From: "James R. Osborn" <flyrotary@lancaironline.net>
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Subject: 20B with RD-1C Prop Options
Message-Id: <D7F4FE45-E8BB-4953-8FB6-A5CBD10B37D8@gmail.com>
Date: Thu, 29 Oct 2015 13:22:47 -0700
To: Rotary motors in aircraft <flyrotary@lancaironline.net>
Mime-Version: 1.0 (Mac OS X Mail 8.2 \(2104\))

Hi guys,

So I am going to be building an RV-10.  I sourced Bobby=E2=80=99s spare =
20B / RD-1C combo and my plan is to work on the motor first, kind of =
bass-ackward but that is what I am doing.  My plan is to build a =
motor/mount test stand and work everything out on the ground before I =
ever put it in an airframe.  I plan to set it up NA using the existing =
side port configuration.  I don=E2=80=99t know if it is ported - I am =
going to attempt to determine this by inspection without cracking it =
open and doing a dynamic compression test to evaluate the health of the =
motor.  If it is necessary to entirely rebuild the motor, I would =
probably go PP.  So I am thinking the target HP as it is would be in the =
275 HP range and probably 325 HP if it ends up being a PP.  How do these =
numbers sound to you all?

I will be looking for a way to dyno it, hopefully borrow one to get some =
data.  But I was also thinking about just getting an appropriate fixed =
pitch prop and working through the bugs based on static run ups.  I like =
the idea of a three blade prop.  I like the idea of optimizing for =
cruise at 75%, say 5800 rpm which would put full throttle at 7733 rpm on =
the 20B.  At 5800 rpm, the prop would be spinning 2035 rpm and at full =
throttle 2713 rpm (using the 2.85 ratio RD-1C PSRU).  Do all these =
numbers sound about right?

If so, then how do I choose a prop that will result in 2713 rpm static =
run up at full throttle, but be tuned for efficiency at 2035 rpm cruise? =
 I am assuming at these reasonable RPMs that it will be a larger swing =
and the three blade makes sense - what do you think?  Is there a =
convenient way to find props out there that will work at the target full =
throttle HP of 275 or 325?  Also if you guys have any good resources to =
learn about how to figure these things out (books, web pages, online =
calculators, etc.) that would be great!

Another option might be to go with something like the IVOPROP Magnum, =
either ground adjustable or electric inflight adjustable.  What do you =
guys think of these?  Would the adjustability really help me adapt to =
however my power plant turns out?  Would the extra complexity be worth =
it?  For the ground adjustable one, I am thinking the process would be:  =
1. select the =E2=80=9Ccorrect=E2=80=9D swing (how?) and go for three =
blades, 2) use ground adjustability and work up to THE pitch while I =
tune the motor until I achieve full throttle static run up around 7700 =
RPM.  Will this result in a reasonably efficient setting for 75% cruise? =
 Am I thinking about this clearly?  All opinions are welcome.

There=E2=80=99s a lot for you to chew on!

=E2=80=94 James