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Module 1: Conceptual Design Estimation

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Conceptual Design Estimation - Lesson Summary

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Initial Sizing: This refers to estimation of Aircraft design takeoff gross weight.
Gross weight: This is the weight of an Aircraft at the start of the design mission profile.
Mission profile: This is essentially a sketch that indicates what the Aircraft is supposed to do.
Mission profile varies with the purpose for which the Aircraft was designed.
Mission profile for a General Aviation Aircraft: This refers to a simple cruise mission profile where;
Mission Profile = Simple cruise + Hold.
Mission profile for a Commercial Transport Aircraft: The mission profile of a commercial transport Aircraft is given as; Mission Profile = Main Profile + Missed approach + Diversion + Hold.
Estimation of Empty Weight Fraction: This is the first step in initial sizing of an Aircraft, and it relies on historical data. The formula is; Ẃe = A•Woc * Kvs Where A and C are Constants; A = Sensitivity of the gross weight to the increase in size. Kvs = Variable sweep which depends on Aircraft type. The values are obtained from statistical curve-fits.
Estimation of Misson Fuel Fraction: The formula is given as; Wfuel = Wmission + Wreserved
Where Wmission = Fuel planned to be used in the design misson; Wreserved = Fuel for emergencies (kept).
Estimation of Mission Segment Weights:
For any ith segment Weight = Wi/Wi-1
Where Wi = Start of segment and Wi-1 = End of segment
Total Fuel Weight Fraction = W6/W0. It is obtained by multiplying the Weight fraction of each mission segments.
Estimation of fuel Weight Fraction
This is determined by using mission profile and historical data for engines. The historical data can be estimated from the Breguet Range equation; where Fuel consumption (dW ) = -tsfc x T x dt.
Estimation of Maximum Lift Over Drag Ratio [L/D]max
The Rule of Thumb usually applies here, where; 7 ≤ ARwing ≤ 11, {[L/D]max = 2 x ARwing}
Take off Weight build up (W0) = Wcrew + Wpay + Wfuel + Wempty