Size of Modern Bomb Bays

[Mithras]

Having no luck here .... I can't find any modern bomb-bay dimensions to port over to a craft I'm designing. Really to give me a reference, and calculate the tonnage of bombs I can pack in there.

Any ideas? I've allocated 6 tons for a bomb bay, but obviously thats volume not weight, and a B-52 today can carry far more than that in metric tonnage. I caught a forum post somewhere where a poster reckoned the B-52 had a 30 sq.m bomb bay, but that's only 2 dtons. If that's right and it seems low, then my 6 dton bomb bay will be a city-buster!

 

[mbrinkhues]

Some of the load-out is carried external on the B52 at full load. But the bay itself is around
30 cubic meter according to an elder Janes. That would be around 2dton in Traveller. Look at some pictures of Vietnam Era 52s during Arclight and you can see how much ordenance they hang from wing spars

 

[tbeard1999]

Having no luck here .... I can't find any modern bomb-bay dimensions to port over to a craft I'm designing. Really to give me a reference, and calculate the tonnage of bombs I can pack in there.

Any ideas? I've allocated 6 tons for a bomb bay, but obviously thats volume not weight, and a B-52 today can carry far more than that in metric tonnage. I caught a forum post somewhere where a poster reckoned the B-52 had a 30 sq.m bomb bay, but that's only 2 dtons. If that's right and it seems low, then my 6 dton bomb bay will be a city-buster!

I use a 1 dton = 5 metric tons conversion factor for military vehicles and heavy vehicles that works pretty well. So, a 60 ton M-1 Abrams will consume 12dtons. This is about right.

However, equipment (like bombs) is denser, so I'd use the old Striker assumption of 1 cubic meter = 1 metric ton. This means that 1 dton would hold 13.5 or 14 metric tons.

And since dtons are measurements of volume, the 30 square meter dimension doesn't give you enough information -- you need a third dimension.

I suggest that you dimension your bomb bay by determining how many bombs you want to carry, then bootstrap up from there. I'd add 10% extra tonnage (and dtonnage) for bomb racks and 10% for the bomb bay doors.

For reference, the US Mark 82 500 lb general purpose bomb weighs (gasp) about 250 kg (exact weights depend on guidance packages). It's the bomb element of the US GBU-38 JDAM system and of the GBU-12 laser guided system. So a 1 dton bomb bay could hold about 56 of these (46 allowing for racks and doors).

The US Mark 83 1000 lb general purpose bomb weighs about 450 kg and again can be fitted with a variety of guidance packages of nominal weight. So a 1 dton bomb bay could hold about 31 of these (25 allowing for racks and doors).

The US Mark 81 250 lb general purpose bomb weighs about 120 kg and again can be fitted with a variety of guidance packages of nominal weight. So a 1 dton bomb bay could hold about 116 of these (97 allowing for racks and doors).

The US Mark 84 2000 lb general purpose bomb weighs about 900 kg and again can be fitted with a variety of guidance packages of nominal weight. So a 1 dton bomb bay could hold about 15 of these (12 allowing for racks and doors).

The Soviets (and the US probably) had massive fuel-air bombs weighing 1500 kg or 3000 kg. WWII "blockbuster" bombs weighed between 1800-5400 kg.

A B-52 can carry about 31,500 kg of bombs internally and on external mounts. The B-52D used in Vietnam carried 84 bombs internally, and added modified underwing bomb racks to carry 24 bombs, resulting in a maximum payload of 60,000 pounds of bombs -- a total of 108 bombs (implying that these were 500 lb bombs).

I'd also note that the advent of precision guided munitions has tended to reduce the size of bombs. The idea is that if you can hit the exact point you want, anything over a 250 lb bombs could be overkill. And since weight is the primary limit on carrying bombs, planes can execute more attacks per sortee with smaller bombs. Of course, some targets require more explosive.

 

[Andrew Boulton]

Don't forget, a dt is *huge*. A 6dt bay is 3m x 3m x 9m.

 

[GypsyComet]

There's one of the big Cold War bombers in the air museum south of here, and that bomb bay is impressive to stand under (they've parked it with the bay doors open, so you can stand "in" the open bay). Even so, I doubt its more than a handful of dTons.

 

[mbrinkhues]

Actually the M1 comes out at around 6.5dtons if one uses it's dimensions the the 1dton = 5 weight tons conversion is way off.

 

[Mithras]

That's some great info there, tbeard in particular - I think you've done alot of calculating work for me. Thanks for the data and the math!

I can crack on with completing my design now; a 200 ton fast attack craft in a small-ship universe where civillians are not allowed armour or double or triple turrets; the military also have the advantage of 50 ton bays and nuclear damper screens. Book 2 with components stolen from MgT.

I class it as a precision strike craft with 2 triple beam laser turrets mounted for forward facing and ground attack strikes, with a bomb bay for additional ground attacks. It jumps in system moves in a 3G with a bunch of others, strikes fast then gets out again. Like the A-10 it is very heavily armoured for survivability against AAA.

Now all I have to decide is what kind of bombs will it use? I'm favouring big ones! Against a low tech foe it could drop its bombs at high altitude, and they would all be guided. Against a high tech foe low-level bombing at very high speed. Against a very high tech foe, perhaps releasing specialized re-entry bombs from orbit although there may be a much larger number of strays and rogues with that approach.

 

[tbeard1999]

Actually the M1 comes out at around 6.5dtons if one uses it's dimensions the the 1dton = 5 weight tons conversion is way off.

Be careful which tons you use and which M1 you use.

M1: 55.7 metric tons; 61.4 tons
IPM1: 57 metric tons; 62.8 tons
M1A1: 61.3 metric tons; 67.6 tons
M1A2: 62.1 metric tons; 68.4 tons
M1A2 SEP: 63 metric tons; 69.5 tons

Since the increase in mass is mainly due to internal components -- increased armor density is the main one, change to the 120mm Rheinmetall gun is second -- volume is about the same with all models. When I calculated this out a long time ago, the 5 metric ton to 1dton conversion was about right, though a little low. But remember that a main battle tank will typically have greater density than infantry carriers. So ideally, you might have a higher number of metric tons per dton for tanks than for APCs (probably 4.5-5.5 or somesuch). But that's *way* too much hassle for me.

Also note that you have to calculate turret volume separately from the hull when determining real world volume. Most dimensions I've come across describe height (for instance) as the maximum height of the vehicle (the turret top).

And the credible few references to volume I've found talk about *internal volume* and omit the volume consumed by armor or the tracks (or the open space under the hull).

So 5-1 worked for me. Feel free to vary from that

In any case, the point of the post was to note that these conversions are probably not ideal for equipment like bombs and the like. As noted, I'd go with Striker's generic assumeption that 1 cubic meter weighs 1 metric ton.

 

[tbeard1999]

That's some great info there, tbeard in particular - I think you've done alot of calculating work for me. Thanks for the data and the math!

Thanks; I've trod this ground before in my small ship universe military vehicle designs.

Note too that using the Striker guidelines implies that 1 dton of magazine will hold 20 starship missiles (50kg each).

Now all I have to decide is what kind of bombs will it use? I'm favouring big ones! Against a low tech foe it could drop its bombs at high altitude, and they would all be guided. Against a high tech foe low-level bombing at very high speed. Against a very high tech foe, perhaps releasing specialized re-entry bombs from orbit although there may be a much larger number of strays and rogues with that approach.

In my opinion--

At higher tech levels, the bombs will almost certainly be "brilliant" munitions with considerable stealth, ECCM and even avoidance capabilities (ability to jink on the way down to avoid interception). This will reduce warhead payload (although improvements in explosives tech may offset that to some degree). Monster conventional munitions will probably be for specialized use; I'd expect that 100-250 kg bombs will be typical. For wide area work, clusterbomb submunitions will be favored (although they tend to leave a "dirty" environment). I'd expect that the distinction between bomb and ground attack missile will blur as bombs become more capable of guidance. In my campaign, the standard attack munition is the 50 kg starship missile optimized for ground attack -- "brilliant" guidance, increasingly sophisticated penetration aids, etc.:

The SGM-21 is a 15cm missile roughly comparable to a heavy artillery shell in effect. It's a "brilliant" munition, with multiple engagement modes ("fire and forget", target designation, autonomous ground engagement, autonomous air engagement). The "A" model has a TDX multipurpose high explosive warhead. The "B" model is a "bunker buster" designed to penetrate heavy concrete or deeply buried bunkers. The "C" model has an anti-tank warhead capable of penetrating all modern main battle tanks from the top. The "D" model is a proximity fused antiaircraft warhead. The exact mix of missiles will depend on the mission.

Using a standard-sized attack munition allows any starship with missile racks to provide ground support. EDIT: The ground attack munitions have far less propellant and considerably larger warheads than the starship missiles. But even the Commonwealth anti-starship missiles can function in ground attack mode (roughly they're an "A" model SGM-21 with smaller warhead).

Hope this helps.

EDIT: Big Danged Bombs (BDBs) are extremely useful at cowing less advanced opponents. Apparently US forces induced an entire Iraqi battalion in Desert Storm to surrender by dropping ONE BDB nearby. So I suspect that all advanced militaries will have some available.

 

[mbrinkhues]

Max size of the pillbox is 9.77x3.66x2.44m (gun to front) => 87.3m3 (with the gun back over the engine it's around 72m3) That amounts to 6.5 dton (5.3 gun back).

6.5x5 is 32.5 and that is about half of what your formula produces not matter what version of the M1 is involved. And remember: That's for the tank in travelling position, not in storing position. There the formular is even more of.

 

[tbeard1999]

Max size of the pillbox is 9.77x3.66x2.44m (gun to front) => 87.3m3 (with the gun back over the engine it's around 72m3) That amounts to 6.5 dton (5.3 gun back).

6.5x5 is 32.5 and that is about half of what your formula produces not matter what version of the M1 is involved. And remember: That's for the tank in travelling position, not in storing position. There the formular is even more of.

Ok, so change the factors to 1 dton=10 metric tons. It's been a *long* time, so I probably remembered incorrectly.

EDIT: Note that a rough calculation shows the Stryker to displace about 3.5 dtons, while its weight is 16.47 metric tons; the similar LAV-25 is about 13 metric tons with similar displacement.

So a better rule of thumb might be 5 mt per dton for light vehicles; 10 mt per dton for main battle tanks.

EDIT 2: I should've done a better job remembering my own rule of thumb. My original rule was the average mass (in metric tons) of cargo would be dtons x 4. I noted that a tank should take the higher of its actual volume in dtons or its Mass in metric tons/4:

My calculations are based on the standard 40' shipping container. It is 67.5 cubic meters, which equates to 4.82 dtons. It can hold a maximum of 26.5 metric tons of cargo, or about 5.5 metric tons per dton. I reduced this to 4 metric tons per dton to account for the fact that not every container would contain its maximum mass.

This yields the rule of thumb -- use the greater of dtons or metric tons divided by 4.

Heavily armored vehicles may require more dtons than their volume suggests as you note. The M1A2 Abrams, for instance, weighs about 60 metric tons and has a volume of about 12 dtons. Using my rule of thumb, it will consume the higher of 60/4 or 12 in dtons. So it would be 15 dtons.

In my example, it looks like I got the M1's volume wrong, but it doesn't matter. Anyhow, I make its effective volume as 8.4 dtons (using 13.5 cubic meters per dton) or 8.09 dtons (using 14 cubic meters per dton). That's with the gun pointing to the rear. With the gun pointing forward, it's 8.81/9.14 dtons. (Per Hunnicutt, M1 Abrams).

But given the fact that a typical cargo ship will allocate about 4 metric tons per dton, an M-1 will take up more than its raw volume implies (in this case about 15 dtons).

And since volume is a particularly hard number to derive for most vehicles anyway, here's my suggested NEW SOOPER IMPROVED rule of thumb to determine Traveller tonnage of vehicles:

Weight in metric tons divided by 4 equals displacement tonnage used.

Actual volume consumed by heavily armored tanks may be significantly less -- something like weight/7 in dtons. But the ship assumes an average tonnage of 4 metric tons per dton, so the tank will use its mass (in metric tons)/4 in dtons.

 

[Mithras]

I am aware of the rapidly developing field of guidance etc for gravity bombs, but I am also aware that my 200 ton ship has 2 hardpoints, and I've 'added' this extra tonnage of bombload 'for free'. I can't let them turn out to be sophisticated self-guiding anti-armour missiles, because that negates another craft in the squadron that is fitted with two triple missile launchers. There must be a definite distinction between free fall ordnance and the ship-to-ship or ship-to-ground guided missiles, or else I am horrible breaking Traveller rules!!

 

[tbeard1999]

I am aware of the rapidly developing field of guidance etc for gravity bombs, but I am also aware that my 200 ton ship has 2 hardpoints, and I've 'added' this extra tonnage of bombload 'for free'. I can't let them turn out to be sophisticated self-guiding anti-armour missiles, because that negates another craft in the squadron that is fitted with two triple missile launchers. There must be a definite distinction between free fall ordnance and the ship-to-ship or ship-to-ground guided missiles, or else I am horrible breaking Traveller rules!!

Oh I agree. I wouldn't allow ships to mount the SGM-21 in anything other than their missile racks. And guided bombs, even highly maneuverable ones would -- and should -- be useless against starships at normal combat ranges.

The Commonwealth likes the SGM-21 because it works with the standard starship missile rack. But Commonwealth forces have access to a wide variety of general purpose bombs.

 

[Mithras]

tbeard - Have you referenced the SGM-21 in another thread I can read??

Dave - That's eased my worries about missile v bomb.

Oh I agree. I wouldn't allow ships to mount the SGM-21 in anything other than their missile racks. Guided bombs, even highly maneuverable ones would -- and should -- be useless against starships at normal combat ranges.

The Commonwealth likes the SGM-21 because it works with the standard starship missile rack. But Commonwealth forces have access to a wide variety of general purpose bombs.

 

[tbeard1999]

tbeard - Have you referenced the SGM-21 in another thread I can read??

http://www.travellerrpg.com/CotI/Discuss/showthread.php?t=11099

 

[PFVA63]

Hi

Having no luck here .... I can't find any modern bomb-bay dimensions to port over to a craft I'm designing. Really to give me a reference, and calculate the tonnage of bombs I can pack in there.

Any ideas? I've allocated 6 tons for a bomb bay, but obviously thats volume not weight, and a B-52 today can carry far more than that in metric tonnage. I caught a forum post somewhere where a poster reckoned the B-52 had a 30 sq.m bomb bay, but that's only 2 dtons. If that's right and it seems low, then my 6 dton bomb bay will be a city-buster!

Hi,

Don't know if this helps and I can't fully vouch for whether these sources are 100% accurate, but here are a couple links to some info on the B-36 bomber. The 1st one suggests that its bomb bay had a volume of over 12,300 cubic feet (over 24dtons if I did the math right) and the 2nd link shows a Mk-17 hydrogen bomb which was meant to fit into its bomb bay. The info says that the bomb was 24ft 8in long and 61.4inches in diameter and weighed between 41,400 to 42,000 lbs.

If this info is correct then the Mk-17 bomb displaced about 14.2 cubic meters (I think - if my math is right) or a little over 1 dton and weighed about 18.8 to 19 metric tons.

Regards

PF

http://pages.nyu.edu/~jh15/b-36.html

http://www.fiddlersgreen.net/models/Aircraft/Convair-B36.html

 

[Peter Schutze]

>Big Danged Bombs (BDBs) are extremely useful at cowing less advanced opponents. Apparently US forces induced an entire Iraqi battalion in Desert Storm to surrender by dropping ONE BDB nearby.

If it is the Fuel-air explosive you're referring to a lot more than a battalion surrendered. Unless you mean a battalion surrendered as a formed unit. The division reported that it had been nuked due to the mushroom like explosive result and was rendered combat ineffective. Most of its personnel were rounded up and marched off to the PoW centres.

The other type of big daged bomb is the penetrator "bunker buster" designed to punch thru metres of concrete/granite before exploding. Thats a car sized package dropped out of a heavy lifter (c-130) more often than a bomber

two totally different effects .... massive damage but limited penetration vs penetrate anything reasonable but only a couple die damage in a smaller area.

that customisable effect (and maneovrability) is what distinguishes bombs from missiles in my campaigns. missiles have to be tweaked for electronics and speed/range as a tradeoff and can stear themselves properly. Bombs just get more expensive with more customisations

 

[Timerover51]

>Big Danged Bombs (BDBs) are extremely useful at cowing less advanced opponents. Apparently US forces induced an entire Iraqi battalion in Desert Storm to surrender by dropping ONE BDB nearby.

If it is the Fuel-air explosive you're referring to a lot more than a battalion surrendered. Unless you mean a battalion surrendered as a formed unit. The division reported that it had been nuked due to the mushroom like explosive result and was rendered combat ineffective. Most of its personnel were rounded up and marched off to the PoW centres.

The fuel-air explosive bombs were dropped from C-130 aircraft using parachutes to slow the descent. Sometimes they worked and sometimes they did not. Reliable functioning is an issue. It is more efficient to use an ammonium nitrate-fuel oil bomb with a TNT or PENT detonator. They have a high reliability of functioning as intended.

The other type of big daged bomb is the penetrator "bunker buster" designed to punch thru metres of concrete/granite before exploding. Thats a car sized package dropped out of a heavy lifter (c-130) more often than a bomber

two totally different effects .... massive damage but limited penetration vs penetrate anything reasonable but only a couple die damage in a smaller area.

The high-penetration bomb used in the 1991 Gulf War was based on an 8 inch naval gun barrel, cut down and packed with high-energy, low sensitivity explosives, and carried externally by a FB-111 Aardvark. You need the high velocity of the jet to ensure penetration, and it also was equipped with a laser guidance system.

The standard load out for a B-52 in Vietnam was eighty-four 500 pound (nominal weight, actual weight 573 pounds) internally on 3 high-density racks of 28 bombs each. The external load was twelve 750 pound (nominal weight, actual weight 823 pound) bombs per external rack, for a total of 24 additional bombs.

A B-36 standard conventional load was seventy-two 1,000 pound (nominal weight, actual weight depended on what explosive they were loaded with) in four bomb bays. For the very large thermonuclear bomb mentioned, nominal yield somewhere between 15 to 25 megatons, the two center bomb bays were combined to carry the bomb as near to the center of gravity of the aircraft as possible to avoid stability problems. The bomb had a retarding parachute to give the B-36 time to get out of the blast radius. I am not sure if the B-52 could carry one of these in its original bomb bay.

 

[BlackBat242]

I guess I need to run out to the USAF museum (Hill AFB, Utah) a few miles south of my house and measure the B-52G's bomb bay doors (and those of the B-1).

I've got photos of the inside of a B-52H bomb bay as well.