8
$\begingroup$

A biplane whose lower wing is significantly shorter in span than the upper is sometimes called a sesquiplane, from sesqui "one and a half." One whose upper wing is shorter (even slightly, because it's so rare) is called an inverted sesquiplane.

Examples include:

Why would a designer of that era have chosen such a layout, instead of making the longer wing the upper one?
For a century now this layout has fallen into disuse, despite modern homebuilt biplanes, even despite Burt Rutan.

All that I can think of is that the enormous Capronis might have needed extra ground effect from the lower wing.

Improve this question
$\endgroup$
5
  • $\begingroup$ I would think materials of the time might be one of the major reasons, and for fighters the shorter wingers are apparently good for dog-fights. $\endgroup$
    – Mr R
    Commented Dec 25, 2023 at 22:52
  • $\begingroup$ @MrR I've narrowed down the question to: why is the bigger wing the lower one, not the upper one. $\endgroup$
    – Camille Goudeseune
    Commented Dec 26, 2023 at 17:21
  • 1
    $\begingroup$ There's this part-time sesquiplane combination Mistel DFS 230 with Bf 109 or with Klemm KL35 $\endgroup$
    – user21228
    Commented Jan 9 at 23:08
  • $\begingroup$ *inverted sesquiplane combination $\endgroup$
    – user21228
    Commented Jan 9 at 23:21
  • $\begingroup$ Brilliant, @jkztd. Big wing on top would have made for an, um, exciting release! $\endgroup$
    – Camille Goudeseune
    Commented Jan 10 at 15:32

2 Answers 2

Reset to default
5
$\begingroup$

This is a really good question. I have to admit that I am baffled by the few designs which use the inverted sesquiplane layout.

Possible advantages I can come up with:

  • You can use the same wing design and place the lower wing halves left and right of the fuselage and join the upper wings directly above the fuselage. Now the lower span will be wider by the width of the fuselage, but you only need one set of jigs.
  • The upper wing will not only have less span, but also less chord (now you need two sets of jigs, bummer!). With less chord it also is less in the way of the pilot's field of view, especially in turns. This is only valid for small planes with the pilot seated close to the center of gravity, but will not apply to the large Caproni designs.
  • If you put ailerons only on the lower wing, where they have a larger lever arm, the control cables can be run directly between the stick and the bell crank for the aileron, so there is less play in the roll axis controls.

But the disadvantages are also obvious:

  • Less bank angle is permissible before you have wing tip contact during landing.
  • With more lower wing chord, less ground view is left for the pilot, especially when seated close to the center of gravity.
  • Especially important for the adherents of the pendulum fallacy: The sesquiplane is believed to be more stable in roll.
Improve this answer
$\endgroup$
5
  • $\begingroup$ Why does the the upper wing's chord shorten? $\endgroup$
    – Camille Goudeseune
    Commented Dec 26, 2023 at 17:33
  • $\begingroup$ The deficit in the upper wing's span is quite a bit more than the fuselage width, in the 3-views I found. But even so, that could have meant fewer jigs. $\endgroup$
    – Camille Goudeseune
    Commented Dec 26, 2023 at 17:37
  • $\begingroup$ Lower-wing ailerons are plausible especially for the CA.73, where they extend past the wingtips. Mr. C. may have thought that improved roll control would prevent tip strikes better than a shorter lower wing. $\endgroup$
    – Camille Goudeseune
    Commented Dec 26, 2023 at 17:42
  • 1
    $\begingroup$ @CamilleGoudeseune Why shorter chord on the smaller wing? Because it is meant to provide less lift. That has often been done on regular sesquiplanes, so why not on inverted ones? I do not refer to any of your examples in particular, but the concept in general. $\endgroup$
    – Peter Kämpf
    Commented Dec 27, 2023 at 1:03
  • $\begingroup$ Pendulum "fallacy" again? Put a few tons of weight (possibly taken from a sailboat keel improvesailing.com/sailboat/keel/weight ) on the bottom end of a long, rigid, fixed pole projecting 50' down below the bottom of the airplane and see if the shift in CG location, coupled with the sideslip dynamics inherent in any uncommanded turn, don't produce a significant change in the hands-off flying characteristics of the aircraft. If still unconvinced, re-position the pole to project upwards above the aircraft rather than downward below-- $\endgroup$
    – quiet flyer
    Commented Mar 4 at 13:38
5
$\begingroup$

One might be especially fascinated by the airliner design, as the sesquiplane plane structural box was strong, tried and true, and allowed a good place to mount the (more efficient) double propeller.

The Caproni CA.73 airliner could lift 2 tons and fly at around 100 knots, well within the aerodynamic speed limitations of biplane designs, with 2 500 Horsepower engines.

The "inverted" sesquiplane very thoughtfully makes use of ground effect to assist in short/muddy field take offs.

Though many may scoff at biplane designs with more modern materials available, one can't help to notice that thinner wings are better in the high subsonic realm that many airliners operate in.

A proposed airliner design bears an uncanny resemblance to the (non-inverted) sesquiplane, which could allow for higher aspect wings with adequate strength.

Improve this answer
$\endgroup$
5
  • $\begingroup$ How do thinner wings, either literally, or greater aspect ratio, relate to the question? $\endgroup$
    – Camille Goudeseune
    Commented Dec 26, 2023 at 21:53
  • $\begingroup$ @CamilleGoudeseune monoplanes with thicker wings are stronger, but the sesquiplane design may make a comeback for high subsonic airliners. Thick wings do extremely well until Mach effects add to drag. $\endgroup$
    – Robert DiGiovanni
    Commented Dec 26, 2023 at 22:45
  • $\begingroup$ Gotcha. The article proposing a strutted airliner makes sense. But how does that relate to why someone chose (and might again choose a century later) the lower wing rather than the upper to have greater span? $\endgroup$
    – Camille Goudeseune
    Commented Dec 26, 2023 at 23:23
  • 1
    $\begingroup$ @CamilleGoudeseune I believe you had it right by suggesting ground effect, as many airfields at that time simply were not made to handle larger aircraft. Using ground effect this way was not a bad idea. $\endgroup$
    – Robert DiGiovanni
    Commented Dec 27, 2023 at 1:52
  • $\begingroup$ So true. Back then the runways for heavier airplanes were usually water. $\endgroup$
    – Camille Goudeseune
    Commented Dec 27, 2023 at 3:37

You must log in to answer this question.

Not the answer you're looking for? Browse other questions tagged .