fes ot jet (pros and cons)

On 8/6/19 4:33 PM, Bob Kuykendall wrote:
On Tuesday, August 6, 2019 at 2:28:30 PM UTC-7, kinsell wrote:

Tried to start his electric low over a high-density urban area, got
nothing but grinding sounds. Too low even to fire the ballistic chute.

Better check your facts on that. As I understand it, it was absolutely not a case of FES not starting. Rather, he'd been running the FES motor for some time before it quit, likely because he ran out of juice.

From the original discussion on this, the pilot who had been flying
with him that day said he had run his motor previously, but tried to
restart with the computer showing 18 minutes left. He got nothing but
grinding sounds. So maybe "as you understand it" isn't correct.




Apparently the gauge said there was 20% capacity remaining. We all know how reliable aircraft fuel capacity gauges are...


Actually, on electric systems they're quite good. You do understand the
difference between electricity and gasoline?




But, yeah, beyond that the whole thing reflects very poorly on the pilot's planning and execution.

Startup interval is an important metric because it determines how soon you know which contingencies remain available. If it takes half a minute to deploy the engine and see if it's going to produce power, and you're coming down at 1000 fpm, your options are dwindling about as rapidly as your pulse rate is excalating. When you can flick one switch and twist a knob and know within a couple seconds that you can drive away from the hole you dug, it's a pretty strong motivator.


--Bob K.


Are you serious about this? You're going down at 1000 fpm and you
really think an FES is going to save you? Wow.

On Wednesday, August 7, 2019 at 4:47:45 AM UTC-7, kinsell wrote:

Are you serious about this? You're going down at 1000 fpm and you
really think an FES is going to save you? Wow.

With an old-school motorglider like a DG400, with the motor deployed and windmilling but not running, yes, you're going down at about 1000 FPM.

--Bob K.

On Wednesday, August 7, 2019 at 7:47:45 AM UTC-4, kinsell wrote:
On 8/6/19 4:33 PM, Bob Kuykendall wrote:
Apparently the gauge said there was 20% capacity remaining.
We all know how reliable aircraft fuel capacity gauges are...

Actually, on electric systems they're quite good.

That's a rather dangerous misconception.
With these cells, the actual amount of energy stored is not easy to estimate.
Quite unlike older cell technology where its easily estimated based on
cell voltage and monitoring of cell performance.
Now one has to know the exact cycle history...

You do understand the difference between electricity and gasoline?

A bit ;-)

In the CT accident, my understanding is the pilot was showing
a sizeable percentage energy remaining when the motor quit.

My Antares drastically under-estimated remaining power with
the motor running, then the estimate came back to reality
sometime after shutdown. Better that than the alternative!
And of course as the battery discharges, the max power available
decreases. Not important in Antares but critical in FES which
has little excess power to start.

With any motor-glider, its foolhardy to ever get in a situation
where you don't have a safe landing option as PLAN A.
That includes during:
- take-off (no short fields departing over woods)
- in-air start (extra time, altitude, and field length needed vs. pure glider)
- in-air cruise (never where complete failure puts you in the trees)

When the motor fails, its easy to execute PLAN A.
Plan B is when the motor keeps running, cause for happiness if not surprise...

FES failures have included spontaneous shutdown due to electronics failure.
No electric system is even close to 100% reliable.
Of course you don't need to ask me how I know that...

Be safe out there,
Best Regards, Dave