AIRDESLEC PRELIMS - Reviewer

Conceptual Design

sketch configurations that meet specifications; decide fuselage shape, wing location, landing gear and engines;

Monoplane

one set of wings

Low wing

at bottom of fuselage; (wing config)

Planform

Outline of an aircraft wing projected onto a horizontal plane.

Stagger

Horizontal fore-aft positioning of stacked wings;
Positive stagger - upper leading edge ahead of lower;
Negative stagger - upper behind lower.

Angle of Incidence

Angle between the aircraft's longitudinal axis and the chord of the wing.

Decalage

Angle difference between the upper and lower wings of a biplane.

Fuselage Shapes

Round;
Oval;
Square;
Rectangular;
Elliptical;
Shallow vs. Deep;
Open cockpit vs. Enclosed cabin.

Conventional Landing Gear (tail wheel)

Two main wheels forward of CG and a small wheel or skid to support the tail.

Tricycle Landing Gear (nose wheel)

Single nose wheel in front and two or more main wheels aft of CG.

Payload

Weight of occupants, cargo, and baggage.

Powerplant

Aircraft engine that produces thrust; Reciprocating and turboprop engines work with a propeller; Turbojet and turbofan produce thrust by accelerating airflow.

IHP

Indicated Horsepower at crankshaft

Preliminary Airplane Specifications

Define requirements to balance strength, weight, economy, payload and reliability over design life.

Design take-off gross weight

total weight of the aircraft as it begins mission for which it was designed.
Wo = Wcrew + Wpayload + Wfuel + Wempty.

Fuel-Fraction Estimation

Fuel fraction = Wf/Wo = 1.06 × (1 - (Wx/Wo)).

Airfoil Selection Criteria

Drag;

Lift-to-drag ratio (CL/CD);

Thickness;

thickness distribution;

Stall characteristics;

Drag-rise behavior.

Wing Area

Projected planform area of the wing.

High Wing

Continuous spar path; good downward visibility; high efficiency; deeper fuselage; less cockpit access.

Low Wing

allows continuous wing path; easy cockpit access; convenient inspection.

Mid-Wing

Minimal interference drag; structural discontinuity in fuselage.

Ailerons

~9% of wing area;
width ~25% of chord;
located on outer 35% of span.

Wing Incidence

1°-3° to fuselage axis for cruise efficiency.

Elliptical Wing Planform

Ideal theoretical form; smallest induced drag; allows lighter spars.

Rectangular Wing Planform

At AR 6, has only 5% more induced drag than elliptical; simpler construction; stall begins at root; ailerons effective when center stalled.

Tapered Wing Planform

1% more induced drag than elliptical; lighter spars; intermediate performance.

Wing Sweep

Reduces transonic flow effects.

Wing Taper Ratio

Ratio between Tip chord and root chord;

low-sweep ~0.4-0.5;

swept ~0.2-0.3.

Wing Twist

Prevents tip stall; approximates elliptical lift distribution; typically 0°-5°.

Wing Dihedral

Upward angle of wings from horizontal; provides roll stability.

Fuselage Design

Shape dictated by minimum comfortable volume; cockpit floor lower than pilot's seat to reduce leg fatigue.

Tail Surface Position

Tail quarter chord placed 2.5-3.0 mean wing chords behind wing quarter chord; adjustable after stability analysis.

Landing Gear Justifications (Tricycle)

Level cockpit entry/exit;

improved forward vision;

eliminates ground loop;

better stability and braking;

small wing incidence → shorter take-off;

leveled taxiing → less tail damage.

Propeller Ground Clearance

7 inches for nose-wheel;

9 inches for tail-wheel;

measured with gear deflected and airplane in critical attitude.

Airfoil

Body shaped to produce lift perpendicular to motion with small drag; lift via positive pressure below and negative pressure above.

Airfoil Drag

At small AOA (<5°) drag nearly constant; beyond +5° drag rises due to frontal area and boundary layer growth.

Lift-to-Drag Ratio (L/D)

Ratio of lift coefficient to drag coefficient (CL/CD).

Camber

Max distance between mean line and chord;

measures curvature;

high camber = high curvature.

Thickness Distribution

Increased thickness → smoother LE radius, more separation resistance; risk of TE separation.

Stall Characteristics

Occurs when AOA > max lift; boundary layer separates → lift ↓, drag ↑.

Drag-Rise Behavior

also called Induced drag which rises as AOA and CL increase; wing tip vortices create induced AOA at tips.

Airfoil Design Considerations

Camber shape affects zero-lift AOA and moment;

thickness distribution affects lift slope, aerodynamic center,

CP location;

LE shape strongly influences stall and CLmax.

Gross Weight (AUW)

Total aircraft weight at any time; decreases during flight as fuel and oil are used.

Empty Weight

Weight of aircraft without passengers, baggage or usable fuel; standard empty weight includes unusable fuel and full fluids.

Useful Load

Crew + passengers + baggage + usable fuel + drainable oil; = max gross weight - basic empty weight.

Payload

Carrying capacity; may include cargo, passengers, crew, instruments or munitions.

6-Series Airfoil Modifications

Five-digit code for laminar-flow profile; "A" indicates straight surfaces near the trailing edge.

Preliminary Weight Estimate

Early weight breakdown to guide design feasibility.

Preliminary Design

refine geometry, weights and performance estimates;

Detail Design

finalize structural, systems and manufacturing drawings.

Full cantilever

wing unsupported externally;

Semi-cantilever

wing supported by struts or wires.

Mid wing

halfway between top and bottom; (wing config)

High wing

at top; (wing config)

Biplane

two sets of wings stacked.

BHP

Brake Horsepower delivered to final drive.

National Advisory Committee for Aeronautics

NACA