flyrotary@lancaironline.net Mailing List Archive

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Rusty,

Your absolutely correct about the frequency and that you must keep that out of the operating range - however my concern is the large torque reversals that accompany that frequency.

As I see it there are two parts to this equation, so although I lean to the harder rather than softer damper it's because the large torque reversals may be still reversing while your trying to push them forward, the shorter you keep the reversal ( to a point) the less this conflict will occur - I believe I have discussed this before.

Now this doesn't mean I am looking at rock hard dampers, it just means I will look at different material such as Polyurethane the same stuff used in 4WD shackle rubbers and although you can get it in different densities the standard material is approx Shore 93.

Although I'm not sure my assessment is correct, I am still working toward this as my solution, I mention it only as a possible option.

George (down under)

I'm all for agreeing to disagree, as well you know, but I'm still looking at making the damper harder, rather than softer as in the 2 rotor.

Hi George,

The way I understand it, there's always a resonant frequency, and not just because we're talking about single rotors. Two and three rotors have them too. You can make the coupling loose/soft, to lower the frequency, or tight/hard to raise the frequency. Either will work just fine, as long as you get the frequency outside of your operating range.

Unless you can be SURE your resonant frequency is well outside your operating range, it's much safer to go with the lower frequency approach. Consider the amount of energy that's available at 2000 rpm vs 8000. At 2000, the drive rattles, and at 8000, the drive breaks. Didn't Everett Hatch break a number of drives this way?

Again, I'm not a mechanical engineer, so this may be totally wrong, but it's the way I "understand" it.   My fear of a harder damper is that it might look great up to the static rpm I can run on the ground, but then fail catastrophically when the prop is unloaded in flight. If I'm going to break something, I'd rather it be at idle :-)

A man of your means may wish to opt for the aluminium end housings,

When I can order a set of "in-stock" aluminum housings online, without having them custom made, I'll be real interested. The parts I have will work just fine for now.

Cheers,

Rusty

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