7 ms·

The real savings come when this tech can be built into the airframe. The airframe can only bend and flex a certain number of times before it cracks and fails.

The real savings come when this tech can be built into the airframe. The airframe can only bend and flex a certain number of times before it cracks and fails. 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.

gilbertbw 3y ago
Pressurised airframes also have a pressurisation cycle limit
- ericpauley 3y ago
  This. My understanding is that airliners basically always hit the pressurization cycle limit before anything else, so wing turbulence cycles are not important.
vlovich123 3y ago
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.
- lagrange77 3y ago
  > Are you imagining small sci-fi rapid thrusters throughout that can generate enough thrust to counteract? That's exactly, what i imagined, at least.
  - vlovich123 3y ago
    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.
    - swells34 3y ago
      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...
    - lagrange77 3y ago
      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.
- capnrefsmmat 3y ago
  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 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.
wrsh07 3y ago
I think route optimization that this will enable (not avoiding certain turbulence) might be valuable (save fuel) - I'm very excited about the potential implications per flight that this might have The lighter airframe is really interesting, too, given the ongoing cost savings
bobthepanda 3y ago
At least with commercial aviation, unless you can’t get ahold of new planes they get replaced much earlier than that due to wanting ever more efficient planes and more stringent noise regulations. 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)
- hef19898 3y ago
  Or they are used as a basis for freighter conversions. 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.
  - sokoloff 3y ago
    Delta operates nearly 200 of the 75s & 76s. (They are the largest operator of both, I'm pretty sure.)
  - awad 3y ago
    Delta and United both do, with Delta being the largest operator of both types.
  - weaksauce 3y ago
    I flew on a 75 on delta the other day
  - bobthepanda 3y ago
    there's not quite a plane on the market with the range and the lower capacity.
- BizarreByte 3y ago
  > or where a market failure has failed to provide a decent equivalent 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.
  - 3y ago
cm2187 3y ago
I am not aware that the aiframe is the main reason why planes are taken out of service. Fuel inefficiency is typically the primary reason, plus increased maintenance cost. I can't remember an accident of a major airliner as a result of the airframe failing post the 1970s. 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.
- mlyle 3y ago
  > I am not aware that the aiframe is the main reason why planes are taken out of service 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 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.
  - cm2187 3y ago
    On the control surface, I mean less the surface itself than the mechanism behind, i.e. the moving parts.
tiffanyh 3y ago
> “ Todays airframes have a lifespan measured in flight hours” 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.
JumpCrisscross 3y ago
> airframes have a lifespan measured in flight hours 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.
warbeforepeace 3y ago
Why do this matter? You can just listen to the frame to hear early cracking signs. - Stockton Rush

gilbertbw 3y ago

Pressurised airframes also have a pressurisation cycle limit

ericpauley 3y ago
This. My understanding is that airliners basically always hit the pressurization cycle limit before anything else, so wing turbulence cycles are not important.

vlovich123 3y ago

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.

lagrange77 3y ago
> Are you imagining small sci-fi rapid thrusters throughout that can generate enough thrust to counteract? That's exactly, what i imagined, at least.
- vlovich123 3y ago
  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.
  - swells34 3y ago
    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...
  - lagrange77 3y ago
    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.
capnrefsmmat 3y ago
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 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.

wrsh07 3y ago

I think route optimization that this will enable (not avoiding certain turbulence) might be valuable (save fuel) - I'm very excited about the potential implications per flight that this might have The lighter airframe is really interesting, too, given the ongoing cost savings

bobthepanda 3y ago

At least with commercial aviation, unless you can’t get ahold of new planes they get replaced much earlier than that due to wanting ever more efficient planes and more stringent noise regulations. 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)

hef19898 3y ago
Or they are used as a basis for freighter conversions. 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.
- sokoloff 3y ago
  Delta operates nearly 200 of the 75s & 76s. (They are the largest operator of both, I'm pretty sure.)
- awad 3y ago
  Delta and United both do, with Delta being the largest operator of both types.
- weaksauce 3y ago
  I flew on a 75 on delta the other day
- bobthepanda 3y ago
  there's not quite a plane on the market with the range and the lower capacity.
BizarreByte 3y ago
> or where a market failure has failed to provide a decent equivalent 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.
- 3y ago

cm2187 3y ago

I am not aware that the aiframe is the main reason why planes are taken out of service. Fuel inefficiency is typically the primary reason, plus increased maintenance cost. I can't remember an accident of a major airliner as a result of the airframe failing post the 1970s. 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.

mlyle 3y ago
> I am not aware that the aiframe is the main reason why planes are taken out of service 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 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.
- cm2187 3y ago
  On the control surface, I mean less the surface itself than the mechanism behind, i.e. the moving parts.

tiffanyh 3y ago

> “ Todays airframes have a lifespan measured in flight hours” 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.

JumpCrisscross 3y ago

> airframes have a lifespan measured in flight hours 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.

warbeforepeace 3y ago

Why do this matter? You can just listen to the frame to hear early cracking signs. - Stockton Rush