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Cal Mil/Bill Jack foam DIY liners.

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ok, i've had this Cal mil shell laying around for many years with no interest in any kind of resto work.

Today I decided to give it some attention and try to line it with foam and here's what I did.

Appoligies, if this has been covered numerous times already, but here goes...

i had an old Memory Foam pad that I was about to throw away, but then thought of using it to do the liner.



I cut ehougn of it to clear both bends in the shell (I think this shell was either an 8 or 10 size wise,


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Then I marked the curvatures with a Sharpie pen and used an exacto to make a 1/4 to 1/2" cut around the shell for a very nice contour.

I placed the Styrofoam head in the shell to help lock the foam in while working with the cut.



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Put the foam back in the helmet and checked for alignment, reinstalled the head and measured the front and nape pieces to install.

These to parts were basically free cut from "eyeballing" the sizes and dimensions (I could have tried to be precise. but...why?)



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I installed the Nylon liner cover. I havent permanently installed fasteners yet, pending trying to find a better Nylon piece

as mine has some damage.

Note: The "Memory" type foam does an excellent job of holding the helmet in place and the pieces can be glued together

with upholstery foam adhesive if desired.

Finally -

Im sure that the Nylon liner does not fit my foam job perfectly, but it will more than "do the job"

for the restoration. Hope this tidbit helps someone who has an interest in the old Bill Jack / Cal Mil / Flight Sound / HGU-9

family of flight helmets, as well as the HGU2 line of helmets which also utilized the foam insert originally

designed for extended, long hour flight comfort, a short lived concept, but a part of aviation history none the less.




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I probably should have added, that - This method of liner restoration, while perfectly suitable for a display on the mantle/shelf,

by no means qualifies the helmet for safety or practical use as a "flight helmet" and should not be used as such under any circumstance.


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interesting note about this helmet shell is the "dimple" that is left forward of the original rearward hole for a comm cord/jack.

I plugged the original hole and set with polyester resin and type E cloth.

The same "multi config." concept that appears on other early shell like the HGU where guide marks (dimples) are

factory pre molded into the shell (ie: HGU-22 shell sub-assembly) for easy build requirements.

The left forward hole may be for oxygen mask cord to helmet speaker jack much like the HGU 2 / 2a/p design.

However, no dimple marks for goggle snaps or the 3 point visor so a lot of question as to the factual similarity

between the 9 and the 16.


Would be nice to find some actual "Technical Order" text on the HGU-9 and other pilot used variants of this shell

regarding actual helmet buildup requirements.

Below is a photo of the dimple that I plan to use (drill out) when I get a Comm harness to install.

Missing from the equation is the slightly oversized black oxide finished metal connector holder that

is seen on most of the "authentic" HGU-9 helmets.


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  • 2 weeks later...

Found some ear cups out of an HGU 9 that of course were hard as rocks and the grey vinyl had turned a yellow(ish) color,

so I decided to look into a possible useful restoration for the helmet project.


I had a nice pair of ear seals (MX 2509) out of a grey Roanwell headset which design wise basically, are based on the same kidney shaped

cup as the HGU-9 seals. I decided to use the base part of the HGU ear cup seals and mate em up with the 2509's.


So the first part was to cut and trim the HGU hardened seals to a flat base to attach to.


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I thought about using a 3m adhesive on the mating surfaces, but they fit so nice (tight) together

that it wont be necessary.

just a note. these ear pads are a softer vinyl than some I've seen on the Roanwel headfsets.

I have seen some that look more like the HGU-9 pads.





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