Keeping wings cool on re-entry

[Superfluous J]

Okay I know about as much about space planes as I do about ... uh... some other topic I don't know much about. The Daytime Emmys. There you go. I know as much about space planes as I do the Daytime Emmys. Maybe less.

Arguably my most successful spaceplane to date was my Astro-glider, which is saying a lot in both directions because from what I can tell, it basically should not have worked at all, ever, even considering the way the old atmosphere used to work.

(ir)Regardless, I've decided to try again now that asteroids behave correctly in atmosphere, and I've come upon a problem: Wings explode. I suspect that there are one or more reasons for this but don't know which of those reasons are - ahem - reasonable and which are not, or if there are any other reasons that I'm not aware of.

Couple this with the fact that if I make any changes to the design I have to reconstruct the craft in orbit by hand, and I hope you all can understand why I'm willing to skip the tried-and-true "keep exploding until you don't" Kerbal methodology.

So here's a pic of what exploded last night:

The ONLY things that exploded were the wings. At least, until it reached the ground. My question is "why?" and here are my guesses:

• They can't distribute heat though the claws either quickly enough or at all.
• Those wings don't handle re-entry very well.
• I'm re-entering too shallow.
• I'm re-entering too steep.
• I'm trying to fly an asteroid which is stupid.

I was at a 100km orbit and brought my Pe down to 40, and the wings blew up somewhere around 40km while still traveling over 2km/s.

So, the full questions:

Which of those is the cause or causes?
How can I mitigate those causes or (better) eliminate them?
Can I just slap radiators on the wings? Will that affect aerodynamics? Can I attach them on decouplers or will the decouplers impede heat flow?

[bewing]

35 minutes ago, 5thHorseman said:

Which of those is the cause or causes?
How can I mitigate those causes or (better) eliminate them?
Can I just slap radiators on the wings? Will that affect aerodynamics? Can I attach them on decouplers or will the decouplers impede heat flow?

Those specific FAT455 wings have an extremely low heat tolerance. They are the one type of wing that is not made to be for spaceplanes. They are the biggest, but they are only made for low-speed atmospheric use. (Note that a determined spaceplane builder can still get them to work with clever engineering, but that's another story.)

BigS delta wings have slightly less area (5 instead of 7), but much better heat tolerance. So using those as replacements would most likely solve your issue.

Radiators do not accomplish much inside an atmosphere during reentry -- their efficiency levels go to hell. You might get a couple degrees out of them, but it won't make a noticeable difference.

There are two types of radiators, fixed and extendable. The fixed ones only have a very short cooling range, so a decoupler mostly defeats the purpose. Yes, they add some drag, but nothing compared to a big fat asteroid. Extendable radiators are sensitive to wind and will snap off in any stiff breeze.

 

[Rocket In My Pocket]

What @bewing said^

Pretty much the entire suite of "747" parts has extremely low heat tolerance. Max temp of 1200, compared to 2000+ for most "re-entry worthy" parts.

That said, I've used them on vehicles that re-enter but it's far from ideal.

[Aeroboi]

What ^they've^ said, luckily there are these BIG-S thingies that do 2400K.

[Gargamel]

5 hours ago, 5thHorseman said:

I'm trying to fly an asteroid which is awesome.

FYP.

But that is part of the problem.  I learned a while back when designing my heavy Eve lander, that trying to land it with a full tank of gas (250t v 100t ish, don't remember exact numbers) resulted in much more re-entry heating as it took longer to slow down. 

So mix a heavy "payload" with flimsy wings, and you have a recipe for disaster.    Sadly, the only thing you can fix is the wing design, unless you first mine the heck out of that asteroid.    If you don't want the resources on the planet, then this might be a good option too. 

[Superfluous J]

39 minutes ago, Gargamel said:

FYP.

But that is part of the problem.  I learned a while back when designing my heavy Eve lander, that trying to land it with a full tank of gas (250t v 100t ish, don't remember exact numbers) resulted in much more re-entry heating as it took longer to slow down. 

So mix a heavy "payload" with flimsy wings, and you have a recipe for disaster.    Sadly, the only thing you can fix is the wing design, unless you first mine the heck out of that asteroid.    If you don't want the resources on the planet, then this might be a good option too. 

Being awesome does not make it not stupid. It may actually help

And having it be full is part of the mission spec because it'll be cooler that way. Or hotter, I guess, speaking literally.

I may experiment with some throwaway airbrakes or maybe even the inflatable heat shield as a Marry Poppins parasol.

[Rocket In My Pocket]

16 minutes ago, 5thHorseman said:

I may experiment with some throwaway airbrakes or maybe even the inflatable heat shield as a Marry Poppins parasol.

I can tell you from experience that Airbrakes help a lot when using the "747" wings.

They typically survive as well, their heat tolerance really isn't too shabby.

Edited November 3, 2018 by Rocket In My Pocket

[Snark]

On 11/3/2018 at 12:52 PM, 5thHorseman said:

Being awesome does not make it not stupid.

^ Indeed, the quest for the "perfect" KSP design might even be described as "trying to come up with something that's stupidly awesome instead of awesomely stupid". 

My own solution for reentering with a really massive asteroid is not to try to maximize the lift, but to go total gangbusters on drag.  That is, give some sizable wing parts and attach them so that the asteroid looks like a badminton birdie with extremely flared "feathers".  It's got wings attached, sticking out sideways with a slight aftwards rotation to keep it aerodynamically stable with the asteroid leading.  The wings are flat-side-on to the oncoming airflow, so the drag is tremendous.  Slows it down nicely, and basically any wings except those big ones you're trying to use have a much higher heat tolerance.

Of course, one drawback to my approach is that it steers about as well as a freight train.    So it's not super useful if you care a lot about precisely where the asteroid comes down.  But as long as you don't care too much about that, it works great, and is pretty easy to set up since there's no need to worry about getting the alignment of the wings precisely right.