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| HI Bill,
I guess there is disagreement about what is attainable! I have no doubt PP is the way to go based on the recent rehash. I have decided however to let the motor decide. If it checks out as a healthy side port, I will probably leave it that way. It seems there are some side port intakes out there that others are willing to part with. If I had to start from scratch though, the ease of the PP intake would weigh in its favor certainly.
— James
James, a side port 20B with a good intake and exhaust can reasonably expect to see about 300 HP at 7000. Mistral's 3 rotor was right there. A peripheral port version quite a bit more. For an aircraft I suggest the p-port. There is almost no down side. My biggest reason is the intake is sooo much easier. They are more efficient in the range we use in aircraft anyway. Bill Jepson
On Oct 30, 2015 8:13 AM, "James R. Osborn" < flyrotary@lancaironline.net> wrote: 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’t 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’t want to start from scratch; we have only one lifetime - 22000 days as the song goes (maybe more like 28000 days now days :).
— 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:
>
> 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.
>
> 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.
> 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%.
>
> 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. :>)
>
> Bill
>
> -----Original Message-----
> From: Rotary motors in aircraft [mailto:flyrotary@lancaironline.net]
> Sent: Thursday, October 29, 2015 9:20 PM
> To: Rotary motors in aircraft
> Subject: [FlyRotary] Re: 20B with RD-1C Prop Options
>
> Thanks for the input Tracy! So is the difference between top speed rpm and
> static rpm the "slip"?
>
>> On Oct 29, 2015, at 6:32 PM, Tracy <flyrotary@lancaironline.net> wrote:
>>
>> 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.
>>
>> Will get those instruction manuals you asked about to you next time I'm in
> the office.
>>
>> Tracy
>>
>> Sent from my iPad
>>
>>> On Oct 29, 2015, at 16:22, James R. Osborn <flyrotary@lancaironline.net>
> wrote:
>>>
>>> Hi guys,
>>>
>>> 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?
>>>
>>> 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
> "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.
>>>
>>> There's a lot for you to chew on!
>>>
>>> - James
>>>
>>>
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