The Avrocar: Visualisation · Signals from the Periphery

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THE RIG

Gap

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Lift

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State

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THE AVROCAR · VZ-9
The saucer that really flew, one metre up
18 ft across, 3 turbojets, one 124-blade rotor
3,150 lb of lift with no ground under it
3,000 lb of empty airframe · 150 lb left over
the ground carried the difference, and only near it
raise the gap · load it up · read the memo

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Evidence

fact ⇄ what kind of claim · live

Max lift out of ground effect 3,150 lb, against 4,285 lb zero fuel

the programme's own figures · it could not hover off the cushion

MEASURED

Empty airframe 3,000 lb leaves 150 lb for pilot, fuel and payload

arithmetic on two published weights · a pilot alone is more

MEASURED

The cushion delivered 0.24 of the textbook thin-jet curtain

the bench's one fitted number · duct losses "never resolved"

MODELLED

The turborotor multiplied 2,760 lb of engine into 3,150 lb

1.14× from a lift fan that should have bought 2× or more

MEASURED

Above about two feet it broke into pitch and roll: hubcapping

critical height reported ~2 ft; ceiling ~3 ft; waveform here is drawn

REPORTED

A 1954 memo: circular VTOL may be mistaken for UFOs

DOW-UAP-D095 · prospective, and a collection requirement

REPORTED

Two airframes, two airfields, about 93.5 flight hours

Malton and Moffett Field, 1959-61, never above ~3 ft

MEASURED

Whether that memo explains any sighting is a reading

it named no case and closed none · the file stays open

READING

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Flight card

The machine

Gap at the rim—

The distance the whole programme lived in. Cushion pressure goes as 1/h, so this slider is the aircraft.

All-up weight—

Empty 3,000 lb · zero fuel 4,285 lb · design transition weights 5,650 and 6,970 lb. The ceiling is 1,038/(W − 3,150) metres.

Forward speed—

Best free flight was 30 kt in 1960 and 20 kt at the final evaluation in June 1961, against a design goal of 300 mph.

The observer

Slant range—

For the Mistake view. An 18 ft disc matches the full moon at about 600 m and falls below the eye's disc resolution beyond about 19 km.

Layers

Ground cushionbrightness is the share of weight carried

Peripheral curtainthe turborotor efflux · illustrative

Downwashillustrative

Scale figure and staff1.8 m · ticks at 18 in, 2 ft, 3 ft

The six-foot ditchit crossed one at 18 in

Labels

Motionthe hubcapping cycle

Readout · live

Lift

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Margin

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Ceiling

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Augmentation

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Carried by ground

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Stability

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What is measured vs modelled here

Measured: every dimension and weight, the 3,150 lb out-of-ground-effect lift, the ~3 ft ceiling, the speeds, the turn asymmetry, the flight hours, the dates and the angular-size arithmetic. Reported: the hubcapping onset near two feet and its forward-flight mechanism, the design transition weights, the design goals, the 1954 memorandum and the 1955 file. Modelled: the thin-jet cushion law and the single fitted constant 0.24, plus the drawn oscillation, the curtain and the dust. Reading: what that memorandum is entitled to explain.

The model, in full

The Avrocar is an annular-jet ground effect machine, so thin-jet momentum-curtain theory applies: cushion pressure is the curtain's momentum flux per unit length times (1 + cos θ) divided by the gap, giving lift = thrust + cushion area × that pressure, or the standard augmentation 1 + D/4h. The bench anchors it on the two published figures, 3,150 lb with no ground and 4,285 lb held at three feet, which fixes the realised fraction of the textbook cushion at 0.24 and collapses the whole aircraft to L(h) = 3,150 + 1,038/h pounds, and the ceiling to h = 1,038/(W − 3,150) metres. Constants are solved in scripts/avrocar-tune.mjs and carried in data.js.

Where this drawing takes liberties

The airframe is built from the published dimensions (18 ft disc, 3 ft 6 in overall, 5 ft turborotor, two canopies, three engine bays) rather than modelled from a photograph, so nothing in its shape is asserted beyond those numbers; it is not a survey of the surviving aircraft, and 31 rotor blades are drawn where 124 were fitted. The figure beside it is a generated mesh, fitted to 1.8 m rather than trusted and standing in for scale only; it is not a portrait of anyone, and a capsule stand-in renders if it fails to load. The curtain, the downwash and the waveform of the hubcapping oscillation are illustrative: only the onset height, the ceiling and the lift are solved or reported. The thin-jet law stops being valid as the gap closes on the curtain thickness, so the ledger does not draw below about 12 cm, where the machine was sitting on its pads anyway.

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