>Fellow DF'rs,
>I am getting ready to hot-wire the wing and canard cores, but am not
>sure a) which lay-up schedule to use for the carbon fiber and therefore
>b) how deep to make the shearweb/spar cutouts in the various templates.
>Any one out there that has been through this help me?
>Thanks.
>Paul-
>
Paul;
I purchased my plans last fall and they include the "beefed-up" canard
lay-up schedule along with a letter from Viking explaining the reason for
the change. They say that although there haven't been any canard failures
attributed directly to overloading yet, it's only a matter of time, given
all the extra goodies that people are throwing into their planes (bigger
engines, more instruments, etc). Even if the original builder intends to
load the plane as per plans, there's no guarantee that subsequent owners
won't weigh it down with extras, so it's better to factor that in now.
As for the depth of the shear web/spar cut-outs, I wondered the same thing a
while back and asked a similar question on the dragonlist. The consensus
seemed to be that the spar cap notch is deep enough already and therefore
does not have to be modified to accommodate the extra carbon. Below is a
copy of the communications on this topic.
Joe
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I'm resuming my calculations on the spar cap notch allowances that will
accommodate the revised lay-up schedule, since the plans still show the
original contours for the templates. I'm doing this in an attempt to avoid
"steps" on the wing/canard surfaces due to the extra layers that have been
added to beef up the structure. To figure it out, without actually doing an
expensive 5-layer carbon sample-lay-up and measuring the thickness, I was
wondering if I could get some feedback from builders.
Those of you who have built the wing and canard with the original carbon
lay-up schedule: did you find the spar cap notches to be the right depth?
(too deep? too shallow?)
Joe
Hmmm. I say that you are probably okay with the original notch size. My
reason is that it seems that everyone needs to fill with a fair amount of
micro in that area (including me ;-)). 5 layers of carbon is still pretty
damn thin, and if I had not already built my wing/canard I'd definitely be
doing the new layup - without changing the cutout.
I'd recommend doing a small (5" x 5") layup of carbon to get a feel for how
thin this stuff is - I was amazed.
Kevin
I haven't done my canard yet, but on the tail, I had to use filler to fill
in the trough that was not-quite-filled by the carbon fiber. However, I'm
not sure I would recommend decreasing the depth of the notch, because it's
MUCH easier to fill a depression later than to discover you've got a hill
and you can't do anything about it!
Dave Morris
I wasn't considering decreasing the notch depth. I've been trying to
determine the amount by which to INCREASE it to account for an extra layer.
By the sounds of it, it seems that there's probably more ERROR in the depth
of the notch (attributed to things like the accuracy of the template
reproduction, speed of hot-wire cut, etc.) that the actual thickness of one
layer of cloth. If I could leave the notch the same depth as the original
x-sections show, as Kevin has suggested, it would simplify things
tremendously. Based on what Kevin has said, and taking error into account,
do you believe there's much chance of getting a "hill" if the notch remains
the same depth and the extra layer is added?
- Joe -
I understand your point, and I agree that the induced errors could easily
outweigh the thickness of a layer of carbon. The question then to ask the
builders would be:
How many of you found you had NOT enough trough and ended up with a hill,
VERSUS
How many of you had to fill later because the plans-specified trough was
TOO DEEP?
Dave Morris
Dave,
When I built my cannard I had more than enough room for the graphite in the
cap using the plans template. I hot wired the cores as opposed to the
computer cut cores. Lay a steel cork backed ruler upside down on the core
over the notch before cutting the leading edge off and you can tell how much
room you will have in the notch. The top notch will proably be plenty deep
enough because of the airfoil shape. The bottom is more flat and may be a
little closer but a little bit of sandpaper will take care of any
discrepency. Try to offset the cross ties of the carbon strip as that will
be
the major source of the height buildup. carefull attentoin to the temp of
the
hot wire and speed of travel is critical to how deep the burndown will be,
make sure to allow the center to catch up with the ends before making the
turns at the notch. Hope this helps. I am still trying to get the alternator
and fuel injection on Dragonfly N211DF then will about be ready for FAA
inspection.
Bob Johnson
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