Rocket flips out even though my rocket has a good design

[Space boy]

does anybody have any idea how to unlock the stage lock mechanism? Yes I did try alt-L nothing happens. It wont even lemme go to staging mode to check other things. I am currently locked in orbit around kerbin unable to do anything. I also missed my maneuver node.

Edited September 6, 2019 by Space boy

[Norcalplanner]

Do you have power?  And if it's being controlled by a probe core instead of a pilot, do you have an antenna with a good connection back to Kerbin?

[Space boy]

6 minutes ago, Norcalplanner said:

Do you have power?  And if it's being controlled by a probe core instead of a pilot, do you have an antenna with a good connection back to Kerbin?

Oops,  i ran out of power. But I do still have an antenna. but the antenna isnt of any use now is it?

[Norcalplanner]

6 minutes ago, Space boy said:

Oops,  i ran out of power. But I do still have an antenna. but the antenna isnt of any use now is it?

Correct.  Sounds like there may be a rescue mission in your future. 

[Space boy]

I have another question. In a video, Matt lowne builds a rocket which has a small payload, but then proceeds to add two flt-800 fuel tanks underneath. He managed to completely keep the rocket under control and reached the mun safely. HOW???

 

2 minutes ago, Norcalplanner said:

Correct.  Sounds like there may be a rescue mission in your future. 

Ha i guess

[BudgetHedgehog]

What's the video? I mean, in general, it's important to keep things as light as possible. You can get some really small Mun-capable rockets with the right parts.

Edited September 6, 2019 by BudgetHedgehog

[mk1980]

if there is a kerbal in a command pod you should actually be able to use staging commands regardless of whether the vessel is out of power. being out of power only disables the vessel if it doesn't have a crew (or if the crew is sitting in a passenger module with no command controls)

you'll still need electric charge to power the reaction wheels and line up the vessel for the next burn, though. so being able to stage won't really help if you don't have solar panels. or if the panels are facing in bad directions and will never be exposed to the sun.

as a rule of thumb - either add a bunch of small panels in different directions (for example in 4 or 6 way symmetry) so your vessel can create some juice regardless of which direction it faces - or make sure that you only go into timewarp after rotating the vessel so at least 1 of the panels will be exposed to sunlight when the vessel is on the day side of the planet.

also check if you're in time warp. i think staging is automatically locked while the game runs at more than 1x speed.

 

[Space boy]

29 minutes ago, BudgetHedgehog said:

What's the video? I mean, in general, it's important to keep things as light as possible. You can get some really small Mun-capable rockets with the right parts.

 

 

7 minutes ago, mk1980 said:

if there is a kerbal in a command pod you should actually be able to use staging commands regardless of whether the vessel is out of power. being out of power only disables the vessel if it doesn't have a crew (or if the crew is sitting in a passenger module with no command controls)

you'll still need electric charge to power the reaction wheels and line up the vessel for the next burn, though. so being able to stage won't really help if you don't have solar panels. or if the panels are facing in bad directions and will never be exposed to the sun.

as a rule of thumb - either add a bunch of small panels in different directions (for example in 4 or 6 way symmetry) so your vessel can create some juice regardless of which direction it faces - or make sure that you only go into timewarp after rotating the vessel so at least 1 of the panels will be exposed to sunlight when the vessel is on the day side of the planet.

also check if you're in time warp. i think staging is automatically locked while the game runs at more than 1x speed.

 

got it, thanks

[BudgetHedgehog]

Yeah, that's your basic Mun rocket there - a small lander that does the job, small transfer stage, and a core with 2 large tanks and a swivel, plus side boosters. The first two stages are essentially the same in that they're 2 fuel tanks and an engine, but with the fuel in the side tanks feeding all the engines at once, when they run out and get detached, the 2nd stage still has all it's fuel still. That gets you into orbit and most of the way to the Mun, the lander is there to get you home. The rest of it is just piloting - no steep or fast turns and keeping it pointing vaguely in the right direction.

I was going to mention on the last page that you could comfortably double the fuel in your rocket and still be able to take off just fine - Reliants are super powerful for early game tech, but the Swivel is going to be your main workhorse for small 1-kerbal rockets.

Edited September 6, 2019 by BudgetHedgehog

[Space boy]

1 minute ago, BudgetHedgehog said:

Yeah, that's your basic Mun rocket there - a small lander that does the job, small transfer stage, and a core with 2 large tanks and a swivel, plus side boosters. The first two stages are essentially the same in that they're 2 fuel tanks and an engine, but the fuel in the side ones feeding all the engines at once, when they run out and get detached, the 2nd stage still has all it's fuel still. The gets you into orbit and most of the way to the Mun, the lander is there to get you home.

I was going to mention on the last page that you could comfortably double the fuel in your rocket and still be able to take off just fine - Reliants are super powerful for early game tech, but the Swivel is going to be your main workhorse for small 1-kerbal rockets.

when I try using swivels and relliants, the TWR becomes too high, as the people above said you want the TWR to be around 1.4 or something like that. So i dont understand this.

[mk1980]

looks like a decent tutorial to me. you should be able to replicate the steps in it.

i guess the thing to take away from that video is that it makes sense to use more fuel tanks on your rockets.

the vessel in the video has a similar engine configuration as the rocket you posted, but it has roughly twice as many fuel tanks for each stage. which means it will have less drag issues from accelerating too fast and the center of mass will move further upwards as the lower stages burn their fuel and lose mass, making it less likely to (try to) flip over.

[BudgetHedgehog]

Keep adding fuel until the TWR is 1.3. The rocket in your original post is about half as tall as it could be.

[Space boy]

3 minutes ago, mk1980 said:

looks like a decent tutorial to me. you should be able to replicate the steps in it.

i guess the thing to take away from that video is that it makes sense to use more fuel tanks on your rockets.

the vessel in the video has a similar engine configuration as the rocket you posted, but it has roughly twice as many fuel tanks for each stage. which means it will have less drag issues from accelerating too fast and the center of mass will move further upwards as the lower stages burn their fuel and lose mass, making it less likely to (try to) flip over.

I see. I did try replicating the rocket, but I just guess I am a bad pilot and i crashed it.

2 minutes ago, BudgetHedgehog said:

Keep adding fuel until the TWR is 1.3. The rocket in your original post is about half as tall as it could be.

Ok, i understand now. Thanks

Edited September 6, 2019 by Space boy

[mk1980]

don't worry about your piloting skills. we've all been there :) it's easy to overdo it.

you don't need much input to get a stable rocket to orbit. you just give it a gentle nudge eastwards shortly after liftoff so it falls into a gravity turn that pretty much gets it into a prograde equatorial orbit with almost no further input (other than cutting the engines when projected AP reaches orbital height and performing a circularization burn once you get close to that AP) 

if it's a stable desgin with fins you can usually even turn off the SAS and it will keep its prograde orientation without any input and "fall" into a gravity turn on its own. or you set it so hold prograde.

[Space boy]

1 hour ago, mk1980 said:

don't worry about your piloting skills. we've all been there it's easy to overdo it.

you don't need much input to get a stable rocket to orbit. you just give it a gentle nudge eastwards shortly after liftoff so it falls into a gravity turn that pretty much gets it into a prograde equatorial orbit with almost no further input (other than cutting the engines when projected AP reaches orbital height and performing a circularization burn once you get close to that AP) 

if it's a stable desgin with fins you can usually even turn off the SAS and it will keep its prograde orientation without any input and "fall" into a gravity turn on its own. or you set it so hold prograde.

I can never get the gravity turn to work. My rocket always has a tendency to face the opposite side of where the gravity is supposed to pull it in. 

[VoidSquid]

Hey @Space boy, took me a bit longer than anticipated, too much work, and this and that, sorry, but I could test your rocket now:

In general it's a good construction, but as you said, it started to flip at around 20km altitude when the Terrier became active. So I made a few modifications:

In the first and second stage I replaced the Swivel with a Reliant which is the better ASL engine due to its higher thrust, lower weight, and better ASL ISP. You are using the AV-R8 winglets, those give you more than enough control to do without the Swivel's gimbaling. I also combined several stages of decouplers and engines.

The third stage with the Terrier became active at around 20km altitude, that's when the flipping started, imo due to the not-so-ideal aerodynamics of the KV-2 pod plus the not-so-ideal drag due to the the gap below the Ant engines, plus the lack of the  AV-R8 winglets fins.

I added 2 x FL-T400 to the first, 1 x FL-T400 tanks to the second stage to let the Terrier start at a higher altitude, decreasing aerodynamic forces when the fins are gone. Finally I wrapped the aerodynamically problematic part in a fairing, this had by far the biggest effect, both on efficiency (losses to drag) and stability. For final fine tuning, I reduced the thrust of the second stage to 80%.

Guess what: works like a charm now  

Spoiler

And here is the modified craft http://s000.tinyupload.com/index.php?file_id=04771673240484642806 

[Space boy]

12 minutes ago, VoidSquid said:

Hey @Space boy, took me a bit longer than anticipated, too much work, and this and that, sorry, but I could test your rocket now:

In general it's a good construction, but as you said, it started to flip at around 20km altitude when the Terrier became active. So I made a few modifications:

In the first and second stage I replaced the Swivel with a Reliant which is the better ASL engine due to its higher thrust, lower weight, and better ASL ISP. You are using the AV-R8 winglets, those give you more than enough control to do without the Swivel's gimbaling. I also combined several stages of decouplers and engines.

The third stage with the Terrier became active at around 20km altitude, that's when the flipping started, imo due to the not-so-ideal aerodynamics of the KV-2 pod plus the not-so-ideal drag due to the the gap below the Ant engines, plus the lack of the  AV-R8 winglets fins.

I added 2 x FL-T400 to the first, 1 x FL-T400 tanks to the second stage to let the Terrier start at a higher altitude, decreasing aerodynamic forces when the fins are gone. Finally I wrapped the aerodynamically problematic part in a fairing, this had by far the biggest effect, both on efficiency (losses to drag) and stability. For final fine tuning, I reduced the thrust of the second stage to 80%.

Guess what: works like a charm now  

  Hide contents

And here is the modified craft http://s000.tinyupload.com/index.php?file_id=04771673240484642806 

That's great. I haven't unlocked fairings yet so i am just going to use the mk1 pod for now and as the people above taught me, keep TWR to 1.4 so that I can escape the atmosphere and not need the fins anymore. Anyways, I appreciate your response.

Does your modified rocket stay in control, like all the times. Whatever rocket I build, always wants to turn over to the opposite side of the gravity turn. IDK why but it keeps happening, I have to keep fighting my own rocket to make it follow one direction and not go in the other direction.

Edited September 6, 2019 by Space boy

[VoidSquid]

Yes, it does. One of the important things when doing the gravity turn is to do it smooothly, try keeping that little dot of the orange level indicator always within the yellow prograde circle, in particular in lower atmosphere. This way the aerodynamic forces have only a small angel of attack. With the F12 key, you can toggle the display of the aerodynamic forces which will give you a good idea why the rocket is flipping over.

And this little tutorial might also be helpful:

Spoiler

 

 

Edited September 6, 2019 by VoidSquid

[Kerbart]

27 minutes ago, VoidSquid said:

Yes, it does. One of the important things when doing the gravity turn is to do it smooothly, try keeping that little dot of the orange level indicator always within the yellow prograde circle, in particular in lower atmosphere. This way the aerodynamic forces have only a small angel of attack. With the F12 key, you can toggle the display of the aerodynamic forces which will give you a good idea why the rocket is flipping over.

That brings back memories of the days before the 1.0 release, when you could go straight up, and then yank your rocket to 45° at 10k altitude without any consequence.

or return from Jool, enter the atmosphere at  90° and aerobreak while running the chutes doing mach 10. But I digress...

Das Valdez calls it “the circle of safety.” Having a pilot and using the prograde widget also helps.

[Aegolius13]

On 9/6/2019 at 12:52 AM, Space boy said:

when I try using swivels and relliants, the TWR becomes too high, as the people above said you want the TWR to be around 1.4 or something like that. So i dont understand this.

Having a high TWR at the start is not necessarily a bad thing in and of itself.  For the first few seconds after liftoff, when you're going too slow for aerodynamics to matter and you're losing a large portion of your thrust to fighting gravity, you want all the TWR you can get.  Things can get out of hand later in the launch, but if you start to accelerate way too fast, that can be solved by throttling down. 

The reason people advise something in the 1.4ish range is more about efficiency.  If you're familiar with the Rocket Equation, it tells you that rockets get delta-v (and hence range) but having a lot of fuel mass and very little mass of anything else, including engine mass.  If you have a very high TWR, it means (1) you're missing out on the opportunity to add fuel, and extend that stage's range, without hurting your performance, and/or (2) you're using a bigger engine than necessary, and thus carrying more dry mass than you really need.  

Thus it's generally not advisable to switch engines just to get a low TWR.  If a less powerful engine fits the profile better, then by all means switch.  But if the alternative engine is worse for the task at hand, no need to switch just to lower your TWR.

The Swivel and Reliant are interesting case studies .  The Reliant has more thrust, less weight, and higher sea-level ISP.  The Swivel's advantages are gimbal and better vacuum ISP.  If you have another means of attitude control, like fins, I find the Reliant is better suited for boosters due to its sheer thrust, while the Swivel can make more sense for a core stage. But the ideal layout can vary from mission to mission.

Which is a really, really long way of saying that if you want to maximize range, using Reliants and adding fuel until TWR falls into the sweet spot is probably the better call.  But if your rocket has enough range with Swivels, that's perfectly fine too.

Edited September 9, 2019 by Aegolius13

[Space boy]

2 hours ago, Aegolius13 said:

Having a high TWR at the start is not necessarily a bad thing in and of itself.  For the first few seconds after liftoff, when you're going too slow for aerodynamics to matter and you're losing a large portion of your thrust to fighting gravity, you want all the TWR you can get.  Things can get out of hand later in the launch, but if you start to accelerate way too fast, that can be solved by throttling down. 

The reason people advise something in the 1.4ish range is more about efficiency.  If you're familiar with the Rocket Equation, it tells you that rockets get delta-v (and hence range) but having a lot of fuel mass and very little mass of anything else, including engine mass.  If you have a very high TWR, it means (1) you're missing out on the opportunity to add fuel, and extend that stage's range, without hurting your performance, and/or (2) you're using a bigger engine than necessary, and thus carrying more dry mass than you really need.  

Thus it's generally not advisable to switch engines just to get a low TWR.  If a less powerful engine fits the profile better, then by all means switch.  But if the alternative engine is worse for the task at hand, no need to switch just to lower your TWR.

The Swivel and Reliant are interesting case studies .  The Reliant has more thrust, less weight, and higher sea-level ISP.  The Swivel's advantages are gimbal and better vacuum ISP.  If you have another means of attitude control, like fins, I find the Reliant is better suited for boosters due to its sheer thrust, while the Swivel can make more sense for a core stage. But the ideal layout can vary from mission to mission.

Which is a really, really long way of saying that if you want to maximize range, using Reliants and adding fuel into TWR falls into the sweet spot is probably the better call.  But if your rocket has enough range with Swivels, that's perfectly fine too.

got it. That was a nice explanation.

10 hours ago, VoidSquid said:

Yes, it does. One of the important things when doing the gravity turn is to do it smooothly, try keeping that little dot of the orange level indicator always within the yellow prograde circle, in particular in lower atmosphere. This way the aerodynamic forces have only a small angel of attack. With the F12 key, you can toggle the display of the aerodynamic forces which will give you a good idea why the rocket is flipping over.

And this little tutorial might also be helpful:

  Hide contents

 

 

I love this mans accent lol, but helpful video though.

[Space boy]

Thank you so much all of you. I think I got the basics to how to design a rocket thanks for all the responses. 

[Guest]

2 minutes ago, Space boy said:

Thank you so much all of you. I think I got the basics to how to design a rocket thanks for all the responses. 

So you got it to work?

[Space boy]

4 minutes ago, Brikoleur said:

So you got it to work?

Yes, i initiated a perfect gravity turn and then landed on minmus and mun that feeling of accomplishment is overwhelming.

Edited September 9, 2019 by Space boy

[VoidSquid]

Congrats, happy to hear, well done!