SSTO Javelin - A Skylon Rip-off

[Zenith Darksea]

Hello, first post here! Long-time KSP player and lurker, first-time poster.

Somebody call Reaction Engines Limited - I just built a stock clone of Skylon, their proposed SSTO powered by SABRE engines (I'm probably not the first to do this). I can say that it flew beautifully in Kerbal Space Program, so I think that the future looks bright for it in real life. That's how these things work, right?

Seriously, after fiddling around with complicated SSTOs with lots of aero-surfaces but not much flying prowess, some of which worked better than others, I decided to do something a bit simpler and crafted this unmanned SSTO, which I call the Javelin. Javelin model I is a cargo-carrying craft, while Javelin model II can carry passengers into orbit. It flew so well; I've never been this proud of a vehicle that I created in KSP, and so I had to share it with people. In essence, all it consists of is a drone core with a cargo bay, docking adapter, some finely balanced fuel tanks, and a couple of SABRE engines (I mean RAPIER, sorry) mounted on small, stubby wings. It took a while for me to learn the proper ascent and de-orbit profiles, but I've figured it out and it works really well. I also think it happens to look quite beautiful.

[Note that the craft itself is entirely stock; however, I flew it with Ferram Aerospace Research, which obviously changes the aerodynamics quite a lot. I don't know how well this would work with vanilla KSP aerodynamics]

Javelin I: http://www.filedropper.com/javelini

Javelin II: http://www.filedropper.com/javelinii

Now for some glamour shots. I forgot to take any on the way out of the atmosphere, for which you have my apologies (I was concentrating so hard on flying it correctly, which is tricky in FAR). I appear to have screwed up posting my album properly (because forum newbie), but it has kindly been posted just below by someone else.

Let me just say that slowing down from Mach 5.5 in FAR is really, really hard.

Edited November 30, 2014 by Zenith Darksea

[Shaun]

Did you know you can use imgur and /imgur in square brackets with the last five characters on the album link to see the album on the forums like so;

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By the way, that's a nice looking craft

[SpaceXray]

You ripped it off of my Nylon!

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[Majorjim!]

You ripped it off of my Nylon!

This is an issue with the new parts.. All replicas using them look the same..

[Rune]

This is an issue with the new parts.. All replicas using them look the same..

But they don't all work the same... I should repost the last one I did, the MkII version was really awesomely efficient.

Rune. It's the craft that got me into serious fuel routing wizardry: all tanks drain symmetrically with only two fuel lines.

[Majorjim!]

But they don't all work the same... I should repost the last one I did, the MkII version was really awesomely efficient.

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

Rune. It's the craft that got me into serious fuel routing wizardry: all tanks drain symmetrically with only two fuel lines.

I see four fuel tanks there right? Fuel lines on the two engines?

[SpaceXray]

But they don't all work the same... I should repost the last one I did, the MkII version was really awesomely efficient.

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

Rune. It's the craft that got me into serious fuel routing wizardry: all tanks drain symmetrically with only two fuel lines.

2? I used some 8 fuel lines on mine

[Rune]

I see four fuel tanks there right? Fuel lines on the two engines?

Yup, four tanks only. And two fuel lines placed without symmetry from the main body to the wing nacelles. But I picked the number of connections between parts along the fuel routes (by placing the fuel lines at the right spot and choosing the order of the body sections carefully) just so the right engine draws from the front tank, and the left one from the back. Or the other way around, don't really remember. A very subtle detail that improves the ship greatly IMO.

2? I used some 8 fuel lines on mine

Yup, I made it work with just two. But it meant the rest of the design was highly constrained as I say above, mind you. Also notice how both ports of the payload are docked... it is not secured with struts.

Rune. It's the little things, like your plane not becoming aerodynamically unstable as it flies, or your payload not poking through the cargo bay.

Edited November 30, 2014 by Rune

[Raptor9]

Some really nice Skylon replicas here. Question: does any of your spacecraft have center-of-gravity issues when low on fuel? Mine looked almost exactly like Rune's, but the CG would move too far aft with low fuel, causing it to want to tumble in the atmosphere. If you all don't, I'll have to go back and revisit my file.

EDIT: I should note that I used TAC Fuel Balancer to balance the tanks, so fuel drainage from front to back wasn't the issue.

Edited November 30, 2014 by Raptor9

[Rune]

Some really nice Skylon replicas here. Question: does any of your spacecraft have center-of-gravity issues when low on fuel? Mine looked almost exactly like Rune's, but the CG would move too far aft with low fuel, causing it to want to tumble in the atmosphere. If you all don't, I'll have to go back and revisit my file.

EDIT: I should note that I used TAC Fuel Balancer to balance the tanks, so fuel drainage from front to back wasn't the issue.

As I said, the CoM stays nailed like a rock to the middle of the payload bay throughout the whole flight in mine. I can temporarily direct you to the MkI version, slightly uglier on account of the fuel lines being much more visible, in this thread.

Rune. You have an unsymmetric fuel load, maybe?

[SpaceXray]

Btw here's the link to my version: http://forum.kerbalspaceprogram.com/threads/96105-Nylon-SSTO-0-25-A-real-Skylon-replica-%28DOWNLOAD-now-available%21%29?highlight=nylon

[Raptor9]

As I said, the CoM stays nailed like a rock to the middle of the payload bay throughout the whole flight in mine. I can temporarily direct you to the MkI version, slightly uglier on account of the fuel lines being much more visible, in this thread.

Rune. You have an unsymmetric fuel load, maybe?

No, I had a similar layout to yours, and used TAC fuel balancer to level all tanks. From front to rear, my components were exactly the same, except no docking port, and the drone core was on the front of the cargo bay. My wing construction was exactly the same amazingly, but I used two Mk1 Liquid fuel tanks on the engine nacelles instead of the LFO tanks. IIRC, my issue was that the RAPIERs were dragging the CoM to far back, but if I moved the wing/nacelle assembly forward, it would throw the lift vector off.

I'll revisit the concept from scratch, maybe I just needed a fresh start. Thanks.

[Zenith Darksea]

Thanks for the welcoming comments, guys. What surprised me was how similar the performance of my Skylon-alike (with FAR) was to the proposed performance of huge real Skylon. It hit Mach 5 at about 26km, just like Skylon is supposed to, although unlike Skylon I could push mine up to about 31km before I had to switch over to rocket mode and close the intakes.

I found it especially interesting that I could do it with such small wings. Playing with Vanilla KSP I had got used to plastering absurd numbers of aero-surfaces all over the place; it turns out however that sleekness is much more important with FAR. I was still surprised though at the enormous distance my SSTO could cover during reentry, as it took absolutely forever to slow down from hypersonic to supersonic flight.