ISO-Plane TRL3

ISO-Plane TRL3 defines the transition of the ISO-Plane program from a validated conceptual architecture toward a technically substantiated engineering definition.

At this stage, the project is no longer limited to architectural feasibility. It enters a phase where the main assumptions must be supported by calculations, simulations, preliminary tests, subsystem sizing and structured technical risk reduction.

TRL3 is therefore the first maturity level where the ISO-Plane becomes an engineering-driven aircraft concept, with the objective of preparing the program for demonstrator design, industrial dialogue and future TRL4 maturation.

Executive Summary

TRL3 corresponds to the analytical and experimental proof-of-concept phase of the ISO-Plane program.

The purpose of this phase is to verify that the selected aircraft architecture can credibly support the transport, autonomous loading, unloading and flight operation of one standard 20-foot ISO container.

The TRL3 work focuses on:

structural feasibility of the fuselage and ventral cargo opening;
validation of the cargo lifting and locking load paths;
aerodynamic refinement of the high-wing twin-engine configuration;
integration of Q400-derived landing gear into the nacelle architecture;
consolidation of mass, balance and mission performance;
preliminary systems architecture definition;
identification and reduction of major technical risks;
preparation of the project for industrial and pre-certification discussions.

TRL3 does not aim to produce a flying prototype. Its objective is to produce engineering credibility.

Program Context

The ISO-Plane is a specialized cargo aircraft concept designed to transport a single 20-foot ISO container while remaining significantly smaller than conventional military transport aircraft capable of carrying containerized freight.

The aircraft is intended to provide autonomous loading and unloading capability, either from the ground or directly from a truck trailer, without requiring heavy external airport handling equipment.

The reference configuration includes:

Parameter	TRL3 reference assumption
Mission	Air transport of one 20-foot ISO container
Payload objective	Up to approximately 8 tonnes of containerized payload
Loading concept	Autonomous loading and unloading through a ventral cargo access system
Propulsion	Twin turboprop configuration using Pratt & Whitney PW150A-class engines
Wing configuration	High-wing architecture
Landing gear concept	Main landing gear derived from Bombardier Q400 architecture, integrated into the nacelles
Cargo bay	Pressurized cargo compartment compatible with a 20-foot ISO container
Cockpit	Pressurized cockpit, crew of two, with operational access independent from the cargo bay
Design ambition	Long-range container air logistics with autonomous ground handling

The TRL3 baseline remains a design target, not a certified aircraft definition.

TRL Context

Technology Readiness Level 3 corresponds to an early proof-of-concept stage.

For ISO-Plane, TRL3 means that the main technical principles selected during TRL2 must be tested against engineering reality.

TRL3 includes:

analytical proof-of-concept;
preliminary experimental proof-of-concept when possible;
subsystem feasibility validation;
first-order structural verification;
aerodynamic model refinement;
mechanical integration studies;
preliminary failure and risk analysis;
preparation of subsystem demonstrators;
identification of technical gaps toward TRL4.

TRL3 is the first phase where the program must demonstrate that the architecture is not only innovative, but also technically defendable.

TRL2 to TRL3 Transition

Status Achieved at TRL2

The end of TRL2 established a coherent conceptual architecture for the ISO-Plane.

The following elements are considered part of the TRL2 baseline:

global aircraft architecture selected;
high-wing twin-turboprop layout retained;
3D digital mock-up created;
loading system concept defined;
ventral cargo door concept selected;
rear access and cargo bay layout investigated;
PW150A engine family selected as propulsion reference;
Q400-derived landing gear integration concept retained;
preliminary fuselage sizing completed;
preliminary mass and performance estimates produced;
initial market and operational studies performed;
first collaborative project structure established between academic contributors.

TRL3 Entry Logic

The TRL3 phase starts when the aircraft is sufficiently defined to allow engineering verification.

The main TRL3 question is:

Can the ISO-Plane architecture withstand preliminary structural, mechanical, aerodynamic and operational scrutiny?

To answer this, TRL3 must convert the digital mock-up into a structured engineering definition.

TRL3 Exit Logic

TRL3 may be considered complete when the critical concepts are validated by analysis and supported by credible simulation or preliminary test evidence.

The expected TRL3 exit condition is not a prototype, but a mature technical dossier enabling the launch of TRL4 demonstrators.

TRL3 Objectives

The main objectives of TRL3 are:

perform detailed structural calculations on critical zones;
validate the feasibility of a large ventral opening in a pressurized fuselage;
refine the aerodynamic configuration using CFD and analytical methods;
verify the mechanical logic of the autonomous cargo handling system;
assess the load paths generated by lifting an 8-tonne ISO container;
consolidate the central wing box configuration;
verify landing gear integration into nacelle structures;
update the aircraft mass breakdown;
refine the center-of-gravity envelope;
assess cargo loading and unloading stability;
identify the highest technical risks;
prepare subsystem demonstrator requirements for TRL4;
initiate structured technical exchanges with industrial partners.

TRL3 Engineering Philosophy

TRL3 is based on a conservative engineering approach.

The objective is not to optimize every parameter immediately, but to identify whether the core architecture is structurally and mechanically viable.

The guiding principles are:

prioritize feasibility before optimization;
validate load paths before refining geometry;
use conservative margins where uncertainty remains high;
separate architectural assumptions from verified engineering results;
document every major hypothesis;
identify the assumptions that must be tested physically at TRL4;
maintain compatibility with open-source collaboration while protecting potential industrial interfaces.

Configuration Baseline at TRL3 Entry

Aircraft Architecture

The ISO-Plane TRL3 reference architecture is a high-wing twin-turboprop aircraft with a pressurized fuselage and a ventral container loading system.

The aircraft is designed around the geometric constraints of a 20-foot ISO container.

The general layout includes:

forward cockpit;
pressurized cargo bay;
high wing and central wing box;
twin turboprop propulsion;
rear empennage structure;
nacelle-mounted main landing gear;
ventral cargo door;
mechanized cargo handling system;
twist-lock-based container attachment interfaces.

Cargo Bay Architecture

The cargo bay must accommodate one standard 20-foot ISO container while preserving sufficient structural continuity around the fuselage.

Key design constraints include:

container external length compatibility;
lateral clearance for loading operations;
vertical clearance for container motion;
structural clearance around the ventral opening;
compatibility with pressurization loads;
integration of lifting arms or mechanized load transfer elements;
integration of locking points;
access to emergency securing systems;
maintainability of the cargo handling equipment.

Ventral Door Architecture

The ventral cargo door is one of the defining systems of the ISO-Plane.

At TRL3, the retained concept is a three-panel opening system allowing ground-level access for loading and unloading a 20-foot ISO container.

The ventral door must:

preserve aerodynamic continuity in flight;
support pressurization sealing requirements;
avoid structural weakening of the fuselage beyond acceptable limits;
provide sufficient opening clearance for the container;
remain compatible with internal floor or guide structures;
withstand local loads from cargo handling interfaces;
support emergency closing and locking logic;
remain inspectable and maintainable.

Landing Gear Architecture

The main landing gear is derived from the Bombardier Q400 concept and is integrated into the nacelles below the high-mounted wings.

This architecture is retained because it avoids occupying the lower fuselage volume required by the cargo bay and ventral opening.

The TRL3 landing gear integration studies must verify:

nacelle structural reinforcement;
landing load transfer into wing and engine support structures;
retraction kinematics;
wheel well packaging;
gear door integration;
compatibility with propeller clearance;
ground stability during loading;
compatibility with truck and ground loading scenarios.

Propulsion Architecture

The TRL3 propulsion reference remains the Pratt & Whitney PW150A engine class.

This engine family is used as a sizing and integration reference for:

power-to-weight estimation;
nacelle sizing;
propeller clearance studies;
fuel consumption modelling;
operational range estimation;
integration with Q400-derived systems and landing gear concepts.

At TRL3, the engine selection is not yet a procurement decision. It is a technical baseline for configuration development.

Technical Work Packages

The TRL3 phase is organized around technical work packages.

Each work package must produce a documented engineering output that can be reviewed, challenged and improved by the project team.

Work Package	Main Objective	TRL3 Output
WP1 — Structural Engineering	Validate the feasibility of the primary structure	Structural models, load cases, stress results
WP2 — Aerodynamics and Performance	Refine aerodynamic assumptions	CFD results, drag breakdown, performance update
WP3 — Cargo Handling System	Validate lifting kinematics and load paths	Mechanism study, load transfer report, FMEA
WP4 — Ventral Door System	Size and validate the lower cargo opening concept	Door sizing, hinge loads, sealing concept
WP5 — Landing Gear Integration	Verify compatibility between landing gear and cargo bay geometry	Gear packaging and structural integration report
WP6 — Mass and Balance	Consolidate the mass model and CG envelope	Updated weight statement and balance charts
WP7 — Systems Architecture	Define preliminary aircraft systems interfaces	System block diagrams and interface matrix
WP8 — Risk and Safety	Identify and reduce major technical risks	Risk register, mitigation plan, preliminary FMEA
WP9 — Industrial Interface	Prepare technical exchanges with partners	Briefing package and supplier question list

WP1 — Structural Engineering

Purpose

The structural engineering work package is central to TRL3.

Its purpose is to validate that the ISO-Plane can integrate a large cargo bay and ventral opening while maintaining sufficient structural integrity for flight, landing, pressurization and cargo handling loads.

Main Structural Questions

The key questions are:

Can a fuselage of approximately 4 m diameter support a large ventral opening?
Can the cargo bay remain pressurized with acceptable structural mass?
Can the central wing box transfer loads without obstructing the cargo bay?
Can container lifting loads be transferred safely into primary fuselage frames?
Can the landing gear loads be routed through the nacelles and wing structure without excessive reinforcement?
Can fatigue-sensitive zones be identified early?

Structural Analysis Scope

The structural analysis shall include:

fuselage shell modelling;
frame and stringer preliminary sizing;
floor beam modelling;
central wing box modelling;
cargo bay reinforcement modelling;
ventral door frame modelling;
landing gear load introduction zones;
engine nacelle support loads;
lifting arm attachment zones;
twist-lock load introduction zones;
local stress concentration assessment.

Primary Load Cases

TRL3 structural load cases include:

Load Case	Description	Critical Zones
Pressurization	Differential pressure between cargo bay and atmosphere	fuselage shell, door seals, pressure frames
Cruise flight	Wing bending, fuselage bending, engine loads	wing box, fuselage frames, nacelles
Landing	Vertical and longitudinal gear loads	nacelles, wing structure, gear attachments
Container lifting	Concentrated lifting loads from ISO corner interfaces	robotic arms, floor beams, frames
Asymmetric lift	Uneven load distribution during container handling	arm attachments, fuselage torsion paths
Ground handling	Loads during loading from ground or truck trailer	landing gear, cargo bay, door structure
Emergency securing	Container restraint under abnormal accelerations	twist-locks, cargo floor, fuselage hard points

Fuselage Structural Challenge

The fuselage is one of the most critical elements of TRL3.

A conventional pressurized fuselage relies on circumferential continuity. The ISO-Plane breaks this continuity by introducing a large ventral opening.

This creates several structural challenges:

loss of lower fuselage stiffness;
local stress concentrations around door cut-outs;
increased frame loads near opening edges;
fatigue risk near reinforced corners;
pressurization sealing complexity;
interaction between cargo floor and fuselage shell;
need for strong but lightweight door locking mechanisms.

Central Wing Box Challenge

The central wing box must transfer the aerodynamic loads from the high wing into the fuselage while preserving the usable cargo volume.

The TRL3 analysis shall verify:

box height and width compatibility with cargo bay geometry;
wing bending load transfer;
torsional stiffness;
interaction with pressurized fuselage structure;
possible local reinforcement requirements;
accessibility for inspection and maintenance.

Structural Deliverables

The expected deliverables of WP1 are:

preliminary finite element model of the fuselage;
preliminary finite element model of the wing box;
local model of the ventral door frame;
load case definition document;
stress map of critical zones;
first mass estimate of reinforcements;
list of structural assumptions requiring TRL4 testing.

WP2 — Aerodynamics and Performance

Purpose

The aerodynamic work package aims to refine the flight performance assumptions made during TRL2.

At TRL3, the aircraft geometry must be assessed with more rigorous aerodynamic tools.

Aerodynamic Topics

The aerodynamic studies shall include:

high-wing aerodynamic performance;
fuselage drag assessment;
nacelle drag and interference effects;
propeller slipstream interaction;
tailplane effectiveness;
rear fuselage flow behaviour;
drag impact of landing gear fairings and nacelles;
effect of cargo door geometry on external shape;
takeoff and landing performance;
climb performance;
cruise performance;
payload-range update.

CFD Scope

CFD studies should be progressively introduced.

Initial CFD may use simplified models, followed by more refined geometry as the digital mock-up matures.

The CFD programme should cover:

clean cruise configuration;
takeoff configuration;
landing configuration;
nacelle-wing interaction;
fuselage-wing interference;
propeller slipstream approximation;
empennage effectiveness;
sensitivity to angle of attack;
sensitivity to sideslip.

Drag Breakdown

A TRL3 drag breakdown should distinguish:

fuselage parasite drag;
wing profile drag;
induced drag;
nacelle drag;
landing gear fairing drag;
tail drag;
cooling and inlet drag;
interference drag;
trim drag;
residual modelling uncertainty.

Performance Outputs

The TRL3 performance model shall update:

cruise speed estimate;
takeoff distance;
landing distance;
climb gradient;
fuel burn;
mission range;
payload-range curve;
service ceiling estimate;
reserve fuel assumptions.

Aerodynamic Risks

The main aerodynamic risks are:

excessive drag due to large fuselage diameter;
interference between nacelles and high wing;
insufficient tail effectiveness;
trim penalty caused by cargo bay and CG constraints;
aerodynamic penalty of structural reinforcements;
possible aeroelastic sensitivity of the high-wing configuration.

WP3 — Cargo Handling System Validation

Purpose

The cargo handling system is one of the most innovative and highest-risk subsystems of the ISO-Plane.

At TRL3, this system moves from conceptual feasibility toward engineering verification.

The objective is to demonstrate that the autonomous loading concept is mechanically credible, structurally compatible and operationally safe.

System Description

The cargo handling system is intended to lift, position, secure and release one 20-foot ISO container.

The system may include:

mechanized or robotic lifting arms;
twist-lock interfaces;
guidance rails or alignment aids;
emergency winches;
local structural hard points;
sensors for position detection;
control logic from the cockpit;
mechanical locking systems;
emergency release procedures.

Validation Pillar 1 — Kinematic Realism

The first TRL3 validation pillar is kinematic realism.

The mechanism must physically fit inside the aircraft and execute its deployment sequence without collision.

The analysis shall cover:

arm deployment sequence;
articulation limits;
retraction envelope;
clearance with fuselage frames;
clearance with the ventral door panels;
clearance with the container;
compatibility with truck trailer height;
ground loading geometry;
emergency retraction cases;
maintenance access.

A major TRL3 objective is to detect early geometric conflicts that were not visible at TRL2.

Validation Pillar 2 — Structural Load Transfer

Lifting an 8-tonne container generates concentrated loads at the ISO corner interfaces.

The load path must be understood from the container to the aircraft primary structure.

The load path includes:

ISO corner casting;
twist-lock interface;
lifting arm end effector;
arm structure;
actuator or linkage system;
arm root attachment;
fuselage frame or floor beam;
primary fuselage reinforcement;
global aircraft structure.

Load Cases for Cargo Handling

The cargo handling simulations shall include:

symmetric vertical lift;
asymmetric lift;
container offset in longitudinal direction;
container offset in lateral direction;
angular misalignment;
dynamic amplification during lifting;
emergency stop;
partial arm failure;
failed twist-lock engagement;
winch-assisted recovery;
truck trailer loading case;
ground loading case.

Validation Pillar 3 — Safety and Redundancy

Autonomous container handling requires fault tolerance.

TRL3 shall define a preliminary safety architecture covering:

loss of one lifting arm;
actuator jam;
twist-lock failure;
sensor failure;
emergency lowering;
emergency winch recovery;
power loss during loading;
communication failure between cockpit and handling system;
mechanical over-travel protection;
ground personnel exclusion zone.

Preliminary FMEA

A preliminary Failure Mode and Effects Analysis shall be performed.

Failure Mode	Possible Effect	TRL3 Mitigation
One arm fails during lift	Asymmetric container load and possible structural overload	emergency winch support, load sensors, automatic stop
Twist-lock fails to engage	Container not secured	lock status detection, cockpit warning, mechanical inspection logic
Door does not fully open	Collision risk during lifting	position sensors, interlock logic
Power loss during lift	Container suspended or partially lifted	mechanical brakes, backup power, emergency lowering
Misalignment with truck	Excessive side load on arms	alignment sensors, tolerance envelope, no-lift condition
Sensor error	Incorrect positioning	redundant sensing, manual verification mode

Ground Clearance Studies

TRL3 shall confirm that loading and unloading remain feasible on realistic airfield surfaces.

The studies shall account for:

landing gear compression;
tire deflection;
ground slope;
truck trailer height variability;
uneven terrain;
container support height;
clearance between container and fuselage;
door clearance during opening;
propeller and ground safety zones.

Primary Objective of WP3

The cargo handling system shall demonstrate credible mechanical integration with controlled load paths, manageable risk and aviation-level safety logic.

WP4 — Ventral Cargo Door System

Purpose

The ventral cargo door is both a structural system and a functional enabler of the ISO-Plane mission.

Its TRL3 validation is therefore critical.

Door Functional Requirements

The ventral cargo door shall:

provide access for a 20-foot ISO container;
support loading from ground level;
support loading from a truck trailer;
preserve fuselage pressure integrity;
maintain aerodynamic smoothness in flight;
provide reliable locking;
allow safe opening and closing on the ground;
integrate with the cargo handling system;
remain inspectable and maintainable;
avoid unacceptable mass penalty.

Three-Panel Concept

The retained TRL3 concept is based on a three-panel opening mechanism.

This architecture separates functions between door panels and movable floor or access structures.

The three-panel approach is intended to reduce individual panel size and simplify certain mechanical functions, while introducing additional hinges, actuators and locking points.

Engineering Questions

The TRL3 door analysis shall answer:

What are the hinge loads during opening and closing?
What are the pressurization loads in flight?
What reinforcement is required around the cut-out?
What locking architecture is required?
How are loads transferred into fuselage frames?
How is sealing achieved?
How is the door inspected?
What happens if one actuator fails?
Can the door be closed manually or through emergency backup?
What is the mass penalty of the door and surrounding reinforcements?

Door Load Cases

Load Case	Description	Critical Element
Pressurized cruise	Door loaded by cabin differential pressure	seals, locks, frame
Door opening	Gravity and actuator loads during ground opening	hinges, actuators
Door closing	Alignment and locking loads	latch system
Ground handling	Possible local loads from cargo operations	lower frame, local panels
Emergency failure	One actuator or lock unavailable	redundancy architecture

Door Deliverables

The TRL3 door package shall include:

door kinematic model;
preliminary hinge sizing;
preliminary actuator sizing;
locking concept;
sealing concept;
structural reinforcement map;
failure scenarios;
mass estimate;
TRL4 test recommendations.

WP5 — Landing Gear Integration

Purpose

The landing gear integration work package verifies that the Q400-derived landing gear concept is compatible with the ISO-Plane architecture.

The main landing gear must not interfere with the cargo bay or ventral door.

Integration Rationale

A fuselage-mounted landing gear would conflict with the ventral cargo opening.

A nacelle-mounted main landing gear offers a more compatible integration path because it preserves the lower fuselage volume for the cargo bay and door.

TRL3 Landing Gear Studies

The TRL3 work shall include:

nacelle structural reinforcement;
gear bay packaging;
retraction mechanism study;
wheel clearance;
gear door integration;
landing load path analysis;
braking energy assessment;
turning radius estimation;
ground stability during loading;
compatibility with motorized nose gear concept.

Ground Stability During Loading

The aircraft must remain stable while a container is lifted, lowered or transferred from a truck.

TRL3 shall verify:

aircraft tipping margins;
longitudinal stability;
lateral stability;
CG shift during lift;
landing gear load redistribution;
braking or parking requirements;
ground slope sensitivity;
wind sensitivity during loading.

Landing Gear Deliverables

The expected deliverables are:

landing gear integration drawing;
nacelle structural concept;
gear retraction envelope;
preliminary landing load calculation;
ground stability analysis;
brake energy estimate;
list of Q400-derived elements requiring redesign or adaptation.

WP6 — Mass and Balance Consolidation

Purpose

Mass and balance consolidation is required to determine whether the ISO-Plane architecture remains feasible after adding the structural reinforcements and mechanisms identified during TRL3.

Mass Breakdown

The updated mass breakdown shall include:

fuselage structure;
wing and central wing box;
empennage;
engines and nacelles;
landing gear;
cargo door system;
cargo handling system;
cockpit systems;
fuel system;
electrical systems;
hydraulic systems;
avionics;
environmental control system;
interior and cargo bay equipment;
operational items;
payload;
fuel.

CG Envelope

The center-of-gravity study shall include:

empty aircraft CG;
fuel loading effect;
container installed position;
container lifting transition;
loading from ground;
loading from truck;
asymmetric loading scenarios;
emergency unloading scenarios;
takeoff CG envelope;
landing CG envelope.

Critical CG Situation

The most critical CG condition may occur during partial container lift, when the container is not yet fully secured in the cargo bay and the aircraft receives temporary external loads through the handling mechanism.

TRL3 shall explicitly model this transient phase.

Mass Control Objective

The main mass objective is to confirm the feasibility of an approximately 30-tonne-class MTOW configuration.

At TRL3, this figure remains a target requiring consolidation.

The main mass risk is the accumulation of reinforcements for:

ventral opening;
pressurized cargo bay;
lifting arms;
landing gear integration;
central wing box;
locking mechanisms;
safety redundancy systems.

WP7 — Systems Architecture Refinement

Purpose

TRL3 shall define the preliminary architecture of major aircraft systems and their interfaces with the cargo mission equipment.

Systems to be Addressed

The systems architecture shall include:

electrical power distribution;
hydraulic power distribution;
cargo handling power supply;
actuator control;
avionics interfaces;
cockpit control interfaces;
emergency systems;
environmental control and pressurization;
fuel system;
landing gear control;
braking system;
door control;
cargo locking monitoring;
sensor network for loading operations.

Cargo System Interfaces

The cargo handling system interacts with multiple aircraft systems.

Interface	Function
Electrical power	Power supply to actuators, sensors and control units
Hydraulic system	Possible actuation source for arms, doors or locks
Cockpit controls	Pilot command and monitoring of loading operations
Structural hard points	Load transfer from lifting system into primary structure
Avionics	Alerts, status monitoring and safety interlocks
Landing gear	Ground stability and aircraft positioning during loading
Door system	Interlocks between door position and lifting operation

Cockpit Control Logic

The cockpit shall provide clear handling system status.

Possible cockpit indications include:

door open;
door closed;
door locked;
arms deployed;
arms retracted;
twist-lock engaged;
container secured;
load imbalance;
emergency stop active;
winch mode active;
ground clearance warning;
loading operation inhibited.

Systems Deliverables

TRL3 systems deliverables include:

preliminary systems block diagrams;
power budget;
actuator architecture options;
sensor architecture;
cockpit interface concept;
interlock logic;
emergency control logic;
systems risk matrix.

WP8 — Risk Assessment and Safety Analysis

Purpose

The TRL3 risk assessment identifies the technical risks that may prevent the architecture from maturing toward TRL4.

Major Technical Risks

Risk	Description	Severity	TRL3 Mitigation
Ventral opening structural penalty	Reinforcements may become too heavy	High	FEA, local optimization, alternative frame concepts
Pressurization around cargo door	Door sealing and pressure loads may be complex	High	sealing study, load cases, pressure frame design
Cargo lifting load concentration	ISO corner loads may create high local stresses	High	load path modelling, reinforcement design
Robotic arm mass penalty	Handling system may reduce payload or range	High	mass tracking, architecture simplification
CG shift during loading	Aircraft may become unstable during container transfer	High	ground stability model, operational limits
Landing gear integration	Nacelle-mounted gear may require major reinforcement	Medium to High	nacelle load analysis, Q400 reference comparison
Aerodynamic drag	Large fuselage and nacelles may reduce range	Medium	CFD, drag breakdown, configuration refinement
Systems complexity	Autonomous loading may add certification difficulty	Medium to High	FMEA, redundancy logic, phased automation
Aeroelastic behaviour	High wing and large fuselage may introduce coupling effects	Medium	preliminary aeroelastic screening

Risk Mitigation Logic

TRL3 risk mitigation is based on:

conservative sizing;
early simulation;
critical load path analysis;
redundancy concepts;
physical demonstrator planning;
industrial review;
failure mode analysis;
configuration iteration.

Safety Philosophy

The ISO-Plane cargo handling system must be treated as an aircraft safety-related system, not as ordinary ground support equipment.

This means that TRL3 shall consider:

fail-safe behaviour;
controlled failure modes;
emergency stop logic;
mechanical locking;
clear crew indications;
maintenance inspections;
safe ground exclusion zones;
prevention of inadvertent release;
prevention of flight with unsecured cargo.

WP9 — Industrial Interface

Purpose

TRL3 initiates structured technical dialogue with industrial stakeholders.

The objective is not yet procurement, but technical validation of assumptions.

Potential Stakeholders

Potential technical discussions may involve:

engine manufacturers;
landing gear suppliers;
aerospace structural engineering partners;
cargo handling system suppliers;
actuator suppliers;
embedded systems suppliers;
certification advisors;
airframe manufacturers;
composite and metallic structure specialists;
simulation and testing laboratories.

Industrial Questions

The TRL3 industrial interface shall prepare answers to the following questions:

Is the selected engine class realistic for the mission?
Can Q400-derived landing gear components be adapted?
What certification issues are raised by autonomous cargo loading?
Can the ventral door be manufactured and maintained?
What structural technologies are best suited to the fuselage?
What level of redundancy is expected for cargo lifting?
What test articles would be most valuable at TRL4?
What subsystem could be developed by an industrial partner?
Which parts of the project remain open-source and which may support private industrial bricks?

Industrial Deliverables

The industrial interface package shall include:

short technical brief;
configuration summary;
mass and performance assumptions;
critical risk list;
subsystem questions;
preliminary supplier mapping;
list of data required from partners;
TRL4 demonstrator proposal.

Environmental and Sustainability Considerations

TRL3 also introduces a more rigorous environmental review.

The ISO-Plane is a fuel-powered turboprop aircraft concept, therefore its environmental performance must be assessed early.

TRL3 Environmental Studies

The environmental work shall include:

updated fuel burn model;
mission-based CO₂ emission estimate;
comparison with alternative freight modes for relevant missions;
sensitivity to payload factor;
sensitivity to mission distance;
structural mass reduction strategies;
Sustainable Aviation Fuel compatibility study;
preliminary lifecycle analysis preparation;
maintainability and repairability considerations;
potential reuse of existing certified components.

Sustainability Levers

Possible sustainability levers include:

use of efficient turboprop propulsion for regional and medium-range cargo missions;
structural weight reduction;
mission optimization;
high payload utilization;
SAF compatibility;
modular containerized operations;
reduced need for heavy ground handling infrastructure;
long service life design;
maintainable and inspectable cargo mechanisms.

Environmental Risk

The main environmental risk is that the aircraft may only be competitive on specific mission profiles.

TRL3 shall therefore avoid generic claims and focus on mission-specific environmental relevance.

Potential favourable missions include:

remote logistics;
humanitarian relief;
disaster response;
urgent industrial logistics;
firefighting with containerized water systems;
military or civil protection support;
cargo delivery to regions with limited ground infrastructure.

TRL3 Verification Methods

TRL3 verification relies on a combination of analytical and preliminary experimental methods.

Method	Application	Expected Confidence Level
Hand calculations	first-order sizing and sanity checks	preliminary
Finite Element Analysis	structural stresses and load paths	medium
CFD	aerodynamic refinement	medium
Multibody simulation	cargo handling kinematics	medium
Mass modelling	aircraft mass and CG consolidation	medium
Failure analysis	safety and redundancy logic	preliminary to medium
Subscale testing	early validation of mechanisms or structural details	medium if available
Industrial review	external validation of assumptions	qualitative but important

Digital Mock-Up Requirements

The TRL3 digital mock-up must evolve from a visual 3D model into an engineering model.

The digital mock-up shall include:

consistent aircraft coordinate system;
defined reference planes;
fuselage frames;
wing box geometry;
cargo bay volume;
container envelope;
door kinematics;
landing gear envelopes;
engine nacelle envelopes;
lifting system geometry;
maintenance access zones;
human access zones;
structural hard points;
mass property allocation.

The mock-up shall be suitable for:

geometry checks;
interference detection;
mass allocation;
CFD simplification;
FEA preparation;
communication with industrial partners;
TRL4 demonstrator definition.

TRL3 Deliverables

By the end of TRL3, the ISO-Plane program shall deliver a coherent technical package demonstrating that the aircraft architecture can survive detailed engineering scrutiny.

Structural Validation Package

The structural package shall include:

global structural calculation report;
local structural calculation report;
fuselage finite element model;
central wing box finite element model;
ventral opening reinforcement study;
cargo handling load path study;
landing gear load introduction study;
fatigue-sensitive zone identification;
structural mass estimate;
list of assumptions requiring physical testing.

Aerodynamic Refinement Package

The aerodynamic package shall include:

CFD simulation report;
updated drag breakdown;
refined lift and drag polar;
propeller slipstream interaction assessment;
updated takeoff and landing performance;
cruise performance estimate;
updated range estimate;
payload-range curve;
aerodynamic risk assessment.

Cargo Handling Package

The cargo handling package shall include:

mechanism architecture description;
kinematic model;
arm deployment and retraction study;
ISO corner interface study;
twist-lock integration logic;
emergency winch concept;
load transfer analysis;
preliminary actuator sizing;
safety interlock logic;
preliminary FMEA.

Ventral Door Package

The ventral door package shall include:

three-panel door mechanism description;
kinematic sequence;
hinge and actuator load estimates;
locking concept;
sealing concept;
pressurization load analysis;
reinforcement strategy;
failure scenarios;
TRL4 test recommendations.

Landing Gear Integration Package

The landing gear package shall include:

Q400-derived gear integration concept;
nacelle structural concept;
retraction envelope;
ground stability assessment;
landing load path analysis;
braking energy estimate;
compatibility with loading scenarios.

Mass and Balance Package

The mass and balance package shall include:

updated mass breakdown;
empty mass estimate;
payload and fuel allocation;
CG envelope;
loading and unloading CG analysis;
sensitivity to cargo position;
MTOW feasibility assessment.

Systems Architecture Package

The systems package shall include:

electrical architecture;
hydraulic architecture;
cargo system control architecture;
cockpit interface concept;
sensor and actuator interface matrix;
emergency power and backup logic;
preliminary systems safety analysis.

Risk and Roadmap Package

The roadmap package shall include:

updated risk register;
technical gap list;
mitigation plan;
TRL4 demonstrator priorities;
industrial engagement plan;
preliminary certification discussion points;
updated project schedule.

TRL3 Acceptance Criteria

TRL3 may be considered successful if the following criteria are met:

Domain	Acceptance Criterion
Structure	Critical load paths are identified and preliminary sizing shows feasible margins
Ventral door	Door architecture is compatible with pressurization, loading and structural continuity
Cargo handling	Container lifting system has credible kinematics and validated preliminary load paths
Aerodynamics	Updated aerodynamic model supports the mission envelope within acceptable uncertainty
Landing gear	Nacelle-mounted gear integration remains compatible with cargo bay geometry
Mass and balance	Aircraft remains within a credible 30-tonne-class MTOW target
Systems	Main system interfaces are identified and no blocking incompatibility is found
Safety	Major failure modes are identified with preliminary mitigation logic
Industrial readiness	A technical package exists for credible external review

Path Toward TRL4

TRL4 will focus on validation in a laboratory or relevant subsystem environment.

The transition from TRL3 to TRL4 requires moving from analytical confidence to demonstrator-based confidence.

TRL4 Priorities

The recommended TRL4 priorities are:

subscale ventral door demonstrator;
structural test article for fuselage opening reinforcement;
cargo handling mechanism demonstrator;
twist-lock and arm load test bench;
ground loading scenario demonstrator;
landing gear packaging validation mock-up;
CFD-to-wind-tunnel correlation if feasible;
cockpit control interface prototype;
preliminary certification discussions;
industrial feasibility assessment.

Candidate Demonstrators

Demonstrator	Purpose	Priority
Ventral door structural demonstrator	Validate hinges, locks, frame loads and sealing logic	Very high
Cargo lifting test bench	Validate arm loads, twist-lock interfaces and emergency lowering	Very high
Fuselage frame section	Validate reinforcement around large lower opening	High
Ground loading mock-up	Validate loading from ground and truck trailer	High
Systems control bench	Validate interlocks, sensors and cockpit logic	Medium
Aerodynamic model	Validate CFD assumptions through wind tunnel testing	Medium

Certification Preparation

TRL3 is not a certification phase, but it must already identify future certification issues.

The following certification topics shall be monitored:

pressurized cargo compartment with large ventral opening;
structural substantiation of door and locking systems;
emergency release and retention of cargo;
autonomous ground loading operations;
cockpit-controlled cargo handling system;
human safety during ground operations;
aircraft stability during loading;
failure of powered lifting systems;
flight prevention with unsecured container;
system redundancy and monitoring;
maintenance inspection intervals;
fatigue and damage tolerance around cargo opening;
compliance strategy for cargo restraint.

A certification advisor should review the TRL3 architecture before TRL4 demonstrator commitments.

Strategic Vision

TRL3 transforms ISO-Plane from a promising aircraft architecture into a structured engineering program.

It is the stage where:

feasibility becomes measurable;
risks become visible;
design choices become traceable;
technical credibility begins;
industrial dialogue becomes possible;
future demonstrators can be defined.

The purpose of TRL3 is not to prove that every part of the ISO-Plane is final.

Its purpose is to prove that the architecture is strong enough to deserve the next level of investment, testing and industrial involvement.

Summary

ISO-Plane TRL3 is the analytical and experimental proof-of-concept phase of the program.

It validates the most critical assumptions behind the aircraft:

the 20-foot ISO container can be integrated into the fuselage;
the ventral loading architecture can be structurally investigated;
the autonomous loading system can be analysed through realistic load paths;
the Q400-derived landing gear concept can be assessed in nacelle integration;
the high-wing turboprop configuration can be refined aerodynamically;
the mass and balance model can be consolidated;
the program can prepare for subsystem demonstrators.

By the end of TRL3, the ISO-Plane shall no longer be only a concept.

It shall become a technically supported aircraft definition ready for demonstrator-oriented development.

ISO-Plane — Engineering the next generation of container air logistics.