#11
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Mike, a few thoughts.
Bigger pressure tube would be better. A bigger cross section gives you a bigger top-end cap, which is what all the (useful) pressure pushes on. 1/2" PVC (.840" dia) gives about .5 sq in which is 25lb of launch force at 50psi; 3/4" PVC (1.05") gives about .86 sq in and 43lb of launch force at 50 psi. A really big tube might cause a pressure drop from what's in the tank to what the pressure tube actually sees, but that shouldn't be a practical problem. The only way to stop the tube from blowing apart (assuming the top plug is solid enough and the glue seam has enough gluing surface to hold) is to increase the tensile strength around the tube's circumference. Haven't done the math but the tensile stress on the card of the pressure tube should be about equal to the launch pressure. So, if you can make a 1" wide test strip that will hold a 50 lb weight, that's what you'll need. Wrapping the tube with strapping tape would likely add too much weight, but might be worth a try to test the principle. My hat's off to you for actually launching that masterwork (probably why I keep my stomp rockets simple - you don't want to see me cry after they land ...) Yogi |
#12
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Hi Yogi,
Didn't know the numbers, but, I guessed at what you're saying. The internal cardstock PSI Tube is fine, the 3/4" PVC on the other side of the valve came apart (not glued together). I launched with the PVC tank psi gauge showing 70# PSI. Used a shorter PVC pipe (33") inside the paper because of binding and wind issues. Ideal plan is to use a PVC launch pipe the same length as the internal paper tube (67"). Used a 1/2" wide glued tab and paid particular attention to the gluing, when the PSI tube was made. Then ran a strip of regular scotch tape down the whole length of the glue seam. A bigger paper chamber will be much easier to make. You can see from the video that there was also a wind issue, along with freezing rain and fog. After reading your numbers above, might do some surgery and install a larger PSI Chamber to fit a little looser around the 3/4" PVC, using masking tape to "shim" the Paper to PVC at the bottom. Right now it is 1.11" I.D.. To split/pop the Tag 125# PSI chamber is going to take more than 70# of air pressure the system supplied. Landing in the wet snow caused a little discoloration to the ink, but, no structural damage. Will carefully remove the present PSI tube and then test until it "pops" this week. Gluing it to a 3/4" PVC coupler attached to the system. Max air pressure won't go over 100# PSI, due to limits of PVC tank launch system valve. Max operating PSI on the valve is 150#, thus giving me a 50# safety factor. Rocket should never see these pressures if it can move freely. Rocket has challenged me to get it to 100' AGL.... quote- "My hat's off to you for actually launching that masterwork (probably why I keep my stomp rockets simple - you don't want to see me cry after they land ...)" I know what you mean-you wouldn't have anything to give to your lucky class members... Mike |
#13
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Quote:
Thanks for the clarification. Why not use cardstock gussets on both sides of fin to strengthen attach points? Drag increase wouldn't be that big of an issue, weight shouldn't be an issue as well. Mike |
#14
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Could a "telescoping" launch system be buildable? If so, would it be worthy?
I think an "inside tube" with a "soft top" and a system to keep it from leaving the base launcher tube (the rocket rises with the inside tube closed, the inside tube reaches its maximum height, and the soft top breaks allowing the air to push the rocket further). One would need quite a big air tank, but this might increase the launch velocity by half again (it depends on a lot of variables though). "soft cap" - maybe some kind of foil taped to the top, and the "softening" system made by shaving blades set to cut the foil... Based on the mass of the rocket versus the mass of the "intermediary stage" one could launch the rocket from halfway the distance up to twice the altitude |
#15
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Mike, my misunderstanding.
I thought you meant the rocket internals blew; if it's the launch system you've got the easy fix with a little PVC cement. If you need to be able to take the system apart you'll have to invest in the screw-together PCV connectors, a little teflon joint tape, and then glue the connectors to the ends of all the tubing. I use a couple of layers of card (1/4" strip) inside the bottom of the tube for all but the simplest (little-hands-type) stomp rockets. Makes it easier to form the tubes and you can adjust the seal by adding another layer to the shim. Yogi calinous - don't get Mike started on "hot-rodding" these rockets, we've got him a slot for rocket-rehab ... just as soon as we can catch 'im. |
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#16
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Quote:
ROTFLOL! Mike |
#17
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Quote:
Got to thinking about what you're saying here. Problem is the rocket needs to seal against the pipe, as you describe it, there are some design issues, however if you turn it upside down the rocket can seal against the outer pipe as shown. To build this system poses a few more challenges, but Yogi, this might be the two stage system you mentioned when I was trying to get the launch rod to work (remember the carbon fiber rod I tried a couple of years ago?). Does this qualify me for multipule spots in the rocket rehab????? Mike |
#18
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Internal PSI Tube Test
Tested the internal Pressure tube today. Used an x-acto knife to remove the internal PSI tube from the Saturn V.
Plan is to install a larger diameter one to get around the binding issues, it is being pre-shaped now, will build after posting this post. Used "industrial" grade strapping tape to tape all of the connections past and to the valve. Same tape was used to tape the internal cardstock PSI tube to the PVC as shown. It takes a bout 10# of pressure off of my airtank to fill the Launch system PVC tank. They equalized a little over 88# of PSI and then I closed the airtank valve. Took a quick photo of the sytem pressured up. Due to a slight leak the PSI was dropping, when I opened the launch valve PSI was around 85#. Last photo is PSI gage to show readings-test was already done at this stage. Internal PSI tube handled the full 85# without issue. Air pressure bled off from around the PVC to cardstock tape joint. Will post more photos when I launch with new PSI tube. Mike |
#19
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New PSI Tube Installed & a 5th Bell too!
New diameter PSI Tube slides easy down full length of PVC 3/4" Launch pipe/tube!
PVC has been sanded with 400 grit wet/dry as well as 600 grit! Smooth operation... Added a 5th Bell; had to camoflauge it though, same bottom diameter, but larger opening to fit the PSI tube inside it at the top. Mike |
#20
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Mike,
You've got a bad case, Mike (but a stupendous rocket!). Any reason you taped the pipe joints vice just gluing them up with PVC cement? Yogi |
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