Making an A-11, WWII Flying Helmet operational
Hello everyone. For the longest time, I've wanted to turn a WWII USAAF A-11 flying helmet into an operational, useful helmet using modern electronics but maintaining the look of the old helmet as much as possible. I've finally gotten around to starting that project. I've had an A-11 in decent shape for quite some time. All I had to do was to find the parts and figure out how to make it work. This thread will report on the project as it goes along.
Just a note:
If you are of the opinion that objects such as WWII flying helmets should not be permanently modified in any way, I completely understand your point of view. However this topic will not be to your liking. So I give fair warning. The modification isn't much but it's there. I'd like to keep the topic to the conversion project and not an argument over whether or not it's ok to modify a WWII USAAF helmet.
Now you can buy AN-H-15's (USAAF Summer weight cloth helmets) that have been modified with modern electronics and ANR. Cost is over $600 which is more than I want to spend.
What you need for this project is:
2 civilian 300 ohm receivers
one civilian electret microphone
modern, civilian 2-plug wire loom
WWII-era mike boom mount.
and of course the helmet. This will work for AN-H-15's as well as A-11's.
I also bought a Mike Muff as I find that helps with noise.
Here's a photo of the stuff that I bought:
I got most of it from Oregon Aero. Here are the SKU numbers:
Civilian Helmet Speakers (2) #98332
MicMuff® Microphone Cover #90015
7" Wire Frame w/Electret Mic & Cord (Black or Gray) #98303-7
3/4″ thick SoftSeal/HushKit® Combo #28034
The boom mount ("U" shaped object in the center of the photograph above) I got from some online source which I cannot remember.
But one such source is Bells Aviation.
Ok. So to begin with, the receivers that came with the helmet fit into circular slots in the oval-shaped rubber earcups on the helmet - the red arrow is pointing to the slot:
The protruding lip on the WWII receivers fit into that slot (red arrow in picture below)
However if your receivers are in the earcups, I've found that the safest way to remove them is to first take the step outlined below regarding removing the interior padding from the helmet. Then unscrew the top half of the receivers and remove it. Then remove the bottom half from the INSIDE of the helmet. The opening on the inside of the helmet is larger than the opening on the outside of the helmet. And it's easier to remove the small flat circular disk that is the bottom portion of the receiver.
Now it turns out that the modern civilian receivers fit quite handily right into that slot. In fact in the picture above, you see the modern receiver sitting to the left of the WWII version. The diameters are almost identical.
But if you put the modern receiver into the slot you see an immediate problem:
The rubber edge covers the holes into which the wires must go. Now one option you have is to cut away the rubber. And in fact there's a form of these rubber earcups - used in headsets - where that was actually done. See here:
Those ramps at the bottom edge of the hole would reveal the holes in the receiver for the wires. If you were careful you could make such ramps and the wires would have a path. This was not done on these sorts of helmets, but as I say it's not unheard of.
I elected to NOT do this for several reasons:
1) In the thread entitled:
Old RAF type leather helmet - adapting to ICOM type handheld?
Ron W correctly points out that these helmets were not made with an emphasis on noise reduction. I bet a lot of the sound you want to hear will run right out the back of the receiver.
2) I'd like some noise protection for my hearing.
3) The original helmet has the bakelite housing of the receivers sticking out the sides. I'd like to retain that look if I could.
So this is why you see, in the parts list above, the "Soft Seal Hush Kit". I got the 3/4" thick kit and the size of the earcups in the kit are slightly thicker and slightly bigger in diameter than the suede padding that originally came with the helmet See comparison in the next two photos:
So the first step is to carefully remove the suede padding from the two earmuffs on the inside of the helmet. They are held on with a very good rubber cement. If you take it slowly and carefully, you can remove the padding without damaging it or the rubber earcups at all.
Given that the Hush Kit earcups are bigger, the sides of the helmet might stick out a little more when you put it on. Some of that will be reduced when you tighten the chin strap. Also I'd imagine the suede padding was thicker originally.
Ok in the next post, I'll show how to fit the receivers into the Hush kit; how to mount the hush kit to the inside of the helmet with Velcro, and how to introduce the wiring into the helmet the Hush kit and into the receivers.
Last edited by Saville; 11-11-2016 at 05:09 PM.
GREAT project. I'm not one to object over modifying a WWII headset. It's not like there's only one or two left. In Appleton, there's an antique store selling what looks to be a complete WWII Navy headset. Cost was only about $80. I was tempted, but it wasn't my size.
Glad to see your attention to hearing protection. A lot of us old geezers wish we'd paid that much attention years ago.....
Your hush kit is the right way to go, but when I converted a Russian headset years ago, I used some left-over dense Temperfoam. Seemed to work pretty good.
Make sure you hit the leather with some leather balm. It tends to dry out and can damage more easily.
If you can find an old-fashioned shoe repair shop, they can often do things like replace broken straps or snaps.
Good luck, and keep us informed!
Anybody who objects to WWII artifacts being "modified" should waste their time trying to get a court injunction against unlimited air racing, before blubbering on at you, Saville. This is a cool project, in the true spirit of reuse/repurpose/recycle. Maybe you'll start a trend with the steampunkers and they'll be inserting all kinds of audio gear in their leather helmets...
I appreciate the comment, thanks.
Originally Posted by crusty old aviator
Other people's opinions about whether or not to modify these helmets wont' stop me - obviously...I'm going to do it.
But I was trying to do a little up from prevention of the thread getting hijacked.
Review: At this point I've removed the interior padding from the helmet, and the original ANB-H-1 receivers are in their place.
It turns out that if you leave the fully assembled receivers in the helmet, that the stacking of that plus the Hushkit makes the sides of the helmet stick out way too far from the sides of your head. This puts stress on the leather and the sewing. It's also very uncomfortable.
So bottom half of the receiver must go, and the speaker element must be removed from the top half of the receiver, and we will use only the Bakelite top half of the receiver.
The top half of the ANB-H-1's will be in place to give the helmet the original look. I intend to remove the speaker element, and stuff the cavity with some soundproofing foam to improve the noise reduction ability of the helmet. However I haven't found a way to remove the element *intact* without damaging the receiver bakelite itself. I had one receiver that was already broken and I attempted to remove the speaker element intact and it seems as if the metal contacts it's soldered to were imbedded into the bakelite when the receiver was formed. If you know of a way to remove the speaker without damaging the bakelite please let me know.
So unscrew the receiver into it's two parts. Twist out the receiver element. You have to remove it because it extends beyond the Bakelite housing as you see here:
After you do that the top portion of the receiver and the element looks like this:
Next, as I mentioned before, the old padding sits in a trench on the inside of the rubber earcup. You can see this in a photo in the first post. What we need to do is pare down the inside of the rubber earcup so that the trench no longer exists. This will allow the HushKit to sit lower in the rubber earcup and the helmet will fit more naturally.
I used a razor sharp woodworking chisel and carefully pared away the inside portion of the "trench". This is the thickest part of the earcup.
Now push the empty top half of the receiver into the hole from the inside of the helmet. Once you've pared away the trench and pushed in the top half of the receiver, it all looks like this:
Next Step - Rotate the receiver elements so that the connections for the speakers are pointed towards the back.
I've also mounted the boom mount temporarily so as to work out the layout of the wiring. It's in there with two small screws. However it will be riveted
because we don't want the pointy end of the screws ripping into the Hush Kit.
Originally the wire loom was tied to a hole in the bakelite receiver for strain relief using the insulation itself. We will do the same with some waxed string. That comes later.
Next, notice on the modern wire loom there are two rubber grommets:
This is great as we will use those for additional strain relief.
Next drill a hole in the helmet's rubber earcup for the wire loom. Drill it outboard of the edge of the bakelite receiver. I used a 1/4" bit. 15/16" might work and give you a slightly tighter fit. Push the ends of the wire loom through the hole and insert the grommet into the rubber earcup.
Here is what it looks like from the outside:
Here is what it looks like from the inside (this is BEFORE the trench was pared away - the full Bakelite receiver assembly is installed, but won't be - it'll be like the photo above):
Notice that the lip of the loom grommet is fully pulled through and engaged in the helmet earcup. One other thing to notice is that the original padding in the helmet sat in a trench in the rubber earcup. The rubber at the bottom of that trench is pretty thin. But because the old padding sat in the bottom of the trench, and the new hush kit mounted receiver is going to sit right on the old receiver, the side of the helmet will stick out more when you put it on, as described above.
Next feed the loom wires through the hole in the Hush Kit earcup that's most convenient. I used the one on the side of the cup:
Notice the velcro hooks - we will put some sticky back velcro inside the helmet to hold everything together.
Now you want to screw the ends of the wire loom into your modern 300 ohm receivers. Once that's done you slide the receiver into the blue sound attenuation foam of the hush kit. The blue foam is actually two glued layers of foam with an opening at one corner:
There's a depression in the middle of the thicker layer of blue foam. You can see one edge of the depression that the receiver sits in, in the photo above.
Lastly, push the blue attenuation foam into the Hush Kit earcup - black side out - and be sure the foam is smoothed out all the way around:
From the side, it looks like this:
Next episode we'll install the velcro, install the Mike boom, slide the mike boom into the boom mount (amazingly the modern boom fits perfectly into the old mount) and try the gizmo out.
Last edited by Saville; 11-11-2016 at 05:31 PM.
The earpiece speaker from an old "ATT rotary dial desk telephone" will work in aviation headsets. I put the quotes on there because I don't know if new production replicas will work or not, but actual old desk phone handsets from the 50's had speakers that fit and performed exactly like the ones in my 1970's vintage DC aviation headphones. Your mileage may vary.
Well I finally gave the helmet the old flight test:
Everything worked fine. There are a couple of physical issues - the chin strap is too short and the Comm cord is a little too short. I'll have to buy an extension.
Biggest problem was that the volume was way too loud. I noticed this in my P3 helmet as well.
I'm going to have to locate a volume control circuit.
You don't need much to reduce volume, just a potentiometer in line with the speakers. Try 40 ohms, I was looking through my junk box last night and happened to notice some pots that were pulled from some old stereo headphones that had built in volume adjustment, they were 40 ohm.
The problem with old telephone speakers is that they're all metal cases, quite heavy.
Ok so I took the A-11 up on a test flight yesterday with the following additional gear:
INLINE VOLUME CONTROL FOR GENERAL AVIATION HEADSET ADAPTER- PA-99
This solved the two main problems with the helmet:
1) The Oregon Aero comm cord was too short
2) I now can control the volume and not have my ears ringing after the flight
In Flight Photos soon.