Brakes: The Drag Brakes - Part5

Drag brakes as the name suggest are completely different braking system, both in characteristics and functioning! As the name suggests, it produces a force which opposes the motion of the vehicle. Drag in normal terms can be described as the force which is applied on a component of vehicle which does not fall in its aerodynamic foil. The ambient air at high speeds, due to relative motion of the vehicle against air, produces a massive amount of air channel in front of vehicle through which the vehicle has to go through else it'll hinder the top speed capacity of the vehicle. After a lot of research in the field of aerodynamics, the researchers mentioned that the shape of the "falling water drop" is the most aerodynamic shape and if somebody might have noticed, the shape of Airfoil is also shape of drop only.
The most common application of drag brakes is aircraft, the common name of drag surface is spoiler in aircraft which is present above the flap and even flap functions somewhat as the drag brake. These are together called as control surfaces and they include: flaps, rudder, aileron, slats, spoilers and elevators which control the 6 degrees of freedom of the aircraft!

Courtesy to NASA

The basic concept of functioning is very simple, when flaps and spoilers are deployed, they work as resistance to the air flowing through the flat surface thus making air as the working medium to stop the vehicle.

The same concept has been used in cars for a very long time, the spoilers in cars does the same thing. There are two types of spoilers, 1) Fixed geometry: which is usually used to create downforce 2) Variable Geometry: also called as Retractable spoilers, they serve as both drag brake system as well as downforce producing system.

Both above images show different types of spoilers.

The above image shows a very conventional drag method to stop high speeding cars like the high tuned drag racing cars! In them, the designers and enthusiasts used to install the parachute behind the car with a deployment circuit through which the driver can deploy it whenever he wants to stop the car. Drag brakes in automotives have been very useful especially in the stopping distance timings of super cars like Bugatti Veyron. They make sure that the Peak force of the friction brakes are always under control!

So, with this we end with the types of braking system and their functioning, in next series we will start with the calculations involved in designing if each of the braking system and we will start from drum brakes.

Brakes: The General - Part1

In these series of blogs, we are gonna discuss everything and anything about brakes, starting from terminology and basics involved in first blog to its calculations and how entrepreneur designers can design their own locomotives. Since Brakes are one of the most important 3 mechanisms of any locomotive, other being power generation and steering mechanism; So, we will give time and explain everything about them gradually! So, let's start with the basics! What is a brake? In easiest words, a system or device that reduces or halts motion. Taking example of cars; brakes reduces the speed of a moving car and eventually brings it to a complete halt. Now, there are various types of braking methodologies, 1) Friction Brakes: The brakes use friction to bring out braking action and usual example include drum brakes, disk brakes, hydraulic disk brakes & pneumatic disc brakes. 2) Pumping Brakes: which use engine and engine's components friction as the required braking action! The most popular ans simple type of Pumping brake is Jake Brake which open the exhaust valve during the expansion stroke of Engine. 3) Electromagnetic Brakes: They bring about the braking action using electromagnets, they are commonly installed in hybrid/electric vehicles and is also the basis of KERS (Kinetic Energy Regeneration System) in cars. 4) Drag Brakes: These types of brakes find their application in vehicles which require deceleration through a fluid medium like air or water; the easiest example is the flaps in the wings of aircraft.

courtesy to www.images.google.com

The above image shows a typical disc-drum arrangement in a modern car and the various components involved in them! In the continuing articles we will explain functioning and detailed information about each component but for basics, I believe, its the best way to understand the braking system. Now, let's talk about some terminology one should know while studying brakes.

1) Peak Force: The peak force is the maximum amount of decelerating effect that can be achieved by the system. The peak force is usually greater than the traction limit value of tyres which results in wheel skid when brakes are applied with full force. The peak force depends on the friction coefficient between the friction components of the braking system and the time of actuation or in drag brakes case: the angle of attack i.e. at which angle the actuated component is to the streamlined fluid.

2) Continuous Power Dissipation: It is commonly affiliated with friction brakes, on actuation a lot of heat energy is produced in the system and after a particular temperature the braking system might breakdown! Thus, the maximum amount of power a braking system can dissipate without breaking down is called as Continuous Power Dissipation. The dissipation is dependent on temperature and speed of ambient cooling air.

3) Brake Fade: Because of increase in temperature, the brakes efficiency might reduce, which is technically termed as Brake fade. It is dependent on the design, and cooling system of brake plays a very important role in determining the Brake Fade of the system.

4) Smoothness: It is more of a physical term than technical term for brake application. It's all about the experience of the driver, if the brakes are harsh, worn out and exert unequal force will produce skids and would be unappreciated by the driver as such system will make him experience that he is driving on a camel.

5) Power: It is the amount of brake force the system produces with respect to the application of brake pedal! In other way, it is the ability of the system that how fast can it reach its Peak Force.

6) Drag: It is the incomplete detachment of one braking component with another because of which the unwanted braking action might be there even during full pedal release. The common causes of drag are misaligned brake shoes, broken springs, over-extended actuator wire or piston failure etc.

7) Durability: Brake systems have frictional parts that wear out at every application of brake and might needs to be replaced from time to time. The durability of systems with higher peak force is lesser.

Well, these are the most important terminology one must know in order to understand braking and braking systems! The braking system is specifically mounted on either wheel or trans-axle depending on application of the braking system. One thing that one must also know is that braking system which may/may not include supporting structure adds into weight of the body thus, it also plays an important factor depending on application. With this, we end our first article on basics of brakes and keep tuned for the next article which will briefly explain each component of braking systems and application-wise differences in them.