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This weekend I saw the Fly Baby at the Smithsonian Air & Space Museum at the Washington Dulles Airport, and it was at some point the smallest airplane (since surpassed by the Bumble Bee II, if I understand correctly). To be able to carry a pilot and lift the plane of the ground in the first place, but still be the smallest airplane, you are mostly limited by wingspan, or more generally, the total width of the airplane.

For the purpose of this question I would like to assume a given airfoil and to exclude modifications to the airfoil itself, i.e. any mechanism that increases lift in pure 2D flow, e.g. camber, slats, flaps, active blowing of the upper surface etc. I would like to limit the scope to the "3D planform" of the wing(s) - e.g. aspect ratio, sweep, depth, winglets/end plates/..., box wings, number of wings etc. The airplane needs to have a fuselage that holds the pilot and an engine. Otherwise the configuration can be whatever it needs to be. If the configuration for maximizing lift depends on the choice of airfoil, then just assume a suitable airfoil.

Both record-holding planes are biplanes, with the Bumble Bee having a relatively large horizontal stabilizer. It also has endplates on the wingtips, reducing lift loss due to the tip vortex.

How can one maximize the lift for a given width?

(I could list all of the ways that come to mind and ask whether and how much they help, but then I'd have "more than one question" and I'm not sure that would be suitable for this format)

Edit: Further clarification: I am asking about maximizing the coefficient of lift of the entire airplane, not about lift itself (which could be maximized by flying faster, to a certain extent). Also, I would like the answer to be valid for low flying speeds (incompressible flow).

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  • $\begingroup$ You're right, I meant the plane needs to only carry a single person. From my understanding, the airfoil is the 2D cross-section of the wing, and the wing is 3D, being a simple extrusion of the airfoil in a straight line, or tapered, or swept ... I tried to add some precision to the question. I wanted to exclude the airfoil and all the tricks to maximize lift in 2D (some I've listed in the question) because the scope would be too large. $\endgroup$ Jan 12 at 13:39
  • $\begingroup$ I clarified further that I am indeed asking about coefficient of lift of the entire plane (yes, fuselage shape has an effect, but speed and weight don't). I think it is very well answerable, since I am pretty sure I am not the first one to think about this, but I personally lack the understanding of intricate 3D flow around multiple wings, that's why I am asking. E.g. could the lift be improved on the mentioned designs by turning the biplane wing into a box wing (everything else being equal)? Is it maximum for 2 wings, or can one add more? $\endgroup$ Jan 12 at 16:19
  • $\begingroup$ The basic design limitations are rather confined, but one must consider the airfoil as a variable in developing that design. Major controlling factors are wing loading and power. One needs sufficient airspeed to get the lift required for flight. $\endgroup$ Jan 12 at 16:22
  • $\begingroup$ Of course, any wing arrangement really (triplanes, box-wings, tandems ...). $\endgroup$ Jan 12 at 16:59
  • $\begingroup$ Of course all we know that horizontal stabilizers always produce downward lift not upward lift-- or-- maybe not? $\endgroup$ Jan 13 at 1:08
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... camber, slats, flaps, blowing of the surfaces

Unfortunately, they are some of the best ways of increasing Coefficient of Lift, far better than trying multiple wings, as seen with the Fiesler Fi 156 Storch.

Deep camber, undercamber, increasing chord (and, proportionally, thickness) are helpful in particular, as are endplates. Another wing or two can be added. Weight should be reduced as much as possible with safe structural strength requirements in mind.

But now you have a very draggy, slow aircraft with limited range, unless you can retract these devices and speed up a little.

Lift is proportional to V$^2$

If you have even more power, and the option to go supersonic, a short single wing like this or a lifting body with no wing at all like this one would suffice.

It really depends on your fuel budget and available thrust. Cost conscious subsonic airliners use retractable lifting devices, and even slower speeds are required only because of airspeed limits, runway length, and the quality of the landing gear (especially tires).

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  • $\begingroup$ Keep in mind some of these "record setting" aircraft may not be very safe to fly $\endgroup$ Jan 12 at 19:00
  • $\begingroup$ Lift is also proportional to S. $\endgroup$
    – Jim
    Jan 12 at 20:36
  • $\begingroup$ "... not very safe" Indeed - don't think about turning in that thing! Ok, maybe 5 degree AOB... $\endgroup$ Jan 13 at 3:08

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