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Could long, aftermarket hydrofoils be added to the water-skids of a plane (like this Cessna with pontoons or smaller)

enter image description here
Cessna 208 Caravan

not designed to have a hydro foil, to increase its ability to land on choppier water?

In theory, the pilot would first enter the water with the skids, clear of the chop, then stall the hydro foil similar to stall landing a plane thus giving the plane a soft or possibly vertical landing.

enter image description here
Grumman JRF-5 with hydrofoils

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    $\begingroup$ The chances of getting the angle of attack wrong when it hits the water the first time seems like it would rule this out. $\endgroup$
    – Ron Beyer
    Aug 2, 2020 at 21:38
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    $\begingroup$ Would you please edit your post to include source attribution for your images. $\endgroup$
    – FreeMan
    Aug 3, 2020 at 11:07
  • $\begingroup$ @FreeMan It took me some time to find them off Google Images, but I'll try to find a website that has these planes. $\endgroup$
    – Justintimeforfun
    Aug 3, 2020 at 16:20

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It's been done. David Thurston designed a system for the Lake LA-4 that was purported to allow it to land on 5ft waves. It may have been a bit of a handful (the Buccaneer is a demanding airplane on its normal hull). It was crashed by someone who took it for a spin without Thurston's authorization, and that was the end of that.

enter image description here

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    $\begingroup$ Nice find on the plane. I'm looking for something or way to make the work for a much smaller and cheaper aircraft. $\endgroup$
    – Justintimeforfun
    Aug 3, 2020 at 4:39
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    $\begingroup$ @Justintimeforfun: But where do you find a smaller & cheaper airplane that will float? $\endgroup$
    – jamesqf
    Aug 3, 2020 at 5:42
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    $\begingroup$ As soon as that hydrofoil touches the water you're going to get a significant pitch down from the moment arm, I can imagine that would make it challenging. $\endgroup$
    – GdD
    Aug 3, 2020 at 9:25
  • $\begingroup$ @GdD right, especially in a plane with such high center of mass. But I think this technology could be quite promising for electric planes, with batteries in the keel making it more stable. If we can even computer-control the hydrofoils' attitude, better yet. $\endgroup$
    – leftaroundabout
    Aug 3, 2020 at 10:59
  • $\begingroup$ So you want to add lots of weight on a long moment arm @leftaroundabout? How's that going to help stability? $\endgroup$
    – GdD
    Aug 3, 2020 at 11:24
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I would make a serious study of this man's work.

Rostislav Alexeyev's "day job" was the design of large hydrofoil ferries, such as the Raketa carrying over 60 people, in the 1950s. This (image from linked article) and its successors are probably the most successful series of hydrofoils in the world.

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He went on to design a series of Ekranoplans, ground effect flying vehicles. (pictured, A-90 Orlyonok, from here

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These, despite being designed at his Central Hydrofoil Design Bureau, all seem to have used conventional stepped hulls like flying boats or seaplane floats.

He is probably the best person to tell you why.

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  • $\begingroup$ The most interesting fact are theses plane are more efficient than modern airliners and hydro foils could allow the a ground effect plane to clear swells in the ocean. It is that rouge wave that makes this dangerous in open seas. $\endgroup$
    – Justintimeforfun
    Aug 3, 2020 at 16:49
  • $\begingroup$ The reason the Ekranoplan uses a conventional hull is pretty simple - a hydrofoil requires a bit of speed to get going and at that point it's already flying. A foil would just be dead weight. $\endgroup$
    – papirtiger
    Apr 2, 2021 at 19:58
  • $\begingroup$ @papirtiger true for a suitable definition of "a bit of speed" ... hydrofoils can lift a hull clear of the water at sailboat speeds ... like 5 knots youtube.com/watch?v=UokOO60dsMU $\endgroup$
    – user_1818839
    Apr 2, 2021 at 20:05

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