Timeline for I don't know where to start with the calculations - rocket engine
Current License: CC BY-SA 4.0
23 events
| when toggle format | what | by | license | comment | |
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| Aug 21, 2020 at 18:34 | comment | added | Organic Marble | @StarshipGood Glad you got it sorted out! | |
| Aug 21, 2020 at 18:29 | comment | added | StarshipGood | If I use the Sutton 7th and 8th edition velocity equations (without the g) it works for me. I forgot that the CEA gives Molecular mass in g/mol and not kg/mol. That's why it came OK if I made the R' 8314 and not 8,314. | |
| Aug 21, 2020 at 18:05 | comment | added | Organic Marble | @StarshipGood Sutton 7th edition gives an example in metric units on page 60 i.imgur.com/K5DLK46.png But it looks like the numbers do not work out unless I also multiply by g under the radical. | |
| Aug 21, 2020 at 17:46 | comment | added | StarshipGood | is it possible that the gravitational constant needs to be added for the imperial unit calculations? | |
| Aug 21, 2020 at 17:29 | comment | added | Organic Marble | @StarshipGood sorry but they are correct i.imgur.com/qe04d6o.png | |
| Aug 21, 2020 at 17:12 | comment | added | StarshipGood | sorry but the units on your equation for throat velocity don't add up. [Here's] (Throat velocity units imgur.com/gallery/CqHmEbB) how I got them canceling and the units cancel out with the 8th edition's equation. I just have to use the gas constant*1000 to get the right velocity. | |
| Aug 20, 2020 at 17:20 | comment | added | StarshipGood | I saw that in the "How to design, build and test..." already and also checked here so I always divide the universal one with M. I still don't understand why they changed a totaly fine equation with a wrong one. | |
| Aug 20, 2020 at 15:43 | comment | added | Organic Marble | @StarshipGood one more thing - you should use R for your gas, not the universal one. From Sutton "where the gas constant R is found from the universal gas constant R' divided by the molecular mass of the flowing gas mixture." It's probably in the output from that program somewhere. | |
| Aug 20, 2020 at 15:28 | comment | added | StarshipGood | thank you for your help. And I meant as in "not giving enough information" type stupid questions haha. | |
| Aug 20, 2020 at 15:20 | comment | added | Organic Marble | These are not stupid questions! Once you supplied some numbers, I found it interesting. | |
| Aug 20, 2020 at 15:19 | comment | added | StarshipGood | oh okay so at least this time it wasn't a stupid question. Guess I'll have to get the 4th edition. | |
| Aug 20, 2020 at 15:16 | comment | added | Organic Marble | Yeah, that is one of the many problems in the later editions. Notice it says that Vt = at. lol. The units are not even right. Here's the correct equation from the 4th edition i.imgur.com/oiWrPCS.png | |
| Aug 20, 2020 at 15:11 | comment | added | StarshipGood | Yeah sorry. The equation is 3-23 in Sutton 8th edition. For both versions of the equations, I had to use the 8314 and not 8.314. All other equation numbers from the 4th are the same in the 8th edition so it is probably the same with this one. | |
| Aug 20, 2020 at 15:04 | comment | added | Organic Marble | @StarshipGood Which equation? Give me a reference I can look at. | |
| Aug 20, 2020 at 14:43 | comment | added | StarshipGood | So I've been going through the equation for the throat and exit velocity that includes R. And for those equations you should use the 8314 universal gas constant and not the 8.314. Am I just missing something here or is there something else? I went through the units and can't find what's wrong on my side. | |
| Aug 20, 2020 at 6:01 | vote | accept | StarshipGood | ||
| Aug 20, 2020 at 1:53 | history | edited | Organic Marble | CC BY-SA 4.0 |
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| Aug 20, 2020 at 1:33 | history | undeleted | Organic Marble | ||
| Aug 20, 2020 at 1:33 | history | edited | Organic Marble | CC BY-SA 4.0 |
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| Aug 20, 2020 at 1:29 | history | deleted | Organic Marble | via Vote | |
| Aug 20, 2020 at 1:28 | history | undeleted | Organic Marble | ||
| Aug 20, 2020 at 1:27 | history | deleted | Organic Marble | via Vote | |
| Aug 20, 2020 at 1:21 | history | answered | Organic Marble | CC BY-SA 4.0 |
