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
mike boom
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:

http://i22.photobucket.com/albums/b3...Components.jpg

I got most of it from Oregon Aero. Here are the SKU numbers:


Civilian Helmet Speakers (2) #98332

MicMuff® Microphone Cover #90015
SKU 90015

7" Wire Frame w/Electret Mic & Cord (Black or Gray) #98303-7
SKU 98303-7

3/4″ thick SoftSeal/HushKit® Combo #28034
SKU 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:


http://i22.photobucket.com/albums/b3...verSlotAnn.jpg

The protruding lip on the WWII receivers fit into that slot (red arrow in picture below)

http://i22.photobucket.com/albums/b3...erLipANBH1.jpg


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:

http://i22.photobucket.com/albums/b3...iverInSlot.jpg

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:

http://i22.photobucket.com/albums/b3...140/s-l500.jpg

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:

http://i22.photobucket.com/albums/b3...Comparison.jpg

http://i22.photobucket.com/albums/b3...Comparison.jpg

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.

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!

Ron Wanttaja

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...

Quote:

---

Originally Posted by crusty old aviator

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.
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:

http://i22.photobucket.com/albums/b3...verElement.jpg

After you do that the top portion of the receiver and the element looks like this:

http://i22.photobucket.com/albums/b3...iverPulled.jpg

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:

http://i22.photobucket.com/albums/b3...fInstalled.jpg

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:

http://i22.photobucket.com/albums/b3...omGrommets.jpg

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:

http://i22.photobucket.com/albums/b3...t_Exterior.jpg


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):

http://i22.photobucket.com/albums/b3...nd_Grommet.jpg

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:

http://i22.photobucket.com/albums/b3...Loom_holes.jpg

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:

http://i22.photobucket.com/albums/b3...it_Opening.jpg


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:

http://i22.photobucket.com/albums/b3...FitsBetter.jpg

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.

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.

Ok so far we have accomplished:

Removing the old padding
Drilled a 1/4" hole for the wire loom
Flattened the trench on the inside of the rubber earcup

So for today's installment we rivet the mike boom mount to the outside of the right Earcup:

http://i22.photobucket.com/albums/b3...derRiveted.jpg

Next we thread the wire loom into the rubber earcup from the outside, making sure that the rubber grommet is fully engaged in the earcup:

http://i22.photobucket.com/albums/b3...nd_Grommet.jpg

Next we wire the loom to the modern receiver, and insert the receiver into the blue foam hushkit holder. Then we slide the blue foam Hushkit holder into the Hushkit earcup.

Next we install the upper half of the bakelite receiver housing in the rubber earcup.

Lastly We aply the "rug" part of the hook and rug velcro to the "hook section that's on the back of the Huskit earcuo:

http://i22.photobucket.com/albums/b3...140/Velcro.jpg


Remove the plastic backing off the velcro and install the Hushkit earcup where it belongs pressing down hardto get a good adhesion.

The inside is complete.

Next we slide the Mike Boom into the Mike boom mount and connect the Mike plug to the mike jack:

http://i22.photobucket.com/albums/b3...mInstalled.jpg

Ok time to test the receivers. I plugged the rig into my handheld radio and tuned to the weather channel. Receivers worked like a champ.


Be sure you've threaded the wire loom into the 3 hold down straps in the back of the helmet. Also thread the goggles strap through there as well.

http://i22.photobucket.com/albums/b3...ruHolddown.jpg

So now the next step is to take it to the plane and give it a Comm check.

After that, if all checks out, I'll be tying off the wire loom to the backs of the Bakelite receiver housings.

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:

https://www.aircraftspruce.com/catal...pilotUSA43.php

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.

Well after some comparison flight tests I find that the A-11 (and AN-H-15 for that matter) rubber earcups do not block cabin noise as well as a decent set of passive noise reduction headphones.

So my next experiment is to remove the rubber earcup/receiver holders from an AN-H-15 and replace it with plastic oval earcups that are roughly the same size and shape.

My question is this:

Is there any sound absorption material places inside the plastic "cans" of modern headsets? I don'e mean the earseal, but, rather, between the speaker and the plastic can the seals are mounted to.

Thanks!

I think the interior soundproofing might vary by brand. When I swapped speakers in a Rugged Radio headset a couple of years back, I don't recall any major stuffing in the cups. Looking at pictures, I see a sort of doughnut-shaped foam ring that went behind the speaker. Don't recall anything else. You can see the ring on the top left of this picture:
http://www.bowersflybaby.com/tech/av_headset.jpg

You can see the ring around the speaker in the cup.

You could try stuffing some sound-deadening material inside the cups. It's probably the easiest way to go, as long as you can find a place that'll sell small quantities. I once used little blocks of dense temperfoam to try reduce the noise level. Seems to help a bit, but never did a scientific measurement.

The second approach is to remove the speakers ("receivers") and install a set of ear buds, instead. Check out this picture:
http://www.bowersflybaby.com/stories/helmet2.jpg
If you look carefully at the bottom center, you'll see the ear buds that dangle out of the original ear cups. These dangle down about ~5 inches below the helmet...set the helmet lightly on your head, insert the buds, and pull the helmet down gently over them.

Now, civilian ear buds don't have the right impedance, so you need an adapter. This is just a simple, tiny audio output transformer with a 300-600 ohm primary and an 8-ohm secondary. Used to be able to buy them at Radio Shack, but online places like Digi-Key and Mouser electronics sell them for ~$4 or so. Here's the diagram to make it work:
http://www.bowersflybaby.com/tech/bud_to_av.jpg
The part number that I use is right on the drawing....XICON 42TL004.

These transformers are small, and easily built-in to tiny boxes. You can build a separate adaptor as show above, or just build it into the headset itself. If you can't find one, drop me a message and I'll stuff a couple of spares in an envelope and send them to you. I made a lot of runs to Radio Shack before it closed. :-)

The photo that shows the ear buds has the transformer located between the lining of the helmet and the leather, right at the nape of the neck. This is also the helmet that I stuffed the dense temperfoam into the cups to add to the passive attenuation.

The neatest thing about this approach? They make ANL ear buds! But I use Plugfones, which are foam ear plugs with speakers inside. They have 24 dB of passive attenuation (same as a passive headset) and cost $25 a set.

Ron Wanttaja

Quote:

---

Originally Posted by rwanttaja

I think the interior soundproofing might vary by brand. When I swapped speakers in a Rugged Radio headset a couple of years back, I don't recall any major stuffing in the cups. Looking at pictures, I see a sort of doughnut-shaped foam ring that went behind the speaker. Don't recall anything else. You can see the ring on the top left of this picture:
http://www.bowersflybaby.com/tech/av_headset.jpg

You can see the ring around the speaker in the cup.

You could try stuffing some sound-deadening material inside the cups. It's probably the easiest way to go, as long as you can find a place that'll sell small quantities. I once used little blocks of dense temperfoam to try reduce the noise level. Seems to help a bit, but never did a scientific measurement.

The second approach is to remove the speakers ("receivers") and install a set of ear buds, instead. Check out this picture:
http://www.bowersflybaby.com/stories/helmet2.jpg
If you look carefully at the bottom center, you'll see the ear buds that dangle out of the original ear cups. These dangle down about ~5 inches below the helmet...set the helmet lightly on your head, insert the buds, and pull the helmet down gently over them.

Now, civilian ear buds don't have the right impedance, so you need an adapter. This is just a simple, tiny audio output transformer with a 300-600 ohm primary and an 8-ohm secondary. Used to be able to buy them at Radio Shack, but online places like Digi-Key and Mouser electronics sell them for ~$4 or so. Here's the diagram to make it work:
http://www.bowersflybaby.com/tech/bud_to_av.jpg
The part number that I use is right on the drawing....XICON 42TL004.

These transformers are small, and easily built-in to tiny boxes. You can build a separate adaptor as show above, or just build it into the headset itself. If you can't find one, drop me a message and I'll stuff a couple of spares in an envelope and send them to you. I made a lot of runs to Radio Shack before it closed. :-)

The photo that shows the ear buds has the transformer located between the lining of the helmet and the leather, right at the nape of the neck. This is also the helmet that I stuffed the dense temperfoam into the cups to add to the passive attenuation.

The neatest thing about this approach? They make ANL ear buds! But I use Plugfones, which are foam ear plugs with speakers inside. They have 24 dB of passive attenuation (same as a passive headset) and cost $25 a set.

Ron Wanttaja

---

Hi Ron,

Yeah if you look at the Oregon Aero upgrade kits, they give you a foam pocket into which you slide the speaker, and the speaker is suspended in the foam ear ring. They don't mention anything about any sound absorbing foam in the plastic cup. I have some high density but thin foam laying around I may put a couple layers in the plastic cup.


How difficult , and expensive, would it be to add a pot to that circuit so that you'd also have some volume control?

Quote:

---

Originally Posted by rwanttaja

I think the interior soundproofing might vary by brand. When I swapped speakers in a Rugged Radio headset a couple of years back, I don't recall any major stuffing in the cups. Looking at pictures, I see a sort of doughnut-shaped foam ring that went behind the speaker. Don't recall anything else. You can see the ring on the top left of this picture:
http://www.bowersflybaby.com/tech/av_headset.jpg

You can see the ring around the speaker in the cup.

You could try stuffing some sound-deadening material inside the cups. It's probably the easiest way to go, as long as you can find a place that'll sell small quantities. I once used little blocks of dense temperfoam to try reduce the noise level. Seems to help a bit, but never did a scientific measurement.

The second approach is to remove the speakers ("receivers") and install a set of ear buds, instead. Check out this picture:
http://www.bowersflybaby.com/stories/helmet2.jpg
If you look carefully at the bottom center, you'll see the ear buds that dangle out of the original ear cups. These dangle down about ~5 inches below the helmet...set the helmet lightly on your head, insert the buds, and pull the helmet down gently over them.

Now, civilian ear buds don't have the right impedance, so you need an adapter. This is just a simple, tiny audio output transformer with a 300-600 ohm primary and an 8-ohm secondary. Used to be able to buy them at Radio Shack, but online places like Digi-Key and Mouser electronics sell them for ~$4 or so. Here's the diagram to make it work:
http://www.bowersflybaby.com/tech/bud_to_av.jpg
The part number that I use is right on the drawing....XICON 42TL004.

These transformers are small, and easily built-in to tiny boxes. You can build a separate adaptor as show above, or just build it into the headset itself. If you can't find one, drop me a message and I'll stuff a couple of spares in an envelope and send them to you. I made a lot of runs to Radio Shack before it closed. :-)

The photo that shows the ear buds has the transformer located between the lining of the helmet and the leather, right at the nape of the neck. This is also the helmet that I stuffed the dense temperfoam into the cups to add to the passive attenuation.

The neatest thing about this approach? They make ANL ear buds! But I use Plugfones, which are foam ear plugs with speakers inside. They have 24 dB of passive attenuation (same as a passive headset) and cost $25 a set.

Ron Wanttaja

---

Ron I love our work. Have you ever thought about doing a workshop at Oshkosh on things like this? You have done a lot of specialty projects for your Experimental that are just awesome. Maybe you have done this already and I am way behind. Keep up this great work and thanks for sharing what you have done. That hand held radio mounted in a panel. Leaves me speechless. As does all your work.

Quote:

---

Originally Posted by Saville

How difficult , and expensive, would it be to add a pot to that circuit so that you'd also have some volume control?

---

You can buy inline volume controls for ear buds pretty cheaply... just enter "volume control" on Amazon. Not sure how they'd work on a 300-ohm aircraft set, but it'd be easy enough to try.

When I mounted my ICOM in the panel, I added a simple potentiometer for volume control. You can see it in this diagram:
http://www.bowersflybaby.com/tech/rad_plug.jpg
However, I have not been too pleased with it. IIRC, it's a 5000-ohm pot (lowest I could find locally in the physical size I wanted) and it has no real dynamic range... headphones are silent until it gets to the last few degrees of adjustment, then you have to adjust it carefully to get a particular setting. Fortunately, I usually run it at full volume anyway, and flick it down only when I'm away from the airport and don't want the distraction.

After more than ten years of use, it's started to get a bit scratchy and finicky. I recently bought a selection of small LOGARITHMIC pots. Next step is to use my test setup in the shop to experiment and come up with something that works a bit better. I'm contemplating some electrical changes to my airplane, and it would be the perfect time to take care of this.

Ron Wanttaja

Quote:

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Originally Posted by 1600vw

Ron I love our work. Have you ever thought about doing a workshop at Oshkosh on things like this? You have done a lot of specialty projects for your Experimental that are just awesome. Maybe you have done this already and I am way behind. Keep up this great work and thanks for sharing what you have done. That hand held radio mounted in a panel. Leaves me speechless. As does all your work.

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Thanks, Tony. I don't come to Airventure very often...every ten, fifteen years or so...and I suspect that a forum on accident statistics might be more of an attraction. Or as someone once told a writer friend of mine when he held a forum, "We came to see if you're as funny to look at as you are to read."

Ron "Funnier in my case" Wanttaja