Why a wing breaks a steel column at speed
Steel has a fixed breaking point. The force arriving at it does not: it grows with the square of speed. Below the line, the wing loses. Above it, the steel does.
Each step right is ten times the last, because these numbers are too far apart to draw on a straight ruler. The dashed line is the same column in both rows.
To get through, the wing has to shove that steel out of its path in the time it takes to cross it.
Go twice as fast and you have half the time, and you need the steel gone twice as quick. Both halves double the force. So force climbs with the square of speed.
Fifty times the speed is 2,500 times the force. That is the whole thing.
Thirty seconds of proof
Sandia fired a complete F-4 Phantom into a concrete block in 1988. It turns to dust. It also hits with millions of pounds of force. Both at once, which is the part people cannot picture.
Sandia National Laboratories
Watch on YouTube →The four things people say next
It was. Completely. It still broke the columns on the way in. A thrown wine glass shatters and the window still breaks.
At walking pace, over about a tenth of a second. Everything has time to flex and share the load, so the wing is the weak one. That flips at speed.
That is the wingtip, the last few feet. No engine, no fuel, thin skin. The strong part is the wing box at the root, holding 15 tons of fuel.
Hollow box columns, 14 inches square, about three feet apart. Four inches thick at the ground, a quarter inch up top. Both planes hit up top.
Why time is the real variable
A column in a wall is strong because it is connected to everything around it. Push slowly and the whole building leans in and helps. That sharing travels through steel as a wave, about three miles per second.
80 ms at ramp speed: the signal crosses 400 metres, the height of the tower. The building helps.
1.6 ms at flight speed: it crosses 8 metres. Eight columns know. The rest of the building has not found out yet.
Same physics, easier to believe
Waterjet cutting
Water cuts steel plate for a living. Nobody finds it suspicious, because everyone has seen it.
Watch →Workshop test
Paper saws wood, because spinning fast is what makes it rigid. Sitting still it is limp.
Watch →Purdue University
The engineers' own model: the skin peels off instantly. Fuel and engine shafts do the damage.
Watch →| Quantity | Value | Type | Source or method |
|---|---|---|---|
| Impact speeds | 443 / 542 mph | Published | NIST NCSTAR 1, north and south tower |
| Perimeter column | 14 in box | Published | NIST NCSTAR 1. Hollow, ~3 ft on centre, plate ~0.25 in at the impact floors and up to 4 in at the base |
| Aircraft mass at impact | ~130 tonnes | Published | NIST, Boeing 767 with ~10,000 gal of fuel aboard |
| Sandia sled test | 480 mph | Published | Sandia National Laboratories, 19 April 1988, into 3.66 m of reinforced concrete |
| Wave speed in steel | ~5,100 m/s | Published | Standard longitudinal wave speed for structural steel |
| Contact time | 80 / 1.6 ms | Derived | Column depth ÷ speed: 0.356 m ÷ 4.5 and ÷ 224 m/s |
| Column shear capacity | ~1.9 MN | Derived | Area ≈ 9,030 mm² × shear strength ≈ 207 MPa (0.6 × 50 ksi yield) |
| Force to clear the path | 7.9 kN / 20 MN | Derived | F = m·v²/d with m ≈ 140 kg (a 2 m length of that column), d = 0.356 m. The v² is why the two rows sit 2,500× apart |
The force figures are a scaling argument, not a structural analysis. They answer one question, which is why the same steel survives one collision and fails the other. NIST and Purdue reach the same place with full finite element models.