Electric power

[Spin]

Extract from the latest RVator, the Vans aircraft online magazine. Dick Van Gruesen is known as one of the thinkers and straight shooters of the homebuilt aircraft design fraternity and I found it interesting and a little disappointing to read that in the case of electric power for aircraft, as with so many other emerging technologies, promises seem to have run well out ahead of delivery. Maybe I'll have to wait a little longer before adding an "elec" endosement........

 

"A year ago, following AirVenture 2009, I wrote an

 

article on electric powered airplanes from my perspective

 

as an owner/operator of one. I compared and contrasted

 

my actual electric aircraft operating experience

 

with the reports and projects being published. Since

 

then, the “press release” news has continued, and I

 

have continued operating my electric self-launch

 

Antares 20e sailplane. Since June of 2009, I have

 

logged over 400 hours of flight time. Just 15 hours of

 

this was “under power”, usually five or ten minutes at a

 

time. This practical application experience has put me

 

in a different position than most people writing or talking

 

about electric airplanes.

 

In our field of interest and endeavor, the calendar

 

year runs from “Oshkosh to Oshkosh”. This year, again,

 

there were a lot of talks and programs about electric

 

airplanes, but not much action.

 

Yuneec had another very interesting POC airplane

 

on display. With a low wing and fixed tractor powerplant,

 

it would normally be classed as a motorglider. It

 

featured a single retractable landing gear and a folding

 

prop to minimizing drag for soaring rather than motor

 

flight. It really looks more like a self-launch sailplane

 

than a general purpose sportplane or motorglider. I

 

don’t mean this to be a bad thing, but rather a concession

 

to the realization that electric technology is not

 

ready for prime time GA; certainly not ready to power

 

an airplane like the Cessna 150 or Katana. Neither of

 

the Yuneec airplanes flew at Oshkosh this year. I

 

heard that they had a system failure of some sort which

 

prevented them from being able to fly.

 

One of the leaders in electric airplanes has been

 

Randal Fishman with his ‘Electraflyer’ aircraft. Starting

 

with a weightshift trike several years ago, he advanced

 

to the Electraflyer C — an electric motor powered Moni

 

airplane in which he flew demonstrations at Oshkosh

 

and Lakeland for a couple of years. He had a very nice

 

looking Electraflyer-X prototype on display at Airventure

 

2009 but hadn’t flown it by Sun’N’Fun 2010, where it

 

was on static display . I did not see or hear of it at Oshkosh

 

this year, so don’t know what its current (pun intended)

 

status is. The last entry on his website is dated

 

July 2009.

 

My friend Dave Nadler had his Antares electric sailplane

 

on display at Oshkosh again this year and performed

 

flight demonstrations during the airshow on two

 

days. I’m not aware of any other electric airplane flying

 

there this year, so the Antares sailplane still appears to

 

be the industry leader. There are about fifty of them

 

operating worldwide in the hands of private owners.

 

Some have been in operation for five years or more.

 

This would indicate that their system obviously works

 

well, demonstrating that they have achieved a good

 

level of operational reliability.

 

Interestingly, the Antares does not get much attention

 

from the aviation press, probably because it is a

 

single seat, special purpose, quite expensive airplane.

 

Why can’t the Antares electric motor system, or a similar

 

level of technology be incorporated into a more general

 

purpose airplane like the Yuneec or Electraflyer?

 

It probably can, but I assume that these folks are

 

working through the teething problems that the Antares

 

people struggled with 10 years ago. It’s also possible

 

that the folks at Yuneec, et al, are trying to develop a

 

more affordable package, and thus not able or willing to

 

“buy” the expensive components that have contributed

 

to the success level that the Antares has demonstrated.

 

Since the aviation press is not yet able to treat us

 

to pilot reports of operating electric aircraft, here’s a few

 

words about my experience.

 

According to the factory information, the Antares

 

has enough battery power to climb to approximately

 

9000 ft. at my normal operating weight. I have never

 

verified this, and do not feel that it could be done in a

 

single “open the tap and go” motor run. My experiencehas been that the indicated battery power starts to drop

 

more rapidly after about 3000 ft. of climb. Normally, the

 

motor is stopped and retracted at about this time; the

 

start of a soaring (or gliding?) flight. After a few minutes

 

following motor shut-down, the battery power indication

 

will rebound by 10-15%. I have also found that

 

by reducing the power to just enough to sustain level

 

flight (about 25% output), the battery power will rebound

 

somewhat and then drop slowly, commensurate

 

with the low draw.

 

It would seem that the batteries need to be “rested”

 

periodically to re-balance themselves, either by shutting

 

them off or operating them at a much lower continuous

 

power draw like the “low cruise” mode.

 

On an ideal flight, I would launch, using battery

 

power to take off, and contact a thermal within a mile or

 

so of the departure end of the runway. I would center

 

the thermal, reduce power to 50% or less and establish

 

that a positive climb rate is probable with no power. At

 

that point, somewhere between 1500 and 2000 ft. altitude,

 

I would stop the motor and retract motor pylon.

 

The high-performance airplane would continue to climb

 

and soar for hours without need to use motor to remain

 

aloft. Total battery use would be 10-15%.

 

A sample flight for a “poor” soaring day might be:

 

Take-off and climb at about 80% power to 3,000 ft., at

 

which time the power meter will be indicating about

 

60% or less. After turning the motor off and retracting

 

it, the power level will rebound to about 70%.

 

At a later point in the flight, I might find myself running

 

out of thermals, altitude, and ideas. I extend the

 

motor and climb about 1500 ft. in the process of getting

 

to another thermal (or getting enough altitude to glide

 

back home). In the process, the power meter may

 

drop to around 35-40% and then rebound to about 50%

 

as the batteries re-balance themselves. Tallying up, I

 

would have climbed a combined total of 4500”: half of

 

the specified performance capability, and used about

 

half of the battery energy. My real world experience

 

has basically validated factory claims.

 

In the real world, I am rarely climbing in stable air.

 

While climbing in sinking air, often unavoidable while

 

trying to reach the area of the “house thermal” energy

 

goes away quickly as the altimeter slowly winds upward.

 

The reverse is true when the thermal gods smile

 

on me, so the above examples are based on averages.

 

During a long soaring flight, the flight instrumentation

 

and radio will use about 2-4% of the battery energy,

 

not enough to seriously deplete the energy available

 

for a “save” if needed.

 

Another characteristic of my system is that the motor

 

should not be operated at high power (high battery

 

discharge) when any of the battery temperatures are

 

below 20 deg. C. When soaring at higher altitudes (low

 

outside temps.), the battery temps can easily drop below

 

20 deg. C. To assure that the motor can be used if

 

needed, there is a built-in battery heating system. The

 

batteries draw from their own energy to heat themselves.

 

This obviously reduces the available energy by

 

a small amount. Normally, I do not activate the battery

 

heater unless the flight is not going well and I feel that I

 

may need to use the motor in the next 5 minutes or so.

 

I do not waste energy keeping the batteries warm during

 

an entire flight.

 

If I should be distracted with the challenge of soaring

 

flight and overlooked heating the batteries, I can still

 

run the motor at low power (level flight or slight climb)

 

while the batteries are heating. The problem is that

 

cold batteries do not deliver energy well and may be

 

damaged by attempting to draw high output when cold.

 

This is true for other common type batteries as well.

 

This is why your car may not crank well, or at all, in

 

really cold conditions.

 

Most of the general purpose electric sportplanes being

 

developed or proposed quote flight duration available

 

from their batteries. Its safe to assume that these

 

flight times are based on low power settings and

 

“economy cruise/ loiter” speeds. However, unless one

 

is to cruise at an altitude of 10 ft., a fair amount of energy

 

is needed to reach even a modest cruise altitude.

 

In the case of my Antares, normal climb rate of 5-6

 

hundred fpm requires a power draw about 4 times that

 

of level flight. So, a large percentage of the available

 

energy is used just getting to altitude. I suppose that at

 

the end of the flight, gliding back down to landing with

 

the motor throttled or shut off, some of this can be offset.

 

Still, it’s a factor to consider, as would be traffic

 

pattern delays at the end of a flight.

 

The bottom line is that, from my experience, electric

 

aircraft operation is not necessarily as “plug-and-play”

 

as some advocates would like you to believe. In some

 

respects, it is. For instance, operating the motor is as

 

simple as pushing a lever forward----the equivalent of

 

ignition, primer, starter, throttle, mixture control, etc., all

 

in one operation. On the other hand, there are concerns

 

such as the limited energy (range) available, and

 

the battery temperature issue. We can continue to

 

hope for breakthroughs to alleviate these concerns, but

 

in reality we probably must not expect more than incremental

 

gains in the near future."

 

 

[Gnarly Gnu]

Electric motor powered aircraft are 100% viable, it's the extension lead that is the killa......

 

 

[facthunter]

extension lead.

 

Especially with aerobatics. Adds a new meaning to getting involved with powerlines. New form of flying. I could become absolutely wrapped in it... Nev

 

 

[Methusala]

Battery power assisted flight.

 

G,day All, Interesting read! Mate and I are building a Mike Sandelan GOAT4 ulrtralight

 

primary glider. Launch means are under consideration and we are quite interested in the developing model a/c technologies which utilise Li/Po energised "outrunner" motors. The

 

most powerful example to date is eqivalent to a 20 h/p 2 stroke! This weighs around 2.5kg and with enough battery capacity to run for around 15 minutes will only weigh twice this.Of course the mission will be similar to that described in the foregoing article,

 

not a cruising sport plane. This type of power unit would have been unthinkable not many years ago. Let the march of development proceed apace. Regards, Don

 

 

[Guest disperse]

I'm of the belief that electric powered vehicles including planes. Is just waiting for either the right storage system (battery) or the right production ie: Hydrogen cells and the like.

 

 

[Methusala]

Saw a piece on ABC - may have been Catalyst, that talked about using nano-tech to create capacitors that used much less mass to store electricity and could be charged quickly at high rates. This is the type of advance that will unlock potential in electric flight.

 

 

[Gnarly Gnu]

'Super caps' (very high value capacitors) are a fantastic advance but one problem is that unlike a battery a capacitors voltage decreases at a linear rate during discharge. They are a great addition to supplement battery power to assist with periods of high current draw for example but using capacitors for power alone? I suggest not anytime real soon. Been wrong before of course....:)