Thursday, September 4, 2008

The Sikorsky X-2: A Half Way Solution

As reported by Aviation Week and Flight Global, Sikorsky has recently completed the first test flight of its X2 high speed, compound helicopter. Sikorsky expects this rotorcraft to have a maximum speed of 250 knots when all stages of testing are complete. The X2 has been in development this decade, and is a follow up to the Advancing Blade Concept Demonstrator of the 1970s known as the Sikorsky S-69 / XH-59. The new X2 is using fly-by-wire controls to help minimize blade vibration that created problems for the earlier S-69 / XH-59.

If the X2 can really fly at 250 knots, it will be about 100 knots faster than most helicopters today. That is a quite significant advance in rotorcraft speed, and Sikorsky should be commended for this advance. A reasonably fast vertical takeoff and landing (VTOL) craft is certainly desirable.

But, at Aeromobile Inc. we think that faster helicopters are still not the ideal VTOL craft. We prefer an airplane with vertical capabilities to a helicopter that flies faster. Our reasons include:
  • Airplanes are inherently safer than helicopters, requiring less maintenance and glidable to earth when power fails. All rotorcraft must have a minimum altitude usually 1500 feet to auto rotate, and it remains to be seen how well the counter-rotating rotors of the X2 auto rotate in the event of power loss.
  • With the X2, the slowing of the rotors to prevent them from going supersonic and vibrating excessively has to be done with computer assistance (the"fly-by-wire" element of the control system). This adds complexity, and we will see how reliable that control system works. We feel that complexity means more expense and more risk for failure.
  • The requirement of special rotorcraft training, and the high price limits the availability of helicopters to many that need vertical flight.
  • Helicopters basically force themselves in the air and need constant rotor action to remain in the air. They do not have the aerodynamic efficiencies of airplanes and consume more fuel, which in periods of high fuel costs makes them even more expensive and therefore less available.
We have touted our Arc Wing VTOL Airplane many times in this blog and on our website. We still feel that an airplane with vertical flight capabilities is the best VTOL of all. Our Arc Wing VTOL will fly 100 knots faster than the proposed 250 knots of the X2. It is mechanically far simpler than any helicopter, especially the more complex X2. It can be flown by an airplane pilot without any computer assistance or complicated mechanisms in changing from vertical to horizontal mode and vice-versa. And, with its simpler design, it will be considerably less expensive to build and operate than a fast helicopter.

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