Nose Gear Strut Crack

[PapuaPilot]

Can you think of any reason this crack has occurred? Have there been hard landings, rough strips or other things that have given the nose gear a beating? Has this happened to other nose wheel Kitfox planes?

I wouldn't hesitate to have it welded. You could even consider adding a doubler to that area to beef it up a little.

[Paul Z]

If I were to talk to Bob S., Senior Fellow Materials & Metalologist Engineer he would say Hydrogen Embrittlement. Basically the welding and/or the foundry process of making high strength steels.

The embrittlement of of metal or alloy by atomic hydrogen involves the ingress of hydrogen into a component, an event that can seriously reduce the ductility and load-bearing capacity, cause cracking and catastrophic brittle failures at stresses below the yield stress of susceptible materials. Hydrogen embrittlement occurs in a number of forms but the common features are an applied tensile stress and hydrogen dissolved in the metal.

Examples of hydrogen embrittlement are cracking of weldments or hardened steels when exposed to conditions which inject hydrogen into the component. Presently this phenomenon is not completely understood and hydrogen embrittlement detection, in particular, seems to be one of the most difficult aspects of the problem. Hydrogen embrittlement does not affect all metallic materials equally. The most vulnerable are high-strength steels, titanium alloys and aluminum alloys.

Sources of Hydrogen
Sources of hydrogen causing embrittlement have been encountered in the making of steel, in processing parts, in welding, in storage or containment of hydrogen gas, and related to hydrogen as a contaminant in the environment that is often a by-product of general corrosion. It is the latter that concerns the nuclear industry. Hydrogen may be produced by corrosion reactions such as rusting, cathodic protection, and electroplating. Hydrogen may also be added to reactor coolant to remove oxygen from reactor coolant systems.

[Dave Holl]

A very good find that's why we inspect our planes!
As was said before has the nose gear been exposed to rough treatment? It does look like the crack formed by the weld so likley caused by hardening of the material in the weld area, I have seen this type of damage re welded successfully but as stated an area to keep an eye on in the future!

[SWeidemann]

Regarding welding on the Kitfox nose gear strut, is there a concern about heat treating of the metal? The text below was copied from the Luscombe Airplanes Yahoo web forum that has technical chatter about the old certified Luscombes.

As far as how this (Kitfox) landing gear in question was treated, I do not know since I am not the builder who put most of the time on it.

"RE: [luscombeairplanes] LANDING GEAR WOES
dcombs@luscombesilvaire.info08 Nov, 2006
The gear legs are pretty highly treated (180KSI), and welding will damage the integrity. The legs must be annealed, welded , stress relieved, the re-treated and finally prepped for corrosion proofing. y the time you do all that you will meet or exceed the cost of a new or previously repaired set of legs done in a 'batch'. Classic aero inventories these in the repaired and new condition.- fully heand properly heat treated."

Skot

[WISDAN]

Hi Skot,
If it were me, I'd just order a new strut from John and Debra. I ordered one from them last summer and I believe it was under 500.00 dollars and fit my plane perfectly and they got the strut to me in a week or so.
By the way my old strut was damaged by a forced landing in a very soft field.

[SkyPirate]

Being a retired certified welder I would either tig it or flame weld it, and as soon as I got it welded I would flash heat it so it didn't cool fast then wrap it up in some old welding gloves and go to lunch, when I got back I would check it, it should be cool to touch then I would walnut blast the area prime it paint it and re install, if you have to mig weld it preheat the repair area to about 300 degrees, flash heat it with a torch, don't hold it in one spot making it cherry red, just flash the flame evenly across the repair area, weld it wrap it cool it walnut blast it paint it

[Xengineguy]

Being a retired certified welder I would either tig it or flame weld it, and as soon as I got it welded I would flash heat it so it didn't cool fast then wrap it up in some old welding gloves and go to lunch, when I got back I would check it, it should be cool to touch then I would walnut blast the area prime it paint it and re install, if you have to mig weld it preheat the repair area to about 300 degrees, flash heat it with a torch, don't hold it in one spot making it cherry red, just flash the flame evenly across the repair area, weld it wrap it cool it walnut blast it paint it

I agree with Chase,
I might add a gusset made from 4130 tubing cut in half,length-wise, and placed
45 degrees between the two tubes and over the original crack. This would move the stress point away from the original repaired area.

[Dave S]

Skot,

I'd agree with the folks indicating re-welding by a competent person if the only issue is a crack with no other underlying problems such as corrosion.

If I understand the photo correctly, this looks to be the bottom of the strut where it is welded to the tube which the nose wheel fork swivels on.....Correct?

I'd check an additional item ......the vertical tube which the nose wheel fork swings on calls for inserting a foam plug during original assembly/build, sealed with hysol up the inside of the threaded end an inch or so to clear the cotter pin.....the reason for this is to seal the vertical tube from moisture and corrosion. Due to the location down in the weeds - this spot is particularily succeptible to corrosion as the inside is not painted or powdercoated. Checking the integrity of this plug is an annual condition inspection point. If the plug is not there, or is damaged, this is a particularily nasty place for moisture to get up and rot the vertical tube from the inside out. The weld is basically naked and unprotected on the inside of the tube without the plug. Tube rust/corrosion from the inside out can make a weak spot where developement of a crack could be a secondary effect of corrosion/rust/thinning of the metal.

If the original plug is intact and no rusting - the plug will likely have to be renewed after welding/treatment as it will probably fry from the welding.

Buying a new one is a certain way to go if it ends up the original can't be safely fixed.


Sincerely,

Dave S
KF 7 Trigear
912ULS Warp Drive

[SilverFox1]

One more opinion. It's great that you posted a photo but I can't be sure from the photo exactly what happened there but it may be that there simply was no weld penetration into the piece that appears to have cracked. What we are looking at may just be the edge of the filler wire bead that failed to get the metal hot enough to melt it and make a good weld. Even if there was some penetration, it may not have been deep enough to make a strong enough weld for the application and this may have allowed the filler bead to break away from the part creating what looks like a crack when it may just be a bad weld. If the metal of the strut did fracture I would replace it, but if it is just a bad weld then rewelding it is the appropriate fix. Like others have suggested I would TIG or GAS weld it with my personal preference being TIG.

[SWeidemann]

Silverfox,

My intent is to take the strut to my regular IA for a look and also my local EAA Technical Counselor. John & Debra's opinion will count too. My guess is it may be a weld issue of not much significance and may have been there for some time. An option is to paint the spot and keep up regular inspections to see if ther is any new cracking activity. However if my IA doesn't like it I will need a fix. I know a new strut will be $$$.

Thanks much, Skot