Advice on motor glider wanted - FES - Jet - Engine

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

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

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.

On Tuesday, January 10, 2017 at 8:50:49 AM UTC-8, wrote:
...Which was it, over-temperature, or under-voltage? These are two very different things.

Not necessarily. I=V/R says that as the battery voltage goes down, the amperage required for specific power level is greater. So when you have a computer-controlled system trying to maintain a commanded power level by regulating current upwards, you can get a situation where low voltage is the direct cause of overheating of specific parts of the system.

Full disclosu I'm not an FES expert, but I am an FES reseller.

--Bob K.

The bottom line: Did the FES overheat before the battery was exhausted? CJ, can you give us an answer?

Hi Ben,

Sometimes work has to come befor gliding (and RAS). An abhorrent thought, I know

I apologize for the ambiguity but battery temperature leading to shutdown was the reason given to me by an individual involved in the incident review. However, that's not to say the situation wasn't misunderstood. Thus, the only way to be sure is to ask the pilot himself which I'm happy to do but that will take time as we're not expected to catch up for a while. If you reply with the portion of your email address that's between the 'hir' and the @ I'll email you his response.

FES are very open with their documentation. Have you reviewed their manuals? Available at http://www.front-electric-sustainer.com/download.php , they specify the temperature limitations for motor and battery, among others. Note that the level to shutdown the system to prevent battery damage occurs prior to battery exhaustion.

CJ

Thanks, CJ. The FCU manual states that temperature is monitored for each battery pack, the motor, and motor controller. It's possible any one of them overheated. There's no rush, but if you could get more detail from the pilot, that would be great. Please post it here so others can benefit as well.