FES underpowered for 18m ship?

I just had a chat with a fellow pilot whose friend sold his LAK 17b FES because he was disappointed by the ability of the FES to gain altitude. The problem being that when applying sufficient power to gain altitude, the battery would get warm to the point where the controller shuts the motor down. I read recently an accident report tied to the same issue, in that case pilot too low and not in reach of a landing spot (pilot mistake) who counted on FES to regain altitude, but as the battery was too hot it wouldn’t power the motor and the pilot crashed. On the other hand FES works reliably to maintain level flight at a lower power ratio.

Does any LAK 17 or Shark 304 FES (or other glider of similar weight) pilot have any feedback on this? In real life, how much altitude are you able to gain, with fresh and semi full batteries? Is it a matter of being patient and accepting a low rate of climb?

It would be disappointing if when you fly “by the rules� and remain above a landing / outlanding spot until you turn power on, that the FES doesn’t allow to regain altitude, but only to maintain level flight. It changes the flight planning strategy altogether.

I find this surprising and I’ll try to get in touch with the pilot who sold his LAK, but thought I would ask the question in the forum in the meantime.

On Monday, September 14, 2020 at 2:58:08 PM UTC-4, Mana wrote:
It would be disappointing if when you fly “by the rules� and remain above
a landing / outlanding spot until you turn power on, that the FES doesn’t
allow to regain altitude, but only to maintain level flight.
It changes the flight planning strategy altogether.

And it will be dangerous and fool-hardy if you DO NOT always:
- keep a landing spot in easy reach, and
- never engage power until the landing is planned in you're in position.

To quote a recent email I received from LBA/EASA:

....please let us point out that the pilot of a powered glider
shall always have in mind, that it might be necessary to operate
his aircraft as a pure glider. The engine of a powered glider,
predefined by airworthiness requirements JAR/CS-22, does not
meet the same safety standards as a "Part-E" engine of a motorplane.

The flight training for powered gliders shall take into account, that
loss of engine power may occur anytime, and result in a scenario, which is
comparable to a cable break during a winch launch or an aerotow.
This deviation to the operation of a motorplane is reflected in several
paragraphs of the airworthiness requirements JAR/CS-22, applicable for a
powered glider. Examples are the specifications for engines, used for
powered gliders (JAR/CS-22 Subpart H) that are less stringent than those
for powered aircraft (CS-23). Moreover, requirements for software are
not mentioned in the JAR/CS-22 at all - contrary to the specification
for large aeroplanes (CS-25).

On 9/14/20 1:31 PM, Dave Nadler wrote:
On Monday, September 14, 2020 at 2:58:08 PM UTC-4, Mana wrote:
It would be disappointing if when you fly “by the rules� and remain above
a landing / outlanding spot until you turn power on, that the FES doesn’t
allow to regain altitude, but only to maintain level flight.
It changes the flight planning strategy altogether.

And it will be dangerous and fool-hardy if you DO NOT always:
- keep a landing spot in easy reach, and
- never engage power until the landing is planned in you're in position.

To quote a recent email I received from LBA/EASA:

...please let us point out that the pilot of a powered glider
shall always have in mind, that it might be necessary to operate
his aircraft as a pure glider. The engine of a powered glider,
predefined by airworthiness requirements JAR/CS-22, does not
meet the same safety standards as a "Part-E" engine of a motorplane.

The flight training for powered gliders shall take into account, that
loss of engine power may occur anytime, and result in a scenario, which is
comparable to a cable break during a winch launch or an aerotow.
This deviation to the operation of a motorplane is reflected in several
paragraphs of the airworthiness requirements JAR/CS-22, applicable for a
powered glider. Examples are the specifications for engines, used for
powered gliders (JAR/CS-22 Subpart H) that are less stringent than those
for powered aircraft (CS-23). Moreover, requirements for software are
not mentioned in the JAR/CS-22 at all - contrary to the specification
for large aeroplanes (CS-25).


Nice words, but I'm sure many FES pilots aren't going to heed them. If
they think the system is safer, they'll just push the limits that much
further.

From the mini-Lak brochure on lak.it:
"The FES propulsion system has no known reports of in-flight failures,
allowing you to stay confident in areas of no-lift."

We've seen the same mentality displayed in some of the Jeta discussions,
which has a more complex system.

On Monday, September 14, 2020 at 9:32:04 PM UTC-4, kinsell wrote:
From the mini-Lak brochure on lak.it:
"The FES propulsion system has no known reports of in-flight failures,
allowing you to stay confident in areas of no-lift."

That's just Nonsense. I know of an instance where the controller failed while
FES was under power and the engine quit. I hardly hear about all problems,
surely there have been others...

On 9/15/20 6:38 AM, Dave Nadler wrote:
On Monday, September 14, 2020 at 9:32:04 PM UTC-4, kinsell wrote:
From the mini-Lak brochure on lak.it:
"The FES propulsion system has no known reports of in-flight failures,
allowing you to stay confident in areas of no-lift."

That's just Nonsense. I know of an instance where the controller failed while
FES was under power and the engine quit. I hardly hear about all problems,
surely there have been others...


Of course it's nonsense, but if you tell people exactly what they want
to hear, they gobble it up. Red meat for the base.

The Silent 2 that went through the roof in Connecticut made quite a
splash, I'd call that an inflight failure. Apparently if a battery
explodes on landing roll, that doesn't count as "in flight".

People say motors have been around forever, that's true. But inverters
that take high-voltage DC, convert it to three-phase power at over 25KW
using transistors, and doing it with limited space and cooling, well
that's not something you run down to Grainger to pick up.

I'm not familiar with the FES accident referenced by the OP, would like
more data on that.

-Dave

I think something has been lost in translation, but I'm pretty sure you will not shut down from battery heat - my batteries barely change temperature regardless of use, and neither controller nor motor have temperature problems even running through most of the capacity at full power.
What does happen is the voltage quickly drops as used capacity goes up, such that while I can get ~20kW (5kt climb) of power at full charge, at 30% charge remaining I can only get 8kW (1-2kt climb). I haven't discharged below that yet but I understand you reach the point where the voltage doesn't sustain level flight at approximately the same time you reach 0% charge.

The FES is most efficient at low power so it's much better to climb to lowest safe altitude, then go sideways at level flight power. I need about 3.5kW for level flight at 350kg (Diana 2-FES), which with the 5.3kWh batteries seems to get me about 150km. I haven't measured the full climb height at high power, but extrapolating my shorter climbs I think I should get 5000ft before I can only go sideways.
Range/altitude seems to scale linearly with weight if you're at 450kg or 500kg like some of those 18m ships with a heavy pilot, you can calculate the fractions accordingly.

I think you can plan on smaller margins with the FES since the engine-not-running drag is much lower with the FES than a stuck-out pylon. You'll have to make your own decisions of course.

On Monday, September 14, 2020 at 8:58:08 PM UTC+2, Mana wrote:
I just had a chat with a fellow pilot whose friend sold his LAK 17b FES because he was disappointed by the ability of the FES to gain altitude. The problem being that when applying sufficient power to gain altitude, the battery would get warm to the point where the controller shuts the motor down. I read recently an accident report tied to the same issue, in that case pilot too low and not in reach of a landing spot (pilot mistake) who counted on FES to regain altitude, but as the battery was too hot it wouldn’t power the motor and the pilot crashed. On the other hand FES works reliably to maintain level flight at a lower power ratio.

Does any LAK 17 or Shark 304 FES (or other glider of similar weight) pilot have any feedback on this? In real life, how much altitude are you able to gain, with fresh and semi full batteries? Is it a matter of being patient and accepting a low rate of climb?

It would be disappointing if when you fly “by the rules� and remain above a landing / outlanding spot until you turn power on, that the FES doesn’t allow to regain altitude, but only to maintain level flight. It changes the flight planning strategy altogether.

I find this surprising and I’ll try to get in touch with the pilot who sold his LAK, but thought I would ask the question in the forum in the meantime.

Thank you Matthew, this is very interesting data, exactly what I was looking for. :-)

BTW battery low = lower voltage, so for same output power to the motor you need more amps, hence the battery warms faster (P=U*I = R*I*I).

On Monday, September 14, 2020 at 9:31:25 PM UTC+2, wrote:
And it will be dangerous and fool-hardy if you DO NOT always:
- keep a landing spot in easy reach, and
- never engage power until the landing is planned in you're in position.

Agreed, of course! But the whole point of a "turbo" is to be able to regain altitude :-) If FES only allowed level flight, then it may expand the area where you'll find the thermal you need, but since you need to keep a landing spot in reach for the exact reasons you pointed out, level flight only would be very limiting.

It could be that the pilot in question used FES regularly during his flights and found himself with battery low towards the end (vs. only using FES once with a fresh battery in case of trouble)? I asked for his contact data to get real facts vs. speculation and I'll report if I'm able to reach him.

On Monday, September 14, 2020 at 3:52:25 PM UTC-4, Mana wrote:
...the whole point of a "turbo" is to be able to regain altitude :-)

Right, but many have extremely slow climb, especially in high/hot locales.
There electric of course doesn't loose much efficiency,
but batteries/motor may suffer.

Antares at Uvalde required low power settings and could only launch
to low altitude before battery temp hit max.

It could be that the pilot in question used FES regularly
during his flights and found himself with battery low towards the end...
I'll report if I'm able to reach him.

That would be most helpful, Thanks!

PS: Does FES motor ever overheat (again especially in hot locales)??

On Monday, September 14, 2020 at 10:07:18 PM UTC+2, wrote:
On Monday, September 14, 2020 at 3:52:25 PM UTC-4, Mana wrote:
...the whole point of a "turbo" is to be able to regain altitude :-)

Right, but many have extremely slow climb, especially in high/hot locales..
There electric of course doesn't loose much efficiency,
but batteries/motor may suffer.

Antares at Uvalde required low power settings and could only launch
to low altitude before battery temp hit max.
It could be that the pilot in question used FES regularly
during his flights and found himself with battery low towards the end....
I'll report if I'm able to reach him.
That would be most helpful, Thanks!

PS: Does FES motor ever overheat (again especially in hot locales)??

BTW battery low = lower voltage, so for same output power to the motor you need more amps, hence the battery warms faster (P=U*I = R*I*I).
Right, but output power is continually coming down as the voltage comes down as it seems amps stay more or less constant or decrease.
I only have a tenuous understanding of electronics and battery chemistry, but I'm told because the FES uses pouch cells rather than cylindrical cells the internal resistance is much lower, which would explain why the battery doesn't seem to meaningfully heat. I have not seen my batteries get above 25c.

I'll be flying it in Australia later this year so I'll return with my experience on motor temperatures. So far in Europe it seems to plateau around 55c at high power. When I asked Luka about Australia, he seemed to think it wouldn't be an issue and told me there was a very large margin of safety on both the motor and controller temperature. Theoretically if you did manage to overheat it though, you could demagnetize the permanent magnets.

Definitely not underpowered for 18m D2c (400 kg)

I can climb quickly from 200m to 400m (500 - 1200ft) then have
enough left for 75km in stillish air. Low power is more efficient so
if you recognise the day is dying earlier you don’t need to invest
the charge in climbing so range is much better. It will never
match the range of a conventional turbo but will always get you
away from a farmer’s field to an airfield near home.

Once the FES is running you’re still “soaring� to maximise range.
Still playing the same game, making the same decisions, just
have way better L/D.

I have access to both and first choice is the FES every time.



At 19:52 14 September 2020, Mana wrote:
Thank you Matthew, this is very interesting data, exactly what I
was
lookin=
g for. :-)

BTW battery low =3D lower voltage, so for same output power
to the motor
yo=
u need more amps, hence the battery warms faster (P=3DU*I
=3D R*I*I).=20

On Monday, September 14, 2020 at 9:31:25 PM UTC+2,
wrote:
And it will be dangerous and fool-hardy if you DO NOT
always:=20
- keep a landing spot in easy reach, and=20
- never engage power until the landing is planned in you're in
position.=
=20
=20
Agreed, of course! But the whole point of a "turbo" is to be able
to
regain=
altitude :-) If FES only allowed level flight, then it may expand
the
area=
where you'll find the thermal you need, but since you need to
keep a
landi=
ng spot in reach for the exact reasons you pointed out, level
flight only
w=
ould be very limiting.=20
=20
It could be that the pilot in question used FES regularly during
his
flight=
s and found himself with battery low towards the end (vs. only
using FES
on=
ce with a fresh battery in case of trouble)? I asked for his
contact data
t=
o get real facts vs. speculation and I'll report if I'm able to reach
him.