Why a wing shears a steel column at speed

Same wing. Same steel.
2,500× the force.

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.

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Is aluminum harder than steel? No. And it never mattered. Shear strength is a pressure, not a contest between materials. Steel shears at about 30,000 psi no matter what is touching it. Water does it in machine shops every day.
Can the wing deliver 30,000 psi? That is the only question, and speed is its only real input. At 10 mph the aluminum buckles first and never gets close. At 500 mph it arrives with ten times more than the steel can hold.
What this column takes before it shears  1,869,000 N
Wing at 10 mph7,963 N · 1,790 lb
Wing folds
Wing at 500 mph19,732,000 N · 4.44 million lb
Steel shears
1 kN10 kN100 kN1 MN10 MN100 MN

The actual arithmetic

Two equations. One of them has a v² in it.

What the column can hold

F = τ × A

τ = 207 MPa   steel shear strength
A = 9,030 mm²   column cross-section
F = 1,869,000 N

What the wing delivers

F ≈ m × ÷ d

m = 140 kg   the piece of column in the path
d = 0.356 m   how deep that column is
v = the only thing that changes

v = 4.5 m/s(10 mph) 7,963 N 0.4% of the limit
v = 224 m/s(500 mph) 19,732,000 N 1,056% of the limit

Same equation. Same column. Same wing. Only v changed.
And the ratio holds no matter what you think of my constants, because they cancel: fifty times the speed is 50² = 2,500 times the force, exactly. You can halve every number above and 500 mph still clears the limit five times over.

The wing does not have to survive. It has to deliver. It carries that pressure for 1.6 milliseconds. It is confetti either way, and so is the column.

Your hand cannot push a nail into wood. A hammer does it instantly. The hammer is not harder than your hand.

Thirty seconds of proof

A fighter jet, 480 mph, into 12 feet of reinforced concrete

Sandia fired a complete F-4 Phantom into a concrete block in 1988 to find out what a jet does to a nuclear containment building. It turns to dust. It also hits with millions of pounds of force. Both at once, which is the part nobody can picture until they watch it.

Sandia National Laboratories

Watch on YouTube →

The six things people say next

"The wing would be destroyed."

It was. Completely. It still broke the columns on the way in. A thrown wine glass shatters and the window still breaks.

"The photo shows a pole winning."

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 with speed.

"That's a wing against one pole."

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.

"It was reinforced steel beams."

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.

"Soft can't beat hard."

A 10 lb goose, meat and feathers, destroys a titanium jet engine at 300 mph. It is why engines are certified by firing bird carcasses into them, and it is what put Sullenberger in the Hudson. A 767 is about 29,000 geese at once.

"Then where's the video?"

Nowhere, and that is expected. Wings hit things at taxi speed constantly and it gets filmed, which is where every photo like this comes from. At 400 mph a jet is at altitude, nowhere near a pole. Nobody has ever been able to run that test on purpose.

Why time is the hidden variable

At 500 mph the column is standing alone

A column in a wall is strong because it is bolted to everything around it. Push slowly and the whole building leans in and helps. That help travels through steel as a wave, about three miles per second, and it needs time to arrive.

80 ms at ramp speed: the signal crosses 400 metres, the full 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 accept

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 →
Every number above, and where it came from
QuantityValueTypeSource or method
Impact speeds443 / 542 mphPublishedNIST NCSTAR 1, north and south tower
Perimeter column14 in boxPublishedNIST NCSTAR 1. Hollow, ~3 ft on centre, plate ~0.25 in at the impact floors, up to 4 in at the base
Aircraft mass at impact~130 tonnesPublishedNIST, Boeing 767 with ~10,000 gal of fuel aboard
Steel shear strength (τ)207 MPaDerived0.6 × 50 ksi yield, the standard shear approximation for structural steel
Column cross-section (A)9,030 mm²DerivedFour plates, 14 in × 0.25 in
Column section mass (m)140 kgDerivedA 2 m length of that section at 7,850 kg/m³
Sandia sled test480 mphPublishedSandia National Laboratories, 19 April 1988, into 3.66 m of reinforced concrete
Wave speed in steel~5,100 m/sPublishedStandard longitudinal wave speed for structural steel
Contact time80 / 1.6 msDerivedColumn depth ÷ speed: 0.356 m ÷ 4.5 and ÷ 224 m/s

F ≈ m v²/d is an order-of-magnitude scaling estimate, not a finite element model. It answers one question: why the same steel survives one collision and fails the other. The constant in front is arguable, the v² is not, and NIST and Purdue reach the same place with the full models.