How is such a small vehicle that connects to an airplane able to push it and direct it away from the terminal?
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Airport tugs are generally quite heavy, have powerful engines and good grip. Tugs for large commercial aircraft often have additional ballast and weight tens of tonnes.
Aircraft are relatively light, even fully laden.
A point to consider: it generally only takes one person to push a car in neutral around, if slowly. What matters is sufficient grip and enough force to get it rolling.
Even then, compare the tug and aircraft to a rail locomotive in a freight train.
95% of the mass of the tug is its engine and transmission. Also when the planes pilot releases the brakes for push-back, the plane is rolling
That small car is the ‘pushback tug’ and weighs over 110,000 lbs, it’s large (looks small sitting in front of a huge plane) and is a heavy vehicle and can pull 75,000 lbf (remember Lb is a unit of mass while Lbf is pound-force) and an aeroplane engine has a 250,000 lbf, to compare powers. Why do they need them? because while the plane is more than capable of moving on its own, if it was to start the engines and push that close to the building and terminals it would cause damage to them as well as other plane engines that now have debris stuck in the fins.
Think of it like a tugboat with a large ship. When you see a large ship only a tiny portion of it is the engine. The rest of it is where it carries the cargo. On the other hand a tugboat is basically just the engine.
Think of that little vehicle moving the plane around as though it was an engine built into the airplane. the benefits being in that little vehicle said it doesn’t have to fly that heavy engine around
Small vehicles can be incredibly heavy and powerful, and that allows them to exert more force than you’d assume for their size. A typical forklift, for example, is smaller than a 5,000 pound SUV, yet they can weigh upwards of 20,000 pounds and while they don’t have much *raw* horsepower, they are geared and tuned to output a fuckton of torque so they can (albeit slowly) move extremely large objects.
Once the brakes are released, the wheels of an aircraft roll independently; they don’t have gearshafts and arent connected to an engine. Basically, the plane is on rollerskates at that point. As a result, even a single sufficiently strong human being could move it; see World’s Strongest Man competitions and exhibitions. Now, to move a plane at a reasonable speed so that it is clear of the terminal and able to taxi inside of a few minutes, the not so small tugs are 50 ton vehicles that are mostly engine.
Much like a tractor…it is all about weight and torque. A little vehicle which is made up of a heavy ballast and a small gear ratio (similar to 4×4 low range) is enough to tow something much larger.
Also, airports are largely flat areas which means that the little tugboat is only fighting the weight of the plane and not gravity.
it’s similar to a forklift carrying huge weights because it’s basically a concrete block driven by a very powerful but slow engine. Smaller wheels are also useful to ensure speed remains low.
The tug just needs to overcome the rolling resistance of the aircraft, some gravity if there’s an incline (like for drainage), and wind. That is all tremendously less force than equivalent to the weight of the aircraft.
An example though, a 747-400 can weigh up to 910,000 lbs at takeoff. The rolling resistance of the aircraft could be around 0.02 (a unitless value). On a level surface with no wind you could move the aircraft with a force of 18,200lbs of force.
The tug just needs to weigh enough to get a grip on the concrete to be able to push that hard. That’s determined by the coefficient of friction between the tires and ground (perhaps 0.8). So the tug would weigh around ballpark of 23,000 lbs. So the tug is massively lighter than the aircraft. Then to make the force needed (the 18,200lbs) you use gearing to increase the engine torque and turn the wheels.
Ford did a gimic commercial like this scenario, except it was a pickup pulling train cars. It may have been 1,000,000 lbs of train, but the rolling resistance of steel wheels on steel tracks is comically low. Thus, a 6000lb truck was able to move a 1,000,000lb chunk of train.
The drag coefficient between the wheels of the plane and the tarmac is low enough that a small vehicle is easily able to overcome it and pull the plane easily,.
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