In conjunction with the 30th anniversary of the current world speed record, set on August 11, 1986 by the Westland Lynx G-LYNX, this page gives further explanation and resources, as a complement to the recent Vertiflite article, The Absolute World Helicopter Speed Record: Held for 30 Years and Counting, Sept/Oct 2016.
From the AHS Vertipedia entry for this milestone:
Absolute World Speed Record for helicopters achieved, Monday, August 11, 1986 — Somerset Levels, Glastonbury, United Kingdom
The modified Westland Lynx AH.1 (registration G-LYNX) acheived the absolute speed record for a rotorcraft (216 kts/400.87 km/hr), piloted by Westland Chief Test Pilot Trevor Egginton with Derek Clews, Flight Test Engineer. The record course covered 15km from East Huntspill to Hartlake Bridge in Somerset, England — see FAI Record Category E-Absolute (Absolute Record for class E - Record ID 11659)
The aircraft was extensively modified, including BERP III type blades and 1,200 shp Rolls-Royce Gem 60 engines, amongst many other modifications. More details of the aerodynamic technology behind the record can be found in the AHS Vertical Flight Library, part of the AHS Online Store: The Aerodynamics of the Helicopter World Speed Record, F. J. Perry, Westland Helicopters Ltd., presented at Forum 43, May 1987.
What about the Russian PSV?
Interfax news stated that the Russian Helicopters Mi-24LL PSV demonstrator has flown to a cruise speed “greater than 405 km/hr (219 kt).” The news report was in late October 2016, though unconfirmed reports suggest that it had taken place several weeks earlier.
The Mi-24LL is a single-seat "Flying Laboratory" ("LL" in Russian) modification of the Mi-24 Hind. The high-speed demonstrator uses blade tips that are similar in shaping to the BERP blades (sometimes jokingly refered to as "RERP" blades). More information on and references for this aircraft is found in the AHS Vertipedia entry.
What About Compound Helicopters?
The FAI has never recognized an official speed record for a wing-augmented and/or thrust augmented helicopter. Although Sikorsky stated that they had received approval from the National Aeronautic Association (NAA, the FAI representative organization in the United States) that the X2 would be considered a helicopter for purposes of a record because it did not have wings, Sikorsky management decided not to test the aircraft beyond its stated goal of 250 kt. As a result, the current helicopter record set by G-LYNX still stands today.
Many other compound helicopters have been built and tested. A few unofficial high-speed tests of note:
- The Sikorsky X2 (with a pusher propeller and rigid coaxial counter-rotating rotors) reached a level flight speed of 252 kt, as well as 262 kt in a shallow 2° - 3° dive.
- The Airbus Helicopters X³ compound (with wings and two tractor propellers) achieved 255 knots (472 km/h; 293 mph) in level flight on June 11, 2013, setting an unofficial speed record for the fastest propeller compound helicopter.
- The Bell 533 (with jets and wings) at 273 kt (509 km/hr; 316 mph) on April 15, 1969.
- The Sikorsky XH-59A ABC (coaxial; with jets and no wings) reached 263 knots (303 mph; 487 km/h) in a shallow dive.
More than two dozen compound helicopters have flown since the 1930s, when the helicopter was first invented. What exactly is a "compound helicopter"? Well, according to Principles of Helicopter Aerodynamics by Prof. J. Gordon Leishman (Cambridge University Press, 2003):
A compound helicopter involves a lifting wing in addition to the main rotor (lift compounding) or the addition of a separate source of thrust for propulsion (thrust compounding).... The idea is to enhance the basic performance metrics of the helicopter, such as lift-to-drag ratio, propulsive efficiency, and maneuverability. The general benefit can be an expansion of the flight envelope compared to a conventional helicopter.
In other words, a “compound” may involve both lifting and/or propulsive compounding. The goal is to “off-load” the rotor from its normal lifting and propulsive duties. This can be done by using a wing and/or auxiliary propulsion.
- The Absolute World Helicopter Speed Record: Held for 30 Years and Counting, Vertiflite, Sept/Oct 2016
- Hybrid Helicopters: Compounding the Quest for Speed, Vertiflite, Summer 2006
- Russia and China Show Off Latest Aircraft and Projects, Vertiflite, Nov/Dec 2015
- Putting the Record Straight (signed by author, David Gibbings). This 20 page booklet — written by the then-Deputy Chief Flight Test Engineer for Westland — details the efforts leading up to the record attempt.
- Rotorcraft World Records, Fédération Aéronautique Internationale