Forum: Military Aircraft of the Cold War

Quote:

Depot Level Support for the F/A-18 Service Life Extension Program (SLEP)
Solicitation Number: N00019-11-P1-ZA016
Agency: Department of the Navy
Office: Naval Air Systems Command

Original Synopsis
Oct 27, 2010
2:43 pm
Solicitation Number:
N00019-11-P1-ZA016 Notice Type...

This announcement constitutes a Sources Sought for planning purposes. This is NOT a Request for Proposals (RFP)... Naval Air Systems Command (NAVAIR)... have established the requirements baseline for the F/A-18 A/B/C/D Service Life Extension Program (SLEP). The intent of this SOURCES SOUGHT is to conduct market research to determine if commercial Depot Level Maintenance and Engineering support facilities are available to support the Government's SLEP requirements.

Interesting... I'm curious if there are any other alternatives?

https://www.fbo.gov/index?s=opportunity ... p;_cview=0

F-16.net Sponsor

Yes, geogen, there is an alternative, but the USN would never do it.

USN uses a structural durability technology called "Fatigue" to determine the structural safety of their airplanes. Basically, that means if a structural crack exists, the airplane is unsafe and is grounded. During design and development (SDD), fatigue analysis and ground test is conducted to four airplane lifetimes of expected usage. When any crack appears, a failure is declared, and corrective action (redesign, beef up, etc) is taken. For an 8,000 hour airplane, it must pass 32,000 hours without cracking. Why are airplanes allowed only 1/4 of ground test lifetime? Due to the extreme variability of fatigue analysis and test and variability in actual usage compared to design usage.

USAF uses a more modern and realistic structural concept called Fracture Mechanics, in which crack growth is analyzed, tested, and tracked during service usage. It was developed about 40 years ago to solve structural problems with the extremely high strength steel in the F-111 wing pivot system and has been applied to all USAF airplanes since then. Due to the much higher knowledge base of fracture mechanics, cracks are permitted in flying airplanes until they reach a critical length. Analysis and ground test are conducted to two airplane lifetimes, compared to four in Fatigue criteria.

The key point is that USAF airplanes are allowed to fly with safe cracks and the USN airplanes are not. The USN method is un-necessarily conservative and leads to earl;y, expensive SLEP programs like the above proposal.

The USN will likely never change their outdated procedures, preferring to do it "the Navy way". Their F-18s will be put through the SLEP program and most of them likely do not need repairs yet.

johnwill,

Would the fact that USN aircraft land on carriers have something to do with why they (USN) use outdated methods for testing structural durability?

Johnwill, did you get involved in any of J.M. Carlyle's acoustic emission testing on the F-111? Our training group was going to develop the training for structural testing when Australia bought the F-111 and McClellan AFB closed their cold chamber.
Extending the service life was going to involve a big investment in setting up and running their own chamber.
fisk

disco,

Interestingly enough, the USAF still uses fatigue criteria for landing gear durability tracking, possibly because the usage of landing gear is much simpler than the airframe and easier to characterize in fatigue terms. To answer your question, I don't know, but I suspect they are suspicious of any technology developed by the USAF, because they feel superior to the USAF. Using fatigue criteria for landing gear and tail hook structure is entirely appropriate, but there is a better way for the airframe.

Here is another example of USN conservatism resulting in added cost to the taxpayer. GD went to some trouble to improve the durability of the fleet of 24 F-16s they sold to the USN for aggressor training back in the 80s. F-16s were designed for a mix of air to air and air to ground missions, and the USN usage was all air to air (higher g and higher speeds involved). After a few years of service the USN withdrew the F-16s since cracks began to appear - cracks which would not have caused grounding in the USAF. So USN spent millions of taxpayer dollars and did not get the available benefits due to their conservatism.

fisk,

I was aware of the acoustic emission technology since one of the engineers was Don Pray in my group. Did Australia ever get a cold test chamber? I'm thinking they did; how else could they keep the -111 fleet going so long after the USAF 111s were retired.

Thanks for that elucidation and standpoint, johnwill.

Given your viewpoint, I wish USN could somehow get by with say, a 'fatigue mechanics analysis' then, or some such hybrid to better economize the potential Life extension. And maybe they could call it a: 'life enabler program' outright, rather than 'life extension'? OK, I've broken enough rules already Thumb

I meant to comment on your choice of title for this thread. Clever, subtle pun indeed, but most readers are too young to understand it unless they are fans of old movies. Cheers

johnwill wrote:

I meant to comment on your choice of title for this thread. Clever, subtle pun indeed, but most readers are too young to understand it unless they are fans of old movies. Cheers

I just thought it was a typo!?

(I'm not about to admit my advanced years. Smile

)

As to Australia getting their cold chamber, I assume they did. It was going to Queensland with bits and pieces from the UK. Teaching the setup and running the acoustic testing was going to be our group's task, the setup was ANCIENT computer equipment, it booted from EIGHT INCH FLOPPY DISKS!
Real Sherman and Peabody stuff.
fisk

Is there anymore information available about what the USN wants to do to their legacy Hornets as part of a SLEP? How up to date are the legacy Hornets in terms of avionics?

fisk,

You stumped me with the Sherman and Peabody reference, so I had to Wiki them. Turns out I'm so old I was out of high school before they came along and I never had the opportunity to watch cartoons after that. I caught a few episodes of Rocky and Bullwinkle when my kids were little, but still don't remember Sherman and Peabody. But I do remember 8 inch floppy discs, thinking what an advance they were over audio tapes in the HP-9820 desktop computers. Seems like the discs had 88k memory, that's "K", not "M".

Was that "k" or "K"?

So if those Hornets are hitting the boneyard with life left in them, why couldn't they be used for awhile with ANG units?

madrat wrote:

So if those Hornets are hitting the boneyard with life left in them, why couldn't they be used for awhile with ANG units?

Oh if it were only that simple.

Ya can't just throw the ANG a buncha USN jets and say, "Make it work". There's a whole slew of stuff involved in spinning a unit up on a new jet. Doubly so for a jet the USAF has no logistics support for. It takes months, if not years. And even if ya did, by the time the unit got to IOC or FMC the life on the jets would be almost gone. So now you've got a mission-ready unit with jets with no time left on 'em.

Also remember that not all jets that go to the Yard are immediately scrapped or parted out. A lot are kept in flyable storage in case they're needed back in the field in the future.

madrat wrote:

Was that "k" or "K"?

kilobytes

I count 50 Hornets at AMARG on Google earth as of roughly this time last year. Anyone know if the Navy plans to apply the SLEP to any of those aircraft sitting in storage?

The presolicitation mentioned something in reference to the potential number of 30 Hornets per year entering SLEP, depending on the industrial capability existing to meet requirements. I know that doesn't answer your Q, but Google E can definitely a blast and truly enlightening (especially since they routintely upgrade sections of image data). Unfortunately, there seems to be conflicting bugs w/ various windows related issues as of late.

Forum: Military Aircraft of the Cold War

USN F/A-18 A-D ... The big SLEP