To test how aerodynamics affects efficiency, I have been using an airfoil simulator, developed at the NASA Glenn Research Center, which allows me to observe the airflow around different shapes of airfoils. The simulation software permits me to test how a wing that I have designed is able to cope with airflow that is simulated in an air tunnel. My initiative in using this program was to determine what affects in the design of a plane’s wing would increase efficiency by increasing lift, reducing drag, and reducing mass.

In general, the size of the wing is defined by its span (the distance from wing tip to wing tip), its chord (the distance from leading edge to trailing edge), its area (span multiplied by chord), and its aspect ratio (the ratio of the span to the chord).

For the first trial, I measured the lift generated from a plane wing’s that has a span of 100 feet, a chord (the thickness of the wing) of 5 feet, and an area of 500 square feet. The lift recorded in this trial was 7,755 lbs while the drag was 340 lbs.

For my 2^nd trial, I increased the span of the wing from 100 feet to 125.1 feet and increased the area of the wing from 500.5 feet squared to a 625.5 feet squared. As a result of this change, the lift generated increased to 9,711 lbs and drag increased to 403 lbs.

Lift is directly related to the surface area of the wing and is perpendicular to the flight direction. If you double the surface area of the wing, the lift generated doubles. Increasing the wingspan while keeping the chord constant (which increases the aspect ratio) leads to a higher lift to drag ratio (displayed as L/D in the images). This indicates how a longer wingspan leads to a gain in lift while enduring a smaller drag penalty. However, the challenge is how you increase the wing area without having to add more weight. A larger wing area results in more materials and structures used in the design, leading to an increase in the weight.

Throughout my internship, I have been using several simulation programs endorsed by NASA where I am able to input theoretical values that affect the principles of aerodynamics and observe what the result may be. Each simulator was used to determine the most ideal environment for flight efficiency and how the design of the aircraft must be altered in order to adapt to such environmental changes. The first program I used was an engine simulator where I explored how a jet engine produces thrust by interactively altering the different engine parameters.

The software allows me to choose from four different types of engines. After I have selected an engine, I am able to alter the speed (measured in kilometers per hour) generated by the turbine as well as what altitude the plane is flying at. Here is an image of my first design of a J85 jet engine where I had set the speed of the engine to 845 km/h and the altitude at 14,333.33 meters.

 
After observing what effect the initial altitude the jet engine had on the engine performance, I decreased the altitude that the aircraft would travel and compared the values of engine performance. As the altitude decreases, the net thrust, gross thrust, and core airflow increases. One specific factor that determines the efficiency of an aircraft's performance is a Thrust Specific Fuel Consumption factor (TSFC). When the speed, altitude, or throttle is increased, the TSFC increases which means that the aircraft becomes less fuel efficient. A lower TSFC value means that the engine is more fuel efficient. Since the altitude has decreased in the second picture, the aircraft is more fuel efficient.

 
As my internship continues, I will be explaining more about how efficiency alters through changes certain variables in these simulation programs.

One of the most vital parts in improving efficiency in flight is improving fuel efficiency. An improvement in fuel efficiency permits a plane to travel at higher altitudes, further distances, and use more power while not consuming too much fuel. The heavier the airplane is, the higher the maximum efficiency speed is, and to achieve the true maximum range, the aircraft must slow down as fuel burns to maintain the same angle of attack and drag. The altitude a plane ascends also effects fuel efficiency. The higher the altitude a plane ascends, the less dense the air is, enabling the plane's turbine to produce less power and save fuel. An optimum altitude exists for every turbine aircraft at its given weight.

In the aviation industry, fuel efficiency is measured through specific range, which is the number of miles the airplane has traveled through air per pound of fuel consumed. Here is an example of how a specific range is determined. A business jet flying at 440 knots and burning 1,200 pounds per hour has a specific range of 0.37, which is satisfactory for a jet. Specific range calculations make it easier to compare the fuel efficiency between planes and enables engineers to develop a strategy where they can address an issue and improve fuel efficiency.

On my quest to determine how efficiency in planes can be increased, one major issue must be understood. The weight of a plane restricts a plane from expressing its true potential and requires engineers to develop solutions where benefits can be made to a plane, without increasing the mass. All airplane designers must construct parts that meet all functional requirements of a plane, while reducing the weight of the plane as much as possible. Less weight permits less thrust to be used, thus decreasing fuel consumption. One way to reduce the mass of an aircraft is to reduce the mass of its material composite, while still having it serve as a sturdy exterior.

Originally, commercial transport aircrafts were made with an aluminum skin over an aluminum frame. Aluminum proved to be a decent material composite for planes, due to being light and being strong when alloyed, until several side effects were encountered. These side effects were corrosion and metal fatigue. Recently, a carbon fiber reinforced plastic, introduced in the Boeing 787, proved to be a lighter weight, corrosion proof, and sturdier replacement for Aluminum. Steel is also a material composite used in planes due to being four times stronger and three times stiffer than aluminum, but is also three times heavier. Steel is commonly found in the landing gear of planes where strength is required and it has also been used in some high speed airplanes due to holding its strength at higher temperatures. Different metals are being alloyed in order to improve the power to weight ratio in aircrafts for the performance of aircrafts to improve while experiencing fewer costs.

The use of material composites allows planes to have an exterior with a lighter mass and to be even stronger when facing harsh weather conditions. Graphite-epoxy consists of strong fibers fixed in a resin and thin sheets of the fiber can be stacked in multiple ways to achieve a certain strength or stiffness. Graphite-epoxy is as strong as aluminum, but weighs have as much, promoting a greater power to weight ratio. 

Another composite found in the structure of planes is titanium. Titanium is about as strong as steel and weighs less and is able to maintain its strength at high temperatures, as well as resist corrosion more than steel or aluminum. The Lockheed SR-71 Blackbird, the world’s fastest jet propelled aircraft, possesses an airframe that is composed mostly of titanium and alloys which enabled it to travel at greater speeds and at higher altitudes, without its exterior corroding or weakening. 

       There are multiple methods in increasing the efficiency and thrust of an aircraft. Using a ducted propeller rather than a traditional propeller is one of these ways. A ducted propeller is able to provide more thrust for the same amount of power (or requiring less power to achieve the same amount of thrust), elongating the life span of batteries and flight times.

       As the propeller rotates, air is pushed to the outside. Low pressure of the air flows over the top of the propeller, while high pressure flows over the bottom of the propeller. However, as the low pressure and the high pressure flow over the propeller, both pressures collide, forming a vortex. This vortex generates noise and heats up the air due to being wasted energy.

       A ducted propeller reduces this wasted energy. The wall encircling the propeller prevents the vortex from forming and uses the energy to generate lift. This is more efficient because the wall encircling the propeller enables more lift to be generated when using a smaller amount of power, thus pushing the aircraft more.

       The design of a ducted propeller is also able to increase efficiency by bending the laws of aerodynamics towards its favor. The lip, also known as the rolled edges, of a ducted propeller increases the amount of lift generated. The lip allows air to flow over a curved surface which causes the pressure to decreases, due to an increase in air flow. High pressure pushed the back of the lip, generating thrust and lift.

       Although the design of a ducted propeller may increase lift and thrust, it also increases the mass of the plane, causing the planes weight to increase. This is the main problem I will be addressing as my internship continues and my data is collected.  

               Now that I have explained the four forces of flight, I can explain how each part of the plane generates enough force for flight. In order for a plane to take off, enough lift must be generated so lift is greater than weight. Wings are responsible for generating the majority of lift. As a plane flies through the air, air splits over the top and bottom of the wing. High pressure pushes the bottom of the wing and low pressure on the top of the wing push the wing up, forcing the plane up. This force due to pressure on the plane is known as the Bernoulli component of lift. As the plane flies forward, air flows over the plane in the opposite direction. The velocity of the air that passes over the wing has a net return and results in a downward force on the air. This causes an upward force on the wing (due to Newton’s 3^rd law) known as the Newtonian component of lift.

               Flaps on a plane are moving parts along the trailing edge of the wing which, when rotated downward, deflect air downward. As the amount of air being pushed down increases, an increase in lift is generated. When the air flows off the top of the wing and the flap is too steep, the air breaks off into swirls, creating more drag. This enables the plane to slow down significantly. In this way flaps are responsible for slowing down the plane and permitting the plane to land on a runway much sooner and more safely than landing without flaps. The diagram below shows the difference between a plane landing with flaps, and a plane landing without flaps. The plane’s landing distance in green is the plane with flaps, whereas the plane’s landing distance in blue is the plane without flaps. When flaps are used, wind is able to slow down the plane by pushing against the plane more, causing the plane to slow down and land sooner. 

             Before I get into detail about aircraft structures and composites, let us address the general question, how do planes fly? There are four principles that determine whether a plane is able to fly. These four forces are lift, thrust, drag and weight. The shape of the wing is responsible when generating lift. The shape of the wing’s cross section is an airfoil. According to Bernoulli’s Principle, relative wind, the wind that passes over the wing, helps the airfoil generate lift by having high pressure flow through the bottom of the wing, forcing the plane up, while the low pressure flows over the top of the wing at a faster rate. The force of thrust is responsible for moving the aircraft forward. The propeller or the jet engine is responsible for generating thrust in order to propel the plane forward. Lift and thrust aid the plane in flying.

               The two other forces counteract lift and thrust and are responsible for encouraging engineers to keep innovating in order to reduce the influence of weight and drag to improve the efficiency of flight. The weight force is the force due to gravity, the gross weight of the plane, pulling the plane down. In order for a plane to fly, the lift force generated must be greater than the weight. The gross weight of a plane is composed of the payload, the amount of fuel, and the empty weight. If not enough lift is generated in order to be greater than the weight, an accident is waiting to occur. The force counteracting thrust is drag. Drag is formed from the aircraft’s existence due to the aircraft’s resistance to move through the fluid of air. The force of thrust must be greater than the force of drag in order for the plane to move forward. This is the general overview of how flight occurs.