From: "James R. Osborn" <flyrotary@lancaironline.net>
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Subject: Re: [FlyRotary] 20B with RD-1C Prop Options
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Date: Fri, 30 Oct 2015 08:12:29 -0700
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To: Rotary motors in aircraft <flyrotary@lancaironline.net>

Hi Bill,

Yeah after I sent that I realized slip was a much smaller difference.  =
The difference between top speed and standing still is 100% slip!

I don=E2=80=99t really know what to expect for HP.  I threw those =
numbers out there for feedback.  So what numbers say for unported site =
port, medium street port side port, and peripheral port on a 20B can we =
reasonably achieve?

Thanks for more input and numbers.  It will be interesting to try to =
work it out on the ground and the more I think about it, adjustability =
will be a real big help.  I did recall correctly that a friend has an =
old dyno I can borrow.  So I guess I will move in that direction first =
and set the prop selection aside for now.

My plan is to buy an in progress RV-10, hopefully way past 50%.  I =
really don=E2=80=99t want to start from scratch; we have only one =
lifetime - 22000 days as the song goes (maybe more like 28000 days now =
days :).

=E2=80=94 James

P.S.  Thanks to you Charlie too and for the invite.  Alas I am pretty =
far West in the SF Bay area.  Someday I hope to make it to some of the =
rotary gatherings back East and South.

> On Oct 29, 2015, at 9:33 PM, Bill Bradburry =
<flyrotary@lancaironline.net> wrote:
>=20
> James,
> There could be some slip involved, but it is mostly the change in =
angle of
> attack as the prop disc is moved forward thru the air.
>=20
> If you can stand the expense, I recommend you get some kind of in =
flight
> adjustable prop.  The rotary power output is really affected by rpm =
and
> being able to adjust it in flight is very helpful.=20
> I also recommend you set a max take off rpm target of 2500 prop and =
7125
> engine.  There are several good reasons for this not the least of =
which is
> that the EC-2/3 has a cutoff at 7500 rpm. (Tracy can straighten me out =
here
> if needed)
> If you dyno the engine be sure and let us know what you get.  I don't =
think
> you will be anywhere near those HP numbers you quote.  Also when you =
get up
> to altitude and cut the rpm back to 48-5200, you will really be =
reducing the
> output.  If you leave the engine at 7125 rpm and climb to 8000 ft, you =
will
> be producing 75%, if you then reduce the rpm to 4800, I don't know =
what your
> percent power might be...but a heck of a lot lower than 75%.
>=20
> Do you plan to try and buy a completed airframe?  It sometimes takes a
> surprising length of time to build one.  Ask me how I know.  :>)
>=20
> Bill =20
>=20
> -----Original Message-----
> From: Rotary motors in aircraft [mailto:flyrotary@lancaironline.net]=20=

> Sent: Thursday, October 29, 2015 9:20 PM
> To: Rotary motors in aircraft
> Subject: [FlyRotary] Re: 20B with RD-1C Prop Options
>=20
> Thanks for the input Tracy!  So is the difference between top speed =
rpm and
> static rpm the "slip"?
>=20
>> 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's 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't
> 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
> "correct" 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's a lot for you to chew on!
>>>=20
>>> - James
>>>=20
>>>=20
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>>=20
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>=20
>=20
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>=20
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