clever ideas for a lightweight strut attach

[Stan]

This should get some of your winter doldrum brain juices flowing...

Anybody have any good ideas for a lightweight but strong way to get
around the lower spar caps on an aluminum strut braced wing?

Assume a 1.5" wide t-cap. The heavy way is to add two strut attach
straps and two 3/4" spacers with thru-bolts.

Ideally it would be best to rivet (vs bolt) the attachment to keep the
stress distributed to all of the elements rather than causing the bolts
to be put into bending (from the elements being disconnected).

Without going to a relatively complex machining (or machined spacer) do
you all have any ideas for transferring this load into the web and caps
without a lot of weight?

Thanks.

Stan

[jls]

Stan wrote:
> This should get some of your winter doldrum brain juices flowing...
>
> Anybody have any good ideas for a lightweight but strong way to get
> around the lower spar caps on an aluminum strut braced wing?
>
> Assume a 1.5" wide t-cap. The heavy way is to add two strut attach
> straps and two 3/4" spacers with thru-bolts.
>
> Ideally it would be best to rivet (vs bolt) the attachment to keep the
> stress distributed to all of the elements rather than causing the bolts
> to be put into bending (from the elements being disconnected).
>
> Without going to a relatively complex machining (or machined spacer) do
> you all have any ideas for transferring this load into the web and caps
> without a lot of weight?
>
> Thanks.
>

What's wrong with the way Cub and Super Cub do it? (and everybody
else)--- two mild steel flanged straps with spacers. Or you can go
4130. The fittings are channels attached with bolts through the shear
web of the spar.

The struts attach with the strut-attach fittings in double shear.
Lightweight, simple, bulletproof. Also unchanged since the 50's
because nothing is better. Brand new Super Cubs still have these
fittings.

[[email protected]]

Dear Stan,

I don't mean to be picky but your question is based on a host of
assumptions -- the use of T-capped spar vs a C-channel, the aluminum
itself, and so on. Having created that particular box the odds are
overwhelming that existing solutions, such as two strut-attach straps
installed upon the shear-web with spacers & thru-bolts will prove to be
the most practical solution. Of course, then I have to define
'practical' :-) But given the venue in which you've broached the
question a fair definition would seem to be 'practical' in the sense of
a relatively inexperienced metalsmith fabricating a single copy of the
design in a home-shop type of environment.

Your chosen box also implies certain factors of cost and
serial-production that might be considerably different for a home-built
airplane.

For solutions outside your particular box you will probably have to
alter the box itself, such as considering a C-channel spar, or perhaps
one fabricated with stock L-type extrusions for the caps. The Zenith
CH-701 offers nice example of the latter in a design optimized for
one-off production in a home-shop environment. In that case, the
strut-attach fitting is little more than another, single, piece of
extrusion attached upon a doubler on the forward face (ie, the
unflanged side) of the shear web.

I'm sure that isn't the answer you were hoping to hear :-) Please
don't read it as a condemnation of your chosen design (ie, T-shaped
extrusions, etc).

-R.S.Hoover

[Stan]

Yes, I purposely boxed in the problem. Knowing the tendencies of this
group to easily venture outside the box (cliche intended) I didn't want
this thread going wild. Sheez, pretty soon someone would have said,
"that's not the way Zoooom would have done it...".

I was leaning towards a simple spacer but was looking for a little
lighter solution that doesn't put the bolts in so much bending.
Preferably a solution made from aluminum that can be riveted to the
spar.

The 701 is built crazy light. I'm amazed it actually can take the
loads though it only has a 1100# gross and is so slow that the gust
loads are minimal so that may be part of it. That and it's use of
..016 skins with huge skin panels that are purposely allowed to buckle.
The plane looks like crap, flies like crap (until you take the slats
off and add VGs), and drops like a brick made from really dense crap,
but I guess it handles the load and is light.

There- that should get some Zenith fans in a fury and spice up this
thread in typical RAH style :)

Stan

Oh, and for more spice.... I hear the 701 flies really reliably with a
120hp VW if you use Hot VW sourced drag racing-parts in the engine
(especially "heavy duty" racing heads, everyone knows those babies are
bulletproof and much better than stock)...

Hee hee, just playin' with you Bob- thanks for your contribution to
this thread and to the group.

Now all we have to do is have Urban jump in his with his ego so that we
can really get things going....

++++++++++++++++++++++++++++++++++++++++++++++++++ ++++++++
wrote:
> Dear Stan,
>
> I don't mean to be picky but your question is based on a host of
> assumptions -- the use of T-capped spar vs a C-channel, the aluminum
> itself, and so on. Having created that particular box the odds are
> overwhelming that existing solutions, such as two strut-attach straps
> installed upon the shear-web with spacers & thru-bolts will prove to be
> the most practical solution. Of course, then I have to define
> 'practical' :-) But given the venue in which you've broached the
> question a fair definition would seem to be 'practical' in the sense of
> a relatively inexperienced metalsmith fabricating a single copy of the
> design in a home-shop type of environment.
>
> Your chosen box also implies certain factors of cost and
> serial-production that might be considerably different for a home-built
> airplane.
>
> For solutions outside your particular box you will probably have to
> alter the box itself, such as considering a C-channel spar, or perhaps
> one fabricated with stock L-type extrusions for the caps. The Zenith
> CH-701 offers nice example of the latter in a design optimized for
> one-off production in a home-shop environment. In that case, the
> strut-attach fitting is little more than another, single, piece of
> extrusion attached upon a doubler on the forward face (ie, the
> unflanged side) of the shear web.
>
> I'm sure that isn't the answer you were hoping to hear :-) Please
> don't read it as a condemnation of your chosen design (ie, T-shaped
> extrusions, etc).
>
> -R.S.Hoover

[Stan]

Yes, I purposely boxed in the problem. Knowing the tendencies of this
group to easily venture outside the box (cliche intended) I didn't want

this thread going wild. Sheez, pretty soon someone would have said,
"that's not the way Zoooom would have done it...". :)

I was leaning towards a simple spacer but was looking for a little
lighter solution that doesn't put the bolts in so much bending.
Preferably a solution made from aluminum that can be riveted to the
spar.


The 701 is built crazy light. I'm amazed it actually can take the
loads though it only has a 1100# gross and is so slow that the gust
loads are minimal so that may be part of it. That and it's use of
..016 skins with huge skin panels that are purposely allowed to buckle.

Stan



Now all we have to do is have Urban jump in his with his ego so that we

can really get things going....


++++++++++++++++++++++++++++++++++++++++++++++++++ ++++++++




wrote:
> Dear Stan,
>
> I don't mean to be picky but your question is based on a host of
> assumptions -- the use of T-capped spar vs a C-channel, the aluminum
> itself, and so on. Having created that particular box the odds are
> overwhelming that existing solutions, such as two strut-attach straps
> installed upon the shear-web with spacers & thru-bolts will prove to be
> the most practical solution. Of course, then I have to define
> 'practical' :-) But given the venue in which you've broached the
> question a fair definition would seem to be 'practical' in the sense of
> a relatively inexperienced metalsmith fabricating a single copy of the
> design in a home-shop type of environment.
>
> Your chosen box also implies certain factors of cost and
> serial-production that might be considerably different for a home-built
> airplane.
>
> For solutions outside your particular box you will probably have to
> alter the box itself, such as considering a C-channel spar, or perhaps
> one fabricated with stock L-type extrusions for the caps. The Zenith
> CH-701 offers nice example of the latter in a design optimized for
> one-off production in a home-shop environment. In that case, the
> strut-attach fitting is little more than another, single, piece of
> extrusion attached upon a doubler on the forward face (ie, the
> unflanged side) of the shear web.
>
> I'm sure that isn't the answer you were hoping to hear :-) Please
> don't read it as a condemnation of your chosen design (ie, T-shaped
> extrusions, etc).
>
> -R.S.Hoover

[Stan]

Yes, I purposely boxed in the problem. Knowing the tendencies of this
group to easily venture outside the box (cliche intended) I didn't want


this thread going wild. Sheez, pretty soon someone would have said,
"that's not the way Zoooom would have done it...". :)


I was leaning towards a simple spacer but was looking for a little
lighter solution that doesn't put the bolts in so much bending.
Preferably a solution made from aluminum that can be riveted to the
spar.


The 701 is built crazy light. I'm amazed it actually can take the
loads though it only has a 1100# gross and is so slow that the gust
loads are minimal so that may be part of it. That and it's use of
..016 skins with huge skin panels that are purposely allowed to buckle.


Stan


wrote:
> Dear Stan,
>
> I don't mean to be picky but your question is based on a host of
> assumptions -- the use of T-capped spar vs a C-channel, the aluminum
> itself, and so on. Having created that particular box the odds are
> overwhelming that existing solutions, such as two strut-attach straps
> installed upon the shear-web with spacers & thru-bolts will prove to be
> the most practical solution. Of course, then I have to define
> 'practical' :-) But given the venue in which you've broached the
> question a fair definition would seem to be 'practical' in the sense of
> a relatively inexperienced metalsmith fabricating a single copy of the
> design in a home-shop type of environment.
>
> Your chosen box also implies certain factors of cost and
> serial-production that might be considerably different for a home-built
> airplane.
>
> For solutions outside your particular box you will probably have to
> alter the box itself, such as considering a C-channel spar, or perhaps
> one fabricated with stock L-type extrusions for the caps. The Zenith
> CH-701 offers nice example of the latter in a design optimized for
> one-off production in a home-shop environment. In that case, the
> strut-attach fitting is little more than another, single, piece of
> extrusion attached upon a doubler on the forward face (ie, the
> unflanged side) of the shear web.
>
> I'm sure that isn't the answer you were hoping to hear :-) Please
> don't read it as a condemnation of your chosen design (ie, T-shaped
> extrusions, etc).
>
> -R.S.Hoover

[Larry]

Stan: I can send you photos of my Boelkow Jr 208C (certified A/C) . You
might be able to use the way the struts are attached. Also look up
MFI-9 ( very similar a/c).

Larry
Stan wrote:
> Yes, I purposely boxed in the problem. Knowing the tendencies of this
> group to easily venture outside the box (cliche intended) I didn't want
>
>
> this thread going wild. Sheez, pretty soon someone would have said,
> "that's not the way Zoooom would have done it...". :)
>
>
> I was leaning towards a simple spacer but was looking for a little
> lighter solution that doesn't put the bolts in so much bending.
> Preferably a solution made from aluminum that can be riveted to the
> spar.
>
>
> The 701 is built crazy light. I'm amazed it actually can take the
> loads though it only has a 1100# gross and is so slow that the gust
> loads are minimal so that may be part of it. That and it's use of
> .016 skins with huge skin panels that are purposely allowed to buckle.
>
>
> Stan
>
>
> wrote:
> > Dear Stan,
> >
> > I don't mean to be picky but your question is based on a host of
> > assumptions -- the use of T-capped spar vs a C-channel, the aluminum
> > itself, and so on. Having created that particular box the odds are
> > overwhelming that existing solutions, such as two strut-attach straps
> > installed upon the shear-web with spacers & thru-bolts will prove to be
> > the most practical solution. Of course, then I have to define
> > 'practical' :-) But given the venue in which you've broached the
> > question a fair definition would seem to be 'practical' in the sense of
> > a relatively inexperienced metalsmith fabricating a single copy of the
> > design in a home-shop type of environment.
> >
> > Your chosen box also implies certain factors of cost and
> > serial-production that might be considerably different for a home-built
> > airplane.
> >
> > For solutions outside your particular box you will probably have to
> > alter the box itself, such as considering a C-channel spar, or perhaps
> > one fabricated with stock L-type extrusions for the caps. The Zenith
> > CH-701 offers nice example of the latter in a design optimized for
> > one-off production in a home-shop environment. In that case, the
> > strut-attach fitting is little more than another, single, piece of
> > extrusion attached upon a doubler on the forward face (ie, the
> > unflanged side) of the shear web.
> >
> > I'm sure that isn't the answer you were hoping to hear :-) Please
> > don't read it as a condemnation of your chosen design (ie, T-shaped
> > extrusions, etc).
> >
> > -R.S.Hoover