On the electric Cri Cri one could say that the throttle was a bit like a dimmer switch. If the throttle was past the detent the motor did nothing drew no power and the props did not turn.
Throttling back to the detent the props had an inertia of about a turn before stopping. I doubt if this would have put any significant energy back into the batteries.
With the size of the props on the cri cri it would have taken a significant amount of wind to charge the batteries, but I don’t think regenerative braking or wind energy was part of the experiment.
What it means is that the motor uses zero power when the throttle is at the detente position. However, creeping it forward a fraction would enable the props to move, and would creep the aircraft forward and so would need to be held against the brakes. As far as I remember there wad no negative position on the throttle which would turn the motor backwards which might act as a brake, but any regenerative energy that could be produced by turning the motor backwards would be cancelled out by the power needed to turn the motor.
But the electric cri cri had one advantage over the jet version and that was that you could drive the electric version to the threshold and still get a decent time in the air.
With the jet version or versions, if the aircraft taxied to the threshold under its own steam, there would be very little fuel remaining for fun in the air.
“At standstill and the prop lever at zero, the prop will stand. It will stand because there are no air flow to move it and produce negative torque.”
I am stationary with a 25 knot tailwind, waiting for clearance to enter runway, turning into wind. No problem with piston engine.
Will the prop turn in reverse? What will be the load to start it turning in correct sense?
The eFlyer. 3 hours endurance.
I thought is already was in production, but that’s obviously a year or two into the future.
A year or two, or perhaps twenty years in the future because the battery supplier (of some fantasy battery that will give three hours endurance at whatever size/weight they need) is “to be announced” according to the website.
It’s always the same story. The aircraft is always great, assuming a battery that does not exist and will not exist any time soon.
Mind you 3 h with no reserve @73 kt which probably corresponds to some <40% power in that sleek airframe…
However 220 NM with VFR reserves would indeed be a milestone. Would…
Just a thought experiment.
Is 3 hrs endurance possible to do with existing and available technology?
Let’s take some data from a PA28 with a Lycoming O-320 engine. We remove the engine (assuming 125 kg) and the 182 liters of fuel (assuming 130 kg). In total, we remove 255 kg which we use for electric motor(s) and batteries, etc.
Obviously, using just one motor is more efficient than multiple, however, I’ve quickly found some data on a “small” motor (https://mad-motor.com/product/mad-m50c35/) which generates 91 kg of maximum thrust at 100 V and 217 A. Assume we use three of those motors. The motor weighs less than 5 kg including ESC, which means that 240 kg would be left for batteries. The propeller obviously needs to be another one to optimize for cruising, so I can’t tell what implications this has…
Found some data on the O-320 engine and static thrust (https://www.atlantis-press.com/article/2629.pdf) on a Cessna 172. At 2700 rpm, it seems to generate a static thrust of around 210 kg, so three electric motors should be well over that number for taking off. At 2200 rpm the O-320 seems to generate a thrust of around 150 kg.
Three of the electric motors seem to generate around the same thrust at 60 A.
Let’s assume we use the Samsung 25R 18650 (2500 mAh), where each cell weighs 45 g, let’s assume 0,05 kg including BMS, wiring, etc. 240 kg then translates to 4,800 cells.
We need to connect these cells in series of 24 to achieve around 100 V, meaning we could have 200 cells in parallel, having 500 Ah available, or say 400 Ah with some reserve on the cells.
Just considering cruising using 150 kg thrust, we use 60 A x 3 = 180 A per hour, then we would have more than 2 hours of endurance without any reserves.
If we are happy with less thrust, using just one motor (more efficient) and an airframe with better aerodynamics, 3 hours without reserves shouldn’t be impossible with existing battery technology…?
There are of course many assumptions here, and some of them are probably incorrect. Also, some practical issues come along where to fit the motor(s) and batteries to ensure correct weight and balance, redundancy, etc.
Graham wrote:
The aircraft is always great, assuming a battery that does not exist
We should go and offer a fusion-driven aircraft, pocket size of course. Just to demonstrate the stupidity of such offers.
Magnus wrote:
Is 3 hrs endurance possible to do with existing and available technology?
It should be. There are Microlights flying with one hour of endurance. So this should in fact be possible with a good load hoaler, preferably. But who wants to certificate this? Making a sleek airframe seems way easier than the certification process, so you’ll end up with the way that you present a new and sleek airframe and head along certification.
Or you skip certification and go microlight. This is where development takes place, until something really reliable is found which is worth enough to throw the money at to get a certification for that.
Rumours tell that certification process of a new (or modified) engine takes about 10 years. Electrical engines are very reliable, probably the most reliable of all engine types. But batteries are not yet.
ULM and experimental is certainly where innovation, design and developement takes place. Its a shame that European regulatory bodies can not keep pace with the speed of developement.
UdoR wrote:
There are Microlights flying with one hour of endurance.
I think we already did this.
An electric ultralight-type aircraft can be made to ‘work’, insofar as the Pipistrel can carry two people for ~50 mins, which is conceivably enough for circuit training, general handling and short-range sightseeing. The major disadvantage to making a commercial operation out of it is that charging is slow and batteries are not swappable, so to keep your training operation moving you need a sizeable fleet of them and when your operation is running at capacity each aircraft spends the majority of its time plugged in and charging. Indeed, Pipistrel’s own marketing material suggests you overcome the long-time-on-ground issue by purchasing more of them. Quite some time ago Southwest and Ryanair demonstrated to us that you make money with aircraft by keeping them in the air.
The sub-600kg class just about works because when you remove the internal combustion engine you remove a significant proportion of the overall weight and make it available for batteries. I always take my PA17 as a case in point – if I remove the C90 engine (~90kg with oil) then I am removing 90kg / 521kg = 17.2% of the MTOW.
In the one-ton four-seater class it doesn’t stack up so well. Switch to the TB10 and removing the 0-360 frees up 125kg / 1150kg = 10.8% of the MTOW.
Thus in the larger aircraft you have a lesser proportion of the total weight available for batteries, as well as needing more power than the ultralight. This takes any design based on current battery technology down from 50 minutes endurance (which some are just about able to argue makes a viable two-seater) to under 30 minutes endurance, which no-one will argue makes for a viable four-seater.
Some of the marketing hype borders on assume a can opener. The other day I saw an EV advert which mentioned how quickly (five minutes) you could put 30 miles worth of charge into the car if you were in a hurry. Very small print at the bottom of the screen said that achieving that required 85kW charging.
It’s all purely a question of the energy density of the fuel that a vehicle needs to carry. This principle has not changed since steam locomotives ran into maximum practical sizes because of the amount of coal and water they needed to haul about.
Let’s see. My Comanche has an IO-540, which brings in about 200 kg (425 lbs according to google’s wisdom). Empty mass is 900 kg, so removing the engine (200/900) reduces mass by 22%. Mass without engine (but WITH propeller and IFR avionics and everything) would be 700 kg, MTOW is just below 1600 kg, there is an STC around to increase another 100 kg when installing the tip tanks. So useful load without engine could be 900 kg, or even 1000 kg when installing tip tanks (sounds funny, but hey why not put batteries there…).
Now say I want to have a payload of 250kg (which is FULL FUEL payload, and thus not bad when comparing to real world numbers) so I can install up to 750 kg of stuff. The engine with all related electronics should not weight more than 100 kg. Leaving 650 kg for batteries.
If I went for a minimum of 100kg payload, I could install 700 (or 800) kg of batteries.
One could think about installing some of the batteries in the wings and some in the cabin to be removed if higher payload is desired.
Now…that’s not too bad isn’t it? @Magnus what about this as a platform? That’s three times the numbers you gave.
The Comanche can safely be run with 180hp (which has been proven, as older Comanches with same airframe were running on the 180hp engine) (but more thrust is always welcome) and electrically driven the power stays constant in all altitudes.
Although the Comanche can be flown with the static thrust numbers @Magnus gave for the 172, it’ll not cruise that fast, maybe 100 KIAS. The same kWh/nm is achieved with higher speed settings (as angle of attack is better and lower drag is obtained).
So a rough estimation sounds like some 5 hours of endurance could be achieved flying about 130 KIAS (which should be independent of altitude, so a flight in the low flight levels would be reasonably possible).
That should result in a significant range and practicability…
(maybe a hybrid installation using hydrogen and a fuel cell type generator would be the more efficient way for this, but then again the gas bottle for storing hydrogen will be way out of payload…just another assumption)
