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Split flap

What is a split flap? · Standard part · basis: Design rules and figures from the cited sources; example geometry by Xem Studio

Also called: split flaps, split flap rc, lower surface flap, intrados flap, split flap vs plain flap, dive flap, landing flap drag

Exact dimensions. True size, with no printing tolerance added.

sizes
3 in table

Notes

  • A split flap hinges down from the lower surface only, leaving the upper surface in place; it gives slightly more lift than a plain flap but high drag, and fully extended it adds high drag with little extra lift (FAA PHAK ch.6).
  • That drag is useful for steep approaches. Arnedo groups the plain and 'intrados' (lower-surface) flap together at a section CLmax increment of about 0.9.
  • The file is a reference example built by Xem Studio from the numbers above. Sizes the sources do not fix are illustrative; scale the example to your own vehicle.

Split flap size chart

parametervalue or rangesource
Section delta-CLmax (intrados flap)0.9Arnedo (Franchini)
Lift vs plain flapslightly greaterFAA PHAK ch.6
Reference buildchord 100, 25% lower-surface flap, 45 degillustrative

Where the files are

Other publishers' files are linked, not hosted. "verify" = check the license at the link before commercial use.

FAAPilot's Handbook of Aeronautical Knowledge (FAA-H-8083-25), Ch. 6 Flight ControlswebPublisher's page; dimensions are facts
LibreTexts (Arnedo, Fundamentals of Aerospace Engineering; data from Franchini et al.)3.4.3 Increase in CLmax (high-lift devices)webPublisher's page; dimensions are facts

Free files

★ Free files 1 parts. Xem Studio design: free to use, print and sell things from; not to be republished as files. Xem Studio Design License. index.json

split-flap-wing-segmentsplit flap: wing segment 100 mm chord × 300 mm, 25 % chord surface deflected 45°STEP · STL
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Plain text: sheet.txt · JSON: /api/geometry?object=split-flap

Split flap, isometric render of a generated part
Render of split-flap-wing-segment from the free STEP; not to scale.

Fits with

Plain flap, isometric render of a generated part
Plain flap6 sizes★ 1 file
Slotted flap, isometric render of a generated part
Slotted flap5 sizes★ 1 file
Fowler flap, isometric render of a generated part
Fowler flap5 sizes★ 1 file
Leading-edge slat and fixed slot, isometric render of a generated part
Leading-edge slat and fixed slot5 sizes★ 1 file
Gurney flap, isometric render of a generated part
Gurney flap5 sizes★ 1 file
Leading-edge cuff (drooped leading edge), isometric render of a generated part
Leading-edge cuff (drooped leading edge)4 sizes★ 1 file

Questions

Why use a split flap on a model?

It is easy to add and gives high drag with a lift gain for steep landings (FAA PHAK ch.6).