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Missile Construction Question

R/C Submarine modelers

Postby Ramius-II » Sun Jan 11, 2009 9:16 pm

Thanks Kevin for the pictures and information! Wow! I found that 1/2" PVC pipe weighed over twice more that 5/8" x .039 aluminium tubing for the same volume. For the schrader valve, I threaded it to 1/4-20 and threaded the 1/8" upper pressure disk. After threading and epoxying the valve, I cut the valve to within about 1/16" to prevent the epoxy going where I did not wish it to go and to reduce weight. Right now the tube, upper and lower disks, and valve weigh only .65 ounces. When completed with o-rings, paint, and fins it should be at about .75 ounces. Hope this helps with your missiles.

Best, Ed
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Postby Rogue Sub » Sun Jan 11, 2009 9:28 pm

How about some pictures of your missile?
My missile weighs in at 1.4oz
Looks like there are signifiant weight reductions to be had that will result in higher launches.
Where did you get your aluminum tubing? What psi is it good to? Have you tried the larger nozzle size?

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Postby Polaris » Sun Jan 11, 2009 10:27 pm

Nuke Power wrote:How about some pictures of your missile?
My missile weighs in at 1.4oz
Looks like there are signifiant weight reductions to be had that will result in higher launches.
Where did you get your aluminum tubing? What psi is it good to? Have you tried the larger nozzle size?

Kevin


:shock: :shock: Well then, sure glad I know exactly what you guys are talking about. :D :D
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Postby Rogue Sub » Sun Jan 11, 2009 10:54 pm

Stuart get it out of the gutter buddy or youll find a missile on its way down south :)
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Postby Ramius-II » Sun Jan 11, 2009 11:59 pm

Hi Kevin, you are right it is about 1/2 the weight of the PVC version. The PSI rating of the tubing is 230 PSI. It is from Mc Master-Carr part number 8978K163 and the cost is $5.24 for a 36" lenght. O.D. is .625, I.D. is .555 I made an error, the wall thickness is .035 not .039. I will take some pictures in a day or so. I figure I will go straight for the 3/32" nozzle size that Matt said is best. Why re-invent the wheel? The tail "plug" with nozzle is .5" thick and counter bored to 82 degrees. After installation in the tubing it will be angled inward at 11 degrees to match the picture of the missile design I posted earlier. Right now the weight before this tapering is at .65 ounces. When tapered it will be lighter. When adding the fins and paint, I'll probably gain all the lost weight back. There is 5/8" x .016 tubing from K&S (Stock number 9415) and since I can flex it with thumb and finger pressure I chose not to use it. Seems too thin.

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Postby Rogue Sub » Mon Jan 12, 2009 4:54 pm

what are you making the 2 caps out of and how are you attaching them to the ends of the tube?
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Postby Ramius-II » Mon Jan 12, 2009 5:11 pm

The truth is I got a little lazy and took a small lenght of the tubing and used a pourable plastic mix to create a "rod" I could simply slice into "disks" of 1/8" and 1/2" thickness. The inside of the tube is sanded with 220 sand paper to provide a rough surface and cleaned with Lacquer thinner before the disks are epoxyed into place. The "valve" part of the schrader valve will be installed after all is done.
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Postby expfcwintergreen » Mon Jan 12, 2009 5:31 pm

Be careful with PVC and pressure. Failure mode=shrapnel.
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Postby Feet Wet » Mon Jan 12, 2009 6:31 pm

I don't know if this will help or if its relevant. Years ago ESTES marketed a freon powered rocket system with a company called Vashon. Theirs was a 1" dia unit with one or more stages. I played around with them and found that they would successfully launch from a tube underwater. The kicker was that NO guidance fins were required for a stable flight. 500 plus feet was an easy altitude to reach, and launch was capable from 7-8 feet underwater.
The nozzle was shaped just like a real rocket engine nozzle and the unit was fired by pulling a plug from the nozzle orifice. That plug was an o ring sealed slug of aluminum. I would think that this would easily adapt to 1/96 or 1/4 scale. These rockets can occasionaly be found on E-Bay.
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Postby Rogue Sub » Mon Jan 12, 2009 9:00 pm

They sound like a good idea the only problem is you can only use it once.

ramius, one of the reasons I have been using the pvc tube is that is is rated for 150 psi, twice the expected pressure inside. Not to mention it has enough wall thickness to where I can machine an inside lip. Then it is just a matter of pouring the alumalite right into the pvc with the end taped off. After it cures the ridge I make will prevent the ends from being shot off due to miss handling. I also took the time to put some thin set CA inside to seal up any holes around the edges that might have formed.

Chris I measured the bulke heads I am using right now and they are 2/3" thick lol I dont think they are going to explode on me yet. Of course this also explains their weight and low flight height. Perhaps I will try to get a bit more but, honestly I dont want them to fly into oblivion. I dont need them landing on people and recovery would be super nice as well.
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Postby Rogue Sub » Mon Jan 12, 2009 9:01 pm

Ramius have you tested your cylinders to pressure yet.
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Postby Feet Wet » Tue Jan 13, 2009 8:39 am

Nuke Power,
Those estes were reusable. They loaded thru one port, while you vented the rocket body. I had many flights. They were discontinued because of the Freon. not sales. Even without a chute recovery system, they did not sustain damage. .
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Postby Ramius-II » Wed Jan 14, 2009 12:30 pm

Hi Kevin
No I have not done a pressure test yet and do not expect any problems, my torpedoes are useing .014 wall thickness (aluminium) and are good to over 100 psi. At a wall thickness of .035, 65-85 psi should be just fine. I just found that as the tube diameter increased so did flexability and a very "ridge" tube seemed more desireable. Right now I am working on the exhaust part of the missile and have a "mental" design for the launch base. On advantage (?) here in California is with almost an hour each day on the freeway there is time to think about more that who is at the head of this line of cars and exactly WHAT are they doing? :? How is your launch "cup" (the copper end cap) constructed? Is it just the cap with a center pin or is there more? (Inquiring minds wish to know!) :)
Best, Ed
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Postby Rogue Sub » Wed Jan 14, 2009 10:25 pm

Ask and ye shall receive. After scrapping the last 2 days worth of work due to dissatisfaction, I took a different approach to my system. One of the big problems I was having was getting the launch tube holes cut into the lexan for the launch module. I tried using squares and spade bits in the drill press but the results werent very good. The spade was so rough on the tube that it made an oblong holes with the centers off by a few cm. The holes being off center were my biggest issue. My tolerances for getting a missile through the turtle deck and past the hatch door with breach is small.
After a few hours at work of contemplating and not working I decided to use graph paper to make a master. I then used a dremel with a carbide bit to slowly make my holes and stay within the LINES!

Image

I also refined my missiles a bit. I trimmed down the size of my shrader valves and the missiles themselves. I also turned down the end of the missiles so the just fit in my cups. Not to tight but just enough. I also came up with a way to get my nozzles in without misalignment. Also took more care in making the counter bores.

I am using a center pin with a gas inlet. You can also see the launch gas chamber I made.


Image

Image

Image

Image
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Postby Ramius-II » Wed Jan 14, 2009 10:41 pm

WoW! How impressive! :)
If it is not a "trade secret" is the copper end cap just empty with a pin or did you do more to it?

Best, Ed
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