Behind the scenes: Aircraft Design

Each aircraft is a complex assembly of many parts. There are a lot of things to do and to think about before designing and building such a “flying-machine”. As our project is special, we, at Pie Aeronefs SA, chose to explain how we went through these steps and show you what happened behind the scenes of the UR-1 all-electric race plane

Determine the mission

The first step in designing any aircraft is to determine the mission. In our case, the mission parameters are fairly well defined: fly 20 km as fast as possible with a pilot and an electrical propulsion. These targets, in addition to a few technical features stipulated by the rules of the Air Race E championship, in which we will participate, form the starting point for the conceptual design of the aircraft.

Preliminary analysis

Before setting pen to paper, however, we undertook a thorough review of research in aerodynamics and aircraft design. In particular, the theory behind V-tail aircraft is much more complicated than for traditional tail designs. This is due to the fact that there's is a stronger interconnection between the size of the wing and the size of the tail.

At some point, we need to make our first decision: how much does the aircraft weigh? This is a much more difficult decision than it might seem, because the more the aircraft weighs, the larger the wing has to be, and the larger it is, the heavier it weighs and vice versa. So we iterated the estimation of mass/surface until we found the right ratio. Then, we have to make sure that each part we plan to integrate has the right size and the right weight. Finally, we do a global estimate of the mass.

Now we have a set of parameters that work well together and it is possible to proceed with the next part. The objective being that the final mass of the aircraft built is close to the initial calculation.

To be said is that estimating mass is particularly difficult for airplanes equipped with innovative technologies or concepts, such as batteries. Indeed, these elements have not yet been tested extensively.

The importance of nomenclature

It is important to assign part numbers to each component and assembly we develop. We chose to use a hierarchical structure so that each part number could be recognized at a glance. This meant that we grouped parts into systems, assemblies, and finally individual components.

The first group we identified was the general aircraft assembly. To create the UR-1, we used following component categories:

  • Structure (fuselage, wing, tail, landing gear etc.)
  • Powerplant (propeller, motor, batteries etc.)
  • Controls (ailerons, ruddervator, flaps, cables etc.)

In a scaling-down process, we then categorized all the sub-components. For example, we distinguished these following components for the wing general structure:

  • Structural assembly (fairings and attachments with the wing)
  • Wing skin (outer layer of the wing)
  • Internal components (such as spars and ribs)

For our work pace, we listed every component and subcomponents in chapters and subchapters numbers. The name length increases as we design subparts of subparts. This allows us to identify each part on which we will work.


Project name - Wing Structure - Number for Wing Skin - Unique and Original Part - Number for Skin upper wing

Every part of this code-number is referenced and allows each team member to work properly.

This procedure is naturally carried out for each part of the aircraft such as the electrical system and legal and technical elements such as lights, radio system, instrumentation, antennas etc. This procedure is done for every single part of the aircraft such as the electrical system and also legal and technical regulations we are dealing with such as lights, radio-emitter, instrumentation, antennas etc.

Detailing the design

Once we have this clear work pace and a better idea of every general component we want to have, we can now start to think about what is the necessary design for each main component, taking into account all variables and limitations such as loads, bending moments, aerodynamic pressure, stiffness etc.

All of this obviously requires a lot of time and work. Thanks to our experienced engineers and technicians, our team is thus able to develop this magnificent project.


In this interview with our CEO, Marc Umbricht, we offer you a personal opinion on these first steps.