What is happening? -- heat shield pushed back

[Spyros]

Hello,

I have a spacecraft with two inflatable heat shields (front + back) and I am trying to land on Eve.

However, when I reach a specific attitude (e.g. around 47/49 kms)  something weird happens: it looks like the heat shield (which faces the heat) is pushed backward more and more until this becomes way too much, and passes through the bottom parts of the craft (e.g. engines, landing legs, etc) leaving them exposed to heat. What follows next is that these parts of the aircraft are over-heated (since the heat-shield is pushed way too back and has passed through them) and so they explode.

I have 200+ hours of KSP (not a veteran and so there things that I don't know yet) and I would like to understand 1) what is happening --- i.e. what is it that makes the heat-shield to be pushed back; which one of the measurement indicators was the alarming one?   ,  2) potential ways to prevent this from happening. I wasn't able to find this information elsewhere as I didn't observe a similar incident occurring in any other video/thread.

Here is a picture of the situation: 

 

Here is a picture in space before that:

 

Here is whatever remained from the vessel after all the explosions that followed:  -- (luckily/funnily enough)

 

P.S. I use the stock version of the game, the only mod I have is Kerbal Engineering Redux.

Edited December 23, 2018 by Spyros

[Snark]

Hello, and welcome to the forums! 

1 hour ago, Spyros said:

what is happening --- i.e. what is it that makes the heat-shield to be pushed back

What's happening here is that the aero forces on the ship are so huge that it's turning your ship into a floppy noodle and wrenching it out of shape.

A major part of the reason for that is that you've mounted your heat shield on a flimsy little narrow girder, which means the connection's a lot weaker than if you used a 2.5m stack.  Skinny parts aren't as stiff as thicker parts.

1 hour ago, Spyros said:

potential ways to prevent this from happening

If you attach it with a part that's the same size as the heat shield itself (i.e. 2.5m), it will be a lot stiffer.

Another option is that you could just turn on the "autostrut" feature for that part-- tell it to "autostrut to heaviest part", for example, and it'll go almost completely rigid, even if you've left it on the skinny girder.

[Spyros]

16 minutes ago, Snark said:

Hello, and welcome to the forums! 

What's happening here is that the aero forces on the ship are so huge that it's turning your ship into a floppy noodle and wrenching it out of shape.

A major part of the reason for that is that you've mounted your heat shield on a flimsy little narrow girder, which means the connection's a lot weaker than if you used a 2.5m stack.  Skinny parts aren't as stiff as thicker parts.

If you attach it with a part that's the same size as the heat shield itself (i.e. 2.5m), it will be a lot stiffer.

Another option is that you could just turn on the "autostrut" feature for that part-- tell it to "autostrut to heaviest part", for example, and it'll go almost completely rigid, even if you've left it on the skinny girder.

Thank you so much for your comments, they are really helpful! I am going to try to do what you suggested. 

Specifically,  my plan is to put a "Rockomax Brand Adapter 2" betwen the stack and the heat shield. 

 

[Ultimate Steve]

Or just use tons of struts.

Noodle rockets have long been a problem in stock, although it's much better than it used to be. There's a mod that fixes this (KJR) but for your purposes struts or a simple redesign will suffice.

[Spyros]

7 minutes ago, Ultimate Steve said:

Or just use tons of struts.

Noodle rockets have long been a problem in stock, although it's much better than it used to be. There's a mod that fixes this (KJR) but for your purposes struts or a simple redesign will suffice.

Thanks for the suggestion!

By the way, how manyof them would you consider being reasonably enough? --- just looking for a vague approximate number instead of going way off the norm

[Spyros]

New design worked all-fine       The ship was shaken a bit but nothing was broken 

[Foxster]

9 hours ago, Ultimate Steve said:

Or just use tons of struts.

Not a good idea if the plan is to fly the craft to orbit again. Struts are very draggy on Eve. 

[Ultimate Steve]

7 hours ago, Foxster said:

Not a good idea if the plan is to fly the craft to orbit again. Struts are very draggy on Eve. 

Going just from the shield to the craft, not the other way around. IIRC once they are attached, the nubs on the craft end will disappear after a save/load, but I may be wrong.

[Foxster]

4 minutes ago, Ultimate Steve said:

Going just from the shield to the craft, not the other way around. IIRC once they are attached, the nubs on the craft end will disappear after a save/load, but I may be wrong.

That's not what you said though. You said the fix to a noodle rockets was to use tons of struts. You might get away with that on Kerbin but not on Eve. 

[Ultimate Steve]

1 minute ago, Foxster said:

That's not what you said though. You said the fix to a noodle rockets was to use tons of struts. You might get away with that on Kerbin but not on Eve. 

Ah, sorry. Looking back on that post, it is worded a bit confusingly, so I didn't exactly say that, but I meant it.

[Spyros]

9 hours ago, Foxster said:

Not a good idea if the plan is to fly the craft to orbit again. Struts are very draggy on Eve. 

Thankfuly I have a decoupler to get rid of the griders (and the heat shield, as well as most of the struts that I used) after I deploy the parachutes and before I land on Eve. If I remember well I only used four struts that connect the main part of the ship with the grider (the decoupler is between and I didn't want the connection to break; there was a bad angle between the decoupler and the grider in the third photo that I uploaded).

 

Ok, I see you guys explained to each other what you meant, nice.

 

[Gapone]

It's simillar to the Wormhole Kraken.