Cost Estimation in Aircraft Design Questions and Answers

Answer: C

Correct answer: Production rate and weight

Tooling cost in a parametric model is driven by the size of the article to be tooled - hence weight - and by the production rate, which determines how many sets of jigs, fixtures and moulds are needed and how they must be built.

A programme building two aircraft a month can work with fewer, simpler tools than one building twenty, where parallel tooling and higher rates of automation are required. Wing loading, crew complement, range and payload affect tooling only through their influence on the size and complexity of the structure.

Answer: D

A cost twenty years away has less present value than the same cost today, so future expenditure is discounted before being added in. The discount rate chosen has a very large effect on the answer and is always stated with it.

Answer: A

Correct answer: Reducing the empty weight

Empty weight drives both halves of the equation. On the production side, engineering, tooling and manufacturing hours all scale with weight in the parametric relations, so a lighter aircraft costs less to design and build. On the operating side, less weight means less lift, less induced drag and less fuel burnt for the same mission.

The others help only one side or neither: more wing area or more engines add weight, cost and drag, and a higher cruise Mach number raises both the design difficulty and the fuel burn.

Answer: B

Engines are costed on their own parameters rather than the airframe's, since they are bought in as complete units. Turbine inlet temperature stands in for the technology level and hence for the difficulty of building it.

Answer: C

Composite manufacture carries different tooling, cure and inspection costs that the historical correlations never saw, and complexity factors are applied to compensate. Uncalibrated use of an old model is a classic source of error.

Answer: D

Correct answer: Airframe labour and materials

Airframe labour and materials form the largest single element of a transport's purchase price - the structure is the bulk of the aircraft by weight and the manufacturer's own value added, involving very large numbers of parts, fasteners and assembly hours.

Engines are a comparable and sometimes larger item but are usually bought in rather than counted as airframe cost. Avionics and interior furnishing are significant but smaller, and flight test, though expensive in absolute terms, is a development cost amortised across the whole run rather than charged to each aircraft.

Answer: A

Correct answer: A high amortised cost per aircraft

Amortised development cost is the RDT&E divided by the number of aircraft built, so a large numerator over a small denominator gives a high charge per aircraft.

This is the structural difficulty of military and niche programmes: a development effort as demanding as a transport's may be spread over a few dozen airframes rather than a few thousand, so each carries tens of millions in development alone. It is also why export sales matter so much - every additional aircraft dilutes a cost that has already been spent.

Answer: B

Correct answer: Advertising and reservations

Advertising and reservations are indirect operating costs: they support the airline as a business but are not attributable to flying any particular aircraft on any particular sector.

The other three are direct - flight crew salaries, fuel and landing fees all arise from operating the aircraft itself. The line between the two matters when comparing aircraft types, since only direct costs distinguish one aeroplane from another; indirect costs reflect how the airline is run.

Answer: C

Correct answer: 85 per cent

The two-hundredth unit is one doubling beyond the hundredth, and a learning curve is defined precisely on doublings of cumulative output. One doubling under an 85 per cent curve therefore costs 85 per cent of the previous point.

The distractor \( 42.5 \) halves that figure as if two effects applied. Note how the saving decelerates in absolute terms: the first hundred aircraft spanned more than six doublings, while the second hundred spans only one - which is why the cost curve flattens markedly as a programme matures.

Answer: D

Correct answer: A configuration unlike anything in the database

Parametric cost relations are regressions fitted to historical programmes, so they interpolate within the experience they were built on and extrapolate beyond it only on faith. A configuration unlike anything in the database - a novel layout, an unfamiliar material system, an unprecedented propulsion arrangement - lies outside that experience entirely.

The other three are all near the data. A slightly larger conventional aircraft, a derivative and a re-engined variant are exactly the cases such models handle well, which is why derivative programmes carry so much less cost risk than clean sheets.