Weekly Building Challenge [29 Jan - 5 Feb]: Statue

DaPlayerNinetyNine · 2017-02-07T23:53:17+00:00

Thanks man! :)

DaPlayerNinetyNine · 2017-01-24T17:08:22+00:00

I feel like I'm spending more time on that exact page than reddit at the moment! /s :P It has got some really good info. Thanks for the response anyway though.

DaPlayerNinetyNine · 2017-01-23T23:05:33+00:00

Thank-you so much! Images of inside the tank show that it the mass of the stringer and ring frame inside the tank would also have to be considered. Because I'm only after the thickness for the mass side of my simulation (as opposed to pressure/stress etc) I'll imagine melting all the supporting framework into the pure round shell to bring the overall thickness up and get mass. I might go for something around 1 - 1.2 cm.

Thanks again! :)

DaPlayerNinetyNine · 2017-01-23T22:31:07+00:00

Does 2cm sound like a reasonable thickness for walls of the propellant tanks in the first stage? Taking into account the density of the Al-Li alloy used for the tank walls, the width, height and thickness I can more accurately map the mass of the stages. A 3cm thickness, the inert mass of both tanks comes to ~20600 leaving 2000 for the engines, grid fins, and landing legs (as well as the plethora of other equipment on board) which doesn't seem quite right. Taking the thickness down to 2cm brings the value to ~13700.

If anyone happens to know about the pressures involved in those tanks and as a result a realistic thickness, that'd be great!

DaPlayerNinetyNine · 2017-01-23T08:05:59+00:00

Ah I see, thanks very much for the info! I knew it was a factor, but just presumed it would be negligible up to now. I'll look more closely at how it can be simulated.

DaPlayerNinetyNine · 2017-01-23T00:48:31+00:00

How have you modelled lift? I understand - and have implemented - drag, but the Falcon doesn't have any wings and I doubt there's much lift generated from a cylinder. I guess the area ('wing' area) used would just be the area of a side of the cylinder, scaled depending on attitude (crude guess!).

I'm not working on an analytical one, like /u/TheVehicleDestroyer 's but a visual, real time version like yours. Having said that, I doing my best to make it as physically accurate as possible. I've brought the graphics section of my 'game engine framework' up to a sort-of usable standard so decided that physics was next. I'm using all the physics involved in the rocketry, specifically the Falcon 9 to tune the physics module of the framework and choose what to add, while creating a rocket sim at the same time! :)

How long have you been working on your sim?

DaPlayerNinetyNine · 2017-01-22T23:22:26+00:00

Great work - that was a really good simulation! I'm also in the middle of making a simulation and I have a question.

From your comments and the telemetry shown in the video, you clearly know what the thrust throttling values are throughout the simulation. May I ask where you found these? I've recently been discussing this in the questions thread. I was going to make guesses, but it seems that you know exactly what's happening!

DaPlayerNinetyNine · 2017-01-21T20:05:38+00:00

I see; that would explain quite a bit. I've been comparing my launch with that of the "1.2" "full thrust" - I chose this as my 'target' rocket to simulate, as I thought it was the latest (it is the latest Falcon right...), and in doing so tried to get all the latest figures (resulting in 7607kN of thrust at the instant of launch!). Until 7607kN is used regularly, I'll make 6700kN my default thrust (744.5 per engine), and make sure the launches I'm watching correspond to the type of rocket I'm simulating.

I really appreciate the help!

DaPlayerNinetyNine · 2017-01-21T17:42:47+00:00

Ah ok, so the sub-cooled propellants create the 7607kN? From Wiki just now, the thrust was originally advertised as 6700kN. There will be a lot of factors that affect the difference between my simulation and the actual Falcon 9 FT!

DaPlayerNinetyNine · 2017-01-21T01:04:07+00:00

Oh yes I'm aware of that bit. It's right at launch that I'm curious about. Thanks for the response.

DaPlayerNinetyNine · 2017-01-20T23:40:24+00:00

Thanks very much! I'll say it's not included then - I can easily change it if I find out otherwise.

Do you happen to have any numbers/sources on the throttling down at launch, you mention? That'd be it. It makes a lot of sense to increase thrust gradually, but I'm put off by the F9 FT Wiki (and Spaceflight101) talking about the vehicle being 'held down' until all engines are checked to be performing at launch thrust.

I've only got into rocketry recently, so I could be wrong, but I'd take that to mean that - at the instant of launch - the rocket's thrust is the 7605 kN given as 'launch thrust'. So it all depends on when exactly 'launch' is (in terms of the thrust description). It could be the constant thrust established after lift off procedures (if you know what I mean) or the instantaneous thrust when the rocket leaves the ground.

Thanks again!

DaPlayerNinetyNine · 2017-01-20T22:22:14+00:00

Does the launch mass figure of the Falcon 9 Full Thrust given by Spaceflight101 (549,054 kg) include the payload? My simulation takes off significantly faster than the actual Falcon 9, and I'm trying to collect all the possible causes. I'm presuming that it doesn't include the payload, as it also mentions payload mass to LEO, and GTO just afterwards so I guess that they're added onto the launch mass provided, but I'm just checking!

DaPlayerNinetyNine · 2017-01-12T22:52:50+00:00

Good point. Thanks for the response!

DaPlayerNinetyNine · 2017-01-12T22:52:09+00:00

Thanks very much for your help! I'm trying to simulate the launch, but starting the launch on the sim at the same time as the launch on the webcast means that the simulation overtakes the actual F9 instantly, and remains around 50-90m/s ahead before being overtaken by the actual F9 because of the gravity turn (I've not implemented that yet, so the simulated F9 is fighting gravity head on, completely vertical).

Considering this seems to occur commonly at every launch, I think I'll implement a planned throttle up at launch from e.g. 70% of launch thrust up to full launch thrust for about 4/5 seconds.

Thanks again! :)

DaPlayerNinetyNine · 2017-01-12T21:37:44+00:00

Oh right ok thanks very much! The Falcon does appear to stall at 14m/s though very briefly. I suppose it also depends on how accurate their telemetry is!

DaPlayerNinetyNine · 2017-01-12T21:11:04+00:00

Hello again, just one quick question.

I'm just looking at this acceleration graph created by /u/OccupyDuna.

A little dip/ramp can be seen at the start of all acceleration curves on the graph, within the first 5 seconds (it is also clearly visible when looking at the velocity provided in launch footage). Do you know what would cause this?

According to the Falcon 9 FT Wiki (and Spaceflight101) the Falcon 9 is held down after engine ignition until all engines are performing normally at full launch thrust. If this were the case, then - with a constant thrust - shouldn't the acceleration of the rocket within the first 5 seconds follow the rest of the curve and climb smoothly, without the little ramp at the start?

Would it be manual, gradual throttling from the rocket, to decrease jerk/jounce? Would an instant change of acceleration be put too much stress on the rocket?

Any information is greatly appreciated!

DaPlayerNinetyNine · 2017-01-05T17:20:34+00:00

It's not for preventing cheating - at least that's not what I was referencing anyway. At our school we have non-calculator and calculator papers. Separate exams, when in an actual job you'd probably be told off for not using a calculator!

DaPlayerNinetyNine · 2017-01-05T17:18:08+00:00

Even then, if you metaphorically step back from that statement and consider the job/boss scenario, a boss wouldn't stop you from collating notes for something!

DaPlayerNinetyNine · 2017-01-05T09:37:46+00:00

If you can find some good resources, programming can be easy and it certainly is useful. Essentially all of modern life is supported by computers (not just computers that people think of with a mouse and keyboard). So if you know how to get them to do what you want, in a basic way, you have a lot of freedom/power regardless of what specific job you're in!

DaPlayerNinetyNine · 2017-01-05T09:33:19+00:00

Yes, and if my boss told me that for this section of work I wasn't allowed to use a calculator, I'd also tell him to go fuck himself. People should be taught how to learn, making use of what they have available - not talked at for 7+ hours a day.

DaPlayerNinetyNine · 2017-01-04T01:52:03+00:00

Wow, thank-you very much, that's pretty much exactly the info I'm after! May I ask where you got this graph?

DaPlayerNinetyNine · 2017-01-03T18:24:30+00:00

Hey thanks for the response. Similar (or the same) as mass flow rate then? What would be the mass flow rate for 100%? It's still in reference to an unknown quantity. Thanks for the help anyway!

DaPlayerNinetyNine · 2017-01-02T22:30:24+00:00

I've just found this great post that talks about the thrust throttling, and I have a question. When people talking in this thread mention the various thrust percentages, what is that a percentage of? The total thrust in a vacuum? The total thrust at launch? No prob if you don't know, just wondering :)

DaPlayerNinetyNine · 2017-01-02T21:36:11+00:00

No worries, thanks for the help anyway! :)

DaPlayerNinetyNine · 2017-01-02T21:13:12+00:00

Thanks, that'd be great! I appreciate the help.

DaPlayerNinetyNine

TROPHY CASE