Danish Government nominates F-35.

[quicksilver]

Generally speaking...

...an hour on a Navy jet is one hour of expended life; it doesnt matter what you were doing with that hour. When that jet gets to its design life limit, it turns into a pumpkin.

The only way life is extended beyond -- in this case -- 6K hrs, is if they do a SLAP (service life assessment) which is a formal teardown and engneering analysis of a representative article for the purpose of determining the feasibility, difficulty and cost of an extension (SLEP) of some specified number of hours. A SLEP is depot level work and expensive. So, if one is normalizing the cost of a 6K hour jet vs an 8K hour jet, one should include the cost of the SLEP for the 6K jet (which in the case of the SH v F-35) is rarely, if ever, done.

More cats/traps and FLE can get you less airframe life. Less of those can get you more airframe life, but only after a SLAP and a SLEP.

[hornetfinn]

To be fair to Boeing, 6,000 vs 9,500 hours might be the difference between CATOBAR vs CTOL operations.

No, or at least that's not our experience with the CF-18s. To start, I should note we don't use a similar metric for judging an aircraft's life: its based on the amount of stress an airframe has received in its lifespan. Nevertheless we don't have many aircraft beyond 6000 hours.

This is what Finnish Air Force has also learned about our F-18s. In FAF use the Hornets have actually got more stress and wear and tear than they have in US Navy use. Target for our F-18s is that they will be flown to about 4,500 hours. Some may get more but there needs to be some headroom in the event of war at the end of their service life. Actually even that requires SLEPing some parts as otherwise the service life would be about 4,000 hours. FAF flies different mission types and profiles compared to USN. Training areas are also close to bases and thus there is not much cruising around. I really doubt Danish Air Force flies their aircraft that much softer that they'd last twice that. With SLEPs anything is possible but that will be true for any aircraft. Fact still is that F-35 is 8,000 hour airframe whereas EF and SH are 6,000 hour airfames. F-35 will last longer structurally before needing SLEP or replacement than either of the two.

[quicksilver]

How expensive to SLEP? Very...

Here's a reference from the US Congressional Budget Office in 2010 -- and the numbers came from the Navy. Depending on the options assessed, the cost to extend was between $2M and $5M per year of airframe life. Assuming 300 hours of life expended per year (their assumption), that's roughly $5-17M per 1000 hours of extension. Want a 9K hour airframe? That is between $15M and $50M -- per airframe -- back in 2010.

Do the math; a cheaper 6K hour airframe doesn't look as attractive when the real costs are part of the calculation (which in this day and age, rarely are), and that's before we talk about things like the fatigue life usage spectrum assumed in the design.

https://www.cbo.gov/sites/default/files ... tories.pdf

[hornetfinn]

Even worse for the Danes is that Super Hornet will be phased out by their main user (US Navy) by about 2040 and that might be optimistic given that Classic Hornets will be retired by 2023 or so and Block 1 Super Hornets will be then 35 to 40 years old and most Block 2 SHs will be about 30 years old or so. AFAIK, US Navy Super Hornets have gotten a lot of hours and that will not decrease when Classic Hornets are retired. Danish fighters will be used until at least 2050 and more likely until or even beyond 2060. This means Danes would likely be the sole users of Super Hornet for at least 10 years with possibly 25 years or so. This means there would be no major upgrades for a long time (like 20-30 years of service) or the upgrades would cost Danes insane amount of money given the small fleet size and small budget. Similarly upkeeping the aircraft would become more expensive as they lose the economies of scale.

Same applies to Eurofighter but they might well be retired in other services a bit later than Super Hornets will be. Still, it's pretty probable that Danes would have been last users of EF for 10-20 years with similar results. IMO, no 4th gen fighter would have made any sense to Danes given their schedule. Besides, how survivable or effective would any 4th gen fighter be in 2050-2060? Like Danes found out, F-35 is the only one which makes sense in military, strategic or economic manner.

[spazsinbad]

Some recent info about SLAP dat Shornet SLEP: http://aviationweek.com/defense/boeing- ... nets-shape

[quicksilver]

Some recent info about SLAP dat Shornet SLEP: http://aviationweek.com/defense/boeing- ... nets-shape

It's behind the curtain Spaz.

[quicksilver]

Even worse for the Danes is that Super Hornet will be phased out by their main user (US Navy) by about 2040 and that might be optimistic given that Classic Hornets will be retired by 2023 or so and Block 1 Super Hornets will be then 35 to 40 years old and most Block 2 SHs will be about 30 years old or so. AFAIK, US Navy Super Hornets have gotten a lot of hours and that will not decrease when Classic Hornets are retired. Danish fighters will be used until at least 2050 and more likely until or even beyond 2060. This means Danes would likely be the sole users of Super Hornet for at least 10 years with possibly 25 years or so. This means there would be no major upgrades for a long time (like 20-30 years of service) or the upgrades would cost Danes insane amount of money given the small fleet size and small budget. Similarly upkeeping the aircraft would become more expensive as they lose the economies of scale.

Same applies to Eurofighter but they might well be retired in other services a bit later than Super Hornets will be. Still, it's pretty probable that Danes would have been last users of EF for 10-20 years with similar results. IMO, no 4th gen fighter would have made any sense to Danes given their schedule. Besides, how survivable or effective would any 4th gen fighter be in 2050-2060? Like Danes found out, F-35 is the only one which makes sense in military, strategic or economic manner.

[Dragon029]

Some recent info about SLAP dat Shornet SLEP: http://aviationweek.com/defense/boeing- ... nets-shape

It's behind the curtain Spaz.

It's free to view so long as you register with the site; nevertheless:

ST. LOUIS—With the U.S. Navy using its F/A-18 E/F Super Hornets more rigorously than initially expected, Boeing has started preliminary assessments of what is needed to overhaul the aircraft, increase its combat life and keep it relevant much later into this century.

That work—along with the accompanying need for more parts and future additional domestic as well as international F-18 family aircraft—is expected to keep the company’s production line going into the coming decades, says Dan Gillian, Boeing F/A-18 and EA-18G Growler programs vice president.

To get an idea of what will be needed to whip the Super Hornets back into shape and help prepare them for future work, Boeing is using its Service Life Assessment Program (SLAP) to put together a Service Life Extension Program (SLEP) that will boost fighters’ life to 9,000 hr. from its current 6,000, Gillian says.

Boeing also will be bringing in two of the earliest, most-used Super Hornets in the coming months, Gillian says. These “learning aircraft” will be used to discern some of the likely mechanical issues. This was a lesson learned from doing some of the life-extension work on the classic Hornet aircraft, Gillian says.

Indeed, the heavy maintenance requirements of classic Hornets has led to the company’s Super Hornet strategy now, Gillian explains. With so many of the older aircraft sidelined, the Navy has been forced to deploy squadrons of its Super Hornets years earlier than originally planned.

“You’re burning up the hours on the Super Hornets now,” he says. And the slippage of F-35 deployments has put a further strain on the Super Hornets.

“Super Hornets have to fill up more of the carrier air wings than originally intended,” he says. “For the long-term force structure, Super Hornets are supposed to be half the carrier air wing from now till 2040. Super Hornets right now are about three-quarters of every deck. There are Super Hornet shortfalls.”

That strain is going to show up in the aircraft, especially given the kind of environmental stress they have to suffer during naval operations. Boeing has been working on analysis and engineering models since 2009 about what to expect, Gillian says.

When the first aircraft hit 6,000 hr. within the next year, the company’s engineers and mechanics will get a first-hand look. “We’ll tear them apart to see with our eyes what’s really happening,” he says.

Early analysis suggests work on the Super Hornets may at least start off earlier than the classic Hornets, he says. “What we’re seeing now is that the Super Hornet is in a better starting point than the classic Hornet was,” Gillian says. “That was by intent. The Super Hornet is the newest airplane in the Navy’s inventory. The Block II was IOC’d [approved for initial operation capability] in 2007. New thought and modern manufacturing went into building the Super Hornet with composite materials such as titanium. People remember the classic Hornet’s center barrel replacement program. We had to cut out a big piece of the fuselage. We don’t see that with the Super Hornet.”

That said, “there are some hot spots that need to be addressed,” he acknowledges. “Flight control surfaces have to be replaced or repaired.”

The scale of the work will be a challenge: Boeing had done a SLEP of 150 classic Hornets. It now has to plan for 568 Super Hornets.

One of the major concerns is corrosion, and the SLAP aircraft will show engineers the extent of the problem. “These aircraft have been flown in conflict for ... a long time on the carrier in a very corrosive environment,” Gillian says. Every time mechanics open up a Navy aircraft they find corrosion and, he notes, it can be of a different nature each time.

“Standardization of what corrosion is all about, that’s the object,” he says. “Can we get to an 80% solution? That’s the biggest single challenge.”

composite materials such as titanium

[spazsinbad]

Thanks 'Dragon029'.

[johnwill]

To be fair to Boeing, 6,000 vs 9,500 hours might be the difference between CATOBAR vs CTOL operations.

No, or at least that's not our experience with the CF-18s. To start, I should note we don't use a similar metric for judging an aircraft's life: its based on the amount of stress an airframe has received in its lifespan. Nevertheless we don't have many aircraft beyond 6000 hours.

Furthermore, flying a CATOBAR aircraft in CTOL operations may not necessarily be "better" for it. To allow for CATOBAR operations the aircraft has to be designed around that extremely demanding requirements (particularly landing). We found that our airframes accumulated a lot of stress because they were extremely rigid and they transmitted the impact of its wheels going over the gaps in pavement slabs right to the structure. While it may not seem like much, the accumulated stress from thousands, if not tens of thousands of micro impacts, became a serious concern. Canada has been really aggressive on how we manage our aircraft stress, and there are a number of issues that the CF-18s had which were related to the aircraft being primarily designed for CATOBAR operations, rather than CTOL.

One further point: I would assume that the F-35's advanced aircraft health management system would be far better at managing an aircraft's lifetime fatigue life than the F/A-18E/F. Counting hours (a defined service life) is a very old approach to managing an aircraft's health, and may lead to a lot of hours being left on the table, or excessive costs.


Edit: also, someone should compile a list of Boeing protests or threatened protests over major competitions they lost. I suspect it would be a long list, and outnumbers programs they didn't protest.

A couple of comments about hb pencil's post --

A characteristic of main gear shock struts not well known is the highly non-linear load vs. stroke on some airplanes. With gear fully extended, the load vs. stroke is relatively soft, say up to about one third max load. Then from that point to about two thirds max load, the strut is a rigid link, no springiness at all. Add more load, from two thirds up to max, the strut is soft again. By design, the strut load during taxi conditions falls into the rigid strut range. So taxiing over thousands of small bumps does become a major durability problem. It sounds like your F/A-18 has that type of strut. Being carrier - based, USN airplanes don't do nearly as much taxiing, so may not have the problem. Why does the strut have that rigid range? To prevent the airplane from tipping over during combined turning and taxiing operations. Heavy underwing stores, especially un-symmetric, could easily drag a wing tip during a turn with soft shock struts. In addition, Navy airplanes generally use higher pressure tires to withstand high sink rate landings. With that rigid shock strut, the tires are the only spring in the gear system during taxi, thus more durability damage during taxi.

No one bases service life on flight hours only. As a matter of convenience, many will say this airplane is a 6000 airplane or that airplane is an 8000 hour airplane. But what they really mean is the airplane is good for 6000 or whatever hours at a specified usage spectrum (speeds, altitudes, weights, maneuvers, stores, mission type, etc). All original design and verification efforts are based on that concept. If actual usage is different, the useful life will be different, either more or less than design, based on usage. That's why USAF carefully tracks the usage of every individual F-16, so it's structure can be inspected more or less often depending on the usage.

[johnwill]

Generally speaking...

...an hour on a Navy jet is one hour of expended life; it doesnt matter what you were doing with that hour. When that jet gets to its design life limit, it turns into a pumpkin.

.

quicksilver, I generally fined your posts to be knowledgeable and reasonable. But this has me puzzled. On the surface that comment goes against every fiber of my forty years of airplane structural experience. I'm not saying it is wrong, but I would appreciate more information to back it up. One possibility I can see is if most of the lifetime degradation is not due to stress cycling (fatigue or durability), but is from corrosion instead.

Thanks in advance.

[spazsinbad]

'JW' the 'AvWeak' Hornet story above highlights the corrosion problem. For A4Gs it was diabolical, and not just from salt water but from the exhaust gases if aircraft left on deck too much. Exhaust gas corrosion not a problem on CVNs - I guess?

[johnwill]

How expensive to SLEP? Very...

Here's a reference from the US Congressional Budget Office in 2010 -- and the numbers came from the Navy. Depending on the options assessed, the cost to extend was between $2M and $5M per year of airframe life. Assuming 300 hours of life expended per year (their assumption), that's roughly $5-17M per 1000 hours of extension. Want a 9K hour airframe? That is between $15M and $50M -- per airframe -- back in 2010.

Do the math; a cheaper 6K hour airframe doesn't look as attractive when the real costs are part of the calculation (which in this day and age, rarely are), and that's before we talk about things like the fatigue life usage spectrum assumed in the design.

https://www.cbo.gov/sites/default/files ... tories.pdf

So we may say that a 6000 hour extension might cost $60M. Here's a thought, why not forget all the SLAP, SLEP, SLOP or whatever cost and simply build complete new airframes and transfer all the systems from the old ones. The contractor could start building new airframes immediately after the last original production airplane rolled off the line. Tooling, suppliers, labor all still in place. So you get a structurally new airplane for half the cost of a complete new airplane.

[quicksilver]

Generally speaking...

...an hour on a Navy jet is one hour of expended life; it doesnt matter what you were doing with that hour. When that jet gets to its design life limit, it turns into a pumpkin.

.

quicksilver, I generally fined your posts to be knowledgeable and reasonable. But this has me puzzled. On the surface that comment goes against every fiber of my forty years of airplane structural experience. I'm not saying it is wrong, but I would appreciate more information to back it up. One possibility I can see is if most of the lifetime degradation is not due to stress cycling (fatigue or durability), but is from corrosion instead.

Thanks in advance.

Did you spend much time dealing w/ NAVAIR in the course of your career in industry? (slight interruption for dinner). Then you know that the services' syscoms take different approaches to the matter.

A case in point would be the F-16N, which I'm sure you remember vividly.

We're also talking, for the most part, to an audience with non-technical backgrounds, so in order to enhance understanding of the general principles or matters at issue, I choose to distill and simplify. Hence, I prefaced the post with "Generally speaking...".

Also, if you note the article posted above on SH SLAP, it -- in general terms -- outlines the common approach to life extension for Navy/MC aircraft. Is it more complex than that? You betcha. For those who want more detail, I'm sure you can illuminate.

[johnwill]

Unfortunately, too much. There was the F-111B (Carrier Suitability test), the A-12 (Structural Flight Test Manager), and believe it or not the P-3C (Re-certification structural flight test advisor to RAAF). So, I'm well aware the USN does things "differently" shall we say.

I wasn't directly involved with the F-16N, having moved on to things like AFTI F-16, F-16XL, etc., but was aware of the structural controversy.

OK, thanks for your observations. I understand the viewpoint you have and the methods you use. I probably give more credit to the audience and try putting a little meat on the bone of discussion, but take great care keep explanations as clear as possible.

And thanks for the reference to the SH SLAP. I'll go back and read it.