Spring Driven Bows/crossbows?

[Saakee]

I did a bit of googling and couldn't find it but I was wondering if anyone out there makes crossbows that use springs behind the arrow inside of a barrel style thing?

Terry Pratchett references it in one of his novels so I'm obviously not the first person to have thought of it and wondered if anyone ever tried to market a device like it. it seems like it would be an easy way to have a rifle style setup for bowhunting.

I know there's the crossbow AR-15 upper as well but just wondering about spring driven arrows or would a spring not be able to be compressed to do enough FPS?

 

[CWL]

Wouldn't really be a crossbow if you didn't need the bow part, would it?

I think you are asking about a spring driven dart gun, or ballistic knife device.

 

[hso]

The limbs of a bow are springs, leaf springs.

Compressed coil springs wouldn't have the displacement to produce much force and wouldn't, as pointed out, be "bows".

 

[Mobuck]

I think a set of springs strong enough to produce sufficient energy to propel an arrow at a decent speed would be monstrously heavy. The containment structure would add even more weight and the length of spring action to give a decent power stroke would make the outfit about 5' long. There would also be a ferocious reverse recoil when the spring hit the end of the containment.
Spring power works for pellet guns because the spring compresses air which does the projecting. This way, the spring can have a short stroke against a piston rather than a long stroke against the actual projectile.

 

[glistam]

Compressed coil springs simply do not have the mechanical properties to propel a large object like an arrow at high velocity. The closest thing to such system is seen in air rifles that use "spring pistons." Spring pistons used a coil spring to propel a plunger (not the projectile) forward in a sealed chamber, compressing the air within and forcing it out a nozzle. It is this air expelling from the nozzle into the barrel that propels the pellet, dart or BB forward. Why the air does this and not the spring itself is a long explanation having to do with the laws of physics, compressibility, elasticity etc. that I am badly unqualified to comment on, but you get the general idea.

There are two non-bow devices I have seen that fire arrows. One is more or less a speargun, which uses elastic bands. Stretching the power source is far more efficient for accelerating to high speed due to the far greater displacement. The other is a rare prototype rifle made in Sweden the used compressed CO2, which involves using hollow arrows fitted over a long tube.

 

[heron]

You're thinking in the wrong direction, Saakee -- check out this piece of insanity, I mean genius:

http://www.youtube.com/watch?v=b8FVLJ_EEP4&feature=related

A longbow made from two scythe blades, a couple of heavy tension springs (I think old hood springs would be good) and some miscellaneous steel parts. Seems to work pretty well.

 

[Saakee]

Heron, that was cool though as I watched I was afraid the dog was going to try to leap and catch the arrow.

I asked because I was just wondering if there was some sort of very compact arrow propelling weapon that could be used for hunting. I was envisioning basically a tube with a pair of channels cut in front half or so making it in to a pair C-shaped guides for the broadhead to follow with the spring in the rear end of the tube with a trigger, winding mechanism, scope and stock of a rifle.

 

[JLDickmon]

Heron, that was cool though as I watched I was afraid the dog was going to try to leap and catch the arrow.

I asked because I was just wondering if there was some sort of very compact arrow propelling weapon that could be used for hunting. I was envisioning basically a tube with a pair of channels cut in front half or so making it in to a pair C-shaped guides for the broadhead to follow with the spring in the rear end of the tube with a trigger, winding mechanism, scope and stock of a rifle.

nah...
the broadhead would be dulled by rattling off the kerfs in the tubing, plus that would slow it down, make a busload of noise, and generally annoy your prey..

 

[heron]

I'm afraid anything you do with compression springs is going to be really noisy, at least, and have other problems, as JLDickmon pointed out.

I've thought of this same thing myself, and could never arrive at a satisfactory idea for it, though I didn't really put a lot of effort into thinking about it. Trying to make something like this -- a mechanical launcher with a narrow profile -- has a lot of problems. The typical diver's spear-gun is probably as good as it's likely to get.

I suspect you'd have a lot of trouble making it accurate without risking damage to the arrow. Now, if you want to design a whole new, purpose-built projectile for this, you might get a little further with it, but I don't know.

It's a fun idea to play with, but I'm sure that greater minds than mine have engaged the problem before, and seeing that no such products have entered the market, I'd say they failed.

The most compact devices you're likely to find for shooting arrows will be compound bows and crossbows of the latest parallel-limb configurations. They're powerful, accurate, and relatively quiet. They just cost a lot.

And as to that scythe-bow, I just hope the bowstring doesn't break while that guy has it drawn, or he'll be in for some spectacular injuries. It needs a fail-safe designed into it, though that could be quite simple. I don't like the idea of shooting through a tube, either; a slight misalignment on release could get the shooter a faceful of arrow shrapnel. It is really clever, and the idea could be carried into other designs.

 

[rcmodel]

Google "British PIAT".

It was a WWII spring loaded anti-tank weapon.
Although it did also employ a small projection charge the huge spring did most of the throwing.

rc