Can you explain the different kinds of aircraft engines?

[guitar0633]

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.

[Daube]

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.

[Dev One]

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).

[BendyFlyer]

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.

[Mach3DS]

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.

[llanning08]

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.

[Daube]

That's 'turbo-charged', isn't it ?

[HvyEng]

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
(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

[Bjoern]

Lots of answers:
https://en.wikipedia.org/wiki/Aircraft_engine

[hairyspin]

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.

[Dev One]

Then there is the rotary engine where the motor rotates about the crankshaft...........piston type of course. No mention of the Wankel or Bradshaw....

[guitar0633]

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?

[guitar0633]

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?

[guitar0633]

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.

[thefrog]

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?


No, if you mean the recently-released 690B Turbo Commander, it is a turboprop - confusing isn't it?

[guitar0633]

No, if you mean the recently-released 690B Turbo Commander, it is a turboprop - confusing isn't it?

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.

[hairyspin]

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?

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:

[guitar0633]

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?

[PhantomTweak]

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☺

[Sundog]

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.

[llanning08]

And let us not forget to mention ...

The Besler Steam-Engined Flight - The Flying Kettle Project (https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=14&cad=rja&uact=8&ved=0ahUKEwiRtuvii5nVAhUJ54MKHY3AB6IQFghjMA0&url=http%3A%2F%2Fwww.flyingkettle.com%2Fbesler6.ht m&usg=AFQjCNGBX-QEJ6MRVgh7yuQ6N63sdkn7Sg)

And yes, this modified Travel Air really flew in 1933!

[hairyspin]

And there we have another fine example of why this site is so useful: do read the linked article on steam flight and try to keep a straight face! Most entertaining.

[Bjoern]

My favourite odd propulsion system has to be the one from the days when problems ranging from power generation or communism to geo engineering* were considered perfectly solvable by splitting some atoms:

https://en.wikipedia.org/wiki/Nuclear-powered_aircraft


*https://en.wikipedia.org/wiki/Peaceful_nuclear_explosion

[BendyFlyer]

Guitar - the confusion comes from the marketing people, not the designers or engineers. In the case of what Carenado calls the Turbo Commander it was always called the Aero Commander 690 and everyone knew it was a turbine that was powered by Garrett turbines, I am not sure why Carenado have chosed to call it a Turbo-Commander. Cessna marketing people were also responsible for the confusion about the 406 by firstly calling it the Twin Caravan when in fact it was the 404 airframe with PT6's (derated ones at that) and it was produced by Cessna at Rheims in France not in the USA. I can think of no example of any aeroplane that kept the same name when they were upgraded to being powered by turbines, except now I think of it the Piper PA31 Navajo or Chieftan there was a turboprop version of that at one stage (there was also a pressurised version about as well) and they still called it a PA31, it later was redsigned and rebuilt, pressurised and called the Cheyenne. You see the dilemma here, for Cessna and Piper, just putting turboprop installations on the airframes gave you a marginal increase in speed and climb but they were still unpressurised so why would you buy one, both were total flops as far as sales were concerned. I actually flew the C406 for a little bit and it was a dog believe me, its engine out performance was dreadful in fact a 404 with pistons performed better on one engine.

As for the Duke it was always turbocharged but never released or built with a turbine or turboprop engine installation and Beech just called it the Duke or BE60.

So your safe to assume if it is referred to as being a Turbo it is a turbocharged piston, it is is a turboprop it is a turboprop but again the marketing people got in the way and for awhile in the early 1960's they were calling the turboprops - PropJets and the pure jets - PureJets, go figure, it was about trying to differentiate in the early days that this new aeroplane was powered by a jet engine, if you want an idea of the ridiculous nature of marketing departments, and that includes the airlines, they once called the 727 the Whispering T-Jet, what a joke, it was one of the noisiest aeroplanes around with three JT-8s at full bore on take off and the reason you do not see any today is they were basically outlawed everywhere around the world because of noise regulations.

A clue to what pistons had turbochargers and which ones did not is found in the ICAO designator, all the turbocharged ones invariably have a T in the designator and P if pressurised. If it has neither then it is a bog standard piston version. I think even the venerable Connie was once modified as a turboprop and had the T in the designator. The diffenentiation was considered unecessary for big aeroplanes as everyone knew that a L188 was an Electra and it had turboprops and a B707 was a pure jet etc etc.

[SkippyBing]

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.

Not strictly true. A turbo prop drives the prop via a gearbox to reduce the rpm, in a turbo fan the fan is connected directly to the turbine at the exhaust end of the engine and a proportion of the air goes around the outside of the engine rather than through the middle. The ratio of air going around the outside to air going through the middle is known as the bypass ratio. The Rolls Royce Trent on airliners has a bypass ratio of around 9:1, the F404 in the F/A-18 has a ratio of about 0.34:1, so more air is going through the middle than not, but it's still a turbofan.
Low bypass turbofans started being used in military aircraft in the '70s* as you get better fuel efficiency and low speed thrust, for a slight drop off in thrust at high speed.

* I think the UK Phantoms were the first with Speys, all other F-4s had turbojets with all the air going through the hot bit.

[PhantomTweak]

I may be wrong, but I'm pretty sure most of the Phantoms had the J-79 in it, not counting the UK birds. I honestly don't know about those. There was a small amount, relatively speaking, of bleed air from the compressor section used for various reasons. Cockpit AC and pressurization, fuel tank pressurization, laminar airflow in the turbine section and tail pipe to keep them cooler, and so on. A "small amount" compared to the total airflow through the engine, that is. Most of the bleed air was from the 17th compressor section. There was more than enough available for what it was used for. But not a lot was used for actual propulsion, as far as I know. That all went through the turbine section as hot gas from the burners.
The Israeli Kfir has the J-79 in it too. Popular engine in it's day.

Have fun all!
Pat☺

[Craig Taylor]

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 don't think I noticed anyone addressing this question. There is in fact a turbine conversion of the Duke, referred to as "Royal Turbine" or "Duke Turbine" or various combinations. Northwest Turbine LLC and Rocket Engineering Corp of Spokane, WA replaced the piston engines with P&W PT6A-35s, making various other modifications to enable the engine swap. You can read about it on their website here (http://royalturbine.com/). As far as I know, RealAir are the only ones who made a version of this for FSX. EDIT: Sadly no longer available.

[Sundog]

I may be wrong, but I'm pretty sure most of the Phantoms had the J-79 in it, not counting the UK birds. I honestly don't know about those. There was a small amount, relatively speaking, of bleed air from the compressor section used for various reasons. Cockpit AC and pressurization, fuel tank pressurization, laminar airflow in the turbine section and tail pipe to keep them cooler, and so on. A "small amount" compared to the total airflow through the engine, that is. Most of the bleed air was from the 17th compressor section. There was more than enough available for what it was used for. But not a lot was used for actual propulsion, as far as I know. That all went through the turbine section as hot gas from the burners.
The Israeli Kfir has the J-79 in it too. Popular engine in it's day.

Have fun all!
Pat☺

All of the operational F-4's had J-79s, except the F-4s built in Britain, they used the RR Spey. However, they did end up flying some US F-4Js for awhile. {url=https://en.wikipedia.org/wiki/No._74_Squadron_RAF}No. 74 Squadron[/url].

[hairyspin]

Bypass air should not be confused with bleed air - all jet engines use bleed air to keep the flame off the metal etc. Turbofans in fighter jets have better low speed performance, so the J79-fitted Phantom was faster in level flight but the Spey-equipped ones took off and climbed better. Turbofan-equipped Tomcats don't need afterburners for carrier takeoff and climb out, significantly increasing their operational range. All from using the engine power to blow extra air out the back.

[simondix]

In reply to a subsequent question of piston prop aircraft being converted to turboprop or jet engines. There were the Basler, Braddick and Dart DC3's. The Conroy Mustang and I believe a Vickers Viking became a jet testbed.

[DaveB]

Yup.. the Viking had a pair of Nene's strapped one under each wing! An unlikely looking jet for sure but it set a passenger aircraft speed record from London to Paris!! Unlike many test aircraft.. the Viking was converted back to props. There was always a hope that one of the team at CBFS would take it on for FS9 but data on it was scarce.

ATB
DaveB:)

[Dev One]

Trent Meteor.......1st propjet aircraft.

[guitar0633]

Love reading the discussion guys, thanks. When I was a boy I used to get my older brothers talking about baseball and football and I could just sit for hours and hear them tell stories about their baseball heroes and memories. It's the same with places like the Sim OH. I love getting some of you knowledgeable guys started talking and giving up your experience and knowledge so I can just kick back and read about it all. Much more fun somehow that watching YT vids. I like those too, but there's just something interesting in reading the thoughts from smart guys like the aviation lovers here.

Thanks again.

[Bjoern]

No mention of the Convair 580, the most successful conversion from piston to turboprop?

The title of reengining queen shall be taken by the Douglas DC-8. Turbojets to low bypass turbofans to high bypass turbofans. The latter squeezed another good 20 years of use out of a design hailing from the late 1950s.
To be fair, some KC-135 models also deserve the title, going the exact same route but being exclusive to the military.





Bypass air should not be confused with bleed air - all jet engines use bleed air to keep the flame off the metal etc. Turbofans in fighter jets have better low speed performance, so the J79-fitted Phantom was faster in level flight but the Spey-equipped ones took off and climbed better. Turbofan-equipped Tomcats don't need afterburners for carrier takeoff and climb out, significantly increasing their operational range. All from using the engine power to blow extra air out the back.

Tomcats were never equipped with anything but turbofans. With the original TF-30s, they were a bit underpowered, requiring afterburner takeoffs and were prone to flameouts. The later F-110s were reportedly the single best aircraft improvement in history with all that power and reliability.

Might want to mention that the bigger intakes and larger frontal area of the Speys (more area = more drag = less effective thrust) were the reason for the reduced top speed. And that the afterburner weakened the carrier deck due to the heat. :biggrin-new:

[hairyspin]

...And that the afterburner weakened the carrier deck due to the heat. :biggrin-new:

Made a mean burger, though...

[Bjoern]

If you want a real oddball of a jet engine, look no further than the RB.199 from the PA200 Tornado. Consider that normal military aircraft engines are built for simplicity, with two independent compressor and turbine sections (spools) at best for at least rudimentary efficiency and as much power as possible. And most modern engines are built with a bypass (turbofan) to increase mass flow through the engine (increasing available power) and to provide laminar air flow for cooling along the engine walls. The burner section in more modern engines is trimmed for reliability and the afterburner section is quite long to ensure proper combustion of the additional jet fuel. And there's a (flexible) nozzle with a shrinking and then expanding diameter to make the best use of the kinetic energy in the exhaust gases for maximum power.

Now you've got the cheeky little, multinational bugger in the Tornado. First, it's a turbofan, which is good and as normal as it gets with this engine. But unlike its brethren, it's a turbofan with three(!) independent compressor and turbine sections (triple spool). First oddball property. Triple spools are only found in Rolls' other modern civilian engines like the RB.211 (think TriStar, 747 and 757) and beyond. The reasoning behind this is that three spools have each compressor section rotate at its optimal velocity throughout its envelope, providing maximum efficiency in compression - in theory. Practically, during power changes, trying to get three independent compressor sections is like trying to get three kids to do chores. The eldest (high pressure section) does what you tell it to without much hesitation, but while you try get either the youngest (low pressure section) or the middle one (middle pressure section) to join in, the other of the two will smply do what it pleases. To the effect that, in the worst case, the chores won't get done as quickly as they should or, worse, that the entire process will momentarily break down. Yep, that's an operational limitation right there. One other property of three spools is a very elaborate system of lubrication because oil rules the world and everybody hates friction. In their infinite wisdom, the engineers devised a bearing and lubrication system that's only really tight at high rotation speeds, meaning that part of the engine oil takes a stroll into other engine compartments at lower power settings. When seeping into the turbine sections, it causes a mild case of combustion visible as smoke and the blackened vertical stab so typical for the Tonka.

Continuing the theme of inefficiency and oddballness, the fuel injectors in the combustion chamber inject fuel in the opposite direction of the air flow. No elaborate mixing into the direction of the flow to optimize things like in other engines, just a simple "Here's fuel, here's air, now sort yourselves out" to keep the combustion chamber as short as possible. Efficient? Not quite.

The turbine section ties a into the compressor section above, but it isn't really special. The exhaust gas bumps into the turbine rotors, basically converting a bit of velocity and pressure into rotational energy and thus driving each of the three shafts and its attached compressor section. Standard, yawn, NEXT.

Aaaand it's the afterburner, which, for a military jet engine is SHORT. So short, in fact, that the reheated exhaust gas doesn't have much time to cool down and expand, giving the Tornado its characteristic blue afterburner flame and the heat signature of an B class star. It's said that a Tonka in afterburner can be spotted with the bare eye from Proxima Centauri and that the only usable countermeasure is a tow array for an O0 (o zero) supergiant star.

As if the intense heat of the exhaust is not bad enough, the nozzle adds insult to injury because it totally does away with the standard shape of tighten-widen and just tightens, essentially trading some thrust for mechanical simplicity (shoulda simplified the compressors instead, eh?). The nozzle, however, still widens to accomodate the added exhaust gas flow when in afterburner, so it's got that going for itself, which is nice.

Just when the exhaust gas thought it was clear of this rollercoaster ride among engine construction, it slams right into the thrust reverser panels, the last oddball characteristic of the 199. The Swedes thought that putting thrust reversers on military aircraft was a superb idea because it saves some poor conscript from having to handle the mess of nylon and lines called a braking parachute or blowing on superheated brakes, so Fritz, Giovanni and Lord Mc Lordface ran the numbers and came to the conclusion that it was perfect to offset the horrendous R&D costs for getting the compressors (again: THREE SPOOLS!!!) to work by reducing the number of required wheel brake changes. Great thinking, folks! What the three musketeers didn't realize, however, is that the exhaust gas gets super miffed at being thrown out in the opposite direction it came in and therefor will merrily deposit anything remotely sooty (lubricant, partially burnt fuel) on any surface of the aircraft it can find - most prominently the vertical stabilizer. This is the reason why any Tornado looks worse than most Air France airliners and why there's absolutely no point in cleaning them around the tail end. Rumors have it that a good number of Tonkas still carry 30+ year old reverser marks...

And this concludes the general oddities about the RB.199. I didn't dive into the minor ones (the starter comes to mind...), but this shall do.
To recap, this bit of drunk powerplant engineering has a very complex compressor prone to hiccups, leaks oil at low RPM like the Exxon Valdez, has inefficient combustion (how they got it smoke free is a mystery to this day), the heat signature of the surface of the sun and a "no tractor needed" reverse gear.
On the upside (yes, rumor has it that these exist), it doesn't need any additional mechanical devices to optimize the flow through the compressors because of the three spools, it's compact, has a good power to weight ratio, a device to shorten the landing roll, hyper ultra awesome blue afterburner flames and an exceptionally sweet sound and noise level. Oh, and its concept's been proven and working for 40+ years by now.

But it's so odd when compared to the other engines, I can't help but love it.

[PhantomTweak]

The F-14's were permitted minimum AB take-offs from shore stations, if really necessary, but not the ships, and no max AB take-offs from anywhere. If they had a flame-out during an AB cat shot, it would cause an un-recoverable yaw moment. Get that on a cat shot, it's all over. Probably all over the bow of the boat.
The engines, in AB, had enough power, far enough off to the side of the plane's centerline, that if one quit, but the second kept running, again, in AB, the plane would start to do a flat spin then and there, no matter how much rudder the pilot input. Grumman even stated the F-14 wouldn't do a flat spin, no matter what, at first. But after loosing a few to flat spins, they changed the NATOPS. No corrective action to a flat spin under any conditions, other than EJECT. Top Gun got that right in the movie anyway.
I can copy the entries from the NATOPS about all this...

The F-14 is a still a fun as heck plane to fly though! Especially if it's modeled with the TF-110 engines, as in the D model '14s. Better than 1:1 thrust to weight, which fighter pilots had been dreaming of since jets came about. Understandably!

Have fun all!
Pat☺

[SkippyBing]

And this concludes the general oddities about the RB.199.

I'm not sure if it's unique to the RB.199 but there's also an arrangement where if electrical power is lost it goes to full throttle. Great if you're airborne and need engine power while you sort out the electrical gremlins, not so much if you're overly enthusiastic getting out of the aircraft at an airshow and get ahead of yourself during the shut down checks. Cue the entire crowd ignoring the flying display and looking towards the increasingly high pitched whine coming from the parking area followed by bits of engine being liberally spread across dispersal.
Took them a couple of weeks before it was ready to be flown out.

[lazarus]

Other oddball turbofan's, the GE CJ-805 and CF-700 aft-fan engines, with an LP turbine at the back driving a nifty transonic fan, with attendant hot gas and oil leakage.
One class of engine not mentioned as it dead-ended-for now-are the compound-turbines, like the Napier Nomad's. A 41.1L/2502 cubic inch H-12 supercharged diesel engine/gas generator driving half a contra-prop and an axial 3-stage turbine/12-stage compressor set that drove the centrifugal supercharger and the other half contra-prop through a combining gearbox. In case this monstrosity failed to provide enough diversion for the fitters, an afterburning system injected more fuel into the turbine on take off. It weighed four and a half thousand pounds, had more moving parts than a box-car full of swiss watches and was highly temperamental on a good day. When it all ran in the same direction at once, it gave 4000 hp/320 lbf at take off, but it's cruise fuel consumption was an amazingly low 0.36 lb/hp/hour@3030hp in cruise.
The Nomad II cut the turbine-propeller gearbox and afterburning for a simplified turbine-compound blowing the diesel and hydraulic clutched to the diesels crankshaft, chopping 1000 pounds and removing most of the gremlin nests.
Nomad II: max take off at a staggering 208" hg boost-4100hp/320lbf thrust.
Cruise sfc @ 11000ft/300kts/3030hp: 0.345 lbs per equivalent horsepower per hour. An unsurpassed SFC. However, the devil is in the details.
Jets burn more fuel, but are (mostly) lighter and simpler, and go faster. The reduced chock to chock times give a comparable average sfc for long distance flight.

[DaveB]

Might want to mention that the bigger intakes and larger frontal area of the Speys (more area = more drag = less effective thrust) were the reason for the reduced top speed.

That was a necessary trade-off for the much improved low altitude performance required to get them off our tichy carriers. Not ideal I know but needs must!
ATB
DaveB:)

[Bjoern]

The F-14's were permitted minimum AB take-offs from shore stations, if really necessary, but not the ships, and no max AB take-offs from anywhere. If they had a flame-out during an AB cat shot, it would cause an un-recoverable yaw moment. Get that on a cat shot, it's all over. Probably all over the bow of the boat.
The engines, in AB, had enough power, far enough off to the side of the plane's centerline, that if one quit, but the second kept running, again, in AB, the plane would start to do a flat spin then and there, no matter how much rudder the pilot input. Grumman even stated the F-14 wouldn't do a flat spin, no matter what, at first. But after loosing a few to flat spins, they changed the NATOPS. No corrective action to a flat spin under any conditions, other than EJECT. Top Gun got that right in the movie anyway.
I can copy the entries from the NATOPS about all this...

The F-14 is a still a fun as heck plane to fly though! Especially if it's modeled with the TF-110 engines, as in the D model '14s. Better than 1:1 thrust to weight, which fighter pilots had been dreaming of since jets came about. Understandably!

Too lazy to dig up "Bye,bye baby!" and find out who to credit for the technique, but with enough altitude remaining, a flat spinning F-14 can be recovered by manually sweeping the wings to 68 degrees, thus moving the center of lift aft which will drop the nose. Not sure if this ever trickled down to the squadrons and if it saved some unfortunate butts, but at least the spin wasn't a guaranteed killer.





I'm not sure if it's unique to the RB.199 but there's also an arrangement where if electrical power is lost it goes to full throttle. Great if you're airborne and need engine power while you sort out the electrical gremlins, not so much if you're overly enthusiastic getting out of the aircraft at an airshow and get ahead of yourself during the shut down checks. Cue the entire crowd ignoring the flying display and looking towards the increasingly high pitched whine coming from the parking area followed by bits of engine being liberally spread across dispersal.
Took them a couple of weeks before it was ready to be flown out.

First time I've heard about that quirk. Neat!

[PhantomTweak]

Too lazy to dig up "Bye,bye baby!" and find out who to credit for the technique, but with enough altitude remaining, a flat spinning F-14 can be recovered by manually sweeping the wings to 68 degrees, thus moving the center of lift aft which will drop the nose. Not sure if this ever trickled down to the squadrons and if it saved some unfortunate butts, but at least the spin wasn't a guaranteed killer.
Thanks for the info, Bjorn!
Not that I'm an expert by any stretch, but I've never heard of that. I don't know how easy it would be though.
The pilot, who is the only one that has control of the wing-sweep, as far as I know, might have some trouble reaching the control. There is a fair amount of what they call "eye-balls out" force involved during a flat spin, and the pilot has it worse than the RIO, who is a lot closer to the center of rotation. It would tend to pin the pilot forward in the harness, arms against the cockpit side-walls, preventing him from reaching the controls, or either ejection handle. Unless he was fast and got things done before the spin developed very far. One of the few things about aircraft Top Gun got right.
Doesn't mean no one ever did it, just means the pilot would have to recognize the impending spin and react to it very quickly. As far as I know, though, the NATOPS just says FLAT SPIN--EJECT, in the Emergency Procedures section. No qualifiers, altitude limits, speed on entry, anything. Just jettison the aircraft. And if it has developed much past the beginning stages of a flat spin, the RIO is going to be doing the ejecting.
Fun times :very_drunk:

Might be something interesting to try in Dino's F-14 in FSX...
Pat☺

[Bjoern]

Thanks for the info, Bjorn!
Not that I'm an expert by any stretch, but I've never heard of that. I don't know how easy it would be though.
The pilot, who is the only one that has control of the wing-sweep, as far as I know, might have some trouble reaching the control. There is a fair amount of what they call "eye-balls out" force involved during a flat spin, and the pilot has it worse than the RIO, who is a lot closer to the center of rotation. It would tend to pin the pilot forward in the harness, arms against the cockpit side-walls, preventing him from reaching the controls, or either ejection handle. Unless he was fast and got things done before the spin developed very far. One of the few things about aircraft Top Gun got right.
Doesn't mean no one ever did it, just means the pilot would have to recognize the impending spin and react to it very quickly. As far as I know, though, the NATOPS just says FLAT SPIN--EJECT, in the Emergency Procedures section. No qualifiers, altitude limits, speed on entry, anything. Just jettison the aircraft. And if it has developed much past the beginning stages of a flat spin, the RIO is going to be doing the ejecting.
Fun times :very_drunk:

Dug through the book* again, but couldn't find anything. I swear I saw it in there, though.

However, and albeit copied from another website, this article explains it pretty well:
http://combatace.com/blog/5/entry-19-tomcat-spin-recovery/




Might be something interesting to try in Dino's F-14 in FSX...

I doubt it can be spun. Besides, being a "D" model, it doesn't have any reason to.

There are some videos for spin recovery techniques for the Aerosoft F-14A though.



*Not that it's a bad book. If you want to read a 200 page love letter to an aircraft, there's no way around it.
https://www.amazon.com/Grumman-F-14-Tomcat-Reminiscences-Service/dp/0760325766

[Victory103]

Beat me to it Bjoern, good post and answers the question. Also agree that Dino's "D" and all late model A/Bs had Digital FCS added, but you can spin the Aerosoft Cat model just fine.


For Pat, it's the B/D's with the GE F-110 motor that have the NATOPS warning about AB on take-off, the original and "not designed for the Tomcat" PW TF-30 allows AB take offs.

Guess no one wanted to take a stab a helicopter turboshaft engines?

[Bjoern]

Guess no one wanted to take a stab a helicopter turboshaft engines?

Turboprops with comparatively slow spinning propellers.

[SkippyBing]

Turboprops with comparatively slow spinning propellers.

Spot on. ~55,000 RPM down to ~360 RPM makes for a big gearbox!

[bbrz]

Spot on. ~55,000 RPM down to ~360 RPM makes for a big gearbox!
? which engine is that if I may ask?

[hairyspin]

A difference between helicopter turboshaft engines and many turboprop or turbofan engines is the turbine powering the helicopter rotors is often a free turbine. This means it's not mechanically connected to the gas turbine sections, it's instead driven only by the hot gas exiting the gas turbine. Watch a typical turboshaft-powered chopper from startup to lift-off and you'll hear the gas turbine start (accompanied by regular sparking sounds), run up to speed and sit there warming until the free turbine engages. The rapid speed-up of rotors to flying speed used to baffle me until it was explained.

[Mach3DS]

The same thing can be seen on an aircraft turboprop. If the exhaust pipes are at the front, it's typically an air coupled or free turbine. Meaning there is no mechanical linkage to the drive assembly other than exhaust gases. This is what is the primary reason for slow power conversion when running at Low rpm and then going quickly to high power....usually have to wait a few seconds for the air coupled to kick in.

[Bjoern]

These are a bit long, but seem to get the point between fixed and free power turbine along quite nicely.

https://www.youtube.com/watch?v=As-NZ5t8sxY

https://www.youtube.com/watch?v=8A2yr3ALt6c

[PhantomTweak]

However, and albeit copied from another website, this article explains it pretty well:
http://combatace.com/blog/5/entry-19...spin-recovery/ (http://combatace.com/blog/5/entry-19-tomcat-spin-recovery/)

Great article! I stand corrected. I was only going by what I read in the NATOPS, NAVAIR 01−F14AAD−1, which is for the D model, the NATOPS POCKET CHECKLIST, NAVAIR 01-F14AAP-1B which is for the B model, and so on.
Apparently, the secret is out now! The Navy brass won't be happy, though. They published the NATOPS, and unless an "official" change is made, it's sacrosanct. Then again, Navy Brass has a "never-wrong" complex... :a1310:
I am glad the info on how-to recover a flat spin got out, though. I hope it saved many lives, and planes. Even if it just saved 1 plane and crew, I'm all for it!
Thanks again for the info. Maybe never used in the Sim world, but it'd still be interesting to try!
Pat☺

[bbrz]

1.If the exhaust pipes are at the front, it's typically an air coupled or free turbine.
2.This is what is the primary reason for slow power conversion when running at Low rpm and then going quickly to high power....usually have to wait a few seconds for the air coupled to kick in.
1. Not really. The 'front' exhaust is there on e.g. the PT6 because it's a reverse flow engine. Has nothing to do with fixed or free turbine.
2. Flown both, fixed and free turbine turboprops but never noticed a significant lag (one of the main drawbacks in FSX/P3D turboprop engine simulation)

[Mach3DS]

1. Not really. The 'front' exhaust is there on e.g. the PT6 because it's a reverse flow engine. Has nothing to do with fixed or free turbine.
2. Flown both, fixed and free turbine turboprops but never noticed a significant lag (one of the main drawbacks in FSX/P3D turboprop engine simulation)

Yeah I meant pitch of the blade, not exhaust...oh well....too tired to care! lol. And it's not a set in stone thing...just a generality. Same with power. I've flown PT6, and yeah, it's not super noticeable there. But perhaps on heavier birds, with underpowered engines for the weight? Not sure. Just know that this is one of the reasons (excuses maybe?) for it. ;)

[Bjoern]

Great article! I stand corrected. I was only going by what I read in the NATOPS, NAVAIR 01−F14AAD−1, which is for the D model, the NATOPS POCKET CHECKLIST, NAVAIR 01-F14AAP-1B which is for the B model, and so on.
Apparently, the secret is out now! The Navy brass won't be happy, though. They published the NATOPS, and unless an "official" change is made, it's sacrosanct. Then again, Navy Brass has a "never-wrong" complex... :a1310:
I am glad the info on how-to recover a flat spin got out, though. I hope it saved many lives, and planes. Even if it just saved 1 plane and crew, I'm all for it!
Thanks again for the info. Maybe never used in the Sim world, but it'd still be interesting to try!

Well, to be fair, something that works for legends like "Hoser" Satrapa, won't necessarily work for Johnny McNuggetface, so the official line of punching out when in a spin is a more sensible solution than risking two funerals and a wrecked F-14.

[PhantomTweak]

Well, to be fair, something that works for legends like "Hoser" Satrapa, won't necessarily work for Johnny McNuggetface, so the official line of punching out when in a spin is a more sensible solution than risking two funerals and a wrecked F-14.
Very good point. A trained, very experienced Test Pilot will be able to accomplish a lot more in a stressful situation than Lt (JG) McNuggetface. Surprisingly, it costs a lot more to replace a pilot (and/or RIO) than a plane. Aside from the economics of it, there are the human considerations, families, relatives, and so on. The Navy would much rather their pilots and RIO's become members of the Martin-Baker club than a smoking hole. After all, that's what the seats are there for. :encouragement:

And now, back to your regularly scheduled engine discussion... :running:

Pat☺

[Bjoern]

Surprisingly, it costs a lot more to replace a pilot (and/or RIO) than a plane.

Cue Army: "You are very much replacable, but this tank isn't."

[PhantomTweak]

Pshaw!
Any farmboy that's seen a tractor can drive a tank.
Of course, apparently most anyone can drive a fighter like the F-14, if our great sim-world is any indication. :biggrin-new:

I do think is takes a little more money to run a guy through flight-school than tanker school, but I've been wrong before. Many, many times...
Of course, what Drill Sergeants SAY and what's true are often two different animals.

Have fun all!
Pat☺