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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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