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FastestThings

Helicopters

Sikorsky X2

Compound helicopter. The Smithsonian prints 250 knots (463 km/h) in level flight on 15 September 2010. Guinness uses that mark as the one the X3 beat.

Also known as X2
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Top speed

Published as 250 knPublished as 250 knPublished as 250 kn

Compound technology demonstrator, level flight. Smithsonian prints 250 knots (463 km/h). Not an FAI absolute record.

VerifiedSmithsonian National Air and Space Museum (opens source in a new tab)

In context

  • 4.4× a cheetah's timed top speedSourced · Cheetah, 29 m/s. Sharp 1997, mean of three timed runs over 201.2 m
  • 1.4 football fields a secondConstant · American football field, 100 yd (91.44 m)
  • London to New York in 12 h 2 minConstant · London to New York, 5,570 km great-circle

Worked out from the sourced figure above, which stays the ranked number.

This list

Why it's so fast

A helicopter's top speed runs into the rotor. The blade going forward sees a much higher airspeed than the blade going backward, and that imbalance is the usual wall.

  1. Retreating blade

    As the aircraft speeds up, the retreating blade can lose lift and stall while the advancing blade is approaching its own limits. Conventional rotors run out of even lift before a jet would.

  2. How the record holders cheat

    Compound helicopters add a propeller or a wing so the rotor does not have to provide all of the forward thrust. The entry says which layout set the figure.

One record holder is the Westland Lynx.

This is how the category works. A note written for this entry appears here once it is in the database.

Provenance

Every measurement

Claimed, measured and official figures side by side, each with its source. The ranked figure is marked.

  1. 463km/h288mph129m/s250knRanked figure

    Compound technology demonstrator, level flight. Smithsonian prints 250 knots (463 km/h). Not an FAI absolute record.

    Verified
    Smithsonian National Air and Space Museum (opens source in a new tab)

Reference

Specs

Class
Compound
Speed
250 knots level flight
Date
15 September 2010
Configuration
Coaxial rotors plus pusher propeller

Context

Background

The National Air and Space Museum prints a level-flight speed of 250 knots (463 km/h; 288 mph) for the Sikorsky X2 on 15 September 2010. Guinness, writing about the later X3, says that demonstrator beat the Sikorsky X2 by 5 knots. Flying magazine says the X3's 255 knots was slightly faster than the X2's 250-knot top speed in 2010. The ranked figure is 250 knots, the unit the museum leads with.

The X2 is a compound, with coaxial rotors and a pusher propeller, built to get past retreating-blade stall. It is on this list with that label. It is not FAI record 11659, which remains the Lynx at 400.87 km/h.

Head to head

Compare Sikorsky X2

Open the speed race

Spot a wrong number?

Every report is read by a person, and corrections are dated on the page.