New electric engine improves safety of light aircraft • Hacker News Board

Re: New electric engine improves safety of light aircraft

#31

Post by keenerd » Mon, Jul 06, 2015, 4:34 PM UTC

unics wrote: post #7

Wonderful idea. I do wonder how that changes the center of gravity and how much weight is diminished for cargo but seems well worth it. When the engine goes out you generally only have 10 seconds to decide where to land. Now it seems you have many minutes to find a place. In most circumstances I'd think this is better then the parachutes for planes because you have a chance to save very expensive airplanes.

Mass estimate: A 40hp motor is around 200kg.

40 hp is 30kW. Assume 100% efficient gearing and motor. Stall speed is around 80 km/hr. For 20km of powered flight, that means 0.25 hours runtime. For high performance li-ion (250 Wh/kg) that is 30kg of batteries.

Add some weight for Speculation: Given the difference in motor vs batteries, either they have an extremely light weight motor technology or they are using lower density li-ion for safety. A LiFePO4 pack (130 Wh/kg) would be 60kg. They could afford to double the battery size, since that is only a 25% increase in weight. Either they have a very lightweight motor technology, or there is some magic price or weight number they are trying to squeak under.

Re: New electric engine improves safety of light aircraft

#32

Post by lujim » Mon, Jul 06, 2015, 4:36 PM UTC

mmaunder wrote: post #29

At the risk of stating the obvious, many crashes would not be affected by this: CFIT (controlled flight into terrain). Sadly common, it's how Kennedy junior died and many others. Stall/spin. Common on take off and landing and avoidance is a huge emphasis in training. Visual flight into instrument conditions. If untrained what often happens is the pilot will end up in a spin/spiral into the ground or doing a CFIT. Als…

That seems like a bit of an pessimistic take on this. Isn't that like saying front impact airbags aren't very helpful in a rear end collision?

CFIT, stall/spin, and VFR into instrument conditions are all training deficiencies. This solution fixes something a pilot can't be trained to avoid, an engine failure at an inopportune time. Training can only take you as far as "glide and crash gracefully" without stalling and spinning.

Also this could easily be made to automatically activate. Many multi engine aircraft will automatically increase power on the good engine by a few percent after an engine failure.

Re: New electric engine improves safety of light aircraft

#33

Post by mikeash » Mon, Jul 06, 2015, 4:37 PM UTC

ju-st wrote: post #27

markab21 wrote: post #14

Earlier quoted context omitted.

I agree that this is better than parachutes , but not because of the cost of the plane. If your engine is failing, your plane failed you and isn't worth saving. that's what insurance is for : ) the moment you pull a parachute (for example the CAPS on the cirrus , the plane is totaled anyway). The most dangerous place to have a failure is during initial take off (low hour student pilot here). The engine kicking on wou…

Commercial airplanes have (at least) two engines because of the high risk of failure at take-off. The next step for this electric engine would be to replace that second heavy, expensive engine every large airplane carries around... Additionally, the full power of the two engines is only needed at takeoff. At cruise they only run at 30-40%. An electric motor with a relativly small battery would be enough to provide en…

It's not just takeoff. Often airliners cruise outside of gliding range of an airport that can handle them, and a total power failure could be catastrophic there.

As long as the electric engine can provide a sufficient backup to get to an airport after a failure in cruise, though, that would certainly be an interesting possibility.

Re: New electric engine improves safety of light aircraft

#34

Post by mrfusion » Mon, Jul 06, 2015, 4:40 PM UTC

keenerd wrote: post #31

unics wrote: post #7

Wonderful idea. I do wonder how that changes the center of gravity and how much weight is diminished for cargo but seems well worth it. When the engine goes out you generally only have 10 seconds to decide where to land. Now it seems you have many minutes to find a place. In most circumstances I'd think this is better then the parachutes for planes because you have a chance to save very expensive airplanes.

Mass estimate: A 40hp motor is around 200kg. 40 hp is 30kW. Assume 100% efficient gearing and motor. Stall speed is around 80 km/hr. For 20km of powered flight, that means 0.25 hours runtime. For high performance li-ion (250 Wh/kg) that is 30kg of batteries. Add some weight for Speculation: Given the difference in motor vs batteries, either they have an extremely light weight motor technology or they are using lower…

200KG for the motor sounds very high?

Re: New electric engine improves safety of light aircraft

#35

Post by pwnna » Mon, Jul 06, 2015, 4:43 PM UTC

digi_owl wrote: post #6

mrfusion wrote: post #4

I wonder if you could use your propeller as a "wind turbine" when landing to recapture some energy? Of fly around in thermals and charge your battery??

I suspect that while landing you really want the engine in "neutral" so you can at any moment kick it into full power if some issue shows up. Landing is damn close to a controlled crash. And i don't think these kinds of aircrafts have the wing surface etc to be floating around on thermals.

Usually when landing you want something like 110% of your stall speed, which means that you're not "crashing" (by which I mean stalling). This involves some sort of engine power.

I am not aware of any plane that lands without power outside of an emergency.

Re: New electric engine improves safety of light aircraft

#36

Post by phillc73 » Mon, Jul 06, 2015, 4:57 PM UTC

ju-st wrote: post #27

markab21 wrote: post #14

Earlier quoted context omitted.

I agree that this is better than parachutes , but not because of the cost of the plane. If your engine is failing, your plane failed you and isn't worth saving. that's what insurance is for : ) the moment you pull a parachute (for example the CAPS on the cirrus , the plane is totaled anyway). The most dangerous place to have a failure is during initial take off (low hour student pilot here). The engine kicking on wou…

Commercial airplanes have (at least) two engines because of the high risk of failure at take-off. The next step for this electric engine would be to replace that second heavy, expensive engine every large airplane carries around... Additionally, the full power of the two engines is only needed at takeoff. At cruise they only run at 30-40%. An electric motor with a relativly small battery would be enough to provide en…

Plenty of "commercial" aeroplanes only have one engine. The Cessna Caravan springs to mind. I run a couple of Cessna 206s for joy flights. Strictly speaking, people pay my company money for this, therefore the aircraft are "commercial."

Re: New electric engine improves safety of light aircraft

#37

Post by phillc73 » Mon, Jul 06, 2015, 5:03 PM UTC

pwnna wrote: post #35

digi_owl wrote: post #6

Earlier quoted context omitted.

I suspect that while landing you really want the engine in "neutral" so you can at any moment kick it into full power if some issue shows up. Landing is damn close to a controlled crash. And i don't think these kinds of aircrafts have the wing surface etc to be floating around on thermals.

Usually when landing you want something like 110% of your stall speed, which means that you're not "crashing" (by which I mean stalling). This involves some sort of engine power. I am not aware of any plane that lands without power outside of an emergency.

Apart from all those thousands of sailplanes people fly every week. They land without power, and very few of those landings would be an emergency.

Re: New electric engine improves safety of light aircraft

#38

Post by guscost » Mon, Jul 06, 2015, 5:06 PM UTC

Honestly I still don't fully accept that having a second engine running on completely different fuel is a good idea for a car. A hybrid airplane seems too ridiculous to even consider, because now both engines have to be lifted up into the sky!

But of course this is based on my own amateur and dated knowledge. With all the work that has gone into hybrids lately, who knows.

Re: New electric engine improves safety of light aircraft

#39

Post by keenerd » Mon, Jul 06, 2015, 5:07 PM UTC

mrfusion wrote: post #34

keenerd wrote: post #31

Earlier quoted context omitted.

Mass estimate: A 40hp motor is around 200kg. 40 hp is 30kW. Assume 100% efficient gearing and motor. Stall speed is around 80 km/hr. For 20km of powered flight, that means 0.25 hours runtime. For high performance li-ion (250 Wh/kg) that is 30kg of batteries. Add some weight for Speculation: Given the difference in motor vs batteries, either they have an extremely light weight motor technology or they are using lower…

200KG for the motor sounds very high?

Find us a lighter one for sale.

Re: New electric engine improves safety of light aircraft

#40

Post by bri3d » Mon, Jul 06, 2015, 5:11 PM UTC

mrfusion wrote: post #34

keenerd wrote: post #31

Earlier quoted context omitted.

Mass estimate: A 40hp motor is around 200kg. 40 hp is 30kW. Assume 100% efficient gearing and motor. Stall speed is around 80 km/hr. For 20km of powered flight, that means 0.25 hours runtime. For high performance li-ion (250 Wh/kg) that is 30kg of batteries. Add some weight for Speculation: Given the difference in motor vs batteries, either they have an extremely light weight motor technology or they are using lower…

200KG for the motor sounds very high?

That's definitely extremely high - brushless motors with much higher power (~80hp) are in the 50kg range (see for example EV218).