How is the cushion thickness of an Airdrop Case set?

Answer: Work back from the permitted peak. At 8 m/s and a 45 g limit the stroke needs about 60 mm; at 80 g, 30 mm is enough.

Does the frame have to be metal?

Answer: No. Small cases can use glass-filled nylon at about 30 percent less weight, but joints need through-bolts, since pull-out is 60 percent of an aluminium frame.

Why can't lifting points sit on a radius?

Answer: Stress concentration above 2.5 means more than double the local stress, and cracks start there. Points belong on flat faces at least 25 mm away.

Why make the corners replaceable?

Answer: A cap adds 0.6 kg at four corners, swapped on its own, so the body is not scrapped.

Airdrop Case Structure and Craft: 5 Key Points

Q: How does a latch stay shut yet open easily?

Answer: Through a second motion rather than a heavier spring. The pin slides sideways before the latch lifts, which one hand can do and a single-direction impact cannot.

Quick answer: An Airdrop Case is read in five places: how the cushion absorbs energy, how the shell joins the frame, where lifting points sit, how latches resist release, and how corners are reinforced. Together they decide whether impact is carried as one body or shed layer by layer.

How an Airdrop Case Absorbs Impact
Joining the Shell to the Frame
Where Lifting and Tie-Down Points Sit
Latches and Anti-Release Design
Landing Attitude and Corner Reinforcement
FAQ

1. How an Airdrop Case Absorbs Impact

An Airdrop Case does not cushion with one slab of foam. It works in three stages: a shell that resists puncture and spreads point loads, a middle layer that stretches the deceleration distance, and a liner that locates. At an impact speed of 8 m/s, a 20 mm stroke peaks near 120 g; at 60 mm it falls to about 45 g.

Layer	Common material	Reference thickness	Function
Shell	Rotomoulded PE or modified PP	4.5 mm	Puncture resistance, spreading
Cushion	EVA foam, expanded PE	30 to 60 mm	Stroke, energy absorption
Frame	6061-T6 aluminium tube	20 × 20 × 2 mm	Shape retention, load path
Liner	Low-density EVA or sponge	10 to 15 mm	Location and wear

Material follows the temperature band. EVA at 45 kg/m³ holds its rebound but stiffens at -40°C, losing about 30 percent of its cushioning; expanded PE stays flatter in the cold but absorbs 20 percent less at equal thickness. Cold-climate cases stack the two, and closed-cell content below 85 percent lets the cushion collapse, so the second impact peaks 25 percent higher.

2. Joining the Shell to the Frame

Shell and frame are two materials with two stiffness values, so the joint fails first. The usual route is an M8 insert moulded into a 4.5 mm PE wall, a 6061-T6 tube frame at 2 mm, and bolts torqued to 12 N·m.

Airdrop Case: a sand case open on a workshop floor, black foam across the lid, a divided liner below, shelving behind

Pull-out strength is the hard number: an M8 insert should hold 3 kN at room temperature, and a wider flange at the base does more than a bigger bolt. A 2 mm nylon washer between frame and skin stops metal grinding into plastic. Hinges run three across at 300 mm centres.

3. Where Lifting and Tie-Down Points Sit

Lifting points decide how load leaves the body, so position beats count. Four points sit either side of the centre of gravity at 2.5 kN each, with a factor of three.

They do not belong on a radius, where stress concentration exceeds 2.5 and more than doubles the local stress; points sit on flat faces at least 25 mm away, backed by a 3 mm steel plate. Six tie-down rings at 25 mm webbing stay near the lower frame nodes.

4. Latches and Anti-Release Design

Latches must stay shut under impact and still open one-handed. The answer is a two-point latch with a safety pin, a PA66 body at 30 percent glass fill, 8 mm travel and about 120 N opening force.

Airdrop Case: a closed sand case on a concrete floor, corner caps and lid ribs visible, two latches and a centre handle

Anti-release comes from a second motion, not a stiffer spring: the pin slides sideways before the latch lifts. The check is a 2-hour sweep from 10 to 500 Hz plus a 1.2 m drop on six faces. Pivot pins go stainless, since glass-filled nylon keeps half its impact strength at -40°C.

5. Landing Attitude and Corner Reinforcement

Attitude at impact follows from centre of gravity and floor shape. Keeping the centre within 40 percent of case height, on two longitudinal skids, makes the long edges land before any single corner.

Zone	Reinforcement	Size	What to watch
Corners	Replaceable cap	8 mm wall, R25	Cap fit, screws recessed
Base	Longitudinal skids	12 mm high, 30 mm wide	Skid wear
Lid	Transverse ribs	120 mm pitch	No sink marks at rib roots

Corner caps are separate: 0.6 kg across four corners instead of weight everywhere, swapped when worn. Lid ribs at 120 mm pitch need a generous wall transition at the root, or a sink mark drops the wall from 4.5 mm to 3.2 mm and the whole Airdrop Case is thinnest along its lid.

Conclusion

The structure of an Airdrop Case is a load path from outside in: shell spreads, cushion stretches the stroke, frame holds shape, latches hold closure, corners take the first contact. Once stroke, torque, pull-out, opening force and wall thickness are fixed, the structure closes, and that is where Airdrop Case reliability comes from.

This article discusses only the container (case body) side of specifications and design intent, and does not cover any handling, loading or use of the contents.