Look closely at the photograph: those are two full-size 1950s automobiles, parked comfortably underneath the helicopter. Above them sits a single rotor so vast that each of its two blades weighs as much as a small car and is wide enough to walk along. And it was spun not by gears, but by jets of fire burning at the very tips of the blades.

This was the Hughes XH-17 — one of the strangest flying machines ever built, and the holder of a record that still stands more than seventy years later.

A Rotor You Could Almost Stand On

The XH-17’s two-blade rotor measured 134 feet from tip to tip — wider than the wingspan of many airliners — and no helicopter before or since has flown with a larger one. Each blade weighed around 5,000 pounds, was roughly six feet wide and a foot thick. The whole contraption grossed more than 50,000 pounds, and was famously cobbled together from the parts bin of post-war aviation, borrowing wheels, tanks and pieces from bombers and transports.

Driven by Fire at the Tips

The cleverest, maddest part was how it turned that enormous rotor. A conventional helicopter uses a heavy gearbox to drive the rotor from the hub, which creates torque that has to be cancelled by a tail rotor. The XH-17 did away with all that. Two General Electric J35 turbojets sat in the fuselage and pumped compressed air up through the hollow blades to the tips, where fuel was injected and ignited. The rotor was, in effect, dragged around by small jet engines at its own wingtips.

Because the drive force was applied at the tips rather than the hub, there was almost no torque to fight — so the giant needed only a tiny tail rotor. On paper, it was elegant.

Why It Never Caught On

In practice, tip-jets are spectacularly thirsty and almost unbelievably loud — the XH-17 could reportedly be heard from miles away. That inefficiency was fatal: the prototype could fly barely 40 miles before running dry. Combined with its cumbersome size, that doomed any hope of a production heavy-lifter. Just one XH-17 was ever built, and a planned larger follow-on, the XH-28, was cancelled.

And yet the idea behind it never died. The notion of a dedicated “sky crane” built purely to haul heavy, awkward loads lived on in later, more practical machines. The XH-17 was a glorious dead end — but it pointed the way.

Sources: Smithsonian Magazine; Simple Flying; Old Machine Press; Wikipedia.