Talk:Jet engine/Archive 1

diagrams and images

this could really use some diagrams and images. Kingturtle 20:05, 21 Feb 2004 (UTC)

I agree, we need good pictures and/or diagrams. I created one with MSPaint; admittedly primitive but gets the idea across. Please replace it with something better instead of deleting it; it goes a long way towards visualizing the process of how a plain (pardon the pun) jet engine works. I've solicited input from some aerospace professors I knew in college but they probably don't read their email, alas. Anyone have anything better?

We should have a diagram for each of the types of engine - simple turbine, ramjet, scramjet, plusejet, etc., with labeled parts. Justanyone 12:44, 29 March 2004 (CST)

Do you think that we should, perhaps, split up the engine types first? I think it would be more useful to have several articles for the different engine types. Pulse detonation engines are already in their own article, for some reason. Also, has anyone found a decent diagram of a scramjet engine? I've never found one before; do all scramjets use pressure to ignite their fuel (I saw one site that mentioned that); do any? Is a flame holder involved, and if so, what type? All I've found are exterior pictures and some really low-quality schematics... --Rei

There's different types of scramjets. I'll share all I know, but it may not be accurate. They don't have flameholders (that would cause a shockwave, so it wouldn't be supersonic combustion anymore). The way you light something without a flame is like diesel engines, heat it up enough, or change the pressure, and it ignites all on its own. Scramjets slow the air down enough that it gets hot enough to ignite, but they don't slow it to subsonic. And there's another way of doing it too, a grad student scramjet expert explained his thesis to me once, but I've forgotten. I think it had to do with whether you put the fuel in before you heat up the air or afterwards. moink 19:27, 29 Mar 2004 (UTC)

Ok, so I'd like to propose something. I agree it would make more sense to split up the subject so we have an entry for each type of engine, and a master link with a short summary of each type here. So, the sections would be:

• 'Jet Engine' as it is at the top, the existing general principles.
• history, as it is in current article;
• discussion of the fact that there are several types, varying by this or that feature (very general). This is intro text to the next section.
• list items in a table of 3 columns: (1) type of engine (jet turbine, turbojet, pulsejet, etc.) with links to each type of engine, (2) short description, (3)limitations/advantages.
• related subjects that are not engine types, like 'jet airplane', 'rocket propulsion', 'nacelle', etc.

I am willing to do this work in a couple of days, including creating a page for each type of engine and a simple diagram of how it works, as best as I can document / research. But, I want to gage reaction to this idea here first. Please comment if you think this work is good/bad etc.??, or would like to build on where it goes. Justanyone 20:34, 29 March 2004 (CST)

I'll second this. That sounds like a much better layout. --Rei

Third. :-) moink 18:30, 30 Mar 2004 (UTC)

I've already created a page under scramjet, mainly because there was a lot of material in the Boeing X-43 article that was really more about scramjet programmes in general than that aircraft in particular. Note that if we're looking for examples of different engine types, we have a list of aircraft engines with links to articles that already exist. --Rlandmann 07:25, 1 Apr 2004 (UTC)

I hope I didn't step on anyone's toes by boldly moving around the images a bit. --Diberri 06:49, Mar 30, 2004 (UTC)

No - I thought the image stackup was in need of fixing myself, you just beat me to it. →Raul654 06:52, Mar 30, 2004 (UTC)

non-american/british examples?

yeah i guess those silly soviets, french, israeli, kfir, etc, never made any supersonic airplanes, which makes you feel the need to have almost all your examples be american and UK. (199.245.163.1)

So the MiG-21 isn't a supersonic Soviet airplane? Rei

And Concorde was a joint Anglo French project!

and the Mig 15 wasent powered by a Rolls Royce engine... oh it sorry no it was, stupid labor government

components section formatting

Maybe the Components section should be put in a table now ? I think it merits being put closer to the top of the article too. We can have an overview, components, and then all the historical stuff later. Wizzy

I'll second that.  :) Perhaps the components list should indicate what type of jet engines use each component (for example, nozzle would be all; flame holder would be all but scramjet, pulsejet, and pulse detonation; compressor and turbine would be for the same except without ramjet as well; propellor would be for turboprop and turbofan; etc). --User:Rei

exhaust velocity physics clarification

Can somebody substantiate this:

"Exhaust air must be accelerated to beyond supersonic at the exit of the engine if it is to provide net thrust"

To my mind this is false. Since the engine is accelerating air, it must be producing thrust - Force = mass x acceleration. The air does not need to "push against" the ambient air, so there seems to be no need to ensure that the exit air is faster than the speed of the aircraft. There may be other reasons for doing this, but I feel the statement is misleading. Has the writer fallen into the layman's trap of thinking that an engine pushes against the air at the back? Graham 01:57, 22 Apr 2004 (UTC)

It all depends on how fast the plane is going. If your jet engine is pushing your plane at 100 m/s, your exit velocity does not necesarily have to be faster than the speed of sound (343m/s) But if your plane is going mach 2, than your exit velocity should be faster than the speed of sound. It all boils down to efficiency. Your engine uses less fuel if you can get the exhaust moving faster without inputting more energy (for example using a nozzle accelerates the air without using fuel) This is true for exactly the reason you stated: Force = mass x velocity so the faster you get yoru exhaust moving, the more efficient your engine can be. of course this has its limits. pretty much the only way you can do this is using a nozzle, and you also have to have a total pressure at the exit thats higher than the atmospehric pressure, or youll get a shock in the nozzle and your flow will go subsonic. For all practical airplanes, you should have a supersonic exit, but a supersonic exit is not aprori needed to produce net thrust.Theon 02:55, Apr 22, 2004 (UTC)

Well, this isn't all that convincing. For a start, Force is mass x ACCELERATION, not velocity. I can see that speeding up the airflow through a nozzle must impart a change of velocity which is acceleration, but my question is why is an exit velocity greater than airspeed needed? As long as the engine accelerates the air from a velocity v1 to another v2, force (thrust) is produced. I'm unclear why v2 must > airspeed. Your explanation seems to be a restating of what the article says; it doesn't really explain why supersonic exit flow is needed for a supersonic aircraft. Sorry ;-) Graham 03:20, 22 Apr 2004 (UTC)

The air starts out stationary (when it enters the engine). It must leave going backwards, to have a momentum change. If it leaves the engine going backwards, ego, it is leaving faster than the plane is moving forwards. Wizzy 07:05, 22 Apr 2004 (UTC)

Incorrect. Since f = ma, thrust is produced as long as a is not zero and m is not zero. This equation says nothing about airspeed, or exit velocities, or the relative difference between the two. I guess what you meant was that if intake air is assumed to be stationary RELATIVE to the engine, then it must exit faster than the engine for there to have been a net a. However, it's perfectly possible for the air to be at an initial velocity substantially lower than the airspeed - in fact for supersonic aircraft this is necessary and vital - an engine will stall if it ingests supersonic air. The engine can still accelerate this to a speed lower than the overall airspeed and still produce thrust. I can accept that supersonic aircraft do produce supersonic exit velocities - my question is, is it necessary for them to do it?, and if not, the article is a little misleading. Graham 07:19, 22 Apr 2004 (UTC)

I guess what you meant was that if intake air is assumed to be stationary RELATIVE to the engine - No - I meant stationary relative to the ground (ignoring the possibility of the wind actually blowing ..). Air - 0 km/hr. Supersonic plane hits, intake accelerates air, air goes through engine (still going forwards relative to ground). There is no momentum change that would drive the plane yet - in fact the plane has accelerated the air. Now we need the nozzle, so that after the plane leaves, the air is moving backwards (always relative to ground). I added the disputed statement to the article. Wizzy 09:00, 22 Apr 2004 (UTC)

Re-reading the article, maybe I see the confusion. When I said Exhaust air must be accelerated to beyond supersonic at the exit of the engine if it is to provide net thrust that meant relative to the plane. You, I think, are reading it as relative to the ground, which is of course, false. I agree it needs to be re-worded, and invite you to do it. Well spotted. Wizzy 10:23, 22 Apr 2004 (UTC)

Call me thick, but I still don't get it. I'm not thinking of it relative to the ground - as a pilot I know the ground doesn't matter ;-) Absolute speeds seem to me to be irrelevant - as long as the engine imparts some acceleration to the air, thrust is generated. I cannot see why the exit speed relative to the plane (or ground) matters. I do follow your argument; I just don't think it stacks up. We know that the air going into a supersonic jet's intake is subsonic, so it could be substantially below the plane's airspeed. The engine can accelerate that mass and get useful thrust out, even if the exit velocity is still below the plane's airspeed - an acceleration of a mass has occurred, therefore a thrust results. To me, it reduces to this simple argument. Now, there may be other good reasons to make the exit gas supersonic, and obviously getting as much acceleration of the air mass as possible is a good thing, but I don't see that the gas HAS to exceed the plane's airspeed to generate net thrust. That's all I'm saying. Let's try some figures: Suppose the plane is going at Mach 2, which for argument's sake we'll call 700 km/h. The engine intake airspeed has to be subsonic, so let's assume that we can arrange it so that it's 300 km/h (83m/s). Assuming unit mass and a transit time through the engine core of 5ms (a reasonable guesstimate?), if the engine accelerates the air to 600 km/h (167m/s), it has yielded (v2 - v1)/t = 16800N of thrust per unit mass, yet the exit velocity is still 100 km/h less than the plane itself. Admittedly that's not much thrust, but it's definitely not zero or negative. Using the same assumptions, a supersonic exit flow of 1000 km/h (278m/s) yields 39000N. Both figures seem low, so this clearly isn't telling the real story - but since the two cases give a similar order of magnitude I still feel that the statement as given in the article is misleading. Tell me where my argument fails if you can - I won't change the article text until I have clarified this in my own mind one way or the other. Thanks for taking the trouble to help sort it out. Graham 11:53, 22 Apr 2004 (UTC)

Ok Graham I've read what you wrote more closely and I think maybe I understand what the confusion is. Yes, on a standard jet engine (not a scramjet) the intake into the actual physical engine has to be subsonic. So the nacelle and various other things slow the speed of the air down to subsonic before they enter the engine. But when I look at it from the point of net behaviour, that is, I look at it from the point of view of an aerodynamicist, I define the "engine" differently. The "engine" has to include all those things that are slowing the air down in order for it to operate properly as well. And what an aerodynamicist would do to analyze this problem is draw a big box, a control volume, around the engine, including the shock wave and anything slowing the air down. The front of this box would have to be far enough ahead of the engine that the air entering it could be said to be at the airspeed of the aircraft. Now, in order to have net thrust, the total momentum of the air leaving this control volume has to be greater than the total momentum of the air entering the control volume. There are no "cool aerodynamic tricks" to get around this basic principle. Any slowing down of the air you do causes additional drag, and you have to overcome that and more to generate any thrust. Thus, the speed of the air leaving my control volume, which is approximately the speed of the air leaving the engine, must be moving faster than the airspeed. moink 15:45, 23 Apr 2004 (UTC)

Tell me where my argument fails if you can - you are not taking account of the drag/momentum change imparted by the intake speeding up the air so it is subsonic thru the engine ? You are saying v1 is 300km/h, I say v1 is 700km/h Wizzy 12:57, 22 Apr 2004 (UTC)

Well, we know it CANNOT be 700km/h, because the engine wouldn't work. I accept that the aircraft is doing work in creating the supersonic shockwave, behind which the air is travelling subsonically, but does this cancel out the thrust? Presumably aerodynamicists have design techniques which allow them to play with t in the above equation - so the force needed to slow the air down may be far less than that imparted by the explosive combustion within the engine (implying a very small value of t there). Of course if the speed of the plane is contant, we know that the overall drag, of which the shockwave formation is a part, is exactly equal to thrust, but I'm still unconvinced that this implies anything about relative exit velocities. Any aerodynamicists/mathematicians wish to take up this discussion? Graham 23:38, 22 Apr 2004 (UTC)

This is obviously some sort of a reference frame problem. I've read the above, but I'm still not clear on what reference frame the speed of the air is being measured in. The standard aerodynamic reference frame is attached to the airplane. In that reference frame, the air has to leave faster (on average) than it comes in. That's the only requirement for the generation of thrust. Does that help at all? moink 23:46, 22 Apr 2004 (UTC)

My explanation above was in the body-fixed frame. Now let's try the ground-fixed frame for completeness. What I call the speed the air is entering my control volume is actually the aircraft's airspeed. The exit speed is then faster than the enter speed in the body-fixed frame, but the body frame is moving forwards at a rate equal to the airspeed. So in the ground-fixed frame, *any* backwards speed is evidence of the generation of thrust. Of course, the faster it's going the more thrust (force=change in momentum, and by 3rd law the momentum imparted forward to the body is the same as the momentum imparted backwards to the air, but don't forget we can use large masses of air instead of just high speeds). I'm trying to be clear here, but I think I might be muddling up laymen who don't know my jargon... moink 23:53, 22 Apr 2004 (UTC)

I think we all like the reference frame is attached to the airplane. but I'm still not clear on what reference frame the speed of the air is being measured in - this is what needs to be fixed. I meant the plane Frame of reference. Your 23:46 comment is clear, and is not dependent on engine technology. Is there another WP article that we can refer to, or should we write it up here ? If it has caused Graham all this confusion, and he is a pilot, the encyclopedia is lacking. The reference frame jargon is good. Wizzy 06:37, 23 Apr 2004 (UTC)

The MOMENTUM OF THE AIR is the important feature here, in my mind. From the plane's point of view, it's like a pump. It has a certain input mass of air that has a certain momentum (mass * velocity) through its pump (engine). It needs to add momentum to that air to generate thrust. If it accepts a mass of air M1 moving at velocity V1, it needs to increase the velocity of that air to V2 (where V2 > V1) to generate thrust. Simple. However, the plane has drag. Thrust must exceed drag to increase velocity. If mass of air M1 enters the engine with supersonic velocity V1, is expanded and slowed (bernoulii), compressed, used for ignition and by heat, compressed further, then expanded out again to supersonic velocity V2, then V2 needs to exceed V1. Pretty simple. Justanyone|talk Fri. 23 April 2004 9:54 am CDT.

Yeah that's a pretty good explanation. V2 does (on average) need to exceed V1. So if V1 is supersonic than V2 also has to be supersonic, "more" supersonic we might say. And V1 is, by definition, the airspeed of the aircraft. Now, that's fine in our aircraft-fixed reference frame. Unfortunately I think many of our readers think about speeds not the way we aerodynamicists do, but in a ground-fixed or air-mass-fixed reference frame. And in those reference frames, the exit velocity just has to be enough to counteract the drag of the aircraft.

Let's look at an example to make sure we all know what we're talking about. Let's say we have an aircraft travelling at Mach 1.5. In our aircraft reference frame, the air travels into some control volume surrounding the engine at Mach 1.5, gets slowed down to subsonic, compressed, burnt, expanded, expelled at let's say Mach 1.7. In the air-mass-frame, the air starts at rest. The engine comes along at Mach 1.5, scoops up the air, and sends it moving backwards at Mach 0.2.

So, I'd say it's not important to say that the air has to be "supersonic" because then we'd have to explain to the readers all of this reference frame stuff. It's more important to say that in *any* air-breathing propulsive system (propellers, jets) the air has to be moving backwards in order for the aircraft to move forwards. And in any inertial reference frame (one attached to a train going by underneath, perhaps?) the only requirement is that the air that leaves the engine be going more backwards than it was before it interacted with the engine. moink 15:36, 23 Apr 2004 (UTC)

In the standard aerodynamic reference frame attached to the airplane, the air has to leave faster than it enters, in order to generate thrust. In the case of a supersonic plane, that requires the Nozzle, as the engine is incapable on its own of creating a supersonic exhaust velocity.

We do not want a long explanation. I do not think we should 'dumb down' our audience. You could even drop the second sentence, but I think it is interesting. Wizzy 06:07, 24 Apr 2004 (UTC)

your all wrong force = rate of change of momentum!! that is the jet engine will produce thrust if the momentum of the air entering it is less than the air exiting it. as the mass flow rate of air throught the engine is constant this equates to the jet velocity having to be greater than the flight velocity! simple as that incidently "newtons law" as you quoted it was never actually stated by him as F=m.a he always reffered to the rate of change of momentum of an object we only get f=ma as a result of having constant mass and letting dt tend to 0 in F=(m.u-(m+dm)(u+du))/dt Richard Mathie july 2006

I would agree that a "momentum change" explanation would be most acurate and easy to understand. It is interesting to note that even if the flow exited the engine at the same speed it enterd, there would be a thrust force due to the added mass flow of the injected fuel. Of course this thrust would be negligible compared to the drag force acting on the engine and its housing, so for any practicle engine the exit velocity needs to be greater than the inlet velocity, (regardless of reference frame or Mach number.)--Ryan.gist 04:24, 29 September 2006 (UTC)

Layout

I think this article would be improved by moving the (interesting) History section further down, and the Types and Components further up. Components could use a table, like the nice Types one. Design considerations only has the Intake - there are other Design considerations of other components scattered through the article. Wizzy 08:08, 26 Apr 2004 (UTC)

Gas turbine

Being a featured article for a while, I think this page has gathered a lot of the theory of Gas turbines that properly belongs on that page. User:Pud has been doing some excellent work over on Gas turbine, and the theory is now spread between the two. I suggest that all theory be moved to Gas turbine, or a separate page be created. Wizzy 09:47, 8 Jun 2004 (UTC)

Turbojet

Re: merge from Turbojet - I suggest a #redirect instead. Wizzy 15:19, Oct 24, 2004 (UTC)

Fundamental error?

"The engine generates thrust because of the acceleration of the air through it—the equal and opposite force this acceleration produces (by Newton's third law) is thrust."

no, thrust is always in the direction of the acceleration.

Thrust is caused by pressure (for jet engines).

Also true... since to accelerate air it has to push against something which inevitably raises its pressure.

It's not the speed of the air moving through an engine

No, it's certainly not. The article says *acceleration* of the air... That's entirely different. For example if it enters at 400 mph, and it leaves at 500 mph then it has been accelerated and you get an opposite and equal forward thrust on the engine.

but rather the amount of pressure created at its exhaust (or its power turbine in the case of turbo-shafts and turbo-props).

The pressures that count are the pressures next to the metallic bits of the engine, since only they transmit thrust to the vehicle. Right? The other pressures cancel anyway but can be very high or low.

By the Venturi concept doesn't acceleration cause lower pressure? It seems that this part of the article could use a bit of tuning.

No, it produces thrust because of the momentum change of the air passing through, not 'pushing' against the air behind it. turbo-props are different - they tap power off and use it to drive a propellor. Re the nozzle - please check the rest of this talk page. Wizzy 10:59, Jan 14, 2005 (UTC)

The venturi effect does indeed cause lower pressure. That's one of the limits on how much thrust can be obtained from hot, high pressure air entering the nozzle. The exhaust pressure must not go below the atmospheric pressure in the nozzle and as it accelerates its pressure does indeed go down; the designers of jet engines try to ensure that the nozzle ends when the exhaust is at ambient pressure since that gives maximum thrust. -Wolfkeeper

There are two kinds of thrust, momentum thrust and pressure thrust. Pressure thrust is the less efficient of the two, so for the ideal case, you get no thrust from pressure because the nozzle converts it to momentum thrust. The formula is thrust = m-dot (vout-vin)+ (PeAe-PiAi).70.144.143.88 (talk) 10:51, 12 March 2009 (UTC)

The page is large, TURBOJET should be split off

The jet engine page is getting large, over 32kB. I think that turbojet should be split off, and the page can be reduced a bit. Every type of jet engine has a page except turbojets (conventional usage). Each of the types of jet engines can probably be reduced in size since they do have main articles. 132.205.45.148 19:40, 20 Apr 2005 (UTC)

I concur and I will be implementing basically what Justanyone purposed previously. Let me know if anyone objects to this. Alanl 14 May 2005

My biggest problem with splitting off Turbo-Jet is that it's basically what we mean in the engineering classes when we say "Jet Engine". I wouldn't recommend that as a way to make the page shorter.70.144.143.88 (talk) 10:53, 12 March 2009 (UTC)

Request for references

Hi, I am working to encourage implementation of the goals of the Wikipedia:Verifiability policy. Part of that is to make sure articles cite their sources. This is particularly important for featured articles, since they are a prominent part of Wikipedia. The Fact and Reference Check Project has more information. Thank you, and please leave me a message when a few references have been added to the article. - Taxman 19:36, Apr 22, 2005 (UTC)

Exhaust

Exhausts are designed to maximize thrust, since venting hot air does not provide nearly as much thrust as venting fast-moving cool air.

I don't like this phrase - anyone like to try to fix it ? Or delete after the comma ? Wizzy…☎ 22:19, 13 September 2005 (UTC)

TS diagram

What's with the graphic in this section, using some weird Fred Flintstone units of energy that so far had only the barest of mention in a single Wikipedia article (plus one talk page)? That's not saying much, since we even have articles with several different flavors of shaku, articles on obsolete Tatar weights and measures and the metre-tonne-second system of units, the pous and the ligne], and maybe even some of those units Rktect tries to sneak in all the time with "3" as a vowel in their names.

How many Wikipedia readers would even know that "CHU" is one unit, not the product of three things, let alone what quantity it measures? Maybe one in ten thousand?

Can't somebody find something decent using normal joules per kilogram-kelvin? Or redo this graph, or something? After all, the conversion isn't all that difficult. Since 1 CHU/lb is the same as a kilogram-calorie (the large calories we use in connection with food and dieting) per kilogram, or a small calorie per gram, 1 CHU/(lbm K) = 4.184 kJ/(kg·K). Or, since 1 CHU/K = 1 Btu/°F, just relabel the damn graph as "Btu/lb·°F' so that at least we have units familiar to more that 20 people in the whole world. That conversion is even easier: 1 CHU/(lbm K) = 1 Btu/(lb °F). Gene Nygaard 20:02, 30 October 2005 (UTC)

Turbofan engines

The mathematical relation in this section does not seem to be all that accurate. Thrust is a force, appropriately labeled F, but the formula described (m·v) does not give a force/thrust, bur rather a momentum or impulse. A more appropriate label should be p (momentum) or, perhaps even more approrpiate in this sense, I (impulse). Or the formula could be altered to actually give a thrust rather than a momentum.

I fixed m to m_dot, thus: [N] = [kg/s] × [m/s] . - marsian 04:28, 8 March 2006 (UTC)

Turboshafts and Turboprops

My feeling is that turboshaft and turboprop engines do not belong on this page at all. They are not considered jet engines. I know this is mentioned (buried) in the article, but they shouldn't be in here at all. 66.35.138.9 05:04, 3 January 2006 (UTC)

I think we have an amazing article here. However, I think it really belongs under Gas Turbine. I would hate to break the flow of what we have, which moving pieces around will do. Wizzy…☎ 06:47, 3 January 2006 (UTC)

The problem is that not all of these engines can easily fall under one category. For instance, if this page was under "Gas Turbines", then rockets and ramjets wouldn't belong. I think the best way would be to have a "Reaction Engines" article, and a "Gas Turbines" article. There would be some overlap, of course. No easy way to group these engines despite the fact that they are all closely related. 66.35.138.9 07:25, 3 January 2006 (UTC)

Reciprocating Rotary Radials

I'm removing the reference to rotary radials being reciprocating engines. They are not reciprocating engines, as the pistons travel in a circle instead of in a back and forth motion. While you could make the argument that from the frame of reference of the cylinders the pistons do appear to move back and forth, that doesn't make it a recip engine any more than a turboprop is a recip engine because a turbine blade appears to move back and forth from the point of view of the engine case, ignoring its circular motion. Also, referring to the rotary as a recip contradicts with the the rotary engine article, which states: "Another advantage, not realized at first, is that the pistons do not actually reciprocate; rather, they travel in a circle around the common center of the connecting rods' "big ends", and only appear to reciprocate from the rotating frame of reference of the cylinders, which travel in a circle whose center is offset from that of the pistons (the centre of the crankshaft is offset from the engines centre of rotation). This lack of reciprocating mass leads to smoother running."

While it's easy and convenient and common to call a rotary radial a recip, it's not technically accurate and doesn't belong here, especially as a side note in a jet engine article. Mexcellent 04:19, 30 January 2006 (UTC), A&P

A reasonable argument, and consistency across articles is a good aim. Your analogy is a bit off though, since turbine blades in a turboprop don't appear to "move back and forth" in any frame of reference. I agree with you though that as a side-comment in an article about a jet engine we don't need to be so hair-splitting. Graham 23:22, 30 January 2006 (UTC)

merge rocket engine in here?

I think it would be a good idea to merge rocket engine with this article, since a rocket engine is really a jet engine which carries it's own oxygen or is propelling a rocket. It is even in the 2nd sentence of the lead. This would stop the duplication of effort between these two articles. --MarSch 10:45, 16 April 2006 (UTC)

My gut feel is that it's a bad idea. After thinking about it:

• the jet engine article is too big already if anything
• rocket engines don't have compressors and don't have air inlets. The exhaust has a different chemical characteristics.
• most people don't think about rocket engines as being jet engines so it would be confusing- people would search for rocket engine and get jet engine; they would probably think it's a mistake. They may even edit things because of this; so the article structure would become unstable. IMO article structure needs to reflect how people generally think about things, rather than how things necessarily are. On the other hand, articles themselves need to reflect how things really are.

WolfKeeper 14:53, 16 April 2006 (UTC)

I think I can summarize the confusion here by saying that a rocket engine is not a jet engine, but rather that both contain a converging-diverging (delaval) nozzle. That both contain the same nozzle does not make both the same thing. Jet engines, by definition, contain compressors and turbines. They include turbojets and turbofans, they're air-breathing, calculations for specific thrust are formulated differently than for rocket engines, material selection considerations are different, and they're quite separate sections in even the most simple propulsion textbook. For all those reasons and to avoid the potential confusions that Wolfkeeper brings up, I'd definitely oppose any merging of the two articles. --ABQCat 21:28, 16 April 2006 (UTC)

Third the opposition; as a spacecraft engineer very familiar with rocket engines, and pretty if not professionally familiar with jet engines, the common fallacy that MarSch states above is just that... a fallacy. It's common enough that a lot of people still believe it, but it's wrong. Rockets and jets are not even vaguely the same in any significant facet of operation or construction, to anyone working on them. Georgewilliamherbert 22:36, 16 April 2006 (UTC)

They are very different in most cases. But then LA is very different to New York, does that make them a different country? And there are borderline examples of varying silliness: is a squid a jet or a rocket (a squid has an inlet)? Would SABRE be a jet or a rocket engine? How about Air-augmented_rocket? Water rockets don't have de Laval nozzles, but they are rockets. Is the Jet Propulsion Laboratory misnamed? Just stuff to think about.WolfKeeper 03:07, 17 April 2006 (UTC)

Anyway, I don't want Rocket engine in here for practical reasons, but I don't find it wrong in a theoretical sense, in fact I think ordinary rockets are jet engines, but they're clearly not turbojets. But that's absolutely not the way people normally think about it.WolfKeeper 03:07, 17 April 2006 (UTC)

That's a very odd way of looking at it. Neither common non-expert usage nor professional usage in engineering or the related physics agree with you. "Jet" doesn't mean "Every propulsion method by which we expel working fluid or gas out a nozzle". Georgewilliamherbert 03:19, 17 April 2006 (UTC)

From the textbook, Aircraft Gas Turbine Powerplants by Charles E Otis, Chapter II Jet Propulsion Theory, page nine, first paragraph: "Jet Propulsion is defined as the reacting force produced by the acceleration of air, gas, or liquid through a nozzle" 65.127.231.5 18:11, 28 June 2006 (UTC)

I fourth the opposition and agree that the two articles should not be merged. - mbeychok 03:35, 17 April 2006 (UTC)

I fith the opposition to merge these articles

I agree with the previous mention that the "Jet Engine" article is too large, and does not need to be expanded.

That said, I believe the article name tends itself to controversy. Turbojet Engine is much more descriptive than Jet Engine. Both Rockets and Turbojets issue exhaust "jets" of high energy flow to create thrust. The distinction lies in the fact that the turbojet utilizes the ambient air as an oxidizer, and turbomachinary in the primary flowpath. A rocket engine on the otherhand must carry its own oxidizer and the primary flow is not used to turn a turbine. The correlation between turbine engines and rockets based on the mutual use of a DeLaval nozzle is incorrect: both propulsion systems can be operated with a simple converging nozzle (in fact subsonic commercial "jet engines" use this type of nozzle, while most rockets use a converging-diverging "bell" nozzle.)--Gistr712 05:03, 29 September 2006 (UTC)

I don't support moving the rocket engine onto this page. Jet engines and rocket engines function very differently, because jet engines are air-breathing engines while rocket engines are not. There's absolutely no special compressor section for compressing incoming air because there is no incoming air, although some advanced rocket engines do use turbines to pump the fuel to their combustion chamber. 70.144.143.88 (talk) 10:56, 12 March 2009 (UTC)

I sixth opposition to merge these articles. I dont agree a rocket is a jet engine again the same point as above a rocket is not airbreathing(as far as i know jet-engines must be airbreathing) and does not use that air for propulsion.Also there is disambiguaty on the topics http://en.wikipedia.org/wiki/Turborocket , first line. Just because rockets use a jet for prepulsion dosent mean they are jetengines. If that was the case you could say ducted props(if they push a jet of air) are jet engines. I will return soon with more info after re-reading my books again.Si Co15 (talk)Si Co15 —Preceding undated comment added 17:14, 3 September 2009 (UTC).

Refeaturing

I think we should get this refeatured. It was defeatured due to lack of references. I've added a reference section, and ref'd the few external links that there were instead of directly linking. If anyone can add some more that would be really good. (Because the article references so heavily within the wikipedia, it's not really needed, but it looks good for the refeaturing.)

Also, if people could read through the words and smooth them out a bit, that would be cool to.

Once we're really happy we can reapply the article.WolfKeeper 02:17, 27 April 2006 (UTC)

Fuel storage

I've been searching around, but where the fuel in a civil aircraft is stored is nowhere to be found. Does anyone know where it is, where in the fuselage?

almost always in the wings. Wizzy…☎ 13:01, 15 June 2006 (UTC)

Depends on the bird. Most transport category aircraft (i.e., commercial airliners) have tanks in both the wing and fuselage. Most smaller aircraft used in general aviation have wing tanks, although some have fuselage tanks as well, and a fair number, especially early business jets, have tanks on the wingtips (Lear 20-series and 35, Westwind I and II, etc.).--chris.lawson 04:07, 16 June 2006 (UTC)

Adding my two cents that most planes I've seen have them in the wings; those are general aviation craft (small planes), because I have no experience with commercial jets.70.144.143.88 (talk) 11:00, 12 March 2009 (UTC)

Integral rocket ramjet

I've changed the integral rocket ramjet entry to air augmented rocket in the table of jet engine types, which is the name of the article that this links to anyway.

The integral part of integral rocket/ramjet refers to the fact that the solid-propellant booster is integrated within the ramjet combustion chamber. Otherwise it's just a normal ramjet. This is a more efficient packaging solution than external tandem (e.g. Sea Dart) or wraparound (e.g. Bloodhound) boosters.

RPM

It would be nice if somewhere in there someone could detail the speed of these critters turn at. Not the speed of the airplane. When I hear planes take off, the whine means that there is KHz sound there, what causes it? There should also be a mention of hobby turbines like the Wren which spin at 100000+ RPM and definitely make a KHz whine when running all out, as you can hear on the model B-52 video when it revs up.

It depends a great deal on the size of the engine. Big ones spin slow and small ones spin fast. A 75,000 lb thrust high-bypass engine may have a maximum fan speed near 3000 RPM and a maximum core speed near 13,000 RPM. A 15,000 lb engine may have a max core speed closer to 20,000 RPM. Smaller geared turbofans may have speeds of 100,000 RPM. Not sure if this is worth working into the article or where you would do it. Kiracofe8 03:13, 6 February 2007 (UTC)

The high-pitched whine is caused by flow interactions between stationary objects in the flow stream and rotating airfoils. A GE CF6 fan has 38 blades, so if the fan is at 3000 rpm, the blade passage frequency is 3000 x 38 / 60 = 1900 Hz. The noise from this source will be peaked at multiples of the blade passage frequency, causing the characteristic whining noise.

--Tex 20:48, 30 March 2007 (UTC)

QUESTION: Stationary uses?

Are there any widespread uses of jet engines on land? Thanks, --Orangehues 13:12, 27 February 2007 (UTC)

All i can think of is when they put jet engines on the back of lorries in the UK in the 1940s and 1950s to melt heavy snow and ice, is that the kind of thing you mean? trash80 (talk) 15:33, 19 April 2008 (UTC)

In tokyo they use them as pumps in their undergound drain recevoir.

They are used to drive pumps in oilfield applications, especially offshore. They are also used at airports as Ground Power Units (GPU) for providing compressed air to an airplane on the ground. This air is used to start the main engines and to drive the Air Cycle Machines to cool the interior. In modern large airplanes there is an Auxiliary Power Unit (APU) to do the same thing, but you still see the old GPUs in use.
--Tex 14:18, 28 March 2007 (UTC)

APUs are gas turbines, which aren't quite the same thing. Pretty much a jet engine is something used primarily for propulsion so more or less by definition, if it doesn't move it's not a jet engine.WolfKeeper 16:49, 28 March 2007 (UTC)

Technically correct, but I don't think it addresses Orangehues' actual question.
--Tex 19:02, 28 March 2007 (UTC)

Engine inlet screen

The screen over the inlet of the engine illustrated in the article is incorrectly described. Its main function is to create a slight pressure drop in the engine inlet. This pressure drop can then be measured and used to calculate the airflow through the inlet. It is often called an air meter for this reason.

The implication that a crew member might be out in the test cell while a engine is running with the throttle advanced beyond idle is absurd. It is safe to enter the test cell, with ear protection, at idle to trim the throttle, check leaks, and the like. Being in the cell with an engine operating at power is extremely dangerous and possibly fatal, due to the high acoustic pressure.

Also the 'tunnel' the exhaust is directed into is incorrectly described. Properly called the augmenter tube, its main function is to act as a giant aspirator pump and pull air through the test cell. Ideally the airflow in the front part of the cell should be smooth and uniform across the entire vertical cross section of the cell, or the engine will tend to run unstably or even stall. The extra air pulled through by the pumping action of the augmenter tube helps accomplish this. This additional air also serves to cool the jet exhaust in the exhaust stack.

After an interval for comment, I'll make the necessary changes.

--Tex 19:26, 28 March 2007 (UTC)

Simple English

Hey, can anyone create a page about Jet engines on the Simple English possibly? here you'll see the articles which don't exist. Rysin3 23:31, 19 June 2007 (UTC)

Hans von Ohain Unaware of Whittle's work? !

"In 1935 Hans von Ohain started work on a similar design in Germany, unaware of Whittle's work."

As indicated on this website:

http://www.cwn.org.uk/heritage/people/whittle/biography.html

Despite pleading with the MOD Whittle's patent details were made public (The MOD thought the idea would never work). It did not take long for copies of the patent to get to Germany! The details were then passed on to all the german engine companies of the day.

It is untenable that von Ohain (and others) were unaware of Whittle's ideas. The engines were also not similar.

If they were not similar that argues that he was unaware of Whittle's work. It's quite possible that Ohain was unaware, but people funding his work may have been encouraged to fund Ohain because they knew of Whittle's work. Anyway, your speculation that Ohain knew is simply WP:OR. Whittle believed that Ohain didn't know.WolfKeeper 19:11, 15 October 2007 (UTC)

Whittle was almost certianly not too happy with his nations actions. The UK goverment ignored Whittle's warnings about the implications of making the patent public (german military intentions), did not fund him, exported his engine to the USA and then under war legislation gave his company to Rolls-Royce. Was von Ohain happy with the Nazi goverment and being a part of its military build up? Was Wagner more honourable? Let's put the people before the national sentiments.

Neustadt01 16:11, 29 September 2007 (UTC)

I have always believed that von Ohain's work was built on Whittle's patents that were wide spread in Germany at the time. I will research a reference. SimonRBailey (talk) 16:24, 11 December 2007 (UTC)

—Preceding unsigned comment added by SimonRBailey (talk • contribs) 13:25, 11 December 2007 (UTC) 

If anybody can get a good reference for this please do. I'm quite open to changing the text with a good reference.- (User) WolfKeeper (Talk) 17:08, 23 February 2008 (UTC)

This page

This page is far too long, it needs to be reduced to a minimal node with links to detailed leaves. The information also needs to be thoroughly reviewed as a number of common misconceptions are now incorporated. For axial engines please see Wikipedia article http://en.wikipedia.org/wiki/Metrovick_F.2 for flight of Griffith's engine 13 Nov 1943 ... Jumo 004 were still under prototyping and design at this stage (see http://en.wikipedia.org/wiki/Junkers_Jumo_004 for account of development and actual dates of real flight-rated engines rather than test-bed releases) Please check squadron service dates of Gloster Meteor Mk 1 and Me262, also combat dates of same in squadron service (Me262 was released to, then immediately withdrawn from service, before finally being released early 1945 from memory). The current page is too long to edit easily, it needs to be modularized —Preceding unsigned comment added by 137.219.43.127 (talk) 03:54, 15 December 2007 (UTC)

Turbo Charger Jet Engine

Would an expert on this subject look at the article: Turbo Charger Jet Engine. I believe the article should be merged into this one and deleted. Carl M. Anglesea (talk) 04:00, 16 January 2008 (UTC)

Whittle versus Ohain

NPOV says that all notable points of view have to be included in the article. An editor (Sirjustinflames and what appears to be a sockpuppet Thaimanfrombk) is repeatedly rewriting the article to contain only one point of view on whether Ohain had read Whittle's patent or not and repeatedly removing a reasonably good reference from a notable source that supports that he hadn't, and adding a reference to an alternative point of view which cannot be traced to any primary source, but just one article reference doesn't seem to have been written by a notable person, and the journal doesn't seem to be a well known or prestigious one.

The bottom line IMO is that without a good reference this edit can't stick, under NPOV we only have to support notable points of view that are supported by good references, but unfortunately I believe that we don't have that right now for the POV that is being inserted, and we do have good references for the POV that is being removed. Given that I don't think I have much choice but to keep reverting. :-(- (User) WolfKeeper (Talk) 17:06, 23 February 2008 (UTC)

I concur with the enforcement of NPOV and reliable sources. Why is it so hard to believe that 2 inventors can come up with similar ideas in a similar time frame, without either being aware of the other's work? If Ohain was Russian, would we be having this conversation, a la Su-24, Tu-144, etc.? Also, correct me if I'm wrong, but wasn't Ohain work axial compressor-based, while Whittle used centrifigal compressor designs? While circumstantial, I would think this argues for independent development. - BillCJ (talk) 18:00, 23 February 2008 (UTC)

To some extent it seems to depend on what you mean by jet engine, and Ohain apparently did manage to get a patent, so somebody seemed to think he had invented something; and he did actually get something running before Whittle. Nobody can take away Whittle's prior patent, but nobody can take away Ohains later one either I suppose.- (User) WolfKeeper (Talk) 19:48, 23 February 2008 (UTC)

There's no actually proof that he was aware. Whittle's son said he thought he was, but there's evidence elsewhere that states that Whittle himself believed Ohain wasn't. I'm going to have to take this out, there's no source on it; the article overstates the case; the only other alternative would be to state both father and son's positions.- (User) WolfKeeper (Talk) 19:48, 23 February 2008 (UTC)

But the Daily Mail has spoken! How can they be wrong? ;) - BillCJ (talk) 19:52, 23 February 2008 (UTC)

Jet versus propellor

I apologise if this is addressed elsewhere on Wikipedia, but what are the considerations undertaken in choosing whether to fit an aircraft with a jet engine or a propellor engine? Is it a cost issue? 78.148.193.136 (talk) 19:25, 9 March 2008 (UTC)

Airspeed. Jet engines are inefficient at low speed:

- (User) WolfKeeper (Talk) 19:31, 9 March 2008 (UTC)

Thank you. 78.148.193.136 (talk) 19:41, 9 March 2008 (UTC)

Assessment comment

The comment(s) below were originally left at Talk:Jet engine/Comments, and are posted here for posterity. Following several discussions in past years, these subpages are now deprecated. The comments may be irrelevant or outdated; if so, please feel free to remove this section.

core topic of aviation, Former FA

Last edited at 22:53, 22 August 2006 (UTC). Substituted at 15:05, 1 May 2016 (UTC)