flyrotary@lancaironline.net Mailing List Archive

Hi Neil,

Congrats on your progress; it looks nice. I like the idea of being able to source some of the parts locally, given that international shipping can cost more than a lot of parts.

The damper issue is a real bummer. IIRC, Tracy's been running a later version of his 2.85 directly coupled to an aluminum racing flywheel. One or two others have used light weight steel flywheels, but I think they were still using Tracy's damper mechanism, which doesn't look too complicated to build with precision machine tools that you obviously have access to.

I know you'll hate to hear this question, but....are there provisions to use the 2.85 ratio in your design? The reason I ask is that many of us have no desire to turn the engine beyond 7500 rpm, and that wide ratio means cruise rpm at the prop of well below 2000 rpm. Most of us are flying planes that can't swing the 7-8 foot diameter prop needed to maintain efficiency at those low prop rpms. It also complicates getting a prop made that will perform correctly, since it's outside the area where most prop makers have worked. It's confused some reputable prop makers here in the USA, even with the 2.85 ratio.

Again, congrats on the new design,

Charlie

On Wed, Sep 16, 2015 at 11:28 PM, Neil Unger <flyrotary@lancaironline.net> wrote:

Gents,

              Finally the first PSRU with a reduction of 3.12 to 1. Pictured is the basic box which is heavily based on Tracy’s PSRU but with the larger reduction and 2 oil lubricated thrust   bearings on the prop shaft instead of a single sealed roller bearing in Tracy’s. This psru will mount directly in place of Tracy's 2.85 reduction PSRU with no modification.

    Now to put to test to see if the practice matches the theory. Already found one fault. The “O” ring seal that seals the main body of the PSRU to the base that attaches to the mounting plate is outside all the attachment bolts, which means that the oil can wick down the bolts and make a lovely mess of your pride and joy. Now looking for more faults as this is easily fixed. Unlike Tracy's , this PSRU is totally sealed with O rings to ease dismantling with no clean up of whatever gasket sealer you have had to use.

    Now the terrible part and still undecided as I am yet to cost a damper on the drive. Sadly it also is not cheap and may yet cost near $500 for a ”bit of rubber”. Then comes a mounting plate as made by Geoff Doddridge which he sells for around $400 USD. There is no point in me trying to compete with Geoff as he does a magnificent job at a cheap price. Freight is always a horrible price so he makes the plate and there is no freight from Aust to be added.

    The total cost in Aust dollars (including Geoff’s plate) will be around the $5000 which equates to $3500 USD. Then freight of possibly $200. Currently looking at further reduction in price if you source the gear set locally saving on freight both ways to Aust and back. I will have to alter the way it is constructed so that all the mods can be done by you the builder. Still looking!

    So far the progress. Neil.

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