I am a hobbyist and in the process of designing a human-powered hydrofoil (see Hydroped for reference) I'm kind of stuck in the calculation of the the maximum buckling load for a strut.

The strut is modeled as a vertical column with a wing at the lower end and the load at the upper end. My question is: how should I set the end conditions for this problem? I was thinking that the lower part could be considered fixed (the wing), because it's relatively still with respect to the water flow, and the upper part could be considered free. But the wing can actually move around in the water, so it should really be considered free as well?

A next step would be figuring out how to calculate the stress on a strut which has a sweep angle, but I guess the best approach is to take one step at a time...Any help is appreciated!

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    $\begingroup$ buckling tends to be for static structures. $\endgroup$
    – Tiger Guy
    Jul 12, 2023 at 21:29

1 Answer 1


I think the most important force is the shock and torque and moments imparted to the post by the hydrofoil. or to the hydroped by the rider.

You would need to take into account that sometimes the thing flies off the crust of the big waves, sours up to 20 feet, and land or crash into choppy waters.

The dynamics of the lift and turning of the foil have significant stresses.

Buckling is the least of concerns when we have moments applied both on the top connection of the post to the board and the bottom connection of the post to the foil. You design the post as a beam-column member.

Some manufacturers of gear use carbon fiber for extra strength! hydrofoil

  • $\begingroup$ I see...keep in mind that this contraption is not meant to fly out of the water as a kite surf foiler, rather it's a low-flying-leisure-time-at-the-lake kind of machine $\endgroup$ Jul 12, 2023 at 20:22
  • $\begingroup$ @PhilSweet, these hydrofoils receive as a command (tilting or shifting CG of the rider) moment, torque, and axial force and deliver as feedback maneuver, lift, moment both transversely and longitudinally, torque, and moment. They are basically wings producing roll, lift, yaw, and turn. These are transferred to the post only if both top and bottom connections are fixed. These are efficient new technologies that take advantage of the huge lift created by the top side of the foil. thus they can be much smaller than the old school gliding on water ideas! $\endgroup$
    – kamran
    Jul 13, 2023 at 0:25
  • $\begingroup$ Sorry kamran, that comment was supposed to be attached to the question, not your answer. But under buckling analysis, fixed ends means that both ends are fixed to the same rigid frame - no relative rotation or translation of the ends relative to each other. Here the ends are not fixed relative to each other, so the shape will be 1/4 of the shape of a doubly fixed structure and 1/2 the shape of a doubly pinned structure. $\endgroup$
    – Phil Sweet
    Jul 14, 2023 at 0:15
  • $\begingroup$ @PhilSweet, they are meant to be fixed at both ends albeit with the understanding that no material is rigid. The fixed joints at both ends make it possible for exact input of steering commands and exact feedback of the maneuvers to the rider. The more tight the frame the more accurate navigation. $\endgroup$
    – kamran
    Jul 14, 2023 at 6:50

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