Friday, May 2, 2008

Tilt Rotor Turmoil

The Dreadnaught blog reported in March a story about the faster than expected wearing out in Iraq of the engines for V-22 Osprey tilt rotor aircraft. This issue is just the latest in a long series of problems this plane has experienced.

An article in the the New York Times on April 14 of 2007, summarized the history of the development of the V-22. That story pointed out the high development cost, $20 billion dollars, high craft cost, $80 million each, and the fatal accidents that have occurred with this plane. The article relates further criticisms, including the lack of any ability to land safely should power fail, or the craft run out of fuel. It also states that the vortex ring state, where the propellers get caught in their own turbulence during landing is its chief operational risk.

From my perspective these criticisms should be expected because the V-22 Osprey, like any other tilt rotor craft, has an inherently flawed design. As I see it, the V-22 is far too complex because it uses the wrong technology for vertical flight and as a result many workarounds and add ons are needed to get it to operate at all. It's flaws include:

  1. The laterally disposed rotors present an asymmetrical lift situation, and any unequal lift from one or the other propellers can cause severe roll moments. It is essential to have centerline thrust to avoid this fatal occurrence.
  2. In total power failure or “running out of gas“, the V-22 is a free falling body below 1600 feet altitude. It cannot use its wing for gliding flight to non disastrous landing, because the large propellers will impact the ground on landing and crash the craft. Again, neither can it auto rotate its propellers like a helicopter.
  3. The complexity of V-22 cross shafting, nacelle tilt bearings, two transmissions, and servos, are inherent failure points, and potentially fatal failure elements.
  4. The V-22 is all computer programmed and controlled, additional elements to fail. The pilots need special training that exceed mere rotor craft training.
  5. In VTOL (vertical take off and landing) mode, the download of the propeller slipstream on the wing costs 10% of the trust for lift, plus there is additional upward fountains of air between rotors causing more loss of lift It has a less than optimal use of the propeller lift.
  6. With the high cost and maintenance of the V-22, only the military can afford it.

At Aeromobile Inc., we have designed and experimented with an entirely different approach to vertical take off and landing. Our Arc Wing VTOL airplane uses deflected slipstream for vertical maneuvers, and is a fixed wing airplane for horizontal flight. It does not have the inherent design problems I listed for the V-22 Osprey tilt rotor craft and will make a far more efficient, safe and inexpensive VTOL aircraft.

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