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Limonadd

I just begin to the game

Question

Hi everyone, I just bought that game 2 days ago. It's kinda hard to play because I have a excrementsty labtop, it takes 10 min to start and sometimes I have 10 fps when i'm building a rocket, but except that I have like 50 fps during trips so it's great. I really love this game but I have a few questions:

My rocket are not always very stable. So I searched on youtube and i found a great tutorial. It explained that the center of lift has to be below the center of mass. But I don't really understand what IS the center of lift?  (thanks to that tutorial I landed on the Mun and went back :) because my rocket was flipping during the lift off )

Sometimes I can't turn my rocket, but I think it's because my center of mass was too low, is it possible?

Also, it's kinda hard for me to build an optimised rocket. How do you guys do? I've seen people that use not that big rockets to go on Eve or Duna. My rocket to go on the Mun was good I think, not that big, but I only used the small tanks and the small booster, the ones that fit with the mk1 pod, because I saw that there is way bigger tanks)

Sorry for my english, I apoligize if I don't use the right terms, I hope you can understand me :)

Edited by Limonadd

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Welcome to KSP and the forums.

  • KSP is hard.  It is rocket-science, although simplified quite a lot, and we all had a very hard time when we began.  I don't know of anyone who threw away KSP because it was too easy when they started!
  • So we all failed - a lot.  If you keep trying and learning you'll soon be designing your own vehicles that can go to the moons or other planets.  It still won't be easy but you'll do it :-)
  • The hardest things to learn for most people are landing, docking and interplanetary transfers.  As above, if you keep trying you'll get it and we all remember the pain of learning those.  (Actually there's a trick to interplanetary transfers - ask about transfer windows when you're ready for that).
  • Your English is fine and your post has fewer errors than most here *grin*.  The community is friendly so don't be afraid to ask anything.

Your actual questions:

  • Most peoples' rockets aren't very stable.  Spinning and flipping on launch are very common problems.  "Centre of lift" should really be "centre of drag", the areas where the air will push against the body of the vehicle and especially fins and other 'wing ike' structures.  You can build aircraft as well as rockets in KSP and then actual wings and lift become significant but that's all harder than getting to space, oddly enough, so stick to rockets for now.
  • In order to turn you need to have something that makes the vehicle turn.  In an atmosphere that might be control surfaces like aircraft elevators / ailerons / rudder or it could come from engine gimballing (steering the exhaust from the engine so it doesn't push exactly straight).  In space it could also come from engine gimballing but more usually from Reaction Wheels of various sizes - small inline reaction wheel, advanced inline stabiliser or advanced reaction wheel module large https://wiki.kerbalspaceprogram.com/wiki/Reaction_wheel - depending on what fits your rocket.  (Reaction wheels also work in atmosphere but aren't as important there).  In general control surfaces (or engines) as far from the centre of mass as possible will work better (they have a longer lever).
  • The simple answer is most people don't build optimised rockets but just about everything requires practice, practice and more practice.  And testing.  Practice, practice, practice and testing, testing, testing.  Perhaps I should add that you ought to practice and test a few more times as well.  If that's not enough try practice and testing, testing practice and practicing testing.  You get the point or, if you don't, I apologise for trying to be "clever" with English and probably just confusing the issue.  Most people (about 80%) who play KSP have never gone to another planet and many haven't even landed on the moons after hundreds of hours having a lot of fun just messing around in Kerbin orbit, building space stations or whatever.  The most useful things to learn about in order to design good (if not optimal) vehicles are delta-V, ISP and TWR.  The community delta-V map (https://i.imgur.com/gBoLsSt.png) tells you exactly how much acceleration your rockets need to get to different places but you don't need to worry about that for a while.

Tips:

  • Because you can do anything in KSP and it's all more fun if you do it your own way, try to learn general ideas (like delta-V) rather than worrying about particular designs.
  • Less is more.  The joke 'answer' to making a rocket do more is "moar boosters".  The real answer is almost always, "strip it down and remove everything you don't absolutely need.  If it works without something then you don't need it."  Hehe, that has the added advantage that your old computer should be beter able to cope with smaller (fewer parts) rockets.
  • You are doing the right thing starting with small parts.  Being able to use them well will help you keep everything else as small as possible.  You only want to use bigger parts when it is impossible to do something with small ones (or to practice and test).
  • If you have designed and built your own rocket that went to Mun, let alone landed on it, then you are already well ahead of many people who have been playing KSP for years.  Congratulations.  If you haven't landed on either moon with your own design yet you have one of gaming's biggest achievements to look forward to.  Congratulations.

Me:
4,0000+ hours practice in KSP.  Still haven't returned from Eve.  Won't offer a ship design unless I've actually built and tested it.  Usually test, launch and refine designs up to 40 times before I accept they're as good as they can be.  Use MechJeb (MJ, autopilot mod) to automate nearly all launches so they are consistent and because they're boring for me now.  Still practice launches as well because otherwise I get caught out when I can't use MJ, doh!

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13 minutes ago, Limonadd said:

After 2 trips on the Mun, and 1 on Minmus with the same rocket ( and I have to say it's actually a lot easier to land on Minmus, because of the even lower gravity) I earned 1300 points of science!!! (I play in Science mode, not career) so now i can unlock a lot of new things, and after building a new rocket i'll try to go on Duna :)

Expert!  Yes, many people like me recommend Minmus before Mun because the landing is so much easier.  Others say it's harder because you need to change plane and it's harder to get an encounter with Minmus's small SOI.

You need to know about transfer windows for interplanetary travel.  Read up on them and check out https://alexmoon.github.io/ksp/.  That will tell you the best time to go and how much deltaV it should take - you'll also be able to see how much worse it is if you try to go at the wrong time.

You may also like to try going to Mun (or Minmus) with one of the larger command pods.  Like Apollo - 3 to the moon or 2 to the surface - you'd need to learn to dock before doing the full Apollo thing though and it's not necessary in KSP.  The idea of that is that you'll get some practice with larger-diameter parts and bigger rockets (it's hard to do a crewed Duna round-trip with just the small parts).

Edited by Pecan

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Just now, Limonadd said:

Okay thanks! I'll train with docking, but to do it you need the RCS right? (the small things that can push in 4 directions)

You don't absolutely NEED RCS, although they make it a lot easier.  Don't rush at docking.  Seriously, don't rush at learning it - it takes a lot of practice - and don't rush at doing it - one of the main things to learn is to take it slowly (but smoothly).  Docking is one of those things you have to 'get your mind right' to do well.  Good luck and remember there's lots you can do without docking, up to and including landing on every planet and moon in the system.  Once you can dock though you can do everything.

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1 hour ago, Limonadd said:

Hey guys! I finally landed on Duna!! :D(and came back :D) it was actually really hard, escpecially the landing and coming back to Kerbin. But I made it! I took a few screenshots.

Congratulations!  You're advancing in this game quite quickly!

1 hour ago, Limonadd said:

for the parachutes:  what does it change if you modify the min pressure ?

That tells the parachute the atmospheric pressure at which it will open.  Parachutes open in two stages; one is called semi-deployed (or pre-deployed), and the other is fully deployed.  The pressure setting is for the semi-deployed state.

Generally, you want to set the pressure high enough that the parachute deploys when you're low in the atmosphere and have lost most of your entry speed, but before you're so close to the ground that you can't slow to a safe speed.  This was once a very important setting; if you got the setting wrong, your parachutes would burn up or rip off.  There's an entertaining Squadcast video of one of the developers who forgot this while live-streaming a landing; his exclamation of, 'Oh, my God, I forgot I'm a dumbS!' rings as one of my very favourite official comments ever.

Now, parachutes usually won't open unless it is safe for them to do so (you can change that setting, however), but it is still possible to get into trouble on Duna where the atmosphere is already very thin.

1 hour ago, Limonadd said:

the ship flipped over :/ do you guys have any idea on how to make it more stable when you enter into an atmosphere?

Those heat shields are made of pure drag in the arrangement you have them.  You are better off having one heat shield sized to cover everything else in the rocket (though if your landing was successful, then you perhaps don't need a heat shield at all), or else you will need to have some draggy bits at the nose of the rocket to help it keep its alignment.

A common workaround, especially when using the inflatable heat shield, is to have a second inflatable heat shield at the other end so the drag forces are equal.  The other typical solution is to have fins, or preferably air brakes (because they are retractable) at the nose end.  Another solution is to have your lander in a fairing, or to use parachutes, or simply to redesign your lander.  Making a lander more squat than long will help you keep it oriented correctly (albeit at the cost of its being difficult to launch through an atmosphere).  If landing in an atmosphere, then you can add wings and landing gear to make a glider, though you'll need to be clever to take off again.  If you have an unwieldy thing that must land intact but cannot be redesigned (such as base-building modules and sometimes rovers), then you can overload it with fuel and big rockets and try for a powered landing.

There are many, many possible solutions to the problem, but for now, I'll say that using one heat shield instead of three would be a good start.

1 hour ago, Limonadd said:

but how do you guys make the pictures appear on the forum?

Imgur photos have their own URL.  You need to paste the URL directly into the reply box and it will embed the link automatically:

EUF1Lxk.png

And this, of course, is one of the photos from your trip:  https://i.imgur.com/EUF1Lxk.png

 

 

And not only is the ninja-fu strong with @AHHans, but we independently chose the same photo to use as an example.

... Please get out of my head, @AHHans.  It's not safe there.

Edited by Zhetaan

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Uh just a correction, for rockets it's (easiest) the center of gravity (not drag) needs to be infront of the center of lift.

 

Also press "T".. - Activating sas helps a lot when your rocket is about stable.

Edited by paul23

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Wow thank you for your answers!! Thanks a lot for the explanations and tips :) And yes I made the rocket to land on Mun (and go back) myself, I prefer to do the rockets myself :) and yes I was already using the SAS before.  Thanks!!!!

Edited by Limonadd

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2 hours ago, paul23 said:

Uh just a correction, for rockets it's (easiest) the center of gravity (not drag) needs to be infront of the center of lift.

 

Also press "T".. - Activating sas helps a lot when your rocket is about stable.

Which is similar to saying, the centre of drag should be behind, below as Limonadd said, the centre of mass.  However, fins and most other objects do not produce lift, whereas wings do.  You almost never want wings on a rocket and when you do have them you need to balance your rocket like a 'plane and it all becomes much more complicated.  Without wings there is no lift (maybe some body lift) and you can mostly just ignore it.  The trouble is that the VAB doesn't show the centre of drag - you just have to add aerodynamic objects like nosecones to the front and draggy ones like fins to the back.  This is one of those things that you learn to judge better with practice, although if you want to make aircraft it is, again, more important and more complicated.

Who knew rocket science would be the easy part!

You are completely right about T and SAS though.  I recommend engaging SAS as soon as you get to the launchpad because more than one of my rockets have fallen over before I got to launch them!

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After 2 trips on the Mun, and 1 on Minmus with the same rocket ( and I have to say it's actually a lot easier to land on Minmus, because of the even lower gravity) I earned 1300 points of science!!! (I play in Science mode, not career) so now i can unlock a lot of new things, and after building a new rocket i'll try to go on Duna :)

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1 hour ago, Pecan said:

Which is similar to saying, the centre of drag should be behind, below as Limonadd said, the centre of mass.  However, fins and most other objects do not produce lift, whereas wings do.  You almost never want wings on a rocket and when you do have them you need to balance your rocket like a 'plane and it all becomes much more complicated.  Without wings there is no lift (maybe some body lift) and you can mostly just ignore it.  The trouble is that the VAB doesn't show the centre of drag - you just have to add aerodynamic objects like nosecones to the front and draggy ones like fins to the back.  This is one of those things that you learn to judge better with practice, although if you want to make aircraft it is, again, more important and more complicated.

Who knew rocket science would be the easy part!

You are completely right about T and SAS though.  I recommend engaging SAS as soon as you get to the launchpad because more than one of my rockets have fallen over before I got to launch them!

 

First of all: a fin most certainly does create lift, almost anything can create lift, only a perfect round shape won't.

Center of lift and center of pressure are synonyms they both are a correspondence of how the curvature of the craft is. It is actually the center of *pressure* (or lift) that stabilizes a rocket. Not the drag. Drag is always parallel to the velocity vector. Lift is perpendicular to the velocity vector. Now why CoL needs to be behind the gravity is due to if a minor change in angle of attack o pitch occurs, the natural tendency of lift force (if behind the cog) is to create a moment which counteracts this change. If lift is in front of the cog, the moment is the other way around, and it increases the aoa/pitch.

 

Fins work perfectly: the small change in aoa makes them not parallel to the airflow thus they start generating lift. Hell even the whole rocket body does this, however since the curvature is typically high at the top of the body (command sphere, or even almost infinite when nothing is on top), the center of pressure and center of lift is very high up.

 

Actually I should add: cog doesn't need to be in front of the col, it needs to be in front of the neutral point. Which is a combination of the col as well as the lifting moment. Though "in front of col" means it is also in front of the neutral point:

 

https://en.wikipedia.org/wiki/Longitudinal_static_stability

Edited by paul23

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17 minutes ago, paul23 said:

Center of lift and center of pressure are synonyms

Parachutes go at the back, whether you want them to or not.

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Hey! I just have another question sorry :)

I would like to make a rover, to drive on other planets :cool:

But how do we do that? I mean, how can we make the wheels turning (rolling? idk how to say it xD)

I think it's with electricity, so is there an electric motor in the game or something?

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2 hours ago, Limonadd said:

But how do we do that? I mean, how can we make the wheels turning (rolling? idk how to say it xD)

I think it's with electricity, so is there an electric motor in the game or something?

The wheels themselves are motorized.  There's a "go forward" key, a "go backwards" key, and "turn left and right" keys.

By default, those keys are mapped to the same WASD keys that control pitch and yaw (for example, with reaction wheels), which can lead to confusing behavior if you have a rover that also has reaction wheels on it.  It doesn't affect you if you don't have reaction wheels on the rover, but if you'd like to avoid some complications (e.g. "it tries to pitch down when I accelerate forward", etc.), then you can use the UI options to map the rover controls to a different set of keys.  (For example, I use numpad 8456 keys, myself.)

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4 hours ago, paul23 said:

???

You said centres of lift and pressure were synonyms and gave me a reference to aircraft stability.  While that's all very nice I was talking about drag and rockets and explicitly trying to eliminate lift as a consideration.  Drag in KSP mainly arises from the cross-section of the vehicle and is unavoidable.  Structural lift is always unnecessary and usually not wanted, as on that design I gave you yesterday which used its classic 'wedding cake' form and engine gimballing to eliminate the fins.  Although in that case the base was wider to accommodate the twin engines it was stable because the greater drag generated there was behind the CoM.

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To build a rover it's easier in the Planes Hangar, using the symetric tool to attach wheels to...whatever rover body you want (try a lander can for starters). Dont forget batteries or it wont move! Solar panels too so they dont deplete.

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Hey guys! I finally landed on Duna!! :D(and came back :D) it was actually really hard, escpecially the landing and coming back to Kerbin. But I made it! I took a few screenshots.

https://imgur.com/a/c8EGind

but it was really hard to land, because I think my lander was too high, so it has not that much balance 

I learned a lot during that trip, but I also have a few questions:

for the parachutes:  what does it change if you modify the min pressure ?

Also, the entry on duna was supposed to be like that xD:

https://imgur.com/a/wSyuE5H

but instead:

https://imgur.com/a/9s5YxX7

the ship flipped over :/ do you guys have any idea on how to make it more stable when you enter into an atmosphere?

here is the full trip: (almost)

https://imgur.com/a/6EFno3j

but how do you guys make the pictures appear on the forum?

Edited by Limonadd

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29 minutes ago, Limonadd said:

for the parachutes:  what does it change if you modify the min pressure ?

Parachutes have two opening stages: semi-deployed and fully-deployed. The "min pressure" defines how soon (at which atmospheric pressure) the semi-deployed stage opens, the "altitude" setting defines when (how high above the ground) the fully-deployed  stage opens.

36 minutes ago, Limonadd said:

the ship flipped over :/ do you guys have any idea on how to make it more stable when you enter into an atmosphere?

You have these huge heat-shields on the bottom of your rocket. They have large amounts of drag when moving through an atmosphere. The aerodynamic forces will try to flip your rocket around. It's like having a deployed parachute at the front of your rocket, that will also try to flip.

For Duna the rule of thumb is to just forget about heat-shields. :cool: The atmosphere of Duna is so thin and the orbital speeds are so small that heating is no big danger. (Well, as long as you don't overdo it.) If you do need to have a heat-shield on a larger rocket (e.g. when landing on Eve), then make sure that you you have enough drag on the top of your rocket to counteract the drag at the bottom of your rocket. (This is why many Eve landers have two of the inflatable heat-shields on at the bottom to actually shield against the heat and one at the top to counteract the drag from the bottom heat-shield.

50 minutes ago, Limonadd said:

but how do you guys make the pictures appear on the forum?

You see the "Insert image from URL" at the bottom right of the editor in the forum? Click in that and then enter the address of the image file, including the "*.png" or "*.jpg". The usual imgur link to a single image does not include the ending, so you need to add that by hand. 

To include the image below I entered "https://i.imgur.com/CIlSFGr.png" as the image link. (And I used <CRTL> - <right-click> on the image to "Edit Image" and make it display smaller.)

CIlSFGr.png

 

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8 minutes ago, Limonadd said:

What is the easier planet to land on after Duna?

If you don't mind a one-way trip, go to Eve next.

Re-entry is tricky, but once you get past the plasma stage, actually landing is really easy.  The atmo is so thick that you don't need very many parachutes.

Getting off of Eve, though, is something else entirely.

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Actually I prefer to land and come back xD i'll do another trip to Duna to train an get some science and i'll try Eve xD ty

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