Basic Aerospace interview questions
150 questions with answers (AER-001 to AER-150). Try each one aloud before reading the answer.
Incompressible Aerodynamics
AER-001 · What are the four forces acting on an aircraft in flight?
Lift, weight, thrust and drag. In steady level flight lift balances weight and thrust balances drag.
AER-002 · What is angle of attack?
The angle between the wing's chord line and the relative wind (the free-stream velocity direction relative to the aircraft).
AER-003 · What is a stall?
A sudden loss of lift when the angle of attack exceeds the critical value and the boundary layer separates from the upper surface of the wing.
AER-004 · What is an airfoil?
The cross-sectional shape of a wing, blade or fin, designed to produce a large lift force with small drag when moving through a fluid.
AER-005 · Define the chord line and camber of an airfoil.
The chord line is the straight line from leading edge to trailing edge. Camber is the curvature of the mean camber line, measured as its maximum distance from the chord line.
AER-006 · What is the lift equation?
L = ½ρV²·S·C_L, where ρ is air density, V is true airspeed, S is wing reference area and C_L is the lift coefficient.
AER-007 · What is dynamic pressure?
q = ½ρV², the kinetic energy per unit volume of the flow. It sets the scale of aerodynamic forces and is measured in Pa.
AER-008 · What does Bernoulli's equation state for aerodynamics?
For steady, incompressible, inviscid flow along a streamline, p + ½ρV² = constant. Where velocity rises, static pressure falls.
AER-009 · What is the Reynolds number?
Re = ρVL/μ, the ratio of inertial to viscous forces. It governs boundary-layer behaviour, transition and skin-friction drag.
AER-010 · What is a boundary layer?
The thin layer of fluid next to a surface where viscosity slows the flow from free-stream velocity to zero at the wall (the no-slip condition).
AER-011 · What is aspect ratio of a wing?
AR = b²/S, the span squared divided by wing area. For a rectangular wing it equals span divided by chord. High AR reduces induced drag.
AER-012 · What are wingtip vortices?
Swirling flows at the wingtips caused by high-pressure air under the wing spilling around the tip to the low-pressure upper surface. They cause downwash and induced drag.
AER-013 · What are flaps and why are they used?
Trailing-edge high-lift devices that increase camber (and sometimes area) to raise C_L,max, allowing lower take-off and landing speeds.
Compressible & High-Speed Flow
AER-014 · What is the Mach number?
Flow velocity divided by the local speed of sound. Roughly: subsonic < 0.8, transonic 0.8–1.2, supersonic 1.2–5, hypersonic > 5.
AER-015 · What is the speed of sound in air and what does it depend on?
a = √(γRT). For air (γ = 1.4, R = 287 J/kg·K) it depends only on temperature: about 340 m/s at sea level ISA (15 °C).
AER-016 · When can air be treated as incompressible?
When Mach number is below about 0.3, because density changes are then under about 5% and can be neglected.
AER-017 · What is a shock wave?
A very thin region across which flow properties change almost discontinuously: pressure, temperature and density rise while Mach number and total pressure fall.
AER-018 · What is a normal shock?
A shock perpendicular to the flow. Upstream flow is supersonic and downstream flow is always subsonic.
AER-019 · What is an oblique shock?
A shock inclined to the flow, formed when supersonic flow is turned into itself by a wedge or ramp. Downstream flow is usually still supersonic.
AER-020 · What is an expansion fan?
A Prandtl–Meyer expansion: a continuous fan of Mach waves where supersonic flow turns away from itself, accelerating with falling pressure and temperature, isentropically.
AER-021 · What is the Mach angle?
μ = sin⁻¹(1/M), the half-angle of the Mach cone formed by weak disturbances in supersonic flow.
AER-022 · What is critical Mach number?
The free-stream Mach number at which local flow somewhere on the body first reaches Mach 1.
AER-023 · What is a sonic boom?
The pressure signature heard on the ground when the shock waves from a supersonic aircraft sweep past, typically an N-shaped pressure wave.
AER-024 · What is stagnation (total) temperature?
The temperature reached if the flow is brought to rest adiabatically: T₀ = T(1 + (γ−1)/2·M²).
AER-025 · What is a convergent-divergent (de Laval) nozzle?
A nozzle that narrows to a throat then widens. Subsonic flow accelerates to Mach 1 at the throat and becomes supersonic in the diverging section.
AER-026 · What is choked flow?
The condition where Mach 1 is reached at the minimum area; mass flow then cannot increase further by lowering downstream pressure.
Gas Turbine Propulsion
AER-027 · What is the Brayton cycle?
The ideal gas turbine cycle: isentropic compression, constant-pressure heat addition, isentropic expansion and constant-pressure heat rejection.
AER-028 · Name the main components of a turbojet.
Intake, compressor, combustor, turbine and exhaust nozzle. The turbine drives the compressor via a shaft.
AER-029 · What is a turbofan?
A gas turbine where a large fan driven by the turbine pushes much of the air around the core (bypass), producing most of the thrust at subsonic speeds.
AER-030 · What is bypass ratio?
The ratio of mass flow passing through the bypass duct to that passing through the core. Modern airliner turbofans range from about 5 to over 10.
AER-031 · What is a turboprop?
A gas turbine whose turbine drives a propeller through a reduction gearbox. Efficient at low speeds and low altitudes, typically below about Mach 0.6.
AER-032 · What is a turboshaft engine?
A gas turbine that delivers shaft power rather than jet thrust, used in helicopters, APUs and some ships.
AER-033 · What is overall pressure ratio (OPR)?
Compressor exit total pressure divided by inlet total pressure. Higher OPR raises thermal efficiency of the Brayton cycle.
AER-034 · What is an afterburner?
A reheat section behind the turbine where extra fuel is burnt in the exhaust to raise jet velocity and thrust, at a large penalty in fuel consumption.
AER-035 · What is thrust-specific fuel consumption (TSFC)?
Fuel mass flow per unit thrust, e.g. kg/(N·h) or lb/(lbf·h). Lower TSFC means a more fuel-efficient engine.
AER-036 · Axial vs centrifugal compressor?
Axial compressors move air parallel to the shaft through many stages, giving high mass flow and frontal-area efficiency. Centrifugal compressors throw air radially, giving high pressure ratio per stage and robustness but larger diameter.
AER-037 · What is a ramjet?
An air-breathing engine with no moving parts that compresses air by ram effect from forward speed. It cannot produce static thrust and works best around Mach 2–5.
AER-038 · What is a scramjet?
A supersonic-combustion ramjet in which the flow remains supersonic through the combustor, intended for hypersonic speeds above about Mach 5.
AER-039 · What is the role of the combustor?
To burn fuel with compressed air stably and efficiently, raising gas temperature to the turbine entry temperature with low pressure loss and emissions.
Rocket Propulsion
AER-040 · How does a rocket produce thrust?
By expelling high-velocity exhaust; by Newton's third law and momentum conservation the vehicle is pushed the opposite way. It carries both fuel and oxidiser, so it works in vacuum.
AER-041 · What is the rocket thrust equation?
F = ṁ·v_e + (p_e − p_a)·A_e, momentum thrust plus pressure thrust at the nozzle exit.
AER-042 · What is specific impulse (Isp)?
Thrust per unit weight flow rate of propellant, Isp = F/(ṁ·g₀), in seconds. It is a measure of propellant efficiency.
AER-043 · What is effective exhaust velocity?
c = F/ṁ = Isp·g₀. It combines momentum and pressure thrust into one equivalent velocity.
AER-044 · Solid vs liquid rocket motors?
Solids store propellant as a cast grain; they are simple, storable and dense but hard to throttle or stop. Liquids pump separate propellants to a chamber; they offer higher Isp, throttling and restart at the cost of complexity.
AER-045 · What is a hybrid rocket?
A rocket using a solid fuel grain with a liquid or gaseous oxidiser, giving throttleability and safety benefits over solids.
AER-046 · What is a hypergolic propellant?
A propellant pair that ignites spontaneously on contact, such as hydrazine derivatives with nitrogen tetroxide. Used for reliable restarts in spacecraft.
AER-047 · What is a cryogenic propellant?
A propellant stored at very low temperature, such as liquid hydrogen (about 20 K) and liquid oxygen (about 90 K).
AER-048 · What is the oxidiser-to-fuel (O/F) ratio?
The mass flow ratio of oxidiser to fuel. Engines often run slightly fuel-rich of stoichiometric to maximise Isp.
AER-049 · What is a monopropellant thruster?
A thruster using one propellant that decomposes over a catalyst, typically hydrazine, used for spacecraft attitude control.
AER-050 · What is electric propulsion?
Propulsion that uses electrical energy to accelerate propellant, such as ion or Hall thrusters. Very high Isp (over 1,000 s) but very low thrust.
AER-051 · What is thrust-to-weight ratio for a launch vehicle?
Total thrust divided by vehicle weight. It must exceed 1 at lift-off; typical values are around 1.2–1.5.
AER-052 · What is rocket staging?
Discarding empty tanks and engines during ascent so the remaining vehicle does not accelerate dead mass, greatly increasing achievable Δv.
Flight Mechanics & Stability
AER-053 · What are the primary flight control surfaces?
Ailerons (roll), elevator (pitch) and rudder (yaw).
AER-054 · What are the three aircraft body axes?
Longitudinal (roll), lateral (pitch) and vertical/normal (yaw), all passing through the centre of gravity.
AER-055 · What is static stability?
The initial tendency of an aircraft to return toward its trimmed state after a disturbance.
AER-056 · What is dynamic stability?
How the aircraft's motion evolves over time after a disturbance; it is dynamically stable if the oscillations or deviations die out.
AER-057 · What is the neutral point?
The CG location at which the aircraft has neutral longitudinal static stability. The CG must be ahead of it for stability.
AER-058 · What is static margin?
The distance between the CG and the neutral point, as a fraction of mean aerodynamic chord. Positive when the CG is ahead of the neutral point.
AER-059 · What is trim?
A condition where the net moments about the CG are zero so the aircraft holds its attitude without pilot input. Trim tabs or a movable stabiliser achieve it.
AER-060 · What is wing dihedral?
The upward angle of the wings from the horizontal. It provides lateral (roll) stability through the dihedral effect in sideslip.
AER-061 · What is adverse yaw?
A yaw away from the intended turn when ailerons are deflected, caused by greater induced drag on the up-going wing.
AER-062 · What is the function of the vertical tail?
It provides directional (weathercock) stability and, via the rudder, yaw control.
AER-063 · What is the mean aerodynamic chord (MAC)?
The chord of an equivalent rectangular wing with the same aerodynamic moment characteristics; used as the reference for CG and stability calculations.
AER-064 · What is load factor?
n = L/W, lift divided by weight. In a level turn n = 1/cos φ, where φ is bank angle.
AER-065 · What are spoilers?
Panels on the upper wing surface that reduce lift and add drag. Used for roll control, descent and as ground lift dumpers after landing.
Aircraft Performance
AER-066 · What is stall speed?
The minimum steady flight speed: V_s = √(2W/(ρ·S·C_L,max)).
AER-067 · What is indicated airspeed (IAS)?
The speed read from the airspeed indicator, derived from pitot-static dynamic pressure, uncorrected for instrument and position errors.
AER-068 · What is true airspeed (TAS)?
The actual speed of the aircraft relative to the surrounding air mass. It exceeds equivalent airspeed at altitude because air density is lower.
AER-069 · What is ground speed?
The aircraft's speed over the ground: true airspeed vector plus wind vector.
AER-070 · What is service ceiling?
The altitude at which maximum rate of climb falls to a set value, commonly 100 ft/min (0.5 m/s) for piston aircraft.
AER-071 · What is the lift-to-drag ratio?
L/D = C_L/C_D, a measure of aerodynamic efficiency. It equals the glide ratio in unpowered flight.
AER-072 · What is rate of climb?
The vertical speed of the aircraft: RoC = (T − D)·V/W = excess power divided by weight.
AER-073 · What is the glide ratio?
Horizontal distance travelled per unit height lost in a steady glide, equal to L/D.
AER-074 · What is V1?
The take-off decision speed: the maximum speed at which the crew can abort the take-off and stop within the runway, and the minimum speed at which they can continue after an engine failure.
AER-075 · What is Vr?
Rotation speed, at which the pilot raises the nose to lift off.
AER-076 · What is the International Standard Atmosphere (ISA)?
A reference atmosphere: sea level 15 °C, 101,325 Pa, 1.225 kg/m³, with a temperature lapse rate of 6.5 K/km up to the tropopause at 11 km.
AER-077 · What is density altitude?
The altitude in the ISA that has the same air density as the actual conditions. High density altitude degrades take-off and climb performance.
AER-078 · What is endurance?
The maximum time an aircraft can stay airborne on a given fuel load.
Aircraft Structures
AER-079 · What is a monocoque structure?
A structure in which the outer skin carries all or most of the loads, with no internal frame, like an eggshell.
AER-080 · What is semi-monocoque construction?
Skin stiffened by stringers, frames and longerons. The skin carries shear and some bending while the stiffeners prevent buckling. It is standard for metal fuselages.
AER-081 · What is a wing spar?
The main spanwise beam of a wing, carrying bending and shear loads from lift to the fuselage.
AER-082 · What are ribs in a wing?
Chordwise members that keep the airfoil shape, transfer air loads from skin to spars and stabilise skin and stringers against buckling.
AER-083 · What are stringers?
Longitudinal stiffeners attached to the skin that carry axial loads and raise the skin's buckling strength.
AER-084 · What is a wing box?
The closed torsion box formed by the front and rear spars with upper and lower skins. It carries bending, shear and torsion, and often holds fuel.
AER-085 · What is limit load?
The maximum load expected in service. The structure must withstand it without detrimental permanent deformation.
AER-086 · What is ultimate load?
Limit load multiplied by the factor of safety (1.5 in civil airworthiness rules). The structure must carry it without failure for at least 3 seconds.
AER-087 · What is fatigue?
Progressive crack initiation and growth under repeated cyclic loading at stress levels below static strength.
AER-088 · What is buckling?
A sudden instability failure in which a thin member under compression or shear deflects sideways at a critical load, well below material yield in thin panels.
AER-089 · What is a bulkhead in a fuselage?
A transverse structural wall. A pressure bulkhead closes the pressurised cabin, while other bulkheads take concentrated loads from wings, tail or landing gear.
AER-090 · What is a sandwich panel?
Two thin, stiff face sheets bonded to a light core (honeycomb or foam). It gives high bending stiffness at low weight.
Aerospace Materials
AER-091 · Why are aluminium alloys widely used in aircraft?
They combine low density (about 2.7 g/cm³), good strength, good fatigue behaviour, easy fabrication and low cost.
AER-092 · What are 2024 and 7075 aluminium alloys used for?
2024 (Al-Cu) has good fatigue and damage tolerance, used in lower wing skins and fuselage. 7075 (Al-Zn) has higher static strength, used in upper wing skins and highly loaded parts.
AER-093 · Why is titanium used in aerospace?
High strength-to-weight ratio, good corrosion resistance, and strength retention up to about 500 °C. Used in landing gear parts, fan blades, firewalls and airframe fittings.
AER-094 · What is a nickel-based superalloy?
An alloy such as Inconel that keeps strength, creep and oxidation resistance at very high temperatures. Used for turbine blades, discs and combustors.
AER-095 · What is a composite material?
A material made of two or more constituents, typically strong fibres (carbon, glass, aramid) in a matrix (epoxy), with properties better than either alone.
AER-096 · What is CFRP?
Carbon-fibre-reinforced polymer: carbon fibres in a resin matrix, giving very high specific stiffness and strength and good fatigue resistance.
AER-097 · What is specific strength?
Strength divided by density. It shows how much load a material can carry per unit weight.
AER-098 · What is creep?
Slow, time-dependent permanent deformation under sustained stress at high temperature; critical in turbine blades.
AER-099 · What is a thermal barrier coating (TBC)?
A ceramic layer, typically yttria-stabilised zirconia, applied to hot-section parts to insulate the metal and allow higher gas temperatures.
AER-100 · What is ablative material?
A heat-shield material that absorbs heat and erodes in a controlled way (charring, pyrolysis, vaporisation), carrying heat away from the vehicle.
AER-101 · What is a single-crystal turbine blade?
A blade cast as one crystal with no grain boundaries, which greatly improves creep resistance at high temperature.
AER-102 · What is corrosion protection on aluminium aircraft?
Methods such as Alclad (a pure aluminium cladding layer), anodising, chromate or non-chromate primers, and sealants to prevent electrochemical attack.
Orbital Mechanics
AER-103 · State Kepler's three laws.
1) Orbits are ellipses with the central body at one focus. 2) The radius vector sweeps equal areas in equal times. 3) T² is proportional to a³.
AER-104 · What is an orbit?
The path of a body in free fall around another body, where its forward velocity makes it continually fall around rather than into the central body.
AER-105 · What is the circular orbit velocity?
v = √(μ/r), where μ = GM (3.986×10¹⁴ m³/s² for Earth). In low Earth orbit it is about 7.8 km/s.
AER-106 · What is escape velocity?
The minimum speed to escape a body's gravity without further propulsion: v_esc = √(2μ/r), about 11.2 km/s from Earth's surface.
AER-107 · What are apogee and perigee?
The farthest (apogee) and closest (perigee) points of an orbit around Earth.
AER-108 · What is eccentricity?
A measure of orbit shape: e = 0 circular, 0 < e < 1 elliptical, e = 1 parabolic, e > 1 hyperbolic.
AER-109 · What is a geostationary orbit?
A circular, equatorial orbit with a period of one sidereal day, at about 35,786 km altitude, so the satellite stays above one point on the equator.
AER-110 · What is low Earth orbit (LEO)?
Orbits up to about 2,000 km altitude, with periods of roughly 90–127 minutes. The ISS is in LEO at about 400 km.
AER-111 · What is orbital inclination?
The angle between the orbital plane and the reference (equatorial) plane.
AER-112 · What is a sun-synchronous orbit?
A near-polar retrograde orbit whose plane precesses about 1° per day, so the satellite passes over a location at the same local solar time each pass.
AER-113 · What is Δv (delta-v)?
The change in velocity a spacecraft must achieve for a manoeuvre; mission Δv budgets drive propellant requirements.
AER-114 · What are the six classical orbital elements?
Semi-major axis, eccentricity, inclination, right ascension of the ascending node, argument of periapsis and true anomaly (or another time parameter).
Spacecraft Systems
AER-115 · What are the main subsystems of a spacecraft?
Structure, power, thermal control, attitude determination and control (ADCS), propulsion, communications, command and data handling, plus the payload.
AER-116 · What is a satellite bus?
The platform that provides power, attitude control, communication, thermal control and structure for the payload.
AER-117 · How are most spacecraft powered?
Solar arrays charging rechargeable batteries (usually lithium-ion) for eclipse periods. Deep-space missions may use radioisotope thermoelectric generators.
AER-118 · What is an RTG?
A radioisotope thermoelectric generator that converts decay heat from plutonium-238 into electricity using thermocouples. Used where sunlight is too weak.
AER-119 · What is ADCS?
Attitude determination and control system: sensors (star trackers, sun sensors, gyros, magnetometers) and actuators (reaction wheels, thrusters, magnetorquers) that point the spacecraft.
AER-120 · What is a reaction wheel?
A spinning flywheel whose speed is changed by a motor; by conservation of angular momentum the spacecraft rotates the opposite way.
AER-121 · What is passive thermal control?
Control without power: multi-layer insulation, coatings and paints, radiators, heat pipes and careful conduction paths.
AER-122 · What is multi-layer insulation (MLI)?
Many layers of thin aluminised film separated by spacers, which greatly reduce radiative heat transfer in vacuum.
AER-123 · What is telemetry, tracking and command (TT&C)?
The subsystem that sends health data to the ground, allows ranging and orbit determination, and receives commands.
AER-124 · What is a CubeSat?
A standard small satellite built from 10 cm cube units (1U), with a mass of roughly 1–2 kg per unit, often used for education, technology demonstration and constellations.
AER-125 · What is a heat shield?
A thermal protection system on a re-entry vehicle that protects it from aerodynamic heating, using ablators or reusable tiles.
AER-126 · What hazards does the space environment pose?
Vacuum, extreme temperature swings, ionising radiation, atomic oxygen in LEO, micrometeoroids and orbital debris, and spacecraft charging.
Avionics, Navigation & Control
AER-127 · What is avionics?
The electronic systems on an aircraft or spacecraft: communication, navigation, flight control, displays, surveillance and monitoring.
AER-128 · What is a pitot-static system?
A system of a pitot tube (total pressure) and static ports (static pressure) feeding the airspeed indicator, altimeter and vertical speed indicator.
AER-129 · How does a barometric altimeter work?
It measures static pressure and converts it to altitude using the standard atmosphere model, with a pilot-set reference pressure.
AER-130 · What is an inertial navigation system (INS)?
A self-contained system using accelerometers and gyroscopes to compute position, velocity and attitude by integrating motion from a known starting point.
AER-131 · What is GNSS?
Global Navigation Satellite System, such as GPS, Galileo, GLONASS and BeiDou. A receiver computes position from signal travel times from at least four satellites.
AER-132 · What is an autopilot?
A system that automatically controls the aircraft's attitude, heading, altitude or flight path using servos on the control surfaces.
AER-133 · What is fly-by-wire?
A system where pilot inputs are sent as electrical signals to flight control computers, which command actuators, replacing mechanical linkages.
AER-134 · What is an Instrument Landing System (ILS)?
A radio approach aid giving lateral guidance (localizer) and vertical guidance (glideslope) to the runway.
AER-135 · What is a transponder?
An onboard device that replies to secondary surveillance radar interrogations with a code and pressure altitude, identifying the aircraft to ATC.
AER-136 · What is TCAS?
Traffic Collision Avoidance System, which uses transponder signals to detect nearby aircraft and issue traffic and resolution advisories.
AER-137 · What is a glass cockpit?
A cockpit using electronic displays (primary flight display, navigation display) instead of individual mechanical gauges.
AER-138 · What is ADS-B?
Automatic Dependent Surveillance–Broadcast: the aircraft broadcasts its GNSS-derived position, velocity and identity for ATC and other aircraft.
Aeroelasticity, Certification & Safety
AER-139 · What is aeroelasticity?
The study of interaction between aerodynamic, elastic and inertial forces on flexible structures.
AER-140 · What is flutter?
A self-excited, unstable oscillation where aerodynamic forces feed energy into coupled structural modes, which can destroy a structure within seconds.
AER-141 · What is divergence?
A static aeroelastic instability where aerodynamic twisting moment exceeds the wing's torsional stiffness, so twist grows without limit.
AER-142 · What is control reversal?
A condition above a certain speed where wing twist caused by an aileron deflection cancels or reverses the intended rolling moment.
AER-143 · What is buffet?
Irregular structural vibration caused by unsteady separated flow or shock oscillation, often a stall or high-Mach warning.
AER-144 · What is a type certificate?
The approval issued by an aviation authority (FAA, EASA) confirming that an aircraft design meets the applicable airworthiness standards.
AER-145 · What is a certificate of airworthiness?
A document for an individual aircraft confirming it conforms to its type design and is in a condition for safe operation.
AER-146 · What is CS-25 / FAR Part 25?
The EASA and FAA airworthiness standards for large aeroplanes (transport category).
AER-147 · What is DO-178C?
The guidance document used to assure airborne software, defining objectives by Design Assurance Level from A (catastrophic) to E (no effect).
AER-148 · What is a flight data recorder?
The "black box" that records flight parameters for accident investigation; it is paired with the cockpit voice recorder.
AER-149 · What is redundancy in aircraft systems?
Providing multiple independent channels (hydraulics, computers, sensors) so that one failure does not cause loss of a critical function.
AER-150 · What is ETOPS?
Extended-range operations rules allowing twin-engine aircraft to fly routes more than a set diversion time from an adequate airport, subject to approval.
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