Weight Estimation Methods Questions and Answers

Answer: C

Correct answer: The static margin increases

Moving the centre of gravity aft moves it towards the neutral point, so the static margin decreases. The other three do follow: the tail download needed to trim falls, so trim drag falls with it, and with less stability the pitch control forces lighten. Those benefits are what make an aft cruise centre of gravity worth arranging, and the loss of margin is what bounds it.

Answer: D

Weight estimation gives the magnitude and mass properties give the distribution, and both feed the sizing loop, the structural loads and the stability analysis. Almost nothing else in the design can be settled without them.

Answer: A

Correct answer: Put weight on a common measure

An optimiser cannot trade a kilogramme against a drag count or a fuel burn figure until all three are expressed in the same currency. The weight penalty function performs that conversion, so that a design change can be judged on a single number. It is an accounting device within the optimisation, not a management sanction and not a certification matter.

Answer: B

A designer needs to know whether a fairing that saves drag is worth its own mass, and the exchange rate settles it quantitatively. The figure is derived from the mission and differs between a short-range and a long-range aircraft.

Answer: C

Correct answer: Fuel is a larger share on long range

On a long-range aircraft, extra weight has to be carried for many hours and needs extra fuel to carry it, which in turn needs more fuel - the compounding is severe because fuel is a large fraction of the take-off weight. On a short-range aircraft the same kilogramme costs far less, so it may be worth accepting to save cost or drag. The rate is a property of the mission, not of the regulations or the materials.

Answer: D

Correct answer: Worthwhile; 3 counts are worth 120 kg

At 40 kg per count, the three counts saved are worth \( 3 \times 40 = 120 \) kg, against a fairing that weighs 100 kg. The change therefore shows a net benefit of 20 kg on the common measure and is worth making. The whole purpose of the exchange rate is to turn a comparison of unlike quantities into this one subtraction.

Answer: A

Correct answer: Both A and R are true, and R is the correct explanation of A

Both are true and the reason is the necessity. A kilogramme and a drag count are different physical quantities and cannot be compared directly; what makes them comparable is that both ultimately show up as fuel burned over the mission. Converting each into that common measure is what allows a design trade to be settled by arithmetic rather than by assertion.

Answer: B

Correct answer: 1 and 2 only

Statements 1 and 2 are correct: the exchange rate expresses weight and drag in a common measure, and it differs between short-range and long-range aircraft because the fuel share differs. Statement 3 contradicts the second - there is no universal rate, and applying a long-range figure to a short-range design would badly overvalue every kilogramme saved.

Answer: C

Correct answer: Determining the aircraft's certification basis

The certification basis is set by the airworthiness regulations and the aircraft’s category, and no engineering trade study can alter it. The other three are exactly what exchange rates are for: judging a heavier but more efficient engine, trading structure against systems, and deciding whether a drag-reducing fairing pays for the mass it adds.

Answer: D

Each of the four activities addresses a different failure mode, from a bad initial estimate to unnoticed growth to a trade made on incomparable quantities. Omitting any one of them reliably produces an aircraft heavier than intended.