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This means that pilots should not fly in areas where visible moisture (fog, rain or clouds) exists and the temperature is below 5°C. As icing is not only a topic on cold and wet days but might also occur on warmer days with a high humidity (QBE Aviation (2011)), it is seen as an import issue to be addressed regarding the Reference PAV in order to attain a good usability over the year performance. The icing issue seems to be quite difficult to cope with though and even aircrafts with an approval to fly into known icing conditions are not advised by the FAA to really do this (Federal Aviation Administration (2008)).
For the Reference PAV, the discussion resulted in the decision that the PAV should be able to fly in icing conditions although the explanations above have illustrated that this ability is not easily obtained.
The consortia also agreed that a flight in a thunderstorm was completely unacceptable due to unfavourable conditions such as turbulences, the potential of lightning strikes, hail stones, etc. and that the flight path of the PAV should be re-routed in such an event or be delayed.
To get a first impression about how tricky it might be to get a similar level of “reliability” or usability for the PAV as of the one of a car, a weather analysis for a transect was conducted in Germany (distance 30 km; location: near Frankfurt). The aim was to see on how many days of a given year a flight from A to B in this region would have been possible at certain times of the day. Weather data from the German meteorological service (Deutscher Wetterdienst) were used to check days (split up in morning and afternoon blocks because of the commuting context) for their weather suitability following pre-defined “no-fly” criteria. The German meteorological service provides special weather forecasts for VFR and IFR pilots at different flight levels which are actualised several times per day.
For the following weather analysis input data from the GAFOR (General Aviation Forecast) were used.
The GAFOR generally breaks the weather situation down into categories following a stepwise division of the visual flight possibilities based on the horizontal visibility on the ground in km and on the cloud base height in ft (for details see Table 2 ). The data are structured in five main flight visibility categories (C – Charlie = clear, O – Oscar = open, D – Delta = difficult, M – Mike = marginal, X – X-Ray = closed)
Table 2 Overview of the Flight visibility categories of the German GAFOR based on the criteria of visibility on the ground in km (first row) and cloud base height in ft over reference height in ft (first column) Source: Deutscher Wetterdienst – Abteilung Flugmeteorologie (2008) For a first analysis, the situation of a PAV able to cope with quite difficult weather conditions was envisioned, and the four flight visibility categories X, M8, M5 and M2 were used as no-fly criteria for the analysis. These four categories represent bad weather situations with a cloud base lower limit of 1000 ft or less and / or a very low ground visibility of 1.5 km or less for parts of the X-Ray category.
The result shows that especially the winter months (November – February) have a high number of days with time periods belonging to the four no-fly categories.5 In a second analysis only the “good” flight visibility categories (C, O and D3) were used as acceptable situations for the PAV flight realisation and all other categories (X, all M, D1 and D4) were used as nofly criteria to cover the range of decreasing requirements for the vehicle and potential user abilities.
This second analysis also gives an impression of the occurrence of days with a higher flight comfort level (assuming that good weather means less turbulences, etc.) The results for this second analysis
with more flight visibility categories used as “no-fly” criteria shows the following result:
For the detailed results please see Meyer et al. 2011 Figure 4: Number of time periods with a GAFOR flight visibility category of X-Ray, M8, M7, M6, M5, M2, D1 or D4 for the year 2010 and four time periods for the GAFOR subpart 45 (“Rhine-Main area and Wetterau”) For this preconditions the numbers of no-fly periods increases sharply, and the winter months are nearly completely blocked for PAV flights under these assumptions.
One last analysis, taking into consideration only the X-Ray category as no fly-criteria, was also done to identify the lowermost limit for the year 2010 when flights would have been possible (under the assumption of only X-Ray as exclusion criteria). Although the results now look quite promising, it should be noted that, right now, the X-Ray category is used for weather situations in which flights following visual flight rules are not possible. Even if the Reference PAV shall have the ability of flying in a visually degraded environment, the flying into clouds is not seen as desirable and, therefore, it is debatable if, in the end, flights in M8, M5, and M2 conditions will be manageable in a safe manner by the Reference PAV. This will also depend on the actual design, especially on the propulsion type and on the sensor equipment of the Reference PAV as well as on the distribution of flight tasks between the human being and the system.
To return to the original aim of the weather analysis, the usability comparison of the PAV versus a
private car; the three analyses lead to the following result on the usability over the year:
Table 3: Percentage of time periods belonging to the “no-fly” criteria of the three different weather analyses for the year 2010 and GAFOR subpart 45 6-8 8-10 17-19 19-21
As one can see in Table 3, the aim of a 90 % usability over the year for the PAV is only reached in the X-Ray category for all four time blocks, and nearly achieved by the X, M8, M5, and M2 group for the 17 - 19 o`clock period with 100 – 12 % = 88 % usability.
Although this analysis was only looking at one certain area in one year, it illustrates that the dependency on weather conditions is quite high, and that the topic of how to expand the operability of the PAV into challenging weather conditions will have to be considered further.
5.3 Energy consumption
One topic contributing to the environmental footprint and to public acceptance is the question of how much energy the PAV will consume. To investigate this, a power requirement calculation for an example mission by the Reference PAV was undertaken by partners of the DLR Braunschweig. For the reference flight a distance of 30 km and a cruising altitude of 500 m above ground level with an average cruising speed of 175 km/h were assumed.6 The total energy consumption for this reference flight (Cref) was calculated to be Cref = 12.81 kWh. To set this into context it would mean that a Li-ion battery with an energy density of 150 Wh/kg (state of the art according to Zhao et al. 2013) with a weight of around 85 kg would be needed to full fill this task.
These rough estimates show that the development regarding the energy storage is on the right way and in the necessary order of magnitude and examples like the e-volo development mentioned before show already today the possibility of a pure electric propulsion for PAVs.
5.4 Noise Noise pollution is of major concern of citizens not only in the EU, but also in Japan and in the United States (Schomer 2001). The European Commission stated in their Green Paper on Future Noise that environmental noise is one of the main environmental problems of Europe (CEC 1996). Although individual noise levels of cars, trucks, and aircrafts are decreasing, this success is offset by traffic growth on the ground and in the air (CEC 1996).
The noise pollution topic in the context of myCopter does affect both residents living close to helipads, airports or flight routes and their users, today’s pilots, who could feel restrictions and forces to use noisy friendly flight profiles especially for take-off and landings. This conflict is sharpened by the aspect that helicopters (beside the helicopter flights for emergency and police services) are often perceived as a rich man`s toy, a transport option for only a very few people which effects a lot of people negatively, though, who never will have an advantage from their operation (London.gov.uk 2006).
For the PAV operation there will, certainly, be specific noise standards to be respected. Besides the pure actual design of the PAV - the PAV should, of course, be as little noisy as possible - also the flight heights and routes as well as the location of the landing and take-off sites and their operational hours could be changed to allow for a quieter operation.
The impression from the authors is that air traffic noise, despite technological improvements, will remain a sensitive issue especially if a high number of flight operations are expected to occur. This means that even if individual noise signatures of the PAVs were decreasing, the general trend of increased ground and air traffic, makes it very likely that this topic will remain of high priority.
For the detailed information on this calculation see Gursky 2011 internal mycopter report
5.5 Parking and Storing of the PAVs While the parking and storing possibilities might be less critical in the sparsely populated areas this issue seems more complex in already congested inner city areas were also parking space for cars is limited and costly (Rodrigue 2009). Strongly connected with the question of where to park the PAVs is the question if they can fly autonomously or not and if they fit into the current automobile dominated infrastructure of the present urban environment. The last question can be answered positively assuming that the dimensions of the Reference PAV will be in the range of a conventional car and, further, assuming a certain ground moving ability. For other PAVs with greater dimensions exceeding this “car infrastructure compatibility” the situation would be different.
The first question regarding the ability of the PAV to fly itself into a suitable parking spot should not be very different to the full autonomous level of flying described in the previous chapters. This could mean that the PAV would transport the user to its desired place and then fly autonomously to the next free PAV garage or parking spot. On the parking spot an automated parking system such as they are already in place for cars could be used to store the PAVs in an automated and space saving manner. These systems use lifts and carriers to move vehicles through the parking system; the user parks the vehicle at an entrance point and gets it returned upon request in only a few minutes (Patrascu 2010). The same could be imagined for PAVs with the difference that the PAV would checkin and out by itself without a person on board. For the “augmented flight scenario” the requirements for the storing or parking infrastructure would increase though.
Another way of handling the “parking problem” is connected with the business model. If the PAVs are shared in private communities or offered in renting concepts they do not have to be parked that often, but are used most of the time, which would reduce the pressure on parking space.
5.6 Perceptions from the public
Next to the mentioned more technical challenges an uncertainty exists what the general public would think about such a new form of transportation. To get a first feeling about the attitudes of potential users the KIT partners conducted a one-day “explorative workshop” in May 2012 with 11 students from the technical university on “new dimensions of urban traffic”. The focus group discussion was structured in a more general first part (mobility of the future) followed by a second part confronting the participants with the idea of using the third dimension for individual air travel. In a last third section the attendees were asked to develop their own PAV vision and to think about requirements for such a PATS.
The output of this workshop was that the participants did not question the technical feasibility of PAVs in general and confirmed the main issues found by the consortium such as noise, automation, parking, availability of this transportation (weather). Additional aspects were mentioned as well such as the idea to have also a usability of the vehicle “on the ground”, which would allow for flying just above street level and be able to “swim” with the car traffic.
Generally doubts about the benefits of PAVs, even after a lively debate about potential advantages, remained and the major part of the participants judged the idea as “Over-Engineering”. In their opinion the level of automation needed to have PAVs safely operating in a city environment would already solve the congestions problems on the ground if implemented in today’s cars.
6 Discussion & Conclusion
The central question we formulated to the beginning of this paper was the question whether more attention should be paid to the ongoing developments in the PAV sector and whether an inclusion of this form of transportation into the scenarios and policies of the future should be taken into account.
After the challenges and problems discussed in this paper it has to be said that a bunch of requirements exists regarding a PATS and the PAVs inside which is not easily to be met. Although some technical issues are on a good way (energy density of storage technology) and single components for sure seem to be feasible (e.g. noise reduction technologies) it has to be said that today’s existing demonstrators are still far away from the described “myCopt” in the full autonomy scenario. Even if for helicopter pilots the described scenario of travelling to work might seem not too far away, their realization for the general user it surely is. Next to the issues regarding the pure vehicle and user competences it has to be said that the surrounding infrastructure for PAVs is as important. Their existence and operation would therefore needed to be taken into consideration for todays planning considerations and construction projects in order to be able to have this transport option available in the future.