From: "James R. Osborn" <flyrotary@lancaironline.net>
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Subject: Re: [FlyRotary] 20B with RD-1C Prop Options
In-Reply-To: <list-8113788@logan.com>
Date: Thu, 29 Oct 2015 19:19:44 -0700
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References: <list-8113788@logan.com>
To: Rotary motors in aircraft <flyrotary@lancaironline.net>

Thanks for the input Tracy!  So is the difference between top speed rpm =
and static rpm the =E2=80=9Cslip=E2=80=9D?

> On Oct 29, 2015, at 6:32 PM, Tracy <flyrotary@lancaironline.net> =
wrote:
>=20
> Hi James,
>   HP targets sound doable, but those rpm numbers are probably off.  =
Remember that with a fixed pitch prop, hp varies as the CUBE of rpm.  =
Would recommend propping for a max power at top speed rpm of about 7000. =
 That will give you a static rpm of around 6000.
>=20
> Will get those instruction manuals you asked about to you next time =
I'm in the office.
>=20
> Tracy
>=20
> Sent from my iPad
>=20
>> On Oct 29, 2015, at 16:22, James R. Osborn =
<flyrotary@lancaironline.net> wrote:
>>=20
>> Hi guys,
>>=20
>> 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?
>>=20
>> 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?
>>=20
>> 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!
>>=20
>> 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.
>>=20
>> There=E2=80=99s a lot for you to chew on!
>>=20
>> =E2=80=94 James
>>=20
>>=20
>> --
>> Homepage:  http://www.flyrotary.com/
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>=20
> --
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