Comment by burnerthrow008 | Hacker News Reader

Comment by burnerthrow008 | Hacker News Reader

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> The article mentions "saves weight and installation space" - it seems this savings come at the expense of massive complexity; how big can the savings be?

Take a step back and look at how complex brake systems have evolved at the present date:

On one hand, sure, it's just a foot-operated hydraulic pump and four hydraulic actuators.

On the other hand, the ABS module has valves to both cut off each brake caliper and to drain hydraulic pressure from each brake to prevent lockup. In an emergency braking scenario, the foot pump will quickly go the floor as pressure is drained, so the ABS module also has an electrical pump to put fluid back into the system.

All US-legal cars have some form of electronic stability control (and often have lane keep assist), which can use the same components to pressurize one or several brakes to make the car follow the driver's intent (as measured by a steering wheel angle sensor and a body yaw rate sensor. Europe-legal cars also usually some form of emergency brake assist which again uses the ABS module components to apply the brakes automatically.

To keep this all safe, you need pressure sensors to monitor valve and pump functions, sensors to monitor driver input, and sensors to monitor vehicle dynamics.

When you look at the system holistically, as it exists today, it is bandaids on top of bandaids and you realize that you no longer have just a simple hydraulic system.

I would make an analogy to the 737 Max vs. Airbus FbW here: We started with something very simple, and then incrementally increased complexity in (seemingly) appropriate ways. Then, many years later, we realized that our "simple" mechanical system is actually more complex and prone to more complex failure modes than a system which started out complex and rigorously managed that complexity.

Funnily enough, A380, A350, B787, and other new aircraft have their brakes connected by Ethernet (specifically AFDX, a modified variant of Ethernet) so braking actuator signals (and sensor data back) goes as UDP messages.

But it makes the system less complex and easier to handle, as there's one kind of cabling, and complex functions like ABS equivalent are handled from avionics bay

Aircraft don't need their brakes to be as responsive as cars do. There is virtually no chance of hitting a person or another plane while landing or maneuvering on the runway.

Aircraft brakes are life or death issues that require instant response times to changing conditions, which is why ABS originated in aircraft.

The aircraft braking systems are very complex, including active thermal management and automated braking systems that take multiple data sources to manipulate breaking force, including understand how long the brakes survive when taken beyond melting point (RTO setting on autobrake)

I don't think ABS originated in aircraft because of the required braking response time. It originated in aircraft because aircraft must regularly operate in wet and icy conditions, and the performance of aircraft brakes is correlated to the length of runway required to land, which relates closely to the cost of everything in aviation. It was thus economical to use cutting-edge tech on planes long before it was economical to do the same for cars, which are mass-produced and must be affordable to individuals.

There is approximately zero chance of an aircraft pilot needing to stomp on the brakes because of a random pedestrian or animal, whereas that happens constantly for cars. Cars stop and go all the time and have to avoid each other. Aircraft hardly do that at all when they are on the runway. They use their brakes to not accidentally roll or be blown about, and in the process of landing. Those applications don't need epic response time.

Being slightly off in adjustment of brakes when landing an airliner results in dead passengers. It's not as visible for manual braking, but that's because the brakes have been "brake by wire" for some time. The scope of inputs in brake control loop is also much wider in aircraft than in typical car, at times including calculated mass, calculated ground speed, brake temperatures, tire temperatures, pressure on gear, etc.

Now consider that the same network used to control the brakes also is sufficient to control every other sensor and servo on the aircraft s well.

That is all pretty interesting but I think we've gotten far away from my original comment, which was that planes don't need brakes to be as responsive as cars do. The typical application you're describing is in landing, not in puttering around in the airport. Landing involves executing some braking program continuously until the plane is on the ground. What I'm really getting at here is that the pilot is not going to be taken by surprise and have to apply the brakes in the same way as a driver would. It stands to reason that despite the lower speeds that cars go, they need to brake spontaneously in all kinds of conditions (on worse surfaces than the typical runway, in many cases). I don't know why this point matters anymore but that's what I was trying to say.

I would like to add, brake by wire may be more reliable on planes than cars because planes are maintained very well by experts. Automobile design should strive for simpler and more failsafe options because owners are usually clueless people with limited budgets, who want to do as little maintenance as possible. The fact that hydraulic brakes work so well even in very old cars says a lot about how good they are. When they do get blamed for poor performance, it's usually due to something stupid like the owner not replacing worn out hoses after 20+ years of heavy use. I only found out about that one recently. Old hoses start breaking down and they gradually get congested.

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