By Bjorn Fehrm, Henry Tam, and Andrew Telesca.

August 13, 2021, ©. Leeham News: Last week, we went through the Certification Application, one of the most important milestones in the Pre-Launch phase.

Now we assume we got a Product Launch approval from our board/Investors. We start looking at the work packages that meet us in the Post Launch phase.

Figure 1. The Program Plan for our Green 19 seater. Source: Leeham Co. Click to see in full scale.

The first steps of the Post Launch phase

Our Program Plan (Figure 1) lists Design Refinement as a first step, together with further work on our Processes and Tools.

Design Refinement

So Design Refinement again? It’s what we worked on in Part 13, about mid-way through the Pre-Launch phase.

Well, we are soon advancing to Detailed Design. It’s where the aircraft’s hundred thousand parts are analyzed and designed. So we must be dead sure we are final on our aircraft’s overall design. This is our last chance for low-impact changes.

Now we do iterative trade studies where we, for instance, check if we can improve the cruise and thus cost performance of the aircraft by improving the sealing of movables (flaps, spoilers, ailerons, stabilizers, rudder), and what this would cost us in increased weight and production cost (we are now chasing sub-kilo weight changes).

We iterate the design back and forth to squeeze the last bit of weight from the aircraft. Every kilo extra means worse field and flight performance. We could also check if a changed climb profile can save a bit of engine life, etc, to improve the operating costs of the aircraft, without changing our operating performance materially.

From now on, any “refinements” in overall design cost time and money. We will have many engineers working on detailed designs, as will our suppliers. The aircraft goes through a final conceptual iteration, and then we freeze the overall specification in all areas possible.

We either update our windtunnel model or manufacture a new, more detailed than the Pre Launch model. We can possibly stay with a low-speed tunnel test only as our cruise speed is low, around 230kts. The tunnel tests once again focus on the take-off and approach/landing data. We use CFD to get the supplementary cruise drag and aero load data for the different parts of the aircraft.

Our system specifications, such as needed engine power at different flight stages, the power and cooling requirements for systems, and the cabin’s demands on the Environmental Control System, ECS, are finalized and frozen.

Final loads on our primary structures like the wing, fuselage, empennage are calculated and documented. Data for landing gear, flaps, rudders, spoilers, windscreens, etc go through one last iteration based on the data from the lastest wind tunnel test. Then the data is fixed.

We finish the Functional Hazard Analysis (FHA) on the aircraft level (engine failure, brake control failure, trim control failure, etc.) and do the first system-level Functional Hazard Analysis iteration. This is so our Certification team can advance our certification status.

Processes and Tools

All data are now entered into our workflow tools to distribute consistent data packages to all our groups and suppliers. Much of the data shall also be documented for Certification work.

We must conduct strict version control from now on, and there is an overall version control which is about configuration management. Documents and specifications are tied to a defined version of the aircraft. We must make sure everyone is working on the same version of data.

If there are reasons to investigate changes in some corners of the aircraft, this is done as a closed project. The current revision of the plane is still the work-to revision until we have concluded any ancillary investigations, and our project management has taken a formal decision that the aircraft will be changed in some respect.

If such strict control is not maintained from now on, we can get instability in the project, and groups can get unsure if they work on the correct data. Our processes and tools are now entering a critical phase when the organization explodes, and these must be mature enough for such a change.

Detailed Design

Next week we talk about Detailed Design and all that it entails for the project.