Advice on motor glider wanted - FES - Jet - Engine

On Sat, 7 Jan 2017 19:54:29 -0800 (PST), 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

The FES system produces 20kw at full power. Most of the gliders
fitted with it will cruise straight and level at about 4-5kw.
Certainly in current versions the system will warm you of a problem
but doesn't shut itself down. 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. Low voltage or
overheating can generally be cured by reducing the power to cruise
power.

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