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Can you explain the different kinds of aircraft engines?

G

guitar0633

Members +
Just as the post says, I get confused on what kinds of engines are in planes.

I realize that at the low end we have normal piston engines, but when they say Turbo, like the Duke later version, or this new Shrike Turbo, is that the same as a turbo prop, a jet with a prpeller, or does that mean a turbo charges poston engine? I wish someone would just start at one end and explain what families of engins have been made for planes what what they are called and nicknames.

Also, why do they make jet engines with propellers? Why would there be a need for propellers when they could just use the jet engine without them? I could see the need for a single engine turbo prop because you need to have a propeller to push air over the outide of the plane and a jet engine exhaust would be aimed toward the inside of the plane. But why would they make a twin turbo prop and not just use the jet engine without the props? So if a Turbo prop is a jet with a prop, I wish they would have called them jet props because piston engines cane be turbo charged and using the word turbo causes confusion for some folks, me anyway.

There are a lot of smart guys here and I would love watching you get in to a conversation on aircraft engines, the what, when, and why they were designed and used.
 
A quick summary would be:

- Piston engines are exactely like car engines. They can be atmospheric, supercharged (like Mercedes "Kompressor" engines) or turbocharged (like regular turbo engines). These engines are used for propellers.
- Turboprop engines are a turbine, which is almost like a jet engine excepted it makes a propeller turn.
- Jet engines are a turbine as well which makes some smaller "props" turn and compress airflow. There are several kind of jet engines with different usages and efficiency. I'd recommend searching on Youtube, I've seen a few excellent videos explaining that.

Now the reason there are still propellers on aircraft is because propellers are the most efficient thing at low altitude and slow speeds.
Jet engines are powerfull of course, but they just waste a lot of fuel for nothing, and they cost a lot to mantain.
Propeller engines are more economic.

Turboprops are somewhere in between. They are more powerful than regular prop+piston egines, they make you go faster and give you more power etc... but they cost a bit more as well, and they also use more fuel. But less than jet engines. Same for maintenance, as far as I understood.
 
Just to muddy the water a bit....the original jet engine design type is now usually called a Turbo (or pure) Jet, whereas the current Jet engine types are technically a By-Pass design - in other words the main thrust is from the shrouded (or ducted) fan - ( a propeller in a duct).
 
Guitar interesting question. Look at this way, piston engines came first, in all shapes sizes and power outputs, inline, liquid cooled, air cooled, radial, V layouts, upright and upside down. They progressed for low powered beasts of about 100 hp or less until they reached their limits with about 3.500 hp on the big multi-bank radials such as on the Constellation and Stratocruiser. You could say it was nothing but pistons until late into WW2 when the gas turbine engine began to be developed for aircraft. Turbines had been in ships for decades probably before WW1 but they were steam turbines so the idea was not new just getting it to burn fuel instead of being rotated by steam was hard due to the temperatures etc. Making them reliable was difficult because they operate at very high temperatures and being a single rotational axis have to be balanced perfectly and lubricated and it took some time for the metallurgy and design to catch up but their power output was phenomenal compared to a piston engine. A turboprop is simply a propeller attached via a reduction gearbox to a gas turbine so the turbine drives the propeller unlike a pure jet where the gas is blasted out the back and the reaction pushes the aircraft forward.

The term 'Turbo' is used a bit freely especially by marketing folks but it generally is understood to mean a heat exchange turbine used like a supercharger on a piston engine, the words GAS Turbine are used to differentiate pure jet engines from other types of turbines. The term turbo-prop is a bit of a bastardisation but has come to mean an aircraft fitted with a gas turbine engine driving a propeller via reduction gearbox.

Why use a turboprop? simple they are capable of producing very large amounts of power for a very low unit weight and why use a turbine instead of a piston, the answer is maintenance, they may cost a lot more but they run for thousands of hours without overhaul are generally trouble free and capable of being built to produce very very high power outputs such as is needed for supersonic flight or very large aeroplanes. A turboprop gives you the advantage of a gas turbine power plant but the advantages of slow speed capability and generally they use considerably less fuel than a pure jet. For example at PT6 the most common turboprop engine about can be built to generate between 500 and 1300 hp burns as little as 300 lbs per hour of fuel and the engine itself will fit into a small box literally less than your refrigerator. A piston engine of comparable output would be 3 times the size and weight 5 times as much. In the aeroplane business, lightness is always the goal, lots of power is always the goal and fuel efficiency is always the goal. A large piston engine ends up being a hideously complicated piece of engineering with two many moving parts and prone to failure, tricky to look after, tricky to start and run and they took a lot of looking after and still do.

Here is another example of what and why. When the Australain Airline Qantas operated Constellations, engine shutdowns and failures were so frequent they invariably could not get a sector done without losing and engine and hence had to keep spare engines all over the world. The time between overhaul on these type of very large piston engines was about 500 hours. This is a very time consuming and expensive process to have to keep pulling engines off aeroplanes and putting the back on. By comparison once they got the 707 with pure turbines they were initially going out to 6000 hours between overhauls and later as much as 10,000 hours. They were capable of flying higher and most importantly fast.

Fuel efficiency - the most fuel efficient engine is the piston it uses less fuel per hp produced than any other engine. Next is the turbo prop and last is the pure jet engine.
 
Only the "High by-pass" type are like that. And only below ~25000 feet where the air density is greatest. Generally it's a rule of thumb that 80% of the thrust below 24000 feet is generated from the high bypass fan. Above that it starts to degrade the higher you go.

Turbo:. Is a mechanism that uses exhaust gases from the listing engine tonspin a a very small turbine wheel which compresses the inlet air flow before it reaches the cylinders in order to simulate a lower density altitude and get closer to seslevel performance from a piston engine.

Turbojet:. Jet engine of either actual flow (straight through) or centrifugal flow (air passes through radially) design. No air bypasses the combustion chamler.

Bypass jet engine. Low and high bypass engines exist. Some amount of airflow bypasses the engine combustion while still creating thrust.

Turbo prop:. A propeller design driven by a small jet engine. Can be direct shaft or air coupled design with planetary gear reduction box.
 
Then there is the Turbo Compound piston such as the later Wright R-3350 series Duplex-Cyclone. These engines used exhaust gas to drive power recovery turbines to increase total horsepower, sometimes by as much as 20% of the exhaust energy.
 
Hello All,

No, the turbo and supercharger are both used to supply air to the intake, the R3350 power recovery turbine (PRT) is a turbine because it uses a shaft and gear to transfer energy back to the crank. See the video below:

https://www.youtube.com/watch?v=Ac7G7xOG2Ag

Wait, wrong one.... (sorry, couldn't resist)

Try this picture, the PRT is the gray and black assembly near the rear at the top.

https://hars.org.au/wright-r-3350-radial-piston-aero-engine/wright-r3350-cutaway/


Essentially, all airplane engines turn something; a propeller, a fan, a compressor, or just fuel into noise. Its how they do it that differs, and in general, as has been pointed out, falls into one of two categories (with a few exceptions), either the Brayton cycle or the Otto cycle. What the particular engine is called after that is how its connected to the turning object. A Brayton cycle machine just moving air= Jet engine, attached to a fan= Turbofan, attached to a propeller= Turboprop, attached to a helicopter rotor=Turboshaft, connected to a generator=Gas Turbine or APU, even if the model number is the same on each. Otto cycle engines are described by cylinder layout (radial, inline, "V" or flat) and induction type, (naturally aspirated, supercharged, turbo, or turbo-supercharged) but all turn a propeller or rotor.

Hope it help!
--Dan
 
There are two other types, both extremely rare for obvious reasons. The pulse jet burns fuel in pulses in between which the shutters on the air intake open to draw in air. They were used on the doodlebug flying bombs so not many have been preserved. The pure ramjet has no moving parts other than the fuel system and relies on the pressure of incoming air with clever aerodynamic design to prevent the jet thrust coming out the front of the engine as well as the back: only works well above Mach 2 or thereabouts and most uses have been on, er, missiles. The SR-71 used turbo-ramjets which combined features of both turbojet and ramjet.

A fascinating subject, especially when you look into the subtleties of jet engine design – an increasingly efficient blend of sheer power and low engineering cunning.
 
Then there is the rotary engine where the motor rotates about the crankshaft...........piston type of course. No mention of the Wankel or Bradshaw....
 
Wow, I knew you guys would have some informative discussions. It's more fun to read discussion from you guys than it is to watch YT vids.

So Carenado releasing a turbo Shrike just means that they have added turbo power to the original piston engines and they didn't put 2 pt6 jet turboprops like the one on the Caravan on each side of the Shrike to make a turbo prop Shrike twin, correct?

I watch the show "Street Outlaws" and they always talk about their cars as having either kits of nitrus or turbos that make their cars really fast. So turbo models like the turbo shrike have basically got turbos added to the piston engines just as the fast cars have turbos. I hope I have it now. I take it this is the same for the Real Air Duke versions, correct? There is no Duke that now has jet turbo props like a Cessna 441, just a version that has turbos added to the piston engines?
 
I was about to ask if there have been any planes that were original piston engines that later had jet turbo props put on, but there is as I even know of one.
Cessna has the C404 Titan that has normal piston engines, and later they took basically the same air frame and put jet turbo props on it and had the 406 twin Caravan, correct?
 
And finally, hoping I can end my confusion for good with this last thought. A piston engine plane that has jet turbo props added in place of the piston engines would never still be called the same model, correct? Hense, the 404 Titan was not called a Titan anymore it was called a 406 tiwn Caravan, and if they ever added jet turbo props to a Beech Duke B60 then it wouldn't be called a Duke B60 any longer it would have a completely different name. So if it's still a Shrike with turbo units added to the piston engines, it's still called a turbo Shrike. If it had turbo jet props added it would be a completely new aircraft called something different.

So I am hoping I have this cleared up.
 
guitar0633 said:
So Carenado releasing a turbo Shrike just means that they have added turbo power to the original piston engines and they didn't put 2 pt6 jet turboprops like the one on the Caravan on each side of the Shrike to make a turbo prop Shrike twin, correct?
Click to expand...
No, if you mean the recently-released 690B Turbo Commander, it is a turboprop - confusing isn't it?
 
thefrog said:
No, if you mean the recently-released 690B Turbo Commander, it is a turboprop - confusing isn't it?
Click to expand...

Uhg, YES. I just went to the Carenado site and sure enough, it says Turbo prop. I wish everyone would have done what Cessna did and just call it a completely different name like they did with the Titan and Twin Caravan. Now there are piston Shrike commanders and jet turboprop commanders. I thought that maybe I had come upon a hard and fast rule that no turbo prop jet type plane would ever be called the same model class as a piston type plane.
 
guitar0633 said:
And finally, hoping I can end my confusion for good with this last thought. A piston engine plane that has jet turbo props added in place of the piston engines would never still be called the same model, correct?
Click to expand...

Oh I dunno, Westland built the Wyvern around a monstrous Roll-Royce 24-cylinder piston engine and then converted to turboprop for the production models. Still called it the Wyvern (and it was still unlovely). :a1310: :mixed-smiley-027:
 
So then can I count on the term "Turbo CHARGED" as always meaning normal piston engines that have had turbo units installed and they will always be piston, turbo charged engines?

In other words, turbo charged would NEVER mean turbo props, correct? So what kinds of Beech Dukes are there? Turbo CHARGED or both Piston AND turbo props?
 
I can't answer to the Dukes, but you are correct in one thing: Turbo CHARGED is always a piston engine with a turbocharger integrated into it.
Turbo PROP is always a relatively small jet engine driving a propeller through a reduction gear box. Many helicopters actually fall into this category. A turbine, or jet engine, driving the rotors. Often more than one turbine engine. Still, identical in operation to a turbo prop fixed wing aircraft. Relatively small, light turbine engine(s) driving a propeller (rotor).
Then, as mentioned before, is the Turbo FAN, a large ducted fan, driven by a small to medium jet engine. SIMILAR to a turbo PROP, but the propeller is enclosed, vastly increasing the efficiency of it. Most, if not all, modern commercial airliners, for example.
There's planes that are powered by a turbine engine, no propeller, no ducted fan, nothing. Just a powerful "jet" engine, like many military fighters have these days. The F/A-18, the F-14, the F-5, T-45, F-4, etc etc. The list goes on. Nothing but suck-squeeze-bang-blow. I love that way of describing a jet engine's operation. Very accurate, but easy to understand.

I know, no better than any one else's answers, but the best I can do, I fear.
Pat☺
 
Hi guitar,

Also, A simple way to think of efficiency and speed, as opposed to engine type, is to look at how big the area is that is accelerating the flow. Whether it's a piston engine, turboprop, jet powerplant, or a rocket motor, they all work by a momentum change; they accelerate a mass, usually air, or air and fuel, and kick it out faster then it came in, generating thrust.

One of the most efficient is a helicopter. It has a large area over which it accelerates the air, the diameter of the rotor. It's called the actuator disk area. It accelerates a bunch of air a little bit and that makes it really efficient; at least in hover anyway. Then you have your general aviation aircraft which use a smaller disk area, but accelerate the air just like a helicopter rotor. Of course, it doesn't have to accelerate as much air as a helicopter because the wing is providing the lift, it just needs to over come all all of the drag up to it's maximum speed. Then you have a jet, which usually has a smaller diameter for the same amount of thrust, but accelerates the air much faster. It has the advantages of a small frontal area, reducing drag, and it can generate thrust at high speeds. Propellers tend to lose thrust rapidly at higher speeds.

Also, just for reference, when airplanes are supersonic, the airflow through the jet engine is still subsonic. Those fancy intakes you see on supersonic airplanes are to slow the air down using shock waves to a speed the jet engine can handle, then it accelerates it out the back at supersonic speeds by using what is known as a convergent-divergent nozzle. The convergent part accelerates the air to Mach one, then the divergent part expands (accelerates) the flow more. Think of it like a water hose, where if you stick your finger in the end of it it accelerates the flow. That's how flow works at subsonic speeds (Bernoulli's Principle). At supersonic speeds, it's the opposite. You have to increase the area to accelerate the flow (expand) or make the area smaller to slow it down (contract). That's why rocket nozzles are shaped like a bell. They're accelerating the supersonic flow, so they get wider along the flow path.

When it comes to propulsion, it's all about the momentum change, regardless of how you generate it.
 
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