welding on a main spar

[daniee]

hey , i am to weld a bracket on a main spar of z-142. what is the material spec on zlin z - 142. what wil the welding rod spec be? .i use tig welding prosses.
thanks danie

 

[Andries]

Hi Daniee,

Welding to a principal structural member such as a main spar sounds pretty dangerous. Is this an OEM-approved mod/repair?

Welding can cause cracking of the spar as well as local deformation.
There are, as you may know, numerous deleterious effects due to welding such as residual stresses, porosity, etc., all of which impact on the strength of the structure.

I doubt whether you will obtain approval for this mod.

Is there no other way of attaching the bracket?

Bear in mind however that even attaching the bracket by means of more conventional means such as rivets must still be subject to thorough engineering input as regards static strength and fatigue aspects. The presence of an additional component such as a bracket could also attract load by stiffening the area locally.

Regards

Andries

 

[Sparweb]

What's the bracket for?

STF

 

[DennisDodge]

Never weld to a primary structural member without approval of a stress engineer from the company that built the structure. Weld repairs can be VERY bad because of localized changes noted by the other writer. Other factors are reduction or removal of heat treat (material reverting back to a lesser strength material). While welding sounds like an easy way to attach the bracket I think you may be in an area you should not be in. Riveting may be a better choice but again never do it without the stress engineer that knows that part. Rivet material, hole size, special treatment (cold working of the holes) are all going to have an impact on what you are doing. Good luck but above all be safe.

 

[daniee]

thanks for al your replys , the end peace of under carrige is bold on to this bracket. it is a welded part that crack lose of the main spar ,after a hard landing, mybe this can help a bit.

 

[StressTheGame]

Another issue with welding aluminium is that besides anealing the material, you will not have reliable allowables (i.e. "A" or "B" basis type allowables) to even show an acceptable level of degradation to your structural components. There are no recognised published allowables on most -T0 materials from ultimate or durability (fatigue and/or damage tolerance) points of view.

 

[BrianR]

This is a shortcut to Jail. Do not do it! Especially if the original bracket has broken off as you have no idea of the condition of the metal in the spar and any welding will probably change the heat treatment of the metal. Keep well away from this one.

 

[Nigel]

You need an approved repair for this, if you need any help with this feel free to email me the details.

Nigel Waterhouse & Associates
Aeronautical Consulting Engineers

Transport Canada and F.A.A approval & certification of fixed and rotor wing aircraft alterations: Structures, Systems, Powerplants and electrical. FAA PMA, TC PDA.
n_a_waterhouse@hotmail.com

 

[rhodie]

it is a welded part that crack lose of the main spar ,after a hard landing, mybe this can help a bit

That type of thinking could get a lot of people killed. Never do anything based upon the concept of "maybe".