Hi fellow engineers, I m looking for a foam to fill space between outer wall and inner wall of a homemade rocket. I need something that will not damage or deform by aerodynamic stress on the rocket. The outer wall is made by “red b*ll” can so I need a foam to support its shape. Thanks
Member • Feb 4, 2019
Is this a solid fuel rocket? What is the material for the fuel container? What is the time of combustion? Is it for single use or multiple use?
If the time of combustion is short and it is a single use rocket, you can use rigid polyurethane foam.
Member • Feb 4, 2019
Sorry, forgot to add details... its only small testing rocket, solid fuel, time of combustion is around 30 seconds... the material was meant to be a can from energy drink, thought it may work just now.
I expect it to fly around 900 ft maybe more, its my first attemp at something like this.
Member • Feb 4, 2019
@ramani_Aswath and I forgot its meant to be very cheap rocket
Member • Feb 4, 2019
Way back in the 1950s we used to make firework rockets with charcoal powder and sodium nitrate. Later in the sixties I tried my hand with a zinc-sulfur solid fuel. It took off and broke the window of the room of my head of the department on the third floor of the engineering institute where I was teaching. We were promptly banished from the campus and told to shift our experiments to unpopulated places.
more mundane issues took over and we stopped. Red Bull can may be too thin. Have you estimated the pressure inside the chamber at full combustion? You may have to consider an SS tube.
Administrator • Feb 4, 2019
#-Link-Snipped-# - How about adding pics of your rocket? ?Â
Member • Feb 4, 2019
@kaustubh_Katdare its just in pure planing process... so I cant show you any pics, i can try to draw it so you can kinda understand the concept. But that will take some time...
Administrator • Feb 4, 2019
Take your time. Would appreciate if you could keep us posted on your progress!
Member • Feb 4, 2019
#-Link-Snipped-# #-Link-Snipped-#Â so I have few bad drawings of my rocket concept here they are... any opinion is good
Member • Feb 4, 2019
We used a much smaller diameter convergent divergent exit nozzle to develop thrust. The drawing shows a full open exit. It may not generate much thrust.
It is possible that I am missing something. Since you do have an SS tube for the fuel, a rigid PU foam insulation should work.
Somewhat on these lines:
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This is the 1957 article from Scientific American, which started me on that circus:
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Member • Feb 4, 2019
#-Link-Snipped-# actually IÂ m just not sure how to make that nozzle by myself... I know that it should be like that but its kind of problem for me right now... i have limited ressources...Â
Member • Feb 4, 2019
#-Link-Snipped-#Â but I have few ideas which I will try... thanks for replying and trying to help. I will come back with outcome for sure
Member • Feb 4, 2019
Maybe you can try making one from clay and bake it. Make a two cm cylinder block that fits the bottom of the SS tube. The converging part can be short (5mm?) The throat maybe 5mm dia. The diverging section end dia can be 8or 10mm.
You can avoid the weight ring since this will serve that purpose.
Member • Feb 5, 2019
#-Link-Snipped-# so I have been thinking about this concept and nozzle problem and I think I found reasonable solution.
Bottom of these tin cans are ussualy stronger to withstand potential pressure inside the can. I can just make hole in that bottom smaller in dia. then the sstube inside and that can work as a nozzle right?
You know I m just learning all of it right now since its just a hobby for me... thanks for your replies and your patience with me??
Member • Feb 5, 2019
It would. However, with less efficiency. The pressure developed inside would depend on the fuel, its burning rate, and the volume of products of combustion. If the hole is too small and the rate of combustion too fast, the unit would explode.
Member • Feb 7, 2019
#-Link-Snipped-# this may give some leads on the exit nozzle design:
<a href="https://www.crazyengineers.com/threads/why-convergent-divergent-nozzle-has-higher-expansion-ratio.102597">Why Convergent-divergent nozzle has higher expansion ratio?</a>
