Aircraft Wheels — Page 115, Lesson 157

Let's talk about aircraft wheels. I want to walk you through the key design features that keep a tyre safely on the wheel, and the materials we use to build the wheel itself. First, the big problem we're designing against: creep. When a tyre is in service, it has a tendency to rotate — to slip — around the wheel. We call that slippage "creep." Now, if that creep becomes excessive, it will tear out the inflation valve and cause the tyre to burst. That's a catastrophic failure, so we take it very seriously. Creep is less likely to occur if the tyre air pressure is correctly maintained. But we don't rely on that alone — we build additional precautions into the wheel design. There are three methods of counteracting or monitoring creep. The first is a knurled flange. The inner face of the wheel flange is milled — that means it's machined with a rough, patterned surface. The side pressure of the tyre then locks the beads — the edges of the tyre — to that rough flange, gripping them so they can't slip. The second is a tapered bead seat. Here, the wheel is tapered so that the flange area is of greater diameter than at the centre of the rim. When the tyre is inflated, the side pressure forces the bead outwards, and because of that taper, it grips the rim. So the geometry itself creates the lock. The third method doesn't prevent creep — it monitors it. These are creep marks. We paint two matched white lines, one on the wheel and one on the tyre. If the tyre creeps, those two lines become misaligned, and that misalignment tells us creep is happening before it becomes dangerous. Now let's move to the wheel material itself. Aircraft wheels are either cast or forged, then machined and ground to the required finish. They're made of two main materials: aluminium alloy, and magnesium alloy, which is known by the trade name Electron. After the initial machining, we apply an anti-corrosive treatment. For aluminium alloy wheels, that's anodizing. For magnesium alloy wheels, it's a chromate treatment. And finally, each wheel gets a finish coat of cellulose or epoxy resin paint. Now, there's a special category: wheels for tubeless tyres. These are similar in construction to non-tubeless wheels, but they have a finer finish, and they're impregnated with Bakelite to seal the material — that's what makes them airtight. Between the parts of the wheel, we use 'O' ring seals to prevent leakage. And here's the key difference: unlike tubed wheels, where the inflation valve is a separate tube, in a tubeless wheel the valve is built into the wheel itself. That means the valve is not affected by creep — it can't be torn out. But note this carefully: creep may still damage the tyre. So even with the valve safe, we still need those creep-control measures to protect the tyre itself. So to sum up: creep is the enemy, we fight it with knurled flanges, tapered bead seats, and creep marks for detection. And the wheel itself — cast or forged aluminium or magnesium alloy, treated against corrosion, and finished with paint. For tubeless, add the Bakelite seal, the O-rings, and the built-in valve.