So, how do we get SSTO's into orbit now?

[XOIIO]

So, I've never been able to get into orbit with my SSTO's (so really they are just SS's I guess), but I have gotten in a few times, and while following the old (or at least what I recall) ascent profile, I couldn't get much above 20km. It's possible that this SSTO can't make it, but maybe I am just not doing it right. Perhaps I need some more intakes? (though from what I read apparently that doesn't do much anymore?)

I was hoping maybe someone could give me some updated tips and test out my SSTO (didn't have any luck in the spacecraft exchange)

https://www.dropbox.com/s/w1sc1gwqb8cmjqn/Nighthawk.craft?dl=0

Edited January 4, 2016 by XOIIO

[Vanamonde]

Your gameplay question has been moved to the Gameplay Questions subforum. 

[steve_v]

20Km is indeed about the limit for the Whiplash, and more intakes won't help. The rapier should make 25-27Km, but after that you'll need to light the rockets.

I immediately see a couple of "old" design features there:
Intake spam - no longer needed, counterproductive due to drag.
Biplane wings - again counterproductive, due to drag. (though I run FAR, so maybe not)

I can't see your engine layout clearly - I see 2 turboramjets and 1 nerva. If that's correct it's probably going to be easier with higher TWR rocketry or rapiers. Nerv powered SSTOs are hard.

For inspiration, check out the Kerbodyne SSTO Division, again, they're set up for FAR but any rated for 1.0.5 should work fine in stock too.

[Wanderfound]

1) You have way more intake than you need. One ramscoop per engine is plenty.

2) Biplanes are aerodynamically horrid (very, very draggy). There is a reason why they stopped building them in the 1930's.

As for how to do it...begin by climbing at a pitch of steepness such that you continue to accelerate, but only just. Level off at around 15,000m, crank up to around Mach 3.5, then lift the nose and zoom up to 25-30km before lighting the rockets.

Demonstration (FAR, but the stock profile is fairly similar these days):

 

[XOIIO]

I actually haven't done two wings before, I just liked the look on this ship, and I've adjusted the plane design some, I added two more jets, removed some of the intakes (the radial ones), and added some sas modules, but was only able to aroumd 30km, with a speed of around 904m/s as my max.

I want to go with an nerv engine so that I can use only liquid fuel and get a lot of range once in orbit, ideally to minimus and back without docking to refuel.

My main limitation is what sort of ascent profile I should use, aside from just trying increase speed as I gain altitude, and balancing the two. I suppose if I had to change to something like the aerospike rocket I could change the precoolers to lf+o tanks but as I said, I really want to stick to the nerv if possible.

 

Edited January 4, 2016 by XOIIO

[Wanderfound]

A pure LF Whiplash/LV-N build is possible, but very tricky. You need to absolutely maximise the height and speed you get from the Whiplash, and you need enough LV-N thrust to maintain your climb in the thin air. Big wings and ruthless streamlining are recommended.

But you don't need that for a long range ship. RAPIER/Nuke combos work very nicely:

 

Or like this:

 

Edited January 4, 2016 by Wanderfound

[Evanitis]

I feel that this spaceplane wants do too many things at once. Eg: you want to fly it to Minmus without refueling, yet I see RCS ports (more than needed). If you ain't docking, it's dead-weight - along with all the monoprop you carry. Ahh, and there's an inline docking port - same stuff. I'd either ditch those, or decide to refuel. Note: MJ wastes a ton of monoprop if you order it to dock - it can burn 2-300 units, when one can do it manually from like 50. SSTO planes can't really afford that luxury.

I'd hunt for even more redundant parts that only add weight and drag. Intake spam was mentioned before. The design in the op also has two extra wings and control surfaces. You could probably use smaller (lighter) gears too.

Finding when a spaceplane design can get to orbit is pretty hard if you start with an overbuilt craft. I suggest trying a test-version as light as possible, than check how much can be added to that.

I suspect you are already familiar with the concept of CoM-CoL balance, and how should is stay relatively the same while the fuel tanks are draining. It -looks- all right on your screenshots, but I thought I mention it anyways. The fact that you mentioned multiple reaction wheels might mean that you have balance issues - maybe you can substitute one (or both) by shifting the wings a bit to gain stability.

EDIT: Ahh, another thing: you'll notice that you can take more oxidizer than you can burn. Check if unused oxy remains after the tanks run dry - that's the amount you can remove in the VAB. More weight saved.

Edited January 4, 2016 by Evanitis

[Evanitis]

5 minutes ago, Evanitis said:

 

Ooops, double post.

Edited January 4, 2016 by Evanitis

[XOIIO]

It's mostly going to be used for crew, but minimus would be a nice bonus.
 

Anyways, I was able to get up to 1.2 km/s at 18km altitude, but then the RCS ports started taking heat damage, but I couldn't go much higher without thrust dropping quite a bit. This was a modification I made with two rapiers instead of the outer two whiplash engines. I'll try again with the whiplash engines, and I'll record my attempt to hopefully get pointers (though it will take a while to upload)

I usually just use mechjeb for the a bit of the setup for docking and the final approach, just to get it right. helps a bit as a trainer too since I didn't do much docking before. I've found it not quite as bad as you mention (though I change the docking speed as you go if I do have it on full auto, leaving it at 5 m/s until the last bit). I've got 120 units of rcs fuel on this plane.

Edit: and I think if I did move the smaller wings forward more I might have more luck keeping the nose up without additional sas modules, but I've had that sort of issue with all my ssto attempts, probably because I'm not getting high enough.

On the latest attempt I couldn't get to 1500m/s even, let alone 3000m/s, not sure why, maybe I'm just going about it wrong. Video should be uploaded and good to view in 1080p in about 35 minutes or so. The audio is kind of crap since shadowplay doesn't record any bass when I use the laptop speakers. (works fine with headphones though, it's odd)

Edited January 4, 2016 by XOIIO

[Evanitis]

19 minutes ago, XOIIO said:

Edit: and I think if I did move the smaller wings forward more I might have more luck keeping the nose up without additional sas modules, but I've had that sort of issue with all my ssto attempts, probably because I'm not getting high enough.

It might be a CoM-CoL issue than. The center of mass should be aligned with the center of lift to keep stability and control. Lift should be a bit behind, kinda' while still touching the CoM ball. Like that:

(CoL maybe a bit ahead here) But the trick is that those should stay while the fuel burns - you can check that by draining all fuel from the tanks (or use the RCS build aid mod) If the CoM-CoL balance shifts too much when the plane is emptied, you might get to orbit, but you'll have serious problems on your way down. But if you allign those properly, you'll most likely won't need the reactions wheels.

Edited January 4, 2016 by Evanitis

[Wanderfound]

1,400m/s is around Mach 4.5; that's about top speed for a Whiplash. A RAPIER can push on to about 1,600m/s if you really make the most of it, but everything past that will need to be rocketry. The old days of airhogging high-altitude Mach 6 on jets alone are long gone.

Have a look at the flight profiles in the Imgur albums above.

Edited January 4, 2016 by Wanderfound

[XOIIO]

Oh derp, I guess I am tired lol, not sure where i got 3000m/s from.

Anyways here is the video, I'm taking a break for a bit, maybe going to sleep, not sure yet. I gave up because I wasn't hitting that target speed, but the couple other similar attempts when I did try I lost speed rapidly with minor altitude gain.

https://youtu.be/ZAEGlBvnRcA

[Evanitis]

Design: Too much stuff = too much weight and drag. I'd remove 80% of those wings, 70% of the control surfaces (eg.: 4 tailfins look cool, but you only need one), 50% of the airbrakes and 70-100% of the RCS stuff. (but really: at first it's better to arrive with a 'useless' plane than failing to orbit a useful one.)

Ascent profile: I feel your initial ascent is too steep: I'd aim for like 30° AoA below 10k, thus you arrive there on like 300 m/s instead of 100. Provided if you don't burn up. If you do, I'd slowly raise the angle (35°, 40°) until I manage to reach 10k meters with like 300-350 m/s. After that you can pitch down to like 10°, so you gain more speed while still on jet engines. If you reach like 1200 m/s before the air gets thin and you stop accelerating on jet trust, your ascent profile is geting close to be perfect. Once you reach your top jet speed, you can switch the rocket engine on, pitch up to like 40° or so, and take it to orbit like you did with every rocket before.  Ahh, 40° is too steep for a Nerve, maybe 10-15 would be good.. To be frank, I never tried a spaceplane with a nuke.

Edited January 4, 2016 by Evanitis

[steve_v]

30 minutes ago, Evanitis said:

Design: Too much stuff = too much weight and drag.

Agreed, as others have said: Build something simple that can get to orbit, then figure out how much extra junk it can afford to carry. Slapping everything on from the start will only cause frustration.
For the ascent profile, milk the jets for all the speed you can, at their most efficient altitude, if that's 18-20km, so be it.
It's entirely possible to go to space with panthers and an ltv45 (and not much else), in this case you'll probably be lighting the fireworks no higher than 16-17km.

Ensure you have enough rocket thrust when the jets die to push on into orbit, if you're dead-set on a low thrust nerv, you'll need to cut as much drag and dead weight as you can - again, loose the extras and/or add a high thrust rocket and some LOX for the first part of the burn.

Edited January 4, 2016 by steve_v

[Val]

Wing panels in Stock KSP are treated as individual unconnected aerodynamic entities. KSP doesn't care if it's a biplane, monoplane, delta or forward swept wings. Makes no difference to how a craft flies. All that really matters is CoL as @Evanitis mentions.

I have a craft with very similar mission profile as the one you have built. You're welcome to study it.

Link includes launch profile description.

[Vegetal]

I didn't see the video, but I can tell you this: If you need *any* reaction wheels during atmospheric flight, something is quite wrong. Check your CoM balance wet and dry.

Also, 120 mono to dock is way too much. I guess I could dock a ship that size manually using 20 or less. Single stage space planes are all about optimization.