From: "James R. Osborn" <flyrotary@lancaironline.net>
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Subject: Re: 20B with RD-1C Prop Options
In-Reply-To: <D7F4FE45-E8BB-4953-8FB6-A5CBD10B37D8@gmail.com>
Date: Wed, 18 Nov 2015 18:05:25 -0800
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References: <D7F4FE45-E8BB-4953-8FB6-A5CBD10B37D8@gmail.com>
To: Rotary motors in aircraft <flyrotary@lancaironline.net>

So I finally got a dynamic pressure test done on this 20B.  Here is what =
I got:

Front: 105-125-105
Center: 105-101-87
Rear: 130-125-120

This is in PSI and was done with all spark plugs out except the rotor =
being tested.  That one got one spark plug and the compression fitting =
with pressure transducer attached in the other.  I used the RD-1C =
installed, but not engaged - I bolted up the flex plate without the =
adapter and bolted up the RD-1C with a starter to be able to crank it =
over.  So the redrive was not slowing things down when I cranked it =
over.  Then I recorded the pressure wave on a laptop and looked at three =
bumps in a row.  I did this a few times for each rotor with a pause in =
between and took the highest readings of any three successive peaks to =
estimate the health of the three faces on each rotor.

My understanding is that higher numbers are better and the same numbers =
across all faces in the motor is better.  I am unclear what an =
unacceptable low number might be.  The actual values you get are =
dependent on a number of factors including how fast you are cranking =
(how well charged your battery is, how beefy the cables are, what kind =
of porting, other losses like the PSRU if it were engaged, etc.) and if =
the motor is broken in or not.  I don=E2=80=99t know if this motor was =
broken in, or if any seals were replaced.  It looks clean inside and =
there is evidence of porting, but I don=E2=80=99t know exactly what =
(this is a side port configuration motor).

When I lost a side seal on my 13B REW in my RX-7, I got something like =
118-120-50 on the rotor that had the problem.  So that was clearly not =
good.  When I rebuilt that motor that time, I had the plates ground as =
they were beyond the wear limit and I used all new side and corner seals =
and springs.  After that rebuild, I got uniformly 120 to 130 on all =
faces which I think is very good.

So, what do you guys think of my 20B numbers?  Is that low face on the =
Center rotor bad enough to warrant tearing the motor completely apart?  =
If I decide to do that, I might very well go PP.  Though Bobby at least =
thinks that is a bad idea due to noise and tuning difficulties with the =
PP.  Or I could just live with it with these numbers, go side port, and =
break it in and start checking this periodically to see if there is any =
improvement or further deterioration.

Thoughts or opinions?

=E2=80=94 James

> On Oct 29, 2015, at 1:22 PM, James R. Osborn <rxcited@gmail.com> =
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