Electric Trainer

[fatmanmedia]

Hi all,

It seems that Pipistrel has done it again, the all-electric trainer, with a flight time of 1 hour (with 30 mins reserve) it could the be future of flight training.

What do people think

More info here

New Electric Trainer from Pipistrel Takes Flight | Flying Magazine (http://www.flyingmag.com/aircraft/new-electric-trainer-pipistrel-takes-flight?cmpid=enews082614&spPodID=030&spMailingID=21345368&spUserID=Nzg3MjM0MjQ5NDMS1&spJobID=381816759&spReportId=MzgxODE2NzU5S0)

[Andrewgr2]

To recharge in an hour would require a recharge rate of the order of 40 kW. Could be quite a challenge to provide power at that rate at the average small airfield. Sounds like cheap (and quiet) flying though.

[Fostex]

Charge time is a major issue in the training environment when one is trying to maximum aircraft usage and essentially 'hot seat' the fleet with little time on the ground. A solution might be user replaceable batteries that could be swapped out but given the regulatory burden associated with that I somehow doubt it!

The other thing to consider is that a substantial proportion of many airfields' revenue is derived from the sail of Avgas and Jet A1. The move to an electric trainer will no doubt hurt that aspect of the aviation ecosystem, albeit not for a long while yet.

[cockney steve]

To recharge in an hour would require a recharge rate of the order of 40 kW. Could be quite a challenge to provide power at that rate

No...It's voltage-dependent.
A car starter-motor can draw a couple of KW for a few moments....but it's normally at 12V........likewise, a welding plant can be fed off a 13-amp socket , but produce ~200 amps welding current.

I don't see a problem with interchangeable battery-packs, it's a whole new ballgame, so presumably the desk-jockeys have a whole new raft of regulations to dream up.

[Pirke]

I have an electric car that charges at 220 volt 16A. I have a dedicated group for it at home, but the car also comes with it's own extension cord for any regular socket. It then charges at 220V 6A or 10A (selectable).

Most indoor hangars have some form of socket available, so charging there for a private owner could be done. But you'll likely get an electrical meter in between so you can pay for the huge power consumption.

Electrical planes are currently best for TMGs, as they shut down the engine anyway. You just lift yourself to altitude, go fly, and when necessary turn it back on.

[Fostex]

Maybe the beginnings of a new sport, flying electric TMG's in thunderstorms with lightning conductors!

1.21 Gigawatts etc etc...

[The Flying Pram]

I'm sorry, but there seems to be some misunderstanding of electrical theory going on here. The website says it has an 85kW (peak?) motor but only a 17 kW hour battery pack - although they call it "Dual Redundant" without specifying what that means. There will always be losses involved when re-charging a battery (particularly at high charge rates), so call it 20 kW hours of power needed for a full charge. The most you can draw from a UK 13 amp socket is about 3 kW - 13 amps x 230 volts = 2990 watts, so you would need a MINIMUM OF 6½ hours if limited to using one of those. To get 20 kWhrs in one hour (never mind less) will require 87 amps, or more than most single phase supplies are fused at... The only realistic way of meeting that sort of demand is from a 3 phase supply, and even then it will still be a significant load for any typical rural flying club scenario.

I note they claim the battery is: "Designed to be quickly replaceable within minutes" which answers one of the questions posed earlier.

They also say: "The WATTsUP is optimized for traffic-pattern operations, where 13% of energy is recuperated on every approach, increasing endurance and at the same time enabling short-field landings" This implies the motor will become a generator during the descent, and is going to be the equivalent of having reverse pitch on a conventional aircraft. Hence the "Short field landings"!!! But this will be a VERY different experience to students than the "glide" performance of the usual spamcan on idle, the engine of which is still producing significant thrust... Even my old flexwing behaved noticeably differently with the engine switched off.

[Andrewgr2]

TFP - thanks for expanding on my post about power. I assumed an average power of around 40 kW from the 85 kW motor (less than 50% power). In practice, I would think the typical Rotax 912 runs at around 60% most of the time so I may have been optimistic.

When I posted, I hadn't seen the battery size. I can't see how 17 kWh could possibly give 1.5 hours from an 85 kW motor. That implies an average power of only 13% or about 11 kW. 11 kW is just about enough to sustain a single seat glider. I can't see it driving a 2 seat trainer round circuits!

[The Flying Pram]

Andrewgr2 - I wondered that as well! Maybe the "Redundancy" means it carries TWO 17kWh batteries? If so then you can double my "time to recharge" calculations! I assume they only run at full power to reach circuit height (1000fpm was mentioned), and then cut right back. Obviously it is a slippery machine, but even so... That being the case it may actually NEED reverse thrust to get back down!

No instructor is going to venture far from the airfield with only 90 minutes (tops) endurance, and what's the betting that we would soon see one declaring a "low fuel emergency" in order to jump the circuit queue, and get down before it all goes quiet? If it was to be used at a fairly quiet airfield with only one or two other aircraft around, AND there was a stock of batteries available for quick turnarounds, it might make sense for teaching basic handling, but there is still the need for "differences" tuition before letting students loose on the rest of the fleet.

And let's not forget that Lithium batteries have very specific charging requirements - overdo it and they have a tendency to catch fire...

[Mark 1]

The best EV battery packs currently are about 6kg/KWh (includin BMS, cooling, enclosure etc), so that would suggest about 100kg for the 17KWhs quoted, so I doubt that it would have a spare for redundancy as it's a low failure risk anyway.

I would guess that the duty cycle they are proposing would be a 1 minute climb to pattern altitude at full power, 2 minutes downwind at say 25HP and 60 knots and a re-gen glide through base and final which would salvage enough energy for the subsequent ground maneuvering, so that's about 2KWhs per circuit.

Even at that the battery would be down to minimum after about 8 circuits.

It would be helpful if they would give more practical examples of different mission profiles, but it looks like the needle would be on empty after about 60NM unless I'm missing something.

There's a good technical paper (http://en.sv-jme.eu/data/upload/2011/12/02_2011_212_Tomazic_04.pdf) about the Taurus G4 that won the Electric Flight Challenge that probably has a lot in common with the technology in the WattsUP, though that carried 90KWhs of charge.

[9 lives]

This certainly has traction as a way of the future. Not the only way, but an important one none the less. Yes, new certification standards will be needed, but it's going to be worth the trouble. It'll be pretty important that pilots and owners to be, make their interest in this new technology known to the CAA, FAA, and other authorities. They need a push to embrace this worthwhile technology - and certify it.

[AdamFrisch]

Good link, Mark. BTW, you back in CA with the RV?

In the facts section in the Mark's link, you can see it it needs 32kW to power the Taurus to 100mph. The Taurus was a 4 seater. That’s 8kW/person or 103lbs/kW. It’s not inconceivable then that 17kW is enough to keep this new little thing flying for that long if it only needs 8kW/person. Throttle back a little to maybe 6kW and it’ll go about 1.5hrs.

Electric motors have linear power output, which recip engines do not. Therefore they can run at a lot less percentage of max power and still produce thrust, which an IC engine can’t. A gas engine is actually only fully semi-efficient from a power-to-weight point of view at absolute max power. Anything else and you’re carrying a lot of dead weight around. Not so with electric motors – they’re as efficient at 1rpm as at 10000rpm. This is actually what makes electric hybrid propulsion not as bad an idea as people think for aviation. It is much better to have a smaller IC or turbine engine running a generator at max power continuously, then lug around a bigger one that you use variably. Have electric motors be the prime mover and variable power unit, not the IC.

In aviation we rarely cruise below 55% of rated power at altitude. Maybe 45% at very long range cruise settings. That's because of two reasons: the IC engine loses steam up there, so the 55% could be close to wide open throttle at altitude. Electric doesn’t have that problem, so as air resistance goes down, you can reduce your power output considerably at altitude. The second reason is of what I described above. When aviation moves towards electric propulsion, you’ll probably see long range cruising power settings of 20-30%, which would be the equiv of 45-55% in an IC engine. I personally can’t wait. I’m done with the IC engine. Such a pain in the a*se that thing.

[Pirke]

Electric engines are not as efficient at 1 rpm as at 10000.

My Chevrolet Volt has 2 electrical engines. 1 150hp main engine and a smaller +/- 70hp (can't remember) second engine. When the battery is empty the 3rd engine (combustion) uses the 2nd engine as a power generator, charging the battery while you keep driving on the first main engine.

When the battery is full only the first engine is used, except when you go faster than +/- 100km/h. The main engine looses efficiency at higher rpm so they throttle the main engine back and use the second engine as well to provide trust. They say this gives a 15% efficiency boost.

[Andrewgr2]

I don't think the efficiency of the electric motor is the issue here. The article about the Taurus G4 mentions that cruise power is around 1/5 of take off power - so would be about 17 kW for the Pipistrelle if that was similar. However, average power has to be less because the trainer needs a reserve in its 17 kWh battery after an hour's flight. The G4 had to fly fast for the challenge but the Pipistrelle doesn't as a trainer. I think two issues are -

1. What can realistically be achieved using the 17 kWh battery in an hour's flight whilst retaining a 30 minute reserve? I suspect less than a 152 with a tank of fuel.

And

2. How do you put around 12 kWh of charge back into the battery in an hour? From a 230 volt ( European) supply you need 50 amps and from a US 110 volt supply, 100 amps assuming negligible losses. Those sorts of supplies will need to be specially provided. A flying school with several planes would need proportionally more. The literature does say that the batteries are quickly replaceable, so maybe the solution is to have multiple batteries charging more slowly but battery packs won't be cheap.

Difficult to see how this technology can be developed for a tourer where you can 'recharge' with enough Avgas for, say, 4 hours flight in 5 minutes...

[abgd]

One solution would be simply not to use a 13A plug. Sockets e.g. for machine tools often have much higher current ratings and it often wouldn't be exorbitant to install them if the existing wiring is up to the job.

You could also install packs of cheaper lead-acid batteries on constant charge (or overnight when energy is cheaper) that you could then use to provide extra power for quick top-ups.

[fatmanmedia]

first flight and a expected price tag of under 100,000 Euros, deliveries next year and is already certified in France.

i see this being the future of training.

Pipistrel?s new electric trainer makes first flight ? General Aviation News (http://generalaviationnews.com/2014/09/02/pipistrels-new-electric-trainer-makes-first-flight/)

Fats

[Balazs91]

It'd be the perfect Cessna 150 alternative for short flights. Does anybody know that we can use WattsUp for hour building towards the CPL requirements? If yes, it's gonna be a big market changer.

[ChrisVJ]

North American supply is 220V. Plus 110v and Minus 110v but both are supplied and divided at the distribution box. Circuits are commonly 15a, 20a and 30a (eg stove and tumble drier.)

There's no problem providing 60a or 100a if you want. Both breakers and cable are commonly available.

[skyhighfallguy]

Will this encourage thunderstorm flying in order to get a free re charge via lightning bolt

(and yes, I am kidding).

Hope there is a fire extinguisher system for a battery fire.

[Big Pistons Forever]

Maybe in EASA land but in North America I can see it now.

" Sorry son you don't have enough recip time to be considered for the job" :rolleyes:

[ChickenHouse]

With all this fuzz around "e" Mobility, I wonder what we will do with all that waste from batteries. After all, mobility started electric and there was a reason why batteries were abandoned a solution, although the mobility needs at first place were quite low - even lower in comparison to todays world.

[abgd]

I believe they're very recyclable.