C ACQ = C MAN − C PRO
2) Less fuel burnt per mission As the fan and the LPC are no more connected to each other, they can both work at their maximum efficiency and that means
3.7 ADVANCED PROPELLERS
2) Acquisition costs Assuming the same amount of profit kept for current electric power systems, we can state that there is no big difference between the acquisition costs of advanced electric power generator and distribution systems and the current ones
3) Operating costs %, as written in table 3.9
4) Disposal costs % as there is no difference between high voltage-low amperage equipment and the high amperage-low voltage one in terms of disposing.
taxes and flight times (there would be no need to follow ascending/descending flight paths that avoid urban areas as the noise emissions would be acceptable).
Figure 3.3 Single blade propeller with proplets[40]
As previously hinted, this technology offers many advantages and the most important ones are:
•
Less fuel burnt Thanks to the efficiency increase and the induced drag reduction, propellers with proplets can save up to 5% of fuel per each mission. This saving will obviously lead to an operating cost saving as well.•
Noise reduction This technology allows a dB noise reduction during take off and landing. This achievement is realized thanks to the shape of the proplets on the edges of the propeller. Basically, they reduce the air vibration on the propeller itself, thus reducing the noise emitted.Unfortunately, producing and implementing this new technology onto new regional/
short-range aircrafts has its own disadvantages. The main ones are:
⟶
⟶ −6
•
Structural constraints Propellers with edge proplets maintain a performance benefit when the proplets are very thin. As a matter of fact, this leads to keep lower rotational speeds in order not to damage the propeller. In general, this technology needs to be taken seriously under control in terms of structural health as the thinner a blade is, the more frequently it may damage.•
Expensive and long-term tests In order to design and test this technology, many tests and calculations must be done. These ones normally requires days (if not weeks) to be completed and thus, incrementing costs and time required to produce them.Studying, developing and testing new propeller designs, in order to improve its performances, is something that has been done for decades. In particular, the idea of applying the winglets technology onto propellers was first developed in 2013 and now it has a TRL of 6. Estimates say that proplets will be fully available on commercial regional airplanes by 2022 and they are only available now for some military aircrafts.
For what concerns the cost categories of this new technology, we can say that:
Table 3.10 Cost categories for advanced propellers [41]
The estimated investment and research cost is around 100 million dollars due to the medium-high TRL this technology has at the moment. In fact, in the aerospace field, this amount of money is not too big and that is thanks to the research and test that have been made so far. The annual operating costs slightly decrease due to a good saving of fuel burnt per mission and to the noise reduction during take off and landing (which translates into a fuel saving too) even if the maintenance costs increase. This latter happens because of the reduced blades thickness. In fact, the less thick they are, the more pronte to crack propagation they will be and thus, it will be necessary to
⟶
⟶
EIR Annual
operating costs
On-aircraft investment
costs
Retrofits costs
Maintenance costs
Production costs
Advanced
propellers 100 M −3 % ∼ 0* % +1.8 % +1.1 %
The retrofits costs are the same as the ones needed for current propellers
**
∼ 0** %
The on-aircraft investment costs are the same as the ones needed for current propellers
*
increase maintenance controls. It is also possible to increase the resistance of the balde with using modern materials like composite and/or new aluminum alloys. This way maintenance checks would be the same as for current materials used for aircraft propellers but, on the other hand, the blades manufacturing cost will definitely increase. For this reason, in one way or another, we have to accept the increase of maintenance cost for this new technology. The production costs increase as well for more accurate machining operations will be necessary in order to shape the correct proplets on the edges of the blades and to make the blades thinner. The retrofits costs are the same as the ones required for mounting propellers without proplets because the installation method does not change at all. The same goes for the on-aircraft investment costs as there is no need to change any part of the aircraft to fit this technology on it. In fact, proplets main innovation is located on the edged of the blades and it has nothing to do with the rest of the airplane.
Moreover, splitting these cost categories into the original four ones we have seen in the first chapter:
1) RDTE costs Around 100 million US dollars. Proplets does not need an intense and complicated research and testing program compared to other new technologies and this cost is also quite “low” due to the previous research, development and testing program that has been made so far
2) Acquisition costs Assuming the same amount of profit for propellers with proplets and current ones, we can say that there is a % of cost because of some extra work needed to produce these new kind of blades
3) Operating costs % per year, as shown in table 3.10
4) Disposal costs % due to less material to get rid off. As a matter of fact, this technology brings many benefits only if the blades are thinner than current ones and that means having less material to be disposed