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An easy guide to engines - part 1. Piston engines essentials

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EHM-1997 Alexander:
Following on from Lis' excellent Ded reckoning guide comes a look into piston engines. (reproduced and edited below with lis' permission. The URL for the original article is http://forums.x-pilot.com/index.php?topic=1830


Easy Livin'

What exactly is an easy guide to such complicated topic, as engine construction and operation? "Push the first, leave the rest", but that's not exactly what I had in mind and probably that's not what you are expecting  ;) On the other hand, writing about everything in detail wouldn't achieve the goal of "easiness" either. There are lots of fantastic and more in depth reading materials around the Internet, as well as in traditional paper books, and rewriting them here in my own words is pointless. Anyone sufficiently interested and motivated can find them and learn all of this stuff, and even more, on his own.

With that in mind, the purpose of this guide is to give you an easy start into all the details regarding piston and turboprop engines operation. I want to get all the essentials gathered in one place, which will serve for a base for further education. There will be some simplifications and details left aside, for the sake of brevity and clarity, so any comments and questions for clarification are always welcome.

Wait a minute! "Piston and turboprops", what about the jets? Now, jets ARE easy  :) When I started "flying", I had the most problems with propeller airplanes and from what I've seen, that's still valid for many new pilots. All these gauges and levers... Sure, you can fly them in a sim, no harm done. But to fly them properly, in an enlightened way, is a different story. Not to mention the real life, where half of the common stunts from simulators, would require an engine overhaul (a rather expensive procedure) or writing a NTSB report (even more expensive thing).

In four moves

For a better understanding of more advanced concepts of piston engine operation and characteristics, I have to recall the basic principles driving the whole device. Some of you know this all already, but please do not skip this part, as there will be some important details there, that will be needed in the upcoming paragraphs.

When I say "piston engine" I think of the most commonly used internal combustion engines, working in four stroke cycle. For such engine to work, it needs air, fuel and spark. Remove any of them and it will stop, provide all the three + initial rotation and it must start up, unless there is a problem of mechanical or other nature. But for now, let's just concentrate on the basic principles.

Here's how the typical cycle looks like:

http://upload.wikimedia.org/wikipedia/commons/d/dc/4StrokeEngine_Ortho_3D_Small.gif

Air and fuel are sucked into the cylinder by piston moving down, then they're compressed on a second stroke and fired up with a spark, in the right moment. This will turn fuel-air mixture into hot gas, which is rapidly expanding and exercising pressure onto piston. Piston is pushed down, which turns the crankshaft and the propeller. On the last stroke, piston is moving up again, but this time to push the exhaust fumes out of the cylinder and a new cycle can begin. Easy enough so far, right?

Devil in the details

Let's complicate things a bit then, as the picture above doesn't show two critical things, for the engine to work properly. Remember, when I've mentioned, that the spark must be fired at the precisely right moment? Contrary to the picture above (and thousands of other pictures "out there"), the spark event must occur before the piston hits it's top-most position, called top dead center or TDC for short. It is caused by the fact, that fuel-air mixture doesn't explode all at once, but it takes the time to fully "light up" and thus create any useful pressure on the piston. By the time the fire and pressure inside the cylinder is becoming pretty developed, the piston had moved already past TDC and is ready to take the pressure and convert it into useful work.

Igniting the mixture exactly at TCD would cause engine to loose it's power. Igniting it too soon would violently destroy it, but more on that later. For now, please remember, that the flame inside the cylinder (as well as pressure increase) takes some time to develop and that it requires very precise timing of this development with piston's movement (as well as crankshaft rotation) to achieve proper engine operation.

Another very important concept, usually not illustrated on the pictures, is fuel-air mixture. You need very specific fuel-to-air ratio, for the engine to work properly. Supply to much fuel (too rich mixture) and engine will start loosing power and it will quit eventually, as it will be flooded by the fuel. Supply too much air (too lean mixture) and the same will happen, but this time the engine will starve without sufficient amount of fuel to sustain fire inside the cylinders.

Take note of one very important concept here: you can make the mixture too lean (for example) by either limiting fuel flow to the engine or by supplying even more air. If you wanted mixture to be more rich, you could have cut on the air supply, without even touching the fuel. It doesn't matter, which component of the fuel-air mixture is changed, the result will always be a change in engine's power. But what would happen, if we pumped into the engine even more air and even more fuel, at the right proportions? That's right, the power would increase even more. For many of you that will ring some bells, but let's leave that at this point for now Wink

One more thing to know, is that the mixture doesn't mix uniformly, regardless of carbureted or fuel-injected engine. There are always mixture pockets of various fuel-to-air ratios inside the cylinders. Some parts of the whole mixture have perfect ratio, some are too lean and others too rich. It has some impact on how the engine performs, but that's all for you to remember about this, for now.

This or that one?

There are many various designs of aviation engines. Different manufacturers, families, types and subtypes, depending on expensiveness, purchaser's specific requirements, performance figures, airframe requirements, reliability or maintainability, to name the most common factors in real life. Since we fly a little "different" kind of planes, all of these considerations are irrelevant and we'll be more interested in differences in engine operation, based on it's type. I've isolated three such groups and would like to have a closer look at them.

Carbureted vs. fuel injected. The biggest difference is the possibility for catching ice in the carbureter, which at first will reduce power available and then stop the engine, if the condition is not recognized and dealt with in a timely manner. The good news is that, such aircraft are equipped with carbureter heater, which can melt the ice and clear the passage for air into cylinders. The bad news is that, the carb heat will "steal" some horsepower on its own (not as much as ice stopping the engine completely, though) and may be unable to fight more severe icing for long. If that is the case, you need to lower your altitude fast, to get below freezing level. That is, if you have the space to do so - always double check enroute weather, before any over-mountain flying!

Other things to remember are that carb heat usually bypasses air filter, by taking warm air from under the cowling or from around exhaust manifold, which enables sucking all kind of bad things into the engine, especially when on the ground or at low altitudes. Also do not reduce power completely during descends, as it can produce carb ice, even in warm weather. Plan your descends early, with gentle power reduction, rather than steep angle. It's really easy, just reduce power to be lower than power required for a level flight at given conditions, but leave it higher than minimal, to avoid ice buildup.

Flat vs. radial. Not much here, really, except for two observations. Most of the hi-powered radials can't be run forever at full power, as opposite to the most flat engines mounted on GA planes (consult the POH, as some of the flats do have such limits). With radials, you have maximum take off power and the name is self explanatory. But 1 to 5 minutes (or so, depending on engine) after getting airborne, you have to set it to so called METO power - maximum except take-off - and this one can be used for the entire climb. The same is true for many warbirds powered by V-12 engines, like Mustang or Spitfire, so maybe the more appropriate criteria would be "new low power vs. old high power"?  ;) Anyway, just familiarize with plane's and/or engine's documentation, as all of these limits are published there. Even if the engine can pull 70inHg manifold pressure, it doesn't mean, that it should to do so (or at least not for a long time).

Another thing is that radials are more sensitive to harsh operation. Flying with them, you have to pay extra caution for observing engine limitations. Also never allow the propeller to drive a radial engine. It is undesirable condition even in a modern flat engine, but it can be literally devastating for a radial engine, because of the details in its oil distribution design.

Naturally aspirated vs. turbocharged. I know, that everyone was waiting for this one  :) Surprisingly, there is more of a difference in aircraft's performance, as well as engine's design and maintenance, than in operating it, with regards to naturally aspirated engines (NA). Just observe engine limits, do not push/pull anything too vigorously or too far (especially the throttle lever) and all should be fine. There will be slightly different gauges or their markings, between these two types of engines and mixture lever is operated somehow differently, but that will be covered later in this guide. For now, let's just stick to design differences.

Mega boost two-stage two-speed bi-turbo super charger

Sounds complicated, huh? Apart from the first word, all the rest are technical terms describing design details of various "turbo" systems and will be described here, as turbos are equally well-liked, as well as misunderstood. But in order to fully appreciate the influence of turbo systems on any given plane's performance, we need to look at NA engine first.

The biggest problem with NA engines is that they loose power at higher altitudes. It is a well know fact, that the higher, the thinner air becomes (mainly because our altimeters wouldn't work otherwise  ;)), so less of it is available for generating power inside the engine. A quick note: it is fuel, that generates power, but it needs air for sustaining combustion process. Because there has to be a specific fuel-to-air ratio, the less air is available, the less fuel must be introduced, (hence leaning the mixture with altitude). So less fuel = less power.

But some ingenious folks got an idea "why not to artificially "pack" the air up to be more dense, in order to maintain sea level pressure at altitude, to have full power there?". That's how turbonormalized engine was born. In simple words, it behaves as if it was working at the sea level, up to the so called critical altitude. Over this critical altitude, it starts to behave as NA engine above sea level - it starts loosing power with altitude. Usually for such engine, the maximum allowable manifold pressure (MP or MAP) is about 30 inHg.

It is caused by two things: there is no need for more power, as the sea level performance is enough (or limited anyway by aiframe structure's strength) and the engine itself may be a NA design, with turbo added only for high altitude performance and therefore it isn't designed for stresses higher, than during normal sea level operations. Remember: packing too much air (and fuel) into an engine may or will blow it up, as the pressure of expanding hot gases overcomes structural strength of pistons and cylinders. This is called overboost and most engines are protected from it by a wastegate, which is a safety valve, designed to release excessive intake air pressure, in order to maintain maximum allowable MP.

But what would happen, if we designed stronger airframe and stronger engine? We could pack up even more air (and fuel) into that, increasing power even at sea level and the airframe would hold together at the higher speeds. Think WW2 warbirds here. They need to be fast at an altitude, but also at sea level. More power means more acceleration, which is even more critical during air combat, than airspeed. FW190 and P-51 had more or less the same dive speed, but it was the faster initial acceleration, that gave FW pilots an edge and allowed escaping from unwanted fights.

So, let's pack as much of this air (and fuel  ;)) as possible! Original warbirds manuals that I posses, show values as high as 54 to 61 inHg takeoff/military power and even as high as 72 inHg war emergency power, with water injection. That's 2,4 times the sea level pressure in the intake alone! Add to that dramatic pressure increase, after the mixture ignited inside confined space of cylinder. It's like exploding a hand grenade in your pocket. Crazy stuff  :D Regardless of the craziness, the critical altitude is still there. It's just the same as was with turbonormalized engine: it is an altitude, above which MP and power start to drop. Below it, the engine can develop full power and you have full MP range available. Wastegate concept is still valuable, though  ;)

The same design principles have been more or less carried onto some contemporary planes, where you can pull off more than sea level pressure on MP gauge and enjoy higher performance, as well as more safety (shorter takeoff distance, better climb, more power reserve).

EHM-1997 Alexander:
The turbo details

This section is not necessary for understanding engine management, but I'll add it as an additional startup guide for anyone wanting to get more into turbocharging.

For the others, I have something reaaally easy, before we move onto something even easier  :)
Uriah Hepp - Easy Livin'
( mwnl ) Uriah Heep---Easy Livin

Turbocharger, sometimes called power recovery device, is a type where hot exhaust gases turn a turbine located somewhere along exhaust manifold. This turbine powers a compressor located somewhere along air intake, allowing for higher MP and more power. The main disadvantage of such design is that it takes some time to spin up and bring that MP up, after throttle aplication.

Supercharger, sometimes called turbosupercharger, is a type where compressor is driven directly by the engine. This takes some power from the engine, but it can develop even more of it, after compressed air hits cylinders. For example, a 1000hp engine uses 200hp to power a compressor, which in turn increases MP to such level, that gives the compressor-encumbered engine additional 500hp. So 1000-200+500=1300hp. Not bad!

But why not to install a bigger (=more powerfull) engine? Sometimes you can't, because the airframe is too narrow, it would badly upset the center of gravity, you don't have such engine or you have, but it's unreliable and has short service life. This is the turbo type mostly used on warbirds (because of instantaneous reaction to throttle application), however not exclusively.

As a side note, one engine can have both types at the same time  :)

Two-stage is a design, where the air is compressed by one compressor and then it goes to a second compressor, where it is compressed even more, before entering the cylinders. The whole design may be set up in such a way, that the first compressor acts as an initial compressor and the second one is used only for obtaining higher to full power (for example anything above cruise power, where only the first compressor is working and the second one being at idle). As you know from physics, compressing air increases its temperature, and hot air has less specific density, which is somewhat counterproductive to all these efforts to put as much air (and fuel!) as possible to the cylinders. Two compressors obviously mean twice the increase in temperature, so ofter there is an intercooler installed between both compressors, which decreases air temperature before it enters second compressor.

Two-speed is a clever design, where supercharger's compressor is linked to the engine by a kind of gearbox, with two (or more) selectable gear ratios. At high altutide, above the critical altitude, where air is less dense, the compressor starts developing less pressure and engine power drops. Then the gear is switched (either manually or automatically) and compressor's speed is increased, which once again allows it to pump sufficient amount of air and the engine can produce full power, until the second critical altitude is reached. This design is more efficient than a single speed "universal" compressor and enables reaching higher altitudes. Again, think "warbirds" here Smiley

Using this high-alt second gear while at low altitude is a bad idea, because the rapidly turning compressor makes too much drag against dense air and it robs the engine from too much power. Another reason is that fast turning compressor could lead to overboosting the engine - depending on a specific design.

Bi-turbo is yet another variant with two turbines installed, each of them supplying air to their "own" part of the engine. For example in V8 engine, one turbine supplies left row of cylinders and the other supplies the right one.

Boost is just another name for MP measurement. It was the most common on British warbirds, where it was referenced as "- boost" being lower and "+ boost" higher than sea level pressure. It was measured in lbs/sq. in. Japanese planes used similar -/+ reference, while German and American planes used absolute numbers (atmospheres and inHg, respectively).
0lb = 1 ata = 30inHg
+25lb = 2,66 ata = 80inHg <- another reason to love Mk.III Mustangs and some extravagant variants of Spitfires Wink

Mega is an indication of the coolness of all these fast rotating stuff Smiley The only single thing better than a sound of powerfull V12 or radial engine, is such an engine accompanied by a whistle of a supercharger Smiley

So much for brevity...

All right, before I've actually hijacked my own post (!!) we were at mixing air with fuel, just in the right proportions, in order to generate power, with a little help from well-placed electric spark. Enough with the theory for now, it's time to move onto more practical things Smiley Inside every piston powered plane, there are 3 mysterious levers, colour-coded black, blue and red. Before you ask, twins have two sets of the levers. Since sometimes the blue is not present, for some odd reason, let's just concentrate on the two that's left.

The black one is a throttle lever and is directly responsible for controlling the amount of air, that the engine receives. Push it for more air and pull for less air. The lever is directly linked to a throttle plate, which turns inside air intake manifold and either allows the air to pass freely or restricts the passage. You can't kill the engine this way, because there is always a little crack between the throttle plate and manifold pipe, that allows in just the right amount of air to sustain idle engine rpm.

As a fact, engines are the most "happy" when running at wide open throttle, provided you won't exceed any other limitations and supply enough fuel for a correct mixture ratio. Unfortunately, that's not always possible, mostly because of speed limits. Also it's more convenient to control the engine "with air", because it's harder to damage it that way.

One more detail to mention, throttle also controls fuel component of the mixture, although not directly. As you push the throttle forward, more fuel is automatically supplied, in order to maintain constant fuel-to-air ratio, so you won't kill the engine in "too lean" (too much air) situation. With throttle fully forward, there is additional and even more excessive fuel inflow, that is used to cool the engine during takeoff and climb, but that will be covered in more detail in another guide in the series. All of this was developed, so you don't have to push/pull both the "fuel" and "air" at the same time.

The red one is a mixture lever and is directly responsible for controlling the amount of fuel, that the engine receives. Push it for more fuel and pull for less fuel. Full forward is the richest mixture possible, with some excessive fuel added to the mix, while fully pulled out is a cut off position, which totally cuts off the engine from fuel supply and kills it cold. That's the proper way for shutting it down, after the flight. Somewhere between these two extremes, there is a such setting, that will produce perfect fuel-to-air mixture, for a give throttle position, altitude of flight, outside air temperature (OAT) and some random variation in a particular powerplant.

Flying with the red lever fully forward all the time is counterproductive, as it uses more fuel, shortens range and fouls spark plugs, which is not a good thing. The only time that the lever should be fully forward is at takeoff at sea level and during the first part of the climb from that takeoff, before altitude effects start to be visible (loss of power). At any other altitude you have to adjust the mixture, that also applies to takeoffs from airfields located at elevations over sea level.

Beware however of one thing: you can destroy your engine, when leaned too much at high power setting. It is generally accepted, that a "safe" power threshold is 60-65% of full rated power for a given engine. Below that set the mixture lever wherever you wish. Above that - beware! But how to tell how much power % the engine is producing? Consult your POH for details, I've said that already Smiley There are (or at least should be...) charts for power being generated for a given power setting (MP,RPM, FF, altitude). Another, though not as elegant method, is to open X-Plane data strips and read the value directly from there. For a 300hp engine, the reading is at 256hp. So 256*100/300=85%. 65% would be 300*65/100=195hp. Now, how to tell whether the mixture is OK, too rich or too lean? Watch the EGT gauge, but more on that later.

Let's stop here for a moment. With that both levers, the pilot has complete control over what the engine is doing. By dosing the amount of fuel and air, you can control the power output of the engine. By changing fuel-to-air ratio, you can tune the engine to the actual conditions (altitude and OAT), on the flight, so to speak. Now, what is the best setting to run the engine during the flight?

Anyone familiar with my previous guide to fuel planning and cruise performance will know the answer. That setting is such a setting, that will produce the power required to fly at a given altitude and at the needed/desired airspeed, be it fast cruise or efficient cruise, for example. And you can achieve that with a proper combination of fuel and air. If it is below 65% power, use full throttle and whatever mixture required, provided that the engine can do that. If it is above 65% power, use a sensitive combination of throttle and mixture, which will produce the required power without exceeding any of the engine's limitations. More on that later.

One thing worth noting, is that regardless of X-Plane's (in)accuracies, the official cruise speeds published in POHs aren't always the best speeds, from aerodynamic efficiency point of view. You know, in real life planes must sell and obviously faster planes sell better Smiley The POH must be respected when it comes to plane's and engine's limitations, because people who wrote it might knew something, that we don't know and they didn't wanted us to find out the hard way. It's also bad for sales Wink But the performance values like cruise speeds and ranges must be taken with a grain of salt. This is supported by the survey that Mr Carson did for his work on cruise speeds (remember "Carson's speed"?). He analyzed recommended speeds for more than a hundred GA planes, than compared them to reality and it turned out, that in majority they're more or less from being truly efficient (both ways).

But, as a pilot, you have complete control over the plane and it's powerplant. You can estimate the "best" airspeeds (refer to the previous guide) and you can set the power that will enable maintaining that airspeeds, without hurting the engine and without burning excessive fuel. All you need is a little bit of insight. That's what's so fascinating and so important about proper engine management! And about propeller-powered planes as well Wink

Darn, I got carried away - again... Shouldn't have listened to "Easy Livin'" over and over again, while writing this  ;)

The blue lever controls propeller RPM (revolutions per minute). Push it for max RPM and pull for min RPM, or even into feather on some twins. In piston engines, the propeller is always connected to the engine, be it directly or by means of a reduction gearbox, so when you change propeller RPM - you change the engine's RPM also. And you guessed it - it chages the amount of power, that the engine develops at the moment. The lower RPM, the less power produced. Rememberthat: the blue lever also influences the power setting!

But how exactly does that work? The blue lever is usually used with constant speed propellers. Most, if not all, of the planes from WW2 and later use either fixed pitch propellers (like the Sundowner) or constant speed propellers (like the Corvalis). But in order to make it any clear, I have to picture it in detail. It is important, as the propeller's setting is the most tricky and least understood from all the three levers.

Let's start with a fixed pitch propeller. A propeller is in fact nothing different from a wing, which is rotating around one of its wingtips, rather than move like a wing should. The lift produced is called thrust and it pulls the plane forward. The drag produced is called drag Smiley but in this scenario it is a force, that the engine must overcome, in order to turn the propeller around. This is the main component of propeller's efficiency: how much power is converted into lift-thrust and how much is wasted on overcoming the drag. X-Plane's efficiency of 0.85 means that 85% of power is used for thrust and 15% is being eaten by the propeller alone. By the way it is a very good result, with regards to reality.

As you know, any wing is has angle of attack (AOA), which is an angle between airfoil's chord and airflow direction. The same is true for a propeller and all the usual angle of attack dynamics apply, but the thing is more complicated because airflow direction depends on plane's own angle of attack, airspeed and propeller RPM. Let's leave plane's AOA for a moment and consider it to be zero - a level flight at high speed. Since it's a fixed pitch propeller (= fixed AOA), we don't have any direct control over its AOA (= blade pitch). Now, the local propeller's AOA is increased, when you either slow the plane down or increase propeller RPM (opposite actions will decrease propeller's AOA), which in a fixed pitch propeller plane would mean reducing or adding the throttle, respectively.

AOA alone is not that much critical (unless it is critical AOA Wink), as much is the lift to drag ratio (L/D) - or should we say thrust to engine load ratio. As is in the case of every airfoil, there is a range or lift to drag ratios, with one specific point, where this ratio is the highest. The AOA at which that L/D happens, is the AOA of the highest airfoil efficiency, because it produces the most lift with the least drag penalty. The same goes for a propeller, but the problem is the following. Such propeller achieves the maximum efficiency only at some specific combination of speed and RPM. If it happens to be a cruise combination (high speed, low RPM), then you'll have trouble at takeoff from short strips. If it happens to be takeoff combination (low speed, high RPM), you'll have a very inefficient cruise, slow with lots of fuel burn. Usually, fixed pitch props are set somewhere in the middle, to have balanced performance throughout the entire useful speeds range, however there is always some efficiency penalty applied to them.

So, some smart folks had this idea, to combine both props in a single one, by means of changing the propeller pitch (= AOA) in flight, low pitch (= low AOA) for takeoff and high pitch (= high AOA) for cruise, with climb setting somewhere between them. At first, pilot had control directly over the pitch, but that was a little bothersome, as each power change required a change in prop's pitch - exactly like each airspeed change requires power adjustment in fixed pitch propeller planes, to maintain selected RPM. In order to remedy this, a governor device was created, which maintains propeller RPM set by the pilot, by means of automatically increasing or decreasing prop pitch, as necessary. In order to slow down the propeller, the pitch is increased and vice versa, but the RPM are maintained and that's why it's being called "constant speed" propeller.

So, when you push the blue lever fully forward, you basically tell the propeller to go as flat as possible and be efficient at low speed-high RPM, that is during takeoff. When you pull it back, you tell it to be efficient at high speed-low RPM, that is during cruise phase of flight (you can cruise at full throttle, but seldom you'll cruise at full power and that always means lower RPM), with climb somewhere in between, as usual.

By the way, why bothering with propeller RPM and all these efficiency stuff? Skyhawk flies good at 80KIAS without that, doesn't it? Cheesy The answer is simple: fuel burn and range Smiley You may remember from my previous guide, that's not the fastest speed, that will you the farthest. Install constant speed prop to your C172 (don't touch anything else) in Plane Maker and you'll be surprised by the results! In real life, fuel costs, so you want to be efficient with it. Also, efficient planes sell better Smiley

Remember, that the slower RPM commanded, the less power developed by the engine? Pulling back on the prop lever slows the engine down, but the throttle + mixture command previous power level, which may be actually high. If you pull the propeller too much, without reducing the power beforehand, it may be too much for the engine and it will thank you for cooperation - even forever. That's the reason to always decrease power first, and only then lowering prop RPM. The other way, first increase the prop RPM and only then power setting. Usually power means throttle, but we know already, that it means also mixture, or both of them. But how much power can be used at a given prop RPM? POH should have data for that, also you can always "cheat" with X-Plane's data stripes Wink Just look for power and prop efficiency. As a very generic rule of thumb, expect max RPM for full power at takeoff, -100RPM for climb and somewhere in the middle of allowable RPM ranges for cruise with 60-70% power, but I'll return to that in the following guide.

There are also other considerations behind selecting prop RPM, both not really applicable to sim flying, but I'll mention them anyway, so our "flying" is more tied to the real one. They are noise and vibration.

Most of the noise generated by a plane is caused by propellers, not the engines. Especially props at high RPM are very noisy (it has to do with prop tips approaching or exceeding speed of sound, which is a rather noisy event - now imagine 2500 * 2 to 3 or more such mini "bangs" per minute), which is annoying for people down there, below our shiny rides cutting through the sky, which is another reason (after the efficiency matter) to not to run these props high all the time. Especially on final! But even at high altitude cruise, the noise can be a fun-killer for the pilot and his passengers, so pull that blue thing, please Smiley

Vibration depends on specific harmonic qualities of engine-propeller team. Some propellers, with some engines, at some RPM, will wildly vibrate, which is bad for their longevity. It is serious enough reason to not to operate them in such RPM ranges. Excessive vibration is also hard for the crew and passengers or any porcelain being carried somewhere in the cargo hold.

###

All right, that would be it, for now. As you can see, even with brevity in mind (yeah, right  ;) ) and with sticking only to the most important concepts, it takes a great amount of time and effort to write a guide on a topic such as aviation engines. Instead of writing one epic post, I've chosen a path of dividing it into a series of separate posts, as it will be easier for me to work that way. Also it will be easier for you, to read only as much in one take and it will make any comments or discussions separated, with topics in mind. I just hope, that all of this is clear and correct enough, to be of use for anyone  :)

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