Border Patrol and Customs 
The current drone used for Border patrol is a General Atomics MQ-9 Reaper (Predator B drone) and has the current usage statistics:
Flight Time: 20 hours Wingspan: 66’0”
Range: 1,150 miles Production Cost: 16,900,000.00 USD
Altitude: 50,000 feet Down Time: 9 hours maintenance (daily)
Payload capacity: 1.9 tons Total drones in service: 14
Top Speed: 300 mph Sensor capabilities: Pressure sensors, high zoom/quality camera, Infrared camera
Quadcopter Basics 
The 7 basics components of a quadcopter are the frame, propellers, motors, electronic speed control (ESC), flight control board (FC), radio transmitter and receiver, and battery.
The frame of the quadcopter is self-explanatory. It is the structure of the craft that houses and holds all components together. Most frames are made of carbon fiber because it is light weight and very strong. The common design or layout of a quadcopter is an X pattern, with a motor on the end of each arm. The rest of the components lay at the center of the frame.
A quadcopter has 4 propellers, one attached to each motor, and each one helps determine which direction the quadcopter flies or whether it hovers in place. The spinning of the propeller blades push air down. All forces come in pairs, Newtons Third Law, which means for every action force there is an equal, in size, and opposite, in direction, reaction force. Therefore, as the blades pushes down on the air, the air pushes up on the blades, thus creating lift.
When looking for motors for a UAV there is some jargon you are going to run into. The first thing to address is what a Kv rating means on the motor. Kv is often quoted in RPM per volt, which means that a 1000 Kv motor on a 10V supply will rotate just under 10,000 rpm at no load. The higher the Kv, the faster the motor will spin but lower the torque. Low Kv motors, for instance on an agricultural drone, will have high torque with large propellers. Another spec to look for is the thrust rating. This spec is straight forward. The amount of thrust the motor is rated for is how much weight it can lift. If a motor has a 2kg thrust rating and there are four motors, then multiply the thrust rating by four and divide by two to give you the max hover weight. In this case, 4kg would be the max weight the craft could be to maintain hovering capabilities. Also, motors come in two variations of rotation, clockwise and counterclockwise. This is so that two motors can offset the moments produced by their rotations.
Electronic speed controls (ESC)
Electronic speed controls are wired components that connect the motors to the battery. They relay a signal to the motors that tells them how fast to spin. At any one time, each of your motors could be spinning at different speeds. This is what lets you maneuver and change direction. It is all conducted by the ESC, which makes them a very important piece. ESCs can come in two varieties. The first is a single ESC for each motor totaling a set of four for a quadcopter. The other setup is a 4-in-1 ESC. It is a single chip with all four ESCs. There are pros and cons to both. The 4-in-1 ESC is lighter and always has more instruments integrated into the chip like a gyroscope, altimeter, and accelerometer. Single ESCs do not have these extras. The downside is, if the 4-in-1 ESC goes bad, replacing it is more expensive than replacing a single ESC.
Flight Control Board (FC)
The “Commander of Operations” is the flight control board. It controls the accelerometer, gyroscopes and ESCs, which control how fast each motor spins. A good flight control board should also include built-in GPS, connections for video, transmitting and receiving, onboard black box, and software flight package. Major sites, like Hobby King, sale a FC with a 4-in-1 ESC in a stack. This puts all the electronic circuit boards in one nice and neat, light weight, convenient package.
Radio Transmitter and Receiver
A radio transmitter is your remote control, and the receiver is the antenna on the quadcopter that talks to the remote control. When you make an adjustment on the transmitter, the receiver is what understands that adjustment and sends it to the rest of the quadcopter system. To stream video and audio feed back to the pilot from the aircraft, the drone will also need to be equipped with a transmitter and the control will need a receiver. This normally takes place over a Wi-Fi signal of about 2.4GHz to 5.2GHz and an aftermarket antenna booster can increase the range of that signal up to 5 km.
The power source for the whole quadcopter is the batter in most cases. This needs to be charged and recharged, because without a battery, you cannot fly your quadcopter. Li-po batteries are the most used battery in the market.
Gas Power VS Battery Power 
Most drones on the market are battery powered and only have about a 20 to 45min flight time. For fossil fuel power transportation produce between 35-37.5 MJ/L (Volumetric) and 42.5-47.5MJ/L(Gravimetric). The best batteries can produce are still unable to top 1Mj/L. In comparison liquids store energy in the chemical bonds and do not need added weight of the oxidant. Lithium batteries have not been improving due to improved device architecture in the anion. The very top lithium battery would be a lithium fluorine battery which at the very max can produce 22 MJ/kg.
Basics of Airfoils
An airfoil, by definition, is a structure with curved surfaces designed to give the most favorable ratio of lift to drag in flight and is used as the basic form of the wings, fins, and horizontal stabilizer of most aircraft. 
With the drone market gaining traction in more industrial/military areas, the use of machine learning/AI is also being applied to aid in drone operation.