Mun Lander Launch Vehicle Redesign

[MrCraftyG]

Greetings.
Firstly let me just explain that I am quite new to the game as I have only been playing for a week or so.

I'm having a bit of difficulty getting my Mun lander into orbit of Kerbin, let alone to the Mun.
My main issue is loss of control - the rocket spins, flips and does whatever it wants, even with SAS enabled, whenever I engage the main liquid engine. It's fairly stable whilst using the initial boosters to get off the ground though...until I fire up the main engine that is...

I have tried many different setups using my brain to design them but to no avail, so I thought i'd ask you guys for some help.
I'm not asking for someone to design a rocket for me (i'm not that lazy), however if what I am doing needs to be binned, then I will happily accept any help that is offered.

My lander and command module is 13T in mass...which might be my first problem.
Here is a screenshot (not including AE-FF1 protective shell - is this needed?) without any of the many rocket designs I have tried below it.

I have tried both slim and fat launch vehicles, usually with 2/4 boosters at the bottom. I have tried attaching some boosters further up near my payload to "tug" it unto orbit and that also doesn't work.

Perhaps I need to learn more about launch profiles, perhaps just rocket design. Either way, I have been trying all day to launch this to no avail. I can get to 80km+ but when I try to round off my orbit, the rocket spins out of control even on quite a low throttle. Redesigning my lander isn't out of the question either.

Does anyone have any tips, suggestions or help please?
 Many thanks in advance.

[DD_bwest]

if your landing can is upside down and if its your root part and controlling from there, itll mess up everytime.  although usually at much lower altitude that you describe.

 

also, if it doesnt have struts to reinforce the joint between the docking ports, youll most likely get lots of wobble

[Foxster]

You likely have a few things going on that are related...

The front end of your craft with all those bells and whistles will be very draggy, the rear much less so, which will contribute to the flip. You will also have the Centre of Mass  shifting as you climb, also contributing to the flip. 

Coupla things that will help: 

1. Stick some fins on the back end. This will add some drag to the back end and if you use something like tailfins then they will help with steering. 

2. Make the front end more pointed to reduce its drag. You could use a fairing or cargo bay to help with that. 

The other thing to watch for with your design is that control is not backwards, caused by that upside-down lander can. Right click the mk1 capsule and do "Control from here" before liftoff. 

Curious. what are the sepratrons for?

Also - those ladder rungs are quite draggy and add up in terms of mass. Better to use one ladder... Oh and do you really need all those lights? 

Edited November 7, 2016 by Foxster

[Karol van Kermin]

The lander is not really the problem. Just add more struts (and dont forget the duct tape)!

[AeroGav]

If opening up the throttle makes your ship spin , while out of the atmosphere, it's not an aerodynamic issue.  The only thing that leaves is centre of thrust not being in line with centre of mass in the vehicle as it exists at that moment (after staging etc).    The picture only shows us the lander, not the engine that's causing the spin.   Nonetheless the lander at least looks symmetrical.

Any chance of a screenshot of the spin ongoing?

Bear in mind there are indicator arrows in the VAB you can turn on to show centre of mass, centre of thrust etc, centre of lift.  And then there's the mod RCS build aid, which shows you a red coloured ball to indicating where CoM will move to when the tanks are empty,  and it also gives a "torque" value indicting how much spinning motion your engine will impart from things not being in perfect alignment.   

[Plusck]

Following what @AeroGav is saying - you can get the "torque" info in the VAB using KER too - a feature it took me a year to dicover.

As for the source of you imbalance:

Although it might feel less realistic, you really don't need ladders for the Mun. EVA jetpacks work fine. Getting rid of all ladders and rungs will probably solve most of your balancing issues.
That drogue chute will be contributing to imbalance too - not a lot but you might want to put a pair on the probe core instead of a single one on the command module.
You really don't need anything more than the command pod's internal antenna unless you have a weak tracking station or you're on the far side of the Mun (but then you need a relay, anyway).

[CubertFarnsworth]

I tried to make something where the root build was upside down and the same thing would happen to me. Once I flipped it back over, that fixed it. I think you can re-root it in the hangar but once out in the field you would have problems. Maybe there is a Mod that can re-root your ship in flight. New player myself as well.

[Tyko]

Lots of great suggestions here. If the tendency to flip is happening right off the pad it's likely an issue with where your control point is as @DD_bwest said. If your control is pretty solid until you're moving more quickly it's likely aerodynamics and drag.

Try flipping your lander right side up. You can actually mate the engine bell of your lander directly to the Docking Port jr on top of your capsule. You use the right-click "decouple node" option to detach it.

For aerodynamics, use a fairing as soon as you have the tech unlocked. All of the legs, the lights, etc are really draggy and can cause control problems.

[AeroGav]

6 minutes ago, CubertFarnsworth said:

I tried to make something where the root build was upside down and the same thing would happen to me. Once I flipped it back over, that fixed it. I think you can re-root it in the hangar but once out in the field you would have problems. Maybe there is a Mod that can re-root your ship in flight. New player myself as well.

If the root part - or rather, the command part, is not facing the way the vehicle is travelling, it can cause an upside down navball with flight controls reversed, but if you've got another part  from which the ship can be controlled - docking port, probe core, lander can - then just right click on that part in flight and select "control from here".  That keeps the blue side up.

I'm struggling to see how a pair of ladders is going to cause wild spinning on his lander.  I mostly only build spaceplanes, they have much more issues out of the atmosphere because the bottom side of the plane has landing gear, the topside has a tail fin etc.  all relatively heavy components  that disturb the symmetry far more than a pair of 10kg ladders would.   So long as you have SAS available (a pilot, or sufficiently advanced probe core) and either an engine that gimbals, or rcs, or reaction wheels, then it should compensate fine.

[Plusck]

1 hour ago, AeroGav said:

I'm struggling to see how a pair of ladders is going to cause wild spinning on his lander.

I've just re-read the OP and I feel a "doh" moment coming on...

OP says that the "boosters" are fine but the spinning happens with the "liquid fuel" engine.
So that does tend to suggest that the problem is simply that the upside-down lander can is the "control from here" point... which is upside down.

SRBs don't care where you're pointing since they can't gimbal. So if the problem starts with the LF engines, that does indeed suggest more than just a question of imbalance.
 

[DD_bwest]

6 minutes ago, Plusck said:

I've just re-read the OP and I feel a "doh" moment coming on...

OP says that the "boosters" are fine but the spinning happens with the "liquid fuel" engine.
So that does tend to suggest that the problem is simply that the upside-down lander can is the "control from here" point... which is upside down.

SRBs don't care where you're pointing since they can't gimbal. So if the problem starts with the LF engines, that does indeed suggest more than just a question of imbalance.
 

yup, its an easy mistake to make.  always the first thing to check when someone needs help with a mun lander.

[MrCraftyG]

Wow what a greatt community here. Thank you everyone for your great suggestions.

I think my issue is the upside down lander can which was the first part I placed...so i'll remove it, let the command pod take root control and give that a whirl.

I've tried many aerodynamic setups using various wings/fins etc with no luck, so I'm sure it's not as aerodynamic issue,  but still thanks for the tips.

To add more detail on my lander concept, the pilot controls from the command pod (which imtsssue clearly messed up on by having an upside down lander can as my root lol), transfers into the lander can, undock and fly that plus the science lander to the mun, land, do stuff, then detach leaving the science hardware and landing engine behind, dock the lander can with the command pod which still has an engine attached, transfer back to pod, dump lander can, fly back to kerbin etc.

I may have gone a bit ott with the comms, solar etc but it looks the part I like an air of realism in games like this so I expect my comms sats for example will have more antennae and power than needed...but if it looks the part, I feel better. Obviously some compromises will happen in due course as i learn more about kerbin rocketry.

I'll post a screenshot of something that works if it turns out to be the upside down lander can causing the problems. ..or a screenshot of a failed design if that doesn't fix it.

Thanks again for responding quickly and with several things to try. it will keep me busy tonight

Fly Safe

Edited November 7, 2016 by MrCraftyG
Spelling fails

[DD_bwest]

15 minutes ago, MrCraftyG said:

Wow what a greatt community here. Thank you everyone for your great suggestions.

I think my issue is the upside down lander can which was the first part I placed...so i'll remove it, let the command pod take root control and give that a whirl.

I've tried many aerodynamic setups using various wings/fins etc with no luck, so I'm sure it's not as aerodynamic issue,  but still thanks for the tips.

To add more detail on my lander concept, the pilot controls from the command pod (which imtsssue clearly messed up on by having an upside down lander can as my root lol), transfers into the lander can, undock and fly that plus the science lander to the mun, land, do stuff, then detach leaving the science hardware and landing engine behind, dock the lander can with the command pod which still has an engine attached, transfer back to pod, dump lander can, fly back to kerbin etc.

I may have gone a bit ott with the comms, solar etc but it looks the part I like an air of realism in games like this so I expect my comms sats for example will have more antennae and power than needed...but if it looks the part, I feel better. Obviously some compromises will happen in due course as i learn more about kerbin rocketry.

I'll post a screenshot of something that works if it turns out to be the upside down lander can causing the problems. ..or a screenshot of a failed design if that doesn't fix it.

Thanks again for responding quickly and with several things to try. it will keep me busy tonight

Fly Safe

you can also just right click the return pod and select control from here.  

[MrCraftyG]

 

Quote

1 hour ago, DD_bwest said:

you can also just right click the return pod and select control from here.  

 

I didn't need to, but that will come in handy when I undock from the command pod when in Mun orbit. 

The rocket flew just fine now the root command pod is the right side up lol now I just need the adjust the design of the rocket to give me sufficient velocity without running out of fuel when trying to orbit....I love this game