Down the Rabbit Hole with Eviation's Alice

[Piotrsko]

Originally Posted by freebeard

It looks like all the air sees is high-efficiency airfoils and propellers sucking any detached airflow for lunch.

Hunh? Not sure what you mean here.

[freebeard]

I'm not sure either.

There're three prop circles that leave the mid-span of the wings and the tips of the tail exposed to free air. The fuselage and engine nacelles should have laminar flow, but any attached turbulence (interference drag at the root of the tail in crosswinds?) is actively managed by the propulsion system.

Maybe there is no advantage.

[Piotrsko]

Not to disagree, but most everything in front of the props should be pretty much laminar unless it is a huge profile change.

I can see some turbulence at intersections and with the tip setup from vortice flow, and I wonder about the drive units operating in disturbed air but that will just reduce available thrust and not decrease drag.

I defer to your knowledge base as mine is mostly deduced from my aviation failures.

[NeilBlanchard]

Originally Posted by freebeard

And more complicated control linkages.

The Alice is fly by wire, so the blending is done by the computer, and servos do the work?

[redpoint5]

What I've always wanted to see is at least 1 electric motor driving the wheels. Rather than needing a pushback, just use the electric wheel to taxi, and only spool up the engines at takeoff (or however long is needed to warm up before takeoff). Perhaps the extra weight isn't justified when there's plenty of infrastructure in place for a pushback, though that whole process takes a couple minutes.

[freebeard]

Originally Posted by Piotrsko

I defer to your knowledge base as mine is mostly deduced from my aviation failures.

Ha! Mine is from lurking on Ecomodder.

[redpoint5]

Maybe it was the 100% fly by wire that made me think of this, but I just listened to "Bit flip" on Radiolab. Apparently the Toyota stuck accelerator issue was due to random bit flipping caused by cosmic radiation. At least that failure mode could be reproduced by simulating/inducing a bit flip in the speed control program. Now the system has redundancy to prevent such a problem (or make it statistically extraordinarily unlikely).

I'm sure an aircraft would have this redundancy built in, but with so much software, there's bound to be weaknesses in the code/redundancy/contingency.

[Piotrsko]

Originally Posted by NeilBlanchard

The Alice is fly by wire, so the blending is done by the computer, and servos do the work?

Afaik, Everything certified so far is redundant mechanical backup of some sort. Hydraulic mechanical actuation of surfaces. Im not sure the FAA is ready for full fly by wire with a multiple "souls" on board. A multi-million $$ fighter with nukes, they are ok with, as long as it has an ejection seat.

[samwichse]

Originally Posted by redpoint5

What I've always wanted to see is at least 1 electric motor driving the wheels. Rather than needing a pushback, just use the electric wheel to taxi, and only spool up the engines at takeoff (or however long is needed to warm up before takeoff). Perhaps the extra weight isn't justified when there's plenty of infrastructure in place for a pushback, though that whole process takes a couple minutes.

https://en.wikipedia.org/wiki/EGTS

[freebeard]

The main landing gear is equipped with an electric motor powered by the auxiliary power unit which allows the aircraft to push back from the gate and taxi without a tug or its jet engines.[1]

The system weighs 300 kilograms (660 lb) and is permanently installed on the aircraft.

So, the weight of 2-3 passengers.
_______________

Originally Posted by DDG

What does 'triple redundant closed-loop digital avionics ...
https://space.stackexchange.com/ques...cs-system-mean
The primary flight system comprises six computers, three sets of two computers each (triple redundancy X dual redundancy). This, along with massive verification and validation (V&V) was enough to satisfy NASA that the Dragon achieves the two fail safe requirement.