This is a Sprat 103 ultralight, it has no ailerons, and no ruddervator (on its v-tail). How then does it fly controllably?

Sprat 103 Ultralight

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    $\begingroup$ Early aircraft had no flight control surfaces either. They achieved control by flexing of the wing structure, much like birds do. $\endgroup$ Commented Sep 11, 2018 at 10:13

1 Answer 1


The wing is split to two halves, each half is mounted on its own axis. By changing each half's angle of incidence (and thus angle of attack) changes the amount of lift generated by the relevant side.

See this video of a scale model.

A scheme of the mechanism

enter image description here

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    $\begingroup$ That gives roll. Moving the two halves together changes the incidence angle (aka decalage) between wing and stabilizer, giving pitch control -- and the vertical fin is sized to avoid excessive side slip and make the craft spirally stable, like a free flight model airplane. $\endgroup$
    – Zeiss Ikon
    Commented Sep 10, 2018 at 12:10

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