COLUMBIA AIRFRAME OUTLASTS STEEL FATIGUE TESTING STRUCTURE 2

[berkshire]

COLUMBIA AIRFRAME OUTLASTS STEEL FATIGUE TESTING STRUCTURE
Columbia Aircraft Manufacturing Corp. announced that one of its Columbia airframes has absorbed the equivalent of 25,000 flight hours of punishment in fatigue testing. The company deliberately inflicted one of its airframes with 100 damage sites and placed it in fatigue testing. The tests were stopped when the steel fatigue testing structure, which is used to bounce and bend the airframe, began to have metal failure.

 

[KENAT]

Don't you love breaking the rig instead of the test article!

 

[kenvlach]

That suggests an overweight frame that wastes fuel and reduces payload.

I'm not familar with aircraft fatigue requirements, but isn't it reasonable to design something with a safety factor of perhaps 5 normal lifetimes? [Although a few DC-3's & B-52's are perhaps way past their expected airframe lifetimes]

 

[MintJulep]

Or simply that the test rig itself was poorly designed for fatigue loading - I see this frequently.

Test rig is inevitably designed by junior engineer, who just selects super heavy stock, which gets joined with partial penitration and fillet welds.

 

[SWComposites]

Actually, the test frame was probably well designed, and the structure is not over-designed (over-weight); composites have very good fatigue performance so its not surprising that the metal test rig failed first (metal fittings/fasteners/etc attached to composite strucure often fail first in fatigue tests), and the structure is sized by ultimate loads rather than fatigue loads as with aluminum aircraft.

 

[rb1957]

pardon my ignorance, but who or what is Columbia ? i first thought they were talking about the shuttle. 25,000 flight hours suggests a military fighter. still i think a well designed tet rig should be able to outlast the specimen. "deliberately inflicted 100 damage sites" ... yawn, so does everybody.

 

[SWComposites]

Columbia makes small general aviation aircraft in Bend, Oregon.

http://www.flycolumbia.com/

 

[TVP]

MintJulep is absolutely correct-- he must be looking at the same fixtures I see down in my test lab. The weld beads always look very nice, but they are tiny compared to the giant thickness of the plates, and therefore "partial" penetration doesn't even begin to describe the geometry...

 

[Kwan]

I'm assuming this is unpressurized. Hence, the fuselage would be no problem.

What is the material used for the wing spars and skin???? I looked on the web site but didn't see mention of material (only did a quick look). It did say composite fuselage and control surfaces.

 

[CompositeGeek]

I built the wings and wing box for the Columbia 300. they are fiberglass skins and ribs secondarily bonded with spars that are made of carbon uni-tape and fiberglass. The fuselage is primarily fiberglass and honeycomgb construction with localized carbon fiber element.

It is a very interesting airplane and won it's type certificate in the late 90s. It and another aircraft (don't recall the name) were the first GA service airplanes qualified to the new GA stall characteristics enforced by the FAA.

One last unique topic for this plane - all composite materials used were qualified on a commodity basis - anyone can make the raw materials.

Had fun building 'em too!


Composites and Airplanes - what was I thinking?

There are gremlins in the autoclave!

 

[rb1957]

kwan,
"I'm assuming this is unpressurized ..." ... the plane goes to 25,000 ft, so it is pressurised.

 

[KENAT]

I think the lesson here is that we all need to build vibration rigs to test our vibration rigs before we try to test something in a vibration rig.

A valuable lesson indeed.

 

[berkshire]

rb1957 (Aerospace)
Just because it goes to 25000 feet, it does not have to be pressurised.
You just wear a nose bag.

Since Composite Geek is building them, He probably has the answer to this.
B.E.

 

[kenvlach]

You can view the test rig & airframe (open shell, no pressurization testing !!!):

Cut & paste

ftp://columbia:columbia@mail.mandala-agency.com/Sun n Fun 07 Media Kit

into your browser to begin, then open the folder 'Images,' the folder 'Columbia Fatigue Test Images' and the file StressRig.jpg

Maybe some wear at an eyebolt?

 

[tbuelna]

Would you fly an aircraft designed by a company that can't even do a simple test rig right?

 

[carney]

Is the plane made of Composites?

If it is...then fatigue loading has very little impact on the structure. Fatigue stress calculation are normally not performed on Carbon fiber components due to it's great damage resistance. Up the composites.

If it is not...then they should have made the rig out of composites. LOL

 

[sigma38]

Was the Airbus composite rudder failure a fatigue issue?

 

[SWComposites]

The Airbus rudder failure is beleived to be due to hydraulic fluid getting into and degrading the honeycomb core in the skin panels resulting in a large area facesheet disbond which led to failure.

 

[jetmaker]

SWComposites,

Do you have some documentation stating such? I was under the impression that the failure was a result of agressive use of the rudder during upset maneuvers. My understanding was that the rudder saw full reversal 5 times then snapped off above the fitting (some fittings were still attached to the airframe) due to aerodynamic overload.

I am unable to say too much on this as I was working for Airbus at the time of litigation, but the hydraulic fluid was not suggested as a contributing factor.

jetmaker

 

[SWComposites]

http://www.ntsb.gov/PressRel/2006/060324.htm