??AP Underwater Rocket Launch??

[boomtube]

I perused the archives here and didn’t find any info of anybody having launched a rocket using an AP motor from underwater, as has been done fairly often using BP motors.

Did I miss anything?

Can someone point me in the right direction or; does anybody here have any experience in this endeavor?

 

[DAllen]

I perused the archives here and didn’t find any info of anybody having launched a rocket using an AP motor from underwater, as has been done fairly often using BP motors.

Did I miss anything?

Can someone point me in the right direction or; does anybody here have any experience in this endeavor?

I would imagine that the same precautions for bp motors would apply to ap motors. In other words everything has to be kept completely dry or it isn't going to work. Can't say I've ever heard of anyone doing that before.

-Dave

 

[boomtube]

One thing I worry about is over pressure of the motor casing. Be it a re-loadable or a one-shot.

What happens to an AP motor if the igniter jams? Nothing good that’s for sure.

Now we have an AP motor that must be plugged some how, presumably with a bit of soft wax, and in addition you have water pressure pushing against the expelling propellant instead of the normal one atmosphere.

Maybe I am over analyzing this but I would like to hear. . .read from somebody that has successfully accomplished this.

 

[fyrwrxz]

uhh, yeah...totally not worth it unless you're doing underwater special effects for filming. (hint-cgi would be less expensive these days) Cleared the pool about 30 feet (lotsa drag down there) and deployed whilst floating sideways in the shallow end. Very hilarious. Crew threw me in for retrieval. Not my best work. Gory details are available but again...totally a waste of time.

 

[ClayD]

Submarine launched Tomahawk????


I designed a boat that has a rocket motor "underwater" at ignition, but once the boat comes to speed would be above water... I thought it would make for some kick butt ignition video.. (i will build it one day...)

I planned on using silicone grease, and filling the nozzle convergant/divergant cone with it. should be water proof to a couple feet.

Motor operation underwater i wouldnt think would be much different, but, if you got water in the motor through a leaky seal before ignition, would be CATOstrophic...

 

[boomtube]

My intention was to launch vertically from a plastic garbage can.

I thought I could start with one of the “Easy to Assemble” kits that include a plastic one piece fin can and a plastic nose cone. I think there is one available with a 24mm motor tube.

Half a dozen coats of Krylon Gloss Paint will pretty much make the body tube water proof so long as no water gets past the nose cone and motor seals.

Another concern is that ignition of an AP motor typically needs/uses more current than a BP motor. Maybe I could use one of the Quest Q2 igniters; I hear they can light an AP motor, at least small ones, though I haven’t actually seen it done.

 

[DAllen]

My intention was to launch vertically from a plastic garbage can.

I thought I could start with one of the “Easy to Assemble” kits that include a plastic one piece fin can and a plastic nose cone. I think there is one available with a 24mm motor tube.

Half a dozen coats of Krylon Gloss Paint will pretty much make the body tube water proof so long as no water gets past the nose cone and motor seals.

Another concern is that ignition of an AP motor typically needs/uses more current than a BP motor. Maybe I could use one of the Quest Q2 igniters; I hear they can light an AP motor, at least small ones, though I haven’t actually seen it done.

Be sure to get the longer Q2 ignitors. I know that in a SU D21 a Q2 leads will barely stick out the bottom of the nozzle so obviously the SU E motors will need more lead.

Edit: Come to think of it, I am not sure if it is the igniter that comes with the SU D that is barely long enough or the Q2...Either way get the long version.

 

[georgegassaway]

The underwater flights I did long ago used the “Dry Silo” method. A large diameter plastic tube, a solid plug at the bottom, attached to an anchor to hold the top of the tube below the water’s surface (often was a public swimming pool after summer, sometimes a pond or lake). The top was sealed with mylar, which was ripped by the rocket nose cone (had 1/2” of a toothpick on the nose tip). A large "ring" of clay was pressed around the outer top sides of the plastic tube, to then press the mylar into and wrapped with a couple of rubber bands to get a good air seal.

Now, that would work fine for any type of solid propellant.

But since you want to launch out of a plastic garbage can, that would not be so great with the dry silo method (Still possible of course).

- George Gassaway

 

[edwinshap1]

anyone watch the episode of mythbusters with the ancient missile thing?

I spoke with the vendor who made the motors for them, and he said he just caulked everything up so that it was all sealed off from the water. didn't over pressure because everything was smooth.

 

[jeffgeraci]

Want a cheap, simple solution? Go to Home Depot and buy a 3” plastic drain pipe for under $5- this is your launch tube. Next, take an 8-inch square of wax paper and score an “X” on the center with a dull pencil (don’t cut! Just score it)

Wrap the wax paper over one end of the tube, then secure it tightly with a rubber band or some duct tape in order to make it air and water tight (this is the TOP of the launch tube). You now have an air/water tight launch tube when inverted, and your rocket’s nose cone will cut through the wax paper like butter. If you experience high air pressure that bursts the wax paper prematurely, you can double up on the wax paper. Test the pressure BEFORE you insert your rocket.

Insert your rocket into the bottom end of the tube, and drill a small hole through the tube walls at least 3-inches up from the end of the tube. Insert a section of wire hanger through the tube and bend the ends so it won’t fall out (this is the “stop” that keeps the rocket from falling out of the tube) Get some coated electrical wire (old headphone cord, a cord from an old cell phone charger, etc) and strip the ends. Connect one set of leads to your igniter, and run the other leads up the side of the tube (you’ll connect to your launcher before launch) The connection to the igniter shouldn’t get wet, since it’s at least 3-inches inside the tube where the air is trapped. Epoxy the launch tube to a cinder block to anchor it.

This process is all just my theory, but I THINK it would work. However, rockets are not torpedos, and water is much more dense than air, and I imagine the water/air interface is going to pose some challenges for you. But what the hell, go for it! I love experimenting with this kind of stuff, and no doubt you’ll learn a BUNCH no matter what happens. Disregard the critics:neener:, but heed the safety warnings and have fun.