We’ll get into the precise nature of those regulations later in the book — Page 280, Lesson 347

Right, so we’ve just been talking about how a propeller aeroplane can use reverse thrust earlier in the landing roll than a jet aeroplane, and it can hold that reverse thrust all the way until it comes to a full stop. That gives the propeller type a real braking advantage during the landing. The key summary point is this: the usable period of reverse thrust in the landing roll is shorter for a jet than for a propeller aeroplane. And because of that, the authorities have laid down less stringent landing performance regulations for propeller aeroplanes. We’ll get into the precise nature of those regulations later in the book. Now let’s shift our attention to the drag force during landing. You’ll recall there are several forms of drag, and the main types are parasite drag and induced drag. But here’s the important addition: while the aeroplane is on the ground, during take-off and landing, we have to consider wheel drag alongside the aerodynamic drag. The whole aim of the landing is to bring the aeroplane to a stop safely within the confines of the runway. To decelerate, we need sufficient rearward-directed forces acting on the aeroplane. So, in addition to reverse thrust, aerodynamic drag plays a crucial role in landing. Let’s deal with induced drag first, since it’s one of the two types of aerodynamic drag. Induced drag is dependent on lift and is proportional to angle of attack. During the airborne section of the landing, there’s still a large amount of lift being generated and the angle of attack is relatively high. That means induced drag is far higher than in cruising flight. But here’s the key change: when the aeroplane’s nose wheel touches the runway, the angle of attack drops to almost nil. And because induced drag is proportional to angle of attack, it’s consequently reduced to zero at that point. So the picture you want to hold onto is this: induced drag is strong while you’re still airborne in the flare, helping you slow down, but the moment the nose wheel is down, that source of drag effectively disappears, and you’re relying on the other forces — wheel drag, aerodynamic drag, and reverse thrust — to bring you to a stop.