#5. Google scholars... love it. Some of us have Engineering degrees from real schools, and even a smidge of design experience with steels, aluminums, Inconel, carbon fiber...

#2. Aluminum fatigue strength and its failure limit is not as nice as steel obviously. Welded will depend on the alloy, the filler, the post heat treat process, and etcetera.

#3. Airplanes have a 15-20 year life, that is quite a few flights. Corvettes and some other modern cars use aluminum suspension components.

#4. If they are testing to a standard... maybe not so much. Definitely not as bad as car magazine articles. Some of them are thinly veiled ads.

Yeah... welded would not be my favorite, but all engineering is an exercise in choosing the best combination of compromises. What tweaks me is that the level XV was shooting for would have Camaro owners lining up in droves to throw money at the MFG. Kind of like the husband/wife team of ex-GM engineers that are making a go of it with Detroit Speed. In the Mopar world they could not make it.

"#2. Aluminum fatigue strength and its failure limit is not as nice as steel obviously....."

I'm confused, is it only obvious to degreed engineers, or is anybody allowed have this opinion?

You suggest some magical alloy welding combination, etc that would make an alum welded K frame be acceptable, yea, maybe for the marketing dept. My bets are it was typical off the shelf generic 6061 T651? stock with 5356 tig filler, and still prone to fatigue cracking in the HAZ with repeated load reversals which if ever driven, it will encounter. Post weld heat treat in the alum? Really? Of course I also countered my position earlier by mentioning not knowing the robustness of the material, it might be so over designed, that it maybe an acceptable compromise, which I really doubt it is, and just by seeing the member in hand, one of knowledge could judge the robustness, and general weld quality to help predict its level of compromise. Fatigue life is difficult to calculate without actual testing on welded members. Let me repeat, its the welding on Alum that is the issue. Airframe useful life is more dependent on use cycles, like take offs/landings, pressurization and depressurization cycles, time only mainly plays a part in corrosion concerns. Vette alum components are forged, zero welding, and the hydro formed alum frame I suspect are roboticly welded judiciously, in areas that are optimum, and greatly tested for the intended purpose, way beyond anything XV could approach in cost or expertise. What does CF, inconel have to do with this topic?

Addendum:
Careful readers will note the next 5? replies do not address one single relevant point/question I made above, but sure are happy to comment OT. Also if you look back carefully, I did not inject "KV" into this magazine article, I mean thread, but responded to the KV design shortcomings as I see when it was brought up.

Don't bother. Save your typing. He's not worth educating.

Taking your own thread down the toilet.

does anybody else think this thread is about something else entirely when they read "K frame strength" in the title?

Still waiting for citizenship proof from Hawaii. I hope this thread doesn't die because of the high school antics of one student. Keep at it Feets!

You started the trip.


Besides, if it's my thread...

You two take your courtship ritual to PM's.

I fixed it.

lol wondered if you were doing penance or something.

The average age of the aircraft fleet is something like 57 years now, mine is 74 years old. Tim

There's DC3/C47's still in commercial service that are older than your Taylorcraft...

CR

Aluminum has a finite fatigue life. That doesn't mean it will fail one day after it's expiration date. Different alloys have different characteristics and their strengths age at individual rates.

Some day it will fail under load. Chances are good that a properly designed structural aluminum for a car will out last the owner of the vehicle.

I think the XV stuff has had it's fair share of fatigue/stress failures when put to the test. Just ask Bill Howell. He had a control arm fail in 2009 on the Road Course in Pahrump and a spindle fail on an autocross course last year in Reno. I'd wager he has the hardest driven XV system out there.

I'm sorry, but I don't believe you understand how loads and fatigue works...

How and if something fails, depends on how it was designed, regardless of the material...

I guarantee I could lay an aluminum I beam on the floor with some 2x4's under each end, and jump up and down on it till the day I die, and it won't fail...

Take the same beam, cut it in 1/2, weld it back together and have fat lady do the same thing, still won't fail...

Take 100 load and apply it to a beam that will only withstand 100 lbs, and yes eventually it will fail.

Now apply that load to a beam that will withstand 1000 lbs.

It will never fail.....

CR

Bill broke an aluminum Upper Control Arm, THE ONLY ONE THAT EVER FAILED.

I personally removed the ALUMINUM Upper Control Arms from XV001, the FIRST car XV ever built, the car that was tested, taken to the race track, driven by editors, and generally thrashed all of its life... They were in perfect condition, but I replaced with steel replacements.

I only use steel upper control arms in my kits...

But please call Bill, he speaks highly of our products...

CR

Convenient you left out the part about the weld. Google it if you have to. The XV K is welded, its not a uniformed loaded I beam, its reversed stress loaded, its got numerous HAZ, the only thing we don't know, is how over designed it is, and how long that over design extends its fatique life, period, for the fourth time?

I'm trying to keep up but this is really getting over my head...

Ok, maybe some helpful back ground, simply:
1. Steel and Alum are really two different animals, in many ways, fatigue, and weldability
2. Some Alum alloys are stronger then steel, but don't weld well, are very expensive and only used in special applications. Some of these alloys are described as not heat treatable.
3. The alloys that are heat treatable and weld well are strong in their heat treated condition and affordable.
4. All alum eventually fatigues, lower stress levels means more cycles before failure, but the outcome is the same. Steel has an almost infinite fatigue life at low levels.
5. ANY welding on ALUm creates a HAZ (heat effected zone), since the part is never at the same temp evenly during the weld process at the weld area.
6. Since a lot of the strength, sought in the heat treatable alum alloys mentioned above, is gained by heat treating at the factory the raw material, the weld process reverts the HAZ back to a natural and less strong alloy in the weld area. You cannot avoid that. The problem is, the joint is always weaker then the surrounding metal in alum.
7. This weakness also causes an inherent stress riser.
8. Things don't like getting bent under load ( such as a k member), but they really hate getting bent both ways.
9. Heat treating a welded alum part is seldom and not easily done, distortion being a big issue.

All the above is easily found and backed up online.

Here something helpful.....

None of any of that matters if the design is such that it's several times stronger than the calculated load.... In any direction... in any material

The difference between steel an aluminum with respect to fatigue, is that aluminum has a finite cyclical factor, so does steel, but to much lesser degree...

You know what building material doesn't have cyclical factor?

WOOD!!!! Wood wing spars do not have life cycle, only a rot cycle...

Anybody have any spruce welding rod????

CR