RJMAZ wrote:Waterbomber wrote:The proposed windmill charging is not very efficient because windmilling brings a lot of drag. It would be much more interesting to charge through a mecanically linked generator.
As I said, there is little merit to the simple hybrid idea. There are ways that hybrid could work in a limited way and in theory but IMHO we're talking about complex combinations and interactions.
Actually one of the most simple hybrid systems would be to have a turbofan engine and place the electric motor on the same shaft just behind the fan.
The electric motor could then double the speed and thrust of the fan during takeoff. The electric motor can then freespin during cruise running entirely off the gas turbine.
The electric motor can then turn into a generator during descent abd there us your mechanically linked generator. So the gas turbine will be at full throttle during descent but most of the energy is being sucked out by the generator. The electric motor/generator can also provide engine starting and power generation so you wont need an APU.
Such a design would still be 80% fossil fuel 20% electric like a Prius. As cool as this design sounds it won't please the environmentalists.
I much prefer the BMW i3 style hybrid as it is 80% electric and 20% fossil fuel. It has a little 25kw generator with a 9 litre fuel tank to top up the battery with 125kw of electric engine power. That tiny 25kw generator allows the i3 to more than double its electric range. If you are doing only short trips in the i3 the petrol generator does not have to turn on.
Using the the i3 style hybrid in an aircraft would work very well. If the flight was only 500kms long they could do it fully electric. If the flight is 1000kms long the generator has to run for the entire flight. This generator would also provide the emergency reserve fuel. For instance if there is bad weather at the destination airport as soon as they get the call mid flight the generator would then get turned on to start extending range. The generator could be sized to provide 50% of the electrical power required at cruising altitude.
These small 50 seat electric prototype aircraft they could simply install a 787 electric APU in the tail. That provides 450kw of electricity and would top up the batteries nicely.
Except that the i3 is an electric car with an optional range extender.
As already discussed, any amount of aircraft can't take off with a battery pack as main source of energy.
The above hybrid with the gas turbine as main energy supply is a challenge as it is to justify.
The ATR72 has 3600kW of total engine output, of which it uses about 75% at cruise. With a range extender APU with 450kW of output you won't get far.