Table 1: Direct Access to the Sub-Disciplines of Aerospace Engineering
|1. Course Organization|
|2. Today's Dreams in Various Speed Ranges|
|3. Designing a Flight Vehicle: Route Map of Disciplines|
|4. Mission Specification & TakeOff Weight|
|5. Force Balance during flight|
|6. Earth's Atmosphere|
|8. Wing Loading|
|12. Flight Control|
|13. Structures and Materials|
|14. High Speed Flight|
|15. Space Flight|
1. Course Organization
For over a century, aerospace engineers have led the progress of human technology, and brought the world closer together. Most simply, aerospace engineering is the realization of grand dreams through careful scientific thinking and planning, bold but informed innovation, and dedicated pursuit of perfection. It is the broadest of engineering disciplines, because it takes the best of all human knowledge to design, build, sell and operate a new (and always better!) aircraft or spacecraft, and to use it to the best advantage. Many aerospace projects appear so "far-out" that most people dismiss them as impossible, until they actually see them working: it is up to the AE to figure out these dreams, and reduce them to simple, step-by-step designs which are clean, simple, safe, cheap and reliable, so commonplace that anyone can use them and feel at home.
Click here to scare yourself thinking about the simple process of flying home for Christmas
So don't be surprised when you read that you can learn to design an airliner, starting out with a high-school background. The approach we take in this course is called the "Runway across Canyons".
The various disciplines of aerospace engineering, such as aerodynamics, propulsion, etc. are like mountain ranges. Sometimes we feel like we have to climb down into a canyon and then up a steep wall to get to another discipline, i.e., to really understand all the things that people have figured out over the years. In this course, we lay out a "runway", bridging these canyons, so that we can go at high speed from aerodynamics to propulsion to flight mechanics, etc., on our way to developing our own conceptual design for an aircraft. We do have a few resources, shown on the control panel of our craft, as we start the takeoff roll...
In this course we will use the motivation of designing a specific vehicle to learn about the various areas of aerospace engineering. So we will go off into one area after another, but always come back at the end of that detour, and do some more calculations or refinement of our design. All that you need is a notebook and pencil, a calculator for elementary calculations, and a spreadsheet.
Likewise, today's designs look extremely sophisticated to us. They can fly over 100 times as fast as the Wright Flyer, and go right out into Space, circle the earth every hour or so, and return to precise touchdowns on earth. Have we reached the limits of aerospace engineering? Many people, even in the 1920s, thought that airplanes had reached the limits of speed and altitude, and had detailed theories proving that not much more could be gained by investing in thought or development of these wierd machines. And today, still, we are just beginning. We have only about 100 years of powered flight experience, whereas the birds and insects that we see have evolved through maybe a million years of experience. We can't yet match them for control precision, landing versatility, payload fraction, engine weight fraction, fuel costs, maneuverability, reconfigurable geometry, or structure weight fraction. Our machines are fragile and clumsy: if their engines quit or a piece breaks off, they fall down quickly or even catch fire. They have stiff, rigid wings that can't flap, twist, fold or thrust to any significant degree. They need long runways and complex traffic control systems. You have to drive through 2 hours of downtown traffic and spend an hour and a half at the airport and another 30 minutes on the taxiway to make a flight of 200 miles. When we launch spacecraft, only about 30% of the structure and 10% of the total launch mass ever reaches orbit: the rest is wasted.
Here are some dreams to consider: some are a lot closer than the others. In each case, try writing out a mission specification, and a typical mission profile, and then maybe you'll keep going, and figure out the detailed design. Someone will, sooner or later, and most of these things will get much closer to reality within the careers of today's students. Consider that when today's professors were born, no human had ever reached orbit (well, excluding anyone kidnapped by green-costumed visitors from the Andromeda Galaxy..)
There are many kinds of flying vehicles today: helicopters, balloons, fixed-wing aircraft (the X-29 is shown), and the Space Shuttle are examples of designs which look drastically different from each other, and are designed for very different missions.
Table 2: Today's Dreams
|Fly like a bird||0 - 100mph; land anywhere, hover, cross mountains & rivers|
|Commute by air||Garage to parking lot to garage. 1 million cars per day above I-85, 300mph, all-weather, safety & traffic management|
|City-city, doorstep service||400mph; VTOL with mild downblast and noise|
|Cross the world in a day||Mach 3, approximately 1800 mph + range of 10,000 miles.|
|Visit low earth orbit||18000 mph; re-usuable spaceliner; comfortable takeoff, acceleration, re-entry and landing. Cheaper than $50 /lb.|
|Visit nearby planets||36,000 to 500,000 mph; months of endurance.|
|Visit nearby star systems||Proxima Centauri, 6 light-years: 5.7E14 km|
|Deep space travel||Millions of light-years.|
|Nano-probes||10E-9 meters size. Numerous applications.|
Of course these are not unprecedented problems: flight on the venerable
DC-3 Dakota airliner , which was the best option available to many of us
when we were younger, also used to make many people sick from the continuous
buffeting, and caused piercing ear-aches, partly from the pressure changes,
and partly from the pleasure of sitting for hours close to something
that sounded like five diesel locomotives at full power.
1: Simplified Design sequence
|Define the mission||What must the vehicle do?|
|Survey past designs||What has been shown to be possible? (don't worry about WHY yet)|
|Weight estimation||How much will it weigh, approximately?|
|Aerodynamics||Wing size, speed, altitude, drag|
|Propulsion and engine selection||How much thrust or power is needed? How many engines? How heavy? How much fuel will they consume?|
|Performance||Fuel weight, take off distance, speed/altitude boundaries|
|Configuration||How should it look? Designerís decisions needed!|
|Stability & Control||Locate & size the tail, flaps, elevators, ailerons etc. Fuel distribution.|
|Structure||Strength of each part, material, weight reduction, life prediction.|
|Manufacturing: concurrent engineering||Design each part, see how everything fits, and plan how to build and maintain the vehicle. Break this down into steps involved in manufacturing.|
|Life-cycle cost||Minimize cost of owning the vehicle over its entire lifetime.|
|Iteration||Are all the assumptions satisfied? Refine the weight and the design.|
|Flight Simulation||Describe the vehicle using mathematics. Check the "flight envelope".|
|Testing||Build models and measure their characteristics, verifying the predictions. Explore uncertain regions. Build & test first prototype.|
|Iteration and refinement||Keep improving, reducing cost and complexity, and extending performance, safety and reliability.|
Table 3: How the Take-off Gross Weight (TOW) of an Aircraft is broken out among the systems
|Component||Fraction of TOW|
|Payload Fraction: passengers+ crew, baggage, food&water (including peanuts& pretzels), cargo||Wpl/Wto|
|Propulsion Fraction: Engines, engine control systems, nacelles, fuel lines, fuel pumps, fuel tanks||We/Wto|
|Structure and Controls: Everything else fixed to the aircraft: wings, fuselage, control surfaces, instruments, landing gear, hydraulic systems, servo motors, airconditioning system, ducting, lights, interior furnishings, movie screens...||Ws/Wto|
For example, if the Payload is 30,000lbs, and the Payload fraction is 0.15, then the TOW is 30,000 / 0.15 = 200,000 lbs.
This is of course an estimate. The rest of the design is to make sure we come in under this estimate, when we calculate everything else. When we have a rough calculation of all the other things, we'll go back and "iterate", many times: refine our estimates, so that the whole vehicle gets better and better.
Click below for aircraft
and engine specifications:
|* Airbus Industrie||* 1 -- Engines|
|* The Boeing Company||* 2 -- Engines|
|* Douglas Aircraft Company||* 3 -- Engines|
|Details and Abbreviations||* 4 -- Engines|
|Extra Abreviations||* 5 -- Engines|
* The aircraft and
engine characteristics provided above were provided by:
Pratt & Whitney
Marketing Operations and Support
Go to the other topics in the course.