1. One of the areas that receives little publicity in the planning of future personal transport systems is volume. How many of these things are going to be using the airspace at one time. Experiments concentrate upo9n getting one vehicle to perform but seldom do we hear about how it will be when 10 or 100 or 1000 are aloft in close proximity. What are the challenges that this facet will bring?
2. Let's try some numbers. There are about 20 million road vehicles in the UK that transport around 60 million people. This averages around 1 vehicle for 3 people. These will not be uniformly distributed but let us assume that they are. If Greater London (metro city) is a city of around 10 million and has an area of about 2,250 sq km. This provides a density of moror vehicles of around 3,300,000 vehicles or about 1500 vehicles per sq km today.
3. Let's assume that with the availability of PTS there will be a transfer of travel to the extent of 10% - not an impossibly high figure maybe. This implies an ownership density of about 150 per sq km. Not all of these will be in use at any one time so let's assume that perhaps only 10% could be used simultaneously or 15 per sq km.
4. 15 PTS in use per sq km is a very much higher density than any other form of air travel. They will not be uniformly distributed and will cluster around the entry and exit routes. So an residential area of maybe 10 sq km could produce 150 PTS all heading into London along a relatively narrow corridor at one time - and of course picking up other users as they go.
5. If we take a single vector into London that is a triangle of angle about 1/10th of the arc around the city this equates to 10% of the London vehicles or 330,000 or about 33,000 PTS of which we are considering 10% being in use say 3,300. So another way of looking at it is to imagine over 3000 PTS approaching London along a single vector over a single time period.
6. How do we stop them crashing, colliding, breaking down or interfering with other traffic. It seems to me that if the vehicle is simple to operate (which is always the aim) then they must be controlled by computer systems. With the growing power of computers it ought not to be insuperable to provide a navigation system that not only controls the route between inserted points but also performs the sense and avoid role for inter-PTS collisions. This may need to be combined with an on-board radar system such as is already beiing develp[ed for road vehicles.
7. These control systems would need to be duplex fitted or perhaps even triplex to give high levels of assurance of serviceability. The maximum height would be controlled and areas of "NO GO" would be pre-imprinted into the flight computers. "Flying" this kind of PTS would be about as complicated as setting your car's navigator. Dial in the destination - press GO and everything subsequently is automatic. The take off would be after a series of computer driven checks - the initial heading would be set and the avoidance plan would kick in to manage the flight in speed, heading and height to avoid fixed and moving obstacles and prohibited areas - the fixed data would be just that and the transient data provided by the collision avoidance radar would allow variatioins of speed, height and heading to allow safe passage.