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[WIP] Skylon Replica for RO/RSS - Help me tweak it into orbit!


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I was sad after seeing a number of good looking RSS/RO Skylon replicas without craft files. And Cpt. Kipard's Skylon mod looks amazing, but distant. So I bit the hypersonic bullet and started making my own derivative to share. But, it's a WIP; urrently, I can only get up to ~5.8km/s. I'd love to get some help tweaking this thing into orbit.

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Here is version 0.14.

It includes a mmcfg for a couple necessary part tweaks (adds new parts so it doesn't resize stuff you already have); be sure to move that to GameData.

Required mods: Procedural Dynamics/Wings, B9 (with RO fixes, firespitter.dll, etc.), AIES, KW, FAR (I've been using 0.13x1), DRE, KJR, Real Fuels, and of course RO/RSS (Check out the RSS Mod Bundler if you're new to it)

This thing is a finicky beast. It's basically unflyable without FAR Flight Assist. I usually have all assist modes active and change these values from the default: Wing Level: k0.05/kd0.01, Pitch: k0.15

Take off gently at 2/3 throttle, and a speed of Mach 0.6

SAS seems to play nicely with everything on this craft so I usually use it, making fine adjustments and hitting F to re-center.

Watch the temp of the forward fuselage - if at ~1k and increasing, lower your throttle.

You may get a HARD roll seemingly randomly. Usually you can carefully correct it, lowering throttle helps.

I make sure I'm at a low throttle before switching to Rocket Mode (Action Group 1).

I have no idea why, but RCS does not want to roll.

Potential tweaks:

- Control surface control values (currently 20)

- Control surface axis toggles (currently all)

- Flap deflection value (doesn't seem to make much difference)

- Max temp for parts, especially procedural wings (I've upped the KW side tank/fuselage from 1450 to 1700)

- DRE directional heat deflection for parts

- All sorts of CoM/CoL/CoT tweaks, but it's tough fitting it to the Skylon schematic

- Engine angle (Real Skylon's engines are angled down ~10 degrees)

- Part masses to represent the advanced lighter structure of the Skylon.

But the limiting factor right now seems to be the amount of LOX I can carry without the thing snapping in two (or three) while maneuvering. Unfortunately with the SABREs, KER and MJ dV stats aren't calculated correctly, so I'm having to determine the necessary amount of fuel by trial and error. FYI, the SABREs also break FAR's Analysis and make the COM indicator disappear :(

I may move to remaking the whole thing with Procedural Parts so I can get it to 1:1 (currently it's about 65 meters while the real thing is 83m) and more easily customize CoM and fuel balancing.

Edited by curiousepic
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Out of all the attempts to make a Skylon out of existing parts this really looks the best. Are you using the joint reinforcement mod? Also KER has been getting some fixes lately; have you updated?

Thanks! Yeah, I'll add KJR to the modlist; even with KJR I needed to add a couple struts between the cargo bay and tail fuselage or it will snap right after takeoff. And I'll check out the new KER and see if it can handle the multi-mode SABRE.

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Hopefully the new joints in 0.23.5 will fix that problem.

What mod does the payload bay come from? You can try and make sure that all the nodes on all the parts along the fuselage are size 2 in the config files. If any of them are smaller then that could be why it's snapping. KJR works best on 2.5m joints and larger.

Edited by Cpt. Kipard
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You can try and make sure that all the nodes on all the parts along the fuselage are size 2 in the config files.

Size 3, in fact :/ It's from B9; I needed to un-re-scale it from the RO version, but that didn't affect the node size.

0.23.5 will probably help, but I'm hoping more that it doesn't break one of the critical RO/RSS mods.

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Size 3, in fact :/ It's from B9; I needed to un-re-scale it from the RO version, but that didn't affect the node size.

0.23.5 will probably help, but I'm hoping more that it doesn't break one of the critical RO/RSS mods.

It probably will unfortunately.

After I finish getting my satellite network into place and my space program working again, I will look at your Skylon project and see if I can find out what is going wrong.

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So, I tried adding some wings to the center of the craft to bring CoL in line with CoM, and along with adding more propellant, I was able to get tantalizingly close to orbit. A few realizations:

- I really need to shift CoL back (without adding extrandeous parts). I tried MMCFGing the procedural wing's lift value to help this, but it didn't seem to work. Are there any RO or other cfgs that overwrite them? Is there a way in the debug menu to see the final part cfg values?

- Even with the craft that almost made orbit, the payload was only around 2.5 tons, far less than the 15 tons of the "RL" version. And the craft is still pretty brittle.

- So, before I start a 1:1 redesign from scratch, I think it's worth waiting for both the .23.5 joint system upgrade, and a final version of Procedural Parts (and of course, all the RSS/RO mod updates to be compatible with .23.5)

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Curiosepic,

I looked at the design, there was nothing wrong with it. For some reason it just burns to much fuel to reach orbit. The TWR is about right to get 15tons to orbit but it just doesnt have the fuel load to do it.

Are you using KJR? I had no real issues with flex in it.

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Can I suggest a different approach? One of the things that makes Skylon different from other planes is that while it's in air-breathing mode, it's angle of attack is a bit higher. Maybe that's the problem. Sorry I can't help much, I don't use RSS...yet.

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I made a skylon replica in version 0.18. This is the only picture I have.

http://i.imgur.com/cx7MGMN.png

Lessons learned:

angle your engines, it helps, especially on takeoff.

use the fuel from the rear tank first, keep all the weight forward

use OMS to circularize. Main engines only used in atmosphere.

Good luck with this!, looking forward to watching your progress.

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If your problem is the amount of LOX without snapping it in half, and you have B9, there are invisible struts (the actual strut is invisible, but the start and end points are visible) you can use to stay with the skylon theme, but still add structural integrity. As well, they match the skylon color decently well. Try em out!

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