Underwater MR launch!

[50+AirYears]

Found an interesting little idea in an engineering mag I get at work. Check out www.designnews.com and go to their Gadget Freaks menu. There is a nice how to for underwater launch of a model rocket. Almost like a Posieden missle. The may have some other relevant ideas in the GF archives.

 

[Micromeister]

As has been talked about in the thread in the low power section about this same article. Launching Mod-rocs from under water isn't anything new, many different sizes shapes and configurations have been flown starting in the early 70's (see the article in the model rocketeer from early 1970).
If you really want to do something that involves a bit more engineering and electronics to water launches try modeling this real missile for around the same era .
Project Hydra is one of the many "Major Launcher/missile projects sitting half done in the shop.... it either needs a larger model or smaller elecronics package and power source to float the entire system simulating the real missile
Data on this project is almost as scarce as folks willing to try modeling it
Please let me know if you'd be interested in trying or help out completing this project

 

[Pem Tech]

Hey, I would be interested in whatever info you have on Hydra.

I am sensing a scratchbuild in my future.......

 

[Micromeister]

Originally posted by Pem Tech
Hey, I would be interested in whatever info you have on Hydra.

I am sensing a scratchbuild in my future.......

Basicly the above photo and some very sketchy dimensions. I was hoping others out there might come up with a good bit more scale data and maybe a color pic.
This project was put on hold about a dozen years ago (the prototype model and launch rig sank) Must have sprang a leak before I could get back to shore to push the button
I started to rebuild the launcher float platform but never got around to rebuild the model..
This time I want to build the model Larger (BT-50 Last time) either selfcontained free floating or with a lighter launch rig and/or maybe some sort of RC system rather then the very thin wire I tried back then. Should have been testing in shallower water also...Lake Anna get Deep real quick! never did salvage the first model or rig when the telephone ga wire parted trying to haul the submerged thing back to shore

 

[Bigander]

Sealed container underwater. Compressed air shoots it out of container. Have pressure sensors on the walls of the rocket to detect the change in pressure from water to air. Engine seal has a rope attached to the silo so that it is pulled off just as rocket comes out of water. The silo part should have an o-ring to help seal it until the rocket is actually launched.

 

[jraice]

I have a few points... Dont think you would need a rope to pull the motor seal out... You can make seals that will take the pressure of submerging but will burst when the motor ignites.

Secondly, why not ignite the motor underwater? Isnt that how it was done in the article? I dont know about composite motors but if you can get a motor to light fast enough, well pressurize fast enough (BP motors?) then it should keep all of the water out.

I would assume if you could design a seal that doesnt break until a specific PSI (just under the motors operating pressure perhaps) it would burst right as the motor actually started thrusting, and from there you should get out of the water rather quickly.

 

[50+AirYears]

The Design News concept uses a sealed rocket with an on-board ignition system triggered by a reed switch and a magnet. The photos in the site show the rocket being launched fom a normal launch rod submerged in a plastic cylinder of water. Ignition blows out or off a waterproof end cap over the nozzle. Ignition is accomplished by bringing a magnet up to the specific spot on the rocket.

A simple starting point for growth.

 

[jraice]

thats what I thought, probably is though is that composite propellants have a tendency to take much longer to come up to pressure and perhaps water would be allowed into the motor if it took to long...

but if somebody could attemp this with a larger MPR rocket that would be very cool...

 

[Bigander]

Originally posted by jraice
I have a few points... Dont think you would need a rope to pull the motor seal out... You can make seals that will take the pressure of submerging but will burst when the motor ignites.

Secondly, why not ignite the motor underwater? Isnt that how it was done in the article? I dont know about composite motors but if you can get a motor to light fast enough, well pressurize fast enough (BP motors?) then it should keep all of the water out.

I would assume if you could design a seal that doesnt break until a specific PSI (just under the motors operating pressure perhaps) it would burst right as the motor actually started thrusting, and from there you should get out of the water rather quickly.

I was thinking OF a more Complicated design. Thats how i beleive the navy launches stuff such as ICBM's out of the subs. I figured the water puts a lot of drag on the rocket compared to the air. So if u push it out with the compressed air first u would get less drag allowing better performance.

 

[jraice]

a lot of compressed air...

Is this really how it is done with navy vehicles? I dont know how it is launched from subs but the tomohawk uses a rocket motor booster to get it up to speed and then a turbine engine. So if the main performance (range factor) is the drag while the turbine engine is running, and the rocket engine is just there to get it up to speed, I see no reason why that missile couldnt use the rocket engine to leave the water, then accelerate a bit before ejecting and switching to jet engine power.

 

[Micromeister]

The biggest problem with the submerged ignition system is keeping the model on the base until the motor ignites. Sealing the model for these very simple launches as shown in the video could have been do much easier by simple sealing of the igniter/connections in wax. Magentic/reed switch operation is simple unnecessary, while requiring the operator to be WAY to close (inside the 15 foot ring) to the model.
Standard controller systems have worked wonderfully for these easy underwater launches for many years. Keeping the model on the bottom is the bigger problem. ususally have to have some type of balanced retainer system just strong enough to hold the boyant model down until the motor ignites

Bigender:
Yes the Navy uses compressed air to Launch all the SLM's, it actually throws the missiles into the air where the motor is fired. but as Jarice mentioned that would take a huge mount of pressure...I'm not sure our models wouldn't be crushed in the precess. Launching thur even very thin foam caused damage to models. so the pressureized silo just seems to have way to many problems. Using a Open silo could certainly be done.

 

[jraice]

Assume that stands for sea launched missiles? So a tomohawk launched from a submarine would have to go, compressed air, solid rocket motor then turbo jet? Interesting, sounds like a complex launch added to an already complicated machine (and expensive at $800,000 a piece!!!)

 

[Micromeister]

Jarice:
Not exactly clear which way tomahawk cruise missles are launched. I got the impression from some Navy buddies they were launched torpedo style which is also compressed air to start from the boat...but thur a different system starting out nearly horizontally... I may be completely wrong on this...I'm sure someone can correct the misconception?
My earlier post was referring to the sub launched Polaris, Trident and Poseidon type ICBMs, Launched from the on-board silos in the backs of the subs.

 

[50+AirYears]

According to some of the Discovery or Nova programs on sub-launched missles, smaller missles like the SLM and the Subroc are fired from the torpedo tubes using the normal compressed air method. The Rocket booster is fired while underwater after some distance has been acheived and the missle has started heading for the surface. The larger missles like Polaris, Posieden, and Trident are fired from their sealed silo tubes by the burning of a modified propellant to generate gas pressure in the tube. Ignition of the rocket motor happens after the missle is out of the water. Reference the old "Sharks of Steel" and several others.

I agree that the use of the magnet and reed switch in the Design News article and video seems to put the operator quite close to the launch. Some kind of mechanical pivot device would be an improvement over what the scheme shows. Or an on-board RC reciever. Just one of many possibilities