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.
Every step across this scale is ten times the step before it. That is the only way both bars fit on one screen — the bottom bar is 2,500 times the top one, not five times.
Photographs, not simulations
Soft things go through hard things every day
None of these is disputed by anyone, and none of them needed an aeroplane. In each one, something everybody agrees is weak arrives fast at something everybody agrees is strong. Speed is the only thing any of them has going for it.
A bird folded every blade in this fan
Feathers, meat and hollow bone, against a certified engine running at full power. Look at the blade tips: not one of them is straight any more.
JT8D fan after a bird strike · Plenumchamber, CC BY-SA 3.0, via Wikimedia Commons
A bird broke this canopy from the outside
The red is what is left of the bird. The cracks run the full width of the canopy, and the fighter is the hard object in this photograph.
F-16 canopy after a bird strike · U.S. Air Force, public domain, via Wikimedia Commons
That is sand, and it is cutting steel
The stream carries ordinary garnet sand. Poured onto the plate it does nothing at all. Carried fast enough it cuts straight through. The sand never changed — only its speed did.
Abrasive waterjet · WARDJet, CC BY-SA 2.0, via Wikimedia Commons
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 = 1,869,210 N
What the wing delivers
F ≈ m × v² ÷ 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 = 4.4704 m/s | (10 mph) | 7,859 N | 0.4% of the limit |
| v = 223.52 m/s | (500 mph) | 19,647,659 N | 1,051% 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.
Filmed proof, and its limits
A fighter jet, 480 mph, into 12 feet of reinforced concrete
In 1988 Sandia drove a complete F-4 Phantom, both engines included, into a reinforced concrete target at 215 m/s — about 480 mph. Watch what is left of the aircraft.
A whole aeroplane, wings level, engines aboard. The pale block ahead of it is the target, and it is the last moment anyone sees it clearly.
The front of the aircraft has already stopped existing. The rest of it has not yet found out.
There is no aeroplane in this photograph. The target is somewhere inside that cloud.
Close-up, slow motion, silent, 9 seconds. The target is the pale block, in frame and intact before anything reaches it. The film ends inside the dust cloud, which is where the camera run ends. Rocket-sled test, 19 April 1988, Sandia National Laboratories, run for the Muto Institute of Structural Mechanics, Tokyo.
Destroyed and harmless are not the same word. An aircraft being pulverised is delivering millions of pounds while it is pulverised. Those are the same event, not alternatives.
One honest warning about this film, because it will be used against you. The target barely moved, and that was the design. Sandia built it 3.66 metres thick and essentially rigid, and states the test was “not intended to demonstrate the performance (survivability)” of any particular concrete structure. A target built to break would have measured nothing. They read the force off instruments against time, not off the wreckage — and found the major force came from the engines. So this is not a film of a wing cutting a column. It is the answer to the one objection that matters: an aluminium aircraft that disintegrates on contact still arrives with millions of pounds behind it.
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. Sandia's test found the major impact force came from the engines, and both of those went in too.
"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
A jet of water and garnet sand 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
| 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, up to 4 in at the base |
| Aircraft mass at impact | ~130 tonnes | Published | NIST, Boeing 767 with ~10,000 gal of fuel aboard |
| Steel shear strength (τ) | 207 MPa | Derived | 0.6 × 50 ksi yield, the standard shear approximation for structural steel |
| Column cross-section (A) | 9,030 mm² | Derived | Four plates, 14 in × 0.25 in |
| Column section mass (m) | 140 kg | Derived | A 2 m length of that section at 7,850 kg/m³ |
| 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 |
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.