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Air-to-Air

MHU-12/M Munitions Handling Trailer (Vietnam era)

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001_Munitions_Trailer.jpg

Hello and welcome to my build of a 1/48 Munitions Handling Trailer.

I'll be using the Skunkmodels Workshop Missile Cart for USAF/NATO as the base for this build.

002_Box_Art.jpg

That's all for now. After I have observed the ritual tradition of the sprue bath, I'll be back with some sprue shots.

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001_Munitions_Trailer.jpg

Hello and welcome to my build of a 1/48 Munitions Trailer.

I'll be using the Skunkmodels Workshop Missile Cart for USAF/NATO as the base for this build.

002_Box_Art.jpg

That's all for now. After I have observed the ritual tradition of the sprue bath, I'll be back with some sprue shots.

Thats a MHU141 by the way!

Selwyn

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Thats a MHU141 by the way!

Selwyn

Thank you Selwyn. Now that's why I like Britmodeller so much. There are people in the forums that know things that cannot be found on the Internet!

I am very thorough in my research but I could not find a name for this particular piece of hardware, hence the rather plain "Munitions Trailer". Thanks to Selwyn's contribution, we can now proceed with the more technically correct MHU141 Munitions Trailer.

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Some time-honoured traditions should always be observed. For me, the sprue wash is one of those. It marks the commencement of the construction phase of a project.


003_Sprue_Wash.jpg


I have set the sprues out to dry. They have been covered so that dust does not accumulate on them.


004_Sprue_Dry.jpg


Ordinarily I would dry the sprues with my airbrush but it is late in the evening and I don't have enough time to set up my airbrush. It's packed away, I've not used it since moving house some months ago.


I will return with some detailed sprue shots in due course.


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Not to be too nitpicky, but the pictured trailer is a MHU-12/M (5000 pound capacity). The MHU-141 is virtually identical, but sits a bit higher off the ground and can handle 500 pounds more weight. For a while the two were used side by side, but eventually the MHU-12's were phased out in the mid-1980's.

FWIW, the MHU-141 can handle a maximum of six Mk 82's or two Mk 84's.

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Dont know if you are a rivet counter type but this might be of help?

http://www.thepdigroup.com/ProductDetails/14

Selwyn

Yes, if there was a spectrum of persons with rivet counting tendencies from zero on the left to an actual rivet counter on the right, I would fall on the right side of that spectrum.

Thank you for the link Selwyn, I hadn't seen that page before (as I didn't know it was an MHU-141 trailer).

Not to be too nitpicky, but the pictured trailer is a MHU-12/M (5000 pound capacity). The MHU-141 is virtually identical, but sits a bit higher off the ground and can handle 500 pounds more weight. For a while the two were used side by side, but eventually the MHU-12's were phased out in the mid-1980's.

FWIW, the MHU-141 can handle a maximum of six Mk 82's or two Mk 84's.

Slater, there's nothing nitpicky about clarifying something for me.

So as I now understand it, in the Vietnam era (which is what I am trying to model), the Air Force used the MHU-12/M trailer.

The MHU-12/M was subsequently phased out and superseded by the the MHU-141 trailer in the mid-1980s.

I suspect that the Skunkmodels kit is based on the MHU-141 given that it's been in service for the last 30 years.

So, if I am to model the MHU-12/M I will have to reduce the height of the Skunkmodels deck slightly.

Whilst we are discussing the designations of various munitions trailers, is it possible to confirm that the munitions trailer below is an MHU-85/M?

MHU-85M_Munitions_Trailer.jpg

[Image source]

The above trailer also figures prominently in the ground support equipment used at Cam Rahn Air Base in the late 1960s.

Thus far, I have not been able to source a 1/48 scale model of that trailer but I did not have its designation until now.

Thanks again for your contributions, they are all adding significantly to my understanding.

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Correct, an MHU-85/M being towed by an MB-4 Coleman aircraft tug. MHU-85's also were withdrawn in the 1980's. Pity, because they were ideal for transporting Mk 84 bombs. As the picture implies, this particular trailer was designed with the preload in mind.

Another very widely used trailer is/was the MHU-110/M (15,000 pound capacity).

Another "fun fact" is that the MHU-12 and MHU-141 were nuclear certified while the MHU-110 and MHU-85 were not.

Edited by Slater

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Correct, an MHU-85/M being towed by an MB-4 Coleman aircraft tug. MHU-85's also were withdrawn in the 1980's. Pity, because they were ideal for transporting Mk 84 bombs. As the picture implies, this particular trailer was designed with the preload in mind.

Thank you for confirming that Slater.

Now for some detailed sprue images.

As part of my build process, I print out these images and use them to research:
  • details that could be added to the parts
  • the colours of the moulded in and additional details
  • appropriate weathering.

005A_Assembly_Guide.jpg005_A1_A2.jpg

006_A3_front.jpg
007_A3_rear.jpg
008_A4_A5.jpg
009_A6_A7.jpg
010_A8_front.jpg
011_A8_front_alt.jpg
012_A8_Rear.jpg
013_B1_B2.jpg
014_B3_B4.jpg
015_B5_B6.jpg
016_B7_B8_B9.jpg
This kind of approach is not everyone's cup of tea. However, it does help me ensure that relevant details I can see in photos of the actual trailer are transcribed on to the model. I don't have the capacity to remember the multitude of small details I discover as I study photos of an actual modelling subject.
The other thing I have to decide is what munitions I am going to display on these trailers as that will determine the support rails I need to finish.
These trailers are to be part of my F-4C Phantom project. The objective of that project is to depict an operational F-4C at Cam Rahn Air Base, Vietnam, circa 1968-69.
The positive thing about an F-4C Phantom build is that there is no shortage of munitions one can load on to a Vietnam era aircraft.
I will return with some ideas in my next update.

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Based on the following photo references from Cam Rahn Bay Air Base, Vietnam, circa 1967 to 69, I have decided to model the following trailer options:

  1. 4x LAU-3 2.75" folding fin aerial rocket pods
  2. 4x M117 750-pound general-purpose bombs
  3. 4x Mk 82 500-pound general-purpose "Snakeye" bombs
  4. 6x Mk 82 500-pound general-purpose bombs "Slicks"
  5. 4x BLU-27 Napalm bombs
  6. 4x AIM-7E Sparrow missiles.

With respect to the last option, I have it on good authority from someone that flew the F-4C at the relevant time, from Cam Rahn Bay, that AIM-7 missiles were never loaded as there was no air to air threat in South Vietnam (thank you Gene K). As you will see in due course, I am just doing that option for a bit of fun and variety.

Mk82s_and_FFAR_pods.jpg

[Image source]

Mk82_Snakeyes.jpg

[Image source]

Mk117s.jpg

[Image source]

Napalm.jpg

[Image source]

AIM-7.jpg

[Image source]

The photos show that the munitions loaded on the trailers did not require complicated support rails. Therefore, I don’t need to clean up and finish all of the support rails in the kit. I may limit my efforts to:

  • Parts of A5 modified to be supports for the FFAR pods, Mk.82 Snakeyes and Mk.117 bombs.
  • Parts of A1 modified to be supports for the Napalm bombs.
  • Parts of B2 modified to be supports for the Mk.82 slicks.

I will have to scratch build something for the AIM-7 missiles as nothing else is close to the support in the image above.

I have three of these kits, six trailers in total, so enough to cover all of these options.

To allay any concern you may have that six trailers in a diorama with an aircraft would look unrealistic, let me assure you that no more than one trailer will be displayed in the diorama at any one time. The six options are merely to offer visual diversity regarding the potential loads of the F-4C Phantom (that will eventually be constructed).

I will return when I have some details about test fitting and construction.

Any input you can offer is always welcome.

Edit:

- Updated trailer option to 4x BLU-27 Napalm bombs. See post below.

- Updated munitions designations.

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Not sure that it really matters unless you are being super-accurate, but part A5 is evidently a single-piece bomb chock. These were the newer iterations introduced in the mid- to late 1990's as a kind of universal bomb and missile chock. In Vietnam (and indeed, on through most of the 1990's) bombs on MHU-12/141's rested on two-piece chocks, i.e., a load of six Mk 82's would require 24 separate chocks. These were attached to the trailer rails by quick-release pins.

Edited by Slater

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Not sure that it really matters unless you are being super-accurate, but part A5 is evidently a single-piece bomb chock. These were the newer iterations introduced in the mid- to late 1990's as a kind of universal bomb and missile chock. In Vietnam (and indeed, on through most of the 1990's) bombs on MHU-12/141's rested on two-piece chocks, i.e., a load of six Mk 82's would require 24 separate chocks. These were attached to the trailer rails by quick-release pins.

Thank you Slater. Again, this sort of input is why I do a work in progress thread. It always results in a better understanding, occasionally puts me in touch with people that used the relevant equipment, and often pushes me to develop my skills in new ways.

I am looking to be pretty accurate on this project.

I am going to see if I can find an image of the two piece chock and quick release pins (my initial efforts to do so haven't turned up much so far).

Thanks again for the input.

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I’ve now located a photo of an MHU-12 trailer with four BLU-27 Napalm bombs.


MHU-12_loaded_with_Napalm.jpg



I’ve edited the trailer options in post #10 above to 4x BLU-27 Napalm Bombs.


MUNITIONS CHOCKS


I’ve obtained some additional images regarding the munitions chocks used on Vietnam-era trailers.


In these images you can see that the rocket pods, Napalm bombs, M177 bombs and Mk 82 bombs all appear to have been chocked using the same support.


Munitions_Chocks_Vietnam.jpg

[unedited image sources: UL, UR, LL, LR]


It appears that the chocks were placed over a rail that had holes for the quick release pins (explained by Slater above).


A couple of more modern images provide further details of the quick release supports.


Munitions_Chocks_Closeups.jpg

[unedited image sources: L R]


When it comes time to model the munitions chocks, I will have to scratch build something to begin with as none of the kit-supplied options are close enough to use as a substitute.


It appears that the AIM-7E chocks were different in that they covered the rail and did not rest on part of it.


AIM-7E_chock.jpg

[unedited image source]


With that issue resolved I will be proceeding with test fitting and construction.


Thanks again for the input, it makes for a more accurate and satisfying build.


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Good luck in your build. Seems that you're tackling an area that has seen little attention in the past.

As a bit of useless trivia, one can see a nylon tiedown strap over the munitions in a couple of the pictures. This is called a CGU-1/B tiedown and is still used today as the primary munitions securing strap in the USAF. To muddy the waters even further, many loads required the use of a shackle in conjunction with the chocks to provide a more secure tiedown. This is a squared-off steel accessory that attached to the same rail as the chocks. I doubt that you would need to scratchbuild this unless you are depicting a load of munitions that are secured by straps.

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As a bit of useless trivia, one can see a nylon tiedown strap over the munitions in a couple of the pictures. This is called a CGU-1/B tiedown and is still used today as the primary munitions securing strap in the USAF. To muddy the waters even further, many loads required the use of a shackle in conjunction with the chocks to provide a more secure tiedown. This is a squared-off steel accessory that attached to the same rail as the chocks. I doubt that you would need to scratchbuild this unless you are depicting a load of munitions that are secured by straps.

Thanks Slater. I can see from the photos that the tiedowns were used to secure some of the loads. I will give this some more consideration in due course.

ONE STEP FORWARD…
I compared the images I have with the parts of the Skunkmodels kit.
Whilst the Skunkmodels kit may be a reasonable approximation of the MHU-141/M munitions handling trailer, there is very little in common with the MHU-12/M munitions handling trailer.
The significant differences include the following.
Tyres
The kit tyres are similar to the MHU-141/M’s bulbous tyres. However, the MHU-12/M has a flat treat pattern and toothed edge on its tread.
017_Trailer_Tyres.jpg
Axles and Steering Rods
The kit axles are tubular. The MHU-141/M appears to have a small axle with a square cross-section. The MHU-12/M has a larger axle with a square cross-section.
018_Trailer-Axles.jpg
The steering rods on both trailers are straight and appear to be about the same thickness. The kit appears to have a sway bar rather than steering rods.
Deck Protrusions
The protrusions from the deck on the kit part are the same dimensions as the MHU-141/M. However, the dimension of the protrusions on the MHU-12/M are different.
019_Deck_Protrusions.jpg
Rails
The kit part effectively has three rails in the fold out panels. The third rail (illustrated in red) is actually incorporated into the munitions supports of the kit. The MHU-12/M only has two rails.
020_Rails.jpg
The edge of the kit part is also significantly raised. On the MHU-12/M there is no raised edge to the fold out panel.
Tool Lockers
The MHU-12/M has tool lockers under the deck (two on each side). The MHU-141/M does not have these and neither does the kit part.
021_Tool_Lockers.jpg
Tie Down Rings
The tie downs on the MHU-12/M are circular. The MHU-141/M tie downs are oval in shape, as are the kit parts.
022_Tie_Downs.jpg
Anti-Skid Surface
In addition to the differences noted above, I’ve realised that the anti-skid plating on the surface is about three times over scale. That’s not a criticism of the manufacturer as it probably has more to do with the limits of injection moulding rather than a disregard for accuracy.
023_Anti_Skid_Surface.jpg
DIMENSIONS
I decided that if I was going to use the deck from the Skunkmodel kit, I should confirm that it was dimensionally correct.
There are not a lot of online sources with the dimensions of the MHU-12/M. I managed to locate an online document that contained the following dimensions [Source].
MHU-12/M Munitions Handling Trailer Dimensions
Length: 120in 126in
Width: 84in
Wheelbase: 90in
Track: 72in
Height: 28in
1/48 Scale dimensions:
Length: 66.7mm
Width: 44.5mm
Height: 14.8mm
Given that the online document recorded that it was a draft, I thought it should obtain a cross-check from another source. I located an online listing for a surplus MHU-12/M [Source]. The online listing confirmed the width and height above but stated the length as 126 inches. The online listing provided photographic proof of the length so I am going to accept the length as 126 inches.
A further cross check was the much easier to obtain dimensions of the MHU-141/M directly from the manufacturer [Source].
MHU-141/M Munitions Handling Trailer Dimensions
Length: 126in
Width: 84in
Wheelbase: 89in
Height: 32in
In short, the deck of the two trailers are the same dimension, 126 x 84 inches. The MHU-141/M is 4 inches higher at 32 inches.
I measured up the Skunkmodels deck.
024_Skunkmodels_Dimensions.jpg
The length of Skunkmodels deck is spot on. The width, however, is oversized by about 5mm.
My objective is to do an accurate build so 5mm is just too much for me.
So I’ve reached a point where I can’t proceed unless I am prepared to scratch build what is required. I was looking forward to scratch building a few things later in the project, after I had finished off a few straightforward diorama accessories. Sometimes model building seems like an exercise in a thousand frustrations.
I’m going to press on with the build as it will be an integral part of the final display.
I guess it’s time to go back to the…
025_Drawing_Board.jpg
I’ve ordered some scale anti-skid made from photo etch. I will evaluate that when it arrives in the post.

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I've prepared a set of dimensioned plans based on the images I have collected from the Internet.

Top View

026_Top_Plan.jpg

Side View

027_Side_Plan.jpg

Front View

028_Front_Plan.jpg

Rear View

029_Rear_Plan.jpg

Not my best work, but it's been thirty years since my last drawing of this nature. The next one will be better if I can get a hold of the tools I need.

The dimensions are for 1/48 scale. I found it worthwhile drawing the plans in 1/48 scale as I reasoned that if it's difficult to draw it will probably be impossible to model.

Some of the dimensions are in tenths or hundredths of a millimetre. For these initial drawings I thought it was important to get as much accuracy as possible. The more important step is the next one: the assembly drawings. We are all constrained by the materials available to us such as Evergreen sheet & rods, brass wire etc. The reality is that most things will have to be constructed from styrene sheet with a thickness between 0.125mm (i.e. an eight of a millimetre) and 1.0mm. The assembly drawings will, in effect, be a documentation of the compromises I am prepared to make to get something with the level of detail that I want, with a reasonably accurate shape, constructed out of readily available materials.

This next step may take a couple of weeks. Bear with me.

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I decided it would be smarter to construct a prototype first, rather than prepare assembly drawings, as construction may result in changes to the assembly steps.


That said, quite a bit of thought has gone into how to assemble the trailer.


This post, and those that follow in due course, are one approach to construction.


The basic deck pieces were cut out first. I'll dimension the assembly drawings so don't be concerned about dimensions at this stage.


030_Under_deck_pieces.jpg


Styrene used in the following steps.


031_Evergreen_styrene.jpg


Some channel is cut to size and fixed to the underside of the deck.


032_Channel_glued_to_deck.jpg


I-beam is also cut to size. Here it is test fitted.


033_Test_fitting_I_beam.jpg


A serif is removed.


034_First_serif_removed.jpg


Then another serif is removed so only an S-shape remains.


035_Second_serif_removed.jpg


I neglected to take a photo of it being glued, but it's the same approach as cementing the channel.


The basic frame was completed with some strip styrene, cut, then sanded to size, with small cut outs for the channel and S-beam.


036_Basic_frame_complete.jpg


More as it progresses...


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I got some Voyager Model Antiskid Plate (TE018) to depict the trailer deck.

037_Voyager_Antikid.jpg


Here’s a closer look at the antiskid surface. The slanted cross pattern measures 0.95 x 0.60mm. The quality was a pleasant surprise; it looks like the real thing.

038_Antiskid_closeup.jpg


To try and improve paint adhesion, I prepared the sheet by first cleaning it with Isopropyl Alcohol and then scrubbing the antiskid surface with soapy steel wool. I used fine sandpaper on the underside of the sheet, to try and improve CA adhesion.


Then I measured out two 44.5 x 25mm lengths per trailer.

039_Deck_antiskid.jpg


The underside of the deck is Evergreen Sheet 9015 0.38mm: 44.5 x 22.75mm.

040_Deck_underside.jpg


Dry fitted to the antiskid.

041_Deck_underside_dry_fit.jpg


At this stage, I paused to make some simple tools that will make my scratch building more efficient. I figured that as I will probably be using these tools for quite some time, I may as well spend a bit of time making them properly. They are made out of aluminium angle and strip. The results of an afternoon’s effort.

042_New_tools.jpg


With the assistance of a steel ruler and cube magnets, they can be used as a square, a styrene cutter…

043_Parts_cutter.jpg


…and a square sander.

044_Square_sander.jpg


At this point, you need to create a measuring tool comprised of two 19.75mm lengths of (1) Evergreen Strip 105 0.25x2.54mm, and (2) Evergreen Strip 135 0.76x2.54mm.


Here are the lengths layered between one another, ready for thin cement.

045_Square_tool.jpg


More in due course.


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I think this should be in the wingy-things section....not armour! :D Just joking. Certainly different and interesting and love the lengths you are going to with it considering the small scale. And I'm impressed with how you use the magnets. Must go look for some.....

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Square up the edge of the deck underside with the measuring tool and use a ruler to mark the edge of the inside frame of the deck. Use magnets to keep everything in position.

046_Frame_alignment.jpg


Remove from the square and using the tip of a knife, score a line along the very edge of the ruler. This line is critical to getting everything properly aligned, which is why I have gone to this effort.

047_Frame_edge_scoring.jpg


Now I am going to mark out the tie down points so that the holes in the deck antiskid and the deck underside align with one another.


Centre lines were marked up at 3.5mm and 11.0mm from the outer edge of the deck underside.


Cross lines were marked at 6.5mm and every 4.5mm thereafter.


Next up I paused to make a small circle template out of clear styrene with my punch and die set. This was then used to mark out the positions of the tie down points on the deck.


These circles were approximately 1.5mm in diameter. They were drawn as a guide so that when using the punch and die, there was a circle to centre within the “barrel” of the die.

048_Template_and_tie-down_positions.jpg


After aligning the circle within the “barrel” of the die, I then punched out the holes in the deck underside with a 1.8mm punch.

049_Tie-down_holes_punched.jpg


More in due course.

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This is a fantastic piece of work ! (and being an aircraft boy I nearly missed it !)

Cheers,

Haydn.

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Square the deck underside with the antiskid. Make sure the score lines are face up otherwise you will have to redo everything as I discovered (you can see in the image below that the score lines are not face up). I did not want the underside moving around on the antiskid whilst I marked the positions of the tie-downs so I used tape to hold the parts together.

050_Antiskid_underside_alignment.jpg


The positions of the tie-downs were then marked with a fine-point Sharpie using the underside as a template. On conclusion, I had to number the parts because the antiskid and underside are now matched to one another.

051_Antiskid_markup.jpg


Once again, align the circle within the “barrel” of the die and punch out 2.8mm holes for the tie-downs in the antiskid. A dry fit of the punched antiskid with the underside beneath.

052_Antiskid_punched.jpg


Having completed the first row of tie-down holes, it was evident that some of them were very slightly out-of-line. Nothing that is noticeable unless you look down the row from a very low angle.


As I continued working, my mind inevitably turned to whether there may be some better way of achieving a perfect alignment with the antiskid rows that align the upper surface. Sure enough, there is! This is one of the things I enjoy about modelling. When you’re patiently working away as some time consuming activity, the mind inevitably starts to throw up rather good ideas on how to make the process faster, more efficient or better.


I recalled that NorthWest Short Line had created The Riveter, a calibrated advancing table with an advancing knob calibrated in 0.001” increments (i.e. 0.0254mm increments) for The Sensipress. However, on closer examination of the relevant tools, it was disappointing to learn that the punch and die accessories for The Sensipress were limited to 0.010” to 0.060”, i.e. 0.25mm to 1.52mm, in graduations of 0.25mm. If it was possible to have the range I have with the RP Toolz Punch and Die (0.5mm to 2mm, in 0.1mm increments & 2mm to 4mm in 0.2mm increments) NorthWest Shore Line would have likely had a sale. I know US$260 is a significant amount of money to pay for tools of this nature, but given the ludicrous amount of money I have already spent on this project buying styrene and the large RP Toolz Punch & Die set, what’s another few hundred for a perfectly aligned set of tie-downs on a 1/48 Munitions Trailer? Hang on, given that they are likely to be mostly obscured by the munitions, one might conclude it’s a bit too much. But an advancing table with 0.001” increments would be a pretty cool tool! Something to think about some other day.

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