Any tips for an Eve lander?

[JacobJHC]

My lander keeps having flight issues such as rapid unplanned backflips.

[Geschosskopf]

Well, it would help if:

• told us what the purpose of the Eve lander was.  Is it a probe that's there for keeps or is it crewed and intended to return?
• you posed a pic of your lander that's flipping

 

[dafidge9898]

Make the COM very low

[magnemoe]

An small probe lander is pretty simple, you might want to use two heatshields in serial or an 2.5 meter one as the atmosphere get dense fast. 
And dafinge says keep COM low, be liberal with reaction wheels.

For an manned landing and accent craft you use the inflatable heat shield, its very hard to overheat and is lighter than the 3.75 meter one.
here its an idea to put lots of airbrakes on top of the accent stage, put them on decoplers so you can drop them before takeoff, you might even drop before landing. 
Again be liberal with the reaction wheels, my eve lander uses two large and 6 medium ones. 

I dump them with the heatshield once I'm slowed down the other option would be to land on them but I had an decent stage with deorbit engines and fuel, then an rover and the accent stage so it was best to split up high in the atmosphere. 

[Snark]

13 hours ago, JacobJHC said:

My lander keeps having flight issues such as rapid unplanned backflips.

Is it a one-way lander that goes down and stays down, or is it something that needs to ascend to orbit again?

If it's a one-way lander, then that's simple:  Keep the CoM as close to the heatshield as possible, so that you don't flip during the hot part of reentry.  Once you're through the hot part, it doesn't matter whether you do backflips or whatever.  For landing, if it matters whether you're right-side up, that's easy-- just put the parachutes on the top of the craft and gravity will take care of things.

However, I'm guessing that you're talking about a lander that needs to climb back to orbit again.  And yes, that can be tricky.

The reason it can be tricky:  trying to have your cake and eat it, too.  Specifically:  which orientation do you want it to be aerodynamically stable in:  prograde or retrograde?

Here's the paradox that a lot of people get caught by:

• When landing, many folks want the craft to be retrograde-stable.  People tend to put the heat shield beneath the craft, so it needs to stay pointed in the travel direction.  Also, when you're landing, you need to land right-side-up so that you can take off again.
• When ascending, you need the craft to be prograde-stable, for obvious reasons.

And it's really hard to have it both ways.  So, what can you do?

There are different approaches, but my personal favorite is, don't even try to have it both ways.  Design the craft so that it's prograde-stable, period.  It enters atmosphere nose-first, and it also leaves nose-first.

My typical Eve lander looks like this:

• Heat shield on the front of the ship.  I like to use the inflatable, since it's easy to launch off Kerbin, and then when inflated is plenty big enough to protect my whole ship.
• Put some hefty fins on the back of the ship, for aerodynamic stability.  For example, a quartet of delta wings, with ailerons.
• As much as possible, try to keep the CoM high, close to the front end of the ship.  However, given the squat nature of the typical lander, this may be of limited practicality.  I don't worry too much about this-- as long as I've got big fins on the back, that tends to take care of the aero stability.
• Enter Eve's atmosphere nose-first, and stay that way all through the "hot" part of reentry.
• The next challenge is to get tail-first for landing.  This is what parachutes are for.  I have parachutes at the top (front) end of the ship.  When I pop the chutes, this changes the ship from being prograde-stable to retrograde-stable.
• The one tricky bit is ditching the inflatable shield.  I typically do that during the unstable transition phase when the ship is tumbling a bit.
• Land with the parachutes, tail-first.
• After landing, blow the chutes (I've got them all mounted on radial decouplers)-- no point in hauling all that heavy, draggy stuff back to orbit.
• When it's time to take off, just point nose at the sky and go.  The fins at the back of the ship keep it pointed the right way.  Keeping CoM forwards is important here.  There are various strategies for this; one way to help do that is to use vertical stacks of asparagus tanks, and hook up fuel ducts in a way that tends to drain the bottom tanks before the top ones.
• Having steerable fins, and sticking strictly to straight-up prograde for the first 20 km or so of the ascent, helps to avoid flipping.  Also, during ascent, be careful not to go too fast.  You want to be sticking close to terminal velocity all the way up.  The hard part is having an idea of what your terminal velocity is... but that's what F5 is for. 

[JacobJHC]

@Snark Thanks alot this covers everything I was having problems with.