lelievre12
Well-Known Member
- Joined
- Jul 15, 2020
- Messages
- 168
With brushless DC motors now easily able to offer 15KW in small packages that weigh less than a typical engine starter its worth considering what the future holds for aviation engines.
The all up weight of a starter, alternator and lead acid battery can be replaced with a single Lithium Ion or LTO Battery and brushless DC ("BLDC") motor that weighs no more.
Its not commonly known that a BLDC motor also works perfectly well as a DC generator provided its controller has a regenerative function. So both alternator and starter can be replaced by a single BLDC. BLDC are commonly available and offer some benefits if the system is fitted to an aircraft.
1. Engine starting is achieved with high RPM due to the large output of the BLDC motor. A typical 12/24V starter is 1-2KW whereas a BLDC could output 15KW. No more slow cranking.
2. During the takeoff roll and for ~5 minutes the BLDC can add 15KW to the engine output just when you need it most. Once battery voltage drops to a preset minimum, the BLDC can revert to battery charging later in the flight.
3. Long descents can 'recover' energy if the BLDC is set to a high output charge. This in effect provides massive braking of the propeller and would be a useful speed brake.
4. A constant speed propeller would no longer be required as a "cruise" pitch prop could be installed. Normally this would prevent engine making max takeoff RPM however the BLDC could add the 15KW to increase RPM. This would mean that the engine + BLDC could spin a cruise prop at takeoff RPM during the roll. When airborne the BLDC would throttle back and the engine could then drive the cruise prop on its own.
My plan is to install a 15KW BLDC and a 1.75KWH Lion or LTO battery pack (weight 20 lb).
The battery pack will provide 7 mins of full power at 15KW or 5 minutes with reserve. The BLDC is timing belt driven off a crankshaft pulley and as discussed will both start/drive the motor as well be driven by it for charging the battery. The controller will be an programmable ESC such as:
It's an interesting experimental project, particularly for smaller canards/lightweight aircraft as the benefits of better starting, increased takeoff power, speed braking and elimination of constant speed prop all come in a package that weighs no more and probably weighs less if you credit the constant speed prop.
I write this just to throw it out there for discussion, opinions and ideas from others whom may be thinking along similar lines.
The all up weight of a starter, alternator and lead acid battery can be replaced with a single Lithium Ion or LTO Battery and brushless DC ("BLDC") motor that weighs no more.
Its not commonly known that a BLDC motor also works perfectly well as a DC generator provided its controller has a regenerative function. So both alternator and starter can be replaced by a single BLDC. BLDC are commonly available and offer some benefits if the system is fitted to an aircraft.
1. Engine starting is achieved with high RPM due to the large output of the BLDC motor. A typical 12/24V starter is 1-2KW whereas a BLDC could output 15KW. No more slow cranking.
2. During the takeoff roll and for ~5 minutes the BLDC can add 15KW to the engine output just when you need it most. Once battery voltage drops to a preset minimum, the BLDC can revert to battery charging later in the flight.
3. Long descents can 'recover' energy if the BLDC is set to a high output charge. This in effect provides massive braking of the propeller and would be a useful speed brake.
4. A constant speed propeller would no longer be required as a "cruise" pitch prop could be installed. Normally this would prevent engine making max takeoff RPM however the BLDC could add the 15KW to increase RPM. This would mean that the engine + BLDC could spin a cruise prop at takeoff RPM during the roll. When airborne the BLDC would throttle back and the engine could then drive the cruise prop on its own.
My plan is to install a 15KW BLDC and a 1.75KWH Lion or LTO battery pack (weight 20 lb).
The battery pack will provide 7 mins of full power at 15KW or 5 minutes with reserve. The BLDC is timing belt driven off a crankshaft pulley and as discussed will both start/drive the motor as well be driven by it for charging the battery. The controller will be an programmable ESC such as:
It's an interesting experimental project, particularly for smaller canards/lightweight aircraft as the benefits of better starting, increased takeoff power, speed braking and elimination of constant speed prop all come in a package that weighs no more and probably weighs less if you credit the constant speed prop.
I write this just to throw it out there for discussion, opinions and ideas from others whom may be thinking along similar lines.
