Mk2 Spaceplanes�stock and non-stock designs

[Wolf Baginski]

I have been looking at the problems in making effective spaceplanes while sticking to stock components. Sometimes you just have to keep an eye on the memory you're using, because of the limits of 32-bit code.

There are a lot of Mk2 Spaceplane mods available, with different features that can make the whole job easier. So I shall first list a few parts Mods which are worth thinking about.

B9 Aerospace Procedural Wings

These can replace most of the wings and control surfaces in the stock range, maybe replacing several components with one. They can also carry some fuel, which helps.

Adjustable Landing Gear

Does the same sort of job for the landing gear. Kerbalstuff warns that it is outdated, being for v1.0.2, but I have never had any problems with v1.0.4 I's not all that important, but the adjustment of gear height can give you a nose-up pitch that makes a take-off rather less frightening.

Interstellar Fuel Switch

There's also a fuel switch in the Firespitter plugin. They both allow you to fill tanks with different combinations of fuel. Most spaceplanes need a bit more fuel than the standard fuel/oxidiser mix. This principle also applies to Monopropellant. Instead of an extra part, you can tweak the fuel-tank contents.

Finally, and rather trivial, I fit my spaceplanes with the flat antenna from Blackleg Industries. It looks right for the job.

There are several mods worth considering for their help with flying a 'plane, and the information they provide.

MechJeb This is more for rockets, although it has a couple of spaceplane functions, and gives good delta-V info. It can be seen as a good training/testing simulator, as a link to the ground-control computers for setting up manoeuvres, or as something with better reactions than you, the player, have.

Pilot Assistant This is for planes, more like a standard autopilot, maybe a little like an FBW system. You can finetune the control response, which can otherwise be excessive for high-speed flight. I reckon that it can be a more useful tool than MechJeb until you get out of atmosphere.

Kerbal Engineer Redux A huge amount of inflight information, for all phases of the flight, things such as live numbers for the periapsis and apoapsis, Mach number (which is important for performance of air-breathing engines), and a lot more. It amounts to your instrument panel.

Finally, the essential Mod for so much. Module Manager There are many things which are a list of changes, applied by Module Manager, when the part is loaded into memory. A call to the fuel switch has to be added to a part's config file, and this is what does it. But the changes are only made if the fuelswitch plugin is there. It's often provided with Mods that need it.

---

I am not recommending a Mod-free game, and while you can manage quite well without any of these, they are generally useful. Let's now look at some of the classes of part which can be replaced by stock parts.

---

Mk2 batteries and reaction wheels

These are parts which fit into a Mk2 fuselage, in the same way as their equivalents for the 1.25m (and larger) rocket stacks. This is one of the trivial things to change, and partly why they're a bit obscure. You can put the stock 1.25m equivalents between an air-intake and its mounting point. The only Mk2 battery I have seen has the same capacity as the 1.25m diameter Z-1k battery, though it has half the mass of the stock battery. This isn't such a bad thing, as it's easy to make a spaceplane a bit tail-heavy. You could also mount it just in front of the engine component to counter a nose heaviness. Spaceplanes need lots of engines and intakes so there's no problem here.

Mk2 cockpits

There are a lot. The basic 2 are enough choice, but I know you're going to ask about the cockpits with air intakes. The main useful answer is to use the inline cockpit and a Mk2 to 1.25m adaptor or bicoupler, set to put the 1.25m node at the front. If you attach a control-surface to a reversed part, remember to reverse the control-surface action.

Another solution may be to use a Mk1 cockpit at the front of the adaptor. It can get canard control surfaces well forward while not using such a heavy structure.

3rd-party intakes

Some older designs appear to have an excess of air-intake capacity, either multiple intakes or part-mod intakes that supply more air. The basic model for air-breathing engines has changed and getting extra air to the engine doesn't make a difference any more. The details here can seem a bit geeky, but the stock 1.25m intakes suit the stock engines. There are some good graphs, and the one on the second page compares the three stock engines. I have had a plane flying at Mach 5.22 on Rapier engines. That's about 1560 m/s. There are no real advantages to excess intake capacity. The differences are not that big. But the Shockcone has the edge at the upper end of the speed range.

I have seen a 3rd-party intake that is essentially a double-capacity Ram Air intake by Intake Air capacity, but no better for intake area. and I am wondering if it is really an improvement.

Engines

There are a few 2.5m engines, such as the bigger version of the Sabre in the B9 set, but none in stock other than rockets. There are also some shrouded adaptors which can mount a single 1.25m engine in a prettier form. Shifting to a stock adaptor isn't a big change, though fuel capacity may matter. The 1.25m version of the Sabre engine is heavier than the Rapier, and has more thrust. 4 Sabres mass the same as 5 Rapiers, but the Rapiers will have more thrust. On the other hand, engine mass is a relatively small part of the whole. And pre-coolers, stock or otherwise, are just fuel tanks with neat textures.

One important difference is that the Rapier doesn't generate electricity. Does that matter? For a spaceplane, maybe not, but in-atmosphere range may be limited by batteries rather than fuel. A fuel-cell in the cargo-hold would be one answer. There is just room on the bulkhead beside a docking port or similar 1.25m part.

A few spaceplanes use recently designed Scramjet engines, which give useful air-breathing thrust at higher altitude and speed than a Rapier. These are so different that you might as well give up on trying to copy the plane with stock parts.

Exploits

Some of the pre-v1.0.0 spaceplanes depend on exploiting bugs and design flaws. Extra air intakes are almost useless. I have seen spaceplanes with one node carrying four different engines. It didn't work in v1.0.4 and staging-by-explosion is not all that effective.

Other implications of stock and non-stock

If you're using stock, you are going to be using the Clamp-o-Tron docking port anyway. And almost all the added space-plane parts which provide a docking port use the Clamp-o-Tron. That counts against all the alternatives. But now there are multi-size docking ports, and plugins that, with Module Manager, let you dock with different styles of port. So it's not a huge problem. For 1.25m stick to the standard Clamp-o-Tron.

There are a few non-stock Mk2 parts which can give you something useful. For instance, the QuizTech pack includes a short Service Bay with doors top and bottom. That's similar to the 1.25m and 2.5m stock service bays, but they can be stacked to give something of cargo-bay size with the double doors.

On the other hand, keeping a Spaceplane in orbit to do science seems a bit wasted. There is a mod with a Science Lab, which can thus generate a lot of science, but that's more a feature of a permanent station.

Several part mods have multi-engine pods, which give a radial mount. For a Rapier, you'd need the CrossFeed Enabler mod, which is a plug-in included with some mods. In airbreathing mode, the Rapier draws fuel from all tanks. Switch to rocket mode, and you need fuel pipes at least. These multi-engine mounts can be replaced with multiple stock nacelles, but each needs its own fuel pipe.

The stock RCS thrusters look a bit sticky-out but you will need some. Way up there I mentioned the Blackbird Industries pack, because of the neat streamlined communication antenna. It also has a few thrusters and parts for small probes

---

Conclusion

Converting a spaceplane into a stock lookalike is possible, but there will be differences. You may use payload capacity, and don't expect to match the original's ascent profile. You'll need to do a lot of testing, and a key point is that you need to get a good acceleration between 300 and 400 m/s. Once you reach that speed the Rapier really gets going, but that seems to apply to all the dual-mode engines. Some of the jet-and-rocket designs may still work out.

Rather than converting a big and complicated design, start with something small. A single-Rapier spaceplane can work, but it is a little bit slow at the critical speed.

This pic shows some of my recent work. That was at 20,000 m with a speed of 1550 m/s, pretty much the ideal altitude for an air-breathing Rapier. I might have got some more speed but I chose to start climbing. I was seeing the thermometers. Since the Mk2 fuselage does generate lift it didn't need huge wings.