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Freeze Plug retaining strap.
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Source：Internet Author：Unknow Pubdate：2008-11-04
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MrHiLok (Aerospace)
22 Sep 08 20:09
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 (Aerospace)
23 Sep 08 8:07
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. 字串7
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 (Aeronautics)
23 Sep 08 19:35
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 (Aerospace)
24 Sep 08 7:00
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. 字串8
MrHiLok (Aerospace)
24 Sep 08 21:54
Thank you everyone for their inputs.
cheers
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