Neil,

The rotary certainly relies on rpm for its power.  That makes it difficult to make proper selections for ratios, props, etc.  I understand that Tracy’s EC-2 and EC-3 have a rev limiter set at 7500 rpm.  I don’t know that for a fact, since I have never hit that limit, but that would be a consideration if someone was using either of those controllers.  Also, while the Renesis is redlined at 8500, I don’t think that you would want to cruise at 8000 rpm.  This makes the rotary a prime candidate for an in flight controllable prop.  Currently the only constant speed prop available is the MT electric.  Perhaps you could add a prop controller to your PSRU?

 

Isn’t it amazing how when you build a mousetrap everybody comes out of the woodwork with ideas about how they think it could be better, or in some cases, different!   :>)

 

Bill

 

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From: Rotary motors in aircraft [mailto:flyrotary@lancaironline.net]
Sent: Thursday, September 17, 2015 11:10 PM
To: Rotary motors in aircraft
Subject: [FlyRotary] Re: New psru

 

Bill,   The ratio is either 2.85 or 3.12 depending what gear set you buy.  My experience is that the Lyco give good torque which is good low speed Hp.  the rotary however has little comparative torque and must compensate with RPM.  I bought a prop for 250 Hp and put it on my rotary with the 2.85 reduction and it killed the rotary.  Could only get a little over 6000 RPM.  The rotary real;ly only comes into its own above 7500 RPM, so I am planning on getting something near 8000 rpm for full HP.  It seems that the rotary must be under proped  or it will struggle to get the HP required.  I may be wrong, but that is my experience.

 

From: Bill Bradburry

Sent: Thursday, September 17, 2015 10:54 PM

To: Rotary motors in aircraft

Subject: [FlyRotary] Re: New psru

 

Neil,

 

This is great news for people wanting to install a rotary!

I don’t know what drives the selection of a gear ratio, but a better ratio would be closer to 2.5 to 1.  This would make the use of more standard props easier.  With this high a ratio, you will need to run the engine at high rpm, or the prop will have to turn at a slow speed requiring a high pitch on the blades.

 

Is the ratio selectable at all?

 

Bill

 

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From: Rotary motors in aircraft [mailto:flyrotary@lancaironline.net]
Sent: Wednesday, September 16, 2015 11:28 PM
To: Rotary motors in aircraft
Subject: [FlyRotary] New psru

 

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.