Sue Sapp/Special to the Telegraph The fuselage of an F-15 is lifted off jacks at Robins Air Force Base.
Posted on 09/02/2011 7:27:12 AM PDT by sukhoi-30mki
F-15 fatigue tests vital to aircraft's future
By WAYNE CRENSHAW - wcrenshaw@macon.com
From a small building in Byron to a lab in Israel and a Boeing facility in St. Louis, a massive effort is under way that will play an important role in the future of the F-15 Eagle.
The two most extensive full-scale fatigue tests ever done on the venerated aircraft, along with complete teardowns of two others, will help determine what maintainers at Robins Air Force Base need to do to keep the aging fighter jet flying safely for years to come. Robins does depot maintenance, program management and life-cycle sustainment for all F-15s in the Air Force.
At Boeing, an F-15E Strike Eagle, which can take on air and ground targets, will undergo a test that will simulate at least 65,000 flying hours. If there are no major issues, that would certify it for a 32,500-hour service life. That’s more than three times the 8,000 hours currently certified for the plane.
For the F-15C, strictly an air-to-air fighter, the test will go to at least 36,000 hours, certifying it for 18,000, twice the current limit.
Randy Jansen, chief F-15 engineer at Robins, said the tests involve a complex system of hydraulics and tabs that apply pressure to aircraft structure as it hangs suspended, simulating air pressure from flying at varying altitudes.
It takes a year just to set it all up. The test has just begun on an F-15C Robins shipped to Boeing last summer, and the F-15E they shipped this summer is being prepped. Aside from pauses to do evaluations, the test will run around the clock until 2014. The F-15E test will go until 2015.
Jansen said the test gives an accurate simulation of the same stresses the aircraft would have during real flying.
“In order to continue to fly the aircraft, we need to know what happens in the future,” Jansen said. “This gives us insight into the future and allows us to do preventative maintenance to reduce stresses.”
Teardowns give look at current condition
While the fatigue tests give engineers a look into the future, the teardowns provide a look at how the aircraft is currently holding up.
In a building in Byron, a small team of contractors over the past two years have completely disassembled an F-15D and an F-15C. The purpose is to get a look at interior structural parts not seen even in programmed depot maintenance done at Robins.
Every square centimeter of the parts is carefully examined and analyzed for signs of problems. The evaluation of the F-15D teardown is finished and nothing of significance was found, Jansen said.
The evaluation of the F-15C teardown, which was only recently completed, is still under way.
Some of those parts have been shipped to Israel for metallurgical analysis. Israel is a major user of the F-15 and is involved because it has the expertise and a vested interest.
While Israel is the only foreign user with hands-on involvement, other nations using the F-15 have been keenly following both the teardowns and fatigue tests.
Tests may go even further
While 65,000 hours for the F-15E and 36,000 hours for the F-15C are the goals set for the test, Jansen said the true intent is to keep going until the planes completely break. He is confident the tests will exceed the goal hours.
Even if inspections show structural issues during the tests, it will not mean the tests will have to stop and the certified flying hours set lower than expected. Jansen said any issues discovered will help determine what maintainers need to look for during depot maintenance and what can be done to prevent those problems.
Current plans call for retirement of all F-15Cs by 2025 and all F-15Es by 2035. While theoretically the successful completion of fatigue tests might indicate those dates could be extended, that wouldn’t necessarily be the case.
Jansen said numerous factors other than structural issues could lead to retirement of the aircraft regardless of any projected date, such as more advanced fighters by potential enemies rendering the F-15 obsolete.
Missouri crash brought issues to the forefront
In 2007 a Missouri Air National Guard F-15C broke apart in midair while on a training mission. The pilot ejected safely, but the accident called into question the future of the F-15 and led to a grounding of the fleet. The investigation determined the accident was caused by the failure of the upper right longeron, a main part of the support structure.
The failure was blamed on the longeron being built thinner than blueprint specifications, but fatigue stress was a contributing factor. The aircraft had seen extensive use, said retired Col. Fritz Heck, who was commander of the Robins F-15 test flight fleet at the time of the accident.
“It had been flown hard,” he said, and that was ultimately what exposed the defect.
Heck said the teardowns and fatigue tests are important to preventing similar accidents in the future. The effort can help identify any such faults that can be corrected before a catastrophic failure occurs.
The accident led to inspections of all longerons, with replacements on five aircraft, and the grounding was lifted.
Aircraft remains important to national defense
A few years ago, the plan was for all F-15s to be retired except for the newer F-15E, with the F-15C’s air-to-air capability to be replaced by the F-22. However, the F-22 proved too expensive, and production was cut far short of what originally had been projected. The F-35 program also has seen extensive delays and problems.
It all means the F-15 is still vital to national defense and likely will be for many more years, Heck said. The F-15E has been used extensively in Iraq and Afghanistan, and the F-15C is the primary fighter for protecting America’s airspace. The F-15D is primarily used as a trainer.
The Air Force currently has 221 F-15Es and 250 C and Ds. Those numbers have dropped significantly in recent months as many of the older aircraft have been retired. The average flying hours have also dropped with the retirements, with the F-15Cs averaging 7,310 hours and the F-15Es at 5,611. Previously, many of the older aircraft had been flown well beyond the certified hours.
Despite the age of the aircraft, Heck said he still has high confidence in the capability and safety of the plane. He has 2,000 hours as an F-15E pilot, including stints in Afghanistan and Iraq. Heck’s son is in the Air Force Academy and wants to be a fighter pilot.
“I would have no problem whatsoever with him flying F-15s for years to come,” he said.
To contact writer Wayne Crenshaw, call 256-9725.
Read more: http://www.macon.com/2011/09/02/1687034/f-15-fatigue-tests-vital-to-aircrafts.html#ixzz1WnyoXdXB
Sue Sapp/Special to the Telegraph The fuselage of an F-15 is lifted off jacks at Robins Air Force Base.
If you can find a copy of the great old Jimmy Stewart movie..”No Highway in the Sky”...it looks like the same test bed (g)
It sounds like the F15-SE has a radar profile that’s similar to the F35. They’ve both got the export market in mind but the F35 has been nothing but a consistent disappointment. The F15 is a proven platform so I’m wondering why it couldn’t replace certain variants of the F35. The F22 has cost problems but it sounds like it has unmatched performance/stealth capabilities.
I guess we’re too far along with the F35 but it seems like it would have been a better investment to focus on the F22 and to upgrade certain proven platforms like the F15.
^My sentiment, as well.
although its considered “old” and military strategists are always chasing the latest high-tech dream - equipment like the F-15 will win wars when they become a seriously tough slog.
Dependable, durable, cheap (relatively) and available in large numbers.
If you want to stick to the concept of an (relatively) light, affordable fighter, you would want something closer to the class of the F-16 or Swedish Gripen rather than the F-15.
This is part of the reason why the USAF leaders are foolish. The article states they are testing the airframe to simulate 65,000 hours flight time if it is sucessfull then they plan on allowing 32,000 as the new limit. Built for 8,000 hours....BS say I common sense says wrong as rain and certain USAF commanders are all ready junking them an tests have yet to be done?
The problem with the USAF leadership is they are wrong as rain. Constantly looking for new toys for the boys. They all said the F5 was no good however there are 15 of them used as bad guys for fighter tactics training....When does the stupidity stop. The army is crying for front line support and the usaf wants to junk the best plane for the job the A10 I see finally it comes out it must go mach 10 or junk it...Give me a break they junked the 141 and replaced it with half the aircraft it replaced oh they said it holds more cargo yep it does however it cannot fly in 2 separate missions at the same time....The B52 fleet is approaching the level of museum piece and the new bomber has to be flown halfway round the world to fly 1 mission an this makes sense...Maybe its time to outsource the USAF...Every time they get a new leader first thing they do is lets change the uniform that will give the enlisted some espirit de corps...I spent 20 years in the USAF and went thru 5 different style shape of fatigues. 1 actually had peg pants?...Grow up USAF there is more to our job than mach 10 fighters.......
and the SE has better range, payload, two engines etc.
Anybody with a brain would S__tcan the F-35 and build a whole bunch of SE with the same surround of cameras and sensors on the F-35 for less than half the cost.
Politics and military procurement don’t mix... there is no brain.
I don't think replacing a 35 year old aircraft that has exceeded its service life is poor management. Poor management would be to continue on with outdated equipment until we got into a war we couldn't win.
We should be building F-15SE’s, “F-16SE’s”, and “A-10SE’s”.
Probably the three best tactical combat planes ever built. Build some brand new upgraded ones and we can stop worrying about our planes breaking apart in mid-air.
That in my mind is a big plus. The SE is a multi-role 5th gen stealth fighter with tremendous performance capabilites plus much more payload.
Israel has indicated they’d like to go with the SE as opposed to the 35 by we’re trying to force feed the 35. Saudi Arabia as well has expressed interest in 72 SE’s.
No it's not.
Where in the article does it talk about radar cross-section profiles? There is absolutely no comparison between an aircraft that was designed from the ground up to be LO vs. one that has some RAM slapped on it in various places on an aircraft designed in the ‘70s.
How can you and all the others on these boards that are deriding the F35 as a failure, determine that, in its current state of flight TESTING, that the F35 has “been nothing but a consistent disappointment.”?
What parameters are you all using to determine SUCCESS vs. FAILURE?
Sheesh, get a friggin’ grip. The F22 went through it’s teething problems as well, just like every other aircraft in our military inventory. Oh, btw, the F22 fleet is grounded right now.
All the more reason why they should have run off more wings and fuselages during the regular production run, and then mothballed them along with the equipment to make more. That way we could replace parts that show wear, rather than grounding the plane.
Which accounts for a higher percentage of the total plane cost: the frame or the things that go into the frame (electronics, engines, etc)? Perhaps we would get more cost-effective aircraft if we had more commonality between old and new types of planes, with new airframes being able to use engines and electronics from older planes, and newer engines and electronics being able to be installed in older airframes as well.
The 35 has been a disaster. The Pentagon now pegs development costs at up to $329 billion from an inflation adjusted $197 billion.
>But further cost growth and schedule extensions are likely, the Congress’s non-partisan audit and investigative arm said.
Lockheed Martin, the Pentagon’s No. 1 supplier by sales, said it had no insight into how the Pentagon established its estimate averaging up to $112 million per F-35. That figure was up from a baseline projection of $59 million in real, inflation-adjusted terms.<
From here:http://www.reuters.com/article/2010/03/20/lockheed-fighter-idUSN1915127820100320?type=marketsNews
A near doubling in per unit cost is what I’d call some pretty serious teething problems.
IMHO the F-15 was the greatest Air-to-Air combat jet of its time. The problem is that they design goes back to the end of Vietnam. It isn't stealthy and it won't survive in today's high tech warfare. It can be seen from 100 miles away by enemy radar and Air to Air missiles can bring it down as soon as it's in range.
With your theory of avionics, we would still be using tube-type radios that weighed 100 lbs.
Our newer engines allow jets to fly at low mach speeds without using the afterburner. They're much more efficient and reliable than older ones.
Was searching to find what a F-15 upper longeron looks like and found this:
http://www.snopes.com/photos/airplane/f15crash.asp
The $329 billion is procurement cost not development cost. And that’s after reducing the number of planes by 409 for the US.
Every new fighter jet gets labeled as too expensive and unreliable during its development. I remember when they were saying that about the F-15, F-16, and F-22. Loose one airplane during testing and everyone wants to cancel the whole program.
Aviation Week article
http://www.aviationweek.com/aw/generic/story_channel.jsp?channel=defense&id=news/VIDF15s021308.xml
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