AerodynamicsME-438

Spring’16ME@DSU

Dr. Bilal A. Siddiqui

Aircraft Design• Aircraft design is a separate discipline of aeronautical engineering.• It is different from analysis.• Aerodynamics, structures, flight controls, propulsion all play a part in

aircraft design.• Design is the geometric description of the thing to be built.• It starts from the concept consisting of few details, and ends in the

actual manufacturing “nuts and bolts” design.• Design must, however begin with requirements!

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Nature & Engineering Design

T=0

T= 1503 AD

T= 1903 AD

T= 2003 AD

The Design Wheel

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So what is the best Design

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The Design Cycle

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Identify need Survey existing solutions

Define Problem (constraints,

requirements…)

Select Possible Solutions

Evaluate Solutions

(simulations)

Select ‘Best’ Solution

Develop and Prototype Solution

Testing and further

improvement

Presentation and

Communicate

optimization

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Design Stages• Initial Design• Preliminary Design• Detailed Design

Three Phases of Design of an AircraftConceptual

Design

•Will it work?•What does it look like?•What tradeoffs can be considered?•What requirements derive the design•How much will it weight and cost?

Preliminary Design

•Freeze the configuration•Develop lofting•Develop tests and analysis procedures•Design major items•Actual cost estimate

Detailed Design

•Design actual components to be built•Design tooling and fabrication processes•Test major items like structure, landing gear etc•Finalize weight and performance estimates

Aircraft Take-Off Weight Estimation• The purpose of an aircraft is to efficiently lift off and fly a given

cargo/payload/ number of people etc.• Aircraft weight is of paramount importance:• Engine selection depends on the weight it is designed to accelerate• Wing size is based on the weight it is designed to lift.

• All-up weight, or take-off weight or gross take-off weight (GTOW) or maximum take-off weight (MTOW) are some of the measures of expressing weight of the aircraft at take off. Denoted by W0.• Can vary from less than a pound to thousands of pounds.

GTOW vs MTWO• Design gross take-off weight (GTOW) is the total weight of the aircraft

as it begins the mission for which it is designed.• Not the same as Maximum Takeoff Weight (MTOW), which is the

overload some military aircraft can take at the expense of reduced performance.• For the purpose of design, GTOW is what we mean when we say take-

off weight.• GTOW includes some provisions for taxiing to the runway and

warmup too.

Take-off weight buildup• Wo can be broken down into• Crew weight• Payload or Cargo or Passenger weight• Fuel Weight• Everything else.

• Everything else is also called the “empty weight”. It includes landing gear, aircraft structure, engines, fuel system (not the fuel itself), avionics….anything not fuel, people, cargo or payload.

A useful form of the Weight Equation

Empty Weight Estimation