porkop

Gday,

Watched a Discovery Channel proggy the other day where they where wrecking an old Boeing plane (757 I think?). They mentioned that they had to treat the tail section carefully and have the EPA on site when they did coz it contained a counterweight of Depleated Uranium.

Now,

1. why a counterweight?

2. why the heck depleated uranium?

3. Does this mean that there is a heap of uranium dust floating about after every plane crash?

4. Just what is depleated uranium?

ta

Porkop

roguefan99

Guess they used it as a counterweight due to its density. I believe its also pretty tough too. As for what it is, its majority U238 which is an isotope of Uranium, that has a low radiation emission (an Alpha particle, a piece of paper is protection against them!) however, if it has contamination by other isotopes or gets hit by the wrong thing then it might be more dangerous. I believe the US military were coating missile tips with the stuff, which caused a bit of an outcry at one time (last Iraq war).

Wikipedia has a guide to Depeleted Uranium I just found while typing the above paragraph.

__________________
Coding in C is like sending a 3 year old to do groceries. You gotta tell them exactly what you want or you'll end up with a cupboard full of pop tarts and pancake mix.

myf360f1

Don't have an answer for you porkop, but for roguefan most militaries use depleted uranium shells in their tanks for anti tank use because of the hardness as you stated. That and their sabo rounds are the most effective in cutting through armour it just depends on what type of cladding/armour they are trying to cut through.

Tecom Master

ssrattus

To help make the plane aerodynamiically stable the center of gravity is in front of the center of pressure of the plane. To achieve this sometimes counter weights are needed. If the center of gravity is behind the center of pressure the plane will be unstable (sometimes deliberately done in computer controlled fighter aircraft). If the center of gravity is too far forward the plane is stable but very slow to respond.

from wiki Static margin - Wikipedia, the free encyclopedia

intelliGEORGE

The U.S love this stuff, just ask the Iraqii's.

A docco they WON'T show

nomeat

I seriously doubt that Boeing would design a plane with up to 1.5 tonnes of counter weights simply to keep it in balance where every kilo of payload counts.
COG trim is normally done on civil airliners by pumping fuel around in different tanks.
It is more likely that these counterweights are attached to the control surfaces to increase inertia so that they don't vibrate in the turbulent air flow that they can create and as a counter balance to release strain on the control mechanism.

porkop

thanks ppl. most interesting, and yes confusing, why add a 1500kg load to a plane, just design it for balance?????

tytower

Maybe when you are trying to get a horse to fly you have to cut corners . It's really just a big rectangular container

ssrattus

Yeah your right. Did some research and that is what it is used for. They have substituted tungsten instead in later models.

Although in the whole scheme of things the weight will have consequences on the balance, especially since it is a long way from the balance point.


Because there are many factors to account for, ie static and aeronautical balances, the positioning of the wings with regards to other structural elements, ie fuel tanks, control surfaces, wheels etc etc, everything has to be factored in.

mandc

The main advantage of depleted uranium seems to be its density [1.7 times that of lead] so a lot of weight occurs in a small volume..perfect for counter-balancing flight surfaces [as nomeat stated] and in the tail it would take up very little room allowing more space for freight. The amount in a 747 seems to vary a lot between sources...some say 1500kg and some only 850kg

porkop

I understand all this, but adding a STATIC load seems silly when no matter what sort of factor mentioned above, the static load is still 1500KG in the tail! I would have thought to counteract this sort of obvious nose heaviness, you would move the wings forward???? Or at least have a dynamic loading ability to position a load at various points?

Anyway, this is probaly why I dont design airplanes.

trash

When you build a plane, the center of gravity needs to be in just right.
If one side of the plane is slightly heavier than the other, then the plane will have a natural bank to it. This requires the pilot to trim the plane to fly level.
That trim adds drag to the aircraft, which over thousands of hours of flight slowly adds up. Same thing with the pitch of the aircraft.
The counterweights aren't very big as the plane is designed to be close to the right ballance. But you can't control the weight of every component of the structure, so every plane will have a slightly different center of gravity.
Of course when the plane is loaded, the crew have to actively manage the ballance of the aircraft. I don't know if they use DU for ballast, but I'll ask a friend who works on aircraft.

In small model aircraft a small amount of blu-tac or a pin ballances the aircraft. But when your aircraft weighs 80 tonnes, it's a big blob of blu-tac.
It's the tonne of feathers or a tonne of lead question. Both weigh the same, but a tonne of lead is a very small volume compared to the feathers.
Uranium is very dense, so it's ideal where you need a large mass in the smallest volume. Space is money in an airframe.

Well that would depend on the type of crash. There is likely to be ballast in one of the wings as well as the tail but both are only going to be a small volume. In a crash where the aircraft did not burn, and just broke up, there wouldn't be much of a problem. The ballast is always at the extremities of the air frame. Uranium metal will burn in much the same way that aluminium or magnesium burns. If the Uranium does burn, the oxide is hazardous but the aircraft crash site itself is a pretty big hazard with some slightly higher priorities.

Natural Uranium is 0.7% U235 and 99.3%U238.
When the MOX is enriched to contain more U235, there is a surplus of U238.
Typically if a tonne of Uranium is enriched to 3% for fuel. Then about 3.3 tonnes of Uranium is depleted to enrich that one tonne.

That Uranium has a number of uses including being transmutated into Plutonium for fuel. The metal is heavy, heavier than lead, and denser than Tungsten. It makes it ideal for use where a large mass is required in a small volume. This is one reason why it's used for special purpose bullets and shells.
The metal's ability to burn is another.

There is always the question Radioactivity with Uranium.
Naturally occuring Uranium also contains daughter isotopes of Uranium.
The older the ore, the more daughters can be found in it.
Each isotope emits its own radiation. Some are Beta/Gamma emitters and some are Alpha emitters.
Depleted Uranium is slightly different. When it is refined, it contains only Uranium. From this point the clock starts ticking. Uranium is an alpha emitter and as mentioned, a sheet of paper is enough to stop this form of radiation.
As time goes by, the Uranium decays into Thorium which decays with beta/gamma to Proactinium which also decays beta/gamma to Uranium (234)
It takes about 3 months for the Thorium to reach equalibrium, and the gamma emissions rise over that time.
But even after all this, Uranium isn't all that radioactive and it's really only a hazard when living tissue comes in direct contact with it. Particular inhaling the oxide dust. It's quite safe to handle, you just wouldn't keep a piece in your pocket.

trash

I forgot to mention where you can buy Uranium. I've seen plenty of it on ebay. (where else). I've even seen enriched Uranium listed on ebay. Don't laugh, the seller was in Sydney. I beat the nuclear regulatory people to the sample to verify it.

But if you just want to buy some without all the fuss from the whingers that complain to ebay, just buy some from Bob Lazar. (yes.. that Bob Lazar).
Though he doesn't sell international, so you need somebody to forward for you. He has all kinds of cool shit, though his prices are a bit steep on Uranium Ore samples which you can buy here locally much cheaper.

porkop

Very informative, Trash.

trash

I finally caught up with one of my aviation friends.
He was not aware of any ballast used in aircraft, though when we discussed it he thought that it made sense that a small amount of ballast should be found in one of the wingtips. There should be no ballast in the nose or the tail because the loading tables are individually callculated for each aircraft.
Payload loading is the first method, fuel the second and finally if they can't control either of those some some reason, there are water ballast tanks they can add to the cargo to compensate.
Just to make sure he stuck his head up the arse of a plane in the hanger. No ballast or any kind was found. He didn't look in the wingtips... said they'd have to remove rivets to get a look.

I wonder about the original discovery show porkop. I'll have to keep an eye out for it and see if I can catch where they got the idea from.

ssrattus

It is counterweights for control surfaces.. see nomeat's post above.

porkop

it was one of those mega structures type ones but involved mega demolisations. Was on Foxtel about 2 - 3 weeks ago.

Story also had a mega demolisation of a hugh bridge prior the the airplane one.

porkop

trash

It's still a bit of a mystery... I've been looking for any ballast in aircraft and haven't been able to find any DU yet. I'm working on getting access to some bigger planes to widen my search

porkop

FYI Trash (and others)

Google revieled these bits of info......

Depleted uranium used in the tails of Boeing 747s - General Discussion - Digital Spy Forums

Uranium Pollution from the Amsterdam 1992 Plane Crash

regards

porkop