 When aircraft started flying above 100,000 feet in the 1950s, all kinds of problems started cropping up thanks to the ultra-thin upper atmosphere in which they were flying. It's not something that us non-pilots tend to think about, but it's a really interesting question. How exactly do planes fly in the atmosphere that they can't fly in the upper atmosphere? So we're going to take a look at the first part of that question today on Vintage Space. The problem of flight control at altitude is linked to how planes fly in the atmosphere. So let's start by looking at how planes fly. And because I don't have a model aircraft handy, we're going to use my model space shuttle. The first thing is lift. Lift is created by air flowing over the aircraft's seize lodge and wings, also called the airfoil. Airfoils are shaped such that the air flowing over the top flows faster than the air flowing underneath. The faster air decreases the surrounding air pressure relative to the higher air pressure underneath the aircraft, creating lift from underneath the airplane. So as long as the aircraft is traveling forward, it has lift. Control is different. There are three axes around which an aircraft can travel. Pitch is the motion forwards and backwards, yaw is the movement sideways, and roll is well the wing's rolling end of rent. To roll the plane right or left, a pilot uses his ailerons, control surfaces on the wings. To roll the aircraft right or left, the pilot uses his ailerons, flight control surfaces on the wings. Raising the right aileron and lowering the left causes the aircraft to roll to the right. Pitch causes the aircraft to descend or climb, and it's done using a control surface called the elevator in the tail. Lowering the elevator causes the airplane's nose to drop and sending it into a dive, while raising the elevators causes the airplane to climb. Yaw control is done using a rear rudder. The aircraft's nose will move in the direction that the airplane's rudder is turned, so if the rudder is turned to the left, the plane's nose will move to the left. Using the ailerons and rudder together make the plane turn. But these traditional flight controls require atmosphere to fight down on. They need the pressure of the air to affect a turn and a motion in the aircraft. So why is this important when we're talking about spaceflight? Well, if you have an aircraft that's flying above the appreciable atmosphere, say at 200,000 feet like the X-15 did, there was no air for the traditional flight controls, the aileron, rudder, and elevator, to bite down on and push against to control the aircraft. This is where reaction controls come in. Small jets on the surface of the aircraft that affect the same small movements to keep the aircraft pointed in the right direction when there's no air to push against. We're going to talk more about reaction controls on Friday's episode, so be sure to come back. But in the meantime, be sure to follow me on Twitter as AST Vintage Space for all kinds of weird old-timey space updates, pictures, and just fun facts every day of the week. And with episodes going up every Tuesday and Friday, be sure to subscribe right here so you never miss an episode.