Drop tanks

[rightwinger26]

A word on missiles: high G at high speeds means large turn radius; higher G capability means tighter turns at any given speed than a manned aircraft, but moving at higher speeds means that this advantage is reduced. A missile may start at upwards of Mach 3 but is coasting from the second the engine goes out, so its speed will deteriorate. You may think this increases its high-speed turning rate, but because to pull a tight turn takes kinetic energy that's not being replenished, the effect is to reduce its overall range and make it easier for the target to escape.

A word on tanks: if memory serves the general rule is that fuel is drawn from external tanks first, to make it easier to drop them empty should the need arise. That, plus inerting systems, plus the strength of structure needed to withstand high-speed high-G flight, may explain why you can use an external tank as surrogate undercarriage.

Thats right, as soon as an aircraft with drop tanks goes weight off wheels, the external fuel system pressurizes, so it transfers first.

[rightwinger26]

True...

Back in 1987,I was ona course at RAF Cosford when Top Gun came out so,a bunch of us Armourers went to see it.At the bit where the Nav ejected, we were all asked to leave the cinema beacuse of the roars of laughter & discussion of the real ejection sequence urined off the cinema usher!

I've got more time on the flight deck than I can count, I have NEVER seen people standing around listening to pilots on the 5MC, everyone in those movies looks way to happy to be there, there are no plane captains in the movies, just green shirts and yellow shirts, its just all WAY to fake. Like Behind Enemy Lines, when they have the dual bleed caution, shuts down and hops out on the cat, I stopped watching at that point

[jbrundt]

That is not necessarily correct.

Actually it is.

It is the vapor above the fuel that is most dangerous. That's why a half filled or near empty fuel tank is more dangerous because of the fuel vapor above the fuel.

It's the leading theory why TWA flight 800 exploded in mid air over Long Island.

You can read many reports of lit cigarettes being tossed into JP-5 and not igniting the fuel. JP-8 is noted for not burning when exposed to a flame. Only when you vaporize it does it become more flammable.

Modern jets use fuel that is less vapor producing because it's safer. The Navy is especially paranoid about gasoline aboard ship because of its propensity to ignite. When we were certifying Scan Eagles aboard USN ships we had to follow stringent routines for fuel storage and use since these UAV's used gasoline. The Navy wants all shipboard equipment to use 'heavy' fuels because they are much less prone to ignition because of vapor formation.

There would have to be several factors all aligning correctly to allow a dropped fuel tank to explode. that initself is highly improbable. And FWIW you cannot just drop a fuel tank over a populated area. it's one thing to jettison tanks over the water but quite another over land. In fact if an aircraft has to drop anything it must do so in an approved area. If it can't then it stays on the plane. Besides those drop tanks are not cheap.

Jeff

[RedHeadKevin]

As for movies that make no sense, the Blue Brothers defies all logic, yet is one of my fave films. Then again, I doubt it ever served as a recruiting tool for any organization

Even the Illinois Nazis?

[jbrundt]

Even the Illinois Nazis?

I hate Illinois Nazi's..........

BTW...I lived in the Chicagoland area when this film was made and released. The reference in the film to Illinois nazi's was actually quite timely. IIRC at that time they (the nazi's) were trying to organize a rally/march in Skokie (which is a predominantly jewish neighborhood). it was a big thing in all the news at the time. I saw them filming the scene where the Illinois State Police car launches into the semi. They must have done about a dozen takes to get it right. They filmed it on Rte 12 not too far from where I lived. I always like watching that movie because i recognize so many of the places where they filmed.

jeff

[rightwinger26]

Actually it is.

It is the vapor above the fuel that is most dangerous. That's why a half filled or near empty fuel tank is more dangerous because of the fuel vapor above the fuel.

It's the leading theory why TWA flight 800 exploded in mid air over Long Island.

You can read many reports of lit cigarettes being tossed into JP-5 and not igniting the fuel. JP-8 is noted for not burning when exposed to a flame. Only when you vaporize it does it become more flammable.

Modern jets use fuel that is less vapor producing because it's safer. The Navy is especially paranoid about gasoline aboard ship because of its propensity to ignite. When we were certifying Scan Eagles aboard USN ships we had to follow stringent routines for fuel storage and use since these UAV's used gasoline. The Navy wants all shipboard equipment to use 'heavy' fuels because they are much less prone to ignition because of vapor formation.

There would have to be several factors all aligning correctly to allow a dropped fuel tank to explode. that initself is highly improbable. And FWIW you cannot just drop a fuel tank over a populated area. it's one thing to jettison tanks over the water but quite another over land. In fact if an aircraft has to drop anything it must do so in an approved area. If it can't then it stays on the plane. Besides those drop tanks are not cheap.

Jeff

FPU-12A, super hornet tank, $127,718.00.

[Edgar]

During the advance up Italy, in WWII, the troops were held up by Germans dug in on the far bank of a river. Makeshift firebombs were made, by attaching grenades to droptanks; the tanks were dropped, pulling out the pins as they went. Apparently, it worked.

Edgar

[MattC]

If a drop tank were to impact from a reasonable altitude, then theoretically it could ignite without any exterior source of ignition, if it were to deform sufficiently to create a sudden and high pressure increase inside the tank (without it splitting). Same theory as compression ignition engines like the small diesel types fitted to flying model aircraft.

I doubt that it would, or could happen, as I expect the tank would either burst, or not compress sufficiently to promote ignition, nor, I suspect, would JP4/5 etc be volatile enough to do so (model aircraft diesel engines use an entirely different fuel comprising methanol, castor or synthetic oil, ether, nitromethane)

As a side note, I was patting the tip tank on a T-33 yesterday and was surprised at just how thin the metal felt.

[Wayne S]

Bottom line, liquid petrol doesn't burn. The vapours burn.

That is not necessarily correct.

Actually it is.

Jeff

Jeff, looking at it just from the vapor stand point in the air, burning; The vapor is burning since the mixture and temperature has changed.

Technically speaking here, for the vapor to be in the air, it already started the burn process anyway. The temperature has changed, for it to go from a liquid state to gas.

If one could have the gas at the same temperature and mixtures, be it solid/liquid, the out come would be the same.

Frankly, from a logic stand point, one could say the surface is the energy source. Majority in this thread wrote of a Explosion which, pretty much, is a rapid release of energy. For something to explode, it does not need to be flammable, even water, a rock and a block of wood can explode.

Edited April 26, 2010 by Wayne S

[Slartibartfast]

Some solids can initiate combustion at room temperature, such as sodium. Liquid hydrocarbons, however, MUST vaporize before they can shake hands with enough oxygen molecules to enter into an oxidation agreement. Their autoignition temperature is easily higher than 450 °F. Flames may appear to originate from a liquid surface but that just isn't the actual case. This isn't voodoo, Harry Ricardo noted this phenomenon while studying internal combustion in the early 20th Century. Jet fuel can burn in open air but its low vapo(u)r pressure makes this a more difficult proposition to initiate than a gasoline-fueled fire.

Just because you have vapo(u)r and air, you won't automatically get combustion. You must have an ignition source.

[Nighthawk117]

Technically speaking here, for the vapor to be in the air, it already started the burn process anyway. The temperature has changed, for it to go from a liquid state to gas.

That is not necessarily correct.

And unlike you, I'll explain. What you described is simply vapourisation, the process of liquids going to gas. It has nothing to do with burning. You don't describe the water in the cup you set on the table for an hour on a hot day as beginning to burn. You say it's begun to evaporate

By the way, going by your example, you're burning every time you sweat. Yeah, when sweat is burning(evaporate) off your body, it's going from liquid to gas. You're burning up, man.

As slartibartfast pointed out, for burning to occur, you need a fuel source (fuel), an oxidiser (oxygen), and an ignition source (spark). Since your example lacks an ignition source, it's not burning. It doesn't fulfill the criteria of burning. So even technically speaking, the burn process has not started because there's no ignition source.

For solids such sodium, the reaction with oxygen is so vigourous that it releases a lot of heat, generating it's own ignition spark.

Edited April 27, 2010 by Nighthawk117

[Heyjoe]

Can a drop tank (jet) really creates fireball when dropped? Or that's just a myth?

We had a VF-102 jet take off with jettison switch depressed sooo, when weight off wheels switch worked as advertised, 2 full drops left the aircraft as pilot eased back on stick. The drops hit the runway concrete and ignited like napalm. Most impressive to watch and most embarassing for pilot.

[Murph]

The drops hit the runway concrete and ignited like napalm. Most impressive to watch and most embarassing for pilot.

Unscorable at six.

[drhornii]

We had a VF-102 jet take off with jettison switch depressed sooo, when weight off wheels switch worked as advertised, 2 full drops left the aircraft as pilot eased back on stick. The drops hit the runway concrete and ignited like napalm. Most impressive to watch and most embarassing for pilot.

I know the F-111 does a "dump & burn" but that takes a whole new meaning.....

[Gundamhead]

If a drop tank were to impact from a reasonable altitude, then theoretically it could ignite without any exterior source of ignition, if it were to deform sufficiently to create a sudden and high pressure increase inside the tank (without it splitting). Same theory as compression ignition engines like the small diesel types fitted to flying model aircraft.

I doubt that it would, or could happen, as I expect the tank would either burst, or not compress sufficiently to promote ignition, nor, I suspect, would JP4/5 etc be volatile enough to do so (model aircraft diesel engines use an entirely different fuel comprising methanol, castor or synthetic oil, ether, nitromethane)

As a side note, I was patting the tip tank on a T-33 yesterday and was surprised at just how thin the metal felt.

Nope, you need spark. Diesel, uses glow plugs as the spark.

[Gundamhead]

Most people think planes drop their tanks when they empty. They drink from the drops first, then they just hang their. The only time the drop them is when entering dog fight combat, or evasive manuevers. Other than that, they stay with the bird.

[Wayne S]

As slartibartfast pointed out, for burning to occur, you need a fuel source (fuel), an oxidiser (oxygen), and an ignition source (spark). Since your example lacks an ignition source, it's not burning. It doesn't fulfill the criteria of burning. So even technically speaking, the burn process has not started because there's no ignition source.

A diesel engine and my R/C plane's engine does not have spark. They have a glow plug/heating device.

Jeff, looking at it just from the vapor stand point in the air, burning; The vapor is burning since the mixture and temperature has changed.

Technically speaking here, for the vapor to be in the air, it already started the burn process anyway. The temperature has changed, for it to go from a liquid state to gas.

If one could have the gas at the same temperature and mixtures, be it solid/liquid, the out come would be the same.

Frankly, from a logic stand point, one could say the surface is the energy source. Majority in this thread wrote of a Explosion which, pretty much, is a rapid release of energy. For something to explode, it does not need to be flammable, even water, a rock and a block of wood can explode.

Instead of looking at this as a confrontation, Look at what is writing. Start with your post 21.

[Slartibartfast]

A diesel engine and my R/C plane's engine does not have spark. They have a glow plug/heating device.

How does this not qualify as an ignition source? An ignition source is anything that is hot enought to initiate combustion. Stick a white-hot branding iron in a vapor cloud of gasoline and tell me that's not an ignition source after they scrape your body off the pavement.

Diesel engines work by compressing air to the point that heat of compression is high enough to autoignite diesel fuel as it enters the combustion chamber. There's your ignition source.

Edited April 27, 2010 by Slartibartfast

[Wayne S]

How does this not qualify as an ignition source? An ignition source is anything that is hot enought to initiate combustion. Stick a white-hot branding iron in a vapor cloud of gasoline and tell me that's not an ignition source after they scrape your body off the pavement.

Diesel engines work by compressing air to the point that heat of compression is high enough to autoignite diesel fuel as it enters the combustion chamber. There's your ignition source.

I try to stay away from the word ignition/autoignition temperature, my self. What your talking about is a Exothermic Reaction.

[MattC]

Nope, you need spark. Diesel, uses glow plugs as the spark

It doesn't, believe me, I've run about 20 of them in different sizes. model size diesel engines are compression ignition, no glow plug or anything, just an adjustable contra-piston which adjusts the compression ratio at TDC which is then sufficient to ignite the fuel/air mixture

[Nighthawk117]

Jeff, looking at it just from the vapor stand point in the air, burning; The vapor is burning since the mixture and temperature has changed. Technically speaking here, for the vapor to be in the air, it already started the burn process anyway. The temperature has changed, for it to go from a liquid state to gas.

If one could have the gas at the same temperature and mixtures, be it solid/liquid, the out come would be the same.

Frankly, from a logic stand point, one could say the surface is the energy source. Majority in this thread wrote of a Explosion which, pretty much, is a rapid release of energy. For something to explode, it does not need to be flammable, even water, a rock and a block of wood can explode.

Instead of looking at this as a confrontation, Look at what is writing. Start with your post 21.

I stated that liquid petrol cannot burn, but you claimed that is not necessarily correct... You still haven't given any example of that. You've only claimed that the process of evaporation is also the beginnings of the burning process, which justifies your statement that liquid petrol does burn. I pointed out that what you described was the process of evaporation, not burning. And your only answer is that I'm confronting you.

Burning is an oxidation process. Phase change is not. The two has nothing to do with each other.

So I really am curious, what example can you give to show that liquid petrol, in special cases, can burn? Liquid petrol, mind you, not vapourised liquid petrol. I've never heard of any special cases, so I really would like to know.

You stated the surface is the energy source and that anything can explode. That is true. As long as it has an energy value, it can explode. But this is a non-sequitur. The source may have an energy value, but it doen't mean it can burn until it undergoes a phase change or has energy input. In liquid fuels, the liquid fuel is the reservoir but only when it vapourises it will burn.

And by the way, the temperature does not change from when a liquid goes to gas phase. When you measure a liquid being heated, the temperature rises until the phase change temp, where it will plateau until the phase change is complete. At this stage, you'll be measuring the temp of the gas. The thermal energy absorbed is used to overcome the intermolecular bonds that keeps it as a liquid.

In a diesel engine, diesel fuel is vaporised and compressed to ignite, using the principle of PV=nRT. The compression heats up the diesel, oxygen mixture enough that it burns. The ignition source, in this case, is the compression of the mixture that generates the heat necessary to ignite the mixture. Although the reaction is exothermic, work needs to be done to compress the gas mixture.

So before you accuse me of seeing it as a confrontation, I suggest you also "Look at what is writing".

Bottom line: Show me a liquid fuel that burns as a liquid and not a vapour/gas.

Edited April 28, 2010 by Nighthawk117

[FlyingSnowmew]

Fire needs oxygen to burn. You can't start a fire in an environment without oxygen no matter how flammable the substances are around you. Fire is merely a rapid oxidization reaction. Try burning a flammable liquid in a tank full of helium.

Edited April 28, 2010 by Uncia Uncia

[Slartibartfast]

I try to stay away from the word ignition/autoignition temperature, my self. What your talking about is a Exothermic Reaction.

"Exothermic" –adjective Chemistry .

noting or pertaining to a chemical change that is accompanied by a liberation of heat (opposed to endothermic).

"Autoignition" –noun

1.Automotive. the spontaneous ignition of fuel when introduced into the combustion chamber of an internal-combustion engine, as a result either of glowing carbon in the chamber or of the heat of compression.

2.spontaneous combustion.

[Wayne S]

I stated that liquid petrol cannot burn, but you claimed that is not necessarily correct..

Below is what you wrote and what we are talking about here now. For your vapor to burn, you are chemically changing the mixture by adding oxygen.

One of the most common misconceptions is fuel/petrol burns. It doesnt! Liquid fuel/petrol is like any other liquids in that it's wet. Drop a lighted match into liquid fuel, and the match will just go out.

What burns is actually the fuel/petrol vapours. Like any other liquid, fuel will evaporate. When a cup of fuel is set on fire, the flames actually start above the liquid, but it gives the impression that the liquid is on fire.

Bottom line, liquid petrol doesn't burn. The vapours burn.

[Nighthawk117]

Below is what you wrote and what we are talking about here now. For your vapor to burn, you are chemically changing the mixture by adding oxygen.

Now you're nitpicking. The point I was making is that petrol needs to be a vapour before it can even burn, with the presence of oxygen. Liquid petrol, with or without the presence of oxygen, will not burn. I was discussing the physical state needed for the burning process to even occur, not the burning process itself. I did not mention oxygen, oxidation, accelerators, etc at all because that was not what I was explaining. The fact that the vapour still needed oxygen to burn was tangential to the point I was trying to get across.

You, on the other hand, took 5 posts, 28 posts later, before you can even explain the nature of your initial objection, which you should have attempted to explain in the first place to avoid any misunderstandings.

A simple explanation: "I think the petrol vapours still need oxygen to burn, the vapours alone still won't burn" would have been immensely helpful as a clarification, but instead you decided to go for:

That is not necessarily correct.

Instead of looking at this as a confrontation, Look at what is writing. Start with your post 21.

And that even leaves out the fact you confused burning with evaporation.

If you're going to correct someone, at least explain. That way everyone can learn. It avoids misunderstandings.

Edit: But I guess since this is an international forum, some people wouldn't have English as their first language and will have difficulty getting their point across. So I apologise for misunderstanding and plese, try to explain even if English isn't your first language; it helps to avoids misunderstandings. Saying less leads to more misunderstandings than saying lots in bad English.

Edited April 28, 2010 by Nighthawk117