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C-130 News: Ghostrider Grounded

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The Air Force’s prototype AC-130J Ghostrider gunship is grounded, pending investigation of an in-flight incident that occurred during a test sortie from Eglin AFB, Fla., earlier this year, according to Air Force Materiel Command. The aircraft “returned to base and safely landed without further incident or any injuries to the crew" after the April 21 mishap, the command told Air Force Magazine in a statement on Monday. AFMC officials on June 15 elevated the accident from a Class-C mishap after "structural analysis suggested damage greater than the $2 million monetary threshold for a Class-A incident," reads the statement. The AC-130J prototype suffered a similar mishap when it departed controlled flight during handling trials in February, exceeding its structural limits and resulting in the addition of two months to flight testing. AFMC is "convening an accident investigation board to investigate the matter based on the updated damage estimate," and will release more information when the inquest is concluded. Air Force Special Operations Command plans to purchase and convert a total of 37 airframes to the AC-130J configuration as part of its $2.4 billion program to replace the legacy AC-130U and AC-130W fleets.

View original article at Air Force Magazine

Photo : Air Force Special Operations Command's AC-130J Ghostrider gunship prototype sits on the ramp at Eglin AFB, Fla., June 26, 2015. Staff photo by Arie Church

 

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This is the second "departure from controlled flight" incident with the AC-130J; the first was in February and was noted in the latest DoD OT&E report. Sounds like some serious structural damage was sustained this time.

Assuming you're able to share, does anyone know any details on the test conditions and the type of departure? I'm wondering if this is something new with the AC-130J configuration, or if the test program is just digging deeper into some of the known control issues with the J, like stall roll-off, rudder overbalance, etc

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Not heard of this.    But if I remember correctly the J had some weird stall characteristics which warranted installation of "stick pusher"?

Because it's a gunship I suspect they were testing stall characteristics in a bank.   Not sure off all the original J testing however.  Pete are you familiar?

What is stall roll-off?  Never heard of that.

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AMPTestFE is correct that all C-130's have stall roll-off, but it is more severe in the J (and the H's equipped with 8-blade props). Stall roll-off is the tendency of the aircraft to roll significantly when in a fully-developed stall. Since these characteristics were prevalent in the J, both a stick shaker and stick pusher were added to warn against and prevent fully-developed stalls.

jbob, you may be on to something with banked stalls. What speed, flap setting, and bank angle is typically used in a gunship orbit?

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It's not quite as bad with the old props, just because the blades aren't nearly as efficient as the new designs.

JBob, I do know that someone who was onboard told me they just about went over on their backs while doing J-model stall tests.  I personally saw over 110 degrees of bank...but now I'm having a hard time remembering if it was with 4 or 8 blades.....I'm getting older.

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I don't recall much stall testing being done on the H-model with 8 blades. But the J stall test program was exhaustive, after the roll-off issue was identified and the stick shaker/pusher was installed.

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Years ago I was told that the stick shaker was only put in to satisfy the FAA certification requirements.

Since the J was certified by the FAA before the USAF and almost all FAA certified aircraft have stick shakers.

Bob

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FAA certification was a requirement of the launch customer (UK RAF) and the stick shaker would satisfy any stall warning requirements. But the stick pusher was added to prevent fully-developed stalls and the accompanying nasty roll-off.

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I heard a similar story, and I know it's a fact of life in producing new variants of old airframes.  For instance, there were many certification challenges (ie, design changes) on the 737 Next Gen that weren't an issue with the 737 classic, only because of newer aircraft certification standards that came out after the classic.  The J is similar in that it was so much different that it had to meet current certification standards.  As far as I'm aware, there was no such thing as a stick shaker in the early 1950's.

Edited by AMPTestFE

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Updating the cert of an old airplane is a massive pain. And Lockheed is feeling the burn again with the LM-100J.

As for the AC-130J, we'll have to wait and see if any other details of these "departures" are released. I doubt it is anything new.

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