Timeline for Why are rockets cylindrical?
Current License: CC BY-SA 3.0
14 events
| when toggle format | what | by | license | comment | |
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| Aug 16, 2017 at 13:09 | vote | accept | Jose Luis | ||
| Jun 2, 2015 at 16:35 | comment | added | Russell Borogove | It's worth noting that a Saturn V launch loses just half a percent of its total impulse to atmospheric drag. There's not that much drag optimization left to be done. | |
| Jun 2, 2015 at 8:33 | comment | added | neelsg | @VladimirCravero Okay fine. I updated my answer to include a link that shows what I am saying better. I didn't mean that the NASA doc is too technical, just that it doesn't show what I'm saying very clearly | |
| Jun 2, 2015 at 8:28 | history | edited | neelsg | CC BY-SA 3.0 |
Improved the quality of the linked sources
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| Jun 2, 2015 at 8:00 | comment | added | Vladimir Cravero | It is not the most easy? There's some kid drawings and a poorly formatted formula. I don't care if that's on NASA site, it's even poorer than the wiki page. The question is about the cross section, not the tip, but I bet that the bullet Cd can change wildly if you tip it with something different than half a sphere. The first part of your answer, I buy it and I agree with it, the second? That's just a guess, and you can't guess in fluid dynamics. I'm no expert but I understand proper proof, and you gave none. | |
| Jun 2, 2015 at 7:00 | comment | added | neelsg | @VladimirCravero That document is not the most easy / direct, but note the following: A bullet has Cd of 0.295, an airfoil has Cd 0.045. That is almost an order of magnitude different. A cylindrical rocket resembles a bullet. A Sears-Haack body resembles an airfoil. The difference between those won't be quite so drastic, but the rocket will certainly have a higher drag coefficient. | |
| Jun 2, 2015 at 6:53 | comment | added | neelsg | @jamesqf That is a good point. The answers to this question has some interesting points around why they are tall and skinny. There certainly is a tradeoff for the sake of aerodynamics... an arrow would not fly very far if it was more the shape of a beer can | |
| Jun 2, 2015 at 1:58 | comment | added | CJ Dennis | Doesn't it matter which direction the drag is? The prism (wedge shape) has the broad side going first. Would there be a difference if the narrow side (pointy end) went first? | |
| Jun 1, 2015 at 21:18 | comment | added | Vladimir Cravero | I can't see how that document relates to the question or the answer. The cross section of the objects is not given thus you can't infer cylinders are somewhat worse or better of any other shape. | |
| Jun 1, 2015 at 17:24 | comment | added | jamesqf | What's interesting is to think about why rockets are rather longer than they need to be if they were optimizing on weight/material of the rocket itself, sans fuel. I think (without doing the math) that the minimum material will be used when it's about the shape of a beer can. Which says there must be a tradeoff between weight and aerodynamic drag, no? | |
| Jun 1, 2015 at 12:34 | comment | added | MSalters | @Joze: What do you mean by that? The drag coefficient is a shape factor that explains the difference in drag force for objects of the same cross section. The drag coefficient is for the entire shape, both the "upstream" (front) and "downstream" (back) part. | |
| Jun 1, 2015 at 12:19 | comment | added | neelsg | I linked another similar question that provides some answers more in terms of aerodynamics. You can also check out the Sears-Haack body wikipedia page | |
| Jun 1, 2015 at 12:02 | comment | added | Jose Luis | Yes I saw that document, the problem is they check the drag coefficient of the wedge downstream whereas I would like to know it upstream. The rest are some good points though. | |
| Jun 1, 2015 at 11:53 | history | answered | neelsg | CC BY-SA 3.0 |