Conceptual Design Process Questions and Answers

Answer: C

Correct answer: 13 to 1

The ratio is

Every pound spent in conceptual design decides the fate of thirteen. It is the quantitative statement of why the phase deserves its senior people and its analytical effort: decisions here are nearly free to change and enormously expensive to change later.

Answer: D

Correct answer: A flat optimum; choose on other grounds

A variation of only 1.5 per cent across the range means the figure of merit barely distinguishes one aspect ratio from another. That is a useful result rather than an error: it frees the designer to select on considerations the plot does not capture - span limits at the gate, structural certainty, manufacturing commonality, ride quality. The variable does have an effect; it is simply small enough to be traded for something else.

Answer: A

Correct answer: 1.8

Sensitivity is the ratio of the fractional response to the fractional change:

so each one per cent of range relaxed returns nearly two per cent of take-off weight. Numbers of this order are typical and are what make requirements negotiation so productive early on: a small concession by the customer on range often buys a much larger saving in aircraft size and cost.

Answer: B

Correct answer: 20 per cent

With weight scaling linearly with thrust,

A rubber engine is a notional engine scaled to whatever thrust the sizing loop asks for, with its weight, dimensions and fuel consumption scaled by simple rules. It lets the loop close without waiting for a real engine to be selected, and it is replaced by a fixed engine deck once a manufacturer is chosen.

Answer: C

Correct answer: 2

Two of the three technologies sit at levels 5 and 4, below the level 6 required, so both need maturation work; the third is already at 6. Counting them explicitly is the point of recording readiness levels: a design may quietly accumulate several immature technologies, each individually defensible, whose combined risk nobody has added up until the programme is committed.

Answer: D

Correct answer: 46.8 t

The empty weight is the fraction times the take-off weight:

The 43.2 t answer uses 0.48, the complement, and 17.3 t comes from dividing rather than multiplying. Empty weight fraction is the single most useful correlation in early sizing, running from about 0.45 for a long range transport to well over 0.6 for a small utility aircraft.

Answer: A

The fuel the mission demands exceeds what the weight budget allows, so something must change: the range requirement, the aerodynamic efficiency assumed, or the payload. This is exactly the situation a diverging sizing loop signals.

Answer: B

Correct answer: 30 minutes

The total is

Half an hour for a two-variable sweep is workable; the same arithmetic with three variables and eighty cases would take two hours, and with four it becomes an overnight run. This is exactly why conceptual design uses low-fidelity, fast methods and leaves computational fluid dynamics and finite element analysis to later phases.

Answer: C

Correct answer: Two thirds

The band narrows from 15 to 5 per cent, so the reduction is

The uncertainty falls because the design is now defined in enough detail for physics-based methods to replace statistical ones - component weights calculated from actual geometry rather than inferred from a regression. It never reaches zero until the aircraft is weighed.

Answer: D

Correct answer: 85 per cent

The commitments accumulate:

By the end of preliminary design more than four fifths of the lifetime cost is locked in, while the great majority of the money has still not been spent. Everything after that point is executing decisions already taken, which is why the design review gates at the end of each phase are treated so seriously.