4 ms·

the three things that make this new, as far as i can see, are: - the configuration. i don't understand what the aerodynamic advantages of a "boxwing" are, but

the three things that make this new, as far as i can see, are: - the configuration. i don't understand what the aerodynamic advantages of a "boxwing" are, but apparently this has those while avoiding problems with stalling. it's also stronger / more compact and places the engine closer to the centre of gravity than a traditional "propeller at the front" design. - the engine. initially, diesel, which is unusual for aircraft, and eventually electric. - suction of air through parts of the wing to give laminar flow (reduce turbulence) and so increase efficiency. a lot of the site reads like over-hyped snake oil, they don't have any published papers (never mind peer reviewed), and it sounds like they don't have good numerical results from full 3d simulations (but argue they are limited anyway). on the other hand, it doesn't seem to be complete bullshit - they have a working 1/4 scale model, for example, and seems to have been accepted into some kind of x-prize-like competition organised by nasa.

deleted 14y ago
[deleted]
- ajross 14y ago
  Vortices generated by induced drag really aren't "horrendous" except in high angle of attack situations. In cruise, even with slow planes like this, most drag is parasite drag. Commercial jetliners have been deploying winglets to mitigate the same effect for decades now, and the effect is something like a 2% fuel savings. It's worth doing, but it's not a game changer.
BenoitEssiambre 14y ago
Yeah I'm not sure this project passes the smell test. I don't know much about airplanes but a few things seems off when I think of this design in terms of basic physics. The "boxwings" seem to be a worst of both world approach. It ads a lot of surface going across the air and thus a lot of drag, without providing the width which would usually make available the torque necessary for stability and control. Torque is (force * distance) and, for roll control, this distance is usually provided by wide wings. An airplane having shorter wings would probably go through the air more efficiently (provided you didn't add a second set of wings on top of the first one) but would not provide much control to enable safe flight in all possible conditions. Short wings don't provide much leverage on the roll axis. It also seems like in this design the top part of the "boxwings" plays the role of the tail of the plane. However, it looks like we get the same (force * distance) problem but on the pitch axis. In order for the tail to give a good amount of torque for pitch control, it has to be located away from the wings and the center of the aircraft. Again, I'm just guessing based on physics here but since there is no tail other than the one located near the bottom wings, it might be difficult to stop the plane from pitching up or down out of control. If we were to design planes for efficiency only, they would look like arrows or missile. They would have minimal wings or fins to slow them down. The reason, we have to have things sticking out far from their middle, is to add the ability to safely control them in a wide variety of conditions. This aircraft has both lots of wing, thus a lot of drag and yet the extra wingage doesn't get the wings positioned away from the center where they would add the most stability and control. Unless the "Laminar Flow", "Wake Propulsion", "Open Thermodynamics", "Subsonic Area Ruling" or the other technobably things mentioned on the website somehow compensate for this, it seems like a lose-lose design.
- Scramblejams 14y ago
  IAAAE (I am an aerospace engineer). Actually, long (or wide, to use your term) wings tend to be more efficient. The term you're looking for is "high aspect ratio," which efficient airplanes (see the Global Flyer, for example) have in abundance. It is the ratio of wing span squared to wing area (viewed from above, not the front). The explanation for why this is true is complicated, but this gives a good overview: http://en.wikipedia.org/wiki/Aspect_ratio_(wing) http://en.wikipedia.org/wiki/Aspect_ratio_(wing)
  - ajross 14y ago
    Yeah, this isn't insane. Basically it's a T-tail horizontal stabilizer where the vertical stabilizer has been split in four sections and placed outboard to clear the rear-mounted propeller. There's nothing wrong about this. The stabilizer might be a little farther forward than some designs (it's not clear where the c.g. would be looking at that drawing, one assumes in the middle of the four passenger seats), but not radically so. That's not saying it's an amazing new design which will break records or anything (it can't be -- subsonic aerodynamics is literally an 80-year-old-mature technology). But it's attractive and looks like a clean design at first glance.
  - BenoitEssiambre 14y ago
    If I understand correctly, this seems like yet another reason why this Synergy design would be sub optimal. The two sets of short low aspect ratio wings are theoretically less efficient than one set of long high aspect ratio wing. Correct?
    - Scramblejams 14y ago
      I don't know what their numbers are, but for an aircraft of its class, the lower wings don't look like they have an abnormally low aspect ratio. The upper wings look to be of a higher aspect ratio than conventional elevators. Since elevators are a source of drag (they usually have to provide some downforce to trim the aircraft in level flight, and you can't make lift without making drag), that could be a win. But then they're close to the CG, so they'll need to provide more trim force (short lever arm as you mentioned), and the advantage might be lost. Of course there are other factors at work. For example, Jet A carries more energy per pound than 100LL and diesels are more efficient, so you carry less fuel for a given range. But the engine needs to be stronger to run a higher compression ratio, so that's some added weight. Every little design feature of an aircraft interacts with every other design feature. Aircraft design can be a tremendously unintuitive affair. That's why it's so fun. So, the proof's in the pudding. The ultimate arbiter of an efficient aerodynamic design is its lift-to-drag ratio, or how much drag is generated for a given amount of lift produced. (See http://en.wikipedia.org/wiki/Lift-to-drag_ratio http://en.wikipedia.org/wiki/Lift-to-drag_ratio) They should be getting good data off their scale model, and if the model's L/D ratio is high and they've done their homework to reflect the full size aerodynamics, then they might have something.
asynchronous13 14y ago
The box-wing is actually a really old design - contemporaries of the Wright brothers were experimenting with it. The main advantage is reduced drag. Airflow doesn't like points, and wingtips contribute a lot to the overall drag. Closed wing means no tip, and therefore less drag. Of coarse box-wing has its problems, too. They claim to have solved some of those issues. I'll remain skeptical until the flight test proves their claims. The 1/4 scale model means almost nothing. A colleague put an electric motor on an 8-ft chunk of foam and flew that around. The power to weight ratio of small r/c aircraft is ridiculous, and it does not scale to full sized aircraft.
- amalag 14y ago
  Well the question is if they scaled everything in the 1/4 scale model, including power. They say it is flying since 2007 so we have to assume they did their homework before trying to make the current full scale prototype.
  - bradleyland 14y ago
    It doesn't work like that because all of the factors don't scale at the same rate. I'm not an engineer, so unfortunately I can't elaborate with much detail for you, but the general concept is that factors like aerodynamic efficiency and power efficiency can't be scaled up and down independently in a rudimentary way.
    - Someone 14y ago
      The simplest one probably is that lift and drag scale with wing area, while aircraft weight scales with its volume. That means that, if you do things at quarter scale, you have 1/64 or about 1.5% of the weight, but 1/16 or about 6% of lift. Consequently, almost everything flies at that scale. The model plane will also be extremely robust, as its landing gear can take 1/16 of the original one, but has to carry only 1/64th. All of these are, of course, only valid to a rough approximation; look up "scaling laws" if you want to learn more)
    - evilkillerwhale 14y ago
deleted 14y ago
[deleted]

deleted 14y ago

[deleted]

ajross 14y ago
Vortices generated by induced drag really aren't "horrendous" except in high angle of attack situations. In cruise, even with slow planes like this, most drag is parasite drag. Commercial jetliners have been deploying winglets to mitigate the same effect for decades now, and the effect is something like a 2% fuel savings. It's worth doing, but it's not a game changer.

BenoitEssiambre 14y ago

Yeah I'm not sure this project passes the smell test. I don't know much about airplanes but a few things seems off when I think of this design in terms of basic physics. The "boxwings" seem to be a worst of both world approach. It ads a lot of surface going across the air and thus a lot of drag, without providing the width which would usually make available the torque necessary for stability and control. Torque is (force * distance) and, for roll control, this distance is usually provided by wide wings. An airplane having shorter wings would probably go through the air more efficiently (provided you didn't add a second set of wings on top of the first one) but would not provide much control to enable safe flight in all possible conditions. Short wings don't provide much leverage on the roll axis. It also seems like in this design the top part of the "boxwings" plays the role of the tail of the plane. However, it looks like we get the same (force * distance) problem but on the pitch axis. In order for the tail to give a good amount of torque for pitch control, it has to be located away from the wings and the center of the aircraft. Again, I'm just guessing based on physics here but since there is no tail other than the one located near the bottom wings, it might be difficult to stop the plane from pitching up or down out of control. If we were to design planes for efficiency only, they would look like arrows or missile. They would have minimal wings or fins to slow them down. The reason, we have to have things sticking out far from their middle, is to add the ability to safely control them in a wide variety of conditions. This aircraft has both lots of wing, thus a lot of drag and yet the extra wingage doesn't get the wings positioned away from the center where they would add the most stability and control. Unless the "Laminar Flow", "Wake Propulsion", "Open Thermodynamics", "Subsonic Area Ruling" or the other technobably things mentioned on the website somehow compensate for this, it seems like a lose-lose design.

Scramblejams 14y ago
IAAAE (I am an aerospace engineer). Actually, long (or wide, to use your term) wings tend to be more efficient. The term you're looking for is "high aspect ratio," which efficient airplanes (see the Global Flyer, for example) have in abundance. It is the ratio of wing span squared to wing area (viewed from above, not the front). The explanation for why this is true is complicated, but this gives a good overview: http://en.wikipedia.org/wiki/Aspect_ratio_(wing) http://en.wikipedia.org/wiki/Aspect_ratio_(wing)
- ajross 14y ago
  Yeah, this isn't insane. Basically it's a T-tail horizontal stabilizer where the vertical stabilizer has been split in four sections and placed outboard to clear the rear-mounted propeller. There's nothing wrong about this. The stabilizer might be a little farther forward than some designs (it's not clear where the c.g. would be looking at that drawing, one assumes in the middle of the four passenger seats), but not radically so. That's not saying it's an amazing new design which will break records or anything (it can't be -- subsonic aerodynamics is literally an 80-year-old-mature technology). But it's attractive and looks like a clean design at first glance.
- BenoitEssiambre 14y ago
  If I understand correctly, this seems like yet another reason why this Synergy design would be sub optimal. The two sets of short low aspect ratio wings are theoretically less efficient than one set of long high aspect ratio wing. Correct?
  - Scramblejams 14y ago
    I don't know what their numbers are, but for an aircraft of its class, the lower wings don't look like they have an abnormally low aspect ratio. The upper wings look to be of a higher aspect ratio than conventional elevators. Since elevators are a source of drag (they usually have to provide some downforce to trim the aircraft in level flight, and you can't make lift without making drag), that could be a win. But then they're close to the CG, so they'll need to provide more trim force (short lever arm as you mentioned), and the advantage might be lost. Of course there are other factors at work. For example, Jet A carries more energy per pound than 100LL and diesels are more efficient, so you carry less fuel for a given range. But the engine needs to be stronger to run a higher compression ratio, so that's some added weight. Every little design feature of an aircraft interacts with every other design feature. Aircraft design can be a tremendously unintuitive affair. That's why it's so fun. So, the proof's in the pudding. The ultimate arbiter of an efficient aerodynamic design is its lift-to-drag ratio, or how much drag is generated for a given amount of lift produced. (See http://en.wikipedia.org/wiki/Lift-to-drag_ratio http://en.wikipedia.org/wiki/Lift-to-drag_ratio) They should be getting good data off their scale model, and if the model's L/D ratio is high and they've done their homework to reflect the full size aerodynamics, then they might have something.

asynchronous13 14y ago

The box-wing is actually a really old design - contemporaries of the Wright brothers were experimenting with it. The main advantage is reduced drag. Airflow doesn't like points, and wingtips contribute a lot to the overall drag. Closed wing means no tip, and therefore less drag. Of coarse box-wing has its problems, too. They claim to have solved some of those issues. I'll remain skeptical until the flight test proves their claims. The 1/4 scale model means almost nothing. A colleague put an electric motor on an 8-ft chunk of foam and flew that around. The power to weight ratio of small r/c aircraft is ridiculous, and it does not scale to full sized aircraft.

amalag 14y ago
Well the question is if they scaled everything in the 1/4 scale model, including power. They say it is flying since 2007 so we have to assume they did their homework before trying to make the current full scale prototype.
- bradleyland 14y ago
  It doesn't work like that because all of the factors don't scale at the same rate. I'm not an engineer, so unfortunately I can't elaborate with much detail for you, but the general concept is that factors like aerodynamic efficiency and power efficiency can't be scaled up and down independently in a rudimentary way.
  - Someone 14y ago
    The simplest one probably is that lift and drag scale with wing area, while aircraft weight scales with its volume. That means that, if you do things at quarter scale, you have 1/64 or about 1.5% of the weight, but 1/16 or about 6% of lift. Consequently, almost everything flies at that scale. The model plane will also be extremely robust, as its landing gear can take 1/16 of the original one, but has to carry only 1/64th. All of these are, of course, only valid to a rough approximation; look up "scaling laws" if you want to learn more)
  - evilkillerwhale 14y ago

deleted 14y ago

[deleted]