USAF photo
“F-35 flight operations have been cleared to resume.”
— F-35 program spokeswoman Kyra Hawn late Thursday, giving a green light to the resumption of flights following a week-long grounding of the fledgling tri-service fighter due to a crack in an engine turbine blade.
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Don_Bacon
Don_Bacon

David Axe, Mar 1, 2013
. . .Pratt and Whitney put the best possible spin on the turbine blade’s potentially catastrophic flaw, which if undetected could have caused a crash. “Prolonged exposure to high levels of heat and other operational stressors on this specific engine were determined to be the cause of the crack,” the company announced late Thursday. “No additional cracks or signs of similar engine stress were found during inspections of the remaining F135 inventory. No engine redesign is required as a result of this event.”

But the F-35, meant to replace almost all of the military’s existing jet fighters, could very well experience similar problems throughout its planned 50-year service life. Originally meant to be long, narrow and highly aerodynamic like most other fighters, the JSF was redesigned to be wider and more squat to accommodate the internal weapons bays that are key for radar-evading planes. “What is different is that this airplane has accelerational characteristics with a combat load that no other airplane has, because we carry a combat load internally,” Lockheed exec Tom Burbage told aviation reporter Dave Majumdar last year.

But the redesign has an adverse effect on the plane’s aerodynamics, making the F135 work harder than is normal for a fighter engine. Generating more than 40,000 pounds of thrust, the F135 is the most powerful fighter motor ever. Even though the Pentagon has downgraded the F-35's acceleration specs to ease the strain on the engine, the F135 runs extra hot — a problem that has concerned Lockheed and Pratt and Whitney engineers for at least seven years and likely contributed to turbine problems in 2007, 2008 and 2009.

. . .So the Pentagon’s mainstay future fighter is probably stuck with its existing engine, as well as with that motor’s high temperatures and fragile turbines. And that means groundings like last week’s could be a distressingly common occurrence.
http://www.wired.com/dangerroom/2013/03/stealth-jets-returns/

Don_Bacon
Don_Bacon

Just-in-time contracting -- what a coincidence that the F-35s have just been cleared to fly.

Contracts, Navy, Feb 28, 2013
  Lockheed Martin Corp., Lockheed Martin Aeronautics Co., Fort Worth, Texas, is being awarded a $333,786,000 fixed-price-incentive (firm-target), advance acquisition contract to provide long lead-time parts, materials and components required for the delivery for the 35 Low Rate Initial Production lot VIII F-35 Lightning II Joint Strike Fighter aircraft:  19 conventional takeoff and landing (CTOL) aircraft for the U.S. Air Force; six short takeoff vertical landing (STOVL)  aircraft for the U.S. Marine Corps; four Carrier Variant aircraft for the U.S. Navy; four STOVL for the United Kingdom; and two CTOL aircraft for the Government of Norway. 
http://www.defense.gov/contracts/contract.aspx?contractid=4988

Don_Bacon
Don_Bacon

Make it a Trifecta -- it was the day before the sequester kicked in.

Don_Bacon
Don_Bacon

Feb 28, 2013
Pentagon lifts order grounding F-35 fighter jets after discovery of crack in turbine blade

WASHINGTON - The Pentagon says it has lifted an order that briefly grounded its fleet of F-35 fighter jets. The jets were grounded on Feb. 21 after the discovery of a small crack in the turbine blade of an engine in one F-35 at Edwards Air Force Base, Calif. On Thursday evening the Pentagon said all 51 planes had been cleared to resume flight operations.

It said prolonged exposure to high levels of heat and other unspecific "stressors" were determined to be the cause of the crack. No additional cracks were found.
http://www.startribune.com/nation/194098441.html

So faced with a half inch turbine blade crack they didn't find any design or material  problems, and there were no other cracks found, so they gave the Lightnings a green light. There were high levels of heat and other unspecific "stressors"!! In a jet engine, just imagine!! 

This is out of my area, but I feel that there is a problem here but they won't try to find it, because of the wrongful F-35 concurrent production/test program.

Don_Bacon
Don_Bacon

more--
WASHINGTON (Reuters) - Pratt & Whitney is 99 percent sure the fan blade problem that grounded the Pentagon's 51 new F-35 fighter jets was not caused by high-cycle fatigue, which could force a costly design change, according to two sources familiar with an investigation by the enginemaker.

Company engineers have concluded that a 0.6 inch-long crack found on a turbine blade in the engine of an F-35 jet at Eglin Air Force Base in Florida was almost certainly caused by lesser issues, such as high heat exposure or a manufacturing problem, that would be easier to solve, the sources said.
http://articles.chicagotribune.com/2013-02-26/business/sns-rt-us-lockheed-fighter-prattbre91q040-20130226_1_f135-blade-crack-pratt-whitney

Lesser issues such as high heat exposure or a manufacturing problem, eh?  You take 'er up.


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