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Pipistrel Electro accident in Norway, and electric propulsion reliability

In France I have cheap rate for 8hrs at night and for 2 hrs during lunch. Its not hard to set timers for pool pump, water heater, washing machine/dryer/dishwasher. We generally have 2/3rd s of our consumption at the cheap rate like this, but in winter the consumption at normal rate does go up somewhat.

Antonio wrote:

byteworks wrote: ASIL D in automotive means life threatening hazards – think of unintended acceleration (ASIL-C) and inadequate deceleration (ASIL D).

I see…so does ASIL-D also address loss of power, rather than excessive accel/decel, as part of the life-threatening modes, as would be the case on aircraft?

No, loss of power is a lower ASIL because its consequences are less risky – the car will still move because of inertia, there is some time to signal to the others and even stop/park to the right/left. But imagine you put the car, at high speed, from 6th gear to the 1st.: strong, abrupt deceleration which can harm the passengers and surprise the participants to the traffic. But also risky is not enough deceleration (so inadequate means both excessive and insufficient), imagine you want to break the car but the engine is still pulling the car with full power.

In the case of an aircraft I would imagine that loss of power while airborne is less risky then, while being on the apron/taxi way with unintended acceleration or insufficient deceleration, this can generate a bad situation.

Last Edited by byteworks at 19 Aug 06:53
LRSV, Romania

In the case of an aircraft I would imagine that loss of power while airborne is less risky then, while being on the apron/taxi way with unintended acceleration or insufficient deceleration, this can generate a bad situation.

Rotax and many other engines are configured so that in the event of a throttle cable breaking, they will continue to run on full power. Lycoming is typically configured to continue running in whatever position the cable broke AFAIK. A car is typically configured to go to idle.

What is most correct, I don’t know, but with the Rotax-way, you at least have a known result which may perhaps be a better in flight solution.

The elephant is the circulation
ENVA ENOP ENMO, Norway

byteworks wrote:

In the case of an aircraft I would imagine that loss of power while airborne is less risky then, while being on the apron/taxi way with unintended acceleration or insufficient deceleration, this can generate a bad situation.

Am I reading this right that you’d prefer to have a loss of power in the air vs when taxiing?

Any throttle runaway in a conventional aircraft can be fixed with the mixture or even the ignition. Modern cars don’t even have an ignition switch!

However most runaway events in cars seem to involve automatics and the (older) driver pressing the wrong pedal.

Forensics on failure modes modern electronics are probably far beyond the aviation authorities, evidenced by the rather unconvincing “swarf might have fallen in the battery” glider fire report. Has anymore been released about the tragic fires in electric aircraft last year?

EGBW / KPRC, United Kingdom

Noe wrote:

byteworks wrote: In the case of an aircraft I would imagine that loss of power while airborne is less risky then, while being on the apron/taxi way with unintended acceleration or insufficient deceleration, this can generate a bad situation.

Am I reading this right that you’d prefer to have a loss of power in the air vs when taxiing?

I did not mention this scenario, loss of power while taxiing :)

Wikipedia has a comparisson between automotive Safety Integrity Level and aviation Design Assurance Levels and the corresponding standards.

LRSV, Romania

Speaking as an electronics design engineer (analog/digital) since the late 1960s, I don’t see that one can perform analysis which will somehow just make sure the motor inverter doesn’t simply blow up one day.

I realise one could say the same about a crankshaft, a camshaft, etc, but electronic bits have orders of magnitude more failure mechanisms than a piece of steel which can be (in fact, is) NDTd for cracks.

I have seen MTBF calculations done for our electronic products and the result, while impressive (hundreds of years) is basically obviously bogus. The popular way is to look at which components there are and for each is a standard MTBF figure (from some MIL spec handbook). Another way is to look at actual failure data (which for our most popular product gives 600 years) but electric planes won’t have that data for a very long time.

One other issue is that you don’t know what other totally unexpected external factor might affect it. Take for example the KFC225 autopilot servo failures. They are airframe type related, so probably wiring layout related. It is no surprise that they also appear to be connected with some ground (RF) installations; see the article. I am sure few people will readily believe that, but combine a piece of wire of just the right length with a powerful radar somewhere… It is the sort of thing which will lead most people to say that you are a paranoid idiot, but they can’t explain three servo burnouts over the same spot in France which actually you almost never fly over otherwise… This is under the heading of EMC (EM immunity in this case) and while there are, ahem, standards for testing to, they are not going to cover every unexpected eventuality. I am sure the KFC225 system complies with EMC specs Also – look at the VW cheat scandal – everybody cheats when it comes to EMC testing. People use spread spectrum clocks which spread the muck around a bit… and every test setup uses beautifully made cables to give yourself the best chance.

Administrator
Shoreham EGKA, United Kingdom

Peter wrote:

the motor inverter doesn’t simply blow up one day.

There are few things more exciting to an electronica (electronics engineer) than the mysterious and inexplicable failure behaviour of inverters. Inductive loads and software generated waveforms…. added to which, in an aeroplane, sustained high power found in few other traction applications. However, the key is volume, and while our (sorry Peter) ‘specialist’ designs lack the volume base for true bug killing, other inverters such as computer power supplies made by the million have achieved admirable reliability records. It helps that they are all made in China and the cost of replacement of one unit eats the profit in dozens.

However, I really doubt that the reliability of modern switch mode power supplies (they are all basically inverters) has been achieved entirely by science. I believe there’s a good bit of trial and error in there, of the sort you can only get through volume production. The sort of volume that eludes aeroplane manufacturers, meaning that we will always be on the wrong side of the curve when trying to adapt consumer electronics to ‘specialist’ applications. That’s why a 430 costs 10x more than an iPad. Is there an appetite for an electric engine that costs 10x as much as a Lycoming? It’s going to be a long, hard road.

P.S. Also with the batteries. Tesla reportedly just cut the cycle depth of their cars in response to a fire in Hong Kong. Again reportedly, people are disconnecting their cars from wi-fi so they don’t get the ‘update’! The revised cycle depth cuts range of course, and this in a mature product with millions of cycles and hundreds of millions of miles under it’s belt. How long will it take aviation with it’s unique high power demand to match that base of experience?

EGBW / KPRC, United Kingdom

Aveling wrote:

sustained high power found in few other traction applications

That’s simply not the case. All boats (including mega huge ships) runs on full power day after day after day continuously. They have huge and heavy engines, but they also run much more than any aircraft engine. Trucks do the same, the large ones cruising across the continents continuously. There is nothing special about aircraft engines in this respect, except weight is a critical issue in an aircraft, hence turbines rule. Turbines would also rule in boats, if it wasn’t for the low efficiency and the fact that weight is not an issue in big ships. A high power Lycoming/Continental with a turbo doesn’t last long before some essential part breaks.

The elephant is the circulation
ENVA ENOP ENMO, Norway

@Aveling, your post really made me smile. I’ve spent a lot of time over the last 7 years dealing with one particular developmental MW power level inverter, exactly as you describe.

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