Conceptual Design Process Questions and Answers

Answer: A

The configuration having been chosen, the work turns to defining the structure, systems and aerodynamics properly and to reducing the remaining uncertainty. Lofting, wind tunnel testing and detailed weight accounting belong here rather than earlier.

Answer: B

Correct answer: Defining the external surface geometry

Lofting is the mathematical definition of the aircraft’s outer mould line - the fuselage cross-sections, the wing surface, the fairings and their blends. The name comes from shipbuilding, where full-size lines were drawn out on the loft floor above the yard. Today it is done with parametric surface models, and the loft is the common reference from which aerodynamics, structural layout, systems routing and tooling all work.

Answer: C

Successive iterations of the weight and fuel estimate cease to change materially, so the design is self-consistent. A design that fails to close, with weight diverging each iteration, is signalling that the requirements may not be simultaneously achievable.

Answer: D

Divergence means each added kilogramme of fuel adds more than a kilogramme of weight, which happens when the mission is beyond what the assumed efficiency can deliver. Either the requirement or the technology assumption has to give.

Answer: A

The empty weight fraction of a jet transport follows a quite different trend from that of a sailplane or a fighter. Applying the wrong regression gives a confidently stated answer that is simply from the wrong population.

Answer: B

Correct answer: 91 t

The three fractions must sum to the whole, so

Twenty tonnes of payload therefore demands a ninety-tonne aeroplane, because each tonne of payload drags with it structure and the fuel to carry both. That amplification is the central fact of aircraft sizing.

Answer: C

Correct answer: Converging

The successive outputs are 91 and then 90.8 - each iteration changes the answer by less than the one before, so the sequence is settling on a fixed point. That is convergence, and it means the design closes: a weight exists at which the fuel needed and the weight assumed are consistent. Oscillation would show the values alternating about a value, and divergence would show them growing without limit, which signals a mission the assumed technology cannot achieve.

Answer: D

Correct answer: 83 t

Recomputing with the improved fraction,

A two point improvement in empty weight fraction removes about eight tonnes from the aeroplane - four times the direct saving, because lighter structure needs less fuel, which needs less structure again. This snowball effect is why weight is fought so hard in early design and why a small technology gain can be worth a great deal.

Answer: A

Correct answer: 20

A full factorial sweep evaluates every combination:

Adding a variable multiplies the count rather than adding to it, which is why design space exploration becomes expensive quickly and why the analysis at this stage must be cheap. It is also the reason for parametric geometry: the twenty configurations must be generated automatically, not drawn one at a time.

Answer: B

Correct answer: 80

The count multiplies again:

Three variables at these levels already require eighty analyses; a fourth would give hundreds. This exponential growth - the curse of dimensionality - is why full factorial sweeps give way to designed experiments, response surfaces and surrogate models as the number of variables rises.