WingHopper · Designer · Guide · Sections · Reef · Methods · Pricing · FAQ
For four ways of building a wing: how it carries load, how it breaks and why, the check that looks for each failure, and where to find it. Each section ends with what no check covers.
Lift bends the wing upward like a cantilever held at the mount. The bending moment and the shear force are both largest at the root and fall to zero at the tip, which is why most failures start near the mount.
Set the construction and materials first in Analyze > Strength > Setup. The checks are only as good as those numbers, so use supplier or measured properties when you have them.
Checks read as a percent of the allowable: amber over 75%, red over 100%. In the full foil view they read as a margin of safety instead, green at zero or above. The bolt and washer checks only run with Model mounting holes turned on in Analyze > Strength > Setup.
The skins work like the flanges of an I-beam. Bending puts the lower skin in tension and the upper skin in compression. The foam holds the skins apart and carries the shear between them. Both parts have to survive, and so does the bond that joins them.
| Failure | Why it happens | Check | Where |
|---|---|---|---|
| Skin breaks | Skin stress is the bending moment divided by skin area and the distance between the skins. A thinner section or thinner skin raises it. | Skin / solid utilization | Analyze > Strength, Color by |
| Bending | Analyze > Strength > Checks; Build > Plies | ||
| Upper skin wrinkles | A thin skin in compression on soft foam buckles into short waves. The stress where this starts depends on the stiffness of the skin and the foam, about 0.5 × ∛(E skin × E foam × G foam), and is often far below the skin's strength. Stiffer foam raises it. | Buckling | Build > Plies |
| Foam shears | The shear force passes through the foam between the skins. Low-density foam is weak in shear, and pumping repeats the load every stroke, so foam can fail in fatigue below its one-time strength. | Core shear utilization | Analyze > Strength, Color by |
| Core shear (peak load); Core shear (pumping fatigue) | Analyze > Strength > Checks | ||
| Core shear | Build > Plies | ||
| Skin shears off the foam | The same shear has to cross the glue line between skin and foam. The model assumes a perfect bond and compares the shear there with the bond strength you enter. | Skin interface shear utilization | Analyze > Strength, Color by, with Model set to Ply skins + foam core |
| Wing diverges in twist | When lift acts ahead of the wing's twist axis, it twists the tips nose up, which adds lift and more twist. Above a certain speed the wing's torsional stiffness cannot stop it. ±45° plies add torsional stiffness. | Divergence | Build > Plies |
| Bolts crush the foam | Bolt clamp and lift press the washer into the foam. Foam crushes at a low pressure unless the area under the washer is potted or has a solid insert. | Core under the bolt clamp | Analyze > Strength > Checks |
| Washer pull-through; Core / hard-point compression | Analyze > Strength > Setup, Mount footprint and fasteners | ||
| Root breaks through the bolt holes | The holes remove material exactly where the moment is largest. Composites do not yield around a hole, so the stress peak at the hole edge, about 3 × the average in an isotropic plate, is what starts the break. | Bolt line (net section) | Analyze > Strength > Checks |
| Root at the bolt line | Full foil / efoil > Analyze > Strength |
Where the wing is too thin for 1 mm of foam between the skins, usually the trailing edge and the tip, Analyze > Strength treats it as solid laminate and does not check core shear there.
Not checked: peel at the trailing edge bond, delamination, skin fatigue, impact damage.
All-carbon, G10 or chopped-carbon wings with no core. The whole section carries bending. Stress is highest at the top and bottom surfaces and zero at the middle, and bending stiffness grows with the cube of thickness, so a thin solid tip is much softer than the root.
| Failure | Why it happens | Check | Where |
|---|---|---|---|
| Breaks in bending | Surface stress at the root passes the laminate's strength. | Skin / solid utilization | Analyze > Strength, Color by |
| Bending | Analyze > Strength > Checks; Build > Plies | ||
| Wing diverges in twist | As above. A laminate with mostly 0° plies is stiff in bending but soft in twist. | Divergence | Build > Plies |
| Root breaks through the bolt holes | As above. Solid laminate is just as notch sensitive. | Bolt line (net section) | Analyze > Strength > Checks |
| Root at the bolt line | Full foil / efoil > Analyze > Strength | ||
| Bolt pulls through or tears out | The washer punches through the laminate, the bolt shank crushes the hole wall, or the bolt tears out toward a nearby edge. | Washer pull-through; In-plane bearing; Edge shear-out | Analyze > Strength > Setup, Mount footprint and fasteners |
| Root cracks from repeated load | Every pump and every bump of chop is a load cycle at the root. | Root fatigue | Full foil / efoil > Analyze > Strength |
Bolt line (net section) reports the stress on the material left between the holes. The peak at the hole edge is in its tooltip, not in the percent.
Not checked: delamination, failure of individual plies, impact damage.
Aluminium is isotropic and ductile. Overload bends it permanently rather than snapping it. In practice fatigue is the limit: aluminium has no fatigue limit, so every load cycle uses up some life, and cracks start at holes and sharp corners.
| Failure | Why it happens | Check | Where |
|---|---|---|---|
| Yields in bending | Combined surface stress (von Mises) at the root passes the allowable. | Skin / solid utilization | Analyze > Strength, Color by |
| Bending, with the construction set to Solid plate / block | Analyze > Strength > Checks | ||
| Root breaks through the bolt holes | The holes remove material where the moment is largest. | Bolt line (net section) | Analyze > Strength > Checks |
| Root at the bolt line | Full foil / efoil > Analyze > Strength | ||
| Fatigue crack at the root | Cyclic stress, raised by the notch effect of the holes, is checked against fatigue strength with the Goodman rule. | Root fatigue | Full foil / efoil > Analyze > Strength |
| Threads strip | Steel bolts in tapped aluminium can pull the softer threads out. | Wing seat: aluminium internal thread | Full foil / efoil > Analyze > Strength |
Not checked: corrosion, including stainless bolts in aluminium, and contact stress under the bolt heads.
Solid prints, a printed shell with infill, and prints with bonded rods. Printed plastic is weaker and less stiff than any fibre laminate, and weaker across layer lines than along them, so the model takes separate properties along the span and along the chord. A shell with infill works like a sandwich: the shells carry bending and the infill carries shear. A bonded rod carries bending because it is much stiffer than the plastic around it, and it only helps as much as the glue joint passes load into it.
| Failure | Why it happens | Check | Where |
|---|---|---|---|
| Breaks in bending | Surface stress passes the print's strength in that direction. | Skin / solid utilization | Analyze > Strength, Color by |
| Infill shears | Sparse infill is weak in shear, like low-density foam. | Core shear utilization | Analyze > Strength, Color by, with Model set to Printed shell + infill + optional rods |
| Rod breaks | The rod carries much of the bending near the root. | Rod N: stress demand | Analyze > Strength > Results |
| Glue lets go of the rod | Load passes from plastic to rod through shear in the glue. The model includes the glue's flexibility, so a soft joint carries less. | Rod N: bond demand | Analyze > Strength > Results |
| Rod does not fit | The rod bore plus a printed wall has to fit inside the section. | Rod fit warning; export stays off until it fits | Build > Export > Print kit |
Printed properties depend on material, print direction, shells and infill. The printed starting values are placeholders until you enter numbers for your print.
Not checked: layer lines separating, creep under steady load, water uptake.
Flex is not a failure, but it changes how the wing rides. Analyze > Strength > Results shows maximum displacement and section rotation, and the Deformation control on the wing scales them up so you can see them. Analyze > Strength > Checks shows Tip flex at cruise, red over 6% of half-span. Printed plastic is much less stiff than carbon, so expect more bend and twist at the same load.
Slam loads from breaching and touching down, impact, bolt contact, build defects, and flex feeding back into the flow. The model is linear: past about 5% of half-span deflection or 5° of rotation it flags the result instead of passing it.
Before riding a new construction, load the real wing on the bench and compare it with the Bench bending / twist test operating condition in Analyze > Strength > Setup.