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I agree with your assessment, Bill
I started out with a 67x72 prop and 2.14:1 gear box. I later switched
to the 2.85 and a 74x88 prop and the takeoff performance was
tremendously improved – not that the 2.14 was bad, it wasn’t. But,
the 2.85 made a good thing so much better in my opinion. I even got
a couple of MPH more on the top end. My experience with the rotary is that
rpm = power produced, my take off rpm rose from around 5200-5500 rpm with the
old set up to 6000-6100 with the new prop. I am uncertain about the 3.12 ratio,
but the 2.85 was a definite improvement as far as I was concerned.
Ed
Sent: Friday, September 18, 2015 12:09 AM
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.
Sent: Thursday, September 17, 2015 10:54 PM
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
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
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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