Anyone launcing from UNDERWATER?

Just got to thinking of a Polaris like launch, I was wondering if it had been done already.
Some reference pix:
<http://www.multiwebs.net/pr/pic-009.html
<
http://roosevelt.larryshomeport.com/assets/images/polaris_A3-a.jpg
TBerk
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I've launched small stuff from underwater (13mm), and I've done underwater static tests of blackpowder engines up to E9s. They all worked fine except one of the E9s that was probably sitting in the water too long and didn't light.
Joseph Nicholas

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Someone posted some info a while back about their experiments with high power underwater launches, from as much as 100 feet deep:
http://www.maxthrust.net/displayarticle209-mode=thread.html
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RayDunakin wrote:

That was me. Not doing that anymore due to the high cost of the rockets/engines, combined with my somewhat altered spending priorities these days. Any way's, here's the advice I can offer if you ant to go a little deeper then 4-5' with little estes engines:
1) Do not use paper or wood. They'll soak up water (yes, even if you paint it), become weak, and immediately turn into pulp the moment you launch.
2) Build your rockets from plastic and fibreglass - lots of it. Water is about 96 times more dense then air so you'll need much greater structural integrity to prevent your rocket from dyeing during launch. On top of that you must not only design your rocket with a lot of front-rear strength, but a lot of strength around the circumference. Pressure increases dramatically as you descend into the water, with pressure increases of 1ATA every 10m/33'. Not enough lateral strength and your rocket will get crushed before you even launch!
3) Learn a little about hydrodynamics. As it turns out the shapes which are the most efficient for rockets in the air are not the most efficient shapes for rockets underwater. Think torpedo - that's the most efficient shape for underwater travel. Short, squat, hemispherical nosecone. I've yet to find a modelling program which can determine the "aerodynamics" for a rocket underwater, but I found that the minimal fin surface for air flight is more then adequate for underwater. But keep above this minimum, otherwise the rocket won't be stable once it breaches.
4) Power is everything. As water is ~96x more dense then air it takes a lot more powerful engine to get things done. I hate to make generalities, but we found "in general" that for every 660m/2000' an engine could propel a rocket through the air it could propel a rocket 3m/10' through the water with sufficient velocity to breach and fly a short distance. That's right, you get about 1/200th the distance you would in the air. That parasitic drag is a real bitch. Also, longer burning engines are better. As water is quite dense parasitic drag becomes a real problem. The added thrust of a quick burning engine can be countered completely by the increased drag found at higher velocities.
5) Supercavitation can dramatically overcome much of the drag, but supercavitation is difficult to achieve, even harder to maintain, and puts tremendous stress on the rocket. Although we had a great deal of success in achieving cavitation (I don't think we ever hit supercavitation) it was difficult, expensive, and cavitators rarely lasted more then one launch.
Any way's I posted quite a bit here, search for my name plus "supercavitation" in google groups and you should pull up most of what I wrote. Any way's our deepest "successful" launch was from 36m (110'). When I say successful I mean the rocket breached - in this case about 4m/12' out of the lake. The rocket then fell into the lake and the recovery charge blew the rockets to pieces. Oh, that brings up point 6:
6) Make sure the recovery charge doesn't go off underwater. For some reason the amount of charge most of us would use for a recovery system blows rockets to pieces underwater. Not really too sure why, but we saw it consistiently with rockets that breached, but fell back to the water before their recovery charge went off.
Bryan
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This should be in the FAQ
--
Jerry Irvine, Box 1242, Claremont, California 91711 USA
Opinion, the whole thing. <mail to: snipped-for-privacy@gte.net>
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Bryan, do you have any pics available of the rockets you built for underwater launching? Or pics of the cavitation nosecones?
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RayDunakin wrote:

I didn't keep much of that kind of stuff - these experiments were done in co-operation with some friends of mine working on their engineering grad projects. I was basically there as I had a great deal of experience building rockets/engines, as well as was a certified SCUBA diver. My only role with the cavitators was to glue them ontop of the rockets I built ;-) Unfortunately, all of this was done before I had a digital camera so the number of photo's I took was rather limited. I used to have a series of images captured from my old VHS camcorder. The quality was crap, but you could see the rocket exit the lake and fly into the air.
Any way's I'll look through my files to see if I can dig up a photo that shows that kind of detail, and Ill see what my friends have on hand, but for now I could perhaps give you a physical description:
We tried two types of cavitators, a "recessed cone" cavitator and a "ball and gear" cavitator. The ball and gear type of cavitator is probably the easiest to describe, but had the poorest performance underwater. Basically these cavitators consisted of a series of thick arms extending radially from a central mounting point (like a gear with long teeth). At the end of each arm was a round ball. These cavitators basically worked by forcing a "hole" through the water. The main problem was that they are extremely difficult to build strongly enough - most of them either lost an arm or had all of the arms bend back onto the body during flight. Loosing an arm meant the rocket was destroyed, as the uneven pressure on the cavitator was sufficient to snap the rocket like a twig.
The recessed cone cavitator is a little harder to describe and build, but works a lot better. Basically these cavitators look like the front of a jet engine - there is a central cone surrounded by a curved "wall". At the base of the cone, where it met the wall, there was horizontal slits through the wall. Basically these cavitators work by accelerating the water and then passing the high-velocity water through the slits at extremely high speeds. In essence the water would enter the top of the cavitator, and as it moved through the chamber would be accelerated due to the cone approaching the wall - basically the same thing that happens in the throat of a rocket engine. The water would then exit from the bottom of the cavitator through the slits - the velocity of the water was sufficient to drop the water's pressure low enough that the water would vapourize. Vola, rockets surrounded by a "chamber" of water vapour.
One thing I didn't note in my original post is that the type of thrust profile you need to make cavitators work is a little different then a conventional underwater rocket. You still want a relatively long-burning rocket, but you need to burst of thrust at the beginning to get the rocket moving fast enough for the cavitators to kick in. We approached this by using clustered engines - we'd have a large, long burning engine for the main, and two or three (and once four) small, quick burning engines to get the whole thing moving. Obviously this causes a lot of extra engineering problems, especially coming up with a way to reliably set off all engines at the same time. Lastly, all attempts we made at staging were essentially unsuccessful. We simply couldn't come up with a staging device that was strong enough for underwater use that would reliably stage.
Bryan
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On Mon, 15 Nov 2004 20:00:56 -0700, Bryan Heit
Sorta the same reason you never fire a rifle with an obstruction in the barrel or with the muzzle submerged. Not sure of the exact physics and/or hydrodynamics, but a recovery charge that will properly fire a cone/chute at 1AT WILL, in a Murphyesque fashion, find the next weakest point of the structure and blow through it due to the overpressure.
And PLEASE don't test that theory with Pappy's old deer piece...do you really want to be in the next edition of the Darwin Awards?

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On Mon, 15 Nov 2004 20:00:56 -0700, Bryan Heit

Here's a guess at a solution: assuming that the main engine is powerful enough, might it be possible to use a very small, low-thrust engine in the nose facing FORWARD, possibly with some suitable multi-exit venting surrounding the nose, to generate a gas layer to stream around the body of the rocket while in the water? Sure, it'd rob you of a little net upward thrust, but you might make that back and more by reducing underwater drag.
chris
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] chris m
] boulder, colorado
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In the 70s, someone did a Polaris super scale at a naram underwater.
Bob should remember who it was, I saw a picture of the rocket in the 'pail' in an old model racketeer.

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The assumption bing that Bob still has a memory.....
Those "Happy Meals" are arterial concrete... B^P
| > | > | > Just got to thinking of a Polaris like launch, I was wondering if it had | > been done already. | > | > Some reference pix: | > | > <http://www.multiwebs.net/pr/pic-009.html | > <
http://roosevelt.larryshomeport.com/assets/images/polaris_A3-a.jpg
| > | > | > TBerk | |
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Same 2 u :-)
    Bob Kaplow    NAR # 18L    TRA # "Impeach the TRA BoD"         >>> To reply, remove the TRABoD! <<< Kaplow Klips & Baffle:    http://nira-rocketry.org/LeadingEdge/Phantom4000.pdf www.encompasserve.org/~kaplow_r/ www.nira-rocketry.org www.nar.org
I support drug testing. I believe every public official should be given a shot of sodium pentathol and ask "Which laws have you broken this week?".
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There was an article about under water launching in an Estes Model Rocket news back around 1963 +/- a year or so. The rocket was similar to an Astron Scout, but without the vent porthole.
Back in the 70s John Kalb of Ft. Wayne built a Super Scale Polaris launched from an underwater submarine.
Many other references in ancient literature.
    Bob Kaplow    NAR # 18L    TRA # "Impeach the TRA BoD"         >>> To reply, remove the TRABoD! <<< Kaplow Klips & Baffle:    http://nira-rocketry.org/LeadingEdge/Phantom4000.pdf www.encompasserve.org/~kaplow_r/ www.nira-rocketry.org www.nar.org
I support drug testing. I believe every public official should be given a shot of sodium pentathol and ask "Which laws have you broken this week?".
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TBerk wrote:

Just got to thinking of a Polaris like launch, I was wondering if it had been done already. <<<
It's come up a number of times on rmr. I'm finally learning to just google reference something I already wrote than to write about it again. Check out the first three hits on this search:
        http://tinyurl.com/7xy9l
Since I hate it when people post links and NOTHING else, here's a copy of the first hit (most recently written) below:
- George Gassaway
From:<A HREF="http://www.google.com/groups?hl=en&amp ;lr=&amp;q=author:gcgassaway%4 0aol.com+"> GCGassaway</A> (<A HREF="mailto:gcgassaway%40aol.com"> snipped-for-privacy@aol.com</A>) Subject: Re: Underwater launch? View:<A HREF="http://www.google.com/groups?hl=en&amp ;lr=&amp;threadm 01020901492 4.09393.00000159%40ng-mm1.aol.com&amp;rnum=1&amp;prev=/groups%3Fq%3Dunderw ater%2Blaunch%2Bgassaway%2Bgroup:rec.models.rockets%26hl%3Den%26lr%3D%26sc oring%3Dr%26selm%3D20010209014924.09393.00000159%2540ng-mm1.aol.com%26rnum %3D1"> Complete Thread (33 articles)</A> <A HREF="http://www.google.com/groups?selm 010209014924.09393.00000159%40ng -mm1.aol.com&amp;output=gplain">Original Format</A> Newsgroups:<A HREF="http://www.google.com/groups?hl=en&amp ;lr=&amp;group=rec.models.rockets"> rec.models.rockets</A> Date: 2001-02-08 22:49:38 PST
snipped-for-privacy@r0dentgolf.com (R0dent) wrote:

A scale Polaris would be cool....<<<
Bob Parks wrote an underwater rocket article over 30 years ago in Model Rocketry Magazine. He used a semi-scale Polaris based on an Estes BT-60 tube. It used rear-ejection, solving the problem of the nose cone to body joint. For the ignition problem he sealed over the bottom of the engine and igniter with wax.
The launcher was submerged into shallow water in a pond or lake, with a few inches of rod sticking out of the water.
There were some other people who did underwater lances too around that time, I do not know how many of those were parallel developments and how many were inspired by his article. Most of the ones other people did made use of barrels or other large containers filled with water, at a club’s regular launch site, rather than using a body of water. One such used a tank that had a large clear plastic (possibly plexiglass) viewing window in the side so the ignition could be seen.
I tried my own around 1972 or 73. Inspired by Parks article, but using a different method. I used the Dry Silo method, using a 2.5" diameter 36" long plastic tube. The tube floated upright, with an anchor and line holding it a foot or so under the surface. The top was sealed with 1/2 mil mylar, and lots of clay applied to the top outer end of the tube so that the mylar could be pressed over it and rubber bands tightly wrapped over the sides to further seal the sides of the mylar.
The rocket was very non-scale. It was a model with about 12-15" of BT-20. The fins were about 3/4" or 7/8” by 9-12". Attached with the 3/4" -7/8” being the span and the 9-12" being the chord. Only the ged a bit. They were far longer than thy needed to be to make it stable but the extra length helped align the model inside of the tube.
The tip of the nose cone had a short toothpick attached to it so it would pierce easily into the mylar, to make it start to rip. Once mylar starts to rip it tears easily. One time the anchor was not heavy enough, so the launch tube floated an inch or two above the surface. Launched it anyway. Looked at Super-8 film of that launch and found that the mylar actually burst 2-3 frames before the rocket flew out. It turned out the mylar burst from engine exhaust pressure before the rocket moved up enough to pierce the mylar.
The mylar seal was not perfect, it leaked a bit. A few attempts that involved delays of minutes underwater sometimes came to a soggy end. I wanted to add a water sensor but at the time didn’t know enough about electronics to come up with something very suitable.
- George Gassaway
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we did some in Iowa years ago from a 4 inch PVC pipe with saran wrap over the top worked about 50% but was fun to try and sure spooked some ducks? Unintentionaly of course.

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There was/is a video file available from www.maxthrust.net called 'junior missile men' which at one point showed an underwater launch in a clear container, not more than a couple of feet deep. Not sure of any details, but if you have/can find the file its a nice video to watch.
Niall
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