Air Transportation: Tilt-Rotor Clutch Curse


March 6, 2023: The United States is once more having problems with troublesome components of its V-22 tilt-rotor aircraft. On February 3rd some V-22s were grounded until a component (Input Quill Assembly) could be replaced. This component is part of the propeller gear box, which also houses the aircraft clutch assembly that enables the V-22 to operate like a helicopter while landing and taking off and a fixed wing transport for the rest of the flight, traveling much faster than a helicopter.

Problems with V-22 reliability never seem to end. In mid-2022 the U.S. Air Force Special Operations Command grounded its 52 CV-22B transports indefinitely, except for emergencies. The air force wanted to discover what was the cause, and cure, for four incidents since 2017 involving HCE (hard clutch engagement) when the CV-22B switches the position of the rotors between vertical (helicopter) and horizontal (conventional flight) mode. There were two fatal accidents involving Marine Corps V-22s. The marines are the first and largest user of MV-22s. Two marine V-22s suffered fatal accidents this year. One was attributed to pilot error in unfamiliar mountain terrain. The other accident occurred on a desert training range. No reason given for that one. Marine V-22s have also suffered from HCE accidents but the marines do not consider these dangerous enough to ground its V-22s.

The V-22 entered service in 2007 and the main user has been the Marine Corps, who wanted a faster transport to provide an edge in combat. The marine MV-22B operated from navy amphibious ships which have a flight deck for helicopters. The MV-22B was more expensive to buy and operate than a helicopter but it proved its worth in Afghanistan and other marine operations. The MV-22B can carry 24 passengers or up to nine tons of cargo. It can also handle casualties on litters and is sometimes armed. Although MV-22B has operated from amphibious ships since 2007 there were some problems, mainly with the ability to operate for longer than 12.5 hours before encountering an equipment or maintenance issue. This was a problem with the MV-22B as well as the SOCOM (Special Operations Command) CV22B model operated by the air force component of SOCOM.

Despite the high cost of buying and operating these aircraft, the V-22 "Osprey" tilt-rotor transport has become a success, although an expensive one that is still having problems with readiness. An early problem was V-22s that landed and took off in sand or loose dirt. Most (nearly 80 percent) of the V-22s are used by American marines, so there is no avoiding operating in areas that involve a lot of sand and dirt. This problem is similar to those long afflicting helicopters throughout the Middle East but the helicopters have managed to develop and implement effective solutions. That sort of thing has eluded the V-22.

The solution to the dirt and sand problem was supposed to be the EAPS (Engine Air Particle Separator), which is similar to what was effective in helicopters. The problem is that the V-22 engines are larger and more exposed than those on helicopters. Keeping the engines free of this debris has been a major cause of accidents and kept the readiness rate low, at about 52 percent. The manufacturer believes they can get that to over 60 percent if they can come up with an improved EAPS. Large transport helicopters like the CH-47 and the CH-53 (which the V-22 replaces) have readiness rates of over 80 percent.

There are currently about 420 V-22s in service and final production will be at least 450. So far twelve V-22s have been lost to accidents along with 42 crew and passengers, but this includes losses before the V22 entered service in 2007. After entering service, the accident rate declined, with only seven lost through 2021, along with twelve people on board. There have been a lot of accidents that caused damage but no fatalities or destroyed aircraft. The most common cause of all these losses has been the lack of an effective EAPS. The last fatal crash (three dead) was in mid-2017. There are enough close calls to remind everyone of the clogged engine risks, although several recent accidents and aircraft losses did not involve clogged engines. Another unique aspect of the V-22 is that it is not an easy aircraft to fly. That problem is being addressed with improved flight control software. That can make a big difference, as the F-117 and F-35 have demonstrated. That kind of software is expensive to create and for the moment clogged engines are a more urgent task.

The clogged engines have not slowed acceptance for the V-22. While there is only one export customer (17 for Japan, with some delivered), SOCOM has ordered more than fifty so far because the V-22 has proved invaluable for special operations tasks.

In 2015 Japan decided to purchase the first five (of 17) V-22 s after more than two years of deliberations. These V-22s are being used to help defend islands both Japan and China claim but Japan currently occupies. Japan received the first of its special operations V22s in 2019 but these are still in the United States where Japanese crews and maintainers are training before the V-22s are moved to Japan. The high speed of the V-22 and its ability to land like a helicopter makes it possible for the Japanese to quickly reinforce the disputed islands if China makes a surprise effort to grab them. This is an ancient Chinese tactic; to quickly seize some disputed territory and then call for peace talks. It works better in the 21st century than it did hundreds of years ago and Chinese military officials talk openly about using it. The V-22 makes this tactic much more difficult to carry out. The Japanese V-22s will also operate from their small aircraft carriers, along with F-35B fighters. These ships are classified as “large destroyers” to get around a clause in their post-World War II constitution that forbids them from having carriers.

Despite the problems, V-22 is rapidly maturing into a reliable and combat-proven aircraft. By 2012 the marines began receiving the "Block C" version, which has better weather radar, improved cabin climate control, better anti-missile defenses, and flat-screen displays in the cockpit and cabin that show what external cameras see from different positions on the exterior of the aircraft. This provides improved situational awareness. Most of these improvements were suggested from combat experience with the V-22. All these items are also important for an aircraft that takes off and lands like a helicopter, then speeds away like a fixed-wing aircraft. This speed has proved to be very useful in combat, as it is more than 120 kilometers an hour faster than the helicopters the V-22 replaces. The V-22 C is now the standard model and older ones are being upgraded.

Most V-22 aircraft are in service with the marines as the MV-22. The other user is SOCOM, which uses the slightly different CV-22 with larger fuel capacity and terrain-following radar for night missions as well as electronic defenses.

Since it entered service in 2007, V-22s have flown nearly 600,000 hours. The 27-ton MV-22C cruises at 445 kilometers an hour and endurance is about 3.5 hours per sortie. The MV-22C can carry up to 32 troops or nine tons of cargo.

While users of the V-22 are happy with their unique hybrid, the accountants are less pleased. Since 2009, users have been struggling to increase V-22 readiness (ready for action) rate from 50-60 percent to the 82 percent that the manufacturer promised. The problem is that, despite being a wonderful feat of engineering that has now proved itself capable of serving in a combat zone, the V-22 is mechanically very complex and expensive, as well as being difficult to keep operational. The V-22 has had lots of trouble with costs and reliability.

Since the V-22 entered service the estimated lifetime cost of operating the aircraft has increased 64 percent to $121.5 billion. Although the major user (the marines) has had an excellent safety and reliability record, the MV-22s are very expensive compared to the helicopters they replaced. This is especially true when it comes to operating and maintenance expenses. In response to this, the marines are also buying 200 CH-53K helicopters. These are slower (315 kilometers an hour) but carry more, are more reliable, and cheaper to operate.




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