Shielded docking port vs shock intakes

[Chaos_Klaus]

58 minutes ago, Edax said:

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.

no. unfortunately that is not how it is. That's why I wrote the opposite. Drag is the most important factor here. 

You reach top speed when thrust and drag are in equilibrium. If you double the thrust and double the drag, your top speed will be the same. 

Also, at high altitude, your engines will produce very low thrust. Drag however (roughly) scales with v² so it has huge impact at high velocities.

Managing heating and not melting the craft is a prerequisite to any successful flight. Without that there is no argument at all, so that doesn't really count.

Edited February 17, 2016 by Chaos_Klaus

[blowfish]

1 hour ago, Nich said:

 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

Well KSP really exaggerates heating at Mach 5 in a highly unrealistic way.  In reality, if you can survive re-entry, heating at mach 5 isn't going to be any trouble whatsoever.

Interesting data: here is REL's data from the Skylon's simulated trajectory.  If you look at the "Re-Entry" tab, you can see the mach number (Mn), AoA (Alpha), and various temperatures (e.g. Tsp is nose temp).  I don't know exactly what materials assumptions they are using, but the maximum temperature occurs around mach 23, at an AoA of about 41° (this might be enough to generate a detached shock but I'm not sure).  By the time you drop down to mach 5 or so, temperatures are very manageable.

[PanzerAce]

2 hours ago, bewing said:

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.

 

Try shifting your fuel around if you can't maintain the AoA that you want. In the traditional pointy dart with wings design, shift fuel backwards to increase AoA, forwards to drop it.

[ment18]

The reason the shielded docking port works so well is because it weighs 0.1t while the shock cone weighs 0.03t.  Having a high AoA during ascent is very bad because it causes huge drag.  During descent it is usually safe to pump all of your fuel to the back of you plane as PanzerAce said.  

9 hours ago, blowfish said:

Well KSP really exaggerates heating at Mach 5 in a highly unrealistic way.  In reality, if you can survive re-entry, heating at mach 5 isn't going to be any trouble whatsoever.

Interesting data: here is REL's data from the Skylon's simulated trajectory.  If you look at the "Re-Entry" tab, you can see the mach number (Mn), AoA (Alpha), and various temperatures (e.g. Tsp is nose temp).  I don't know exactly what materials assumptions they are using, but the maximum temperature occurs around mach 23, at an AoA of about 41° (this might be enough to generate a detached shock but I'm not sure).  By the time you drop down to mach 5 or so, temperatures are very manageable.

Does skylon reenter much higher than where it goes mach 5?  Also, skylon has cooling systems so it burns all of its heated fuel(dumps extra lh2/lox in orbit right?).  Also during reentry skylon weighs very very little and has a much larger surface area.

[numerobis]

10 hours ago, blowfish said:

Well KSP really exaggerates heating at Mach 5 in a highly unrealistic way.  In reality, if you can survive re-entry, heating at mach 5 isn't going to be any trouble whatsoever.

IIUC, KSP uses a decently realistic heating model, but scaled such that players have to worry about heating despite the low speeds you reach on Kerbin. It's similarly realistic as having a 600km diameter ball that has Earth gravity at its surface or that tanks have a 1:8 dry:fuel ratio -- based on physics, but scaled to make a better game for the impatient.

Skylon, on the other hand, is a long way from existing.

[blowfish]

53 minutes ago, ment18 said:

Does skylon reenter much higher than where it goes mach 5?  Also, skylon has cooling systems so it burns all of its heated fuel(dumps extra lh2/lox in orbit right?).  Also during reentry skylon weighs very very little and has a much larger surface area.

The precooler cools air entering the engines, not the skin.  And yes, re-entry happens much higher than the final leg of the air-breathing ascent.  But that doesn't change the fact that most of the heat is experienced at higher mach numbers - the power dissipated by drag is roughly proportional to v³, but only linearly proportional to density.  And the air-breathing ascent is actually pretty low in the atmosphere for the speed (it experiences up to 64 kPa of dynamic pressure!)  During re-entry, it weighs very little, yes, but that has no effect on the shock temperature it experiences at a given mach number, it just means it can slow down faster.

18 minutes ago, numerobis said:

IIUC, KSP uses a decently realistic heating model, but scaled such that players have to worry about heating despite the low speeds you reach on Kerbin. It's similarly realistic as having a 600km diameter ball that has Earth gravity at its surface or that tanks have a 1:8 dry:fuel ratio -- based on physics, but scaled to make a better game for the impatient.

Yes, atmospheric heating in KSP is scaled up a lot because in reality, you'd barely have to worry about heat in an earth-like atmosphere going at mach 6-7 (re-entry on Kerbin).  Which means that inevitably, parts start to overheat near mach 5 lower in the atmosphere.

19 minutes ago, numerobis said:

Skylon, on the other hand, is a long way from existing.

Sure, but I'll trust that their numerical simulations are probably pretty reasonable.

[Edax]

Well, I can definitely confirm the OP's assertions from my own experiment.  Made my own test with this Thermal Test Prototype.

Flying as level as I could manage with this simple craft, I achieved a top speed of 1576, with no heat warnings what so ever.

 

To further test the heat resistance of the shielded docking port, I aimed for a steep descent.  At 2000m/s at 22k attitude (right in the thick of the soup), I had no heat warnings triggered what so ever flying pro-grade.  It appears shielded docking ports are great for reentry to provide more aerobraking options..

Edited February 19, 2016 by Edax

[AbacusWizard]

On 2/17/2016 at 9:43 PM, RokRoland said:

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.

Of course; when you get to Minmus you have to have something conical to put the mint ice crea--uh, I mean, surface samples in.

[Curveball Anders]

On 2016-02-17 at 3:54 AM, LordKael said:

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

Nathan is a witch! He turned me into a newt! Burn him! Burn Him!

 

[cerberusti]

I did recently notice how superior the shielded docking port is as a nosecone. I noticed this on somewhat large planes (200 - 500 tons), I do not know how well it works with small ones.

 

 It lets you fly a better (and more forgiving) ascent to get more out of the jets, which seems to let me get more to orbit than I can with less drag and more heat worries.  Not needing to worry about riding the line with heat as much, and the convenience of a docking port at the front also help its case.

 

[Fearless Son]

On 2/17/2016 at 8:27 PM, 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?

Only on the frontmost part.  You probably want the rest of the craft to still be as streamlined as possible.  

[NathanKell]

And, again, not "the blunter the better", just "blunt enough to detach the shockwave by the time it gets hot enough you can't survive an attached one".

[AbacusWizard]

I've been quite frequently using the shielded docking port for any small craft that needs a docking port on the front, even orbital ships that are never going to enter an atmosphere again. It makes it a little easier to launch, it only adds a small amount of mass, and it looks so much cooler.

[Fearless Son]

I admit that I have found myself preferring a small procedural fairing for spaceplanes instead of any of the stock nosecones or an intake, mainly because it has good heat resistance, can be adjusted to make it as blunt or narrow as needed, and has internal space to put some small components I want to have but do not want to clip in (like batteries.)  

[Kerbal101]

On 2/19/2016 at 9:07 PM, NathanKell said:

And, again, not "the blunter the better", just "blunt enough to detach the shockwave by the time it gets hot enough you can't survive an attached one".

Nathan, can you provide example of other nose cones?

Some background: https://kerbalx.com/Kerbal101/Strangelove-Bspec

I have few ideas to improve the craft, but I found nothing which could "bisect" the heat like Shielded Port. The issue - its a port, not dedicated nose cone. It gives a feeling (of suddenly discovering) that "cooking oil is better for rocket engines, than kerosine".

Thank you.

[theend3r]

What are you people even talking about? Heating problems can be solved by... spinning!  

[Kerbal101]

54 minutes ago, theend3r said:

What are you people even talking about? Heating problems can be solved by... spinning!  

I've attached the craft above. Do try that without shielded dock ports.

[theend3r]

15 hours ago, Kerbal101 said:

I've attached the craft above. Do try that without shielded dock ports.

I would, but I'm still on 1.0.5 because of mods and I plan to upgrade only after 1.2 comes out.

[sdj64]

Also, in the reliable tradition of KSP debates like this don't end without testing!  So I did some.  I wanted to compare different nose cones commonly used on planes to see what works and what doesn't.  The test was done by remaining between 14000 and 15000 meters, and putting the throttle on full.  Except for the shock cone, all of the planes had 4 ramp intakes to provide air for the engine.

It appears that, as everyone is suggesting, the shielded docking port has much less heating than the others.  However, it also reached a much lower top speed because of its higher drag.  The cockpit probably would have exploded first.  I also tested the previously bugged communotron spike, which is no longer heat proof in 1.2 build 1553.  Interestingly, the aerodynamic nose cone reached the highest top speed before exploding, confirming @NathanKell's assertion that the best nose cone is "blunt enough" but not too blunt.

http://imgur.com/a/Kyfvm

 

 

[Sresk]

So this is a little counter intuitive to the discussion but I've been throwing pointy antennas on the front of all of my noses to manage heat which is the exact opposite of the blunt nose... how does the communitron effect the shock wave?

[Kerbal101]

On 10/3/2016 at 10:06 PM, sdj64 said:

Also, in the reliable tradition of KSP debates like this don't end without testing!  So I did some.  I wanted to compare different nose cones commonly used on planes to see what works and what doesn't.  The test was done by remaining between 14000 and 15000 meters, and putting the throttle on full.  Except for the shock cone, all of the planes had 4 ramp intakes to provide air for the engine.

It appears that, as everyone is suggesting, the shielded docking port has much less heating than the others.  However, it also reached a much lower top speed because of its higher drag.  The cockpit probably would have exploded first.  I also tested the previously bugged communotron spike, which is no longer heat proof in 1.2 build 1553.  Interestingly, the aerodynamic nose cone reached the highest top speed before exploding, confirming @NathanKell's assertion that the best nose cone is "blunt enough" but not too blunt.

http://imgur.com/a/Kyfvm

Nice. That was with "KSP 1.2 pre release build 1553."

Well, in 1.1.3 (currently - "stable"), anything explodes within 1350m/s, only shielded docking port makes it to 1600m/s, where other parts start to heat instead.

The importance is because a lot of people use newer aerodynamics of 1.2-pre for challenges without explicit mention, causing other part of the crowd into the "WTH?" zone.

[magnemoe]

On 18.2.2016 at 4:07 AM, numerobis said:

IIUC, KSP uses a decently realistic heating model, but scaled such that players have to worry about heating despite the low speeds you reach on Kerbin. It's similarly realistic as having a 600km diameter ball that has Earth gravity at its surface or that tanks have a 1:8 dry:fuel ratio -- based on physics, but scaled to make a better game for the impatient.

Skylon, on the other hand, is a long way from existing.

This, Falcon 9 first stage reach around 2.4 km/s at 60 km before returning to pad, it returns with engines first. 
2.4 km/s is Kerbin orbital speed so it could reach orbit with the second stage and payload. 

To balance the low speeds heating is far stronger than real world, TWR and fuel fraction is also much lower. 

[Kerbal101]

3 hours ago, magnemoe said:

This, Falcon 9 first stage reach around 2.4 km/s at 60 km before returning to pad, it returns with engines first. 
2.4 km/s is Kerbin orbital speed so it could reach orbit with the second stage and payload. 

To balance the low speeds heating is far stronger than real world, TWR and fuel fraction is also much lower. 

This was done in KSP before Falcon even existed.

[sdj64]

4 minutes ago, Kerbal101 said:

This was done in KSP before Falcon even existed.

I'm pretty sure Falcon existed in 2015...

Also it's easy to reenter from LKO with just about any ship, particularly if you can slow down with your engines first.

5 hours ago, Kerbal101 said:

Nice. That was with "KSP 1.2 pre release build 1553."

Well, in 1.1.3 (currently - "stable"), anything explodes within 1350m/s, only shielded docking port makes it to 1600m/s, where other parts start to heat instead.

The importance is because a lot of people use newer aerodynamics of 1.2-pre for challenges without explicit mention, causing other part of the crowd into the "WTH?" zone.

Also I did say that it was in 1.2, both in the post and the imgur album.  There was a bug in 1.1.3 where certain animated parts are almost completely heat-proof.  These include, at least, the shielded port and the communotron 16.  According to my testing, that bug has been fixed for 1.2.

[Kerbal101]

7 minutes ago, sdj64 said:

I'm pretty sure Falcon existed in 2015...

Also it's easy to reenter from LKO with just about any ship, particularly if you can slow down with your engines first.

No, I also invented this in 2015 (and only few weeks later discovered Warzous thread) and also knew no Falcon even close. And its not just returning from LKO, its about reusable single stage rockets (SSTO-R).

13 minutes ago, sdj64 said:

There was a bug in 1.1.3 where certain animated parts are almost completely heat-proof.  These include, at least, the shielded port and the communotron 16.  According to my testing, that bug has been fixed for 1.2.

Very interesting! So you mean this is more bug than feature. I think its both - because whilst docking port does not heat (bug), it implements "detached shockwave" - which I discovered before finding this thread.
For example, my vehicle created for a challenge uses this feature to shield the intakes against heat in 1.1.3.
Here are more information (linked post and below). The others used 1.2-pre, which has completely different dynamics, as also Claw confirmed in streamcast.