Preliminary Aircraft Design Process • Mission Specification • Configuration Design • Weight Sizing • Performance Sizing • Fuselage Design • Wing Design • Empennage Design • Landing Gear Design • Weight & Balance Analysis • Stability & Control Analysis • Drag Polar Estimation • Final Design
1. Mission Specification • What exactly is the airplane expected to do? Ex. TWA specifications for a modern luxury transport – 02 Aug. 1932: • All metal tri-motor monoplane • Carry 12 passengers • Range = 1,080 st. mi. • Crew = 2 • Top Speed @ sea level = 185 mph (min) • Cruise Speed @ sea level = 146 mph • Landing Speed = 65 mph (max) • Service Ceiling = 21,000 ft (min) • Rate of Climb = 1,200 fpm • Max Gross Weight = 14,200 lbs • Passenger cabin must have ample room for comfortable seats, miscellaneous fixtures and conveniences. • Airplane must have the latest radio equipment, flights instruments, and navigational aids for night flying
Requirements are extremely important because they • Drive the design • Are the yardstick by which the success of the design is measured
Aircraft companies have lost large amounts of $$ because they followed a bad or inappropriate set of requirements:
Spruce Goose (Hercules), 1947Designed by Howard Hughes700 passenger (cargo + troop carrier) 8 x 3,000 hp 8-cylinder engines: largest piston engines ever produced for an acUrgent government project in 1942, had lost all priority by 1944
C-5 Galaxy, June 30, 1968LG Design, LG: 28 wheels, tires can be inflated / deflated in fight !
Length = 3 – 4 in. Weight = 0.25 oz. Takeoff & Landing: Vertical Speed = 60 mph Range = 1 mile Flight Altitude: less than 1,000 ft Heart Rate: 1,200 / min (20 / sec) Wing Beats: 70 - 200 / sec Control: Very Precise Refueling: In-flight Consumes: 155,000 calories / day its own weight in fuel every 18 hrs Visits 2,000 flowers / day to feed To sustain same level of activity a human would have to eat 220 lbs of hamburger per day.
2. Configuration Design Refers to the positioning of the major parts of the airplane Wing Fuselage Empennage Engines Landing gear in relation to each other. What will the airplane look like?
2. Configuration Design • Ideal configuration: the cg of WE, WF, WPL are all at the same longitudinal location. Why? • Limits cg travel. • Reduces Swet because there is less need for trim control power. • Think: • Light • Simple • Accessibility • Maintainability • Cost
2. Configuration Design • Minimize interference D. • At high M<1 it may be necessary to apply local area ruling to reduce Dwave(B-747)
2. Configuration Design • For M>1 airplanes, area ruling at several M is necessary.Ideal shape: Sears-Haack body of revolution
2. Configuration Design • Structural Synergism: major intersecting structural components should be arranged to avoid duplication of special heavy structure.
Preliminary Sizing • Weight Sizing • Performance Sizing
3. Weight Sizing • TOW or WTO is a very important design parameter; it sizes the entire vehicle • Wing size = f (WTO) • Landing Gear size = f (WTO) • Acquisition Cost = f (WTO)
4. Performance Sizing To determine: • Wing Area S • Takeoff Thrust TTO (jet ac) or Takeoff Power PTO (propeller ac) • Maximum Lift (CLmax) for clean, takeoff, landing configurations
Typical Performance Requirements • Field length • Takeoff dTO • Landing dLND • Speed • Stall Vs • Cruise Vcr • Maximum Vmax
Typical Performance Requirements • Climb • Rate-of-climb (ROC) – AEO, OEI • Time-to-climb (TTC) to some altitude • ROCmin @ some altitude (operating ceiling) • Balked landing • Climb Gradient (CGR) • Military Climb Requirements
Typical Performance Requirements • Maneuvering • Min turn rate (Y) – utility, agricultural, aerobatic, military ac • Min turn radius • Specific Excess Power (Ps) • Airworthiness • Phoenix AZ 1990: airport closed for 3 days because of the heat; no civil ac could meet the takeoff field requirement
9. C.G. Excursion Graph Location of Center of Gravity: From Nose: 2.36 ft From Ground: 1.6 ft
11. Drag Polar L/D = 9.3