misdrilled hole on on tubular aluminum spar question

[patrick mitchel]

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

[Stache]

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


Answer: There is a repair, but a DER structural engineer should review
the repair. The repair is to ream the hole to accept a bronze bushing
and maybe a doubler depending on the location, edge distance, and
material make up. This is no place to guess or just replace the spar.

Stache

[J.Kahn]

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. 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. 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.

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


John

[Orval Fairbairn]

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.

[jerry wass]

Orval Fairbairn wrote:
> 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.

RIGHT! RIGHT!RIGHT--READ THE WHOLE PROBLEM. It is a Strut Braced wing !
-he's installing a jury strut, so he is between the load restraining
points of the spar, Always under compression with Pos. G's Would go
into tension with Neg G's--but how much can you load this type of
construction with Neg G's??
>
>
>
>
>
>>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.

[Orval Fairbairn]

In article >,
jerry wass > wrote:

> Orval Fairbairn wrote:
> > 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.
>
> RIGHT! RIGHT!RIGHT--READ THE WHOLE PROBLEM. It is a Strut Braced wing !
> -he's installing a jury strut, so he is between the load restraining
> points of the spar, Always under compression with Pos. G's Would go
> into tension with Neg G's--but how much can you load this type of
> construction with Neg G's??

Go back and draw in your stress paths! There may indeed be neutral
stress on the spar between the root and the strut attach point, but it
is likely in tension. The strut takes up the entire moment of the wing,
however.


> >>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.

[Capt. Geoffrey Thorpe]

"Orval Fairbairn" > wrote in message
...
> In article >,
> jerry wass > 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
> >>>

<snip>
>
The strut is in tension and at an angle to the spar which puts a compression
load on the spar. Aerodynamic forces between the strut and the root tend to
lift the wing, which increases the compression on the bottom of the spar
between the strut and root (supported at both ends).The moment applied at
the strut from the outboard portion of the wing tends to put the top in
compression, the bottom in tension. The net result (tension or compression)
depends on the details of the geometry - how far out is the strut and what
kind of angle is it at.

In any case, I would want to put a doubler over the hole...

--
Geoff
The Sea Hawk at Wow Way d0t Com
remove spaces and make the obvious substitutions to reply by mail
When immigration is outlawed, only outlaws will immigrate.

[Rich S.[_1_]]

"Orval Fairbairn" > wrote in message
...

Am I missing something here? Is this a low wing or a high wing?

Rich "Mid Wing" S.

[J.Kahn]

Rich S. wrote:
> "Orval Fairbairn" > wrote in message
> ...
>
> Am I missing something here? Is this a low wing or a high wing?
>
> Rich "Mid Wing" S.
>
>
Well, I am assuming it's a high wing strut braced ultralight where the
tubular spar forms the leading edge, with the strut attachment at around
60% of span, or else a Kolb deal where the tubular spar is at the more
typical spar location.

Interestingly the DeHavilland Canada Twin Otter has its lift strut only
at about 1/3 span, so it could be said to be more of a "semi-cantilever"
wing. The loads on the root fittings are strongly downward and inward.

John

[Capt. Geoffrey Thorpe]

"Rich S." > wrote in message
...
> "Orval Fairbairn" > wrote in message
> ...
>
> Am I missing something here? Is this a low wing or a high wing?
>
> Rich "Mid Wing" S.

Well, there you go, I was assuming a high wing what with it being an
ultralight and all. But I could be wrong. Eh?

--
Geoff
The Sea Hawk at Wow Way d0t Com
remove spaces and make the obvious substitutions to reply by mail
When immigration is outlawed, only outlaws will immigrate.

[patrick mitchel]

"Rich S." > wrote in message
...
> "Orval Fairbairn" > wrote in message
> ...
>
> Am I missing something here? Is this a low wing or a high wing?
>
> Rich "Mid Wing" S.

high wing- pat

[Canalbuilder]

patrick mitchel wrote:
> "Rich S." > wrote in message
> ...
>> "Orval Fairbairn" > wrote in message
>> ...
>>
>> Am I missing something here? Is this a low wing or a high wing?
>>
>> Rich "Mid Wing" S.
>
> high wing- pat
>
>
In that case the strut will be in tension during flight, and compression
while the microlight is on the ground (unless it's very windy). Either
way, the best thing to do is consult the designer and do exactly what
they say.

Ed

[jerry wass]

Capt. Geoffrey Thorpe wrote:
> "Orval Fairbairn" > wrote in message
> ...
>
>>In article >,
>>jerry wass > 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
>>>>>
>
>
> <snip>
>
> The strut is in tension and at an angle to the spar which puts a compression
> load on the spar. Aerodynamic forces between the strut and the root tend to
> lift the wing, which increases the compression on the bottom of the spar
> between the strut and root (supported at both ends).The moment applied at
> the strut from the outboard portion of the wing tends to put the top in
> compression, the bottom in tension. The net result (tension or compression)
> depends on the details of the geometry - how far out is the strut and what
> kind of angle is it at.
>
> In any case, I would want to put a doubler over the hole...

You're SO RIGHT --I forgot to tack on the overhanging portion of the
wing---Jetty
>
> --
> Geoff
> The Sea Hawk at Wow Way d0t Com
> remove spaces and make the obvious substitutions to reply by mail
> When immigration is outlawed, only outlaws will immigrate.
>
>