The part behind my heat shield is getting hotter than the shield and exploding.

[SpaceFoon]

Not sure if this is a bug or just how the heat works in this game but I made a very similar design with the same heat shield work a few years ago. Using the inflatable heat shield so I wasn't expecting ablator or anything. When the problem first happened I put 2 regular heat shields in between the inflatable and the nose cone(pictured without inflatable for reference). This didn't do a thing it seems. the "in-between" shields seem to not get hot but its hard to tell since I can't right click them. One thing for sure is they don't lose any ablator.

From the pictures you can see the nose cone gets hotter faster than any other part. The inflatable heat shield DOES do quit a bit though as testing showed me when its deployed vs not deployed.

https://imgur.com/a/RVeQnRj

When I make it to KEO I have about 1500 DV left so I'm gonna be hitting EVE pretty hard. Like I said an older and very similar design did just this a few years ago. It wasn't easy but it worked.

[Wobbly Av8r]

There exists the idea of heat transfer between parts - you can read about it in the KSPedia (the in-game instruction 'book').

If that is too much reading, you can prevent your type of problem by ensuring that the part that the heat shields are attached to are rated at, say, 2000K. Typically the parts that fail in the manner you've described are usually only rated at 1200K (sometimes 1400K) which allows the heat transfer between adjoining parts to far exceed that relatively low value even though the heat shield is rated much higher.

[ Edit: If the part that is getting too hot must be used, a radiator attached to it can sometimes keep the heat in check, YMMV... ]

Edited December 29, 2020 by Wobbly Av8r

[SpaceFoon]

14 minutes ago, Wobbly Av8r said:

There exists the idea of heat transfer between parts - you can read about it in the KSPedia (the in-game instruction 'book').

If that is too much reading, you can prevent your type of problem by ensuring that the part that the heat shields are attached to are rated at, say, 2000K. Typically the parts that fail in the manner you've described are usually only rated at 1200K (sometimes 1400K) which allows the heat transfer between adjoining parts to far exceed that relatively low value even though the heat shield is rated much higher.

[ Edit: If the part that is getting too hot must be used, a radiator attached to it can sometimes keep the heat in check, YMMV... ]

Yea I was reading a bit about heat transfer. It makes sense but in this case seems to not be working exactly as intended. The nose gets a ton of conduction heat but doesn't really pass it on. That's why a put the two normal heat shields in between as a buffer but the nose is still hotter than even the inflatable heat shield is.

And yea the nose cone of a blimp is gonna have lower heat tolerances but at 1900k that seems pretty OP for a hollow shell.

Once i put a bunch of radiators on the cone by the shield and they didn't seem to do anything ever. I'm about to put some of the foldable one insude the hanger bay to at least normalize the heat though out the ship(if that's how they even work).

Thanks for the tips though!

 

[Wobbly Av8r]

No problem - sorry I wasn't able to help.

Good luck - it'll be interesting to see what you find as the final resolution...

[ Edit: Maybe your 'nuclear' parts are internally generating too much heat? ]

Edited December 29, 2020 by Wobbly Av8r

[SpaceFoon]

Oh no you helped by at least confirming things.

Yea I usually turn the nuke generator off long before reentry.

I will post the fix when I figure it out.

 

 

[Wobbly Av8r]

One last idea based on issues I've had:

Parts that have unnaturally high drag will also incur huge heat penalties on reentry. These are not always obvious - they 'look' streamlined but internally/programmatically, they are very inefficient. One such example I encountered was a thrust plate shroud that allowed the probe core underneath it to heat up even though it was sandwiched between two large fuel tanks and not subjected to aerodynamic forces... supposedly.

In your case it could be something like 'because the front of your fairing is not fully closed (terminates against a heat shield) the underlying components are taking the full brunt of the reentry heat', or something along those lines. Just another idea, FWIW.

Edited December 29, 2020 by Wobbly Av8r

[SpaceFoon]

I haven't looked at the drag for individual parts yet but i use the FAR tool while flying and the drag on the inflatable is ridiculous  but when deflated my total drag is unrealistically low it seems. I'm just glad I can't break Mach 1 at sea level like old stock or something haha.

You know I just looked at my own pictures again and I think I see the problem. the thermal mass for the nose cone is only 1000kj/K but the heat shield its 30k Look at how the internal temp of the shield is 336 and the nose cone is 772. Even the skin is hotter. Less mass = less ability to soak up heat, makes sense but how could the cone get hotter unless its taking heat from air friction or some type of refrigeration is taking place?

I though maybe the aero model was messed up because I tweak scaled the inflatable and use FAR on 1.11 but I took FAR out and the nose still exploded first. When hit that atmo at 45 degrees everything heats up like it should so I don't get it.

[Wobbly Av8r]

2 hours ago, SpaceFoon said:

how could the cone get hotter unless its taking heat from air friction or some type of refrigeration is taking place?

Exactly - depending on how you attached things back at the VAB, the nose cone may be acting as the leading edge despite the heat shield (again, I've had similar problems of the same issue and had to experiment with what 'hid' the part getting too hot. I think you're almost at the solution!

[king of nowhere]

your ship is big enough that the shield does not cover it entirely. also, with a big draggy shield in front, it is at risk of flipping

[SpaceFoon]

 

5 hours ago, Wobbly Av8r said:

Exactly - depending on how you attached things back at the VAB, the nose cone may be acting as the leading edge despite the heat shield (again, I've had similar problems of the same issue and had to experiment with what 'hid' the part getting too hot. I think you're almost at the solution!

Well I noticed all the heat is coming from convection. All the glowing parts in the picture are taking in convection heat  but all the red parts are not when the shield is open. All the hull parts behind the nose cone take 0 convectional heat unless the shield is deflated.

Just did some testing and I unclipped the inflatable to make sure the cone wasn't actually in front of it or something but that didn't do anything. I scaled the shield up to be 10meters before inflation. Nothing. I put a piece a couple meters tall in between the shield and nose cone. Nothing. I put a piece like 8 meters tall in between and presto! It works for some reason.

https://imgur.com/a/r1fU0g9

The whole thing seems to be weird. Look at what gets hot and what doesn't Then entire hull takes nothing. Most of the gondola take nothing except for 2 parts that are next to other parts that take nothing. The right and only right rudder is convection but no the left one? 

Edit: Also I did when the aero and The heat shield gives a ton of down force when pitched up and lift when pitched down. Not sure if that's related but it also doesn't make sense to me.

Edit 2: Ok so I noticed all parts are effected by convection flux while sitting on the runway. When I start flying some parts (mostly hull) the rate just goes to 0 while other parts convect until the head shield is open then they go to 0. But not all of them! Symmetry doesn't even matter! I have found the problem but what it is caused by?

Edit 3: Its FAR...

4 hours ago, king of nowhere said:

your ship is big enough that the shield does not cover it entirely. also, with a big draggy shield in front, it is at risk of flipping

Yea I just needed it to protect the hull its not a end all solution for sure. also I've been building this thing for years lol it don't flip. The wings drag a lot and I have 4 rudders with drag as well. My older design had big air brakes to stop that because it was my biggest problem but this one is just balanced perfectly or something. Its also 225 tons dry and very long so maybe that helps a bit.

Edited December 30, 2020 by SpaceFoon