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DGCA Technical General · 181 questions

Aerodynamics & Performance: DGCA Technical General Questions and Answers

181 practice questions on Aerodynamics & Performance with answers and explanations, plus the key concepts and formulas, from the TrueHeading question bank.

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About this topic

Use this page to revise Aerodynamics & Performance for the DGCA Technical General paper. Below are the key ideas first, then 12 practice questions with answers and explanations, picked from the 181 questions in the TrueHeading bank for this topic.

In short: Lift balances weight; thrust balances drag.

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Key concepts: Aerodynamics & Performance

14 ideas to know cold.

Forces in steady level flight?

Lift balances weight; thrust balances drag.

L=12ρV2SCLL=\tfrac12\rho V^2 S C_L
D=12ρV2SCDD=\tfrac12\rho V^2 S C_D
  • Lift increases with density, speed squared, wing area and lift coefficient
  • Same form for drag with CD
LiftWeightThrustDragsteady level flight: Lift = Weight, Thrust = Drag

What causes a stall?

The wing exceeds its critical angle of attack (about 15–16°) and the airflow separates.

  • A stall depends on angle of attack, not on speed
  • Stall speed rises with weight, load factor, forward CG and flap retraction
  • Recovery: reduce angle of attack first
critical angle ≈ 15–16°CL rises with αflow separatesangle of attack →CLstalls at the critical AoA, any speed

Parasite drag and induced drag: how do they vary?

Parasite drag grows with the square of speed. Induced drag falls with the square of speed.

CDi=CL2π e ARC_{D_i}=\frac{C_L^2}{\pi\,e\,AR}
AR=b2SAR=\frac{b^2}{S}
  • Total drag is lowest at VMD, where the two are equal
  • High aspect ratio reduces induced drag
VMDinducedparasitetotalairspeed →dragat VMD induced drag = parasite drag

What happens in a level turn?

Lift must increase, so load factor rises with bank angle.

n=1cos⁡ϕn=\frac{1}{\cos\phi}
VS,turn=VSnV_{S,\text{turn}}=V_S\sqrt n
  • 60° bank: n = 2, stall speed up by 41 %
  • Rate 1 turn: 3° per second, bank ≈ TAS/10 + 7°

Turn rate and radius formulas?

Both depend on speed and bank angle.

Rate(∘/s)≈1091tan⁡ϕV(kt)\text{Rate}(^\circ/\text{s})\approx\frac{1091\tan\phi}{V(\text{kt})}
r=V2gtan⁡ϕr=\frac{V^2}{g\tan\phi}
  • Higher speed: larger radius, lower rate
  • Steeper bank: smaller radius, higher rate

What is ground effect?

Within about one wingspan of the ground the downwash is restricted. Induced drag falls and lift rises.

  • The aircraft floats on landing, and may lift off below its normal flying speed on take-off
  • Less induced drag, so less power is needed to hold level flight close to the ground

High-lift devices?

Trailing edge flaps raise CL max and drag; leading edge slats delay the stall to a higher angle of attack.

  • Plain, split, slotted and Fowler flaps
  • Krueger flaps on the leading edge
  • Lower stall speed, shorter take-off and landing runs

Effects of wing sweep?

Sweepback raises the critical Mach number.

  • Lower CL max
  • Tip stall and pitch-up tendency
  • Dutch roll: needs a yaw damper

Wing-tip vortices and wake turbulence?

Vortices are strongest behind heavy, slow, clean aircraft.

  • They sink and drift with the wind, and stay on the ground in a calm
  • Stay above the preceding aircraft’s flight path on approach; land after its touchdown point
  • Winglets reduce induced drag

Range and endurance: where are the speeds?

Related to drag and power curves.

glide ratio=LD=distanceheight\text{glide ratio}=\frac{L}{D}=\frac{\text{distance}}{\text{height}}
  • Glide ratio = L/D = distance ÷ height, best at VMD
  • Propeller: max endurance at minimum power speed, max range at VMD
  • Jet: max endurance at VMD, max range at about 1.32 × VMD
  • Weight reduces as fuel burns, so speeds fall

What is the lift equation?

L = ½ ρ V² S CL.

L=12ρV2SCLL=\tfrac12\rho V^2 S C_L
Vs=2WρSCLmax⁡V_s=\sqrt{\dfrac{2W}{\rho S C_{L\max}}}
  • Lift increases with the square of speed
  • CL depends on angle of attack, flap and shape
  • Stall speed Vs = √(2W / ρ S CLmax)

What affects the stalling speed?

Weight (↑), load factor (↑), flap (↓ with flaps), CG forward (↑), altitude (TAS ↑, IAS same), ice (↑).

Vs,turn=VsnV_{s,turn}=V_s\sqrt{n}
  • Vs ∝ √(weight)
  • Vs in a turn = Vs × √(1/cos φ)
  • Wing contamination reduces CL max

What are the types of drag?

Induced drag (from lift) and parasite drag (form, skin friction, interference). Wave drag at high Mach.

  • Induced drag ∝ 1/V²
  • Parasite drag ∝ V²
  • Minimum drag where equal

What is the best glide ratio?

L/D at the best angle of attack: height lost × L/D = distance.

Range=h×LD\text{Range}=h\times\dfrac{L}{D}
  • Does not change with weight (speed does)
  • Headwind reduces range
  • Typical airliner L/D: 15–20

Practice questions: Aerodynamics & Performance

Tap “Show answer” after you have tried each one.

Q1The load factor in a steady, level, co-ordinated turn at 40° of bank is:

  1. 1.63 g
  2. 1.44 g
  3. 1.31 g
  4. 2.09 g
Show answer

Answer: C. 1.31 g

n = 1 ÷ cos 40° = 1.31.

Q2The 1 g stalling speed is 90 kt. The stalling speed in a level co-ordinated turn at 50° of bank is approximately:

  1. 180 kt
  2. 140 kt
  3. 101 kt
  4. 112 kt
Show answer

Answer: D. 112 kt

Vs(turn) = Vs × √n = 90 × √1.56 = 112 kt.

Q3The 1 g stalling speed is 70 kt. The stalling speed in a level co-ordinated turn at 30° of bank is approximately:

  1. 120 kt
  2. 75 kt
  3. 56 kt
  4. 45 kt
Show answer

Answer: B. 75 kt

Vs(turn) = Vs × √n = 70 × √1.15 = 75 kt.

Q4At FL280 in ISA conditions (OAT -40 °C) an aircraft flies at Mach 0.78. The TAS is approximately:

  1. 394 kt
  2. 417 kt
  3. 510 kt
  4. 463 kt
Show answer

Answer: D. 463 kt

LSS = 38.95 × √(T in K) = 38.95 × √233 = 594 kt; TAS = M × LSS = 463 kt.

Q5The outside air temperature is 20 °C. The local speed of sound is approximately:

  1. 667 kt
  2. 734 kt
  3. 934 kt
  4. 567 kt
Show answer

Answer: A. 667 kt

LSS = 38.95 × √293.1 = 667 kt.

Q6The bank angle required for a co-ordinated rate-one (3°/s) turn at a TAS of 290 kt is approximately:

  1. 39°
  2. 29°
  3. 31°
  4. 35°
Show answer

Answer: A. 39°

tan(bank) = V × ω ÷ g = 149.2 × 0.0524 ÷ 9.81, so bank ≈ 39° (rule of thumb: TAS/10 + 7).

Q7A climb gradient of 3% is flown at a groundspeed of 170 kt. The rate of climb is approximately:

  1. 310 ft/min
  2. 520 ft/min
  3. 390 ft/min
  4. 830 ft/min
Show answer

Answer: B. 520 ft/min

ROC = gradient × GS × 101.3 = 0.03 × 170 × 101.3 ≈ 516 ft/min.

Q8Sea-level ISA (ρ = 1.225 kg/m³): TAS 90 m/s, wing area 28 m², CL = 0.7. The lift is approximately:

  1. 48.6 kN
  2. 97.2 kN
  3. 119.1 kN
  4. 194.5 kN
Show answer

Answer: B. 97.2 kN

L = ½ ρ V² S CL.

Q9The stalling speed in straight and level flight is 100 kt. In a level 70° banked turn the stalling speed is about (kt):

  1. 58
  2. 171
  3. 292
  4. 855
Show answer

Answer: B. 171

Vs increases by √n = √(1/cos φ).

Q10An aircraft with a best glide ratio of 14:1 loses engine power at 5 000 ft above terrain in still air. The maximum glide distance is approximately:

  1. 7 NM
  2. 6 NM
  3. 12 NM
  4. 23 NM
Show answer

Answer: C. 12 NM

Distance = height × L/D (1 NM ≈ 6 076 ft).

Q11Parasite (profile) drag:

  1. increases with the square of airspeed
  2. decreases as airspeed increases
  3. is greatest at the stall
  4. is not affected by airspeed
Show answer

Answer: A. increases with the square of airspeed

Parasite drag ∝ V².

Q12Wing loading is defined as:

  1. wing area divided by weight
  2. lift divided by drag
  3. thrust divided by weight
  4. weight divided by wing area
Show answer

Answer: D. weight divided by wing area

W/S, typically in kg/m² or N/m².

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