You had your belt wrap around the prop? How is this possible, or did
I misunderstand what you said?
The belt should not be able to enter the swept area of the prop under
any cir***stances. Was there a lot of vibration in your craft? There
shouldn't be. Balance all your props again, and keep them balanced so
there is no vibration. It's not only quieter and more pleasant to
ride that way, but your parts will last longer. A heavily vibrating
belt can cause hundreds of pounds of vibrating force on your hull.
It sounds like you have a vibration which causes a harmonic motion in
your belts. The absolutely simplest solution to that is to not run at
2800 rpm at all. Keep it at 2900 or 2700. You can hear the
difference, if your craft starts to hum or vibrate at any engine RPM
then change it so that hum doesn't happen.
A better solution is to add a touch bar in your belt run path. This
is just a piece of wire that the belt hits, which causes the belt to
stop shaking. You can use a screwdriver to find the place to mount
the touch bar. Don't put it at a place which will be harmonically
interesting. For example, if you put it exactly between the two
pulleys defining that segment of belt, then the vibration could simply
double in frequency the way harmonics in a guitar work. The same
thing can be said for 1/3 or 1/4 of the length. Find a spot, probably
just off of 1/2 the distance, and that will probably be best for all
RPMs. It's still a good idea to avoid resonant frequencies of your
parts, but this helps minimize the damage.
I would avoid drilling into your hull from the top. I was thinking
about just using fiberglass, actually. Rough up the current surface
of your hull, get all the weakly bonded crud off it like paint or
foam. Then make a thick paste of epoxy and some sort of structural
filler and plant your duct back in place, then glass it down using the
paste that squishes out to make a fillet under the glass. That's
probably a bit heavy duty, but as you discovered it kind of sucks to
have to walk back home.
Snow is worse than water for belt slippage. The snow gets into the
bottom pulley and then melts as it gets compressed. If you're going
to operate in the winter, you need something to cover your belt. What
you had sounds perfect, you don't want it to tear things up if it
fails. You'll also experience icing all over your hull, including the
prop.
I do hover in the winter, but you have to plan for a lot more things.
Check out http://www.hoverclub.net/ColdHovering.pdf
or Google on
ColdHovering.pdf and read through that. It's my thoughts on winter
hovering safety, along with suggestions from a few dozen more people
on several continents. I read it again every year even though I wrote
it, believe it or not. It's been stable for quite a while now. It's
a PDF (Adobe Acrobat) file which has clickable cross-referenced links
in it.
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