Yes the belt wound right up in the prop. On the 13p the prop mounts
directly onto the upper drive pulley. With the belt off it is right there
in the blades. I don't think it is a problem of harmonics. I have been
running many miles in the 2650 to 2900 range. Early on I had lift fan
vibration but rebalancing took nearly all vibration out. I wonder if
running the thrust belt in a different groove on the engine would help? I
have it in the bottom grove so if it comes off it is free of the engine.
I
could move it into the upper groove so the lift belt would hold it on the
engine pulley. Does anyone have experience or recommendation on this.
"Ken Roberts" <forums@[EMAIL PROTECTED]
> wrote in message
news:4fae462e-23f1-4f41-92f7-9fa28d624fb4@[EMAIL PROTECTED]
> 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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