I don’t think anyone wrote that.
AdamFrisch wrote:
Divide 238kWh by 43kWh and we have the endurance = 5.5hr, no reserve. Assuming aircraft can make 120kts, that would be a no wind range of 660nm with no reserves.
You also need to climb to cruising alt. That is when you need power. You will need something like that Siemens engine (350 hp). It weighs 50 kg. Add another 50 (alt least) for converter and so on, and we have 100 kg easily for the drive train.
Then you start to think. Hmm, what kind of engine could I get for 100 kg? I could get a brand new Rotax 915 iS, producing 140 hp. It weighs only 85 kg. It can, with minor adjustment only, run on bio-ethanol made from wood. Now, the 915iS exists, bio-ethanol from wood exists. You can have all this today (at least from a technological perspective). Or, the obvious solution – run the SR22 on bio-ethanol. No technological advancements whatsoever is needed, only for FAA/EASA to issue some paperwork. All infrastructure in place (except some industry size biofuel factories), nothing to change, and it’s all carbon neutral, and no food is being used.
Lots of research are being done with bio fuel. There are two “generations” of biofuels. Generation 1 is based on plant oil or plant sugar. Generation 2 is based on “non foods” such as plant material (wood, grass and so on). ENGM was the first airport to offer bio jet fuel for everybody in 2016. By 2030, 30% of all jet fuel in the Nordics (EU?) will be based on generation 2 biofuel. All of this can be made from waste products from the existing wood industry. It’s more than enough wood to fire up all the airplanes in the foreseeable future, literally speaking.
But, the thing is, the process industries need to change from carbon processing to bio processing. This is a huge change of unimaginable proportions, it takes time, and can only be done gradually. At the same time, battery power has more than enough showed it’s potential. It’s simpler, cheaper and better solution altogether by an order of magnitude compared with vehicles using combustion engines. However, the battery technology with enough energy density to completely make such a transition is nowhere to be seen, not even in the wildest fantasies. It may never exist. Long distance aircraft and ships is such a “niche”, as well as lots of other more specialized stuff. A huge (humongous) industry of biofuel processing is being developed as we speak. It’s a reality, it’s the only viable reality if carbon footprint is to be reduced, and long distance travelling is to continue. Some people say long distance travelling is a luxury, but it’s not. It’s of vital importance for the survival of the human race.
So I’m thinking. What will be best for GA? If we are going to keep on flying with a mix of new and vintage planes, then biofuel is obviously the only alternative. At the same time, battery technology is being developed, and because it offers a potential of being so much cheaper than combustion, it will eventually take over. Trainers, and lots of derived GA will become electric in a few years, and it will expand due to the economy of it. 5 years, 10 years, 50 years ? who knows, 10+ years is long enough for something completely different to pop up.
Yes, you will need to climb to altitude at higher power settings. But here’s a side benefit, the electric motor does not lose efficiency with altitude, meaning you could regularly get to altitudes where you can have greater TAS without any penalty.
As for the 30%, since electric has a linear power curve, we can not compare that directly to piston engines. If you were to fly a piston at 30%, I agree, you’re probably almost falling out of the sky. But that’s not the case with electric aircraft. Look at 9:23 of this clip of the Pipistrel Alpha Electro. He’s doing 90kts on 21kW of power. The Alpha has a 60kW motor, so 21kW is a 35% power setting.
But as I said, we will need to start to design aircraft differently. Bigger, slower turning props, or multiple distributed props (as NASA is trying now with the LEAP project, see below), longer wings, emphasis on aerodynamics and light weights. There are some suggestions saying that by placing a prop at the very wingtip that rotates counter to the vortex generated by it, you can reduce tip drag by up to 15%.
Just one more thing from this interesting project. Listen to engineer at 1:42 in this clip where he says “with the distributed propulsion we need 5 times less power than a regular aircraft”. If that’s true, then for sure we have seen the end of combustion for GA aircraft. That’s a huge game changer. But since project has just started practical testing, it’s too early to tell if that’s true.
LeSving wrote:
You will need something like that Siemens engine (350 hp). It weighs 50 kg. Add another 50 (alt least) for converter and so on
I doubt the ESC will weigh anywhere near that much – we aren’t using huge iron core transformers any more. The actual switching elements that control the current to the motor windings (e.g. an IGBT, a type of transistor) don’t weigh much – IGBTs that are capable of controlling over 100kW of power only weigh 30 grams. (Of course there’s extra stuff that has to be added, heatsinks, control circuitry, wiring etc) but I suspect it’s not going to get close to 50kg.
Some pics of the Siemens kit are here.
My guess is that the electronics and cables, for the whole aircraft, weigh the best part of 50kg. The cable alone is really thick and heavy.
I’ve just had some 25mm2 cable delivered (50m) and can’t really lift the box. The Siemens stuff looks like 35mm2. They won’t have 50m but they will have a fair bit, going around the battery pack, etc.
I have given a couple of lectures on this at recent engineering events, I am available to give it again in the UK on request. Going electric is a major medium term goal for our work machine, being a buoyant aircraft we have a lot of advantages over aeroplanes and helicopters. I cannot give the entire lecture in a few lines on a forum but here are a few key thoughts.
Studies by us and others have I think made it quite clear that the current state of art in batteries means that a two seat 100 euro slice of cake aircraft is technically feasible now but at a very high purchase price. Looking bigger than that, if you want an aeroplane rather than an evolved arship (which only works where A-B speed is not required) then it is a long way off. Biofuel has all the problems already listed by an earlier contributor. Hydrogen fuelled diesel engines can be done (it was demonstrated very nearly a century ago) but the tanks are so heavy. Batteries, we just cannot see the power problem being fixed in the essential timescale. Hybrid is not a good idea for flying machines, two powertrains in one vehicle means too much excess weight. The one we see working is fuel cells.
A problem at the moment is the hype curve of eVTOL and other fanciful machines soaking up attention and cash. VTOL is energy intensive however one does it. Multiple propellers from one electrical system does not make for redundancy. Propellers on the wing tips are engine failure after take-off deaths waiting to happen. Writing DAL A software, getting down to 10E-9 probability for catatrophic failure cases and eliminating common cause failures are all non-trivial to say the least.
The document linked below is not by me but by a friend who is much better informed than most, certainly more so than me:
https://www.aerosociety.com/media/10179/guy-gratton.pdf local copy
Thanks for posting Joe, informative!
As to long distance slow and electric travel we probably should look at the craft in your profile pic. I guess there may be some room for batteries 
Guy Gratton has been active on EuroGA, under his usual UK social media name
There are various presentations on this topic. One I went to, by a respected researcher specialising in electric vehicles, is here. It was really interesting. Nothing was stated as impossible, but the challenges are clearly numerous.
AdamFrisch wrote:
As for the 30%, since electric has a linear power curve, we can not compare that directly to piston engines. If you were to fly a piston at 30%, I agree, you’re probably almost falling out of the sky.
I have been driving electric car for 5 years already. My next car will also be electric. Electric propulsion (with batteries) is in many ways much better than combustion engines. I would say an order of magnitude when it comes to short distance travel. But, there is NO, repeat – NO – battery powered alternative for longer transportation. The battery needed for this does not exist, and probably never will. One should never say never, but basic physics doesn’t leave much room for such a battery, It has to be something very special, very different than current battery technology.
Anyway, modern gasoline engines are insanely efficient over a huge power band, from 10-20 hp to 200+ This is achieved using tiny turbocharged engines with VW leading the pack.
Biofuel is the only alternative for long distance. This is what the ship and aviation industry is transitioning to. It is happening, and has been going on for some time already. It is not some fairy tale about non existent future miracle battery and equally non practical vehicles. There are lots of dreamers around. We like to dream about new and exotic miracle stuff. But we can dream as much as we want, it doesn’t make it real.
