13-Jun-2013 Source: HeliHub.com
Here in the HeliHub.com office, we’ve been wondering how Eurocopter have decided that the X3 speed is an “unofficial speed record”. What are they measuring it against? Who have they beaten? What makes it a record?
The Eurocopter X3 is a hybrid aircraft which has vertical lift and hover capability, but features two massive tractor propellers on stub wings to assist with forward speed. The presence of those propellers makes this a different type of aircraft entirely and there is no comparable aircraft type in the world today. So whatever speed it goes, it’s only a record against itself. It’s clearly an advance for potential future customers to have a faster speed over the ground – corporate users in particular – irrespective of how or when Eurocopter chooses to implement the technology into a production aircraft. But is it a record, achieving 263 knots in a shallow dive or 255 knots in level flight?
Two other particular aircraft spring to mind – Sikorsky’s X2 and the Westland Lynx.
Sikorsky took their X2 aircraft to 260 knots in a shallow dive. The X2 is a coaxial design with two sets of rotors on a single mast, along with a pusher prop on the tail to add to the forward speed. Ultimately it never quite reached the point of being the fastest Sikorsky, being a couple of knots short of the XH-59A – also known as the Sikorsky S-69. The X2 was retired after after accumulating 22 hours over 23 test flights, but this American manufacturer is ahead of the curve taking their X2 research and development to market with their S-97 Raider military proposal and the first prototype of that military offering may take to the air later this year or early next.
Westland (now part of AgustaWestland as we all know) stills hold the record for the speed of a true helicopter with a main rotor and a tail rotor at 216 knots. Aerodynamic limitations of this format of helicopter mean that this record – broken 27 years ago in 1986 – is likely to be held for a long time.
In conclusion, we think there should be separate records for each format of rotorcraft. There’s no real comparison between a standard main and tail rotor design, a coaxial with (or without) a pusher prop, a tandem design or the X3 style hybrid. HeliHub.com calls on the FAI to create the separate categories to handle this, and implore readers to read press releases carefully. Eurocopter’s published headline “Eurocopter’s X3 hybrid helicopter makes aviation history in achieving a speed milestone of 255 knots during level flight” is misleading as they then describe the X3 as a “technology demonstrator for an advanced, cost-effective vertical takeoff and landing (VTOL) transportation system” and then adds that it “offers the speed of a turboprop-powered aircraft and the full-flight capabilities of a helicopter.” Eurocopter is NOT saying it is a helicopter, but has the capabilities of a helicopter (among other capabilities). It is not a helicopter. It’s speed cannot be compared to anything other than another design which has a main rotor and propellors.
Perhaps there is scope for a discussion on “the differences between a helicopter and a rotorcraft”?
Jeremy Parkin – HeliHub.com