GBU-38 500 lb JDAM

A scale modeler's guide

Since its introduction to combat in 2004, the GBU-38 has given air forces across the globe the ability to hit ground targets with greater precision and confidence to avoid unnecessary collateral damage. It is capable of being delivered from every tactical fighter in the US inventory as well as several air frames that have since been retired. The GBU-38 has also been cleared for use on an assortment of foreign aircraft. Such widespread use means that a modeler who intends to build a subject of a modern jet fighter that has been involved in the Global War on Terror stands a great chance of being able to mount the JDAM on their kit. Having the right references for just such a circumstance is key.

The Bomb

Together the US Navy and Air Force conceived requirements for a new precision guided munition at the end of the first Gulf War. The venture was named JDAM, for Joint Direct Attack Munition and soon found success using GPS assisted inertial navigation systems that could be packaged into guidance kits and attached to legacy "dumb bombs". These JDAM kits could be fitted to a variety of bomb bodies thus giving existing munitions a powerful new ability.
The foundation of the typical GBU-38 is the Mk82 bomb body but may also be the BLU-111 (identical to the Mk82 except that it contains PBXN-109 explosive filler rather than Tritonal) or the composite case warhead BLU-129.

Mk82 500 lb bomb body capable of being converted to a GBU-38 JDAM. This particular one is inert as shown on the stencil.

Two BLU-129/B composite bomb bodies about to receive their guidance packages to become JDAMs. The yellow diamonds denote the high explosive hazard of the munitions and denote that they are composite cased warheads.

The BLU-111 is favored by the United States Navy, as seen here. The three yellow stripes are an indicator that they are indeed BLU-111 500 lb bomb bodies. The USN uses two stripes to indicate that a munition is a high explosive hazard and has had a thermally protective coat added to it. The third stripe indicates the PBXN-109 explosive filler.

The Nose

Part of the process for turning a "dumb bomb" into a more intelligent munition involves adding a few accessories to improve its accuracy. Several features on the nose of the GBU-38 are distinct and make them easy to identify from other munitions.

Each GBU-38 is fitted with aerosurfaces, or strakes, that are strapped around the nose of the bomb body. This improves aerodynamics. Typical USAF versions feature a copper colored ring into which the conical nose plug is installed as you see above.

Though the US Navy uses the name aerosurfaces as the USAF version, generally they do not use the conical nose plug seen on Air Force GBU-38's. Instead, they prefer the MXU-735 solid nose plug fitted into the retaining bolt of the nose of the bomb. The solid nose plug provides better penetration of hardened targets. You can see they weather nicely.

The MXU-735 solid nose plug may also be painted in olive drab as seen in this photo.

The US Air Force and the Navy have both been known to use the DSU-33 proximity sensor on their GBU-38's. Here, a USAF F-16C pilot describes the features of a GBU-38's DSU-33 to a visiting celebrity. The USAF mounts the proximity sensor to the copper colored ring in the same fashion as the conical nose plug.

Here you can more easily see the DSU-33 and copper colored ring in these GBU-38's inside the bomb bay of a B-2.

This GBU-38 is loaded on an F-18 Hornet and also features the prominent DSU-33 proximity sensor. You can see the NAVAIR versions do not use the copper colored ring used by the USAF.

Of course, it is only the aerosurfaces that determine the weapon is a GBU-38. The conical nose plug, the MXU-735 and the DSU-33 are not unique to the JDAM and do not factor in the bomb's status as a smart munition. However, such features help distinguish the GBU-38 from its brother, the GBU-54 which has similar characteristics.

This is a GBU-54 which looks nearly identical to the GBU-38. A careful comparison will show that the black nose is actually a DSU-38 laser homing target detection device and not a DSU-33. The GBU-54 will always wear the distinctive black DSU-38 and several bandit straps around the bomb body which help to differentiate itself from the GBU-38.

The Tail

The KMU guidance kit is probably the most important part of the JDAM as it contains the actuating fins, GPS antenna and umbilical receptacle to interface with the aircraft. 

Along the side of each KMU is the small oval shaped fuse access door. Decent model kits or aftermarket resin will have this engraved. Another prominent feature is the large white sticker that displays such data as the national stock number, lot number, and model number.

 

This munitions technician is adjusting the positioning of the umbilical receptacle. This is configured depending on the air frame or pylon the munition will be loaded on. It interfaces to the aircraft with a Mil Standard 1760 cable.

Here you can see where the fins are able to actuate, thus guiding the bomb to the target. At the rear of the KMU is the GPS antenna.

Thermally Protected vs Non Thermally Protected

Eduard recently released two sets of 1/48 GBU-38's, one being thermally protected, the other not. But what does this mean for the modeler? As mentioned briefly above, the US Navy applies an ablative coat to their munitions, a requirement after the 1967 fire aboard the USS Forrestal that killed 134 sailors. It essentially lengthens the cook off time for munitions should they be enveloped by fire, allowing fire fighters more time to douse the flames.

These bombs clearly have the ablative thermal coating applied. Two dead give-aways of this feature are the incredibly rough textured appearance and the dual set of yellow stripes.

More recent NAVAIR bombs show applications of the thermal coat that are much more smooth and grey in color, such as these GBU-38's on an F-18.

A closer look at this NAVAIR version shows the slight texture of the thermally protective coat, as well as a DSU-33 on the nose.

While the thermal coating is a requirement for shipboard operations, the NAVAIR style bombs are not exclusive to US Navy and Marine Corps use.

A USAF F-16C pilot examines his weapons load before a sortie in Afghanistan. The GBU-38 is clearly NAVAIR style weapon, featuring a DSU-33 without the copper colored ring, three stripes indicating PBXN-109 explosive filler and thermally protective coat. 

USAF personnel are assembling NAVAIR style GBU-38's that even feature a yellow stripe along the back third of the bomb body.

So, while companies like Eduard specify between USN and USAF versions, in some cases, the difference does not matter. Ultimately, the ordnance in the ammo dump will be used by whatever air component needs it.

Racks

The GBU-38 is compatible with every tactical fighter and bomber in the US inventory and can be hung from an assortment of different pylons and bomb racks, to include B-52's, smart racks, and Digital Improved Triple Ejector Racks.

An A-10 flies in support of Operation Inherent Resolve, loaded with several GBU-38's, among other things.

A pair of GBU-38's on an F-18's smart rack on the right wing.

GBU-38's on a B-52.

A pair of GBU-38's on an F-16's BRU-57 smart rack.

Certainly capable of carrying more, this F-15E only shows two GBU-38's loaded.

A USMC AV-8B with two GBU-38's on the right wing loaded to a new DITER supporting Operation Inherent Resolve, 2017.

Inert

The features of an inert GBU-38 are the same as a live except they do not contain explosive filler. Visually they are identified by either a blue stripe or a completely blue BDU-50 bomb body.

An inert GBU-38 being assembled. The single blue stripe indicates this munition is inert and not for flight. This will likely be used as a load crew trainer or to train munitions personnel on assembly.

Inert GBU-38's with completely blue BDU-50 bomb body. These are capable of being flown and dropped by aircraft and are about to be loaded on the F-16 in the background.

An inert GBU-38 on an F-18.

You may also see an inert DSU-33. In some cases, though not all, non functioning sensors may have a blue stripe as well.

Some Final Shots

Norwegian Air Force F-16 being loaded with a GBU-38

Republic of Singapore F-15 with inert GBU-38's loaded.

A Japanese Mitsubishi F-2 with GBU-38 loaded.

Spanish AV-8 with GBU-38.

Review - Eduard Brassin 1/48 GBU-38 Non-Thermally Protected Bomb

If you're thinking that a GBU-38 review feels like deja vu, you wouldn't be far off. Several weeks ago, I completed the review for Videoaviation's 1/32 version of the vaunted 500 lb JDAM. Now, however, we will be transitioning to a smaller scale as we take a look at one of Eduard's latest additions to the ordnance aftermarket. The GBU-38 has been in the US inventory since the early 2000's and is now a staple of air-to-ground operations for the United States Air Force, Navy and Marine Corps as well as many other foreign countries. Though the GPS guided munition has been available in this scale for some time, with Attack Squadron and Wolfpack for instance, it is the first time Eduard has tackled the subject. They have released both a thermally protected variant and the non-thermally protected version which I am showcasing here.

What's in the box?

Instructions

The instructions come in two separate sheets printed on both sides detailing construction and color call-outs for three possible versions of the bomb. Option A is the USAF variant, B details the US Navy version, and option C covers the fairly specific B-2 version which only differs from the standard USAF option in the use of part R74 vs R72.
The instructions are clear and easy enough to follow if you've had any experience building a model at all, let alone a resin kit. If there is more than one option available to the modeler, Eduard conveys that plainly except in one case. For the B-2 variant, the instructions only call for part R70 (the nose plug) to be used when it is also acceptable to mount the DSU-33 (part R68) in its place.

GBU-38's in the belly of a B-2 all utilizing the DSU-33 proximity fuse. The option for the B-2 version is curious in itself because, unless I'm mistaken, there is not currently a Spirit on the market in 1/48 scale.

Decals

The markings will not be incredibly legible in this scale but they look like words and that is enough for me. More importantly, they appear fairly accurate and include extras because how many of you haven't messed up a decal before?
What you should notice is the lack of yellow stripes to indicate the high explosive hazard. This is by no mistake of Eduard's. You will have to paint them on, carefully, as they are covered up by the aerosurfaces on the front of the bomb.

Masks

Eduard masks will be a life saver for this kit. They've included a small sheet which I did not photograph as it will appear as just a yellow piece of paper here. You can see in the photos of the instructions above that the masks will aid in painting the aerosurfaces on the nose of the bomb. In this scale, it will be a meticulous undergoing without the masks so bravo to Eduard for the forethought here.

Photoetch

It would not be Brassin without the proper photoetch. In this case, Eduard has included a small square fret that contains eight representations of the prominent GPS antennae that resides at the rear of the tail section. Considering there are only four bombs in the pack, you have two chances per bomb to get this right.

A cart full of GBU-38's on the deck of an aircraft carrier. You can see the GPS antenna on the tail end of each bomb.

 The Bomb

The pack contains enough parts to build four bombs which should be plenty for most modern fighter load configurations, unless you're arming up a Strike Eagle. Never the less, each bomb is faithfully detailed to represent the real thing. The bombs all have lugs, a lovely addition if the ordnance is to be displayed off the aircraft and on a trailer, otherwise you'll have to clip them off in order to mount them to a pylon. 

The initiator, which is located just aft of the front lug is also finely molded, though a little inaccurate but barely worth a mention. 

At the front, the aerosurfaces are molded on and there is an opening in the nose to accommodate either the nose plug or DSU-33 fuse.

The back end will require a little clean up after cutting away the pour block. Also notice the rectangular notch which will accept the parts representing the umbilical receptacles. The fuse access door is also neatly molded into the tail assembly.

 

The KMU tail kits have a circular opening to allow the cylindrical peg from the aft of the bomb to fit. A snug and secure join is important, and I'm glad they engineered it this way instead of forcing us to either drill our own holes or mate two flat surfaces.

The above photo shows the top and bottom views of the three options for the umbilical receptacles (parts R72, R73, and R74). There are slight variations in length between all three parts. On the real JDAM, the receptacle is configured differently depending on the air frame the bomb will be loaded on. It is an interesting inclusion.

These gentleman at Ellsworth AFB are configuring the umbilical receptacle on these GBU-38's in preparation to be loaded on B-1 Lancers. The receptacles are configured differently per air frame so check your references.

Eduard also included two different sets of nose plugs. The set on the left is the standard sort of ogive nose plug used primarily by the USAF while the set on the right is the MXU-735 solid nose plug favored by the Navy.

If nose plugs are not your thing, the kit also provides two versions of the DSU-33 - one for the USAF (left) and one for the US Navy (right).

Conclussion

Several things stand out to me after taking a look at Eduard's new bombs. First, they are nicely detailed and feature all the characteristics I would expect to see on a scale GBU-38. Nothing important is missing.

Second, I appreciate the options which give builders the ability to create several different versions of the weapon though I am still a little confused over the decision to cater to the B-2 when that is a subject yet to be seen in 1/48.

I also have to wonder at why Eduard decided to include a Navy option for this set considering it is not thermally protected. The US Navy ensures its shipboard weapons have an ablative coat to protect them should a fire break out aboard ship. If Eduard already released a thermally protected version of the GBU-38, why include the Navy option here? Granted, some ablative coats appear more textured than others, so perhaps they were giving modelers the option of a less pronounced feature.

These GBU-38's have an obvious thermally protective coat, giving the bomb a wrinkled look, while the photo below, the finish is much smoother.

Whatever the case, the set of bombs looks brilliant and I can't wait to build them. Be sure to watch this space for the upcoming build review. I will also be doing a reference guide to the GBU-38 in the near future as well. 

Thanks for reading and thanks to Eduard for allowing me to review their product.