SE Vehicles

Anatomy of an eVTOL modular Flying Car

Sep 09, 2017

Lots of text in my previous two blogs to contour the prospect of a flying car that can takeoff and land vertically, with the use of battery power. Time to recap what's essential. 'New iSetta' offers pictural suggestions how an eVTOL modular Flying Car concept might work by taking 'elements' separately (anatomy), instead of claiming that a certain eVTOL design -will- work.

Will the electric car 'really take off' this time? Part 1
Will the electric car 'really take off' this time? Part 2

'New iSetta' does not make claims that cannot be substantiated, or sidestep concerns, like some eVTOL developers seem to be doing to convince investors. Here is an overview of the eVTOL concepts that have been covered in the media, together with their affiliations, stakeholders or principal investors. - click. If you want a 1-page pdf overview with handy links to more info, send me an email. My "What If?" suggestions are threefold.

1. To begin with, use an airfoil, so no energy is wasted on keeping the craft up in the air, during which only the rear rotor will be used in a push-capacity. This in itself will be beneficial to range. Don't complicate things by having to use a wing that needs unfolding. Also from a maintenance (costs) point of view.
2. The rotors that you see in the picture are primarily used to VTOL. They also replace an aircraft's traditional control surfaces; roll and pitch can either be kept in check or actively induced (climb, turn). Don't complicate things by trying to integrate the thrusters or fans into an aircraft-type design. Reliable performance is a prerequisite for safety.
3. Why not 'dual-use' the traditional fuselage by turning it into a streamlined, lightweight road vehicle, in which you can straightaway drive off upon landing? What the benefits are, have been described in my previous two blogs: cut costs, eliminate pre- and post-flight. Click here for a quick overview.

There is just no way of ignoring the two complicating factors that make or break an eVTOL design: batteries (energy density and weight) and the sheer power that is required to VTOL. To start with the airfoil, what should it be shaped like to maximize lift, to minimize drag and to be able to function as a container for the batteries? Secondly come the rotors. What diameter should they have in order to be able to airlift the whole craft? How should they 'blend in' with the airfoil? Thirdly, the fuselage that constitutes a road vehicle obviously needs tinkering to make it as slippery as possible. Serious attention must be given to the connecting & disconnecting mechanism with which the road vehicle is attached to the airfoil, if only for the passengers' ease of mind. A single pylon may not suffice. Last but certainly not least, what is the maximum takeoff weight? What range will be possible at what cruising speed? It may well be the case that with the present battery technology a decent range is not feasible. On the other hand, developments are going fast. For instance, Toyota says that its solid state battery (that addresses four important things: energy density, safety, charging time, weight) will be ready by 2020. Many other issues may be solved too in the time that it takes to engineer New iSetta Modular Flying Car, such as regulations, air traffic control, auto-piloting - development in the wake of other eVTOL projects that are already further down the road is a clear advantage.

A note on the airfoil as it is preliminarily depicted here. It clearly signifies three things:
1. the importance of structural rigidity and the inherent, open invitation to new materials developers to come up with an 'airfoil-shaped box' that's strong, durable and lightweight at the same time;
2. strength, lightweight, manufacturing ease and low cost can be brought together by not opting for the fancy type of airfoils some eVTOL designs are featuring, that either have a high-aspect ratio (which supposes extensive crossbracing) or are articulated or even foldable;
3. Although energy efficiency will ultimately determine how the airfoil will turn out, speed will not be this concept's primary concern. Why is that? We shouldn't forget that since range is limited any way because of the batteries, speed is not that important. The time gain will be in eliminating pre- and post-flight that is related to using separate eVTOLS and separate ground transportation.

Ralph Panhuyzen, sevehicle@gmail.com

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