Difference between revisions of "Talk:Thrust-to-weight ratio"
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How are you able to slow down with a TWR below 1? A TWR below 1 basically says, that the thrust is lower than the weight and this means that there is still a remaining force pulling the craft down. And instead of slowing it down it should accelerate such craft. It only reduces the acceleration, but you will still get faster, and considering that most parts break at relatively low impact speeds it won't help much. I would say the main reason to thrust is to loose mass (and therefore weight). — [[User:XZise|xZise]] <small>[[[User talk:XZise|talk]]]</small> 17:08, 6 October 2013 (CDT) | How are you able to slow down with a TWR below 1? A TWR below 1 basically says, that the thrust is lower than the weight and this means that there is still a remaining force pulling the craft down. And instead of slowing it down it should accelerate such craft. It only reduces the acceleration, but you will still get faster, and considering that most parts break at relatively low impact speeds it won't help much. I would say the main reason to thrust is to loose mass (and therefore weight). — [[User:XZise|xZise]] <small>[[[User talk:XZise|talk]]]</small> 17:08, 6 October 2013 (CDT) | ||
| + | : Crap, I suppose that it would only be useful if you had like a TWR .99 and fired full blast before you started free falling. Even if you had those conditions and did that, you would soon burn enough fuel to get a TWR > 1. I suppose that it's not really practical then. I'll edit it out. [[User:Zombie Elvis|Zombie Elvis]] ([[User talk:Zombie Elvis|talk]]) 18:29, 6 October 2013 (CDT) | ||
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| + | == Acceleration == | ||
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| + | I think the acceleration formula is not correct. It should be: | ||
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| + | <math>a = \frac{F_T-F_G}{m} = \frac{F_T-mg}{m} = \frac{F_T}{m} - g = g(\text{TWR}-1)</math> | ||
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| + | But of course this is just the acceleration at t=0, when the fuel burns it increases. To get an accurate formula which describes acceleration over time we would have to solve a differential equation... | ||
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| + | Please correct me if I'm wrong. --[[User:FauleSocke|FauleSocke]] ([[User talk:FauleSocke|talk]]) 12:43, 1 November 2013 (CDT) | ||
| + | :I guess you are partially correct: It depends on the direction of thrust relative to the gravitational force which is the reason why the acceleration rises when performing a gravity turn. It may be obvious when you can treat them as vectors: | ||
| + | :<math>\vec{a} = \frac{\vec{F_T}+\vec{F_G}}{m}</math> | ||
| + | :But of course on lift off those are directly opposing each other. This holds only true for vertical launched vehicles, so craft have a higher acceleration when started horizontally. — [[User:XZise|xZise]] <small>[[[User talk:XZise|talk]]]</small> 08:17, 3 November 2013 (CST) | ||
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| + | ::A good point. I think changing <math>F_G=-mg</math> and instead adding the forces in the equation is a good idea. I will change this in the article. The direction of the forces should be clear so no vectors are needed. --[[User:FauleSocke|FauleSocke]] ([[User talk:FauleSocke|talk]]) 16:24, 17 November 2013 (CST) | ||
Latest revision as of 22:24, 17 November 2013
Slowing down with a TWR below 1?
How are you able to slow down with a TWR below 1? A TWR below 1 basically says, that the thrust is lower than the weight and this means that there is still a remaining force pulling the craft down. And instead of slowing it down it should accelerate such craft. It only reduces the acceleration, but you will still get faster, and considering that most parts break at relatively low impact speeds it won't help much. I would say the main reason to thrust is to loose mass (and therefore weight). — xZise [talk] 17:08, 6 October 2013 (CDT)
- Crap, I suppose that it would only be useful if you had like a TWR .99 and fired full blast before you started free falling. Even if you had those conditions and did that, you would soon burn enough fuel to get a TWR > 1. I suppose that it's not really practical then. I'll edit it out. Zombie Elvis (talk) 18:29, 6 October 2013 (CDT)
Acceleration
I think the acceleration formula is not correct. It should be:
But of course this is just the acceleration at t=0, when the fuel burns it increases. To get an accurate formula which describes acceleration over time we would have to solve a differential equation...
Please correct me if I'm wrong. --FauleSocke (talk) 12:43, 1 November 2013 (CDT)
- I guess you are partially correct: It depends on the direction of thrust relative to the gravitational force which is the reason why the acceleration rises when performing a gravity turn. It may be obvious when you can treat them as vectors:
- But of course on lift off those are directly opposing each other. This holds only true for vertical launched vehicles, so craft have a higher acceleration when started horizontally. — xZise [talk] 08:17, 3 November 2013 (CST)
- A good point. I think changing and instead adding the forces in the equation is a good idea. I will change this in the article. The direction of the forces should be clear so no vectors are needed. --FauleSocke (talk) 16:24, 17 November 2013 (CST)
