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What PSRU Can we Really Trust???

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Tom Kay

Well-Known Member
Joined
Aug 10, 2007
Messages
409
Location
Canada
Hi;

Well, I've been meaning to ask this for a while. I find it frustrating that a very critical part of many homebuilts is also perhaps the least understood, regulated, or reliable. OK, if re-drive manufacture were truly regulated by a governing body, then costs would be even more through the roof than they are right now for a gear box or a belt drive. But, this has begged the question, at least in my mind, "What manufacturer of PSRU's can be trusted?"

Those who might want to build a fighter replica have some choices, but for engines, the V6 and V8 power plants seem to be likely candidates, based on the shape of the engines. It seems wrong to stick an opposed 4 onto a scale Spitfire or Mustang, and even though I'm sure the Isaac's Spitfire is a wonderful piece of work, I just don't like the look of it. After all, it is supposed to be a replica fighter.

So if we use a V-engine, who's re-drive do we trust? The makers of gear boxes seem to come and go rather quickly. Those who are still making these things may not be real experts about that enemy, torsional vibration (even if they claim that Hyvo chains or belts damp out torsional vibrations because they have a slack side).

Vesta's Jason Day uses Hyvo chains, and states that vibrations fed back through the system to the engine are damped. If you talk to Jack Kane of EPI (the only guy who REALLY seems to make an effort to address the issue of a variety of vibration modes), he'll tell you that this assumption is wrong and potentially dangerous. Having said that, others may know if EPI's products, notably its Mark 9 gear box has ever suffered failures. (I really don't know).

Dan Hawken of Alberta designed his re-drive for the Titan-51 with a 3" Goodyear Hawk Kevlar belt and cogged pulleys. Titan has offered the Suzuki V6 2.7 litre as an alternative to the Rotax 912 for a few years now, and seem to have had a good run with this setup. But, they've just experienced their first failure, a crankshaft that, upon 3rd party inspection, was found to be a victim of torsional vibration. And this was a forged crankshaft (the strongest type, is it not?).

Now Titan is adopting the New Zealand gearbox. This maker claims that some units in Australia have over 1000 hours of sevice on them. When I write to the company about costs, availability, and any failures that may have happened throughout their history, I don't get any reply. This bothers me a bit, and the information trail ends there. Maybe they're just jammed busy.

Can we all name a few of these PSRU makers that have come and gone in the last decade or so? Probably.

So here's the bottom line: if we want to use a V engine, from 150 to 400 HP, who's reduction drive would YOU use, and why?

For a guy who's not an ace at torsional vibration (and never will be) this is really a case of trust, hopefully built on some manufacturer's documented, reliable track record.

I'm thrilled about the idea of using auto engines, but very concerned about reliability.

Thanks, Tom.
 
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