the pistons and the cylinder walls. This is why air-cooled engines require more frequent oil changes than water-cooled. Make sure you use an oil that is acceptable for your engine. Continental starter adapters don't like the additive that is required by some Lycomings. Lycomings that require this additive genuinely need it.
2) Some engines are prone to detonation, and others are not. Typically, the turbocharged and high-power engines are the ones prone to detonation. The various (G)(TS)IO-520s, (TS)IO-550s, and (T)IO-540s rated at 300 hp or more are the most susceptible to detonation. Your 150 or 172 will not suffer detonation on 100LL unless there is something very, very wrong with it, or you've put in a Navajo engine (which would be impressive). The rule of operating at 65% power or below to pretty much eliminate the "red box" is accurate for most engines. Detonation is an event that has many factors involved (and beyond the scope of this thread). Some engines on 100LL do not have a red box at all. Again, this subject is more complex than the scope of this thread. Each airplane is different, and it is important to know your airplane.
3) There is nothing wrong with leaning your carbureted engine until it is rough and then richening it until it is smooth. This has worked well for millions of flight hours. It even works for some (but not all) fuel injected engines.
4) When you buy an engine monitor, don't panic at the numbers you see. Many calls to technical support are made because pilots install an engine monitor, and are suddenly convinced their engine is about to explode. Remember that it has run in the exact same plane without an engine monitor for decades and thousands of hours before you purchased this piece of equipment. CHTs and EGTs will be different, that is normal. They will vary with the condition of your cooling baffles, the inherent quality of the cooling system design (on many aircraft this is best described as "very poor", and would be graded a D- were it a class).
5) Lycoming recommends keeping your CHTs at or below 425F for climb and 400F for cruise. Continental recommends keeping your CHTs at or below 380F. I aim for 380F or below on the hottest cylinder regardless of Lycoming or Continental. Your engine will not explode if you get over these numbers. Extended operation above these numbers will reduce the life of your cylinders, but don't panic if, especially in the summer, you have trouble staying below these temperatures. In my aircraft, I will aim for 380F or below, running LOP. In the 380-400F range I'll keep a closer eye on it. By the time I hit 410F on the hottest cylinder, I will transition from LOP to ROP (if I don't have an engine that will allow me to run further LOP without roughness) to keep CHTs cold. Note that this is on the 310 and the Aztec - neither of which have optimal cooling, and both of which are naturally aspirated. If I were operating a turbocharged airplane, especially with Continental engines, I would be especially strict about the 380F, but exceeding that still won't cause the engine to explode.
6) LOP won't hurt your engine and ROP won't hurt your engine, provided each one is done properly. Millions of flight hours have been done both ways. The people who have longevity problems are the ones who treat the limits (CHT, EGT, and oil temperature) as goals.
7) Preheat your engine in the winter. It will thank you in the form of better longevity. You can do much more damage by doing a hard cold start on your engine than you can by running above 400F on your CHTs for a few hours. The electric pre-heaters that attach to your engine directly are preferable to the propane heaters, because they will heat the crankcase, crankshaft, oil, and bearings as well as simply the cylinders. All of these are important. A propane heater is still better than nothing.
8) If you have a high-powered engine, an engine monitor is a must, in my opinion. It becomes progressively less important as you have lower-powered engines, but I would put one in any plane I own. Once you have it, make sure you learn how to interpret the numbers that it provides you. I offer courses in this, both on the phone and in your airplane. There are several other good options as well. Any course (from someone who knows what they're talking about) you take will save you money in the long run.
9) With a few exceptions, operation above 75% power for extended periods is not going to provide you much besides high maintenance costs. Regardless of what the Beechcraft, Piper, Cessna, or Cirrus manual tells you: 79-86% power is not a proper cruise power point for longevity, especially on a turbocharged engine. The maintenance bills and engine life for people who agree or disagree with this point speak for themselves.
10) Your POH provides important guidance as far as acceptable power settings, especially on high-powered engines. These power settings may not all be optimal as far as speed and economy, but they are ones that have been considered appropriate because the engine did not suffer from any ill effects that would cause immediate, catastrophic damage. Operating outside of these settings makes you a test pilot. As an example, my Aztec limits you to 26" manifold pressure below 2300 RPM. This is due to propeller vibrations. The Navajo allows leaning to peak EGT (and therefore LOP) below something around 30"/2300 RPM (don't quote me on that). At 40"/2400 RPM, leaning is not permitted - full rich only. Failure to adhere to this limitation will likely very quickly turn your cylinders into piles of molten aluminum. Unless you have the documentation related to certification of your airframe's engine and propeller combination, you don't know if the limits they put in place are due to detonation, harmonics, or marketing, but I follow them anyway. The extra few knots I might gain in a turbocharged aircraft by increasing my MP past the top of the green arc won't make much of a difference anyway.
This is by no means all-inclusive, just a top 10.
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