
Sun Flyer, an Electric Trainer Aircraft - sohkamyung
http://spectrum.ieee.org/aerospace/aviation/cheaper-lighter-quieter-the-electrification-of-flight-is-at-hand
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dsfyu404ed
>its high torque, available over a magnificently wide band of motor speeds

A broad torque curve isn't really useful since aircraft engines are already
optimized for sustained operation at cruising speed and the range of speeds
you can operate at is limited by the propeller and physics. There's no need to
have a ton of torque at 1800rpm and at 6000rpm

>At 20 kilograms (45 pounds), the motor can be held in two hands, and it
measures only 10 centimeters deep and 30 cm in diameter

And what's the horsepower rating and duty cycle rating on this motor? Power
density is not an area where electric motors have a large advantage over ICE
unless you're trying to build a cylindrical package. The article talks about
doing away with durability requirements that impede a lightweight design.

>with no power-sapping transmission

Most small aircraft are direct drive.

Electric power certainly has advantages but this article may as well be a
marketing brochure full of fluff.

~~~
blktiger
The weight of the electric motors is definitely a lot less, but what most
people don't think about is that the main weight of an electric airplane is in
the batteries. The battery pack in a Tesla Model S is ~1300 lbs. The batteries
required for an aircraft to have an hour long flight time still add too much
weight. Batteries have gotten light enough to make it feasible, but we still
need major advances in energy density to make electric airplanes make a lot of
sense.

~~~
sokoloff
Petro-fueled airplanes also have the advantage that they can be flown lighter
for short trips, trading off either performance and/or cabin load for fuel
load. They also land shorter (by virtue of being lighter) at the end of
typical flights.

Battery airplanes that carry the full weight of the batteries all the time
have worst-case takeoff, climb, and landing performance on all flights.

It's easy to notice even 100 pounds difference in loading on light airplanes.
That's a little under 17 gallons of avgas or about 90 minutes' fuel burn for a
typical trainer.

If I want to take 2 extra 175# adults on a local flight, I can just leave off
60 gallons of fuel and have the same performance for a short flight.

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HNaTTY
One thing that always bothered me about airplanes is the energy used to take
off. On aircraft carriers, they use a launch device, allowing the airplane to
"push off" against the carrier. Compare this to airplanes taking off on land,
they just nail the throttle and take off by pushing air...

A land-based launch system would have a lot of advantages; lower peak power
would be needed from the motor and batteries, the engines could be made
smaller, the energy used to take off doesn't have to be stored on the plane,
everything gets lighter and more efficient.

~~~
justadeveloper2
Catapults don't save energy--they shorten runway. The jet is at full throttle
on takeoff and military aircraft are not exactly fuel misers.

~~~
ndespres
Sure, they don't save energy in the sense that the laws of physics must still
be obeyed- but by using the power of the catapult to increase the plane's
velocity at takeoff, the motor can be optimized for flight rather than takeoff
and less battery weight needs to be carried.

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pdelbarba
For the record, this is not new. Pipistrel has had a relatively successful
electric trainer for a couple years now based on one of their popular LSA
airframes. The only catch is that at this time I don't believe it has yet
achieved FAA certification in the states.

Flight instruction is currently about $100-120/hr for aircraft rental and
$40/hr for the instructor (not paid if you are soloing). This would likely
halve the rate for the aircraft as fuel is currently averaging about
$4.50/gallon and a C172 burns on the order of 6-8 gallons/hour and requires
more maintenance. Insurance on electric aircraft will likely be cheaper too
given the lower mechanical complexity, though this has yet to be seen.

~~~
blktiger
Fuel ends up being about $50 an hour (depending on the price of fuel, but most
C172 trainers burn close to 11 gal/h). While an electric trainer would save
almost all of that money in fuel costs, most FBOs don't pay for a _new_ C172
they but one of the thousands of used ones. Buying a new electric trainer
would be quite a bit more expensive than a used C172 and I'm sure that would
change their rental rates for the aircraft. I think it's likely to offset the
cost savings you'd get otherwise. Then again, maybe with the additional
reduction in maintenance costs it might end up a bit cheaper to fly.

~~~
pdelbarba
I actually just emailed sunflyer about pricing since that's the biggest factor
initially. I will update if they get back to me. I suspect that they'll be
relatively inexpensive compared to a new C172SP @ around $330,000. Maintenance
is the biggest difference IMO. Aircraft ICEs burn through oil and parts like
nobody's business and only last ~2000hrs before they need a $20+k overhaul.
The motors should last the life of the airframe, but this will be offset by
battery degradation. By the time these need battery replacement, it could be
quite cheap though.

~~~
microcolonel
> Aircraft ICEs burn through oil and parts like nobody's business

Yikes, trainers don't have turboprops yet? I get that the initial cost would
be higher (though not that much, I would think), but _engine on time_ is the
commodity that training airfields sell, it seems ludicrous that they would
accept the piston tax.

~~~
pdelbarba
A 550hp PT6 turboshaft engine (pretty much the smallest one you'll see in use)
is around $300k new. OEM pricing on an IO-360 180hp piston engine is about
$30k. Turbocharged engines in the same hp range as the PT6 can be had for
around $100k.

The dirty secret they don't tell you is that turboprop's have miserable
efficiency. A 1950's era carborated piston will outperform them every time in
terms of fuel economy. The Cessna caravan or Pilatus PC12 will burn on the
order of 50gal/hr of jet fuel at cruise and as turbine engines get smaller,
they lose further efficiency.

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god_bless_texas
Please someone invent better batteries that can be mass produced. My drone, my
airplane, my car and my phone desire you!

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awongh
does anyone know the viability of hydrogen fuel cell electric motor airplanes?
It seems like this is a more logical step, since from what I've read the
energy density of batteries really isn't optimal for something like an
airplane, even with technologies projected to come to market in the next
couple of decades. And the whole thing still has the possibility of being
zero-emissions.

~~~
audunw
> And the whole thing still has the possibility of being zero-emissions.

Well, so does a hybrid plane, if it's fueled with biofuels. Zero net CO2
emissions anyway. I would imagine other emissions are less problematic since
it happens far away from populated areas.

I'm not sure why hydrogen is desirable. Hydrocarbons have higher energy
density and is easier to store and fuel.

I can imagine that the closed loop of H2O + electricity <-> electricity + H2 +
O is more efficient than the hydrocarbon equivalent. But neither technology is
near their theoretical limits, so it's a bit hard to say yet.

Regardless, if we build hybrid planes, we can use whatever technology makes
the most sense. It shouldn't be too hard to swap out the energy storage
mechanism. Who knows, maybe we'll invent a good rechargeable aluminum-air
battery and replace everything with that.

~~~
awongh
why does bio-fuel mean net zero emissions? I assume you're talking about bio-
disel or ethanol? Don't both of these still produce cO2 when you burn them?

But if you're producing the hydrogen with zero emissions, then it's a 100% cO2
free process, isn't it?

~~~
eru
When a tree makes wood, it takes CO2 out of the atmosphere. When you burn the
wood, you release exactly that carbon.

Similar for making ethanol.

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ph0rque
Is there any way to do the analogous of regenerative braking on the descent in
an electric airplane?

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thearn4
I think the issue is that by the time you are on descent, the flight is
nearing an end, so the benefits for range extension aren't great.

~~~
pdelbarba
In this case, the students will likely be doing pattern work in these aircraft
which involves repeated takeoff and tochdown. In particular they will often do
a touch-and-go where the aircraft maintains forward speed and takes off again.
In this case, the regeneration should allow one extra circuit for every ten or
so circuits.

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purpleidea
I didn't read the whole article, but if they even mentioned how long it will
fly for, they sure hid that carefully. Stop wasting my time until you have a
decent product!

~~~
aphextron
3 hours of flight time is more than adequate for training purposes. Not only
is it a huge win for fuel savings, but safety is the number one reason I can
see primary trainers going 100% electric over the next decade. Learning to
deal with the intricacies of an ICE across the full range of flight conditions
is half your training time wasted, and the myriad of things that can go wrong
simply wont exist anymore.

~~~
gruturo
Unfortunately that defeats the purpose of a trainer, because "real" planes,
which the trainer is supposed to prepare you for, won't be electric for quite
a bit, so you _do_ need to learn all about the intricacies and issues which
can crop up on those planes.

Even assuming a rather speedy pace of improvement in battery tech, the
power/weight ratio won't be there for quite a while. Batteries also don't get
lighter as their energy is consumed, like fuel does, and many planes cannot
even land with the same weight they are allowed to take off with.

~~~
grecy
Of course, this means a student can start in this electric trainer, and focus
on learning the _flying_ right off the bat.

When a student has that down, they can graduate up to a trainer with an ICE,
and then learn all of that stuff.

Exactly like learning to drive a car in an automatic first, then once you have
the actual vehicle control/traffic/etc down, you graduate up to a stick shift.

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rowyourboat
Except that in countries where stick shift dominates, you start off learning
to drive a stick right away.

~~~
mrob
Unlike airplanes, cars have no stall speed. You first lesson involves driving
at very low speeds, away from traffic. If you have any trouble shifting you
can just stop. Airplanes are less forgiving.

~~~
pdelbarba
Electric vs ICE trainers won't have much in the way of differences. The main
procedural differences will be engine start (just follow the checklist) and
low power conditions where carb heat is required (becoming slightly less
common now that fuel injection is available and relatively cheap). The most
common trainer is the C172 which is high wing and therefore doesn't need an
electric fuel pump or tank switching so that's about it.

