How is differential braking different from regular braking? How do you accomplish differential braking and why would you need to use it?
Aircraft with toe brakes have the brake pedals at the top of the rudder pedals. You press the left one with top of your foot and it applies the left brake(s). Press the right one to apply the right brake(s). Normally you press them at the same time and with the same force to keep the airplane from veering to one side (imagine just locking up the brakes on one side of the airplane).
Differential braking is when you press one brake pedal harder than the other. It is used as an additional form of directional control when:
- You have no other forms of steering (either because the steering has failed or there is no nose-wheel steering)
- The rudder/nose-wheel steering is not effective enough (because you are going too slow or the wind is too strong).
You want to be careful when doing this, though because you can over do it and create more directional control problems than you originally had. If you use differential braking during the takeoff roll, it will increase the amount of runway that you use since you are applying the brakes (even though it is only on one side, it will keep you from accelerating as fast).
Simply put, differential braking means you can apply different brake pressure for each brake. In a car you have one pedal that applies equal braking to all of your wheels. In many airplanes you have two brake systems and you control the left side brakes independently from the right side -- this is differential braking.
To make use of differential braking, you need two brake pedals, these are typically actuated by applying toe pressure to the rudder pedals (known as toe brakes). You press the right toe brake and the right main gear wheels have brake pressure applied -- likewise for the left toe brake.
You use this to aid in turning the aircraft, as in many light airplanes the nose wheel is free castering, you cannot control it. In larger airplanes you have a tiller to steer the nose wheel, but differential braking can still be used to make tighter turns.
I don't have a citation for this, but the classically famous Mikoyan-Gurevich MiG-15 jet fighter was fitted with differential braking, which operated via the rudder pedals in conjunction with a lever on the joystick. As I recall, the instructions were: to brake in a straight line, remove feet from both rudder pedals and squeeze the brake handle. To use brakes for turning, deflect one rudder pedal and squeeze the handle.
Typical USSR equipment. Astonishing performance considering the technology available, but if you don't know exactly what you're doing you can kill yourself just trying to get off the ramp.