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6th Jun 2009, 10:45

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Dan Reno

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Hot-Breathing Osprey Sparks Five-Acre Fire

By David Hambling
June 5, 2009 |
2:47 pm |

An unfortunate incident last month when a MV-22 Osprey was damaged in a grass fire is just the latest indication that the tilt-rotor’s fearsomely hot exhaust can cause real problems; it can even damage ships’ decks.
Eagle-eyed Osprey-watcher Springbored noticed some differences between the Marine Corps explanation of the event and the coverage on a local news channel in North Carolina, where the incident occurred.
In the official version, the aircraft landed due to mechanical problems at 7 pm in Holly Shelter Game Land in Pender County, NC. When it was preparing to take off, the heat from the exhaust ignited the grass underneath it.
“The grass fire was quickly extinguished by the crew chief, but caused an undetermined amount of heat damage to the aircraft exterior,” according to a rather bland Corps statement.
The News 14 version is more colorful. They say that fire-fighters did not bring the blaze under control until 11 pm, implying a larger conflagration that could not be put out by one man with a portable extinguisher. Springbored quotes another local news source saying that brush was set on fire. Local emergency management director Eddie King added, “It burned a little less than five acres.”
Springbored can claim some foresight on this one. In April, he stated, “we’ve known for years that V-22 downwash is notorious for setting nearby vegetation afire” and questioned how this would affect training exercises in Southern California during the dry season” “Are MV-22s going to be restricted to landing at only neatly-groomed, nicely leveled backwoods landing sites? Or do Marines just like hopping off their transport with fire extinguishers?” (Cue the joke about arriving in a hot Landing Zone.)
A few fires are one thing, but the hot exhaust can also cause trouble on board a ship, where it can warp steel. Last month Aviation Week reported that as well as reliability issues, the exhaust was a problem:
It was discovered that on smaller deck amphibious ships, heat from the downward-pointing nacelles could potentially warp the stringers [horizontal structural beams] underneath the deck plates. “We’re concerned with heat on the LPD and LSD decks because the steel is so thin,” Trautman said, adding that the service has “worked through that challenge.”
There are two suggested solutions. One is to angle the nacelles forward rather than leaving them vertical, which would allow the aircraft to remain for about half an hour. The alternative is to add deck plates which would give ninety minutes of protection.
Secrecy and a refusal to disclose details of the aircraft’s operational rate in Iraq (rumored to be poor) have increased the rumblings of doom; a Marine general has suggested buying less Ospreys and more helicopters. At least the Osprey involved in last month’s incident avoided serious damage: explaining how your $73 million aircraft came to be destroyed by a forest fire it had started would be really embarrassing.
ALSO:

http://www.wired.com/dangerroom/2009/06/hot-breathing-osprey-sparks-five-acre-fire/