Comment by vlovich123 | Hacker News Reader

Comment by vlovich123 | Hacker News Reader

Parent Full thread

First, I don’t understand what “build it into the airframe” means. These are sensors that are used to predict turbulence and then generate forces in opposition. Are you imagining small sci-fi rapid thrusters throughout that can generate enough thrust to counteract?

Secondly, the turbulence prediction is extremely hard for an airliner because it’s traveling so fast - you’d need sensors extended comically far forward and at that point you’ve got real risk of them breaking off mid flight meaning you would have to add significant amounts of weight to strengthen them (assuming you could). You’ve also got the problem that you need to retract this stuff on landing probably which adds more weight and complexity. Adding even more problems, generating sudden thrusts to counteract turbulence for a commercial airliner seems really difficult since that’s not how the engines work (eg you probably can’t generate a countervailing force quickly enough).

This is a neat concept but keep in mind this is a PoC on a very lightweight craft going relatively slow. It’s not clear how big/fast an aircraft it can scale up to. An easier turbulence reduction would be to mount the passenger area in something that could actively mechanically stabilize like optical image sensors. If you could decouple things so that the airframe could be repaired/replaced cheaply independent you everything else in the aircraft, that would be much more cost effective. However I suspect the mechanical stabilization itself would add a lot of weight/also need replacement and you wouldn’t see fuel savings I think, just a more comfortable ride.

These problems are hard, but have already been solved. The B-1 Lancer has active turbulence reduction built into the airframe, via the small canards on its nose. https://ntrs.nasa.gov/citations/19840005129

It's designed to work at Mach 0.85, and was meant to increase the lifespan of the airframe during low-altitude penetration flights where lots of turbulence could be expected.

Do you have a feel for how the maneuverability of a B-1 being controlled by the canards compares to that of a typical airliner?

It seems like a system like this would need to respond very quickly to changes in the air mass, and the weight and slow response of an airliner might make this system less feasible unless you could somehow measure airflow a reasonable distance in front of the plane.

I think the real idea is to have surfaces or controls distributed that could unload turbulence from individual surfaces nearly instantly.

This could be a few extra control surfaces, like a canard or actuated slat, or it could be through something like Active Flow Control -- https://www.scientificamerican.com/article/the-next-darpa-x-... -- where puffs of bleed air or electrostatics adjusts airflow rapidly.

I think systems-- like the B-1 Lancer highlighted by a sibling comment-- show it's not completely impractical for larger aircraft.

Neat. The best way to learn something is to post something wrong on a forum and wait for experts to correct you :). I hadn’t considered using puffs of air. I do still think adapting it for a commercial airliner may be tricky but it would be neat if one day a bunch of tech came together to realize this.

You don't need thrusters (which would be impractical). I think you can get most of the benefit by sensing with tiny canards in the front next to pitot tubes, and using electric motors to adjust ailerons/flaperons/spoilerons multiple times a second.

AV-8B and F-35B use bleed air for thrusters (for stability and low speed maneuvering).

Obviously this impacts engine efficiency, so not 100% sure how great it would be for cruise, but doesn't seem entirely impractical?

I think those are great examples of platforms that are not practical - they are only used in situations where they absolutely must get a plane to take off/land vertically, no matter the cost (in maintenance overhead or efficiency). I don't think they clear the bar in commercial aviation - a bleed air thruster system, even confined to the wing, would add a ton of complexity and hazards and weight. By comparison, the actuators, control surfaces, and airflow sensors are already there in commercial planes - in some planes it might even be possible to retrofit without introducing any new hardware, aside from more, bigger, more sensitive AoA sensors perhaps (which Boeing needs to do anyway, zing.)

I believe the final solutions for airliners would be using LIDAR to detect airflow in front of the plane based on the particles in the air. There's a few scientific articles about it if you search, and I believe from second hand information that the big manufacturers (airbus and Boeing) are testing prototypes for deployment on next gen airliners.

Probably not the “final solution” to airplane turbulence, though it might help a lot!

This may be equally scifi, but for sensors I'm imagining small jet powered drones flying in formation a few hundred metres ahead of the passenger plane.

Given how slow and cautious the industry is (and for good reason), even if someone has been working on this for a decade already, I don't expect to see anything like that before 2030.

> Are you imagining small sci-fi rapid thrusters throughout that can generate enough thrust to counteract?

That's exactly, what i imagined, at least.

Yeah unfortunately I don’t think such tech exists and at our current tech level I wouldn’t imagine it would work and could present real safety issues - you’d have fuel pipelines running throughout the airframe which is likely a significant amount of really serious fire risk, all of this adds a significant amount of weight and maintenance cost, I don’t believe such adjustment thrusters exist but I could be wrong, and I’m sure you would still get things wrong in your prediction which means your thrusters would add wear and tear on the airframe as well.

This article is about a PoC where they put sensors extended out of the airframe of a small slow moving aircraft and demonstrated a 60% prediction accuracy for a 10% fuel savings. It’s unlikely this approach would scale up to an airliner. The sensor problem might be but I have big questions about the adjustments an airliner moving at 600-900 mph can make to successfully counteract the prediction.

Doppler radar systems can detect airflow vectors in arbitrarily large areas, so I imagine that we have the tech for that portion, but I too am concerned about trying to take something with that large a mass and surface area and counteract turbulent forces with it. That's also going to stress the airframe and avionics, cause maintenance schedule changes, etc...

Yeah, i was joking. Those thrusters would have to be insanely powerful to accelerate such a big mass fast enough to counteract the rapidly changing forces, caused by turbulence.

Reply on news.ycombinator.com