Large Eve lander keeps flipping while using 10m heat shield

[Magzimum]

So, I built this large lander to get Jeb a chance to hop around on Eve. It keeps flipping. I already tried to keep it as short and wide as possible, with its CoM (center of mass) as close to the heat shield as possible. The ship has 8 Advanced inline stabilizers (that's the Mk1 reaction wheels) and plenty of electricity to keep them running for a few minutes.  

Would anyone care to comment how I can keep that heat shield under the lander?

p.s. Other comments on the lander are welcome, but not the purpose of this post.

Edited August 8, 2016 by Magzimum
First time uploading a picture onto this forum.

[Cornholio]

If I understand game mechanics correctly, you could try adding some more reaction wheels at the bottom of the SRBs attached with separators.  That would 1) lower your COM slightly and 2) provide higher torque at the bottom of the heat shield.

[bewing]

Some vernors at the top can help.

Some tailfins at the top can help -- especially in pairs, if you set the pairs to deploy in opposite directions.

[ForScience6686]

Torque is easier achieved when applied further from the com.  So put them as far away as possible.  Or another option is to increase the drag at the rear.  Attach a girder to the top and place air brakes at the end to deploy on re entry.  I've used this technique for dropping large items inside fairings.  It looked like an egg with a cocktail umbrella sticking out the top.

[Signo]

7 minutes ago, ForScience6686 said:

Attach a girder to the top and place air brakes at the end to deploy on re entry.  I've used this technique for dropping large items inside fairings.  It looked like an egg with a cocktail umbrella sticking out the top.

Definitely this ^, but they will easily burn if you deploy them on Eve, just give'em yaw/pitch.

BTW, huge stuff you have there. Sea level ascent? 

 

[Broco]

I heard all those tips with the fins at the far end of the craft and tried it with my lander but it still wasn't enough. In the end I used RCS-Thrusters + fins which I put on the top of my Craft with steel beams which I got rid off once I reached a height at which I could use chutes.

Moving down your command pod closer to the heat shield also helps.

Edited August 8, 2016 by Broco

[Magzimum]

Ok, so I am actually on the right path with this, but haven't over-engineered it yet. More wheels, and some fins/airbrakes. I'll put them on another separator, together with the parachutes (that I have not put on yet while testing). 

How do you deal with the obvious lack of aerodynamics that a girder with airbrakes has at the top? Fairing? Or just moar boosters?

11 minutes ago, Signo said:

BTW, huge stuff you have there. Sea level ascent? 

First time ascent, so not sure where I will land...

In all fairness, I don't know Eve so well yet, and I decided to find out while playing rather than reading and asking online. But now I did need help cos I wasn't even getting there.

[fourfa]

Everything that you don't need for ascent - mount to decouplers and blow off before Eve launch.  Parachutes, ladders, girders, landing gear, heatshields, aero surfaces, everything.

[Signo]

7 minutes ago, Magzimum said:

How do you deal with the obvious lack of aerodynamics that a girder with airbrakes has at the top? Fairing? Or just moar boosters?

TBH I do not use airbrakes with a girder - I stick them on radial separators with the chutes, so they are closed and inoperative when I ascend from Kerbin (and a minimal drag add on for a huge craft) and they are gone when I ascend from Eve.

[swjr-swis]

1 hour ago, Magzimum said:

So, I built this large lander to get Jeb a chance to hop around on Eve. It keeps flipping. I already tried to keep it as short and wide as possible, with its CoM (center of mass) as close to the heat shield as possible.

In Eve's atmosphere, drag is almost all-overwhelming, and the 10m heatshield is the unchallenged king (queen?) of drag.

The 10m heatshield really should be renamed to '10m airbrake', because in it's intended deployment environment, Eve's atmosphere, that is what it really does above anything else: it's a huge source of drag that is meant to slow down your heavy fully-fueled lander - and on the side, it also affords a little extra protection against the entry heat. So what I see in your pic is a craft composed of a very aerodynamic top, with very little drag, and a ginormous airbrake at the bottom, with the CoM pretty much halfway between them. Not surprising it flips on the way down.

Reaction wheels are not likely to prevent that, a considerably portion of your craft would need to be reaction wheels to compete against the aerodynamic forces. You need to either push the CoM practically inside the heatshield (does not seem likely with that design), or add a plethora of fins/chutes/airbrakes to the top, or a combination of both.

[ForScience6686]

I don't consider it to be a big drag on lift off from kerbin.  You're talking about a 5 minute trip through the atmosphere, and the rest of the craft will cause much more drag then your cocktail umbrella.  But I would ditch it once you've slowed down enough to pop chutes.

[bewing]

An alternate solution is just to put another 10m inflatable heatshield on the top. Then, if it flips, it flips. That can save a lot of engineering steps.

[foamyesque]

3 hours ago, bewing said:

An alternate solution is just to put another 10m inflatable heatshield on the top. Then, if it flips, it flips. That can save a lot of engineering steps.

It also acts as a giant drag source in its own right, which will both tend to prevent flipping in the first place and will make the lander slow down much faster, making heat even less of an issue.

[Foxster]

What works is a lot of air brakes at the top. No need for them to be on girders or whatever, they don't need to protrude far from the craft as the KSP physics model doesn't work like that. In fact you want them tucked away from the air stream and behind the "tube" of the heat shield to protect them. As already suggested, mount them (along with a load of 'chutes) so they can be detached before lifting from Eve. You might need up to a dozen air brakes. 

Don't plan to make it a science hopper. You'll likely not have the fuel for it, it's hard enough making one landing and return. Drop a separate science rover for that. This means not having to cart the science stuff back to orbit - it is essential to minimise the payload, so drop the experiments before lifting. 

Swap out the lander-can for a mk1 capsule (mono removed). It is slightly more massive but much less draggy and that is all-important on Eve. 

Use only mk1 stacks - they have much less drag than all those fat tanks you have. 

Dump the landing gear and reaction wheels before lifting. 

Get rid of all those struts. They are massive and very draggy on Eve. 

Don't use those angled nose cones. They might look cute but they are draggy. Use round air intakes instead, less mass and drag. 

Are those SRBs? Not efficient. Aerospikes are the most efficient engines for Eve. 

[swjr-swis]

5 hours ago, bewing said:

An alternate solution is just to put another 10m inflatable heatshield on the top.

Thus began the Age of the Oreospace Engineer....

[Spricigo]

13 hours ago, Cornholio said:

I 2) provide higher torque at the bottom of the heat shield.

Wrong

12 hours ago, ForScience6686 said:

Torque is easier achieved when applied further from the com.

Also wrong. 

Where you put reactions wheels don't matter.  You misconcept torque. 

Torque is cross product  of applied force and distance between rotation axle and where the force is applied(arm lever)   In mathematical language:

[torque] =[force] X[arm lever] 

The misconception here is that actually there is such thing as applied torque. Torque is the effect of an applied force, arm lever and angle between both. This effect don't need to have the same "*point of incidence*" of the applied force,  it actually has an "*axle of incidence*"  that by the proper definition of torque act in perpendicular direction of both force and arm lever. 

Now to the OP problem. 

This heatshield is causing too much torque.  You need to reduce it or counter it.

To reduce torque you need to either reduce drag force,  distance from CoM (lever arm)  or deviation between vessel alignment and airstream (angle of atack). Any of this will be a challenge without a complete redesign. 

To counter it you need a opposite torque. There is the poblem of HS's torque being variable in intensity and direction so you need to counter it with an also variable restraint-torque. Fortunately there's a easy  way to accomplish that, drag behind CoM as others pointed in previous answers. 

Other advices: 

I don't see any ladder in your ship,  don't forget it. 

 

[foamyesque]

8 hours ago, Foxster said:

Use only mk1 stacks - they have much less drag than all those fat tanks you have.

I don't think it is; a single stack is more streamlined than a group of smaller ones IME (which would also match reality). That assumes the same amount of fuel packed into the same height, however, so it might be worth considering going long and thin. You run into stability issues in a hurry that way if you're planning on executing a vertical landing though.

 

This is one more reason why every single return mission I send to Eve is a spaceplane

Edited August 9, 2016 by foamyesque

[Firemetal]

1 hour ago, foamyesque said:

I don't think it is; a single stack is more streamlined than a group of smaller ones IME (which would also match reality). That assumes the same amount of fuel packed into the same height, however, so it might be worth considering going long and thin. You run into stability issues in a hurry that way if you're planning on executing a vertical landing though.

 

This is one more reason why every single return mission I send to Eve is a spaceplane

Spaceplanes are easier to survive re-entry in but harder to ascend with. And one stack would be either short and wide or thin and tall.