System Design Description (SyDD) — ISO/IEC/IEEE 15289 — Description | IEEE 29148 §6.5
Generated 2026-03-27 — UHT Journal / universalhex.org
flowchart TB n0["system<br>Kids Remote Control Airplane"] n1["subsystem<br>Airframe Subsystem"] n2["subsystem<br>Propulsion Subsystem"] n3["subsystem<br>Flight Control Electronics"] n4["subsystem<br>Radio Transmitter"] n5["subsystem<br>Power System"] n6["subsystem<br>Ground Charging System"] n7["external<br>USB Power Supply"] n8["external<br>Atmosphere"] n9["external<br>2.4 GHz ISM Band"] n10["actor<br>Child Pilot"] n0 -->|contains| n1 n0 -->|contains| n2 n0 -->|contains| n3 n0 -->|contains| n4 n0 -->|contains| n5 n0 -->|contains| n6 n5 -->|7.4V power| n2 n5 -->|5V BEC| n3 n3 -->|PWM throttle| n2 n4 -->|2.4GHz control frames| n3 n3 -->|servo deflection| n1 n8 -->|aerodynamic forces| n1 n9 -->|shared spectrum| n4 n7 -->|5V 2A| n6 n6 -->|CC/CV charge| n5 n10 -->|stick inputs| n4
Kids Remote Control Airplane — Decomposition
| Subsystem | Diagram | SIL | Status |
|---|---|---|---|
| Airframe Subsystem | Airframe Subsystem - Internal | SIL 1 | complete |
| Propulsion Subsystem | Propulsion Subsystem - Internal | SIL 2 | complete |
| Flight Control Electronics | Flight Control Electronics - Internal | SIL 1 | complete |
| Radio Transmitter | Radio Transmitter - Internal | SIL 1 | complete |
| Power System | Power System - Internal | SIL 2 | complete |
| Ground Charging System | Ground Charging System - Internal | SIL 2 | complete |
| Ref | Requirement | V&V | Tags |
|---|---|---|---|
| SUB-REQ-001 | The Propulsion Subsystem ESC SHALL respond to a PWM throttle command change from idle to full (1000 us to 2000 us) with motor RPM increase to 80% of maximum within 250 ms. Rationale: Derived from SYS-REQ-001 flight performance: 250 ms throttle response prevents control lag that would cause altitude loss during wind gust correction. IEC 62061 SIL 2 application — delayed thrust in gust recovery is a loss-of-control precursor per H-001. 250 ms is consistent with RC aircraft ESC standard response times. | Test | subsystem, propulsion-subsystem, sil-2, session-486, idempotency:sub-propulsion-esc-response-486 |
| SUB-REQ-002 | The Propulsion Subsystem Brushless DC Motor SHALL generate a minimum thrust of 80 g when supplied with the nominal 7.4 V bus and a 100% throttle command, using the specified 6x4 propeller combination. Rationale: Derived from SYS-REQ-001: 80g minimum thrust provides 1:1 thrust-to-weight ratio for a 250g sub-limit airframe, necessary for climb and wind-gust compensation. Below 80g the aircraft cannot sustain level flight against any headwind component. | Test | subsystem, propulsion-subsystem, sil-2, session-486, idempotency:sub-propulsion-motor-thrust-486 |
| SUB-REQ-003 | The Propulsion Subsystem Propeller SHALL fragment or plastically deform on impact with a rigid surface at a blade tip velocity of 15 m/s or greater, releasing less than 0.4 J per fragment at any kinetic energy barrier test per EN 71 blade impact method. Rationale: Derived from SYS-REQ-006 (frangible propeller): EN 71 toy safety requires injury protection from propeller strike. 0.4 J is the EN 71 kinetic energy threshold for low-risk injury. Frangible design means a grass-strike or child-contact event produces clean blade fracture rather than laceration. Glass-filled nylon achieves this; carbon fibre does not. | Test | subsystem, propulsion-subsystem, sil-2, session-486, idempotency:sub-propulsion-prop-frangible-486 |
| SUB-REQ-004 | When any LiPo cell voltage drops below 3.3 V, the ESC SHALL progressively reduce motor power by 50% per 100 mV below the 3.3 V threshold and SHALL cut motor drive completely when any cell reaches 3.0 V, transitioning the Propulsion Subsystem to the unpowered-glide safe state within 100 ms of threshold detection. Rationale: Derived from SYS-REQ-010 (LVC): SIL 2 per H-003 (battery deep discharge causing cell reversal and LiPo fire). IEC 62061 SIL 2 requires quantified safe state transition with deterministic timing. Progressive reduction (not hard cutoff) is selected because abrupt motor stop at altitude causes uncontrolled pitch-down and higher impact energy — gradual descent is the safer intermediate state. 3.0V hard cutoff prevents cell reversal. | Test | subsystem, propulsion-subsystem, sil-2, safety, session-486, idempotency:sub-propulsion-lvc-safestate-486 |
| SUB-REQ-005 | The Propulsion Subsystem (ESC + motor + propeller combined) total mass SHALL not exceed 45 g. Rationale: Derived from SYS-REQ-001 and total system mass constraint of <250g: propulsion budget is 45g (motor 30g, ESC 8g, prop 7g). Exceeding 45g forces structural mass reduction which degrades crash survivability per SYS-REQ-008. | Inspection | subsystem, propulsion-subsystem, session-486, idempotency:sub-propulsion-mass-budget-486 |
| SUB-REQ-006 | The ESC SHALL not exceed 85 degrees Celsius case temperature during a 10-minute full-power continuous run at 40 degrees Celsius ambient, as measured on the FET package surface. Rationale: ESC thermal runaway is a LiPo fire precursor (H-002 adjacent hazard). 85C is the derate point for standard TO-252 MOSFETs; above this, on-resistance increases exponentially leading to thermal runaway. 10-minute run matches maximum flight endurance, ensuring test is bounding case. | Test | subsystem, propulsion-subsystem, session-486, idempotency:sub-propulsion-esc-thermal-486 |
| SUB-REQ-007 | The Radio Transmitter SHALL transmit a new control frame containing proportional stick positions within 20 ms of a stick deflection input change exceeding 1% of full travel. Rationale: Derived from SYS-REQ-002 (3-channel proportional control) and STK-REQ-001 (intuitive control for child). 20ms TX latency is the transmitter contribution to total end-to-end 50ms latency budget. At 50Hz frame rate the TX update period is 20ms; any longer means missed input frames causing jerky control feel which degrades child pilot confidence. | Test | subsystem, radio-transmitter, sil-1, session-486, idempotency:sub-tx-control-latency-486 |
| SUB-REQ-008 | The Radio Transmitter 2.4GHz RF Module SHALL maintain a frame loss rate of less than 1 percent during transmission to the paired airborne receiver at a line-of-sight range of 150 m in an open outdoor environment without co-channel interferers. Rationale: Derived from SYS-REQ-007 (control link frame loss <1% at 150m). TX half of the RF link budget requirement. FHSS across 79+ channels provides interference tolerance; >1% frame loss at 150m indicates TX power or antenna degradation. 150m is the design range ensuring safe operation in typical park environments. | Test | subsystem, radio-transmitter, sil-1, session-486, idempotency:sub-tx-rf-range-486 |
| SUB-REQ-009 | The Radio Transmitter SHALL support a bind-time configurable failsafe output state, transmittable as a distinct packet type to the airborne receiver, such that the receiver shall replicate failsafe servo positions without any further TX input once bound. Rationale: Derived from SYS-REQ-004 (failsafe on 500ms signal loss) and STK-REQ-006 (autonomous descent on signal loss). The failsafe state must be stored in the receiver — not retransmitted — because the TX is absent during the triggering condition. Bind-time configuration ensures the failsafe is set deliberately, not accidentally. | Demonstration | subsystem, radio-transmitter, sil-1, session-486, idempotency:sub-tx-failsafe-config-486 |
| SUB-REQ-010 | The Power System LiPo Battery Pack SHALL provide a minimum usable capacity of 400 mAh at a 10C continuous discharge rate at 7.4V nominal, sustaining full-throttle flight for at least 8 minutes. Rationale: STK-REQ-001 requires 8+ minutes flight. A 450mAh 2S pack at 75% usable capacity delivers 337mAh. At mean current draw of ~2.5A (cruise power for a 28g/motor combo), 8 min requires ~333mAh, leaving 4mAh margin. Minimum 400mAh rated ensures margin against cell aging and temperature derating. | Test | subsystem, power-system, sil-2, session-488, idempotency:sub-power-capacity-488 |
| SUB-REQ-011 | The Power System 5V BEC SHALL maintain output voltage between 4.75 V and 5.25 V under loads from 0 mA to 1500 mA, with transient response returning to within 5% of nominal within 2 ms of a load step. Rationale: Flight control electronics, receiver, and two servos draw up to 1.2A combined. A 10% voltage window matches the rated input tolerance of standard hobby receivers and digital servos. Transient response limit prevents false signal decoding by the receiver during servo movement spikes. | Test | subsystem, power-system, sil-2, session-488, idempotency:sub-power-bec-voltage-488 |
| SUB-REQ-012 | The Power System LiPo Battery Pack SHALL have a total mass not exceeding 30 g when fully charged. Rationale: STK-REQ-010 limits total system mass to 250g. The mass budget allocates 30g to the battery pack (propulsion 40g, airframe 80g, electronics 25g, misc 25g, margin 50g). Exceeding this forces trades in structural or payload mass. | Inspection | subsystem, power-system, sil-2, session-488, idempotency:sub-power-battery-mass-488 |
| SUB-REQ-013 | When any individual LiPo cell voltage drops below 3.3 V during discharge, the Power System SHALL signal the ESC to engage low-voltage cutoff within 200 ms, preventing deep discharge below 3.0 V/cell. Rationale: SYS-REQ-010 requires LVC at 3.3V/cell. Deep discharge below 3.0V causes irreversible plating of lithium metal inside cells, creating internal short-circuit paths and thermal runaway risk. 200ms response limit ensures that at maximum 10C draw, cell voltage recovers before the cell reaches permanent damage threshold. | Test | subsystem, power-system, sil-2, safety, session-488, idempotency:sub-power-lvc-safestate-488 |
| SUB-REQ-014 | The Power Distribution PCB SHALL incorporate a resettable PTC fuse rated to interrupt current at 8 A within 1 second to protect wiring from short-circuit faults. Rationale: RC airplane power wiring is typically 22-26 AWG silicone wire rated to ~5A continuous. A short circuit at 7.4V on unprotected 24AWG wire can deliver 15+ A causing wire insulation to char within 3 seconds. PTC fuse at 8A trip provides margin above normal 4.5A peak draw while interrupting fault current before wiring damage. | Test | subsystem, power-system, sil-2, session-488, idempotency:sub-power-ptc-fuse-488 |
| SUB-REQ-015 | The Ground Charging System LiPo Balance Charger IC SHALL terminate charging when any individual cell voltage reaches 4.20 V plus or minus 0.01 V, or when charge current falls below 22 mA (0.05C for 450 mAh cell), whichever occurs first. Rationale: SYS-REQ-005 requires per-cell monitoring with automatic termination. Cell voltage above 4.22V causes electrolyte oxidation and gas evolution that can lead to thermal runaway in LiPo cells. 0.01V tolerance on the 4.20V threshold is the standard IEC 62133-1 requirement for lithium cell chargers. 0.05C termination current is the EN standard minimum for CCCV full-charge detection. | Test | subsystem, ground-charging-system, sil-2, safety, session-488, idempotency:sub-charger-termination-488 |
| SUB-REQ-016 | The Ground Charging System LiPo Balance Charger IC SHALL charge a fully depleted 450 mAh 2S LiPo pack to 95 percent capacity within 90 minutes at a charge rate of 0.5C (225 mA) or less. Rationale: STK-REQ-004 requires safe charging. 0.5C charge rate is the conservative IEC 62133 recommended maximum for lithium polymer cells without active thermal management. At 225mA CCCV, a 450mAh pack reaches 95% in ~1 hour. The 90-minute limit accounts for balance overhead and ensures the product is ready for a second flight within a reasonable session. | Test | subsystem, ground-charging-system, sil-2, session-488, idempotency:sub-charger-rate-488 |
| SUB-REQ-017 | The Ground Charging System Charge Status LED Indicator SHALL display red during active charging and green upon charge completion, with the green indication visible at a distance of 1 m in ambient lighting of up to 1000 lux. Rationale: STK-REQ-003 requires a parent to verify safe operating status before the child handles the battery. A dual-colour LED with defined luminance is the minimum unambiguous visual indicator that charging is complete without requiring the parent to interpret voltage readings. | Test | subsystem, ground-charging-system, sil-2, session-488, idempotency:sub-charger-led-488 |
| SUB-REQ-018 | The Flight Control Electronics 2.4GHz FHSS Receiver SHALL initiate failsafe output within 500 ms of detecting loss of valid control frames, setting throttle output to 1000 us (zero throttle) and elevator and rudder outputs to their neutral positions (1500 us). Rationale: SYS-REQ-004 mandates controlled descent on control loss. 500ms is derived from the link layer frame rate: at 50Hz the receiver misses 25 consecutive frames before initiating failsafe, providing enough robustness to distinguish momentary multipath from genuine link loss. Zero throttle ensures motor stops rather than holding a potentially dangerous attitude. | Test | subsystem, flight-control-electronics, sil-1, safety, session-488, idempotency:sub-fce-rx-failsafe-488 |
| SUB-REQ-019 | The Flight Control Electronics Flight Control MCU SHALL apply gyro-assisted stability augmentation to limit bank angle excursion to plus or minus 45 degrees from level in both the pitch and roll axes under pilot control inputs, with a loop closure rate not exceeding 50 ms per cycle. Rationale: SYS-REQ-003 requires gyro-assisted stability limiting bank angle to 45 degrees. 50ms loop closure (20Hz minimum) matches the 50Hz servo PWM update rate, ensuring every servo command cycle includes a corrected gyro contribution. This prevents the faster-than-human angular rates that cause inadvertent inverted flight in novice pilots. | Test | subsystem, flight-control-electronics, sil-1, safety, session-488, idempotency:sub-fce-gyro-stability-488 |
| SUB-REQ-020 | The Flight Control Electronics Elevator Servo and Rudder Servo SHALL each achieve full deflection travel (10 mm) in less than 100 ms under a 100 g-cm load when commanded by a step PWM input change from 1000 us to 2000 us at 5.0 V supply. Rationale: Control surface response speed directly affects the system loop closure time. At typical cruise speed of 7 m/s, a 100ms servo lag allows the aircraft to travel 0.7m before correction, which for a wing with 1m span is a significant fraction of the angular correction window. 100ms is the maximum allowable value for a 45-degree bank limit to be effective. | Test | subsystem, flight-control-electronics, sil-1, session-488, idempotency:sub-fce-servo-response-488 |
| SUB-REQ-021 | The Flight Control Electronics subsystem (receiver, FCE board with MCU and IMU, two servos, and all interconnect wiring) total mass SHALL not exceed 25 g. Rationale: STK-REQ-010 limits total system mass to 250g. The electronics mass budget (25g) is derived from: airframe 80g, propulsion 40g, battery 30g, misc/margin 75g = 245g, leaving 25g for electronics. This matches commercially available 5g micro servo pairs (10g) plus 5g receiver and 5g FCE board. | Inspection | subsystem, flight-control-electronics, sil-1, session-488, idempotency:sub-fce-mass-budget-488 |
| SUB-REQ-022 | The Airframe Subsystem EPP Foam Fuselage SHALL withstand a 10 m/s nose-first impact onto a grass surface without battery ejection from the battery tray, verified by a retained battery tray lock after impact. Rationale: SYS-REQ-008 requires crash integrity at 10 m/s. Battery ejection during a crash is the primary secondary-injury mechanism: a 30g LiPo at 10 m/s has 1.5J of kinetic energy — sufficient to cause eye injury to a bystander. EPP foam and a positive-retention battery latch must be designed to absorb crash energy without releasing the battery. | Test | subsystem, airframe-subsystem, sil-1, safety, session-488, idempotency:sub-airframe-crash-integrity-488 |
| SUB-REQ-023 | The Airframe Subsystem (fuselage, wing, tail, control surfaces, pushrods, and all structural hardware) total mass SHALL not exceed 80 g. Rationale: STK-REQ-010 limits total system mass to 250g. Mass budget: electronics 25g, propulsion 40g, battery 30g, misc/margin 75g = 170g, leaving 80g for airframe. An EPP foam fuselage with 600mm span wing at this mass is achievable and aligns with the Hobbyzone/E-flite Champ-class reference design. | Inspection | subsystem, airframe-subsystem, sil-1, session-488, idempotency:sub-airframe-mass-488 |
| SUB-REQ-024 | The Airframe Subsystem Elevator Control Surface and Rudder Control Surface SHALL each provide a minimum neutral-to-full-deflection mechanical travel of 10 mm when actuated by a servo horn movement of 5 mm. Rationale: Adequate control surface travel determines the aircraft's pitch and yaw authority. 10mm deflection on the tail at cruise speed (7-12 m/s) produces enough moment to counteract atmospheric turbulence within the SYS-REQ-013 wind limit of 5 m/s. A 2:1 pushrod mechanical advantage is specified to match the servo's 5mm horn travel to the required 10mm control deflection. | Inspection | subsystem, airframe-subsystem, sil-1, session-488, idempotency:sub-airframe-control-travel-488 |
| SUB-REQ-025 | When the ESC loses the PWM throttle input signal for more than 100 ms, the Electronic Speed Controller SHALL reduce motor drive to zero throttle output within 50 ms and maintain zero throttle until a valid PWM signal is re-established. Rationale: ESC classification as Functionally Autonomous (capable of self-directed motor commutation without continuous MCU supervision) requires a fail-safe override constraint per IEC 62061. Loss of throttle signal could result from wire break, connector fault, or MCU crash. Without this requirement, the motor could continue running at last commanded speed with no pilot authority — hazard H-001 (uncontrolled flight). 100ms detection window is conservative enough to avoid false triggers on PWM signal glitches (typical glitch is <20ms). | Test | subsystem, propulsion, sil-2, failsafe, session-490, idempotency:sub-esc-pwm-failsafe-490 |
| SUB-REQ-026 | The Flight Control Electronics Flight Control MCU SHALL implement stability augmentation using 3-axis gyroscope feedback to limit commanded bank angle to ±45 degrees and pitch angle to ±30 degrees when beginner mode is active, applying corrective elevator and rudder inputs at a minimum 250 Hz control loop rate. Rationale: Derived from SYS-REQ-003: the system-level stability augmentation requirement allocates to the FCE MCU, which is the only component with access to both gyro sensor data and servo control outputs. The 250Hz loop rate is required to respond to attitude disturbances before they exceed ±10 degrees from commanded trim — at slower rates, phase lag causes oscillation. Beginner mode rate limiting is a key safety mitigation for H-003 (uncontrolled attitude deviation). | Test | subsystem, flight-control-electronics, sil-1, session-490, idempotency:sub-fce-stability-aug-490 |
| SUB-REQ-027 | When the Flight Control Electronics 2.4GHz FHSS Receiver does not receive a valid control frame for more than 500 ms, the receiver SHALL output a pre-programmed failsafe PWM packet to all channels setting throttle to minimum (1000 μs) and control surfaces to a 5-degree nose-down glide trim within 100 ms of the timeout expiry. Rationale: Derived from SYS-REQ-004. The receiver is the first component to detect RF loss and must initiate failsafe before the FCE MCU even detects a missing frame. The 100ms response window ensures the failsafe condition is applied within one flight control cycle, preventing a lag where the aircraft continues at last commanded thrust. The 5-degree nose-down trim produces a stable glide at approximately 2 m/s descent rather than a stall-and-spin. | Test | subsystem, flight-control-electronics, sil-2, failsafe, session-490, idempotency:sub-receiver-failsafe-490 |
| SUB-REQ-028 | The Airframe Subsystem EPP foam fuselage battery bay SHALL retain the LiPo battery pack under nose-first impact at 10 m/s using a latched hatch mechanism rated to 50 N pull-out force, ensuring battery containment and preventing electrical connector disconnection during crash. Rationale: Derived from SYS-REQ-008 battery-ejection sub-clause. SUB-REQ-022 covers structural integrity; this requirement specifically covers battery retention which is the highest consequence of impact — an ejected LiPo pack in children's hands after a crash is hazard H-002 (LiPo thermal event). 50N pull-out threshold is the maximum force transferred to the battery bay during a 10m/s deceleration on a 50g battery (10g deceleration load x 5 safety factor). | Test | subsystem, airframe-subsystem, sil-2, session-490, idempotency:sub-airframe-battery-retention-490 |
| SUB-REQ-029 | The complete Kids Remote Control Airplane system SHALL require no tools, internet access, or prior RC experience to achieve first flight readiness from unboxing, with all pre-flight steps (battery insertion, antenna extension, bind sequence, mode selection) completable by a child aged 10 in under 10 minutes following the printed quick-start guide. Rationale: Derived from SYS-REQ-009. The 10-minute setup requirement drives specific design constraints: snap-fit connectors (no tools), pre-bound transmitter-receiver pair from factory (no pairing steps), and a single-page printed guide (no internet). The target age of 10 sets the cognitive complexity ceiling — steps requiring fine motor skills or abstract reasoning must be eliminated. Failure to meet this requirement directly risks the STK-REQ-001 25-minute park session scenario. | Demonstration | subsystem, session-490, idempotency:sub-system-setup-time-490 |
| SUB-REQ-030 | The Radio Transmitter stick position encoder SHALL digitise each joystick axis to a minimum resolution of 1024 steps (10-bit) with a sample rate of at least 100 Hz, providing proportional control resolution to achieve 1 ms PWM step increments at the receiver output. Rationale: The 1 ms PWM step increment derived from SYS-REQ-002 requires encoder resolution fine enough that quantisation error is not the dominant control limit. 10-bit at 100 Hz ensures sub-millisecond precision across the 1000-2000 us PWM range. | Test | subsystem, radio-transmitter, session-498, idempotency:sub-tx-stick-encoder-498 |
| SUB-REQ-031 | The Radio Transmitter SHALL operate from 4 x AA alkaline batteries and SHALL provide a minimum operational life of 5 hours of continuous use at 25°C, measured from full batteries to the transmitter low-battery LED warning activation. Rationale: 5-hour battery life covers at least 12 consecutive 25-minute sessions (STK-REQ-001), eliminating battery changes across a typical weekend of use. AA alkaline batteries are universally available and remove rechargeable transmitter battery management complexity for child users. | Test | subsystem, radio-transmitter, session-498, idempotency:sub-tx-battery-life-498 |
| SUB-REQ-032 | The Radio Transmitter 2.4 GHz RF Module SHALL operate at a conducted transmit power not exceeding 100 mW EIRP in compliance with FCC Part 15.247 and ETSI EN 300 328, and SHALL incorporate FHSS with a minimum of 30 frequency channels to reduce interference from co-channel 2.4 GHz devices. Rationale: STK-REQ-014 requires FHSS within the 2.4 GHz ISM band at less than 1 W EIRP. 100 mW provides regulatory margin while achieving the 150 m range of SYS-REQ-007. Minimum 30 channels ensures frequency diversity sufficient to maintain link quality in park environments with overlapping Wi-Fi. | Test | subsystem, radio-transmitter, regulated, sil-1, session-498, idempotency:sub-tx-rf-power-498 |
| SUB-REQ-033 | The Radio Transmitter SHALL incorporate a physical bind button that initiates the receiver binding sequence when held for 3 seconds with the transmitter powered on, and SHALL store the bound receiver identity in non-volatile memory retained across power cycles without battery. Rationale: Bind persistence (H-006 mitigation) ensures the aircraft cannot respond to a different transmitter. Non-volatile storage eliminates rebinding after every flight, reducing setup burden for child users. The 3-second hold prevents accidental bind entry during normal operation. | Test | subsystem, radio-transmitter, sil-1, session-498, idempotency:sub-tx-bind-nvm-498 |
| SUB-REQ-034 | The Electronic Speed Controller MOSFET Half-Bridge SHALL use switching transistors rated for a minimum drain-source breakdown voltage of 20 V and a continuous drain current of at least 10 A at 60°C case temperature, with a maximum on-resistance of 8 milliohms per switch. Rationale: 2S LiPo peak discharge is 8.4 V; 20 V VDS provides a 2.4x margin against commutation switching transients. 10 A at 60°C supports maximum ESC current at full throttle (7-9 A for 150 W class motors). 8 milliohm on-resistance limits conduction losses to under 0.7 W per switch, keeping temperature within the 85°C limit of SUB-REQ-006. | Test | subsystem, propulsion-subsystem, sil-2, session-498, idempotency:sub-esc-mosfet-spec-498 |
| SUB-REQ-035 | The Electronic Speed Controller Gate Driver IC SHALL enforce a minimum dead-time of 100 ns between the high-side and low-side MOSFET gate signals on each half-bridge to prevent shoot-through current during commutation transitions. Rationale: Shoot-through creates a near-short-circuit across the battery, generating heat that can exceed LiPo maximum discharge current and contribute to H-002 (thermal runaway). 100 ns is the minimum practical dead-time for MOSFET gate capacitances of 1-10 nF; it eliminates shoot-through while adding less than 0.5% duty cycle error at 8 kHz commutation frequency. | Test | subsystem, propulsion-subsystem, sil-2, safety, session-498, idempotency:sub-esc-deadtime-498 |
| SUB-REQ-036 | The Electronic Speed Controller Microcontroller SHALL execute the motor commutation loop with a maximum cycle time of 20 µs to support sensorless back-EMF commutation at motor speeds up to 10000 RPM. Rationale: A brushless motor at 10000 RPM with 7 pole pairs completes one electrical cycle in 860 µs. Sensorless commutation requires back-EMF zero-crossing detection at a minimum of 50 samples per cycle, requiring a loop time no greater than 17 µs. 20 µs is the achievable limit for embedded MCUs at 16 MHz clock and supports the smooth torque delivery that SUB-REQ-001 (100 ms throttle step response) depends on. | Test | subsystem, propulsion-subsystem, sil-2, session-498, idempotency:sub-esc-mcu-loop-498 |
| SUB-REQ-037 | The Flight Control Electronics 2.4 GHz FHSS Receiver SHALL output a CPPM stream at 50 Hz frame rate on a single signal wire, encoding all received channels with pulse widths in the range 1000-2000 µs within a 20 ms frame period. Rationale: CPPM reduces wiring from one wire per channel to a single signal wire, saving approximately 4 g of wiring mass in the airframe. The 20 ms frame period aligns with the 50 Hz servo update rate in IFC-REQ-011 and IFC-REQ-013, and is a prerequisite for the gyro-corrected mixing algorithm in SUB-REQ-026. | Test | subsystem, flight-control-electronics, sil-1, session-498, idempotency:sub-rx-cppm-output-498 |
| Ref | Requirement | V&V | Tags |
|---|---|---|---|
| IFC-REQ-001 | The interface between Kids Remote Control Airplane and USB Power Supply SHALL accept 5 V DC input at 2 A maximum via USB-A or USB-C connector, with reverse polarity protection and over-current fusing at 2.5 A. Rationale: External interface: USB is the universal household power source. 5V/2A provides 10W, sufficient for 1C charging of a 450mAh 2S LiPo (7.4V × 0.45A = 3.3W plus charger losses). Reverse polarity protection prevents damage from non-standard cables. Over-current fuse protects the USB source. | Test | interface, external, session-485, idempotency:ifc-ext-usb-power-485 |
| IFC-REQ-002 | The interface between Kids Remote Control Airplane and the Atmosphere SHALL generate positive lift at airspeeds between 5 m/s and 15 m/s at air densities from 1.007 kg/m3 (2000 m AMSL, 40 C) to 1.341 kg/m3 (sea level, -5 C), with a minimum lift-to-drag ratio of 4:1 at cruise speed. Rationale: External interface: the atmosphere is the aerodynamic medium. The density range covers the full operational envelope (-5C to 40C, sea level to 2000m AMSL). L/D of 4:1 ensures the aircraft can maintain altitude at cruise without full throttle and glide safely in failsafe mode. | Analysis | interface, external, session-485, idempotency:ifc-ext-atmosphere-485 |
| IFC-REQ-003 | The interface between Kids Remote Control Airplane and the 2.4 GHz ISM Band SHALL operate within the 2.400 to 2.4835 GHz frequency range using FHSS modulation across a minimum of 40 channels, with total radiated power not exceeding 1 W EIRP per FCC Part 15.249. Rationale: External interface: the 2.4 GHz ISM band is a shared public resource. FCC Part 15.249 and ETSI EN 300 328 mandate the power ceiling. FHSS across 40+ channels provides interference resilience in WiFi-dense environments. The transmitter and receiver both operate as Part 15 intentional radiators. | Test | interface, external, session-485, idempotency:ifc-ext-ism-band-485 |
| IFC-REQ-004 | The interface between the Radio Transmitter and Flight Control Electronics SHALL carry 3-channel proportional control data (throttle, elevator, rudder/aileron) plus trim offsets and failsafe configuration via 2.4 GHz FHSS at a frame rate of at least 50 Hz with end-to-end latency not exceeding 20 ms from RF transmission to PWM output. Rationale: Internal interface: this is the primary control data path. 50 Hz frame rate provides smooth proportional control (20ms update interval). 20ms RF-to-PWM latency leaves 30ms budget for servo mechanical response within the 50ms total system latency requirement (SYS-REQ-002). Failsafe config must be stored in receiver to enable autonomous failsafe when TX is off. | Test | interface, internal, session-485, idempotency:ifc-tx-fc-control-data-485 |
| IFC-REQ-005 | The interface between the Power System and Propulsion Subsystem SHALL deliver 7.4 V nominal (6.0 V minimum, 8.4 V maximum) at up to 8 A continuous via XT30 connectors with 18 AWG silicone wire, with voltage drop not exceeding 0.2 V at maximum current. Rationale: Internal interface: the power bus to ESC/motor is the highest current path in the aircraft. 8A at 7.4V is 59W peak power. XT30 connectors rated for 30A provide margin. 18 AWG wire limits resistive losses to 0.2V at 8A over the short fuselage run (~15cm). Voltage drop beyond 0.2V causes ESC brownout at low battery. | Test | interface, internal, session-485, idempotency:ifc-power-propulsion-485 |
| IFC-REQ-006 | The interface between the Flight Control Electronics and Propulsion Subsystem SHALL carry a PWM throttle signal (1000 to 2000 microseconds pulse width at 50 Hz) on a single signal wire with 3.3 V logic level, with the ESC acknowledging motor-stop command within 200 ms. Rationale: Internal interface: standard RC PWM protocol. 1000us = motor stop, 2000us = full throttle. 200ms motor-stop response is required for failsafe (SYS-REQ-004) — the motor must be confirmed stopped before the aircraft enters glide mode. ESC must not rearm without a deliberate throttle-up sequence to prevent accidental motor start during handling. | Test | interface, internal, session-485, idempotency:ifc-fc-propulsion-pwm-485 |
| IFC-REQ-007 | The interface between the Electronic Speed Controller MOSFET Half-Bridge and the Brushless DC Motor SHALL provide three-phase commutation at switching frequency 8 kHz to 32 kHz, phase current up to 20 A continuous (30 A peak 5 s), phase voltage 0 to 7.4 V, with inter-phase dead time minimum 200 ns to prevent shoot-through. Rationale: Drives the BLDC motor commutation requirement. 200ns dead time is minimum for the selected MOSFET pair turn-off time (typically 100-150ns); insufficient dead time causes shoot-through destroying both FETs and causing uncontrolled full-power motor runaway — a SIL 2 failure mode. | Test | interface, propulsion-subsystem, sil-2, session-486, idempotency:ifc-esc-motor-3phase-486 |
| IFC-REQ-008 | The mechanical interface between the Brushless DC Motor shaft and the Propeller SHALL maintain positive engagement under a minimum axial extraction force of 20 N and torsional torque of 0.3 Nm, using a prop adapter or collet nut to the motor shaft with tightening torque per motor manufacturer specification. Rationale: Propeller separation during flight is a SIL 2 hazard: a released 7x4 propeller at 12000 RPM has kinetic energy sufficient to cause eye injury. 20N axial retention exceeds worst-case aerodynamic unloading force during negative-g manoeuvre. Collet nut design preferred over set screw for field-replaceable positive retention. | Test | interface, propulsion-subsystem, sil-2, session-486, idempotency:ifc-motor-prop-mech-486 |
| IFC-REQ-009 | The interface between the ESC Microcontroller and the Gate Driver IC SHALL use 3.3 V CMOS logic levels for commutation signals, with propagation latency from MCU output to gate driver output of less than 150 ns, to ensure BEMF zero-crossing alignment. Rationale: MCU to gate driver signal integrity determines commutation accuracy. >150ns propagation shifts zero-crossing detection window causing higher phase current at commutation, increasing MOSFET switching losses and motor heating — degrading LVC accuracy and potentially masking thermal runaway. | Analysis | interface, propulsion-subsystem, session-486, idempotency:ifc-mcu-gatedriver-logic-486 |
| IFC-REQ-010 | The interface between the Radio Transmitter 2.4GHz RF Module and the transmitter antenna SHALL exhibit a feed impedance of 50 ohms ±10%, with VSWR less than 2.0:1 across the 2.400-2.4835 GHz band, ensuring less than 20% reflected power. Rationale: 50-ohm match is the standard for 2.4GHz RF circuitry. VSWR >2:1 means >11% reflected power returning into RF module PA, causing distortion and output power reduction. On toy-grade PCB antennas, impedance mismatch is the primary cause of reduced range — below 150m LOS — triggering false failsafe at normal operating range. | Test | interface, radio-transmitter, session-486, idempotency:ifc-tx-rf-antenna-486 |
| IFC-REQ-011 | The interface between the Flight Control Electronics and the Elevator Servo SHALL carry a standard 50 Hz PWM signal with pulse width between 1000 us and 2000 us at 3.3 V logic level, providing proportional elevator deflection of plus or minus 30 degrees. Rationale: Elevator servo requires standard RC PWM signal from FCE to actuate control surface; 50Hz frame rate and 1000-2000us range are universal RC servo standards ensuring compatibility with any replacement servo during field repair per STK-REQ-008. | Test | idempotency:ifc-fce-elevator-servo-487 |
| IFC-REQ-012 | The interface between the Power System and Flight Control Electronics SHALL deliver 5.0 V regulated DC at up to 500 mA sustained current via the ESC BEC output, with voltage ripple less than 50 mV peak-to-peak. Rationale: FCE receiver and gyro MCU require stable 5V supply; ESC BEC is the designated power source per ARC-REQ-002. Voltage tolerance from STM32-class MCU and RC receiver datasheets requiring 4.75-5.25V. | Test | idempotency:ifc-power-to-fce-5v-v2-487 |
| IFC-REQ-013 | The interface between the Flight Control Electronics and the Rudder Servo SHALL carry a 50 Hz PWM signal with pulse width between 1000 us and 2000 us at 3.3 V logic level, providing proportional rudder deflection of plus or minus 25 degrees. Rationale: Rudder servo requires standard RC PWM from FCE identical to elevator servo; shared signal standard ensures field replaceability per STK-REQ-008 without bespoke components. | Test | idempotency:ifc-fce-rudder-servo-487 |
| IFC-REQ-014 | The interface between the LiPo Battery Pack and the ESC SHALL use a polarised XT30 connector rated at minimum 15 A continuous current, with female connector on the battery side and male connector on the ESC side, polarity marked by red positive and black negative wiring. Rationale: XT30 connector rated for 30A peak/15A continuous exceeds maximum ESC draw (burst ~10A for the target motor class) while remaining compact and lightweight. Polarisation markings prevent reverse-polarity connection which would destroy the ESC and may cause battery fire. | Inspection | idempotency:ifc-battery-esc-xt30-487 |
| IFC-REQ-015 | The interface between the LiPo Battery Pack balance tap and the Ground Charging System SHALL use a JST-XH 3-pin connector (2S configuration), providing individual cell voltage monitoring access to each cell during charging, with all three pins (negative, cell-1-positive, cell-2-positive) consistently wired. Rationale: JST-XH is the industry standard balance connector for 2S LiPo packs; per-cell monitoring via this connector enables the charger to implement the individual cell voltage termination required by SYS-REQ-005, preventing overcharge of unbalanced cells. | Inspection | idempotency:ifc-battery-balance-jst-487 |
| IFC-REQ-016 | The mechanical interface between the Flight Control Electronics board and the Airframe SHALL mount the FCE PCB on 4 rubber-damped standoffs achieving a minimum 20 dB vibration attenuation at frequencies above 50 Hz, and constrain the PCB within plus or minus 2 mm displacement under a 10g shock event. Rationale: Gyroscope on FCE PCB is sensitive to airframe vibration from motor and propeller; 20dB attenuation at 50Hz reduces IMU noise floor to acceptable levels for the 250Hz control loop. 10g shock constraint prevents connector disconnection during a hard landing. | Test | idempotency:ifc-fce-airframe-mount-487 |
| IFC-REQ-017 | The interface between the Radio Transmitter and the Pilot SHALL provide two self-centering proportional joystick axes for throttle/elevator on the left stick and aileron/rudder on the right stick, with spring-loaded centring force of 100-200 gf, and a spring-return throttle trim accessible with the thumb. Rationale: Mode-2 transmitter layout is the global standard for beginner RC flying; spring-centering force in the 100-200gf range is confirmed comfortable for hands aged 8+ without fatiguing for 15-minute sessions, addressing STK-REQ-001 for the target 8-14 age group. | Inspection | idempotency:ifc-transmitter-pilot-hmi-487 |
| IFC-REQ-018 | The interface between the IMU (3-axis gyroscope) and the Flight Control MCU SHALL use SPI at 1 MHz or I2C at 400 kHz, delivering gyroscope rate data at a minimum of 1 kHz sample rate with a noise density below 0.05 deg/s per root-Hz. Rationale: FCE MCU runs a 250Hz attitude control loop; 1kHz IMU data rate provides 4x oversampling for digital low-pass filtering before control loop execution. 0.05 deg/s/sqrt(Hz) noise density ensures attitude estimate error stays below 0.5 degrees at 250Hz loop closure, which is consistent with the plus or minus 45 degree bank angle limit in SYS-REQ-003. | Test | idempotency:ifc-imu-mcu-spi-487 |
| IFC-REQ-019 | The interface between the Ground Charging System and the AC Mains Supply SHALL accept 100-240 V AC at 50-60 Hz via an IEC C7 or USB-A or USB-C input rated at a minimum of 10 W, providing a minimum 90 percent power conversion efficiency at rated output. Rationale: Universal input voltage range (100-240V) allows use in all markets (EU, US, UK, Asia) without an adapter, addressing STK-REQ-011 which requires a packaged complete system ready to use globally. 90 percent efficiency limit ensures the charger does not exceed 0.5W idle draw under EU ErP regulations. | Test | idempotency:ifc-charger-mains-input-487 |
| IFC-REQ-020 | The interface between the Power System (LiPo pack) and the Flight Control Electronics voltage monitoring circuit SHALL provide battery voltage to an ADC input via a resistor divider with a full-scale range of 8.4 V (2S full charge) scaled to 3.3 V, with measurement accuracy of plus or minus 50 mV. Rationale: FCE must detect per-cell voltage to implement autonomous descent below 3.3V/cell (SYS-REQ-004). 50mV accuracy at the cell level is sufficient to trigger the 3.3V threshold reliably before the ESC low-voltage cutoff (3.0V) is reached, providing a safe margin. | Test | idempotency:ifc-fce-lipo-voltage-sense-487 |
| IFC-REQ-021 | The interface between the LiPo Battery Pack and the Power Distribution PCB SHALL use an XT30 polarised connector rated to 30 A continuous, with the positive rail protected by the PCB PTC fuse before any branch point. Rationale: IFC-REQ-014 already specifies the battery-to-ESC connector; this requirement extends the same polarisation and current-rating constraint to the power distribution path. XT30 was selected over XT60 to save 3g while still carrying 30A burst current. | Inspection | interface, power-system, sil-2, session-488, idempotency:ifc-battery-pdpcb-xt30-488 |
| IFC-REQ-022 | The interface between the AC-DC Power Supply Module and the LiPo Balance Charger IC SHALL provide 12 V DC at up to 500 mA with voltage tolerance of plus or minus 0.5 V and ripple less than 100 mV peak-to-peak. Rationale: The LiPo balance charger IC input voltage specification (typically 7-15V for a 2S charger) sets the 12V nominal. 500mA at 12V provides 6W, sufficient for 225mA charge into 8.4V (1.9W) plus charger overhead. 100mV ripple limit prevents false charge-termination triggering due to supply noise. | Test | interface, ground-charging-system, sil-2, session-488, idempotency:ifc-psu-charger-ic-488 |
| IFC-REQ-023 | The interface between the Radio Transmitter and the Flight Control Electronics Receiver during the binding procedure SHALL exchange a unique transmitter identifier over the 2.4 GHz FHSS channel set, with the receiver storing the identifier and refusing control frames from all other transmitters after binding is complete. Rationale: H-006 (RF cross-binding) requires that each aircraft respond only to its bound transmitter. The binding protocol must authenticate transmitter identity at a session level so that unbound transmitters in the vicinity cannot seize control. This is the interface-level specification for the bind function described in SUB-REQ-033 and SUB-REQ-018. | Test | interface, radio-transmitter, sil-1, session-498, idempotency:ifc-tx-rx-bind-protocol-498 |
| IFC-REQ-024 | The interface between the Radio Transmitter RF Module and the Flight Control Electronics Receiver SHALL convey a Received Signal Strength Indicator (RSSI) value updated at a minimum of 10 Hz, with the receiver activating failsafe output when RSSI falls below a configurable threshold corresponding to the start-of-packet loss at the current range. Rationale: RSSI monitoring provides the leading indicator for impending loss-of-link before the 500 ms frame-loss failsafe timeout triggers (SYS-REQ-004). A 10 Hz update rate ensures the pilot receives a warning in time to react. This interface is the link between the RF physical layer and the failsafe logic in SUB-REQ-018 and SUB-REQ-027. | Test | interface, radio-transmitter, sil-1, session-498, idempotency:ifc-rssi-threshold-498 |
| IFC-REQ-025 | The interface between the Electronic Speed Controller MCU and the MOSFET Gate Driver IC SHALL use 3.3 V CMOS logic level gate control signals with a rise time of less than 20 ns to drive the gate driver input, and the gate driver SHALL provide output gate drive voltages of 10-15 V to the MOSFET gate pins. Rationale: The 20 ns MCU signal rise time ensures clean digital transitions that minimise gate driver input jitter. Gate drive voltage of 10-15 V ensures MOSFET full enhancement (minimising on-resistance) across the operating temperature range. This interface specification constrains the gate driver IC selection to types compatible with 3.3 V logic input and 10+ V gate output, ensuring the MOSFET bridge meets the 8 milliohm specification in SUB-REQ-034. | Test | interface, propulsion-subsystem, sil-2, session-498, idempotency:ifc-mcu-gatedriver-498 |
| IFC-REQ-026 | The interface between the Radio Transmitter Joystick Axes and the 2.4 GHz RF Module SHALL sample stick position at a minimum of 100 Hz and SHALL transmit updated channel values in each RF frame with a maximum frame interval of 20 ms at 50 Hz frame rate. Rationale: The 50 ms end-to-end control latency budget (SYS-REQ-002) allocates approximately 20 ms to the RF transmission path. A 20 ms maximum frame interval ensures the RF link contribution to latency is bounded, leaving the remaining budget for PWM decode and servo response. This interface links the stick encoder (SUB-REQ-030) to the RF module (SUB-REQ-032). | Test | interface, radio-transmitter, sil-1, session-498, idempotency:ifc-tx-stick-to-rf-498 |
| Ref | Requirement | V&V | Tags |
|---|---|---|---|
| ARC-REQ-001 | ARC: Flight Control Electronics — Integrated receiver, gyro, and mixing on a single PCB rather than discrete modules. Grouping justification: the receiver, gyroscope, and mixing microcontroller share a common 5V power rail, communicate via SPI/I2C at MHz rates, and execute a single 250Hz control loop. Separating them introduces inter-board wiring that adds mass, latency, and failure points. Alternative considered: separate receiver and standalone gyro stabiliser (common in hobbyist builds) — rejected because the two extra connectors and 3g wiring mass are unjustified in a sub-250g aircraft where every gram matters. The co-location also enables the MCU to implement failsafe logic without inter-board communication. Rationale: The <50ms latency requirement (SYS-REQ-002) and 250g mass budget (SYS-REQ-001) jointly constrain the flight control architecture to a single integrated board. Discrete modules add 5-8ms of inter-board latency and 3-5g of wiring mass. | Analysis | informational, architecture-decision |
| ARC-REQ-002 | ARC: Propulsion Subsystem — ESC with integrated BEC rather than separate BEC module. The ESC already contains power MOSFETs and a microcontroller; adding a 5V linear or switching regulator to the ESC board eliminates a separate BEC module, saving 2-3g and one connector. Alternative considered: dedicated external BEC — rejected because in sub-250g aircraft, the ESC's switching noise on the BEC rail is manageable with a 100μF capacitor, and the mass/connector savings are critical. Trade-off accepted: ESC failure takes down both propulsion and avionics power. Mitigated by the failsafe glide being aerodynamic (gravity-powered descent), not requiring powered avionics beyond the initial motor-cut command. Rationale: Mass budget constraint (SYS-REQ-001) drives integration. A separate BEC adds 3g (1.2% of flight mass) for redundancy that provides minimal benefit — the aircraft glides safely without power. | Analysis | informational, architecture-decision |
| ARC-REQ-003 | ARC: Ground Charging System — Separate charging unit rather than onboard charger. The balance charger with per-cell monitoring, thermal sensing, and fault alarms weighs ~50g and draws 5V/2A from USB. Putting this onboard would add 50g to flight mass (20% of budget), making sub-250g impossible. Alternative considered: simplified onboard charging (single-cell monitoring only) — rejected because H-002 (LiPo thermal runaway, SIL 2) demands per-cell monitoring with thermal cutoff. The safety requirement cannot be compromised for convenience. Trade-off accepted: the child must remove the battery to charge, adding a step to the workflow. Rationale: H-002 (SIL 2) requires per-cell monitoring and thermal cutoff. The charger implementing this weighs 50g — incompatible with 250g flight mass budget (SYS-REQ-001). Safety and mass constraints jointly force ground-based charging. | Analysis | informational, architecture-decision |
| ARC-REQ-004 | ARC: Airframe Subsystem — EPP foam construction rather than balsa/monokote or injection-moulded plastic. EPP absorbs crash energy through reversible compression rather than fracturing, enabling field repair with CA glue. Balsa frames shatter on impact, are destroyed after one crash, and are unsuitable for children. Injection-moulded plastic is crash-durable but heavier and cannot be field-repaired. EPP density 20-30 g/L gives the best strength-to-weight ratio for a crash-tolerant toy. Trade-off: EPP surfaces are rougher, increasing drag by approximately 10-15%. This drag penalty is within the performance margin of SYS-REQ-001 (5-15 m/s flight envelope, 80g thrust at 250g mass). Rationale: Field repairability (SYS-REQ-008, STK-REQ-008) and crash integrity (SYS-REQ-008) jointly require a material that absorbs impacts without shattering and can be glued by a child. EPP is the only material satisfying both constraints within the mass budget. | Analysis | informational, architecture-decision |
| ARC-REQ-005 | ARC: Radio Transmitter — Split architecture with ground transmitter as a separate handheld unit rather than smartphone-based control. A physical transmitter with mechanical gimbals provides tactile feedback, proportional control without visual attention, and zero latency compared to touchscreen Bluetooth control. Alternative considered: smartphone app over Bluetooth LE — rejected because touchscreen controls lack haptic feedback (children look at screen instead of aircraft, losing situational awareness), BLE latency is 20-40ms higher than direct 2.4GHz FHSS, and requiring a smartphone contradicts the no-internet, no-tools setup requirement (SYS-REQ-009). Trade-off accepted: dedicated transmitter adds to product cost (~$12 BOM) and box size. Rationale: Novice pilot control requirement (STK-REQ-002) and no-internet setup requirement (SYS-REQ-009) demand a dedicated transmitter. Smartphone control fails on tactile feedback, latency, and independence from external devices. | Analysis | informational, architecture-decision |
| ARC-REQ-006 | ARC: Power System — 2S LiPo rather than 1S LiPo or NiMH. A 2S (7.4V) pack delivers the 80g minimum thrust required for a brushless motor at 250g flight mass; 1S (3.7V) cannot drive a brushless motor to the required thrust level without doubling current draw (exceeding XT30 connector ratings of 15A continuous). NiMH is heavier by approximately 40% for equivalent energy density, pushing total mass over the 250g regulatory limit. Trade-off accepted: 2S LiPo has higher fire risk than 1S or NiMH, but this is mitigated by the balance charger (Ground Charging System) and the low cell count limiting cascade failure. Rationale: Mass budget (SYS-REQ-001 <250g) and thrust requirement (80-200g static) jointly require 2S LiPo. 1S lacks voltage for efficient brushless drive; NiMH is too heavy. Fire risk mitigated by SYS-REQ-005 (balance charger with thermal cutoff). | Analysis | informational, architecture-decision |
| ARC-REQ-007 | ARC: Power System — 2S LiPo with passive power distribution PCB and ESC-integrated BEC rather than dedicated battery management IC. A kids airplane at 250g all-up mass requires <30Wh energy; a dedicated BMS IC adds 5g and £3 BOM cost with no measurable safety gain over the ESC's built-in LVC. The polyswitch fuse on the distribution PCB provides short-circuit protection without sacrificing the field-replaceability required by STK-REQ-008. This approach matches designs used in mass-market sub-250g foam trainers (Hobbyzone, E-flite Champ). Rationale: Mass budget (SYS-REQ-001) and field-replaceability (STK-REQ-008) jointly preclude a dedicated BMS IC. The ESC LVC and polyswitch fuse provide equivalent protection at zero added mass. Approach validated by E-flite Champ and Hobbyzone Firebird sub-250g trainer designs. | Analysis | informational, architecture-decision |
flowchart TB n0["component<br>Electronic Speed Controller"] n1["component<br>MOSFET Half-Bridge"] n2["component<br>Gate Driver IC"] n3["component<br>ESC Microcontroller"] n4["component<br>Brushless DC Motor"] n5["component<br>Propeller"] n3 -->|PWM commutation| n2 n2 -->|Gate signals| n1 n1 -->|3-phase AC| n4 n4 -->|Shaft torque| n5 n0 -->|Contains| n3
Propulsion Subsystem - Internal
flowchart TB n0["component<br>Transmitter Stick Gimbal (x2)"] n1["component<br>Transmitter MCU"] n2["component<br>2.4GHz RF Module"] n3["component<br>Transmitter Battery"] n0 -->|Analog position 0-3.3V| n1 n1 -->|SPI/UART packet| n2 n3 -->|3.3-6V power| n1
Radio Transmitter - Internal
| Entity | Hex Code | Description |
|---|---|---|
| 2.4 GHz ISM Radio Spectrum | 04056858 | External electromagnetic interface for kids RC airplane: the 2.4 GHz Industrial, Scientific and Medical radio band (2.400-2.4835 GHz) shared with WiFi, Bluetooth, and other ISM devices. Governed by FCC Part 15 (US), ETSI EN 300 328 (EU). System must operate within this shared spectrum using FHSS or DSSS modulation to coexist with other users. |
| 2.4GHz FHSS Receiver | D4F57018 | Frequency-hopping spread spectrum radio receiver in kids RC airplane flight control electronics. Receives 2.4GHz control frames from the ground transmitter, outputs proportional PWM signals (1000-2000us) on throttle, elevator, and rudder channels at 50Hz. Binds to paired transmitter only. Implements 500ms frame-loss failsafe: on timeout sets outputs to pre-configured failsafe positions (throttle 1000us, elevator and rudder neutral). Compatible with DSM2/DSMX or AFHDS protocol. |
| 2.4GHz RF Transmitter Module | D6E57018 | 2.4GHz FHSS transceiver module in hand controller of kids RC airplane. Typically CC2500 or NRF24L01+ chip on sub-PCB. Generates spread-spectrum RF output at <100mW EIRP (FCC Part 15 compliant). Performs frequency hopping across 79-125 sub-channels in 2.400-2.4835 GHz ISM band. Transmits control frame (3+ channels) at 50-100 Hz update rate. SMA or PCB trace antenna. Operates from 3.3V rail from TX MCU or dedicated LDO. Bind sequence to paired airborne receiver. Range: 150-400m line of sight. |
| 3-axis Gyroscope IMU | D4D55008 | MEMS inertial measurement unit providing 3-axis gyroscopic rate data to the flight control MCU in a kids RC airplane. Measures angular rates on pitch, roll, and yaw axes with range +/-2000 dps, resolution 16-bit, output rate 1kHz via SPI at 8MHz. Used exclusively for stability augmentation (angular rate damping) not attitude hold. Integrated in flight control board alongside the MCU. |
| 5V BEC Voltage Regulator | D6C53018 | Battery Eliminator Circuit (linear or switching regulator) embedded in ESC or mounted on power PCB in kids RC airplane. Steps down 7.4V LiPo to 5V regulated for flight control electronics, receiver, and servos. Rated at 2A continuous. Output voltage tolerance ±5% (4.75-5.25V). |
| AC-DC Power Supply Module | D6C51058 | Mains-to-DC converter in the kids RC airplane ground charging system. Accepts 100-240V AC 50/60Hz input and outputs 12V DC at 1A (12W). Includes IEC 60950 isolation transformer and regulatory approval (CE, FCC). Housed in a wall-plug form factor. Provides the input power for the LiPo balance charger IC. |
| Aircraft flyaway beyond visual line of sight | 51000201 | Hazard in Kids Remote Control Airplane during Normal Flight: aircraft flies beyond radio range or VLOS due to wind, disorientation, or stuck-throttle condition. Aircraft continues powered flight in uncontrolled direction, potentially striking people, vehicles, or property at distance. Consequence: property damage, potential injury to bystanders, loss of aircraft. Child pilot may not recognise spatial disorientation until too late. |
| Airframe Structure | CE811008 | Foam (EPO/EPP) or balsa/ply construction fixed-wing airframe. Conventional tractor configuration with fuselage, two wings (semi-symmetrical NACA profile), horizontal stabiliser with elevator, vertical fin with rudder. Design load factor ±4g at maximum flying speed. Wingspan 600-1200mm, chord 120-200mm. Ailerons hinged with CA adhesive or control horns. Impact-resistant nose section to absorb crash energy. Gross weight at-rest 400-600g including battery. Maximum speed 60 km/h, stall speed 18 km/h. |
| Airframe Subsystem | CE851008 | Subsystem of Kids Remote Control Airplane: EPP/EPO expanded foam fuselage and wing panels with embedded carbon-fibre spar. 600mm wingspan, flying-wing or conventional layout. Provides aerodynamic lift and drag surfaces, houses all electronics in fuselage bay, protects battery in crash via foam crush zone. Designed for field repair: modular wing panels bolt to fuselage, foam cracks repairable with CA glue. Mass budget 80g. Must survive 10m/s nose-first grass impact without structural failure exposing sharp edges or ejecting battery. Operating environment: -5C to 40C, UV exposure, grass and dirt landings. |
| Atmosphere as aerodynamic medium | 06010000 | External physical interface for kids RC airplane: the ambient atmosphere provides the aerodynamic medium for flight. Air density (1.225 kg/m³ at sea level ISA), wind speed and turbulence, temperature, and humidity directly affect aircraft performance. System cannot control this interface — must be designed to tolerate expected atmospheric variations. |
| Battery Charging mode of Kids Remote Control Airplane | 54F47200 | Battery charging mode: LiPo battery removed from aircraft or charged in-situ via USB-C balance charger. Charger monitors individual cell voltages during CC/CV charge cycle, typically 1C rate (1-2 hours for full charge). LED indicators show charge progress. Thermal protection cuts charge if battery temperature exceeds 45°C. Entry: battery connected to charger, charger powered. Exit: all cells reach 4.2V (full charge) or fault detected (over-temperature, cell imbalance). Child or parent supervises charging. |
| Battery Critical Emergency Landing mode of Kids Remote Control Airplane | 54F47A00 | Emergency landing mode for kids RC airplane: triggered when LiPo battery voltage drops below safe discharge threshold (typically 3.3V/cell). ESC reduces available throttle progressively, eventually cutting motor entirely to prevent cell damage and thermal runaway risk. Pilot must execute immediate landing with remaining altitude energy. Visual/audible warning from transmitter if telemetry equipped. Entry: battery voltage below 3.3V/cell threshold. Exit: aircraft landed, battery disconnected for charging. |
| Brushless DC Motor | D6D51018 | Outrunner brushless DC motor for kids RC airplane propulsion. Permanent magnet rotor rotates around wound stator. Receives three-phase commutation from ESC at up to 50A peak. Generates shaft torque 0.05-0.20 Nm at 8000-15000 RPM range. 1806-2212 size (stator diameter ~22mm). Mass <30g including mounting hardware. Output: mechanical shaft power to propeller. Key failure modes: bearing seizure, winding short circuit, magnet delamination. |
| Charge Status LED Indicator | D4DC4000 | Dual-colour LED (red=charging, green=complete) on the ground charging unit for the kids RC airplane. Driven by the LiPo balance charger IC status output pin. Visible at 1m in outdoor lighting conditions. Provides the parent with immediate visual confirmation that charging is complete before the child handles the battery. |
| Charging Safety | 50B73000 | System function of Kids Remote Control Airplane: manages the battery charging cycle with safety monitoring to prevent thermal runaway. USB-powered balance charger with per-cell voltage monitoring (4.20V ±0.025V termination), NTC thermistor for 45°C thermal cutoff, audible and visual fault alarms. Charging rate 1C (450mA). Must detect damaged-cell voltage imbalance from crash-compromised batteries. Drives H-002 hazard mitigation. Used in domestic environment by non-technical parent/child. |
| Child Pilot | 00080A51 | Primary operator of the RC airplane, aged 8-14 years. Limited fine motor control and situational awareness compared to adult pilots. Uses handheld 2.4GHz transmitter with two joysticks and a throttle stick. Requires adult supervision per CAA/FAA regulations for under-16 operators. Key safety concern: inadvertent full-throttle input, loss of aircraft orientation at range, and propeller contact during pre-flight setup. Learning curve from simulator to field typically 2-5 hours. |
| Child Pilot (RC Airplane Operator) | 00080000 | Primary operator of kids RC airplane: child aged 8-14 who flies the aircraft using the handheld transmitter. Responsible for pre-flight checks, launch, in-flight control, landing, and basic post-flight inspection. Limited fine motor coordination compared to adult, developing spatial awareness, may panic under stress (e.g., loss of orientation). Key needs: intuitive controls, forgiving flight characteristics, clear feedback on system state. |
| Consumer Electronics and Toy Retailer | 408410D8 | Distribution stakeholder for kids RC airplane: retail outlets (online and brick-and-mortar) that stock, display, and sell the product. Concerned with packaging size, shelf appeal, return rate, warranty claims, product liability insurance requirements, age-rating labelling, and shipping classification for LiPo batteries (IATA DGR Section II). |
| Electrical shock from exposed LiPo wiring | 54400001 | Hazard in Kids Remote Control Airplane during Post-crash and Charging: crash damage exposes battery leads or ESC power wiring. LiPo battery delivers high current (20-40A peak) at low voltage (7.4-11.1V). While voltage is below shock threshold, short circuit causes extreme heat in wiring, burns from hot components, and risk of arcing that could ignite surroundings. Child may touch exposed hot wiring after crash. |
| Electronic Speed Controller | D4F57218 | Brushless DC motor ESC for sub-250g RC aircraft. Controls MOSFET bridge switching at up to 32kHz to regulate motor RPM from PWM input (1000-2000μs). Integrated 5V/1A BEC on PCB. Accepts 2S LiPo (7.4V). Accepts PWM throttle signal from flight control MCU. Includes low-voltage cutoff at 3.3V/cell, thermal protection at 85°C. Rated 10A continuous, 15A burst. Motor commutation via back-EMF sensing. Responds to throttle changes within 25ms. |
| electronic speed controller for kids RC airplane | D6F53018 | ESC in a kids RC airplane: brushless motor drive controller receiving PWM throttle commands (1000-2000µs) from flight control electronics, converting 7.4V 2S LiPo power to 3-phase commutated drive for brushless DC motor. Integrates BEC providing 5V regulated power to avionics. Has over-temperature and over-current protection. Physically enclosed in heat-shrink tubing mounted in airframe. |
| Elevator Control Surface | CE900000 | Moving horizontal tail surface of the kids RC airplane airframe. Hinged to horizontal stabiliser with flexible polypropylene hinge tape. Travel range plus or minus 15mm from neutral to provide pitch authority at 5-12 m/s airspeed. Connected to Elevator Servo via 1mm music wire pushrod. Constructed from same EPP foam as main structure. Fail-safe: if hinge tears, surface deflects to trailing edge horizontal reducing pitch authority but maintaining glide. |
| Elevator Servo | D6F53008 | 5g micro servo actuating the elevator control surface in a kids RC airplane. Receives 50Hz PWM signal (1000-2000us) from flight control MCU. Produces 10mm control throw at less than 0.1 seconds per 60 degrees under 100g-cm load. 5V supply from BEC. Nylon gears (not metal) to limit force during propeller ingestion. PART OF Flight Control Electronics subsystem from a command/control perspective though physically mounted in the airframe. |
| EPP Foam Fuselage | CE8D1008 | Expanded polypropylene foam fuselage and wing structure of a kids RC airplane. Weighs approximately 60g for fuselage, boom, and wing combination. Wing span 600-750mm. EPP foam (not EPS/styrofoam) chosen for crash resilience: EPP deforms and returns to shape rather than shattering. Must withstand 10 m/s nose-first impact onto grass without battery ejection per SYS-REQ-008. Contains battery tray, FCE board mounting points, and motor mount. Repaired with low-temp hot glue or foam-safe adhesive. |
| esc | D4F57018 | Electronic Speed Controller (ESC) for a sub-250g brushless motor kids RC airplane. Three-phase MOSFET H-bridge controlled by 8-bit MCU executing sensorless BEMF commutation. Receives standard hobby PWM throttle signal (1000-2000μs, 50-400Hz) from receiver. Outputs variable-frequency 3-phase AC to drive brushless DC motor. Integrates 5V BEC for avionics power. Implements LVC at 3.3V/cell to protect LiPo battery and thermal protection at 85°C. Responds deterministically to PWM input — no autonomous decision logic beyond protective thresholds. |
| ESC Microcontroller | D1F53018 | 8-bit microcontroller (STM8 or similar) within ESC for kids RC airplane. Runs sensorless BEMF (back-EMF) zero-crossing detection algorithm for motor commutation timing. Reads PWM throttle input from flight controller (50-400Hz, 1-2ms pulse). Converts throttle setpoint to 6-step commutation sequence via gate driver. Implements low-voltage cutoff at 3.3V/cell. Implements thermal protection. Clock speed 16MHz, firmware in flash ROM, typically not user-reprogrammable in toy-grade ESCs. |
| Falling aircraft striking bystander | 46400201 | Hazard in Kids Remote Control Airplane during Normal Flight and Failsafe: aircraft in uncontrolled descent or deliberate dive strikes a person on the ground. At 500g mass and terminal velocity of 15-25 m/s, kinetic energy sufficient to cause bruising, head injury if striking unprotected person. Children and pets in park environment may be in impact zone. Particularly hazardous during failsafe glide if descent path crosses populated area. |
| Flight Control | 50F53208 | System function of Kids Remote Control Airplane: translates pilot stick inputs from 2.4GHz transmitter into proportional servo/motor commands via mixing algorithm. Inputs: 3-channel PWM from receiver (throttle 1000-2000μs, elevator ±500μs, rudder/aileron ±500μs). Outputs: ESC throttle signal, servo deflection commands. Constraints: <50ms end-to-end latency, gyro-assisted attitude limiting in beginner mode (±45° bank, ±30° pitch). Drives SYS-REQ-002, SYS-REQ-003. |
| Flight Control Electronics | D4F57018 | Subsystem of Kids Remote Control Airplane: integrated flight controller board containing 2.4GHz FHSS receiver module, 3-axis MEMS gyroscope (MPU-6050 class), microcontroller running PID stabilisation loop at 250Hz, and servo output drivers. Receives RF control frames, decodes pilot inputs, reads gyro angular rates, computes mixed servo commands with attitude limiting in beginner mode (±45deg bank, ±30deg pitch). Outputs PWM to servos and ESC. Also implements 500ms failsafe timeout with motor-cut and nose-down trim. Mass budget 8g. Powers from 5V BEC rail. |
| Flight Control MCU | D0F53008 | 8-bit or 32-bit microcontroller in the kids RC airplane flight control electronics board. Reads PWM inputs from receiver (50Hz), reads gyro angular rates via SPI (1kHz), runs gyro-mixing algorithm to limit bank angle to 45 degrees, outputs corrected PWM to elevator servo and rudder servo at 50Hz. 3.3V supply, <5mA operating current. Firmware fixed at factory, not user-programmable. |
| Flight Control System | 50E53018 | Onboard signal mixing and servo actuation system. Receives 6-channel PWM from 2.4GHz receiver, mixes channels per aircraft geometry (delta, conventional, flying wing), outputs PWM signals to 3-4 Hitec/Futaba-compatible servos at 4.8-6.0V. Manages aileron differential, elevator throw, rudder coupling. No onboard IMU or stabilisation — pure passthrough mixing. Servo travel ±45° with 180ms/60° speed. Critical path for aircraft attitude control; failure mode is aircraft divergence from desired flight path. |
| Gate Driver IC | D4F53018 | Gate driver integrated circuit within ESC for kids RC airplane. Receives low-level PWM commutation signals from ESC microcontroller (3.3V logic) and drives MOSFET gate electrodes at sufficient voltage/current for fast switching (±2A gate drive current, 10-15V gate voltage). Provides dead-time insertion to prevent shoot-through, bootstrap capacitor bootstrap for high-side gate drive, propagation delay <100ns. Key failure mode: if gate drive fails, motor phase becomes uncontrolled. |
| Ground Charging System | D6F41018 | Subsystem of Kids Remote Control Airplane: USB-powered balance charger unit (5V/2A input), separate from aircraft. Contains per-cell voltage monitoring circuitry (4.20V ±0.025V termination per cell), NTC thermistor temperature sensing (45C thermal cutoff), CC/CV charge control at 1C rate (450mA), LED status indicators (charging/complete/fault), piezo buzzer for audible fault alarm. XT30 battery connector. Detects cell imbalance from crash-damaged batteries. Must operate safely in domestic environment on kitchen counter. Mass ~50g. |
| kids remote control airplane | DEEC1058 | Kids RC airplane: a sub-250g electrically-powered foam fixed-wing radio-controlled aircraft designed as a toy for children aged 8+. 2-channel control (elevator/rudder), brushless motor, 2S LiPo battery, gyro-assisted stability. NOT biomimetic — does not replicate bird musculature or behaviour. Aerodynamic shape is conventional trainer wing planform, not a biomimetic design. Operates via proportional radio control at 2.4 GHz FHSS within visual line of sight by a child operator. Subject to EN 71 toy safety and CE marking. |
| Kids Remote Control Airplane | DEEC5058 | Battery-powered fixed-wing model aircraft for children aged 8-14, controlled via 2.4GHz radio transmitter at ranges up to 300m. Gross weight 150-500g, wingspan 600-1200mm. Comprises an airframe with flight control surfaces, brushless motor with propeller, lithium polymer battery, electronic speed controller, 6-channel receiver, and 3-4 servo actuators. Operates under visual line of sight in open recreational spaces. Subject to CAA/FAA small UAS regulations. Primary safety concern is propeller strike and loss of control. |
| LiPo Balance Charger IC | D4F57058 | Dedicated lithium polymer balance charger integrated circuit for kids RC airplane ground charging system. Charges 2S (7.4V) LiPo packs using CCCV profile: constant current phase at 0.5C (225mA) until 8.4V, then constant voltage until charge current drops to 0.05C (22.5mA) signalling full charge. Monitors individual cell voltages via balance tap, terminates if any cell exceeds 4.2V, and illuminates LED indicator. Implements EN 62133 charging safety profile. |
| LiPo Battery Pack | D6D51019 | 2S 450mAh 30C lithium polymer rechargeable battery pack for kids RC airplane. Nominal voltage 7.4V, fully charged 8.4V, minimum discharge 6.6V (3.3V/cell). Weighs ~28g. Supplies main bus power to ESC and BEC. XT30 connector output. Safety-critical: thermal runaway on overcharge/overdischarge. |
| LiPo Fire During Charging Emergency Scenario | 54400210 | Emergency scenario for kids RC airplane: battery damaged in earlier crash develops internal short during charging, leading to thermal event requiring household emergency response |
| Lithium polymer battery thermal runaway and fire | 44500211 | Hazard in Kids Remote Control Airplane during Charging and Post-crash: LiPo battery cell punctured in crash, over-charged, or over-discharged leading to internal short circuit and thermal runaway. Consequence: fire, toxic fume emission, burns. LiPo fires reach 500°C+ and cannot be extinguished with water. Particularly dangerous because children may not recognise early signs (battery swelling, heat) and product is used in domestic environment. |
| mechanical interface | CE850008 | Mechanical interface between components of a kids RC airplane: physical mating surface or connector point where two structural or mechanical parts physically contact and transfer force. Examples: servo horn-to-pushrod clevis, motor shaft-to-prop adapter, wing saddle-to-fuselage joint. Has measurable physical extent, material properties, and structural load capacity. |
| MOSFET Half-Bridge | D6F53018 | Three-phase MOSFET switching bridge within ESC for kids RC airplane. Six N-channel MOSFETs arranged in three half-bridge pairs, each switching one motor phase. Rated 30V/30A continuous, handles 7.4V bus. Controlled by gate driver at switching frequency 8-32 kHz (field-programmable). Converts DC bus power to three-phase AC power for motor commutation. Key failure mode: thermal overload causing FET short or open causing motor runaway or lockout. No heatsinking — relies on motor cooling airstream at front mount. |
| Motor Mount Assembly | CE841008 | Forward motor mount structure in kids RC airplane airframe. Accepts 1304-1806 size brushless motor with 16x16mm or 19x19mm bolt pattern. EPP foam engine nacelle with embedded plywood reinforcement plate (1.5mm ply) to resist motor torque reaction. Designed to shear away from fuselage at impact forces exceeding 50N to prevent fuselage tearing and reduce transmitted kinetic energy to battery during nose-first crash. |
| Normal Flight mode of Kids Remote Control Airplane | 54FC3218 | Normal flight operating mode: child pilot controls aircraft via 2.4GHz transmitter using throttle, elevator, rudder, and optionally aileron channels. Aircraft maintains aerodynamic flight at 5-30m altitude within visual line of sight (VLOS), typically 50-200m range. Stability augmentation gyro assists in maintaining wings-level attitude. Flight duration 8-15 minutes per battery charge. Entry: successful pre-flight, hand launch or ground takeoff. Exit: pilot initiates landing approach, or battery voltage drops to cutoff threshold. |
| Outdoor park flying environment | 04000000 | Operating environment for kids RC airplane: open grass areas in public parks, school fields, and back gardens. Temperature range -5°C to 40°C (limits of LiPo safe operation and child outdoor comfort). Wind conditions 0-15kt normal operation, 15-25kt marginal, >25kt no-fly. Humidity 0-95% non-condensing. Ground surface: grass, dirt, paved paths. Obstacles: trees, fences, buildings, power lines, other people. Altitude: sea level to 2000m (air density affects performance). Lighting: daylight only, no night flying capability. |
| Parent Guardian | 010908A1 | Adult supervisor responsible for child pilot safety at RC flying site. Purchasing decision-maker who selects age-appropriate aircraft. Responsible for battery charging, pre-flight checks, and enforcing range limits. First responder in crash or injury event. Accountable under duty-of-care obligations for child at public recreational space. Concern: unexpected loss-of-control events, battery fire during overnight charging. |
| Park Bystanders and Public | 04000001 | Passive stakeholder for kids RC airplane: members of the public in the vicinity of the flying area — other children, dog walkers, picnickers in parks. Have no control over the aircraft and may not be aware of its presence. Exposed to risk of impact from uncontrolled aircraft or flyaway. Includes nearby property owners whose buildings, vehicles, or gardens may be struck. |
| Post-crash Inspection and Repair mode of Kids Remote Control Airplane | 44881A08 | Post-crash maintenance mode for kids RC airplane: after any ground impact or hard landing, child/parent inspects aircraft for structural damage (cracked foam, broken control horns, bent pushrods), verifies battery integrity (no puffing/swelling), checks propeller for cracks. Minor repairs performed with CA glue and spare parts from included kit. Battery showing any swelling is retired and disposed per hazmat guidelines. Entry: unplanned ground contact or crash event. Exit: aircraft passes pre-flight check again or is declared unserviceable. |
| Power Distribution PCB | D6851018 | Simple PCB in kids RC airplane power subsystem that distributes 7.4V LiPo power to ESC main bus and provides individual cell voltage sense lines to ESC for LVC monitoring. Includes XT30 battery input, inline fuse (5A polyswitch), and solder pad outputs. No active components except PTC resettable fuse. |
| Power Management | 50953000 | System function of Kids Remote Control Airplane: stores, distributes, and monitors electrical energy for all aircraft subsystems. 2S 450mAh LiPo battery (7.4V nominal) with XT30 connector. Provides 7.4V to ESC, 5V BEC rail to receiver and servos. Monitors cell voltage for low-voltage cutoff (3.3V warning, 3.0V hard cutoff per cell). Constraints: battery mass <35g, 8-12 minute endurance at cruise throttle, must survive 10m/s crash without ejection. |
| Power System | D6D53018 | 3S (11.1V nominal, 12.6V fully charged) lithium polymer battery, 1300-2200mAh, 30C continuous discharge rating. Battery elimination circuit (BEC) within ESC: 5V/3A regulated output to receiver and servos. Balance charger required for cell-level equalisation. Low-voltage cutoff at 3.0V per cell (9.0V total) to prevent battery damage. Thermal runaway risk if over-charged (>4.2V/cell), physically damaged, or short-circuited. Battery weight 80-180g, typically 25-35% of total aircraft weight. |
| Pre-flight Check mode of Kids Remote Control Airplane | 54882A00 | Pre-flight operating mode: child or parent inspects airframe for damage, verifies battery charge level via LED indicator, checks control surface movement by deflecting sticks on transmitter, confirms propeller is securely attached. Entry: power-on of transmitter then aircraft. Exit: all checks pass, pilot moves to open space. Duration 1-3 minutes. Failure mode: dead battery detected, broken control surface linkage. |
| Propeller | CEC50018 | Two-blade plastic propeller for kids RC airplane. Converts shaft torque from BLDC motor to thrust. APC or similar 6x4 to 7x3.5 size (6-7 inch diameter). Constructed from glass-filled nylon or similar polymer with designed yield points at root — EN 71 / ASTM F963 compliant frangible design. Balancing tolerance <0.1g tip-to-tip. Generates 80-200g thrust range depending on motor RPM. Mass <10g. Failure mode: blade strike on hard surface causes clean fracture at root (designed), reducing thrust to zero. Mounting: collet nut or prop adapter to motor shaft. |
| Propeller strike causing laceration or eye injury | 44000001 | Hazard in Kids Remote Control Airplane during Normal Flight and Pre-flight: rotating propeller (8000-15000 RPM) contacts child's fingers, face, or eyes during hand launch, catch attempt, or while aircraft is on ground with motor armed. Consequence: lacerations, potential eye injury. Particularly dangerous because children may instinctively grab at aircraft. Propeller tip speed approximately 30-50 m/s. |
| Propulsion | 54D53008 | System function of Kids Remote Control Airplane: generates thrust for sustained flight. Brushless outrunner motor (1806 class, ~2200KV) driving 5-inch frangible propeller. Input: ESC PWM signal (1000-2000μs). Output: 80-200g static thrust. Constraints: <250g total aircraft mass budget means motor+ESC+prop must be <40g. Max current draw ~8A. Motor must be stoppable within 200ms for failsafe. |
| Propulsion Subsystem | D6D53218 | |
| Propulsion System | 55F53018 | Brushless DC motor (1000-1400KV) driving a 9x4.7 or 10x4.7 APC propeller. Powered by 3S 11.1V LiPo through a 30A electronic speed controller. ESC receives throttle PWM from receiver, outputs 3-phase variable frequency AC to motor. Motor produces 200-350g static thrust at full throttle. Propeller tip speed 120-180 m/s. Primary hazard: propeller strike laceration to fingers; prop guard optional. Prop strike to face in crash scenario. Thermal limit on ESC 85°C; cutback at over-temperature. |
| Radio Control Link | 54E57018 | 2.4GHz frequency-hopping spread-spectrum radio link between hand-held transmitter and onboard receiver. Transmitter provides 6-channel proportional control (throttle, aileron, elevator, rudder + 2 aux channels) with PWM/PPM output at 20ms frame rate. Link range 300m at 100mW transmit power. Failsafe activates on link loss: throttle to zero, surfaces to neutral within 200ms. Shared spectrum environment with other RC aircraft and WiFi devices. |
| Radio frequency interference causing loss of control on adjacent aircraft | 04000001 | Hazard in Kids Remote Control Airplane during Normal Flight: multiple RC aircraft operating in same area on 2.4GHz band. Frequency hopping spread spectrum (FHSS) mitigates but does not eliminate co-channel interference. If binding protocol fails or legacy 27/40MHz transmitter is used nearby, cross-control event possible where one transmitter controls another's aircraft. Consequence: uncontrolled aircraft, potential mid-air collision or ground strike. |
| Radio Transmitter | D6ED7018 | Subsystem of Kids Remote Control Airplane: handheld ground control unit held by child pilot. Contains 2.4GHz FHSS radio transmitter module, 3 proportional gimbal sticks (throttle, elevator, rudder/aileron), trim buttons, power switch, LED status indicators, low-battery buzzer, and 4xAA battery holder. Encodes stick positions into FHSS frames at 111Hz, hops across 80 channels. Includes bind button for receiver pairing. Ergonomically sized for child hands (ages 8-14). Must be operable with gloves. Mass ~150g with batteries. FCC Part 15.249 compliant at under 1W EIRP. |
| RC Airplane Product Manufacturer | 40843859 | Lifecycle stakeholder for kids RC airplane: company that designs, manufactures, and distributes the product. Responsible for design safety, material selection, quality control, regulatory compliance (EN 71, ASTM F963, FCC Part 15, CE marking), user manual writing, warranty support, and product liability. Must balance cost, durability, performance, and safety for a consumer price point under 00. |
| Regulatory Authority | 008578FD | CAA (UK) or FAA (US) small UAS regulatory body. Defines operational category for sub-250g and sub-500g aircraft: CAA Flyer ID requirement for aircraft 250g-500g, registration for over 250g with camera. FAA Part 107 recreational exemption for model aircraft under FRIA rules. Sets no-fly zones around airports (5km exclusion), maximum altitude (120m AGL), and VLOS requirement. Enforces via civil penalty; accident reporting mandatory for injuries. |
| Routine Maintenance and Battery Replacement Scenario | 50881A08 | Maintenance scenario for kids RC airplane: periodic maintenance tasks including battery lifecycle management, servo inspection, and propeller replacement after wear |
| Rudder Control Surface | C6951000 | Moving vertical tail surface of the kids RC airplane airframe. Hinged to vertical fin. Travel range plus or minus 15mm from neutral. Connected to Rudder Servo via 1mm music wire pushrod. Used for yaw control and coordinated turns. Constructed from EPP foam. Secondary safety role: at zero throttle and neutral elevator, a rudder-only input produces a coordinated banking turn enabling the failsafe descent manoeuvre. |
| Rudder Servo | D6F51008 | 5g micro servo actuating the rudder control surface in a kids RC airplane. Receives 50Hz PWM signal (1000-2000us) from flight control MCU. Produces 10mm control throw at less than 0.1 seconds per 60 degrees under 100g-cm load. 5V supply from BEC. Paired with Elevator Servo as the complete 2-axis control surface actuation system. |
| Signal Loss and Failsafe Activation Scenario | 00B43200 | Degraded operations scenario for kids RC airplane: aircraft flies behind obstacle causing signal loss, failsafe activates and aircraft glides down |
| Signal Loss Failsafe mode of Kids Remote Control Airplane | 40B53A00 | Failsafe operating mode of kids RC airplane: activated when receiver detects loss of transmitter signal for >500ms. Receiver commands throttle to idle (motor off) and control surfaces to neutral or slight nose-down trim to induce a controlled glide descent. Aircraft descends unpowered in a predictable direction rather than flying away uncontrolled. Entry: loss of valid 2.4GHz control frames for 500ms. Exit: signal reacquired (returns to normal flight) or aircraft touches ground. |
| Small parts ingestion hazard for young children | 40000051 | Hazard in Kids Remote Control Airplane during all modes: small detachable components (propeller nut, control horns, landing gear clips, battery connector pins) present choking hazard for children under 3 who may be siblings of the intended 8-14 year old user. Components smaller than 31.7mm diameter cylinder test per ASTM F963. Also risk of button cell battery (in transmitter) ingestion causing oesophageal chemical burns. |
| Stability Augmentation | 55F53808 | System function of Kids Remote Control Airplane: measures aircraft attitude via 3-axis MEMS gyroscope and blends correction signals with pilot commands to prevent attitude excursions. Runs PID control loop at ≥250Hz. Inputs: gyro angular rates (roll, pitch, yaw). Outputs: corrective servo deflection commands mixed with pilot input. Beginner mode: hard-limits bank ±45°, pitch ±30°. Advanced mode: rate damping only, no attitude limiting. Critical for making the aircraft flyable by children with no RC experience. |
| structural integrity | 00010000 | |
| Supervising Parent or Guardian | 000C08A1 | Supervisory stakeholder for kids RC airplane: adult parent or guardian who assists with initial setup, supervises early flights, performs post-crash safety assessment, manages battery charging, handles maintenance requiring tools or adhesives. Makes purchase decision. Responsible for ensuring flying site is suitable and that younger siblings are kept clear. May have no RC experience themselves. |
| Toy Safety and Aviation Regulatory Authority | 008578FD | Regulatory stakeholder for kids RC airplane: government bodies that set and enforce standards. Includes toy safety regulators (CPSC in US, market surveillance in EU) enforcing EN 71/ASTM F963 for choking hazards, flammability, chemical safety. Aviation regulators (FAA, CAA, EASA) defining weight thresholds for registration and airspace rules — sub-250g exempt from registration in many jurisdictions. Radio spectrum regulators (FCC, Ofcom) governing 2.4GHz ISM band emissions. Product must comply before it can be legally sold. |
| Transmitter Battery Pack | D6CD0018 | Power source for handheld transmitter of kids RC airplane. Typically 4x AA alkaline cells (6V nominal, 4.5V minimum cutoff) or single 18650 Li-ion in premium models. Provides 500-2000 mAh capacity for 8-20 hours transmission. Low-voltage LED indicator built into TX MCU logic. Battery bay in transmitter handle or rear body, accessible without tools for cell replacement. Not rechargeable in AA configuration (parent replaces cells). |
| Transmitter MCU | D1F57008 | Microcontroller in handheld transmitter of kids RC airplane. Reads 4x ADC channels from stick gimbals, applies trim and rate mixing, encodes 3+ channels as FHSS protocol packet, sends to RF module via SPI/UART. Hosts bind sequence logic, failsafe programming, and LED/display driver. Low-power 8/32-bit MCU (STM32F0 or similar), 3.3V, 16-48MHz. Powers RF module. Manages battery LED indicator (AA cell or 18650 Li-ion pack). Not field-reprogrammable on toy-grade units. |
| Transmitter Stick Gimbal | C6CD5018 | Two-axis Hall-effect or potentiometer gimbal assembly in kids RC airplane hand controller. Provides proportional pitch/roll control (right stick) and throttle/yaw control (left stick). Spring-centered on elevator and aileron axes; ratcheted on throttle. 10-12 bit ADC resolution (1024-4096 counts full travel), ±60 degree mechanical travel. Encodes pilot intent as analog voltage to TX MCU. One per axis = 4 total analog channels. EN 71 compliant physical grip with tactile stops for endpoint feel. |
| USB Power Supply for Battery Charger | D48C0008 | External interface for kids RC airplane charging system: standard USB-A or USB-C 5V power source (wall adapter, laptop port, power bank) providing 5V/2A to the balance charger module. Interface is the USB connector — system does not control the power source. Availability depends on household infrastructure. |
| Weekend Park Flight Scenario | 14080280 | Normal operations scenario for kids RC airplane: a child and parent visit a local park on a Saturday afternoon for recreational flying |
| Wind Gust Crash and Recovery Scenario | 00080200 | Degraded operations scenario for kids RC airplane: unexpected wind gust causes crash, child assesses damage and attempts field repair |
| Component | Belongs To |
|---|---|
| Airframe Subsystem | Kids Remote Control Airplane |
| Propulsion Subsystem | Kids Remote Control Airplane |
| Flight Control Electronics | Kids Remote Control Airplane |
| Radio Transmitter | Kids Remote Control Airplane |
| Power System | Kids Remote Control Airplane |
| Ground Charging System | Kids Remote Control Airplane |
| Brushless DC Motor | Propulsion Subsystem |
| Electronic Speed Controller | Propulsion Subsystem |
| Propeller | Propulsion Subsystem |
| MOSFET Half-Bridge | Electronic Speed Controller |
| Gate Driver IC | Electronic Speed Controller |
| ESC Microcontroller | Electronic Speed Controller |
| Transmitter Stick Gimbal | Radio Transmitter |
| 2.4GHz RF Transmitter Module | Radio Transmitter |
| Transmitter MCU | Radio Transmitter |
| Transmitter Battery Pack | Radio Transmitter |
| LiPo Battery Pack | Power System |
| Power Distribution PCB | Power System |
| 5V BEC Voltage Regulator | Power System |
| AC-DC Power Supply Module | Ground Charging System |
| LiPo Balance Charger IC | Ground Charging System |
| Charge Status LED Indicator | Ground Charging System |
| 2.4GHz FHSS Receiver | Flight Control Electronics |
| 3-axis Gyroscope IMU | Flight Control Electronics |
| Flight Control MCU | Flight Control Electronics |
| Elevator Servo | Flight Control Electronics |
| Rudder Servo | Flight Control Electronics |
| EPP Foam Fuselage | Airframe Subsystem |
| Elevator Control Surface | Airframe Subsystem |
| Rudder Control Surface | Airframe Subsystem |
| Motor Mount Assembly | Airframe Subsystem |
| From | To |
|---|---|
| Electronic Speed Controller | Brushless DC Motor |
| Electronic Speed Controller | Flight Control Electronics |
| Brushless DC Motor | Propeller |
| MOSFET Half-Bridge | Gate Driver IC |
| Gate Driver IC | ESC Microcontroller |
| Transmitter Stick Gimbal | Transmitter MCU |
| Transmitter MCU | 2.4GHz RF Transmitter Module |
| 2.4GHz RF Transmitter Module | Flight Control Electronics |
| 2.4GHz FHSS Receiver | Flight Control MCU |
| 3-axis Gyroscope IMU | Flight Control MCU |
| Flight Control MCU | Elevator Servo |
| Flight Control MCU | Rudder Servo |
| Component | Output |
|---|---|
| Propulsion Subsystem | Thrust: 80-200g at 5-15m/s airspeed |
| Brushless DC Motor | Shaft torque: 0.05-0.20 Nm at 8000-15000 RPM |
| Propeller | Thrust via torque-to-airspeed conversion |
| Electronic Speed Controller | Three-phase PWM commutation to motor |
| 2.4GHz RF Transmitter Module | FHSS control frames at 50-100Hz over 2.4GHz ISM band |
| Transmitter Stick Gimbal | Proportional analog position 0-3.3V per axis |
| LiPo Battery Pack | 7.4V DC bus power |
| Power Distribution PCB | fused power distribution |
| 5V BEC Voltage Regulator | 5V regulated output |
| AC-DC Power Supply Module | 12V DC at 1A |
| LiPo Balance Charger IC | CCCV charge profile with per-cell balance |
| Charge Status LED Indicator | visual charge status indication |