Story 2015-01-07 2WP2 Boeing developing experimental hybrid-electric aircraft

Boeing developing experimental hybrid-electric aircraft

in hardware on (#2WP2)
story imageResearchers from the University of Cambridge, in association with Boeing, tested the first aircraft to be powered by a parallel hybrid-electric propulsion system, where an electric motor and petrol engine work together to drive the propeller. The demonstrator aircraft uses up to 30 per cent less fuel than a comparable plane with a petrol-only engine. The aircraft is also able to recharge its batteries in flight.

Though increasingly common in the automotive industry, the technology has never before been brought to the aerospace sector. During take-off and climb, when maximum power is required, the engine and motor work together to power the plane, but once cruising height is reached, the electric motor can be switched into generator mode to recharge the batteries or used in motor assist mode to minimise fuel consumption. The same principle at work in a hybrid car.
Reply 6 comments

Great idea (Score: 0)

by Anonymous Coward on 2015-01-08 02:54 (#2WP7)

Will it scale to commercial airlines though

Re: Great idea (Score: 1)

by on 2015-01-09 00:25 (#2WPA)

I hope it is, but I doubt we will see any drop in ticket prices. Greedy, all of them!

Re: Great idea (Score: 2, Interesting)

by on 2015-01-11 03:15 (#2WPD)

As a middle class private pilot who owns his own plane (cheap little one) I can tell you there are plenty of costs to aviation which the public does not directly see. Here is a small list from my experience owning a plane for just a few years.

. annual inspection (about $400 for my little plane, much more for a 747)
. 100 hour inspection - yep every plane in commercial service must be inspected every 100 operational hours at about the same level as the annual inspection
. landing fees - to land and take off from JFK, LGA, or EWR costs over $100 for my little 2 place plane
.fuel of course
.lubrication oil
.replacement parts for time limited parts - ex a gen-set may be rated at 10,000 hours after which it must be replaced even if in perfect order
. mandated engine overhauls - my engine must be given a complete overhaul every 500 operating hours
. recurring training for pilots - for private pilots this comes out to something between $500 and $2000 every 2 years, for ATP pilots (airline pilots) the costs are greater and so is the frequency
.cost of operating slots at major airports - yep the airlines have to pay for take off and landing times at LGA,JGK, LAX, SFO etc.

So while we would all love to see lower costs I can not say it is all due to greed. Something I read several years ago claimed that airlines only made a few percent profit. I have not been part of an airline, but I am friends with owners of small charter operations and I can tell you they have real thin profit margins.

From what I see the best use of hybrid technology in aviation is for small general aviation aircraft like mine, and then the small to medium sized puddle jumpers used by the regional operators and charter operations. The technology does not lend it's self well as a replacement for jet propulsion, so the bigger faster planes will not benefit from this work in the foreseeable future.


Re: Great idea (Score: 1)

by on 2015-01-11 05:13 (#2WPJ)

The technology does not lend it's self well as a replacement for jet propulsion, so the bigger faster planes will not benefit from this work in the foreseeable future.
I'm not so sure... I'd like to see how much more quickly a 787 with electric motors on the landing gear could reach takeoff speeds.

Re: Great idea (Score: 0)

by Anonymous Coward on 2015-01-11 15:21 (#2WPK)

Actually, it doesn't matter when you use the battery energy. LiPo just doesn't have enough energy density to be a viable energy source for big aircraft, especially so for long haul. This is important because fuel consumption is directly affected by the weight of the aircraft. So, if you have a lot of dead batteries on board, you're going to pay for them with fuel.

I just looked up the specific energy densities for LiPo and Jet A-1. They are 0.56 vs 43 MJ/kg. There is something like a 80 times difference. Let's say that you replace 100kg of fuel with equivalent batteries. The batteries will weigh 8 tons. This will make you burn 800 kg more fuel than normal, for a short 3 hour flight. I fly 320s and I simply doubled the numbers for A320 to get at 787. It is probably incorrect, but I'm sure it's in the ballpark. For a long flight like 10 hours, you burn 2500 kg more fuel just to carry the dead batteries.

I didn't mention a couple of things here: with regular fuel, consumption per hour reduces as the flight progresses and the aircraft becomes lighter. Also, for big electric motors, you will have another weight penalty, probably measured in tons. Electric motors are more efficient than turbofans, but I don't see how that could offset the costs I have mentioned because turbofan engines are also quite efficient, something like 70% IIRC.

In order to SAVE fuel using batteries, something drastic needs to be done, such as shutting down
engines during cruize or something similarly extraordinary. You could maybe do that with smaller aircraft, but never with a big aircraft like 787.

Re: Great idea (Score: 1)

by on 2015-01-11 18:11 (#2WPM)

The take off roll is only a matter of seconds at most airports before the wheels are off the deck, unless the pilot is holding it down on purpose as he might do in gusty conditions.

There are of course the exceptions such as Quito where the altitude makes the take off run longer, or of course very hot places like Vegas in the summer where sometimes low power GA aircraft like the Piper J3 have to take off before sunrise.

I do not think the size of electric motors that could drive the wheels of a large jet would have significant impact on takeoff distance. I do think that they would be good for taxi purposes, but since the jets need to be spun up anyway there would probably be little gain of economy.