Shielded docking port vs shock intakes

[Nich]

Most of my SSTO designs were riding the knifes edge of blowing up when I used a shock cone in front (95-98)  I have since switched it to a shielded docking port for an additional 200 heat resistance and now nothing gets over 45%  can anyone explain? Did they implement a shock boundary heating model?

[Evanitis]

22 minutes ago, Nich said:

can anyone explain?

I think I'm not getting something. It can't be that you are really asking if a nosepiece's higher heat-resistance results in resisting more heat...

I rarely build planes with enough TWR for that to matter, but when I do, I usually pick a shielded port... Mainly for I heard it's good against overheating.

[Norcalplanner]

1 hour ago, Nich said:

Most of my SSTO designs were riding the knifes edge of blowing up when I used a shock cone in front (95-98)  I have since switched it to a shielded docking port for an additional 200 heat resistance and now nothing gets over 45%  can anyone explain? Did they implement a shock boundary heating model?

Nich, I recall reading something recently by NathanKell stating that a blunter object going fast enough will generate a boundary layer effect and therefore result in less heat transfer to that object. The context of that discussion was capsule reentry, but it may just be that the shielded docking port generates a similar result.

OK, i just found it: 

 

Edited February 16, 2016 by Norcalplanner

[Temstar]

Also worth pointing out - the hotter your rocket gets without blowing up, the more heat it's capable of radiating away into its surrounding environment. So extra 200 heat capacity could have given you a sweet spot where your rocket is radiating away as much heat per second as its picking up, where as with less heat resistive parts that same sweet spot might have been just out of reach.

[Nich]

Norcalplanners post explained it perfectly.  it is a detached shockwave.  With a shock cone max temp was getting over 2400.  With the docking port max temp are the wings at 800 (45%).  Not even sure what the docking port is at as it is not the critical part.

[Jetski]

Worth noting that the port has higher drag

 

[FullMetalMachinist]

3 hours ago, Nich said:

Norcalplanners post explained it perfectly.  it is a detached shockwave.  With a shock cone max temp was getting over 2400.  With the docking port max temp are the wings at 800 (45%).  Not even sure what the docking port is at as it is not the critical part.

I don't know enough myself to refute this with evidence, but from posts I've seen from people who do, I don't think that stock KSP's aero model is sophisticated enough to model this. I could be wrong, but I just don't see it happening. Perhaps @NathanKell could grace this thread with his presence and explain.

31 minutes ago, Jetski said:

Worth noting that the port has higher drag

 

^ Also this.  In the world of SSTO space planes, drag is the enemy, and should be reduced at all costs. 

Edited February 17, 2016 by FullMetalMachinist

[NathanKell]

@FullMetalMachinist au contraire, I did write attached/detached shockwaves into the thermo model.

(The forward most part creates a cone, with angle equal to the shockwave angle--and it will be attached or detached based on the taper of the part, and the temperature behind the shockwave will vary. If a part is not inside that cone, it creates its own cone, and so forth.)

[FullMetalMachinist]

Just now, NathanKell said:

@FullMetalMachinist au contraire, I did write attached/detached shockwaves into the thermo model.

(The forward most part creates a cone, with angle equal to the shockwave angle--and it will be attached or detached based on the taper of the part, and the temperature behind the shockwave will vary. If a part is not inside that cone, it creates its own cone, and so forth.)

Well then I stand humbly corrected, and I apologize for underestimating you.

Learn something new every day!

[NathanKell]

Always happy to (positively) surprise.

[LordKael]

37 minutes ago, NathanKell said:

@FullMetalMachinist au contraire, I did write attached/detached shockwaves into the thermo model.

(The forward most part creates a cone, with angle equal to the shockwave angle--and it will be attached or detached based on the taper of the part, and the temperature behind the shockwave will vary. If a part is not inside that cone, it creates its own cone, and so forth.)

This sounds suspiciously like witchcraft... I love it!

[PanzerAce]

So if I'm understanding this, the blunter the better, so long as you've got the extra thrust to get into the high mach's anyway?

[Edax]

15 minutes ago, PanzerAce said:

So if I'm understanding this, the blunter the better, so long as you've got the extra thrust to get into the high mach's anyway?

Sweet, another excuse to have moar engines!

[PanzerAce]

9 minutes ago, Edax said:

Sweet, another excuse to have moar engines!

Yup.

 

I'm actually kinda annoyed at this, since my 11 part SSTO can't use this to it's advantage

[RokRoland]

1 hour ago, PanzerAce said:

So if I'm understanding this, the blunter the better, so long as you've got the extra thrust to get into the high mach's anyway?

I am understanding this as "if SSTO blows up on re-entry, consider nosecone as part of payload and attach it with the shielded docking port". Because nosecone is payload, it is still SSTO. Kerbals on orbit need the nosecones for hats. Yes, hats. And to make snack cones.

[NathanKell]

You don't need to make the nose as blunt as possible, just blunt enough to detach the shockwave at the speed by which it needs to be detached (or you melt).

[Gargamel]

Huh... well this explains why test SSTO's were barely making orbit while the service versions with docking ports were doing fine.  Good to know. 

[Hotaru]

32 minutes ago, NathanKell said:

You don't need to make the nose as blunt as possible, just blunt enough to detach the shockwave at the speed by which it needs to be detached (or you melt).

Does this work for reentries at steep AoA, as with the Shuttle? I've always preferred to build low-drag, high-TWR SSTOs that blast out of the atmosphere before any serious heat builds up, and then reenter at ~70º AoA, bringing the nose down to glide in somewhere around 900 m/s and 15,000 meters, after heating has died down. 

[NathanKell]

@Hotaru In that case the 'forward-most' part becomes the belly, which is plenty blunt. Forward-most is in relation to the airstream.

[Temstar]

Hmmm interesting. That means the ideal nose cone would be a rather blunt shape to deal with hypersonic flight, where it lifts the shockwave away from the nose and therefore reduce heating. This would for example allow you to attend higher speed on jet engine while climbing at very shallow angle without the nose melting. But then also have the capability to deploy a long skinny spike out of the nose to fool the air into thinking it's a pointy cone when the craft is flying at supersonic speed, ie while flying in lower atmosphere where heating is not a big issue and low drag is more important.

Edited February 17, 2016 by Temstar

[blowfish]

@Temstar Careful.  A detached shockwave makes heating easier to deal with, but also increases drag.  For re-entry you want to maximize drag while not roasting, so blunt shapes make sense.  For sustained hypersonic (or any) flight you want to minimize drag, which means that you don't want a blunt shape.  Note that most proposed hypersonic aircraft in the real world are actually very pointy.

And I'll add that for real world re-entries, most of the heating happens at very high Mach numbers (15-20?), so comparatively, for flight at a moderate Mach 5 or so heat is much less of an issue.

Edited February 17, 2016 by blowfish

[Chaos_Klaus]

Well, stock KSP has unnaturally high heating. If it were realistic, we wouldn't have any difficulty with reentry. Kerbin is just too small (roughly 1/10th of Earth's radius). So to spice things up, heating was increased to make for more interesting gameplay.

 

Shielded docking ports make no sense as space plane nosecones. To get to space efficiently, you need to gain lots of speed on jet engines. Your top speed depends mostly on drag. So pointy is good. 

For reentry, you don't want to go nose first anyway. You want to go belly first and bellies are generally pretty blunt.

[bewing]

That is, if you can maintain your attitude when you are flying belly first. But a belly doesn't usually give you much to work with for attitude control -- and a spaceplane usually must have extra drag toward the rear for stability, which makes the attitude control even more of a challenge.

 

[Edax]

2 hours ago, Chaos_Klaus said:

 

 

Shielded docking ports make no sense as space plane nosecones. To get to space efficiently, you need to gain lots of speed on jet engines. Your top speed depends mostly on drag. So pointy is good. 

For reentry, you don't want to go nose first anyway. You want to go belly first and bellies are generally pretty blunt.

I think the top speed depends more on engine power, don't you think?  If you just attach another engine, even if it doubles your drag, you will still go faster and accelerate harder.  You will burn more fuel though.

[Nich]

  While Drag  is important what's really important at the end of the day is TopSpeed on air breathing if you can buy an extra 200 dv by going blunt on air breathing your circularization  is that much less.

 Also I highly suspect that hypersonic craft are not going pointy not only do you increase the heating but unlike in KSP were you get the whole nose cones mass to distribute heat in a real nosecone you really only get the first one or 2 inches and once that melts The front end of the plane explodes

Edited February 17, 2016 by Nich