karoliina.t.salminen
Well-Known Member
Re: Next configuration to be discussed: Boomerang configuration and other multi-pods
No, it is not an alternator. Brushless DC electric motor is very compact and lightweight for its power. You can't look at slow turning industrial AC motors or
aircraft alternators when designing a series hybrid. Electric RC planes are closer example of what is possible with electric motors. Motors used in aircraft,
if desired to be long lasting, may need a bit different design (for example for lubrication), but the gap is not very high.
There are not many such motors available which would be exactly at the spec for this, it might require fabrication of the motor and
generator. On the other hand, there are already commercial manufacturers developing these and few examples are already available, even for this
power rating, Yuneec is a notable example. Yuneec power system may not be directly suitable for this because it is a complete package for pure electric aircraft
and assumes too much to be customizable. However, the Yuneec motor can be used as an example for the weight for the generator (it is not alternator, our Lycosaurus has alternator, this
is a motor, which is not turned by electricity, but it is turned by the combustion engine!), and it surely does not weight 100 kg. One thing to remember about electric motors is
that there is no power rating for a motor (neither for generator nor drive motor), electric motor does not reach point where it delivers maximum power. Instead it is limited by
current, how much current the motor can handle before it fails. The control electronics has to be designed so that it limits the current before it reaches the level that damages the motor.
There are few new motor manufacturers which make lightweight and rather inexpensive motors. The electric Lazair has pair of those. I don't remember the manufacturer but they are
something like 17 kW each and cost around 1000 dollars per each (they are inrunners, unlike the Turnigy Outrunners Burt Rutan was raving about in Oshkosh),
but in theory, nothing prevents putting more than one of these to the same shaft. High motor rpm allows to make the same output power for a smaller and more lightweight package.
Generator is a motor too, instead of rotating it with energy, engine rotates it and it generates energy.
This is how Toyota Prius hybrid system works. On downhill the gasoline engine shuts down, and the
electric motor turns by the rotation of the wheels and it generates energy. (may be obvious that I drive a Prius, and I think it is the best car hybrid system at the moment on the market - unfortunately too heavy for aircraft). Prius has ridiculously small gasoline engine and the acceleration power comes from electric motor. SUVs can't take over me on highway, because the electric motor gives torque very rapidly and despite the gas engine is small, it accelerates still at highway speed (the acceleration at zero speed is not phenomenal, but fun thing is that it is still feeling almost the same at 65 mph!).
The Prius system is made to have short charge-discharge cycles, but in airplane and with the Lipo batteries that would be a problem. Prius parallel planetary drive system is very nice for car, but not so useful for aircraft - series hybrid is better for aircraft. However, that is not the point. The batteries are only used for first 5 minutes
of the flight and then they are empty (not actually empty, but electronics disallows further discharge after a point where they have discharged enough to be considered empty, discharging
Lipo deep empty would actually destroy it, that has happened to one Lenovo laptop I have for example - lid closed, sleep, no wall charger connected, after weeks, the battery was gone forever).
They can be charged back with balancing charging from the combustion engine during a longer period of time, for
example 30 minutes. Batteries are the heavy part, not so much the motors or control system. If the batteries would be absent, the installed weight would not
be so much higher than a "auto conversion" for the same engine, especially in case of a diesel, for example looking at the austro diesel and the gear reduction drive and clutch system which weights the same as electric motors combined apparently because of the not so good experiences with lighter system in the Thielert (some local experience; same flying club, two engine failures, two forced landings, and one of them to sea due to Thielert failure). The batteries, depending on how much these are on board, may turn the balance to the realm of weight compared to aircraft engine as you say.
No, it is not an alternator. Brushless DC electric motor is very compact and lightweight for its power. You can't look at slow turning industrial AC motors or
aircraft alternators when designing a series hybrid. Electric RC planes are closer example of what is possible with electric motors. Motors used in aircraft,
if desired to be long lasting, may need a bit different design (for example for lubrication), but the gap is not very high.
There are not many such motors available which would be exactly at the spec for this, it might require fabrication of the motor and
generator. On the other hand, there are already commercial manufacturers developing these and few examples are already available, even for this
power rating, Yuneec is a notable example. Yuneec power system may not be directly suitable for this because it is a complete package for pure electric aircraft
and assumes too much to be customizable. However, the Yuneec motor can be used as an example for the weight for the generator (it is not alternator, our Lycosaurus has alternator, this
is a motor, which is not turned by electricity, but it is turned by the combustion engine!), and it surely does not weight 100 kg. One thing to remember about electric motors is
that there is no power rating for a motor (neither for generator nor drive motor), electric motor does not reach point where it delivers maximum power. Instead it is limited by
current, how much current the motor can handle before it fails. The control electronics has to be designed so that it limits the current before it reaches the level that damages the motor.
There are few new motor manufacturers which make lightweight and rather inexpensive motors. The electric Lazair has pair of those. I don't remember the manufacturer but they are
something like 17 kW each and cost around 1000 dollars per each (they are inrunners, unlike the Turnigy Outrunners Burt Rutan was raving about in Oshkosh),
but in theory, nothing prevents putting more than one of these to the same shaft. High motor rpm allows to make the same output power for a smaller and more lightweight package.
Generator is a motor too, instead of rotating it with energy, engine rotates it and it generates energy.
This is how Toyota Prius hybrid system works. On downhill the gasoline engine shuts down, and the
electric motor turns by the rotation of the wheels and it generates energy. (may be obvious that I drive a Prius, and I think it is the best car hybrid system at the moment on the market - unfortunately too heavy for aircraft). Prius has ridiculously small gasoline engine and the acceleration power comes from electric motor. SUVs can't take over me on highway, because the electric motor gives torque very rapidly and despite the gas engine is small, it accelerates still at highway speed (the acceleration at zero speed is not phenomenal, but fun thing is that it is still feeling almost the same at 65 mph!).
The Prius system is made to have short charge-discharge cycles, but in airplane and with the Lipo batteries that would be a problem. Prius parallel planetary drive system is very nice for car, but not so useful for aircraft - series hybrid is better for aircraft. However, that is not the point. The batteries are only used for first 5 minutes
of the flight and then they are empty (not actually empty, but electronics disallows further discharge after a point where they have discharged enough to be considered empty, discharging
Lipo deep empty would actually destroy it, that has happened to one Lenovo laptop I have for example - lid closed, sleep, no wall charger connected, after weeks, the battery was gone forever).
They can be charged back with balancing charging from the combustion engine during a longer period of time, for
example 30 minutes. Batteries are the heavy part, not so much the motors or control system. If the batteries would be absent, the installed weight would not
be so much higher than a "auto conversion" for the same engine, especially in case of a diesel, for example looking at the austro diesel and the gear reduction drive and clutch system which weights the same as electric motors combined apparently because of the not so good experiences with lighter system in the Thielert (some local experience; same flying club, two engine failures, two forced landings, and one of them to sea due to Thielert failure). The batteries, depending on how much these are on board, may turn the balance to the realm of weight compared to aircraft engine as you say.
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