Aerial Bombing Question

[Zipper730]

I got a couple of questions regarding aerial-bombing, particularly level-bombing with iron-bombs...

I. Measuring Average Error

There's CEP which if i recall is the radius where half the bombs land. There's something like average/median radial error which I think is the radius in which 100% of the bombs fall. I'm curious if there's any way to convert between the two?

I'm also curious about if the average error is measured on where each bomb lands relative to where it should be, where each aircraft's bomb-track/bomb-train lands versus where it was intended to, or where the whole bomber formation/stream lands it's bombs versus where it should.

II. Bomb-Train/Track

This has to do with the fact that the bombs do not appear to all be released at the same time but over the course of a couple of seconds. Since each bomb follows a ballistic path after being released, would I be correct to assume that if one bomb is released a second ahead of the next they would land however many feet per second the bomber flies?

 

[GregP]

For II. above, yes, that is correct. The theory was that if they all got dropped at the same time, and they missed, the entire load was wasted. If they "staggerd" then slightly, then there was a higher probability at least some would hit close enough to do some damage. Interestingly enough, there weere several planes that could release all at the same time.

The main problem with doing it was that, many times, the bombs would not quite fall completely aligned with the relative wind, and they would sort of rock around before settling out nose first. If they managed to hit one another while rocking around, they could and sometimes did explode right under the bomb bay, taking the bomber out or, at minimum, severely damaging it. There were more than a few instance of that happening. Thye solution arrived at was to slightly stagger the bomb releases, resulting in a typical bombing pattern. There were also some deliberate choices made on the order of release, some being simultaneous but not adjacent in the bomb bay. Serendipty happened and it was also an optimum solution, but they still occasionally had the "bombs exploded right under the bomb bay" missing aircraft report.

I'd have to go back and dig out for item I, and don't have time just now, but it'll probably get answered before I do. I'll probably look it up anyway as it is a good question. I have a couple of books on artillery mathematics, but that is not quite bombing error, although CEP is also involved with artillery fire. Lots of knowledgeable people in here. The math involved makes it apparent how complicated bombsites were. For instance, when a bomber released a bomb, the distance of fall is not the altitude of the aircraft. It is the altitude of the aircraft minus the altitude of the target. So dropping and getting hits on a mountain slope was not a simple thing to do, and was more of a learned art than a good calculation, sort of like getting a feel when dive bombing.

The bomb also accelerates due to gravity, but not infinitely. Like a skydiver, it has a terminal velocity beyond which it will not go any faster due to air drag, just like an aircraft. It accelerates until thrust (gravity) equals drag. Each type had it's own Cdo and equivalent flat plate area. Artillery calculations are quite involved, and bombs are no less complicated to calculate. Artillery math can be boiled down into tables assuming no crosswind, and I'd think bombs are simular. The bombsite needs to look at the fall distance, make the time-of-fall computation accounting for the bomb type being dropped, and account for any entered crosswind components.

So it doesn't quite come out as though calculating the ballistics in a vacuum, as one might expect after taking a first course in college Physics.

 

[Elmas]

There are many other parameters to be considered, for example the gradient of air density and air temperature from the ground to the bombing level.
This make the bombs skid on the air like a stone on a lake, with unpredictable results, sometime more than 10% of the bombiing level.

 

[GregP]

Lots of variables, to be sure. There are several good books on it. I like, "Elementary Calculations in Artillery Fire" as a good reference for those rounds.

I looked up CEP and it uses a bivariate Normal probability density function. So, if you have a CEP of, say, 100 meters, Then 50% will fall within 100 meters of target. Another 43% will fall between 100 m and 200 m; another 6.68% between 200 and 300 m; and only 0.32% outrside of 300 m.

So if you have 1,000 bombs dropped with a CEP of 100 m, then 500 will fall within 100 m, 930 will fall within 200 m, 997 will fall within 300 m, and the last 3 will be outside 300 m.

I made up the 100 m CEP above, so don't take that for WWII CEP accuracy! In tests, the Norden bomb bombsight demonstrated a CEP of just 27 m at medium altitudes. In practice, it wasn't quite so good, with 1943 CEP average at 370 m. As a result, the Navy turned to dive bombing and skip bombing.

 

[Zipper730]

For II. above, yes, that is correct.

Okay, that's good to know.

The theory was that if they all got dropped at the same time, and they missed, the entire load was wasted. If they "staggerd" then slightly, then there was a higher probability at least some would hit close enough to do some damage.

So you'd want the aim-point to be slightly ahead of the target, so when the first bomb start dropping out they'll land short, the bulk will land on the target, and the remaining few will go long...

Interestingly enough, there weere several planes that could release all at the same time.

Do you know which planes could?

I know the Avro Lancaster had a series of buttons on the right-side of the bombardier's station (if I recall right) that could be used to adjust the release interval. I don't know what the settings were and if it could release all at once (unless it was carrying one bomb at least...)

The main problem with doing it was that, many times, the bombs would not quite fall completely aligned with the relative wind, and they would sort of rock around before settling out nose first.

Like that wobbling/directional hunting thing that they'd sometimes do? I've seen that happen with some bombs coming out the bay...

If they managed to hit one another while rocking around, they could and sometimes did explode right under the bomb bay, taking the bomber out or, at minimum, severely damaging it. There were more than a few instance of that happening.

I thought they had some kind of propeller/screw like device which was spun by the wind and after a certain number of spins, it would arm... I've seen a B-24 get a wing taken of by a falling bomb (it didn't blow up, but that bomber was doomed).

Thye solution arrived at was to slightly stagger the bomb releases, resulting in a typical bombing pattern.

Honestly, up to this point, I thought the minimal interval was how quick the bomb-shackles could let go of all the bombs and they would all be able to clear the bay, lol.

There were also some deliberate choices made on the order of release, some being simultaneous but not adjacent in the bomb bay.

I know the B-29 had an electronic sequencer so that they didn't have CG shifts as they dropped...

they still occasionally had the "bombs exploded right under the bomb bay" missing aircraft report.

I assume the report was made by another crew?

when a bomber released a bomb, the distance of fall is not the altitude of the aircraft. It is the altitude of the aircraft minus the altitude of the target.

Was the altitude of the target set on the bombsight, or guesstimated?

The bomb also accelerates due to gravity, but not infinitely. Like a skydiver, it has a terminal velocity beyond which it will not go any faster due to air drag, just like an aircraft. It accelerates until thrust (gravity) equals drag.

And gravity pulls down with a force of 1g provided the bomb is going straight down and presumably some fraction if it's on an angle.

Each type had it's own Cdo and equivalent flat plate area.

Cdo is like coefficient of drag? What's an equivalent flat-plate area?

Artillery calculations are quite involved, and bombs are no less complicated to calculate.

And mathematics was never my strong point...

Artillery math can be boiled down into tables assuming no crosswind, and I'd think bombs are simular. The bombsite needs to look at the fall distance, make the time-of-fall computation accounting for the bomb type being dropped, and account for any entered crosswind components.

How did they determine crosswind on land? On water, they'd probably use the shape of the waves...

In tests, the Norden bomb bombsight demonstrated a CEP of just 27 m at medoium altitudes.

What constituted medium altitude?

In practice, it wasn't quite so good, with 1943 CEP average at 370 m.

Was this based on each bomber, or the whole formation?

As a result, the Navy turned to dive bombing and skip bombing.

The USN realized by 1940 that the Norden would be inadequate for ship-bombing if I recall. Dive bombing and torpedo bombing were already being used, they might have done some glide-bombing with PBY's, but I didn't know they did a lot of work on skip-bombing, though I know the USAAF did a lot of work with skip and masthead attacks.

 

[Zipper730]

There are many other parameters to be considered, for example the gradient of air density and air temperature from the ground to the bombing level.

Complicated stuff dropping a bomb through miles and miles of air...

This make the bombs skid on the air like a stone on a lake, with unpredictable results, sometime more than 10% of the bombiing level.

Skid on the air?

 

[GregP]

Looks like you need to do a bit of research, Zipper. You may be able to find a Norden bombsight handbook online or on ebay, and you'll need to look at bombardier handbooks for individual aircraft to find out the particulars of which could release in what order with wnat available timing settings.

 

[tyrodtom]

If a bomb explodes close to the aircraft there's no way you can know if it was caused by AA getting a lucky hit right withing the stream of bombs or if a defective fuse allowed a bomb to detonate before it was armed. The only way someone could know was if a camera with ultra slow motion ability was filming during the bomb drop. Otherwise people are just guessing, because a bomb exploding can set off a unarmed bomb next to it far faster than the human eye can register the event.

The bombs have a arming propeller on the fuse that doesn't arm until it's dropped what is considered a safe distance from the dropping aircraft. The propeller has a wire holding it stationary until the bomb drops from the bomb rack.

The bomb can be dropped unarmed, with the arming wire still attached, it usually won't explode on contact with the ground, unless it hits something very hard, like bedrock, or thick concrete.

AF bases while I was in the USAF had drop areas away from the runways where aircraft could drop bombs that hadn't released when the aircraft were on it's mission.
It's called a hung bomb, no pilot wants to land with a hung bomb on his aircraft, just think of the possibilities.
So they fly over the drop area, do abrupt maneuvers, etc. to try and dislodge the stuck bomb, or drop bomb and bomb rack.
They'd always drop the bombs unarmed, the bombs usually didn't detonate on impact. EOD went around later and detonated them in place.

When you remember how many bombs were dropped by the allies during WW2, and how many fuses were required, usually 2 per bomb, during the mass production required to keep up with those numbers, some less than perfect examples had to have slipped though whatever quality control they had.

 

[GregP]

I think you are thinking of modern bombs, not WWII 500 - 1,500 pounders. Here's a pic of a 1,000 pound under a Corsair:

Perhaps it was fitted with a propeller arming device later, but they routinely dropped them without those, too. I know tehre a place for one to be mounted on the tail ofg the bomb.

I'd bet that if the pilots always had their preference, they'd ALWAYS have them!

 

[wuzak]

It likely has a tail fuse

 

[wuzak]

From Catalog of Standard Ordnance Items

 

[GregP]

This, of course, under ideal conditions.

If you go to Joe Baugher's page and download his entire set of WWII serial number files, you can find a LOT of bombers that were damaged or lost from bombs exploding just beneath the aircraft, many with MACRs. So, if you are interested, you can spend a lot ot time reading about it.

 

[stona]

The bomb can be dropped unarmed, with the arming wire still attached,

That was certainly the British system. The wire was on a reel fitted to the aircraft. It was locked electrically (using a solenoid) when the bomb aimer selected 'live' on his arming panel. If he did not do this then when the bomb dropped the wire would simply unwind of the reel and depart the aircraft with the bomb, which therefore remained 'safe'. It is most unlikely that such a bomb would subsequently explode.

It was not unknown for crews to drop entire loads 'safe' under the stress of combat. With the British system the absence of the arming wires(s), which had left with the ordnance, was irrefutable evidence.
I am not familiar with the American system, but there is a USAAF figure for the 8th AF for loads dropped 'safe' which is surprisingly high. Unfortunately I can't find it at the moment.

Cheers

Steve

 

[Elmas]

Complicated stuff dropping a bomb through miles and miles of air...
Skid on the air?

Certainly you've been in an aeroplane in some "bumpy" flights.
After one of such flights, I personally didn't kiss the soil after landing, like the Pope often does, I literally did bite the soil...
Do you think that bombs are less subject to those "bumps" than you have been?

 

[Joel Dobson]

The B-29s, and I think the B-24s and B-17s, had an electrical gadget in the bomb bay called the intervalometer, which would time the release of bombs.

 

[mikewint]

From Vietnam the result of two B-52 bombing runs. We were often asked to run BDAs after a 52 strike. The actual target was the tree-line so two separate misses

 

[tyrodtom]

A lot

I think you are thinking of modern bombs, not WWII 500 - 1,500 pounders. Here's a pic of a 1,000 pound under a Corsair:

Perhaps it was fitted with a propeller arming device later, but they routinely dropped them without those, too. I know tehre a place for one to be mounted on the tail ofg the bomb.

I'd bet that if the pilots always had their preference, they'd ALWAYS have them!

Just because it's on the aircraft, doesn't mean it's mission ready . I can see the cap on the front fuse well, no fuses, no boom.
They probably loaded bombs the same way we did, you load the bomb onto the aircraft, then you fuse it.
Even aircraft with in internal bomb storage, you install the bomb on the rack before you fuse it. Because it's too easy to damage a fuse during the loading operation. Sometimes we might load the bombs hours before the fuses were installed.
There may be pictures out there of bombs sitting on a bomb trailer already fused, but by the time I was in the USAF they had changed that procedure, because of crews damaging fuses during loading. Nothing pisses a pilot off more than risking his butt to drop a bomb on a target, and then have it not go off.

We were using mostly Korean war era bombs during Vietnam, but at NKP we still saw WW2 era box finned bombs too, even some WW2 era British bombs. And most of our fuses were WW2.

 

[mikewint]

Tyro, your post reminded me of the "Instant LZ" bombs (old left-over 10,000lb bomb from WWII). Trying to find clearings in the jungle big enough for a helo to land was tough and naturally the VC knew where each one was located. Thus the 10,000lb instant LZ. The Army used CH-54 skycranes to drop them. The bomb made a 400 - 500yd clearing in the triple-canopy jungle and the shock wave pretty well knocked out anything for about a mile. That meant that the helo had to be at least at 6000ft to avoid the worst of the wave and thus it was tough to get one to hit where you wanted it to be and the massive explosion announced your arrival.

 

[tyrodtom]

By the time I was there in the Army in 71 they were dropping those instant landing zone bombs from C-130s.
The bomb was mounted on rollers, secured by big straps, with a parachute mounted where the tailfins normally would be.

With the better navigation aids on the C-130 accuracy was said to be better, and the greater speed made it safer for the dropping crew.

It was tried one time not too far from Pleiku, they tried for a mountain top landing zone. It missed .

 

[mikewint]

Yea, that was the big problem, getting them just where you wanted them. Even in '65 the VC/NVA had every natural clearing pretty well staked out or had troops nearby. Was tough to get in and even tougher to get extracted