On Tuesday, September 10, 2019 at 11:11:36 AM UTC-7, wrote:
On Tuesday, September 10, 2019 at 1:41:04 PM UTC-4, Tango Eight wrote:
On Tuesday, September 10, 2019 at 1:24:46 PM UTC-4, wrote:
On Tuesday, September 10, 2019 at 11:09:12 AM UTC-4, Tango Eight wrote:
On Tuesday, September 10, 2019 at 7:45:04 AM UTC-4, Peter F wrote:
At 08:05 10 September 2019, krasw wrote:
There has been FES selflauncher accident because powerplant failure and
one
really close call. They aren't any better.


Can you provide links to these incidents?

I would expect them to ba at least 1 order of magnitude better than the
traditional turbo.

https://app.ntsb.gov/pdfgenerator/Re...relim&IType=LA

"His last calculation of remaining battery energy was about 20 minutes from DXR,
when he noted about 20% battery life remaining. As he prepared to enter the DXR traffic pattern for landing on runway 26, he noted that the glider's altitude was low. He turned on the electric motor; however, it produced only minimal power and the glider continued to lose altitude until it impacted trees and a house 2.7 miles northeast of DXR."

That one was neither a close call (alas), nor a powerplant failure. Rather an empty battery, due to prior self-launch and cruise, without securing alternatives. Analogous to running out of gasoline. It is not evidence against the claim that FES is inherently more reliable than traditional turbo. Besides the electric motor starting reliably (as long as one keeps some "fuel in the tank"), there is also no added drag like from the boom of a retractable engine (of any type).

Accident due to (imo) poor procedures, yes. Presuming that the pilot's story is correct on the facts, it also reflects shoddy engineering.

T8

Presumably the "shoddy engineering" you allude to is the implication that the battery gauge was saying 20% but the electric motor refused to run. The story did not mention whether the motor was run further AFTER the 20% reading, and then shut down, before the restart attempt later. It seems unlikely to me that the motor ran OK up to the moment when it was shut down, and then some minutes later refused to start and produce significant power again, as the battery should not have run itself down in-between.

Anyway, gauging how much charge is left in a battery is notoriously difficult, especially when near-empty. I wouldn't count on a 20% battery reading any more than I would count on a 20% gas tank reading - in both cases I'd look for a safe place to land ASAP. On the first trip in the Cessna I had many years ago I landed (after dark, in scattered thunderstorms weather) with only about 10% fuel left (determined from how much fuel was then pumped into the tanks). I learned the lesson not to do that again!

It is interesting that the pilot reported "calculating" the energy remaining, but not how the calculation was done. The Electro has a crude bargraph display of energy remaining (it has only 10 bars); why didn't he mention that? Was he assuming he had more energy remaining than the bargraph indicated? The only way to know with any certainty the energy content of a battery is to do a discharge test. This can be done very easily with an FES - you simply operate the motor at full power climb and time the operation to battery depletion. You would also need to do this in a partial thrust situation, as happened in this accident. Compare your actual results with the glider's state of charge display. Then, add a safety margin to this (20% would be reasonable).

He was very lucky to have survived this accident. He penetrated the roof near vertically, but impacted between the rafters. He climbed out of the wreckage on his own and scared the hell out of the home owner:
http://www.kathrynsreport.com/2019/0...ro-n66911.html
His attitude towards the homeowner was indicative of a less than humble person, and not how you handle damage to other people's property.

Tom