Electric Test Flight Gone Bad

Old news, but the final report is a good read. Painful, but good.

Nauga,
who knows ignorance is not bliss.
 
“Insufficient ground testing” is an interesting choice of words.
 
iamtheari said:
“Insufficient ground testing” is an interesting choice of words.
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The noted lack of experience and systems familiarity was what grabbed my attention. In a chokehold.

Nauga,
and the things he has seen...
 
nauga said:
The noted lack of experience and systems familiarity was what grabbed my attention. In a chokehold.

Nauga,
and the things he has seen...
Click to expand...

This excerpt from the BBC article about pressure on the experiment team sounds as if it could apply to some recent Boeing programs, Raptor, and others-

The report also said the experiment team "had a high workload and there was pressure on them to achieve a long duration demonstration flight by the end of May 2021".

The operator's investigation found that some staff were showing signs that pressure was influencing them to make decisions based primarily on expediency," the report said.
 
nauga said:
The noted lack of experience and systems familiarity was what grabbed my attention. In a chokehold.

Nauga,
and the things he has seen...
Click to expand...
I was just amused by the ambiguity between testing the aircraft on the ground and testing the electrical grounds in the aircraft. I haven’t read the report yet, just the news blurb.
 
iamtheari said:
“Insufficient ground testing” is an interesting choice of words.
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Keep reading ... "and the failure to review the risk assessment after the loss of propulsion on two previous flights."

It seems they were in somewhat familiar territory ... o_O
 
Daleandee said:
Keep reading ... "and the failure to review the risk assessment after the loss of propulsion on two previous flights."

It seems they were in somewhat familiar territory ... o_O
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Yikes. And assuming that they'd use some sort of regen when descending, over-voltage protection is an absolute no-brainer.
 
Kenny Phillips said:
Yikes. And assuming that they'd use some sort of regen when descending, over-voltage protection is an absolute no-brainer.
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It sounds like the over voltage protection worked great. It protected the entire electrical system from an over voltage initially caused by the windmilling propeller, all the way to the ground. Of course, that’s not the kind of protection you, I, or any other pilot would choose. This worked a lot like a twin engine plane protecting you from VMC by having the magnetos on an oil pressure switch from the opposite engine so the loss of one kills the second for you.

Redundant single-point failure. It’s a thing. I expect it in an experimental powerplant, but I also expect it to be engineered out of the design fairly early on. It doesn’t sound like they took advantage of all the earlier opportunities to do that.
 
I fly both a self-launching electric sailplane and a Malibu so this post interested me.

The sailplane is pretty bulletproof. It has two removable 16kg batteries that generate 33kW on takeoff. The biggest stress on the electrical system is getting the plane moving to takeoff speed and then taking me up to 500 ft AGL.

I run the motor full power for 1 minute and then bring it back to 15kW for cruise climb. While the motor is running I monitor motor temp, battery temps and controller temp, as well as kW, voltage, and amps drawn. All data is saved in an igc file. The system will warn me of anything critical (I've just had warnings on motor temp when it's really hot outside - as usual you drop the nose and decrease power slightly.)

Motor and prop are on the nose cone, so just a wire from batteries to the nose. When I shut the motor down the prop folds neatly to the fuselage in a few seconds and creates no extra drag.

I can't even imagine the power needed in kWatts to get the a Malibu to 85 kts. Motor heat will be an issue for sure. Fires are always a possibility with these systems. How long they can keep a Malibu flying as a pure electric is something I'm curious about. Right now I can fly for 45m with the glider. Newer model batteries should give me 30m more! (Remember that a glider like this has a 50:1 glide ratio, so this is so 90m with batteries (with cruise power at only 5kW) will take me a long way.

I'd like to see all the data mentioned above for this accident, but it sounds as if error management in the software had not been worked out fully and the system design may have some basic flaws. They would have saved themselves big bucks if they had tried everything out in a model RC plane and then moved to the Malibu.

With regards to the glider, I have not seen any glitches with the system yet. It's pretty awesome, and with gas prices at current highs, this combination is a sure winner.

Check out a video here:
 
iamtheari said:
It sounds like the over voltage protection worked great. It protected the entire electrical system from an over voltage initially caused by the windmilling propeller, all the way to the ground.
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Having dealt with that on a somewhat different "aircraft" I'm very surprised that back EMF or regen or whatever you want to call it was not accounted for. I'd be interested to know if that was a known or unknown risk at the design level...if they got that far.

Nauga,
and his risk register
 
If I’m reading the report correctly, they planned the switchover at the end of the downwind, but did it elsewhere due to not being at the proper altitude. Seems like that location might have been intentional as well, as it would probably allow them to make the runway in case of the failure that happened.
 
30957126.jpg
 
MauleSkinner said:
If I’m reading the report correctly, they planned the switchover at the end of the downwind, but did it elsewhere due to not being at the proper altitude. Seems like that location might have been intentional as well, as it would probably allow them to make the runway in case of the failure that happened.
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Several changes made on the fly (no pun intended) were noted in the report and have drawn some attention in flight test circles. Autonomy (professional, not digital) give you options, but also the ability to really foul things up.

Nauga,
who has stood on the edge and looked down, and it's a loooong fall.
 
MauleSkinner said:
If I’m reading the report correctly, they planned the switchover at the end of the downwind, but did it elsewhere due to not being at the proper altitude. Seems like that location might have been intentional as well, as it would probably allow them to make the runway in case of the failure that happened.
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That matches my take on when they removed power. Timing is everything when testing operating equipment.

The engineering failure to properly take into account the power, and resulting voltage, that would occur when all destination for regeneration power was removed, is a fundamental one. They did provide for protecting the electronics of the interface between the battery and also the fuel cell. In commercial power plants, when the outgoing AC breaker trips, the DC field is instantly killed, to prevent generation of dangerous high voltages.

If they had that failure any time from abeam the numbers, to turned final, an engine out landing should have been a non event. The previous occurrences of power loss in flight doubtless took place as this one was intended to be, and the plane was re useable. The pilot and assistant working to regain power to the propeller continued too long, and ability to return to the runway was lost.

I wonder if the previous events were similar, the cause was not puzzled out, and the pilot instructed to do a more detailed attempt to restart? If so, they should have been doing the test at much higher altitude, to provide more time to trouble shoot, yet still have glide to land available without any doubt. This test at 1,000 AGL leaves far too little time for proper analysis and recovery. The planners, not the aircrew seem to be responsible for this outcome.

Edited to add: The last half of my career in power plants was centered on those regulation, control, and protection devices.
They are immensely complex, and powerful. The instruction book on the largest that I worked on was 2 inches thick.
 
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It's weird when threads line up. This is kind of an example of why shouldn't jump start a car that doesn't have a battery. The weird surges may hurt something. To pile on what everyone else has been saying, yeah, that should be obvious to anyone used to large electric motors.
 
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