Weight & Cost · AE481 Lesson 6

Sizing equation: solve for wing area and weight

Choose a design-point wing loading and thrust-to-weight ratio, then combine them with historical airframe, engine, and mission-fuel fractions. The component terms are solved first and inserted into the sizing equation.

S = W_p(W_TO/S) − (W_a/S) − (W_e/S) − (W_f/S)

W_aS = (W_aW_TO)(W_TOS)

W_eS = (W_eT_SL)(T_SLW_TO)(W_TOS)

W_fS = (W_fW_TO)(W_TOS)

Sized Wing Area (S)—ft²

Sized Weight (W_TO)—lb

Sized Thrust (T_SL)—lbf

Airframe weight—lb

Installed engine weight—lb

Mission fuel weight—lb

Structural weight follows geometry and loads

A more accurate wing model is needed to approach actual weight. Explore the qualitative direction of the major drivers identified in the lesson.

Lighter relative structure1.00×Heavier relative structure

Design checkpoint

Low aspect ratio, low maximum load factor, little sweep, and a thicker wing tend to reduce structural demand. Which choice would you change first—and what aerodynamic or mission penalty would it create?

Build weight from statistical models

Early estimates come from existing aircraft. Area-based values scale by each component’s reference area; fraction-based values scale with takeoff weight or thrust.

W_componentS = W_componentS_referenceS_referenceS

Component	Model value	Reference area	W/S portion	Estimated weight

Area-modeled structure—lb

Structural W/S—lb/ft²

Material reduction—lb

Weight-fraction components

Aircraft W TO

T SL /W TO

Live fraction estimates

Landing gear—lb

Installed engines—lb

All other / misc.—lb

Values reproduce Tables 8.1 and 8.2 from the supplied lesson deck. Carrier adjustment applies to jet-fighter wing and fuselage models.

Cost follows weight—but weight is not the only driver

Compare an independent current-dollar cost-per-pound rule of thumb with the RAND DAPCA IV acquisition-cost model implemented in the JET11 Cost worksheet. DAPCA estimates engineering, tooling, manufacturing, quality-control, development-support, flight-test, material, engine, avionics, and investment costs.

RAND DAPCA IV Model

Flyaway cost—Recurring unit cost plus allocated tooling

Non-recurring cost—

Rule of Thumb—C_ROT = W_TO × cost intensityThe Rule of Thumb is an independent current-dollar comparison.

Rule of Thumb cost intensity

Assumed W_TO —

Average acquisition cost per aircraft—Total escalated DAPCA acquisition program cost divided by production quantity

Recurring unit cost—Manufacturing, quality control, materials, engines, and avionics

Total acquisition program—

RAND DAPCA IV is a historical military-aircraft cost-estimating relationship; this implementation follows the JET11 Cost worksheet and escalates its 1999-dollar acquisition estimate with a direct CPI-U multiplier.

RAND DAPCA IV equations

H_E = 7.07 W_e^0.777 V^0.894 Q^0.163 F_DF

H_T = 8.71 W_e^0.777 V^0.696 Q^0.263 F_DF

H_M = 10.72 W_e^0.82 V^0.484 Q^0.641 F_DF

H_Q = 0.133 H_M F_DF

C_DS = 66 W_e^0.63 V^1.3

C_FT = 1807.1 W_e^0.325 V^0.822 FTA^1.21

C_mat = 16 W_e^0.921 V^0.621 Q^0.799

C_eng = 2.251[0.043T_max + 243.25M_max + 0.969T_t4 − 2228](1000)n_engQ

C_av = AFC_subtotal · C_inv = ICF(C_subtotal + C_av)

C_current = M_CPIC₁₉₉₉

C_acq = H_ER_E + H_TR_T + H_MR_M + H_QR_Q + C_DS + C_FT + C_mat + C_eng + C_av + C_inv

Non-Recurring Cost

Engineering, tooling, development support, flight test, investment, and other program costs not included in recurring production.

Recurring and Flyaway Cost

Recurring unit cost covers production elements. Flyaway cost adds tooling allocated across the selected production quantity.

… but how do you build it?

Composite and exotic materials can improve strength-to-weight ratio, but manufacturing, tooling, inspection, and repair change with them.

Large aircraft wing structure on an assembly line — Large wing assembly

Interior structural view — Load-carrying internal structure

Cutaway view of a Cessna 172 — Conventional semi-monocoque layout

Composite fuselage barrel in manufacturing tooling — Composite fuselage barrel fabrication

Weaving a Fuselage Composite Fuselage Video 2 Composite Fuselage Video 3