Another take on electric aircraft here.

Fairly light on detail but it it looks as if they've got it working in real life. There appears to be some serious work that's gone into it by an experienced team, and they have real backing, so it's not a 'vapourcraft' :D

Whether the predictions will come true is another matter, nevertheless good luck to them!

FP.

OK, it has flown so the engineering must be sound enough, I guess, but to my eye that Lilium thing just looks so unbalanced...but perhaps to a millennial it just looks cool.

I would suggest that in the 'future' (now!) how it looks is almost as important as how it flies for commercial success!

I'm no millennial, but I was raised on 'Thunderbirds' (:O); to my mind it looks a bit like '2', which was always my favourite, so I'm ok with the looks. Also, I think the full-size version looks a little more reasonable dimensionally?

However I was a little concerned at the way it appeared to pitch into a turn, not certain they quite had the stability algorithm right at that point. No doubt it will be improved (or it was possibly just something in the way the video portrayed it)...

FP.

Personally I don't like the Lillium aircraft - for one thing that's a small model without any significant payload. It simply looks 'wrong' as if it needs a larger canard on the front

However, a few posts back someone pointed out that to compete with a spamcan you would need to carry a huge amount of batteries. One way you can do this is to improve your batteries. Another way is to make your airframe more efficient.

Electric aircraft can do VTOL relatively easily compared to IC engine powered aircraft. This means that you can get away with a much lower wing area as you don't need to worry about stall speed in the case of an engine failure - especially if you also carry a ballistic parachute. Also, if you have to divert or land in an emergency you can land on a postage stamp, so having an excess range becomes less important - you shouldn't need to carry the same amount of reserves as an IFR spamcan. So long as you have two minutes' warning of the batteries running out you should be able to put it down somewhere. Unless you're over water, of course.

The regulators' heads must be hurting.

How do you figure that?

G

The power to weight ratio can potentially be much larger. The motors will give you many horsepower/kg and the batteries often have a huge power density, if not necessarily a large energy density.

It's a while since I did the sums but I believe electric motors for radio control aircraft are now managing 10-15 horsepower/kg whereas on O320 will give perhaps 1.6hp/kg.

Some batteries can be drained in less than a minute, so you could potentially carry enough batteries and motors to achieve 2 jump take-offs and landings on a far smaller mass budget than if you were trying to achieve the same thing with an IC engine.

You might be able to combine the VTOL capabilities of an electric aircraft with a relatively small cruise motor burning fuel, to achieve a very efficient hybrid system.

Okay, so you are distinguishing between power density and energy density. You may be right.

An interesting perspective - any calculations available?

G

Off the cuff figures:
A 5C current is reasonably sustainable from power optimised cells for a short period depending on cooling etc (i.e go from 100% SOC to minimum in 0.2 hours) so a 20 KWh pack could deliver 200KW of power at a cost of about $4000 and a pack weight of 100-150kg.
A 200KW IPM motor and planetary reduction gear could weigh down to about 40-50kg.

So you could have a 250 HP auxiliary motor with ~10 minutes endurance for a weight penalty of about 150-200kg.

That's conservative. A123 batteries I've used in my model helicopters are said to be able to go from full to empty at 35C and can manage 60C for short periods. There are Lithium Polymer batteries on the market that are claimed to be good for 150C or more. In practice they probably won't manage many cycles if you do that to them with any regularity, but it wouldn't surprise me if you could get 60C reliably and A123 cells are pretty bombproof.

What would you actually need to be able to do? Climbing to 300 ft then accelerating to 140mph needn't take too long. You'd need enough reserves to maneuver for a bit then land pretty much immediately if required. It sounds feasible to me. If you put a 250hp motor with 3 minutes of endurance in a sub 200kg 1 person aircraft, it should do 0-140 and 0-300 feet pretty quickly.

You can pedal a fuselage like this up to 80 - 90 mph on a kilowatt or so (human power + gravity with a 2/3% gradient) so presumably you could get it up to 160mph on 10 horsepower or so - without wings.
https://www.ohio.edu/mechanical/prog...gham_81mph.jpg
https://www.pprune.org/data:image/jp...QHTuSSVMvs/9k=
How big would you need the wings to be to attain a stalling speed of 140mph? How much induced and parasitic drag would they have? This is the part of the question that I really don't know how to answer, but I imagine if you were to design an aircraft to fly at high speed without any requirement to be able to fly at low speed (because this is taken care of by the VTOL system) you could make them considerably more efficient. I suspect you might have a better handle on this than I do, Genghis?

Perhaps given a more modest cruising speed you might be able to power such an aircraft very efficiently - perhaps just a few horsepower to fly straight and level at 100+mph? Obviously a practical aircraft needs some excess power to outclimb downdrafts and outclimb terrain. Also, most people find being in an HPV claustrophobic. However, I bet you could find a compromise hybrid or wholly electric vehicle that would give you a vehicle with VTOL capability and a half-decent range, and that it could end up looking not altogether unlike the Lillium.

An interesting observation from the Space X people is that powered recovery is best delayed until the very last moment, because every second spent decelerating or hovering is an extra 32 ft/sec/sec. That's why the boosters plummet and only light up at the very last moment (or not).

I wonder how this would compare with a parachute recovery system in an aircraft already equipped with electric VTOL? It's not clear that the 'G' would be any more than for a parachute arrival. The amount of residual, or even segregated battery capacity could be very small. And no pyrotechnics.

An interesting example of Lipo power is in Rocket Lab's Rutherford engine which flew to orbit recently from NZ. Instead of turbopumps, which in Saturn V famously had more horsepower than a Navy destroyer, they use reportedly 50HP motors driving dual impeller pumps for 8 minutes of powered flight. With multiple units, these numbers are quite similar to our own VTOL requirements.

There is a lot of practical knowledge we can draw from electric cars, the weight of a Tesla S is similar to an M5, performance is similar, range is probably less with electric but not much. The main downside is the time taken to refuel, around 1 hour if you have a 120 amp supply, cost per mile is much less because no fuel tax.

Because engine weight offsets battery weight a practical electric trainer with a decent range looks feasible, longer range the battery weight overhauls the performance. Others have proposed 5x energy efficiency gains, we have not seen this in cars, maybe improved batteries would change the power weight balance.

The next question, is there a manufacturer willing to develope, certify and build such an aircraft that will probably sell at a few dozen each year.

Here's another project:

https://www.stuff.co.nz/technology/1...-in-canterbury

Shows as a registered aircraft, s/n 002 o perhaps there is/was another:

Zephyr Airworks Mule SPA s/n 002 MCTOW 1224kg Aeroplane Air No. 0

FP.

.........."cost per mile is much less because no fuel tax."

Need to be careful with this assumption. When we all go electric, tax will still need to be raised ..........somehow, we just don't know what, how, when?

How are Electric aircraft progressing ?
 

Hi Everyone,

With the recent thread on operating costs of a light single , I was left wondering about how our electric aircraft are developing?

would anyone have any updates to the thread?

I would imaging operating costs to be significantly cheaper (I have been wrong before) when we subtract the fuel , oil , hydraulic and air systems required.

1 or 2 more questions :
how has battery energy density increased since the old lithium based batteries ?
and do you foresee future light aircraft being more of a drone style multi-prop than a regular fixed wing ?

I'm merely curious as to how technology has moved on since we last spoke about this. One or two friends of mine have fully electric cars and would never look back at a 'smoker' car again.

All thoughts and opinions welcome,
Thanks,
Fionn