Let's pick up with the tread and the runway surface — Page 122, Lesson 162

Let's pick up with the tread and the runway surface. We've already covered the basic construction of a tyre cover, so now I want to walk you through the tread patterns and the special features you'll find on nose wheel tyres. First, there's a tread pattern called the Diamond tread pattern. It's not seen as frequently now, but it's still termed the all weather pattern. So if you hear someone refer to an "all weather" tread, they mean the diamond pattern. It's a specific design that's been around for a long time. Now, let's talk about nose wheel tyres, particularly those fitted to aircraft with the engines mounted on the rear fuselage. These tyres may have a chine moulded onto the shoulder of the tyre. A chine is a raised rib or ridge. Its purpose is to direct water away from the engine intakes. This is to prevent flameouts due to water ingestion. So when the nose wheel rolls through standing water on the runway, the chine deflects that water sideways, away from the engine intakes, so the engine doesn't suck in water and flame out. Here's an important detail: a nose wheel tyre fitted to a single wheel installation will have a chine moulded onto both sides of the tyre. That makes sense — if there's only one wheel, water can be thrown off either side, so you need protection on both sides. Now let's move on to Inner Tubes. An inner tube is manufactured by an extruding machine. This machine forces a compound of hot rubber through a circular die, producing a continuous length of tubing. The requisite length is then cut off. The ends are butt welded together, and a valve is fitted. The tube is then placed in a mould, inflated, and vulcanized. Vulcanization is the process of curing the rubber with heat and pressure to give it its final properties. This produces the finished tube to the required dimensions. Now, here's a critical point about heat. During braking, excessive heat is generated in some types of brake unit. This heat could cause damage to a standard base tube. So, depending on the design of the wheel and the type of brake unit, the tube may have a standard, thickened, or cord reinforced base. The base is the part of the tube that sits against the wheel. If you have a high-energy brake unit, you might need a thickened or cord-reinforced base to withstand that heat. When renewing a tube, it must be replaced by one of the same type. You can't just swap in any tube — it has to match the specification. Now, the Inflation Valve. The tube is inflated through an inflation valve. The stem of the valve is attached to the rubber base by direct vulcanization, and the rubber is vulcanized to the tube. Because of this, renewal of the inflation valve is not permitted. You can't replace just the valve — it's permanently bonded to the tube. Each inflation valve is fitted with a Schrader valve core. This operates as a non-return valve, meaning it lets air in but prevents it from escaping. However, the valve core is not considered to be a perfect seal. Therefore, the inflation valve must always be fitted with a valve cap. The valve cap serves two purposes: it provides the final seal, and it also prevents dirt from entering the valve. The older type of valve core has a spring made of brass, but the modern type is fitted with a stainless steel spring. Now let's look at Tubeless Tyres. These tyres are similar in construction to a conventional cover that would be used with a tube. But there's a key difference: an extra rubber lining is vulcanized to the inner surface and the underside of the beads. This lining retains the gas pressure and forms a gas tight seal on the wheel rim. The gas seal depends on a wedge fit between the underside of the tyre bead and the taper of the wheel rim on which the beads are mounted. So the bead — that's the edge of the tyre that sits on the rim — wedges against the tapered rim surface to create the seal. That's how a tubeless tyre holds its pressure without an inner tube. So to summarise what we've covered: the diamond tread pattern is the all weather pattern, nose wheel tyres may have chines to deflect water away from engine intakes, inner tubes are extruded, butt welded, and vulcanized, with different base types for heat resistance, the inflation valve is permanently vulcanized and must always have a cap, and tubeless tyres rely on a wedge fit between the bead and the rim taper for their gas seal.