Performance Constraint Analysis Questions and Answers

Answer: A

Correct answer: Both Statement I and Statement II are correct

Both statements are correct and the second explains the first. Thrust costs engine weight, purchase price, maintenance and fuel burn, so the lowest acceptable \( T/W \) is preferred; and a higher wing loading gives a smaller, lighter wing with less wetted area, so the highest acceptable \( W/S \) is preferred.

Pushing both objectives to their limits lands the design point on the boundary of the feasible region, and specifically at a corner where two constraints intersect. That is why a well-sized aircraft normally has exactly two active constraints.

Answer: B

Correct answer: Statement I is incorrect but Statement II is correct

Statement I is incorrect: constraint analysis is one of the earliest steps of conceptual design, not something done after the structure is complete.

Statement II is correct and is precisely the reason. The wing area and installed thrust that the analysis produces are inputs to almost everything downstream - structural layout, fuel volume, weight estimation, engine selection, drag build-up - so they must be established before any of that work can begin. The analysis is revisited as estimates improve, but it leads rather than follows.

Answer: C

Correct answer: 2, 4, 1, 3

The order follows the logic of the method. First the performance requirements and certification rules are collected (2), since they are the raw material. Each is then converted into a relation between wing loading and thrust-to-weight and plotted as a line on the plane (4).

The intersection of the acceptable sides is the feasible region, and a design point is chosen within it (1) - usually at the corner giving the lowest thrust and highest wing loading. Finally that point is converted into physical quantities, wing area and installed thrust (3), by dividing and multiplying by the design weight.

Answer: D

The lift coefficient is the cause, the constraint line moves in response, the allowable loading rises with it, and a smaller wing follows. Each step in the chain is a direct consequence of the one immediately before it.

Answer: A

Correct answer: 2, 3, 1, 4

Each quantity depends on the one before it. The performance requirements (2) come first, from the customer and the certification rules. Plotting them gives the feasible region, from which the wing loading and thrust-to-weight at the design point (3) are chosen.

Those ratios combine with the design weight to give the wing area and installed thrust (1). Only then can an engine be selected from the available ratings (4), by dividing the installed thrust among the engines - and if no catalogue engine matches, the design point must be moved and the sequence partly repeated.

Answer: B

Correct answer: 2, 1, 3, 4

The chain runs from requirement to consequence. A longer range is specified (2); meeting it requires more fuel, so the fuel weight rises (1); the design weight rises accordingly (3); and since wing area and installed thrust are both proportional to weight at a fixed design point, both rise (4).

The chain does not in fact stop there: a heavier aircraft with a bigger wing and bigger engines has more structural and propulsion weight, which demands more fuel again. This is the weight growth spiral, and it is why sizing is iterated to convergence rather than computed once.

Answer: C

Correct answer: 1, 2, 3, 4

The phases follow the flight path. The aircraft accelerates along the runway in the ground roll to lift-off speed (1); it rotates and climbs to the screen height, which completes the certificated takeoff distance (2).

With the gear retracted it flies the second segment at V2 to 400 feet, holding the required gradient with an engine failed (3). Only above that height does it accelerate and retract the flaps (4). The takeoff field length constraint covers the first two phases and the second segment climb constraint the third, which is why they appear as separate lines.

Answer: D

Correct answer: Only three

Three pairs are right. Landing field length plots as a vertical line, being independent of thrust; takeoff field length plots as a line rising to the right, since a higher wing loading needs more thrust for the same distance; and the cruise constraint is a curve with a minimum, because induced drag falls and parasite drag rises with wing loading.

The fourth is wrong. Second segment climb sets a gradient that must be achieved with an engine failed, which is a requirement on thrust, so it plots as a roughly horizontal line - not a vertical one.

Answer: A

Correct answer: Only three

Three pairs are right. Better landing flaps raise the landing \( C_{L,max} \), permitting a higher wing loading, so the landing line moves right; a higher aspect ratio cuts induced drag, so the cruise constraint moves down; and a relaxed runway requirement lets the takeoff constraint move down.

The fourth is wrong. Both axes are ratios - thrust to weight and weight per unit area - so a heavier design weight does not shift the diagram at all. It changes the wing area and thrust that the same design point implies, but not the position of any line.

Answer: B

The first three are the usual figures, and the spread between a transport and a fighter is the single most striking feature of the comparison. A sailplane has no installed thrust at all, so no meaningful ratio exists for it.