On another thread, Simon Clifton wrote:Let's start a thread on electric motor development.
Here's that thread! Where to start? The known quantity is the internal combustion engine, whether diesel and spark-ignition, piston or rotary, 2 stroke, 4 stroke & (even) 6-stroke. So, if one is to look for an alternative, one has to identify what is the ideal power source for an aircraft, and to identify the characteristics of what's on offer. I suggest the ideal aero-engine is: compact, lightweight, powerful, smooth, economical and reliable. How do existing motors match up?Brian Hope wrote:Major feature on alternative power systems coming up in the next couple of issues of LA.
4-stroke diesel piston: very economical & reliable, but heavy, bulky and prone to vibration. If based on a car-engine, it needs to be modified to accept Avtur rather than road diesel. All diesels need to be turbocharged for optimum power.
2-stroke diesel piston: as above, but lighter, more powerful and still economical; purpose-made for aviation, so may be expensive.
2-stroke petrol piston: light, cheap, compact, powerful, if rather thirsty and unreliable. Oil-injection is better than pre-mix; and the use of reed-valves, disc-valves, and exhaust power-valves (all common on motorbikes) improve the power characteristics. Direct fuel injection into the chamber after the ports have closed eliminates unburnt fuel in the exhaust, giving better economy and reducing emissions. However, almost all current aviation 2-strokes are still as basic as can be, which is why only microlights use them.
4-stroke petrol piston: the mainstay of GA. Expensive to buy, very reliable, heavy, not compact, and a poor power-to-weight ratio. Modern engines are more economical than the thirsty American dinosaurs.
Wankel rotary: very smooth, small, lightweight & powerful. Reasonably economical but some doubts on reliability; uncommon and unknown to most engineers. However, they can spin at high revs without damage (if the bearings & tips can cope); they are not sensitive to fuel quality and can run on Avtur as a spark ignition engine. They almost never seize as the "crankcase" expand more than do the rotors.
Reduction gear or Direct Drive? Direct drive is simple and reliable; but a gearbox allows a smaller, lighter engine to run faster and deliver peak power.
Electric motors: compact, lightweight, smooth, powerful, and reliable. Almost perfect! Economical? There's the rub. Batteries are still heavy. No doubt Simon Clifton will expand on this. Fuel cells? Over to you, Simon!
A good compromise might be a hybrid aircraft, with a small bank of batteries powering a geared electric motor driving a feathering VP prop. Batteries would be charged while on the ground from the mains, and in the air by a small Wankel industrial engine and by an array of solar panels on the wings. To save fuel and weight, the aircraft would be able to be winch-launched, which means that we're considering a lightweight aircraft with only one or two seats. Imagine that: a winch launch to 1500 feet; then run on the batteries, relying on sunshine to keep you flying; and then start the charging engine only when the volts start to drop!