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French pneumatic mortars in WWI

Post questions and info about pneumatic (compressed gas) powered cannons here. This includes discussion about valves, pipe types, compressors, alternate gas setups, and anything else relevant.
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Unread postAuthor: Hotwired » Sat Mar 26, 2011 7:34 am

jackssmirkingrevenge wrote:
Hotwired wrote:Do not like the 50mm mortar.

You'd have to dump a barrel of compressed air just to fire the projectile.


This is whatthis basic diagram of the device suggests. I remember a Junkyard Wars episode where they made a bowling ball cannon with a burst disk at the muzzle *cringe*

Here's how I would make it, much more efficient and the hollow tail also provides stability:


Every time I post there's a link to a muzzle burst disk design using hollowtail projectiles :P

But still, it looks like they fill the entire tube with compressed air then waste the barrel section of it.
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Unread postAuthor: jackssmirkingrevenge » Sat Mar 26, 2011 7:41 am

You never posted damage pics :)

Hotwired wrote:But still, it looks like they fill the entire tube with compressed air then waste the barrel section of it.


The description suggests it was one of first models made and had relatively short range:

This weapon does not appear in textbooks in 1918 and likely had been withdrawn from service before the end of the conflict.
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hectmarr wrote:You have to make many weapons, because this field is long and short life
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Unread postAuthor: LeMaudit » Sat Mar 26, 2011 8:02 am

Here's the translation for those French links:

WW1 Pneumatic Weapons

This work is strictly private and restricted to our forums, as I didn't ask permission to copy the various materials. So private usage is fine I guess, but do not put this link on a page were Google or any other search engine could find it. Thanks.

If you find more French material, I'll be glad to add it and translate it as best as I can.
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Unread postAuthor: jackssmirkingrevenge » Sat Mar 26, 2011 8:14 am

Nicely done, thanks for the effort!

According to this link you posted, it seems one of the 60mm Brandts was recently fired :D
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hectmarr wrote:You have to make many weapons, because this field is long and short life
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Re: French pneumatic mortars in WWI

Unread postAuthor: jackssmirkingrevenge » Fri Oct 18, 2019 7:54 am

I found this great page that details early pneumatic weapons including the French air artillery that is the subject of this post.

Particularly illuminating is the animation of the valves of two of the French mortars.

The Brandt 60mm design is a barrel sealing coaxial piston valve that is mechanically locked by an eccentric cam:

Image

The Boileau-Debladis valve is essentially a chamber sealing pop-off valve that actuates a diaphragm once a certain pressure is reached, then rapidly re-closes which probably means it was quite an efficient device.

Image

Description of the firing sequence from the source:

"The valve is a balanced pressure design. The drawing shows it in the open position . Missing from the drawing is the lower part of the corps du canon with the sealing ring seat from the reservoir d'air.

"When the air pressure in the reservoir is low the outer piston is forced down against the seal ring by the large spring. As the air pressure increases, flowing through the restriction in the central piston shaft, the outer piston is held down against the seat by pressure above the diaphragm (barely visible in drawing). The valve opens when the reservoir pressure is enough to lift the central piston against the adjustable spring load.

"When the central piston has lifted enough for the top seal (leather presumably) to open to the ports, the pressure above the diaphragm drops rapidly and pressure from the reservoir d'air forces the outer piston up, opening the valve.

"High pressure air trapped between the restricted orifice in the bottom of the outer piston, and the central piston lower seal will keep the central piston up and the top valve open, until it escapes both to the barrel and up via the ports.

"When the central piston is able to move down (forced by the adjustable spring) and close the top ports , pressure will equalise on the diaphragm and the valve will close, ready for the next shot.

"The above probably happens fast enough to preserve a substantial amount of pressure in the reservoir d'air."
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hectmarr wrote:You have to make many weapons, because this field is long and short life
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Re: French pneumatic mortars in WWI

Unread postAuthor: Moonbogg » Fri Oct 18, 2019 10:15 am

Those are frickin awesome. My first drafting job was drawing and designing pressure relief valves for ships. They looked very much like that pop-off valve. Also, I think the French would have enjoyed the simplicity of modern barrel sealing designs that use air pressure to seal the valve. Cool to think our hobbyists have improved on designs like this.
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Re: French pneumatic mortars in WWI

Unread postAuthor: jackssmirkingrevenge » Fri Oct 18, 2019 2:18 pm

Moonbogg wrote:I think the French would have enjoyed the simplicity of modern barrel sealing designs that use air pressure to seal the valve. Cool to think our hobbyists have improved on designs like this.


I wouldn't necessarily call it an "improvement", rather a different way of doing things. Certainly it's something that is easier for a hobbyist to put together with standard parts, but on the other hand there are some downsides, for example the pilot volume represents a greater consumption of air. Also, the piston can only open as fast as the pilot volume is dumped, while the mechanical lock allows it to move freely as soon as it is unlocked.
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hectmarr wrote:You have to make many weapons, because this field is long and short life
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Re: French pneumatic mortars in WWI

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Re: French pneumatic mortars in WWI

Unread postAuthor: hectmarr » Sat Oct 19, 2019 9:41 am

It's like you say Jack. It happens that the valves operated by air pressure, spend air for their operation, regardless of the air used to propel the projectile. If the valve is opened by a mechanical, magnetic system, or something else, the air consumption will be only that necessary to drive the projectile, that is, less.
This "premise" works isolated from other contexts such as ease of construction, costs etc.
An example that has always seemed educational to me, is the case of the famous glow engine of aeromodelling 0, 49, which is a small two-stroke engine, without carburetor, (in the full sense), without rings, without bolt on the piston. .. a great simplification, which makes it possible to fly some things with an engine that is almost a "functional diagram" :shock:
To my mind, fans have opted for a solution that allows almost anyone to build a piston valve. In reality as a whole, where several factors appear apart from just performance, it is an excellent solution. :)
This "simplified" engine has a few constitutive parts, compared to a motorcycle engine, which has many more and yields more.
Performance itself is not everything. I prefer to evaluate these things based on a more general context, where aspects such as ease of construction are as important as thermodynamic performance or compressed air consumption.
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Re: French pneumatic mortars in WWI

Unread postAuthor: Moonbogg » Sat Oct 19, 2019 3:52 pm

Yes, the simplicity and avoidance of having to machine so many intricate parts came to mind. If they had the resources then it's not an issue I suppose. Less parts to fail with a simple piston might have been attractive as well. I don't know how they got their compressed air though. Probably some sort of manual pump I guess. For trench warfare, I don't think the range needed to be very extreme. Maybe a couple hundred yards? A hand pump might have done the job.
In any case, it's surprising to see something so similar to a spud gun having been used as a real mortar. It looks almost exactly like a typical barrel sealing coaxial cannon, just with a bunch of complicated parts to machine. Maybe they used a punch press or something to make it easier.
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Re: French pneumatic mortars in WWI

Unread postAuthor: hectmarr » Wed Oct 23, 2019 8:23 am

Probably with a large air pump, operated by more than one person, I don't know, but it sounds possible :roll:
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Re: French pneumatic mortars in WWI

Unread postAuthor: ToasT » Fri Oct 25, 2019 4:24 pm

jackssmirkingrevenge wrote:I found this great page


Nice find, I had looked at this thread a few months back and wondered how these actually worked.

Topically, I decided a while ago now that the game of pétanque could be vastly improved with the addition of a mortar and a bigger field of play.
Hopefully in the next few months...
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Re: French pneumatic mortars in WWI

Unread postAuthor: jackssmirkingrevenge » Mon Oct 28, 2019 7:17 pm

ToasT wrote:Topically, I decided a while ago now that the game of pétanque could be vastly improved with the addition of a mortar and a bigger field of play.


You'll definitely have those balls landing with a massive "PETANK!!!" hundreds of feet downrange, ce n'est pas exactement le cricket :D
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