Advice on motor glider wanted - FES - Jet - Engine

I believe the logic is that it is
better to destroy the batteries or motor should the pilot feel that
shutting down will cause a desperate situation.

Hi Eric,

You're right, a quick read of the manual suggests the FES will step through alerts and warnings but it's ultimately the pilot that decides when to shut down. In the case of battery temperatu
- "Batt. Ext. High 55°C, Stop FES motor!" (red), &
- "Batt. Critical 75°C, Land immediately!" (red)
The latter suggesting a thermal runaway and/or fire is imminent.

CJ

Hi all

The new proposed electric 20m Mini Stemme looks an exiting prospect

http://www.rs-uas.com/products/sk10e-elfin/preface/

Muttley

I believe that any emergency system designed to protect equipment should
have a manual override capability. Think of that Airbus flying happily
into the trees while the pilot struggled unsuccessfully to pull up.

Though I have a highly reliable engine in my Stemme, I never fly outside
of gliding distance of a suitable runway. Of course, this limits my
flying in the great southwest somewhat but, having no trailer, there are
plenty of places I could land safely but would not like to take off from.

On 1/7/2017 8:54 PM, wrote:
We had a member place a similar level of faith in his FES to that shown above, using it to climb away from unlandable terrain. The system powered up and climbed away as advertised - initially. During the climb, the battery overheated and the FES shutdown, as it's designed to do, to protect the battery and ultimately, the aircraft. The pilot was now at moderately low altitude and presented with an unexpected outlanding (startle factor) over terrain that hadn't been assessed for such (complacency / over reliance on FES). A successful outlanding was achieved in that the pilot walked away unharmed. The glider was extensively damaged.

My personal opinion is that electric sustainers are the future and in time, will be the hands down winner when it comes to glider propulsion. That day is yet to arrive because of current limitations in battery technology, namely energy density and safety/reliability.

I have a jet sustainer in my glider which I love but at the same time don't trust. I climb in the vicinity of my chosen & assessed outlanding field until I feel it's safe move on (terrain dependent but usually 1,800ft or so). A friend, knowing I'd flown over an area with a lot of unlandable terrain, once asked "would you go there in a pure glider?". The answer was yes, because I only ever go to places I wouldn't go in a pure glider, preserving glide out to a landable area. The sustainer is an installation of convenience to me, to get me back to my home airfield instead of sitting in a fly blown paddock in the middle of nowhere. It's not a substitute for basic gliding principles and judgement.

CJ

--
Dan, 5J

On Saturday, January 7, 2017 at 7:54:32 PM UTC-8, wrote:
We had a member place a similar level of faith in his FES to that shown above, using it to climb away from unlandable terrain. The system powered up and climbed away as advertised - initially. During the climb, the battery overheated and the FES shutdown, as it's designed to do, to protect the battery and ultimately, the aircraft. The pilot was now at moderately low altitude and presented with an unexpected outlanding (startle factor) over terrain that hadn't been assessed for such (complacency / over reliance on FES). A successful outlanding was achieved in that the pilot walked away unharmed. The glider was extensively damaged.

[snip]
CJ

CJ, can you give us more detail about this incident? This is the first FES failure I've heard of. You said the FES had to be shut down at "moderately low" altitude, which suggests it didn't run for very long. It's surprising that it could overheat so quickly. How long did the FES run before the shutdown? What was the OAT at the time? What altitude MSL did it fail at? Was the battery damaged? Was there any smoke or burning smell? Has the manufacturer or owner inspected the FES system since the incident?

-Ben

CJ, can you give us more detail about this incident? This is the first FES failure I've heard of. You said the FES had to be shut down at "moderately low" altitude, which suggests it didn't run for very long. It's surprising that it could overheat so quickly. How long did the FES run before the shutdown? What was the OAT at the time? What altitude MSL did it fail at? Was the battery damaged? Was there any smoke or burning smell? Has the manufacturer or owner inspected the FES system since the incident?

Hi Ben,
I wouldn't classify it as a 'failure' as the system worked as advertised. Like any other sustainer (jet, internal combustion, etc) a FES has capacity and operating temperature limitations. These were reached and in accordance with system warnings, the pilot shutdown to prevent damage. To answer your questions (to the best of my knowledge):
- Duration: It had been run previously, hence low capacity and high temp
- Duration immediately before incident: Unknown
- OAT: 86F (approx)
- ALT: Unknown (suspect 2,500AMSL, approx)
- Damage: Nil, it was shutdown in accordance with system warnings. No smoke/smell reported.
- Inspection: Yes. Owner and maintenance provider.

The de-identified summary of the incident is publicly available so I can reproduce it below:

"RUNWAY EXCURSION LAK-19

The pilot was flying cross-country on a weak day and decided to return to the home airfield using the electric sustainer motor. The pilot subsequently flew through lift and decided to continue on task. On return from the turn point the pilot found himself getting low again, so he restarted the electric motor and headed towards some hills in search of lift. Unfortunately, the battery power was low and the motor warning lamp illuminated. The pilot turned off the motor and was immediately faced with an outlanding. While the aircraft was now over hilly terrain with limited landing options, the pilot located a paddock of suitable dimensions with some minor slope. The glider landed at speed and it is suspected that the wheel and starboard wingtip touched the surface simultaneously, resulting in the wing catching in long Lucerne and causing the glider to ground loop. The aircraft was substantially damaged - suffering a bent undercarriage and separation of the starboard wing extension. Pilots of gliders capable of self-retrieving need to fully understand the limitations of their type of motor and must make decisions at sufficient height and with safe landing options available."

Please don't misunderstand the intentions of my post. I'm a fan of the FES in theory and in practice. Personally, I think the next jump in battery technology will push it over the top. It's just that discussions on this topic often include comments on the 'infallibility' of the system. My post was intended to give a real world example of why we still need to apply basic gliding principles to this propulsion type, just like the rest of them.

CJ

Yea...Running out of "gas" is no good no matter the propulsion type

On Monday, January 9, 2017 at 7:07:34 PM UTC-7, Tony wrote:
Yea...Running out of "gas" is no good no matter the propulsion type

Indeed...What Tony said!!!

snip It's just that discussions on this topic often include comments
on the 'infallibility' of the system. My post was intended to give a
real world example of why we still need to apply basic gliding
principles to this propulsion type, just like the rest of them.
CJ

Very well put. It is for just the above reason that, though I have a
very reliable engine, I never get out of range of a safe landing field
and, for me, that means an airport.

--
Dan, 5J

Thanks for the additional detail, CJ. The fact that the motor was run previously in the flight changes the picture significantly. However, it's still not clear why the pilot had to shut down the motor. In your original post, you said the battery was overheating, but the incident report says "battery power was low", which suggests the battery voltage had reached it's minimum. Which was it, over-temperature, or under-voltage? These are two very different things. If it was low voltage, then most likely the battery power was simply exhausted. If it was overheating, that suggests a failure of some sort. An OAT of 86F is not extreme, so it would be surprising to me if the battery overheated. Does the FES have any known limitations on motor run-time? My assumption was that it could safely be run continuously until the battery was empty.

I am also a fan of FES and am considering purchasing a sailplane equipped with it. I hope it's not true that the battery could overheat under such seemingly normal operating conditions.

It would depend on the airfield. I don't mind landing on grass and I'd
even take off from it. Likewise I'd land on gravel in an emergency but
don't want to take off from it out of concern about damage caused by
rocks thrown up by the tires and damage to the carbon prop. I don't
want to land in an unprepared field due to the possibility of nosing
over and the fact that I wouldn't want to take off from a rough field.

Realistically speaking, it's rare to be out of gliding range of a paved
airport except for the leg between Cedar City and Minden. Very lonely
out there...

On 1/10/2017 11:55 AM, Henry wrote:
Dan Marotta wrote expansively:

though I have a very reliable engine, I never get out of
range of a safe landing field and, for me, that means
an airport.
Won't an airfield do?

--
Dan, 5J