Gravity Turn ascent trouble.

[vv3k70r]

11 hours ago, Spricigo said:

Why did you quoted half of my sentence?

Nothing personal - just quoted intresting text, not the whole meaning.

[Spricigo]

44 minutes ago, vv3k70r said:

Nothing personal - just quoted intresting text, not the whole meaning.

Not taking it as personal, but not really getting the message you wanted to convey either.

Unless you really mean my previous comment become interesting once taken out of context. I hope not.

[vv3k70r]

4 minutes ago, Spricigo said:

Unless you really mean my previous comment become interesting once taken out of context. I hope not.

I mean I commented quoted text, not the whole meaning of block. I just found this piece worth of additional comment, because everything else where explained and commented already.

Week ago I was explaining it to my son why his rocket dosent get from lounchpad for few second and what is waste in design. There are lot of such things that such be highlighted - it could be not so intuitive (burning so much mass so fast).

Context is TWR.

[paul_c]

My (limited) understanding, is that:

* TWR must be >1, otherwise its not a rocket and/or won't go up like a rocket
* Anything above 1 means it accelerates. Since its flying in the atmosphere (initially) then drag will need to be overcome (and its losses are proportional to v²)
*  The bigger the lever arm (ie like a dumbell, the weight at the top and bottom - don't worry about the bottom the engine and sloshed fuel will be there) the more control.
* The larger the TWR the more control too (but we don't want excessive TWR due to drag)
* Fins help with control/stability but add drag and weight

So that's why there's an "ideal" value for TWR, its not arbitary its a tried and tested performance figure which is a good balance of control and performance/efficiency.

[Spricigo]

29 minutes ago, paul_c said:

So that's why there's an "ideal" value for TWR, its not arbitary its a tried and tested performance figure which is a good balance of control and performance/efficiency.

The value certainly is tried, but tested? By who?  When?  How? 

If all we have is some vague references to KSP's conventional wisdom, that is what we call arbitrary.

Otherwise, let's reproduce those test and see if we also reach the same conclusions.

 

 

[paul_c]

Phraseology - "Tried and tested" is figurative - I don't have links to scientific papers on it (although I dare say they do exist, since rocket science is an academic profession). Its KSP's conventional wisdom, which is based on the laws of physics, which is what KSP is (with tweaks here and there) based on.

Another aspect I forgot is payload/crew comfort and Max-Q considerations - of course, these don't exist in KSP but do in real life - this is why when demonstrating new airplanes they don't do barrel rolls, although they could.

[Spricigo]

4 hours ago, paul_c said:

I don't have links to scientific papers on it

In not asking for scientific papers, I'm asking if anyone used something different than "whatever has been told in the forums" to figure out those ideal values and, if that is the case, what is the metric that shows the difference.

Not that there is a problem in going with something that works, but what works is often a far wide range of situations that just conventional wisdom.

 

[paul_c]

It depends what you want to achieve, I guess. If you like to delve into a programme of testing various rocket designs, then that's a brilliant way to spend time in KSP. I've done similar.

Sometimes the focus isn't so much the actual rocket, but the destination or the payload - for example in career mode, you might have a satellite to launch with an unusual requirement. Or have your own personal goals of eg "getting to the Mun" or elsewhere. Me personally, I like building/launching satellites and controlling the costs as much as possible on them. So I'll spend an amount of time slimming down the rocket design, looking for the most efficient orbital transfers in dV, etc etc I'll spend an amount of time on the launch rocket but its one phase of a mission with a number of phases.

If its a new or very different payload, which means one of my previous rocket designs isn't working out so well, I might end up doing say 5 test flights before I'm happy with it. I don't mind doing 5 flights and looking at the pertinent figures like TWR, dV per stage, etc. But I'll look at external guidance too, rather than doing say 20-30 flights to find for myself the 'best' TWR.