In article ,
"J.Kahn" wrote:

patrick mitchel wrote:
There's a discussion on a ul ng about a guy that built a strut braced light
plane and in a fit of overkill (apparently ) decided to add a (non plans)
jury strut. He drilled a hole (3/16") on the bottom of the tubular alum
spar. Then realized he may have made a mistake. Whats the outcome and is
there a fix without putting in a new spar. Just curious (and I didn't do
it!!) Pat



The bottom of a strut braced spar in the mid span location between the
fuse and main strut attach will be under compression, not tension, so
the hole may be benign if it is filled with a rivet to restore most of
the compression strength in that area.

WRONG! WRONG! WRONG! The bottom of a wing spar (assuming +G) is ALWAYS
under tension! The hole creates a stress concentration and can impair
the ability of the spar to carry design loads.




Possibly a doubler patch is in
order to prevent buckling of the weakened area, but the doubler has to
be properly designed minimize the effects of the sudden change in
resistance to buckling due to the patch, depending on the local loads.
The good news is a tubular spar must be sized to deal with the loads at
the highest stress point, which is on the outboard side of the strut
attach fitting, so for the rest of its length it is overbuilt.

Two options:

1 He should confess what he did to the plans maker and ask for a repair
scheme or recommendation.

Mandatory!

I would be surprised if he didn't ok a plug
rivet in the hole, especially if there are already rib attachment holes
in the same area to each side.

I would be surprised if the designer DID approve of plugging the hole
with a rivet, as a rivet will add stress to an already stressed part.

2 If the plans maker says he has to buy a new spar, find a structural
repair specialist for a recommendation.

Buy the new spar and chalk one up to experience and ignorance.