Weight Estimation Methods Questions and Answers

Answer: A

Correct answer: Tank capacity, then payload is traded

The payload-range diagram has three regimes. At short range payload is capped by the maximum zero fuel weight; in the middle both payload and fuel can be carried until the take-off weight limit is reached; and at long range the tanks are full, so extra range can only be bought by removing payload. That last trade is the sloping segment at the right-hand end of the diagram.

Answer: B

Cabin fit accounts for a substantial share of operating empty weight and varies widely with configuration, so a high-density layout and a premium one differ considerably. Airlines sometimes specify lightweight seats purely for the fuel saving.

Answer: C

Correct answer: A weight statement broken down by group

The weight statement lists each group - wing, fuselage, undercarriage, powerplant, systems, furnishings - against its allocated target, so an overrun can be traced to the group that caused it. A single aircraft-level number would tell you that the aircraft is heavy without telling you where, which is of no use to anyone trying to recover the weight.

Answer: D

Roughly half empty, a quarter fuel and a quarter payload is a reasonable first picture for a long-range aircraft, though the fuel share rises and the payload share falls as range increases. Short-range aircraft carry proportionally less fuel.

Answer: A

Manufacturer's empty weight, operating empty weight and delivery empty weight all differ in what they include, and quoting one against another flatters whichever aircraft is described by the narrower definition. The basis must always be checked.

Answer: B

Correct answer: 70 t

Zero fuel weight is everything the aircraft carries except usable fuel: \[ \mathrm{ZFW} = \mathrm{OEW} + \text{payload} = 48 + 22 = 70\ \text{t.} \] The limit on it exists because payload sits in the fuselage and adds to wing root bending, whereas fuel sits in the wing and relieves it - so the structure is sized on the case with the most payload and the least fuel.

Answer: C

Correct answer: 0.809

Segment fractions are ratios of weight at the end of a segment to weight at the start, so they multiply rather than add: \[ 0.97 \times 0.985 \times 0.86 \times 0.99 \times 0.995 = 0.809. \] Adding them would give a number greater than one, which is the usual error. The 0.86 is the cruise segment and dominates the product, as it should.

Answer: D

Correct answer: 0.202

The fuel actually burned is \( 1 - 0.809 = 0.191 \) of the take-off weight. Reserves, diversion allowance and unpumpable fuel are not part of the mission, so the figure must be increased: \[ 1.06 \times 0.191 = 0.202. \] Taking 0.191 as the answer is the trap, and in a real design it would size the tanks too small to be certified.

Answer: A

The moments total \( 240 + 360 + 176 + 92 = 868 \) t m and the weights \( 39 \) t, so the centre of gravity is \( 868/39 = 22.26 \) m from the datum. The datum's own position does not matter provided it is used consistently.

Answer: B

Correct answer: 25 per cent MAC

Centre of gravity position is quoted as the distance aft of the leading edge of the mean aerodynamic chord, divided by that chord: \[ \frac{22.26 - 21}{5} = \frac{1.26}{5} = 0.252 \approx 25\ \text{per cent MAC.} \] The subtraction is what the distractors omit - 22.26 divided by 5 has no physical meaning, since the datum is not the leading edge.