# Why don't small aircraft produce tyre smoke when landing, but big aircraft do?

On almost any recording of big aircraft landing, a huge cloud of smoke can be seen. This even applies to the relatively small Cessna Citation. But I never saw such smoke, at least not visible one, on a landing of a, say, Cessna 210.

If it is simply the touchdown speed (140 on a Boeing 777, 60 - 70 for a Cessna 210), what is the decision speed between smoke / no smoke ?

It is not only the speed, but the combination of several effects:

• Landing speed: The much higher wing loading of airliners, even at the end of their trip, results in touchdown speeds in the area of 120 - 150 knots while GA airplanes will have only half that speed at touchdown. The kinetic energy of the rotating tire is proportional to rate of rotation squared, so an otherwise identical tire needs to change its energy by a factor of four when you compare airliner to GA conditions.
• Tire size: Your average GA tire has much less inertia (the quantity which determines how much energy is needed to spin up the tire) than the much larger and heavier airliner tire. Still, spinup happens by friction between rubber and concrete, with much the same limits on material strength and melting point. Inertia is proportional to mass and radius squared, and if you compare the dimensions of GA and airliner tires, radius grows from 24 cm on a Beech Bonanza (main tire mass is 5.8 kg each) to 68 cm on a Boeing 777 (main tire mass is 125 kg each).
• Area load is much higher in airline tires. Just compare the typical tire pressure to get an idea how much more weight per area the airliner tires have to carry.
• Landing technique: Whereas you want a firm touchdown with airliners so the load on the landing gear will allow spoiler deflection and brakes can immediately be effective (resulting in a spinup time of just 0.07 seconds for airliner tires), the much shorter landing distances of GA airplanes allow to strive for a "greaser" at touchdown, where wheel spinup is gradual and the heat at the contact area of the rubber surface will stay well below its melting point.

As a result, the wear volume (the volume of rubber used up) in a GA landing is insignificant while it reduces the number of landings between tire changes for airliners to just 200. This study shows in detail how wear volume can be calculated while this study goes into the dynamics of how landing smoke is caused for different pre-rotation speeds.

• Also consider that most light aircraft pilots have to pay for their own tires :-) Though you can get some smoke when practicing short field landings. Nov 22, 2021 at 2:59
• I'm surprised by your last bullet point. I always thought a firm touchdown spins up the tires faster and therefore produces less smoke (and vice versa). Nov 22, 2021 at 9:24
• and of course the smaller size would mean a smaller amount of smoke if there is smoke and it being less visible to an observer (and visible for less time, especially as it's also blown away more by the prop). Nov 22, 2021 at 10:09
• Have they considered, on large aircraft, adding motors to get the wheels spinning at approximately the correct speed prior to landing? The motors would add some expense, but might save a lot in the long run in constant replacement of tires... Nov 22, 2021 at 14:58
• @DarrelHoffman See this question: Why are aircraft tires not pre-spun prior to landing to preserve them? Nov 22, 2021 at 15:40

The smoke produced from a stationary tire of, say, 12 inches diameter, contacting pavement at 70 kts, is not enough to be clearly visible because there isn't enough heat energy created during the contact and spin-up.

You have two big factors at work; the contact velocity is low, and the wheel's inertia is low, so that the tire is able to accelerate to its rolling rpm quickly and doesn't spend much time skidding along.

The 777 tire on the other hand contacts at 140kt or whatever it is, and spends maybe half a second to a second spinning up to the full rolling velocity. That's a lot of sliding rubber at very high velocity, lasting long enough to make a lot of heat.

If you are landing a light aircraft and touch down fast and get hard on the brakes, you can get the tires to smoke quite nicely in some cases.