Background: Now that I've been successfully flying this plane
for awhile, I decided to do a separate webpage containing some of the
construction details which have worked out nicely.
Design goals:
Keep it light. Keep it simple. Minimize or eliminate
epoxy. Attachment methods in order of preference: rubber bands,
tape, hot glue, foam safe CA.
Wing construction:
I won't repeat information already on the main
page. Since writing the main page, I've found that the hot
glue bond line holding the lower skin to the upper skin varies in
quality considerably. When puting on the lower skin it was
necessary to lay down 2 to 3 feet of hot glue before joining the
skin. Where the glue had cooled, the bond has come loos over
time. I've used forecepts to pull out the bad line of hot glue
and used fresh hot glue to re-attach the upper and lower skins.
Since this usually only invloves replacing glue in 6 inches or so at a
time, the glue is hot, and the bond is strong. If I had it to do
over fresh, I would start with a single line of glue along a central
rib, do each rib seperately, working out, and finish with small
sections of the skin perimeter. This would take a bit longer than
laying down all the glue at once, but every line of glue would be fully
hot.
|
| Interior of wing before bottom skin was added. |
Motor mount:
For maximum flexability in experimenting with different motors, I went
with a stick style motor mount. Just about every outrunner or can
style brushless motor out there can atach to a stick mount. Plus,
I already had several clamp style mounting brackets made up for
attaching outrunners to a stick. Currently, the stick is held on
with machine screws threaded into tapped threads in the uppe sheet of
laminate. If the threads ever strip, I can add nuts and washers,
but thus far, this arrangement has proven more than adequate.
These pictures also show my method for attaching the nose and tail
carbon tubes to the wing. The button head cap screws are threaded
into the arrow shaft inserts that formerly held the arrow tips.
The screws are a bit long, so when bottomed out in the insert the
screws leave enough of a gap that rubber bands fit nicely under the
screw head. The arrows are held laterally by two strips of balsa
hot glued to the wing on either side of the arrow shaft at the leading
and trailing edges of the wing. This gives an extremely secure
attachment that disassembles in seconds.
  |
| Motor mount area. |
Nose attachment:
The current nose is a chunk of packing foam with a thickness
approximately the same width as the space between the nose arrow
shafts. These pictures also show the forward attachment points
for the tail shafts. The nose foam is roughly cut to shape and is
held to the nose shafts with a couple pieces of tape and a rubber
band. The rear of the nose has a notch that fits over the leadign
edge of the wing. I regard the nose as completely disposable, and
I've hacked it and tweaked it to experiment with camera mounting.
The critical feature is that it is very cushy and the connection to the
wing is fairly soft. This does two things. First, the
camera is pretty well insulated from motor vibrations. Second,
the plane can lawn dart from a reasonable height (so far about 10 feet)
with zero damage to the wing.
  |
| Nose attachment. |
Tail details:
Like most things about this plane, I regard the tail as
experimental. It is pretty flimsy, so I expect it to get trashed
sooner or later. Currently though, it has twin rudders that
are connected with a wire between them and actuated by a servo which
directly grips that wire. This is a bit crude in that the wire
bends down when the servo actuates. Still, it is weight efficient
and simple. The hinge between the horizontal tail surface and the
elevator is a design I took from an Electrifly Flat-out Foamy I
built. I used parts left over from that kit in this tail. A
carbon tube is glued to the TE of the horizontal tail. Little
plastic brackets with C's on the front get glued into slots in the LE
of the elevator. These snap over the carbon tube and give a nice
hinge that stiffens the length of the elevator. Unfortunately,
the little C brackets are pretty delicate, and I'm running out of
replacements for the ones that break. I expect that eventually
this will become a simple tape hinge, if the whole tail doesn't get
replaced first.
  |
| Tail details. The elevator extensions didn't last past
the first test flight, and the elevator now ends at the rudders. |
Camera Mounting:
Most of the camera mounts I've seen around the web I feel to be way too
complicated and heavy for the function they perform. I tend to
push the envelope on seeing what I can get away with in the opposite
direction. Of course, when you push the envelope you tend to find
where the edge of the envelope is. That's my justification for
having two cameras fall from the sky thus far. :) The
camera mount shown below seems to be a nice balance between light
weight, security, and ease of removal. The camera is bolted to
the plywood base, and the base is rubber banded to the nose with two
rubber bands. This provides a very nice shock mounting for the
camera, is easily removable, and seems to be utterly secure. As
an added measure of security, a lanyard could be used to attach the
camera to one fo the nose tubes.
  |
| Camera mounting. |