Namely, how exactly do they work? I've got a loose idea of what it means (the word "afterburner" itself lends a lot of ideas). In my mind it either ignites residual fuel in the jet exhaust or it recirculates it somehow.
Care to clarify for me?
sigpic courtesy of This Guy, original modified by me
They inject fuel into the exhaust and ignite it. That provides higher-volume, faster-moving exhaust, which translates into more thrust.
Another interesting way to increase thrust is how earlier versions of the B-52 did. We would inject 10,000lb of distilled water into the later stages of the engines on takeoff, to increase the mass of exhaust, giving us the thrust to lift off at heavy gross weight. 
Afterburners eat fuel like there's no tomorrow, though, so their use is strictly limited. An F-15 in afterburner consumes fuel at more than 100,000lb/hr, for example. And they don't carry nearly 100,000lb of fuel . . . so afterburner is strictly a limited-use thing.
Hope that helps.
If you have any other questions, I'd be happy to help. I'll be back in a few hours, after class. I'll ask one of my fighter pilot buds to clarify, too.
--Satan, quoted by John Milton
And just in case you're wondering, I was looking at my car's engine the other day and there's a little fuel reclamation thing. Basically it takes residual fuel not burned in the cylinders and recirculates the gas-rich stuff through the engine. Didn't know if an afterburner was something similar on a larger, more open scale. It clearly isn't hehehehe...but better to ask and know I guess.
sigpic courtesy of This Guy, original modified by me
Sar...
And I'm not a mechanic. I might sound like I know what I'm talking about when I goof off as Deth IC with his gadgets and such, but the extent of my knowledge of mechanics is how an internal combustion engine works, some general idea of how a jet engine works (my great-uncle worked for NASA when I was little and got me stuff on airplanes and such when I was a kid...wanted to be an astronaut hehehehe), and stuff I've gleaned from Popular Mechanics, Popular Science, and the occasional car magazine. Which is why I ask basic, stupid questions about stuff I'm unsure of...easier to build info up from a common ground than correct damaged thinking.
I'm better with biology (which is actually pretty sad, considering I hated biology...but I read up a lot there to keep up with Lyinar who's into genetics...) [ 06-05-2002: Message edited by: Ja'Deth Issar Ka'bael ]
sigpic courtesy of This Guy, original modified by me
Jet engines have various stages, where the air is compressed by the fans. Afterburners inject and burn additional fuel in any one of the last five stages (for an F-15).
Full AB provides a 40% increase in thrust.
I was also too conservative on the fuel consumption: the F-15 AB consumes 186,000lb/hr per engine. It has two engines.
The B-52 system was only for takeoff assist. The newer ones don't even use it, as they have better engines.
But the basic principle is that you increase the density and speed of the exhaust, which gives more thrust.
Cars work on different principles, though, since you're not talking about using exhaust as thrust, as we do with jets.
Not sure about the fuel reclamation thing--I'm not that into cars.
--Satan, quoted by John Milton
quote:
Lady Snoota had this to say about Punky Brewster:
B-B-B-B-B-Benny and the Jets.
You thought you were a big shot? Didnt you?
YOu had to open up your mouth
Okay, here's another one...
WTF is a "Ramjet" ? I've heard it described some sort of high altitude rocket/jet engine hybrid.
sigpic courtesy of This Guy, original modified by me
quote:
Ja'Deth Issar Ka'bael had this to say about (_|_):
40% eh? That's some nice boost, then, seeing as how Fighters move pretty damned fast in the first place.Okay, here's another one...
WTF is a "Ramjet" ? I've heard it described some sort of high altitude rocket/jet engine hybrid.
I suck at explaining stuff. So here goes.
Ok, you know how a normal jet engine uses a large turbine in order to compress the air enough so that fuel can be injected, ignited, and thrust be made? ..
Well a ramjet doesnt do that. It uses the force of air coming in to compress, and ignites it using almost no moving parts (I think!). Only problem is you need to be goin pretty fast to make it start working, so you need minirockets or something to get it going at sea level, then as it gains tons upon tons of speed, you go up and up, and hopefully, into orbit. Thats the idea, anyway.
Ramjets are still experimental if I'm not mistaken.
A normal jet engine compresses air using a series of fan blades and chambers to produce thrust.
A ramjet, on the other hand, has no moving parts, using its shape and the velocity of incoming air to provide the compression. Here is a diagram of a ramjet.
There is also a more advanced kind of ramjet called a scramjet that operates at even higher velocities.
Hope that helps.
--Satan, quoted by John Milton
I forgot that they wanna use Ramjets for things like low orbital hops across the globe.. LA to london in 5 hours or some crap, and no plane changing.
Or (more likely) I don't know what I'm talking about.
Diagrams are very helpful. Thanks Sage. And you too, Delphi
sigpic courtesy of This Guy, original modified by me
[ 06-06-2002: Message edited by: Kermitov ]
F-15 total fuel capacity, configured for Ferry purposes: 5400 gallons
5400 gallons X 6.6 LBS/Gal = 35,640 lbs
Lbs/hour in full afterburner on two engines (using Bloodsage's number)= 372,000 pounds per hour.
35,640lbs/372,000lbs/hour = .096 hours X 60 minutes = 5.75 minutes of full afterburn until fuel exhaustion. Counting engine start, ground checks and taxi you're probably down to about 5 minutes even once you hit the runway.
this is in ferry configuration too with no armament and all external stations occupied by fuel tanks + FAST pack conformal fuel tanks.
I'm not sure what the taxi numbers or cruise numbers are.
But, yeah, if they're loaded, and doing an AB takeoff, they're headed straight to a tanker for more gas.
--Satan, quoted by John Milton
quote:
This one time, at Bloodsage camp:
You're not going to be in burner except after taking the runway just prior to takeoff.I'm not sure what the taxi numbers or cruise numbers are.
But, yeah, if they're loaded, and doing an AB takeoff, they're headed straight to a tanker for more gas.
Taxi numbers are in there because you're using fuel while you're taxiing
That isn't to say you'd be taxiing in afterburner but it is to say you can sometimes get held on the ground for ground checks, waiting for clearances (I would assume that the military has to conform to the same basic air traffic requirements unless it's an emergency) or other reasons.
I meant that I don't have the fuel consumption rates for idle and taxi, but that they're not all that high.
Fighter sorties are of limited duration for many reasons, and one of them is fuel consumption, but running numbers based on AB gives a false impression of how short they are.
And the high rate I quoted was for full AB, which isn't used that often.
Still, on a hot day and fully loaded, the first thing a fighter will do after takeoff is rendezvous with a tanker and get gas.
But with a ferry configuration like you mentioned, it could easily fly several hours without needing fuel, depending on the flight profile.
I was just pointing out that AB is an anomaly as far as fuel consumption goes. Normal fuel consumption is far, far less.
--Satan, quoted by John Milton
quote:
Bloodsage thought this was the Ricky Martin Fan Club Forum and wrote:
That's not what I was saying.I meant that I don't have the fuel consumption rates for idle and taxi, but that they're not all that high.
Fighter sorties are of limited duration for many reasons, and one of them is fuel consumption, but running numbers based on AB gives a false impression of how short they are.
And the high rate I quoted was for full AB, which isn't used that often.
Still, on a hot day and fully loaded, the first thing a fighter will do after takeoff is rendezvous with a tanker and get gas.
But with a ferry configuration like you mentioned, it could easily fly several hours without needing fuel, depending on the flight profile.
I was just pointing out that AB is an anomaly as far as fuel consumption goes. Normal fuel consumption is far, far less.
Ahh I see. No what I was trying to point out was that AB is rarely used just as you say and to give an impression of just how much fuel we're talking about here.
Sorry if it wasn't clear
I misunderstood. In that case, you're right!
I haven't been sleeping much, lately, so I'm probably not reading as closely as usual.
--Satan, quoted by John Milton
sigpic courtesy of This Guy, original modified by me
If I remember right, jet fuel is more closely related to kerosene than to gasoline.
--Satan, quoted by John Milton
quote:
Ja'Deth Issar Ka'bael spewed forth this undeniable truth:
What's the biggest difference between jet fuel and, say, gasoline? Denser, I would gather. Hotter burning. More hydrogen in it?
Not much... both are petroleum distillates
Jet fuel is a high grade Kerosene. It burns much hotter than gasoline... put a little Jet A in your car and you'll find out what I mean real fast.* There are gasoline based jet fuels but it's not very common to use them anymore due to their volatility and evaporation problems.
Gasoline is lighter than Kerosene, burns cooler and slower and is better suited to reciprocating applications that tend not to take well to high combustion chamber pressures.
*not that your car would run very well with Jet A in it but DO NOT TRY THIS AT HOME. [ 06-06-2002: Message edited by: Kermitov ]
One of the disadvantages of going Mach 3 is the fact that you generate such a tremendous amount of heat on the leading surfaces of your aircraft.. and as of yet, they havent developed any type of plastic or sealant that can withstand that tempurature. So the thing leaks like a seive!
Once it gets up to speed, however, the seams go away, and you've got one HELLUVA plane for spying.
This random tidbit brought to you by my fucked up mind! Whee! 
It also used a special jet fuel delivered by only one kind of specially-modified tanker, the KC-135Q.
About five years ago, the Air Force switched from JP-6 to JP-8 as the standard fuel.
Jet A is for civil applications, if I remember right.
--Satan, quoted by John Milton
Oh, here, it took me a while to find this.
This is your engine on Jet A:
[ 06-07-2002: Message edited by: Kermitov ]
Makes you wonder how they got around it with the later stealth aircraft (IE do they leak too? or go slower with better radar defracting technology?)
And yeah I heard the flashpoint of jet fuel is higher. Stories of how some stuff is so stable to "normal" fires you could toss a glass of it on a small fire to put it out. That sort of thing.
sigpic courtesy of This Guy, original modified by me
Also, static electricity is the big danger when fueling. The fuel moving through the pumps generates a lot of static electriticy, which is dangerous as hell if everything isn't properly grounded.
Also, I'm pretty sure the military jet fuels have more than just anti-icing additives. Haven't really looked into it in-depth, though, since I'm not flying actively at the moment. 
--Satan, quoted by John Milton
Like if the gas gets sprayed into a fine mist, its SUPER easy to ignite.. they found an additive that prevents that. And put it in EVERY single jet fuel. I found it spiffy... Cos they burned a helluva lot of dummies to test it.
quote:
Delphi Aegis had this to say about Robocop:
I've read that they also have antifireball components..Like if the gas gets sprayed into a fine mist, its SUPER easy to ignite.. they found an additive that prevents that. And put it in EVERY single jet fuel. I found it spiffy... Cos they burned a helluva lot of dummies to test it.
They tried to... but it didn't work too well.
link to video:
here
quote:
Nobody really understood why Kermitov wrote:
..
Jet fuel is a high grade Kerosene. It burns much hotter than gasoline... put a little Jet A in your car and you'll find out what I mean real fast.* There are gasoline based jet fuels but it's not very common to use them anymore due to their volatility and evaporation problems.Gasoline is lighter than Kerosene, burns cooler and slower and is better suited to reciprocating applications that tend not to take well to high combustion chamber pressures.
*not that your car would run very well with Jet A in it but DO NOT TRY THIS AT HOME.
Actully you have it a little reversed, gasoline burns hotter than kerosene. The reason jets use kerosene instead of gasoline is because they would burn out the turbines . If rember right you get better BTU's out kerosene.
Kerosene is an oil, pretty much the same thing as desial. If you ever get a chance to stop at a big truck stop, usaly in ruarl area's you will see it labled at the pumps as #1 desial fuel, were normal desial fuel is #2 desial fuel.
quote:
Everyone wondered WTF when Kermitov wrote:
Are you sure about that? I'm pretty sure Kerosene burns hotter... I mean look at that piston up there.... it handles gasoline just fine but burn a little kerosene in the cylinder and you get that melted mess.
Nope I am quite sure it's gasoline that burns hotter. Are you sure it's Jet Fuel and not AV gas that was burning in that picture? because a normal engine shouldn't be able to burn Kerosene, unless it is a desial. Could be maybe something they add to jet Fuel, I know AV gas isn't good to run in normal engines be if i rember right they still put Lead in it. looks like he piston in that pic was lacking in Lubcication to become like that.
Anyhow I will double check and ask my Dad when he gets up, he knows all this shit. He used to work for Westren Oil and Hess, did drilling and refining.
quote:
Pike enlisted the help of an infinite number of monkeys to write:
Nope I am quite sure it's gasoline that burns hotter. Are you sure it's Jet Fuel and not AV gas that was burning in that picture? because a normal engine shouldn't be able to burn Kerosene, unless it is a desial. Could be maybe something they add to jet Fuel, I know AV gas isn't good to run in normal engines be if i rember right they still put Lead in it. looks like he piston in that pic was lacking in Lubcication to become like that.Anyhow I will double check and ask my Dad when he gets up, he knows all this shit. He used to work for Westren Oil and Hess, did drilling and refining.
That picture was an aircraft piston from an engine run on Jet A because someone misfueled the airplane with Jet A instead of 100LL. Aircraft engines WILL run on Jet A, usually long enough to get to the runway and into the air... and then the engine melts from all the excess heat.
Diesel: You squeeze the hell out of it, and then spark it and it goes BOOOOM, lots of power, just slow.
General aviation fuel: You squeeze it mildly (in the middle) and it kicks a hole in the top of your pistons.
Jet fuel: No idea, never used the stuff.
