8 ms·

> Flying wings have been known to be more efficient for a long time Source needed

by zymhan 7y ago

walrus01 7y ago
In the UAV world, the longest endurance loiter time fixed wing craft are either relatively slow and with long, straight wings (the 30 hour version of the rq-9, or the global hawk), or are flying wings...
- zymhan 7y ago
  Sure, but those are not features you want in a cargo or passenger aircraft. The Global Hawk has a wingspan over 50% as long as an A350, yet it weighs 1/10th as much. There is no comparison.
  - SECProto 7y ago
    > The Global Hawk has a wingspan over 50% as long as an A350, yet it weighs 1/10th as much. There is no comparison. I agree that there is no comparison - in the sense that the two cannot be compared that way. For example: A childhood toy of mine (a compressed-air plane) needs a wingspan 1% as long as an A350, yet it only weighs 1/1,000,000th as much - and can still only stay airborne for 30 seconds! This discussion [1] on the different most-aerodynamic plane shapes is fairly interesting, and certainly doesn't confirm the person above who claimed that a flying wing is the most aerodynamic shape. [1] https://aviation.stackexchange.com/questions/17119/what-is-theoretically-the-most-efficient-shape-for-an-aircraft-assuming-you-d https://aviation.stackexchange.com/questions/17119/what-is-t...
  - ummonk 7y ago
    Well, given that mass would scale as square of wingspan that is only 2.5x as bad.
  - usrusr 7y ago
    > Sure, but those are not features you want in a cargo or passenger aircraft Depends on the use case: for a feeder aircraft (regional to international airport) load, range and speed isn't terribly important, but fuel economy still is, for economical reasons (and for ecological reasons, which translate into economical by making the tickets an easier sell to a climate-aware population). In well developed regions, the main draw of feeder planes over ground transportation is not travel speed, but the convenience and piece of mind of checking in at your home airport. Since a lot of regional (or effectively regional) airports are wildly overbuilt in hopes of attracting bigger connections there could be a market for a plane that fills the available width with a modern high aspect ratio wing to max out efficiency for small loads. If new aircraft designs weren't prohibitively expensive or fuel would be much more expensive this kind of plane would exist. Basically, put the wing of a Global Hawk on an ERJ-145.
Atiim 7y ago
https://en.wikipedia.org/wiki/Boeing_X-48 https://en.wikipedia.org/wiki/Boeing_X-48 Note 1: Boeing once toyed with a blended wing-body, a sort of flying wing, to produce dramatically better aerodynamics and fuel efficiency. Passengers would have sat in a wide cabin, rather like a small amphitheater. But tests with a mock-up produced such a negative reaction that the company dropped the technology, except for military refueling aircraft.
- zymhan 7y ago
  That link provides nothing to backup the previous claim.
- toast0 7y ago
  Unfortunately the source of that note, an article in the Economist from 2006, doesn't indicate when they tested. Standards and expectations of airline passenger comfort have degraded significantly over the years, so it might be reasonable to retest. Although, I found an article from 2018 [1], quoting a Boeing VP of Product Development and Future Airplane Development, which basically says a blended wing design for commercial passenger aviation is unlikely because the required minimum height for passenger loading implies a minimum width that is quite large, and may not be very compatible with existing airports. [1] https://leehamnews.com/2018/04/03/dont-look-for-commercial-bwb-airplane-any-time-soon-says-boeings-future-airplanes-head/ https://leehamnews.com/2018/04/03/dont-look-for-commercial-b...
nabla9 7y ago
Lift to drag ratio. Aerodynamically the wetted area that generates drag without lift is undesirable. You need a wing generate lift, but everything else is there for something else like stability, handling, payload etc. In conventional "tailplane" configuration the fuselage and tail are just providing drag and almost no lift (tail has little wings 'upside down' generating negative lift and trim drag). If you have canard or some more exotic wing configuration you can have all wings generating lift but there is still drag from the body. In clean flying wing, there is nothing else except the lift producing wing.
- holoduke 7y ago
  Not entirely true. In a flying wing there is constant flap adjustment needed to counter balance a CG (center gravity) offset. The amount of counter drag is higher than a narrow winged tailplane. Obtaining a correct CG is therefore also more crucial. With variations in passengers and other load this will be a challenge.
- usrusr 7y ago
  But thick, deep wings are not exactly known as the very definition of aerodynamic efficiency either. Are we sure that a sleek long tube added to a well-designed wing can be beaten by a wing that is full of compromise to accommodate seating?
  - nabla9 7y ago
    It's the thickness-to-chord ratio that matters, not absolute thickness. Swept wing in the Flying-V is clever way to get a optimal thickness-to-chord while keeping the total surface area in check.
- FabHK 7y ago
  Concerning the horizontal stabiliser providing negative lift: it's possible and frequently so, but not necessary for stable flight. (If I understand correctly, what is required is that its angle of attack is lower than the one of the main wing, or equivalently (if the wings have the same shape) its wing loading.) See section 6.1 here, for example: http://www.av8n.com/how/htm/aoastab.html#sec-basic-stability http://www.av8n.com/how/htm/aoastab.html#sec-basic-stability

> Flying wings have been known to be more efficient for a long time Source needed

by zymhan 7y ago

> Flying wings have been known to be more efficient for a long time Source needed

In the UAV world, the longest endurance loiter time fixed wing craft are either relatively slow and with long, straight wings (the 30 hour version of the rq-9, or the global hawk), or are flying wings...

zymhan 7y ago
Sure, but those are not features you want in a cargo or passenger aircraft. The Global Hawk has a wingspan over 50% as long as an A350, yet it weighs 1/10th as much. There is no comparison.
- SECProto 7y ago
  > The Global Hawk has a wingspan over 50% as long as an A350, yet it weighs 1/10th as much. There is no comparison. I agree that there is no comparison - in the sense that the two cannot be compared that way. For example: A childhood toy of mine (a compressed-air plane) needs a wingspan 1% as long as an A350, yet it only weighs 1/1,000,000th as much - and can still only stay airborne for 30 seconds! This discussion [1] on the different most-aerodynamic plane shapes is fairly interesting, and certainly doesn't confirm the person above who claimed that a flying wing is the most aerodynamic shape. [1] https://aviation.stackexchange.com/questions/17119/what-is-theoretically-the-most-efficient-shape-for-an-aircraft-assuming-you-d https://aviation.stackexchange.com/questions/17119/what-is-t...
- ummonk 7y ago
  Well, given that mass would scale as square of wingspan that is only 2.5x as bad.
- usrusr 7y ago
  > Sure, but those are not features you want in a cargo or passenger aircraft Depends on the use case: for a feeder aircraft (regional to international airport) load, range and speed isn't terribly important, but fuel economy still is, for economical reasons (and for ecological reasons, which translate into economical by making the tickets an easier sell to a climate-aware population). In well developed regions, the main draw of feeder planes over ground transportation is not travel speed, but the convenience and piece of mind of checking in at your home airport. Since a lot of regional (or effectively regional) airports are wildly overbuilt in hopes of attracting bigger connections there could be a market for a plane that fills the available width with a modern high aspect ratio wing to max out efficiency for small loads. If new aircraft designs weren't prohibitively expensive or fuel would be much more expensive this kind of plane would exist. Basically, put the wing of a Global Hawk on an ERJ-145.

Atiim 7y ago

https://en.wikipedia.org/wiki/Boeing_X-48 https://en.wikipedia.org/wiki/Boeing_X-48 Note 1: Boeing once toyed with a blended wing-body, a sort of flying wing, to produce dramatically better aerodynamics and fuel efficiency. Passengers would have sat in a wide cabin, rather like a small amphitheater. But tests with a mock-up produced such a negative reaction that the company dropped the technology, except for military refueling aircraft.

zymhan 7y ago
That link provides nothing to backup the previous claim.
toast0 7y ago
Unfortunately the source of that note, an article in the Economist from 2006, doesn't indicate when they tested. Standards and expectations of airline passenger comfort have degraded significantly over the years, so it might be reasonable to retest. Although, I found an article from 2018 [1], quoting a Boeing VP of Product Development and Future Airplane Development, which basically says a blended wing design for commercial passenger aviation is unlikely because the required minimum height for passenger loading implies a minimum width that is quite large, and may not be very compatible with existing airports. [1] https://leehamnews.com/2018/04/03/dont-look-for-commercial-bwb-airplane-any-time-soon-says-boeings-future-airplanes-head/ https://leehamnews.com/2018/04/03/dont-look-for-commercial-b...

nabla9 7y ago

Lift to drag ratio. Aerodynamically the wetted area that generates drag without lift is undesirable. You need a wing generate lift, but everything else is there for something else like stability, handling, payload etc. In conventional "tailplane" configuration the fuselage and tail are just providing drag and almost no lift (tail has little wings 'upside down' generating negative lift and trim drag). If you have canard or some more exotic wing configuration you can have all wings generating lift but there is still drag from the body. In clean flying wing, there is nothing else except the lift producing wing.

holoduke 7y ago
Not entirely true. In a flying wing there is constant flap adjustment needed to counter balance a CG (center gravity) offset. The amount of counter drag is higher than a narrow winged tailplane. Obtaining a correct CG is therefore also more crucial. With variations in passengers and other load this will be a challenge.
usrusr 7y ago
But thick, deep wings are not exactly known as the very definition of aerodynamic efficiency either. Are we sure that a sleek long tube added to a well-designed wing can be beaten by a wing that is full of compromise to accommodate seating?
- nabla9 7y ago
  It's the thickness-to-chord ratio that matters, not absolute thickness. Swept wing in the Flying-V is clever way to get a optimal thickness-to-chord while keeping the total surface area in check.
FabHK 7y ago
Concerning the horizontal stabiliser providing negative lift: it's possible and frequently so, but not necessary for stable flight. (If I understand correctly, what is required is that its angle of attack is lower than the one of the main wing, or equivalently (if the wings have the same shape) its wing loading.) See section 6.1 here, for example: http://www.av8n.com/how/htm/aoastab.html#sec-basic-stability http://www.av8n.com/how/htm/aoastab.html#sec-basic-stability