Author Topic: Drop tanks (Read 4137 times)

Debonair · « **Reply #30 on:** May 24, 2006, 03:56:27 AM »

the tree has mixed emotions:noid

Pooface · « **Reply #31 on:** May 24, 2006, 06:18:42 AM »

kermit, it's odd really, and you would think that it wouldnt do that would you? you see, the thing with dropping them in water is that you have one that floats. neither will float in air, and the difference in density doesnt matter very much, makes very little difference. what does matter is the surface area of a given object for a certain volume. both the droptanks have the same volume, one just isnt filled.

ok, how best to explain this...

take a steel ball, and then take one the same size and melt that second one down, and mould it into a kind of spikey star shape. now they both have the same density, but different surface areas, and they fall at different speeds. you try it in a vacuum, and they fall together.

now, i can see exactly where all of you are coming from, i used to think the same way. i used to have a theory that it wasnt to do with surface area but to do with a mass/surface area ratio, and that that would explain the vacuum stuff too. but when you look at advanced mechanics, it doesnt go that way.

common sense has this annoying quality of being wrong lol. the science behind it is weird, and it's hard to understand, but 500 years of scientists have also been thinking about it, not not been able to disprove it.

it's just like some maths. you know the first time they went to the moon they had big problems because all the mathematical formulae were wrong. they think it was due to the fact that these bedrock principles of maths were invented by the greeks, who firstly didnt understand about changing gravity, as they didnt know it existed, and that they, secondly, simplified formulae and their answers so that they were easier to remember. now those formulae worked great on paper and in maths classes, but when we actually went into space we had big problems

you never know, you could be right, all science is theory, nothing is ever proven, and maybe you can devise an experiment to show that falling objects dont go like that, but 500 years worth of scientists have tried and not found a way.

lol, im getting text wall syndrome

i hope that kind of clears it up a bit nemeth and kermie:aok

Krusty · « **Reply #32 on:** May 24, 2006, 10:04:47 AM »

Consider, however, that the empty drop tank will weigh a LOT less, and while gravity is a constant, the air resistance required to slow it down (terminal velocity) is much less than for the full DT. So they will fall the same.... until the empty one hits terminal velocity first, and the heavy one keeps accelerating. But that's a ways down the road. For the 150 feet or so that you see them fall from your plane in AH, they would be identical.

Kermit de frog · « **Reply #33 on:** May 24, 2006, 12:51:59 PM »

What if 1 drop tank is filled with fuel.
And the other is filled with helium.
And let's say the shell of the drop tank is not metal but some kinds of light paper that's very strong and holds together well.

The drop tank with fuel would fall to the ground. The drop tank with helium would float and never hit the ground. Lets say they were dropped at 30k. And the drop tank with helium doesn't float at 30k, but at 5k. I'm thinking both drop tanks would not fall at the same rate.

The total density of the drop tank with helium would eventualy stop falling around 5k. While the drop tank with fuel would keep going until it hit the hard ground.

So total density was a factor.

Let's say they were dropped over the ocean. The drop tank with fuel would slpash through the surface of the water and keep falling until it reached 2 miles under the surface. At that depth, it would fall anymore and might not be denser than the water at that depth, and it would then stop falling and be boyant.

Do I fall at 9.8m/s/s in water? It's only air? What kind of air? Air has different pressure at different altitudes on different days.

This whole time i'm talking about having the same shape, and same surface density. What is changing though is the total density of the drop tank.

Pooface · « **Reply #34 on:** May 24, 2006, 01:08:23 PM »

well, yes, you do fall at 9.81m/s2 in water, but there is more drag, so you fall slower, and that is if you aren't floating anyway. what you're talking about is floatation, and that is totally different to a falling object. to be honest, im not really sure how it would work, dunno if anyone here does, but back to the topic at hand, droptanks, both being more dense than air will fall, and they should fall at the same rate.

had a thought... you drop 2 balloons one filled with water one not, they fall at different speeds, not sure if it's to do with density like you say, or that infact the surface of the ballon has changed because of the water, although the first is more likely.

lol im confused haha

BUT....

exhaled air is less dense than the outside air. now i really am confused.

i guess if you can actually prove it you might even win the nobel prize lol

thing with the sciences is that they have a strange habit of teaching you something false in order for you to understand it better, anyone do physics at uni and know anything more about this??

i'd actually be very interested to hear a bit more about it. i always thought the same way as you kermie but was told it was wrong by tons of physics teachers

Brenjen · « **Reply #35 on:** May 24, 2006, 02:15:32 PM »

I think the equal shaped objects of different weights falling at different speeds can be explained like this;

If you have let's say a brick. One brick is made of mortar & one is made of lead.

Both are exactly the same size & shape.

The lighter brick will not hit the ground at the same time as the heavier brick if they have enough time/distance to fall.

I believe the reason is, (if I remember my high school science class correctly) that the force of the air or air resistance or drag if you like, will push against the lighter brick enough eventually, to cause it to reach whats called "maximum velocity" It can't fall any faster because of the density of the air pushing back against it that it is trying to accelerate through. The heavier brick will reach a higher "max velocity" before it hits this same invisible wall.

I could be wrong, I've been out of school a long time, but I'm sure someone will fla...I mean correct me.

Pooface · « **Reply #36 on:** May 24, 2006, 04:38:32 PM »

im not sure brenjen. i cant say i know a whole load either, but terminal velocity is more about the air resistance

blah, this is really mssing with my head, because that isnt supposed to happen. the clay brick will have a larger surface area i reckon, seeing as it's porous and has a rougher surface than the lead.

my head hurts. on one hand we have 500 years of brilliant minds that say otherwise, but on the other hand we have common sense. maybe gallileo was wrong............

or maybe we just need a decent explanation lol

Brenjen · « **Reply #37 on:** May 24, 2006, 05:00:57 PM »

Well part of it is distance traveled, shape of the object etc. Like the piece of paper I mentioned earlier, if it turns in the air & falls edge first instead of cathing the air & flipping around, it can really move fast, because of it's aerodynamic properties which dimenish the effects of drag. Of course it will probably do all sorts of twists & turns & slow itself down. Where the paper wad will fall the same over & over again. And they both are the same mass just with different shapes.

I know Newton would have loved to get in on this discussion, but I am certain, the overall effects for the purposes of this discussion, would need to have the speed of the aircraft at drop, the shape, density & the effect of gravity, and maybe even the properties of liquid & it's sloshing around in the tank all factored in. I would be willing to bet no two drops would be exactly the same, even if they varied only by milliseconds due to the unpredictable tumble. I just can't get past the shape & drag part of the equation & it's effects on the tanks when tumbling.

Pooface · « **Reply #38 on:** May 24, 2006, 05:11:00 PM »

when we think about what we're actually hijacking, does it really matter what speed a droptank falls at, and is it worth reinventing physics on a bulletin board for it?

Krusty · « **Reply #39 on:** May 24, 2006, 05:37:09 PM »

Y'all are making it too complex. Oh, and I mentioned terminal velocity first

They fall at the same speed, neglecting wind resistance. Wind resistance will eventually build up on the empty DT, keeping it from accelerating any faster. [EDIT: snip, that part will just confuse folks]

super SUPER simplified version

So the empty tank would cut through the air for a while, then the air would start pushing back. The full tank would keep cutting through the air for a longer period of time before the air pushed back. Until the air pushes back on either one as they cut through it, they'll fall the same.

Billy Joe Bob · « **Reply #40 on:** May 24, 2006, 05:53:38 PM »

Quote

Originally posted by Murdr
Two stories. One, a flight of P-38s find a Japaneese cargo ship. They have no bombs, so they buzz the ship and release their drop tanks on the deck. One 38 incidently buzzed to close and caught his wing on an antenni or something, was damaged but flyable. The 38's extended reversed, and ignited the fuel with a straffing run. The ship burned into the night, and was confirmed sunk early that AM by Navy observers.

wow that was clever of them

Phtom · « **Reply #41 on:** May 24, 2006, 05:56:03 PM »

I guess Nemeth what it all boils down to is:
If you want to blow things up...put on bombs..not drop tanks

Nemeth · « **Reply #42 on:** May 24, 2006, 08:17:00 PM »

man i shoulda left out the physics part... (bangs head agaist wall)
and the decent of the drop tanks was just an observation...

and it takes me alot to get somthin thru my head (concusions does wonders!)

Phtom that really isnt the point... if im countering BnZ i usually up a spit 9 or 14 (with DT's most of the time), these planes dont have bombs, only DT's. So if i want to bomb somthin i have to rtb (or get shot down), and up a plane that has ord... wasting time... and if DT's actually did damage i could hit a GV or AA (saving time

).

yes DT's do "explode" but they dont put a dent on the ground or hurt. You can drop DT on the belly of your plane and they will "explode"

Raptor · « **Reply #43 on:** May 24, 2006, 08:56:44 PM »

Didn't you ever do that experiment in school with the bowling ball and ping pong ball?

I do not see how you expect DTs to do damage. Even if they hit a tank, most damage I would expect is a ringing sound left in the tank crew's ears. I don't think it is worth the time to model the correct falling of a DT. Once it has been dropped, it no longer a factor to the game. If you want to catch things on fire using fuel/bombs, ask for Napalm instead.

Raptor · « **Reply #44 on:** May 24, 2006, 09:16:44 PM »

Terminal velocity is not effected by weight, but by wind resistance. Why does a baseball fall faster than a large piece of plywood (assuming it is not falling on it's side).
You could look at it this way. Instead of looking at drop tanks, compare planes. Say you take a P51D at 20k with 100% fuel and a P51D with 25% fuel. Both will compress at the same speed.

As for what Murdr said about the P38s using DTs to sink a Japanese Cargo Ship. The ship probably caught fire from something that the bullets were hitting, sparks from metal containers or ammunition cargo. But because the ship was covered in fuel from the DTs, it was able to ignite and burn more rapidly and for a longer duration of time. (Ever use gasoline to start a camp fire?). That would explain why the P38's had success in destroying something with the aid of DTs. While the P51s, having dropped their tanks on the side of a mountain, had nothing to ignite the fuel when they fired at it. The bullets would have gone into the ground too rapidly to rely on them to start a fire, and trees don't exactly spark when you shoot them.