Underwater Ballistics

[918v]

As many of you well know, the most efficient profile for traveling underwater is a teardrop. The most efficient profile for traveling through the air is a spitzer. The two designs come into conflict when developing a multi-purpose round.

Hornady boat-tailed 147gr XTP and FMJ bullets can be loaded backwards for underwater shooting, yet the nose of such a round still maintains some ballistic efficiency. The boat-tail becomes the nose. Have any of you tried it?

[Steve Koski]

No, but we got some of these for easter, and have been having a ball with them at the rec center.

http://pooltoy.com/ortoy.html

Them buggers go forever!

[ISUSteve]

Teardrops are also the best for traveling through air. Thats why drops make the drop shape, because it is the most efficent.

[Steve Koski]

I don't think so. If you could talk the water into holding a different profile, water drops would fall faster. Could be friggin' deadly.

[ISUSteve]

Teardrop are the most efficent. A spherical shape provides good approch streamline charectistic, but the air becomes turbulent on the departure. A pointed object almost always cause turbulent airflow around the entire surface of the object, increasing drag. The best is a rounded front, which provides laminar flow, and a tapered back. This allows a streamline for the air to come back together, eliminating a turbulent airflow. This is all below the speed of sound. Once you reach Mach 1, it all changes.

[MakeMineaP99]

Exactly. You need to run the calculations and deminsional analysis before you finalize a design.

What's the flow?
Boundary layer?
Turbulet?
Compressible?
Attached shock?
Detached shock?
Oblique?

I hated fluids!

[ISUSteve]

I'm in a fluids class right now. Its easy, but not fun. I was in aerospace before I switched to mechanical. Just liked cars more than planes.

[918v]

The only thing that's bothering me is whether the hollowpoint of the XTP will open-up in the process.

[MakeMineaP99]

I'm in a fluids class right now. Its easy, but not fun. I was in aerospace before I switched to mechanical. Just liked cars more than planes.

Fluids is very important in vehicle design.

If fluids is easy, I'll send you my fluids professor, he'll own you, every class.

<---Finishing his thesis at an auto school.

[Tailgunner]

<--will sit back and watch while you 2 discuss theoritical ballistics, and fluid flow, in the conditions I play with at work IE: down into the 10-6 Torr range.

[damndirtyape]

My cat's breath smells like cat food.

[918v]

Hey!

Don't make fun. You just may find yourself shooting at stuff in the swimming pool one day.

[MakeMineaP99]

<--will sit back and watch while you 2 discuss theoritical ballistics, and fluid flow, in the conditions I play with at work IE: down into the 10-6 Torr range.

Naw, you should get into the discuss. You can probably play engineer better than I can. :biggrinjester:

[MakeMineaP99]

Hey!

Don't make fun. You just may find yourself shooting at stuff in the swimming pool one day.

Well, then I'll get me a spear gun.

[918v]

Does your spear gun come with a hi-cap magazine?

[AdamN]

A stick of dynamite or an electrical current would be more effective

[918v]

What if you're in the water?

[AdamN]

Get out first

[ISUSteve]

or sit in a metal boat

[918v]

It is impractical to have a metal boat in the pool.

[MakeMineaP99]

Alright, use a fiber glass boat.

[AdamN]

Rubber dingy

[Steve Koski]

My cat's breath smells like cat food.
Thanks Ralph. You can sit down now.

[Steve Koski]

I'm in a fluids class right now. Its easy, but not fun. Wow, all those partial diff eq's kicked my butt!

[Steve Koski]

Then why are subs and torpedoes so much longer than a sphere? Seems that if a sphere-ish tear drop shape was best, our boomers would be big teardrop shaped balls with tails. Instead, they look more or less like the "toypedo" that I posted.

They do have a sphericalish nose.

[AdamN]

When you have to carry people, or explosives some compromises to someones idea of a "perfect" shape are made. The same reason airplanes are not always a "perfect" shape

[ISUSteve]

They are long to get more crap inside. The back is tapered though to allow for the water to come back together smoothly. The prop in the back causes a little problems. The big thing with subs is that you really don't want turbulence. TUrbulence can increase the chance of cavitation and that can be picked up sonar.

[Tailgunner]

Let's see, the reason a water drop forms a sphere is surface tension and that a sphere has the smallest surface area to volume ratio. A tear drop shape is a water compromise between round and wind resistance.
Ref torpedos, actually some of the fastest ones out now use a standoff flat disc designed to INDUCE cavitation that in turn reduces drag along the front 2/3's of the torp, (see "super cavitator"). There is also a DG solid bullet that uses the same princaple to maximize penatration on "meat" targets.

Subs use the rounded / spherical shape more as a water pressure resistance measure than as a "drag reduction" design (subs, and even torps are relitivly SLOW moving when compaired to a "powder launched" projo). A "fast" torp @ 60mph is only moving 88fps, vs something as slow as a 45ACP that's launching at 880fps (or for the tech guys, a full order of magnatude faster).

The biggest obsticle to overcome in underwater stability is the twist rate of the barrel (denser medium = higher spin rate required), you would be better off using a smooth bore FSDS type of projectle, which combines the benifits of a self stabilizing projectle AND a much lower resistance to forward movement.

[MONTEGOD7SS]

Just get ya one of these and be done with it.

http://www.enemyforces.com/firearms/aps.htm

[MakeMineaP99]

TG, Would that be first or second order differential equation? :supergrin:

[kidcop]

Glock claims their pistol can be fired under water. I also know the bullet will go about 8 feet maybe.

[ISUSteve]

Glock claims their pistol can be fired under water. I also know the bullet will go about 8 feet maybe.

But you have to have the hydro-cups!

[Tailgunner]

TG, Would that be first or second order differential equation? :supergrin:

First order Knuckle dragger thinking :animlol:

Some questions about the bullet answered here (Norbert is the designer): http://www.grosswildjagd.de/update.htm

http://www.grosswildjagd.de/SuperPenetrator%20Update%20-%20The%20Accuratereloading%20Forums-Dateien/superpea.jpg


There is a discussin of the torp design (and a bunch of "long hair" math stuff( here:
http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6VJS-4GP7PF2-1&_user=10&_rdoc=1&_fmt=&_orig=search&_sort=d&view=c&_acct=C000050221&_version=1&_urlVersion=0&_userid=10&md5=06bfecccd3d9c60d37fa5688d888fe71