The problem is that a lot of those old ISA drivers were peeking and poking card registers as fast as the bus would allow, which was over 1 MHz (less than 1 microsecond per transaction), not DMAing data to RAM (though some did that too).
With a modern 4 GHz CPU, that means your budget is only 4000 clocks per interrupt. The context save alone can make it hard to hit 1MHz, and you really want to have your interrupt code pinned to the L1 cache because a few memory reads will blow your entire budget.
As nice as USB4 is, I’ve never heard anyone claim it has single-digit microsecond latency, to say nothing of sub-microsecond latency. The typically-quoted ~20 usec latency of USB4 limits it to around 50 kHz for an emulated ISA card.
Often people confuse latency vs throughput/bandwidth. With streaming and batching USB4 will shuffle a lot data through on average per second. But it will never hit reliable microsecond level or even submicrosecond latencies.
At the same time ISA card will never reach 40Gbps throughout with CPU clocking at tens of MHz only or often less.
So… while that’s true of most astronav systems to date (particularly the ones meant to be used during daytime, and especially with reference stars potentially near the horizon), I’m not sure that’s really a hard requirement.
If you restrict the domain to nighttime or exoatmospheric, a high-resolution wide-angle camera paired with an offline astrometry database has the makings of a strapdown astronav.
Widening the domain again, the natural motion of the vehicle is probably enough, when combined with inertial sensors to aid pixel-shift image stabilization, to achieve the same kind of processing gain as the older systems got with shutter-synchronous detection.
Maybe because literally the entire world is currently using that system, and sending machine-readable clearances to just some airplanes means that the non-equipped planes are denied situational awareness?
Yea, they couldn’t get the left gear down because they they had enough airspeed to execute a go-around!
Literally 5 consecutive minutes of making 100s of wrong decisions snatching defeat from the jaws of victory.
According to news reports, a magistrate judge at OSHA has been sandbagging an investigation into retaliatory firings by this airline (of pilots who reported unsafe practices with maintenance, CRM, training, scheduling, everything). I wonder if the NTSB will include that judge in the investigation. It seems like he or she has a lot to answer for.
This is like saying "you can build a nuclear power plant anywhere, zoning be damned" because it's regulated at the state level and they aren't legally bound to honor municipal zoning. It's not lying, but it's basically the derivative of lying because it's only true in the most technical sense.
Most of those state processes are a) reserved for businesses b) discretionary and they exercise their discretion not to approve anyone.
If it was something that was practically doable every 200k HHI household that drives old cars and has good health insurance would take advantage of them.
> That being said, I wouldn't be surprised if they didn't start the generators during critical phases so they may end up using some fuel for a flight, but not much.
I would guess the opposite. Many parts in a turbine engine are "lifetime limited" by number of engine starts. That is, you are required to tear down the engine and replace certain parts after a certain number of engine cycles.
That makes the economics of the turbine hybrid radically different if you need to start it every time you land vs. only the rare cases where you need to dip into fuel reserves.
For example, the PT6A (a common 500-1000hp turboprop) requires the turbine and compressor disks to be replaced every 16,000 cycles. That's about 5 years of commercial service at 4x round trips per day. But if you only start the engine once in every 10 flights, now those components (theoretically) last for 50 years of flying.
> vs. only the rare cases where you need to dip into fuel reserves.
There aren't that many existing flight routes that will fit into the 125 mile range (though the existence of this plane might change that), so I suspect we will see most of these planes go into service on slightly longer routes. So they will probably still need one cycle per flight.
Though... The video isn't quite clear if the 125 miles is what they can fly without starting the turbines or if it's what they can fly without needing the turbines ready to act as an emergency reserve. I actually suspect it's the later and this aircraft can make it to 200+ miles without starting the turbines.
Where I live, there aren't that many 125 mile flights, but there are a lot of 200 mile fights.
I also suspect the turbines are sized so that only need to start one of the two turbines on most flights, which would extend lifetime a lot. Ideally the turbines would be sized so that one is enough for cruising, and with two you can actually charge the batteries after a go-around (enough to enable a second and third go-around)
> They’d likely need at least double, probably triple battery capacity to fly useful routes all-electric with enough reserve stored in batteries.
Yup. And to bring this point home:
"Only" doubling the battery capacity likely eats well over half of the payload capacity, in terms of mass. So your 38 seat plane is now a 19 seat (or fewer) plane.
But... given that turbine APUs already exist for ground power and are already engineered to be as light as practical, my naive guess would be that it's easier, simpler and faster to just use a COTS APU as a series hybrid rather than trying directly couple a turbine to the propeller.
On inspections and overhauls: I'd expect that not needing to start the turbine at all on a given flight massively helps the economics of the airplane. Turbines often have parts that must be replaced after a given number of (startup) cycles, and that's going to be especially important for a turbine that is only expected to run for a short time (if at all) at the end of a flight.
If you only start the turbine on, say, 5% of flights, that means you get 20x as many flights before overhaul/inspection. I could see that being incredibly attractive to airlines.
With a modern 4 GHz CPU, that means your budget is only 4000 clocks per interrupt. The context save alone can make it hard to hit 1MHz, and you really want to have your interrupt code pinned to the L1 cache because a few memory reads will blow your entire budget.
As nice as USB4 is, I’ve never heard anyone claim it has single-digit microsecond latency, to say nothing of sub-microsecond latency. The typically-quoted ~20 usec latency of USB4 limits it to around 50 kHz for an emulated ISA card.
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