Its not so much how hard it is to break the rod when its in good
condition. It's plenty strong. Its knowing when the strength has
been compromised with cracking after a few dork landings or an
unfortunate vertical arrival. They become very easy to break once
they have a crack starting to develop.
Each pilot is going to have to decide the issue for himself. For me,
if they're not at least 1/4" in diameter I'd rather use steel. The
nose weight is not a consideration. I won't use a center wing rod of
carbon in any case.
Rick
At 12:09 PM 4/25/2008, [EMAIL PROTECTED] wrote:
I've seen this topic for years and so decided to see what it would
take to break a 1/8" carbon rod with my hands which have
considerably higher bending capability than a stab on one side of a vertical.
Try it for yourself, try to use your hands to break a 1/8" carbon
rod, just past half way along its length.
It will be interesting to hear your findings bout how easy or hard
it is...and why it might be possible for a stab to put that kind of
force on the rod, with out it breaking first.
Note I didn't say it was hard, I'm asking you interested parties and
suggesters to 'do' something then report.
Gordy
In a message dated 4/25/2008 9:55:54 A.M. Eastern Daylight Time,
[EMAIL PROTECTED] writes:
That may be overkill, if the 1/8 was almost strong enough. Assuming that
the wall is pretty thick, 1/4" would be 8X as strong and 16X as stiff,
if I'm not mistaken. I wonder if the problem is that the rod is not very
strong crosswise, so if there's a hint of a sharp edge, maybe it will
crunch. A steel tube might be a good compromise, though the yield
strength, unless you go pretty high tech, will be maybe half or less
that of music wire. Presumably the diameter would make up for that,
given the right wall thickness, etc. (I'm assuming you'd use a little
piece of 4130 or something from Aircraft Spruce)
I wonder if one glued short lengths of brass tubing over the carbon at
the appropriate places if that wouldn't help keep local loads from
messing it up. Especially if you ground the edges to a taper. Or maybe
that's just too much trouble.
The 1/4" carbon might weigh 7 grams or so if it was 4" long.. A 1/8"
steel rod would weigh about the same for the same length. The carbon
would be much stiffer, of course. And if you loaded it carefully, with
only smooth edges, a heck of a lot stronger. However, assuming a 24"
stab with 100 square inches or so, the 1/8" joiner on the tail would
stand up to an airspeed comparable to that of a 1/2" steel rod of the
same yield strength on the wing. However, music wire tends to have a
really high yield strength. (plus or minus a lot depending on design
details)
> : <[EMAIL PROTECTED]> wrote: Ray, I have used 1/8 cf rod
> for stab axles, and had them break. This was on my Yardbird design,
> 130". I went back to steel rather than try to go to a bigger tube. My
> latest will use 1/4 cf tube for stab axles. Jack
> --
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