Kerbin Circumnavigation Challenge - updated for KSP 1.10

[linuxgurugamer]

Latest test run is now 40:53.  Making progress, but I have to go to work now, will continue later

[Bob_Saget54]

My newest iteration is now capable of sustained cruise speeds of 1740+ m/s. I'm starting to think I think that I am approaching the limits of engine technology in KSP, which means I'm gonna have to see how fast this thing can come in while still retaining control.

[MakerTribe]

2 hours ago, Bob_Saget54 said:

My newest iteration is now capable of sustained cruise speeds of 1740+ m/s. I'm starting to think I think that I am approaching the limits of engine technology in KSP, which means I'm gonna have to see how fast this thing can come in while still retaining control.

Your takeoff and approach must be pretty intense already. My cruise speeds are hitting a sustained 1750 now but still, 39m flat has been my best test run so far. Getting down in my craft is...interesting. I've come up with a pretty effective "Crazy Ivan'" kind of maneuver that is pretty reliable but timing is everything.

[GDJ]

Getting closer!

This is officially the fastest plane I've ever built since I started KSP (0.13)

And my unofficial time so far.....

[zolotiyeruki]

6 hours ago, Bob_Saget54 said:

My newest iteration is now capable of sustained cruise speeds of 1740+ m/s. I'm starting to think I think that I am approaching the limits of engine technology in KSP, which means I'm gonna have to see how fast this thing can come in while still retaining control.

I believe the maximum speed the RAPIERs will work at is 1753m/s.

[GDJ]

52 minutes ago, zolotiyeruki said:

I believe the maximum speed the RAPIERs will work at is 1753m/s.

With some testing on my planes about 1747 m/s @22500 metres ASL and they fart out. Seems they don't like running below 7.2 kN thrust (ie really fast).

[linuxgurugamer]

Rules question. Is a parachute allowed to be used?

[linuxgurugamer]

Hmmm.  The one thing I"m taking away from this is that the fastest planes tend to be the smallest.  Based on my experience, I've gotten my plane up to 1715 m/sec with 8 Rapiers, at 23000

I think I'll try replacing the Big S wings with something a bit smaller; less drag should compensate for losing some engines

[zolotiyeruki]

4 hours ago, linuxgurugamer said:

Rules question. Is a parachute allowed to be used?

Yes

2 hours ago, linuxgurugamer said:

Hmmm.  The one thing I"m taking away from this is that the fastest planes tend to be the smallest.  Based on my experience, I've gotten my plane up to 1715 m/sec with 8 Rapiers, at 23000

I think I'll try replacing the Big S wings with something a bit smaller; less drag should compensate for losing some engines

Last I heard, wings in KSP do not create parasitic drag unless they're in a stall, although they create some component of lift-induced drag, due to their mass.  This is something that makes the wet strakes awesome--they have the same lift-to-mass ratio as other wings, but they also carry fuel, so you get fuel capacity *and* lift without the parasitic drag or additional dry mass of a normal cylindrical fuel tank.

[linuxgurugamer]

7 minutes ago, zolotiyeruki said:

Yes

Last I heard, wings in KSP do not create parasitic drag unless they're in a stall, although they create some component of lift-induced drag, due to their mass.  This is something that makes the wet strakes awesome--they have the same lift-to-mass ratio as other wings, but they also carry fuel, so you get fuel capacity *and* lift without the parasitic drag or additional dry mass of a normal cylindrical fuel tank.

The Big S wings are also wet

[zolotiyeruki]

10 hours ago, linuxgurugamer said:

The Big S wings are also wet

True, but the mass ratio of the fuel is less advantageous (300 units for a 500kg wing) than the strakes (100 units for a 100kg wing).  In an optimization challenge like this, that can make a difference

[Krazy1]

On 9/16/2020 at 4:40 AM, swjr-swis said:

Offer is still open to send you the craft file, so you can compare them for yourself and verify it performs as shown. I'm specifically not posting it here to respect your choice of not sharing your craft, but I have no issue letting you have it - it's your design anyway, with a few tweaks.

Huh... strange. Maybe my drag is messed up from rerooting? I have higher AoA on the wings to get the fuselage level at a higher altitude. There's a big difference somewhere though. 

I posted the model I used: https://kerbalx.com/Krazy1/Rapier-biplane2

I'll try to fly it again at lower altitude to compare and update later. Thanks

[Lt_Duckweed]

13 hours ago, Krazy1 said:

I have higher AoA on the wings to get the fuselage level at a higher altitude.

What AoA are you using?  Hypersonic lift/drag ratio of wings begins to fall off after 5 degrees AoA so if you are using, say, 10, that would degrade your l/d ratio, while also having you flying at a higher altitude, meaning more drag and less thrust for a lower top speed overall.

Edited September 21, 2020 by Lt_Duckweed

[swjr-swis]

9 hours ago, Krazy1 said:

I posted the model I used: https://kerbalx.com/Krazy1/Rapier-biplane2

I can't do anything with it right now due to time constraints, but I've downloaded it and will let you know what I find.

This is the one I used or the screenshots: https://www.dropbox.com/s/xrd0cdsy4p9yk4z/0circ1.craft?dl=0

 

Upfront I can say that I agree with @Lt_Duckweed regarding the AoA. 5 degree is generally the maximum to get good performance, although usually close enough to optimum that I hardly ever bother to tune further (*). In the above tweaked version, you'll see I used the exact 5 degree snap as well. You also run the risk of flying too high, where the RAPIER power curve quickly drops and you'll start getting flame outs well before the speeds you would need to get the savings for long ranges.

(*: there are exceptions - when the goal is top speed at the cost of everything else, and if you can handle the heat, it usually pays to employ a much lower AoA, one that allows the craft to stabilize very low in the atmosphere where engine power curves allow thrust to continue even at higher Mach numbers. Don't expect to get any practical ranges out of such craft though.).

[swjr-swis]

On 8/30/2020 at 5:01 AM, zolotiyeruki said:

*swjr-swis - 8 times around (KSP 1.3.1)

@zolotiyeruki Can you please remove my entry from the leaderboard entirely? I don't know how this escaped me, or anyone else for that matter as it's right there for everyone to see, but that entry is not legitimate - it breaks the rule regarding nothing stuck to the end of the rapiers.

I have no explanation nor excuse to offer, but the screenshots clearly show a RAPIER drag value in the PAW that I can only explain if the engine's aft node has been 'plugged'. I must've somehow flown the attempt with a slightly different version than the craft I thought I used.

So please remove my entry entirely. If I get around to repeating the attempt with a legal entry, I will repost and it can be evaluated on its own merit. My apologies.

[zolotiyeruki]

45 minutes ago, swjr-swis said:

@zolotiyeruki Can you please remove my entry from the leaderboard entirely? I don't know how this escaped me, or anyone else for that matter as it's right there for everyone to see, but that entry is not legitimate - it breaks the rule regarding nothing stuck to the end of the rapiers.

Will do, and thank you for your honesty.  Way back when I was participating in the 1.3 or 1.4 version of this challenge, just as a test, I stuck a shock cone intake on the back of a RAPIER, and it resulted in something like a 30% reduction in fuel burn. Crazy stuff.

[etmoonshade]

I have yet to finish my own entry for this (I'm trying for speed as well - I find that making a plane that can circumnavigate is relatively easy...) but this whole thing reminds me of the old KSC -> Wideawake runs in my old Orbiter days (not my video, but I ran this run many many times...):

If only we could use rockets...

Edited September 22, 2020 by etmoonshade
Replaced the video with a slightly slower, but better-edited one.

[zolotiyeruki]

Yeah, making it around once isn't too bad.  Making it around many times, or going really fast, is where the challenge lies!

[etmoonshade]

17 minutes ago, zolotiyeruki said:

Yeah, making it around once isn't too bad.  Making it around many times, or going really fast, is where the challenge lies!

Oddly, I'm finding a speed challenge WITH rockets to be rather difficult as well - I'm basically trying to follow the example in the video I posted, but the rockets available have horribly low Isp so the fuel requirements are disgustingly high. It also doesn't help that stock aero is kinda crap, but I need to get a good long burn first before I worry about that.

Of course, it's kind of mutated into something that technically fits the challenge parameters as given, so we'll see. :V

[zolotiyeruki]

Remember that only air-breathing engines are allowd

[etmoonshade]

19 minutes ago, zolotiyeruki said:

Remember that only air-breathing engines are allowd

Oddly, I'm starting to think that you can't do this faster with rockets anyway, at least not within the remaining parameters of the challenge. Tsiolkovsky is a harsh master, and I think that (again, with stock parts) you won't be able to build something rocket-powered that simultaneously has enough dV to thrust continually through a full orbit, enough TWR to actually accelerate at any decent speed, and enough wing area to even get off the ground in the first place. Even TweakScale being allowed would probably let me do it, since the biggest problem I'm having is that there aren't any decent Mk3 engines in stock. Of course, stock aero being crap means that you can't really do the coasting thing that the video shows...

But yeah, I'm well aware of the formal challenge limitations. I just wanted to see if changing that particular parameter would let me do something similar to the old KSC to ASI runs, as far as flight profile goes. Maybe I'll fiddle a bit and see about posting a challenge for between KSC and Dessert Airfield...

 

[zolotiyeruki]

That's an interesting aside.  When I've done a mk1-sized craft with a single RAPIER, near the end of the flight, it's only generating a couple kN of thrust to sustain near-1700m/s speeds at 27km altitude. An LV-909 at max thrust will burn 3.5 units/second of fuel, according to the wiki (is that LF only, or combined LF/Ox?), and produce 60kN.  If it only needs to produce 5kN, that's 1/12th max thrust, so 3.5/12 ~=0.3 units/second.  Two FL-T800's would give you about 800 units total LF/Ox, which would be more than enough for the 40-minute trip, assuming you use a RAPIER to get you up to 1700m/s and 27km.

In fact, it's better than that, for two reasons:
1) using a rocket engine would allow you to fly at 29,900m and encounter significantly less parasitic drag
2) higher altitude and velocity means you're closer to orbital speed, and you need less lift to maintain altitude.  It gets a bit nerdy, but I figured out that the amount of lift you have to provide is proportional to (GM/R^2 - V^2/R).  With some hard numbers plugged in, if you're at 1700m/s and 27km, you only have to supply about 48% of the baseline lift, and at 1,900 m/s, you're down to about 36%.  Note that the percentage of lift you have to supply doesn't change much with altitude.

Actually, thinking about it a bit more, just using a RAPIER in closed cycle mode would probably be better, despite the Isp hit, since you'd eliminate the dead weight and drag of a second engine.

[swjr-swis]

Ok, ensuring this time everything was within the rules, I redid the run in 1.10.1, which was a lot more trouble than expected. Not because of the plane's performance, which was better than in 1.3.1, but because bugs. Sigh. Seriously... why does anyone use 1.10.1?

1. I had to rebuild the plane part by part from scratch in 1.10.1, because the imported RAPIERs from the otherwise entirely identical 1.3.1 version started flaming out continuously for no reason at all, while still well within the engine's power envelope.
2. There is a constant phantom torque forcing what should be a completely stable plane to roll right all the time, which necessitated babysitting it during the entire flight, tapping roll left to counter.
3. How does anyone endure those jet sounds for any amount of time???

This was a frankly horrible experience and it'll be my last endurance entry for this challenge. I just can't do this again, not in 1.10.1. Especially not when it's clear that performance-wise, a 1.3.1 entry is only at a disadvantage, making this torture for torture's sake.

So, until a better entry comes in, I give you the swis-circ 2b-10, clocking 11 laps around Kerbin in 7h14m7s.

Craft file - essentially identical to the already-shared 1.3.1 version, but rebuilt part for part in 1.10.1 to circumvent bugs (and with the previously-empty fore Mk1 tanks filled and prioritized): swis-circ 2b-10

Full imgur album: https://imgur.com/a/COvDSnW

Quick highlights:

Spoiler

This version is part for part identical, rebuilt in 1.10.1 to avoid the import bugs. I did fill up the fore Mk1 LF tanks that were previously left empty, and prioritized them to be used during ascent to cruise.

Just before take off.

First time halfway around.

Lap 1. Notice the RAPIER drag value, which is about 14x higher than in the 1.3.1 screenshots - the difference between a plugged and unplugged aft node.

Coming in to land after 7 long long, long long long, loooooong hours. (I have no words to express how much this experience has renewed my sincere hatred of the new jet sounds....)

F3 results after 11 laps and a safe landing. It'll have to do, I'm not trying this again.

 

 

[zolotiyeruki]

So you're telling me that you constantly corrected the roll offset for over seven hours!?  Or, if you were at 4x time warp, for almost two hours!?  Holy smokes man, you're dedicated!

(Incidentally, that's why I've taken on the maintenance of Pilot Assistant, so you don't have to do exactly that)

Congratulations, you're at the top of the leaderboard.  You certainly earned it.  Even before 1.10, the engine noises got so irritating that I turn off the sound when running this challenge.

[swjr-swis]

1 minute ago, zolotiyeruki said:

So you're telling me that you constantly corrected the roll offset for over seven hours!?  Or, if you were at 4x time warp, for almost two hours!?  Holy smokes man, you're dedicated!

Well, I had to make up for my previous oversight, and I guess a slight matter of honor was at stake. But no, I did not do this 7 hours straight... I paused the game after every lap to get a break and do other things, including sleep, food, and other trivialities. That session ran for the better part of two days.

The roll correction was... highly annoying. It meant I couldn't leave the game window running in the background while doing other things, like I did the previous run. And time warp is not recommendable in this challenge - it affects fuel consumption rate negatively.

 

4 minutes ago, zolotiyeruki said:

Even before 1.10, the engine noises got so irritating that I turn off the sound when running this challenge.

The previous sounds weren't ideal either, I'll agree. But for some reason these ones just seem to drill into the skull after anything more than 10 minutes. Ugh.