esteban wrote:
Umm, are there such very efficient generators around? Where are they and what is their efficiency and power-to-weight?
A permanent magnet (PM) generator is about 98% efficient, the prop motor about the same. Other non-PM types of machine lower, although they have the safety advantage of being able to turn off the field. The power electronics have greater losses and might be 94% efficient, meaning if all three are in play you lose about 10%, roughly, i.e 90% combined conversion efficiency. In cruise you’d want to be under full power on the IC engine with the generator directly coupled to the motor, reducing the conversion loss to say 5%. Then that loss would be counteracted by whatever efficiency benefit is gathered by a three-quarter size IC engine running at nearly 100% power, which btw requires a turbo at altitude, compared with a higher power engine running at 65-75%, full throttle at altitude. It’s not clear to me that such an engine is actually more efficient, and hauling around a generator, motor, batteries, power conversion, controls, and cables doesn’t make the plane itself any more efficient.
A training plane varies power setting more often, more like a car, so I’d think training planes are a more likely hybrid application, technically. I don’t know which would attract government research money better, and I suspect that may be key here.
Silvaire wrote:
A permanent magnet (PM) generator is about 98% efficient, the prop motor about the same.
Sorry, I meant “Are there IC engines optimized for efficient lightweight power generator at fixed RPM. What is their power/weight and efficiency?”
You can possibly strip several things from a standard engine (alternator, starter, transmission/clutch, …?)
Uff, with turbines what you save in weight of engine you lose in weight of fuel… :-)
I hope it comes with one throttle lever for each engine. Can’t trust some pesky computer do the engine inop work.
http://www.nasa.gov/press-release/nasa-hybrid-electric-research-plane-gets-x-number-new-name-0
One day, not too far away, when battery technology allows enough energy to be stored in a volume and weight equal or better to gasoline, small airplanes may actually become popular again….for a start the main complaint of NIMBYs is the noise…which would be dramatically reduced…
One day, not too far away, when battery technology allows enough energy to be stored in a volume and weight equal or better to gasoline
It’s going to be more than “not too far away” since currently the gap is about 45:1.
Admittedly one doesn’t have to achieve quite 1:1 because of the relative efficiencies of IC v. electric motors, etc, but there is still a very long way to go.
It may not be achieved in any of our lifetimes.
Realistically NASA should have consulted this forum before buying the demo airframe and issuing their four year guidance :-)
Seems to have attracted some R&D funding. The NASA distributed propulsion project uses a Tecnam fuselage.
http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20100036222.pdf
Graphene polymer batteries apparently 1/3 the weight and four times the capacity are on the horizon?
With a similar actuarial table as Peter I hope to see some of the technology in practical use in our lifetime.
Realistically NASA should have consulted this forum before buying the demo airframe and issuing their four year guidance :-)
Shorrick, I am certain that you have some level of scientific/engineering education, so instead of posting a cheap swipe, why not apply a little bit of scientific scepticism to yet another press release from NASA, whose PR / fundraising machine has been in overdrive since 1972 ?
Hope to validate…
Eliminating carbon emissions? So, they have sorted out nuclear fusion already? They have been awfully quiet about that one 
I too would like to see massive advances made in technology e.g. nuclear fusion, medicine, battery capacity, etc. But these things take a lot longer than it takes to write press releases.
Battery technology needs roughly another 15x to 20x improvement to deliver a similar overall power train efficiency as liquid fuel (weight being more important with aircraft than with cars) and then you are still stuck with the generation problem which is roughly where it was 50 years ago.
