Tutorial: Spaceplane basics
If you're tired of big rockets that use tons of fuel and disintegrate in the atmosphere when coming back to Kerbin, this tutorial is perfect for you! This tutorial will help you with the basics of spaceplane flight, and will help you avoiding the most common errors that could ruin your perfect day as a spaceplane pilot! This is just a general briefing section with lots of "to do" or "not to do" things: when you think you get it all right, check the Aeris 4A tutorial mission to learn how to get into space easily.
Jet section
While having the same stock parts as in VAB, the way to design spaceplanes differs from the one for spacecrafts. First of all, since the launch happens horizontal, you will have to include gear bays, and you may want to include Jet engines for the first stage: jet engines need a little time to warm up after ignition, so they cannot be used for vertical spacecrafts, but they offer large advantages: first, they burn fuel at a much slower rate compared to liquid fuel engines, which means a spaceplane can travel the same distance of a spacecraft with much less fuel. Second, jet fuselages, since they don't carry oxidizer, are lighter than normal liquid fuel tanks. However, the fuselages Mk2 and Mk3 aren't rounded and they have their own adapters (which also act as additional fuel tanks) to connect them to the other rounded stock parts. The Mk3 Cockpit has on the back the same size of a Mk3 Fuselage, greatly simplifying the process of designing a plane with this cockpit.
As you would expect, spaceplanes need wings: they have various shapes and dimensions, and they differ basically in lift rating: you will want to have as much lift rating as possible. It is also advisable to add some control surfaces to your plane to have some extra control in the atmosphere: you can manually add them to the wings or choose winglets with effective control surfaces, like the Standard Canard. Keep in mind that lift rating and control surfaces are not connected: lift rating is basically the capacity of your wings to sustain the weight of your ship, while control surfaces are parts of wing that can be moved to change the flow of the air around the plane and through this change a plane's direction, angle of attack or inclination. This is an important distinction, because a plane with great lift rating but any control surfaces at all will fly easily but will be almost uncontrollable, vice versa a plane with lots of control surfaces will be perfectly controllable (maybe even too much) but will have big difficulties taking off.
Finally, keep in mind that jet engines are air-breathing, and this means: first, you need to include Air intakes in your spaceplane, otherwise the engine won't even ignite; second, as you fly higher the intakes will be less effective and you will come to a point when the engines will shut down, due to the lack of air. At that point, the plane could start spinning around due to the very high drag of the open intakes and the absence of any thrust. To avoid that, keep an eye on the "Intake Air" on the resources panel: the engines will shut down when they have less of 0.05 intake air each, so you need to close the intakes and shut the engines basing on how many engines are active (for example, with two jet engines you will need to close the intakes at 0.10 intake air, or you'll risk to screw up the whole flight). After shutting the engines down, you will need to start the second part of your space mission.
Rocket section
When your jet engines stop work, it is time to ignite the old, reliable liquid fuel engine. It is hard to design a staging system for a spaceplane, since the wings are a big obstacle, unless you plan to remove them in the stage separation, so, if you decide to keep the wings and the jet engines, to make easier the landing part, make sure to close the air intakes to reduce drag. Keep in mind that at this point control surfaces and winglets will no longer work, so you need to add RCS thrusters and relative fuel.
As long as you're in space, your spaceplane won't differ from any spacecraft: you will probably want to add batteries and generators to prevent the command pod from running out of power. It is also common to add an Inline Clamp-O-Tron, which, unlike all the other docking ports, can be placed in the middle of the spacecraft (a handy solution, since there is not much space at either end of the craft) to allow your plane to dock with space stations or other spacecrafts.
Re-entering in the atmosphere and landing
The most difficult part of a spacecraft flight is landing: the easier way is to decouple everything from the command pod and open parachutes to slow down. While this is obviously a simple and effective solution, it also is very inefficient talking of stock parts recovery: every single part of the craft except the command pod and the parachutes will crash into the ground and be destroyed. Anyway, if you aren't experienced players you may want to just use this method.
To recover a good part of the ship, you will need to perform a safe landing (if you want to try to land on the runway at the Space Center, this tutorial, although it has been written for spacecraft and not spaceplanes, is a great help). As soon as you enter Kerbin's atmosphere, the drag produced by the wings will hopefully slow you down quick enough to perform a safe landing. You can land on any plain area you happen to fly on, and recover the vessel from the tracking station.
