Cargo aircraft can carry pallets and ULD containers that weigh hundreds or thousands of kilograms, so crews need systems that reduce friction and guide loads accurately. A cargo loading system turns the hold floor into a controlled moving surface using ball mats, roller tracks, powered drives, and locks. This matters because fast loading saves time on the ground, while secure restraint keeps the aircraft safe in flight.
Good loading also protects the freight, the aircraft structure, and the people working near heavy moving cargo.
Ball mats use many free-spinning balls so a pallet can move in several directions during positioning, while roller floors guide cargo mainly forward and backward along the hold. Locks, stops, guides, and restraints hold each pallet or container at approved locations so loads cannot shift during taxi, takeoff, turbulence, or landing. The crew must also follow weight and balance limits because every container changes the aircraft center of gravity.
In practice, cargo loading combines simple machines, friction reduction, structural limits, and careful procedures.
Key Facts
- Rolling contact reduces the force needed to move cargo compared with sliding contact.
- Work to move cargo is W = Fd, where F is the applied force and d is the distance moved.
- Weight is W = mg, where m is mass and g is about 9.8 m/s^2.
- Friction force can be estimated by Ff = μN, where μ is the coefficient of friction and N is the normal force.
- A pallet must be locked in place so flight loads cannot make it slide, tip, or rotate.
- Weight and balance use moments: moment = weight × arm, and total center of gravity = total moment ÷ total weight.
Vocabulary
- ULD
- A Unit Load Device is a standardized aircraft pallet or container used to group cargo for loading and restraint.
- Ball mat
- A ball mat is a floor section with many rotating balls that let cargo move in several directions with low friction.
- Roller floor
- A roller floor is a set of rollers that supports cargo and helps it move mainly along a chosen loading direction.
- Cargo lock
- A cargo lock is a mechanical restraint that holds a pallet or container in an approved position during flight and ground handling.
- Center of gravity
- The center of gravity is the balance point of the aircraft and its load, found from the distribution of weight.
Common Mistakes to Avoid
- Treating the floor as frictionless, because ball mats and rollers reduce friction but do not remove it completely.
- Forgetting to engage cargo locks, because a load that moves freely can damage the aircraft and change the center of gravity.
- Confusing mass with weight, because mass is measured in kilograms while weight is the force mg measured in newtons.
- Loading only by available space, because cargo positions must also satisfy structural limits and aircraft weight and balance requirements.
Practice Questions
- 1 A 1200 kg ULD is on a roller floor. If the effective coefficient of friction is 0.03, estimate the horizontal force needed to keep it moving at constant speed.
- 2 A pallet weighing 18,000 N is moved 7.5 m through the hold with an average push force of 450 N. How much work is done on the pallet?
- 3 A crew can place a heavy container either near the aircraft center of gravity or far behind it. Explain which choice usually reduces the effect on balance and why cargo locks are still required.