What the split strut does to an inflatable wing canopy

The patent

US7032864B2 — Wing with inflatable struts

Filed / granted

December 2003, priority December 2002 / April 2006

Named inventor

Tony Logosz, alone

Cited by

18 later patents

What was the canopy doing before this?

An inflatable wing is a pressurised frame with a membrane on it. The leading edge is the spine, the rib struts run back from it, and the canopy is the surface that actually does the work of making lift.

The obvious way to join those two things is to lay the canopy over the struts and sew it down along the top of each tube. It is simple to build, and it works. But it makes the strut something the canopy hangs from — a spar underneath a membrane. The membrane still has to hold its own shape in every panel between one strut and the next, and under load it does that by stretching until the pressure and the tension find a compromise. The compromise is rarely the profile anyone drew.

What changes when you attach it twice?

Tony's patent describes securing the canopy to each rib strut "at two radially spaced points on the circumference" of the tube, along its length. Two attachment lines instead of one, sitting either side of the tube's crown.

That sounds like a sewing detail. It is a structural change — and it is upstream of every number anyone quotes about a wing, because span, profile and area only describe a shape while the shape is still there under load. With two lines the strut is no longer suspended below the surface; it is part of the surface, taking span load directly along its length. The canopy either side of it is a shorter unsupported panel with a stiffer edge to work against.

So where does the gust relief come in?

The patent claims the member as "elastically deformable" — it gives under a spike in load and bleeds some of it off rather than transmitting all of it to the rider. That is a real behaviour and it is in the claim language.

But it is an effect. The invention is the structure that produces it. OXZA's own founder record called this patent a "gust-relief canopy" for two years, which is a bit like describing a truss as a way of not falling over: true, and it tells you nothing about the idea. The patent record now names it correctly, which took reading the claim rather than the summary.

Why did the rest of the industry end up here?

Eighteen later patents cite this one. That is the measurable part. The unmeasurable part is that the construction became normal — the thing you would have to explain yourself for not doing.

The riders are the visible half of that. The kites carrying this construction took world titles in 2011 and 2012, then four in a row from 2015 to 2018, and none of those results belong to OXZA — they belong to the riders and to the company Tony designed them at.

Does any of this reach a hydrofoil?

Not the part number, and not the patent — those are assigned to Slingshot Sports LLC, and OXZA neither owns nor licenses them. What carries over is the habit behind it.

The same question shows up every time a load path meets a joint: is this part hanging off that part, or are they one structure? A canopy sewn over a tube is the first answer. A canopy split around it is the second. Twenty years later the OX Lock connection is the same argument in aluminium and carbon — a shoulder that carries load in shear rather than bolts asked to hold two separate things together.

This is the first entry in Hood Memory Lane, which is a record of what got built in Hood River before OXZA existed, told in the past tense because that is where it happened. The dated version lives on Tony's timeline, the parts of it we could not confirm are listed rather than smoothed over, and the current work is the REVSTAR system — where the same question is being asked of a foil.