Freeze Plug retaining strap. 1

[MrHiLok]

I am repairing a damaged hole in the T chord flange of trailing edge structure of the wing by freeze plugging. There is a fitting installed at the location and the hole (0.25 inch Diameter) goes through the T chord flange and fitting.
The damaged hole is in the flange of the T chord and the fitting hole is undamaged.
The hole is used to secure an aerodynamic panel using a screw.
To retain the freeze plug, I will be installing a strap.
I would like to know how to work out the thickness, material and length of the strap. The chord and the fitting are made of 7075-T6.

 

[bf109g]

MrHiLok -

All you are trying to do is trap the "free" side of the plug. This would be easy if the hole was for a permanent fastener - just use a washer larger than the freeze plug.

Pretend you are reinforcing a blendout on the T and apply the straps (you will want one on each side of the T) per SRM guidelines for extrusion repair.

 

[jetmaker]

MrHiLok,

If the stack up is fitting, T-Chord, panel, then if the freeze plug is confined to the T-Chord, no retention is required as it is trapped between the fitting and the panel.

Another option is to use a countersunk freezeplug with the csk side between the fitting and the T-Chord. This would be fully self-retaining.

You need to look at the straps anyways from a strength restoration issue as mentioned from bf109g.

jetmaker

 

[RPstress]

If you really want to do a calc and if the freezeplug is bigger than the nut (assuming the head is csk into the attached panel or similar) then you could do a simple sum with the pull-off force in the fastener. Perhaps treat the strap as a plate with a ring load on it at the nut periphery with simple support in a ring at the freeze plug periphery. Roark's circular plate formulas would work ok.

 

[MrHiLok]

Thank you everyone for their inputs.
cheers