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Kerbin Circumnavigation Challenge - updated for KSP 1.10


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Ah, interesting--I've never tried to fly a RAPIER at sea level that fast.

You'll have to excuse my asking lots of questions--you've beaten the previous record by a substantial margin, so I want to make sure everything is kosher.  For example, wings attached to parts inside a fairing, and sticking out of the fairing, *might* be an exploit.  If having them attached internally but protruding through the fairing affects their performance, that's an exploit.  The rules don't say anything against ablator being consumed, and the heatshield stays attached, so that's ok.

No, deploying a fairing (i.e. shedding it) is not allowed--all the parts need to stay attached throughout.  Out of curiosity, what did you have in mind?

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2 hours ago, zolotiyeruki said:

For example, wings attached to parts inside a fairing, and sticking out of the fairing, *might* be an exploit.

It's not an exploit - if a part is occluded, it can't produce lift. Consequently, if a part produces lift, it also must produce drag. (With the exception of certain magic wings, and those have been fixed in the newest version of KSP anyway.)

Additionally, it's possible for a part attached in a fairing and offset outward to have less drag, but this requires it to be node attached, not radial attached. So in my design, this would really only serve to reduce the drag of the nose cone, but that's just on the front of the fairing anyway, so its drag is already at a minimum. Wings can't be node attached.

Even if it were an exploit, the wings are attached to the fairing base, so I wouldn't be taking advantage of anything.

2 hours ago, zolotiyeruki said:

No, deploying a fairing (i.e. shedding it) is not allowed--all the parts need to stay attached throughout.  Out of curiosity, what did you have in mind?

Inside the fairing would be a big ball of very lightweight and draggy parts - struts, sepratrons, empty fuel tanks, etc. Blowing the fairing would make that ball of parts serve as a giant airbrake, letting me dive down to the ground way faster.

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7 minutes ago, camacju said:

Inside the fairing would be a big ball of very lightweight and draggy parts - struts, sepratrons, empty fuel tanks, etc. Blowing the fairing would make that ball of parts serve as a giant airbrake, letting me dive down to the ground way faster.

A 1.25m service bay, while adding one more part, would net you the same result without needing to 'shed' anything.

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9 minutes ago, swjr-swis said:

A 1.25m service bay, while adding one more part, would net you the same result without needing to 'shed' anything.

Yeah, that's what I was thinking as a replacement. Bit more annoying to get all the node occlusion right however, plus it's still got some parasitic drag.

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48 minutes ago, camacju said:

Bit more annoying to get all the node occlusion right however

Honestly, in this particular challenge node occlusion tricks kinda push the grey area, since the rules very specifically and repeatedly ask not to do things that exploit the physics. It even explicitly identifies 'putting nose cones on the back of engines' as a banned item, which technically isn't any different from 'putting nose cones on the front of a stack and then offsetting it back into a fairing' - since the intended and achieved effect of both is to reduce the total drag of the 'capped' part.

You have a good thing going and I want to see it make a valid entry that'll up the bar for everyone. The 'sudden death' air brake idea is a good one (extra tip: depleted heatshields in the service bay, for extra effect) and you definitely need to implement it. And I do see the benefits of the extreme drag reduction. Just keep in mind the spirit of the challenge, that's all.

All just my own opinion, and I'm not the challenge owner.

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19 hours ago, zolotiyeruki said:

Hey @camacju would you mind posting the craft file for the airplane you took around 23 times?  I'm trying to replicate it in stock KSP, and can't seem to match the arrangement.

I actually don't have the craft file with me - it was only ever an auto-saved ship and then my next mission overwrote the craft file.

If it's helpful at all, the fairing is the root part, and the Rapier, cockpit, and air intake are attached to the interstage nodes. I also attached a couple nose cones to the other interstage nodes,

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4 hours ago, zolotiyeruki said:

Why would you put the intake on the inside of the fairing?  And what's the benefit of putting nose cones inside the fairing as well?

Putting things on a fairing's interstage nodes reduces the drag of the fairing in some cases

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7 hours ago, zolotiyeruki said:

Do you have a reference for that?

Not that I could link to - I learned that trick on Bradley Whistance's discord server.

7 hours ago, zolotiyeruki said:

This is the first I've heard of that particular trick.

I wouldn't be surprised - it's pretty obscure because it's hard to discover by accident. The fairing has to be the root part of the vessel and the parts attached to the fairing have to be the right physical size - the size of the attachment node doesn't actually matter.

Edited by camacju
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The reason I ask is because it feels pretty exploity--in the real world, putting a nose cone inside a fairing won't affect your parasitic drag.

What are the 0.625m LF tanks arranged around?  It looks like you've got eight, radially attached, but I can't fit 8 around a 6.25m tank without overlapping, and if I attach them to a 1.25m core, there are gaps between them.

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14 minutes ago, zolotiyeruki said:

What are the 0.625m LF tanks arranged around?  It looks like you've got eight, radially attached, but I can't fit 8 around a 6.25m tank without overlapping, and if I attach them to a 1.25m core, there are gaps between them.

They're attached to a 0.625m tank and slightly offset outward. While they're not as densely packed, I don't need as long of a fairing, which makes the plane easier to maneuver while climbing.

14 minutes ago, OHara said:

This, or a very similar glitch of KSP1's drag model, came to light here:

I didn't know that worked with service bays also! However that doesn't really produce any beneficial effects, as the service bays will always have a free front and back node to occlude.

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34 minutes ago, camacju said:

They're attached to a 0.625m tank and slightly offset outward. While they're not as densely packed, I don't need as long of a fairing, which makes the plane easier to maneuver while climbing.

I didn't know that worked with service bays also! However that doesn't really produce any beneficial effects, as the service bays will always have a free front and back node to occlude.

Thanks for the info on the tanks.

Ok, having gone down a few of those rabbit holes about KSP's drag model, I unfortunately have to classify the nose-cones-in-a-fairing as an exploit.  It is similar in a lot of ways to the "stick a shock cone on the back of the engine and offset it inward."  At one point, out of curiosity, I actually ran the comparison with and without that rear nose cone, and found that it reduced drag by something like 30%.

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2 hours ago, zolotiyeruki said:

Ok, having gone down a few of those rabbit holes about KSP's drag model, I unfortunately have to classify the nose-cones-in-a-fairing as an exploit. 

That's fine - I have some ideas to get even more range anyway, and this is the perfect opportunity to try them out.

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MnWpIac.png

First lap is complete. I have 84.4% of my initial fuel as compared to 83.6% in my previous run, but I believe I was less efficient on the ascent this time.

Assuming equal ascents, I am using fuel 19% more efficiently but I have 12% less fuel, for a 5% increase in overall range. That translates to a range of about 24.7 laps, and I believe that this craft can glide to a 25th lap. I guess we'll see tomorrow.

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Cool!  Let us know how it goes, and post the craft file if you can as well.  You might also try using something like Precise Editor to vary the AoI of the wings--when I experimented with it, 3 or 4 degrees (and more wings) was more efficient than 5 degrees and fewer wings.

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2 hours ago, zolotiyeruki said:

You might also try using something like Precise Editor to vary the AoI of the wings--when I experimented with it, 3 or 4 degrees (and more wings) was more efficient than 5 degrees and fewer wings.

I think 4 degrees is the best for hypersonic lift/drag ratios. I stuck with 5 degrees however, and simply increased the wing loading. Leaves a bit of room to squeeze out further range from the craft if desired. Is 30 laps possible?

2 hours ago, zolotiyeruki said:

Cool!  Let us know how it goes

Well, the craft went a good deal further than 25 laps.

Initial ascent

Spoiler

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In SPH. I reduced the mass of the craft but increased the wing loading, for overall better efficiency.

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On runway, spooling up engine

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On runway, brakes released

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Accelerating at sea level

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Climb

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Point at the horizon, open up the throttle. It's going to be a long few days.

Laps 1-10

Spoiler

 

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Lap 1

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Lap 2

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Lap 3

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Lap 4

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Lap 5

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Lap 6

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Lap 7

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Lap 8. At this point the plane has used up half its fuel. Notably, its speed is higher than the previous attempt, and still increasing even after several hours.

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Lap 9

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Lap 10

After 10 laps, the estimated range of the craft is 22 laps, but I know that it can probably do 25. At the very least it'll easily beat the previous record.

Laps 11-20

Spoiler

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Lap 11

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Lap 12

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Lap 13. At this point, the reduced drag from the higher wing loading means that I have more fuel now than I did at lap 13 in the previous mission, even though I started out with 600 less. Additionally, the reduced mass of the plane means that I will always be using less fuel. The plane is now half of its mass at takeoff.

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Lap 14

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Lap 15. Thrust drops below 10 kN; estimated range is 9 more laps, for 24 total.

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Lap 16

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Lap 17

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Lap 18

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Lap 19

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Lap 20

Estimated range is 6 laps, but a seventh is possible because this craft has quite good glide performance.

Laps 21-27

Spoiler

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Lap 21. The engine starts flaming out so I reduce throttle

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Lap 22

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Lap 23. Record is tied here

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Lap 24 and a new record

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Lap 25 - throttle is reduced further. Estimated range is under 2 laps, with a glide making up the difference.

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Lap 26

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Out of fuel!

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The glide performance is way better than I expected for a craft with such small wing area

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On final approach - stall speed is really low

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Landed, after almost three days of flight

27 laps around Kerbin * 600 km Kerbin radius * 2pi = 102,000 kilometers range.

2 hours ago, zolotiyeruki said:

and post the craft file if you can as well.

Link to craft file:
https://drive.google.com/file/d/13kK7BonPxk5ay5fCuNEACpR32ukdDTrr/view?usp=sharing

Link to loadmeta file:
https://drive.google.com/file/d/1Sk6wfQgtkaqEWVd1poHkQxfiMA4lAqW9/view?usp=sharing

Edited by camacju
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