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.
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.
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.
That's exactly, what i imagined, at least.
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.
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.
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.
Obviously this impacts engine efficiency, so not 100% sure how great it would be for cruise, but doesn't seem entirely impractical?
The old clunkers still around are mostly used in sanctioned countries, or where a market failure has failed to provide a decent equivalent (757/767)
A whole lot of weird, or just simply old planes still operate in Canada for this reason. Until this year you could still find 737-200 flights in the north.
No other 737 got the gravel kit
Not sure who still flys 757/767s so, at least for pax. Most shoupd have been replaced by 777/787/A350s by now.
Edit: Totally forgot about Delta.
The lighter airframe is really interesting, too, given the ongoing cost savings
Will be interesting to look at fatigue of the control surfaces though, if they get used many times more per flight to adjust for minor turbulences.
This is true--- these days. We've been tending to replace planes before the airframe life limits are met.
> I can't remember an accident of a major airliner as a result of the airframe failing post the 1970s.
Well, on the other hand, this is mostly true because airframe life limits and expensive inspection programs that we established after horrific accidents.
And things like https://en.wikipedia.org/wiki/Aloha_Airlines_Flight_243 (1988).
> Will be interesting to look at fatigue of the control surfaces though, if they get used many times more per flight to adjust for minor turbulences.
Control surfaces are on bearings and have, in general, a lot of excess strength to minimize internal deflection. Even if there were a trade in wearing out control surfaces faster, they are a more easily inspected and replaced part of the airplane.
Isn’t the lifespan related to the number of cabin pressurizations (not flight hours).
Which is why long haul planes like 787 have longer lifespans than a 737, because 737 are doing way more quick turn trips (more pressurizations) than a long haul international flight plane.
For general aviation, yes. For pressurised cabins, life is measured in pressure cycles. A long flight wears the structure about as much as a short one; it's the inflating and deflating that counts.
- Stockton Rush
Todays airframes have a lifespan measured in flight hours, and an estimation is done as to how much turbulence will be hit per hour of flight. At the lifespan limit, the plane is typically scrap.
If this tech can reduce the flexing of the airframe during flight by 80%, you can probably get 5x the flight hours from the airframe before it becomes too weak to be safe (or more - half the flexing typically more than doubles the lifespan)
Alternatively, you can make the airframe thinner and lighter for the same number of operating hours (and that's what is likely to happen, since aircraft manufacturers don't want to put themselves out of business). Thinner and lighter airframe saves fuel and makes the aircraft cheaper.