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Charlie, The 250 hp prop was a Prince P tip 70 inch dia with a
90 inch pitch. My renesis P port is supposed to produce the 250 HP.
To be honest, Bull droppings!! I then bought a whirlwind ground adjustable
expecting a huge improvement. Nope, did not happen, in fact I think it was
worse. That prop has a max HP of 200 and with the setting at the usual
man. specs ( I cannot recall) I did get close to 7500 rpm, so with
calculations on the back of an envelope, it would appear that the P ported
renesis is developing somewhere around the 210 HP max. at 1000 feet above
sea level. Now in hindsight I believe that the Prince prop is equal to
better (marginally) than the Ground adjustable and significantly cheaper.
My aim of 8000 rpm is solely for take off HP, and then
will be extremely happy with 5500 to 6000 for cruise, or less. No never
did get the engine onto a dyno due to difficulties in attaching quickly, so what
hp I have is it, and basically guess work. Still working on a second
engine to replace the existing one. I have improved the cooling drag
second time around, and narrowed the frontal area quite a lot. Part of
this was to get Jeff Doddridge to alter his mounting plate to make the
mounts equidistant from the prop centreline. The only other alteration I
think should be done is to move the starter over to the RH side of the motor to
get it away from that hot exhaust. It never ends. Neil.
Sent: Saturday, September 19, 2015 1:15 AM
Subject: [FlyRotary] Re: New psru
I understand about debugging what you've got, before
going off in a new direction. That's why I hated to bring it up now.
:-)
The prop doesn't know how fast the engine is turning; it just knows
how fast *it* is turning, and how fast it's moving through the air. I think that
the problems start when the prop carver gets out of his comfort zone, which is
2700 design rpm and around 72" maximum diameter (usually less). When diameter
goes up to 74"-76" and design rpm starts to drop, they seem to get a bit
confused. For those of us who never expect to exceed 7500 rpm, with cruise
down around 5500-6000, a 3.12 ratio would mean prop at 2400 rpm max, and around
1900 at cruise. Nothing wrong with that if we could swing a 7 foot diameter
prop, but with small, short legged a/c, you just can't do it.
I couldn't
find anything in my old emails about the prop you had problems with. What were
its specs & mfgr? Was the 6000 rpm static, or full throttle in flight at low
altitude? Did you ever get your engine on a dyno? I know what Lamar claimed for
his p-port Renesis, but if those were 'corrected' dyno numbers, they are pretty
useless for real world flying at higher than sea level and anything above
'standard day' temperatures (which almost never happens). 250 HP seems pretty
optimistic for a normally aspirated 2 rotor actually flying in an a/c, but I
hope you can get it working. I've been very tempted to find another Renesis core
& send the housings out to get them p-ported, & if you're successful,
you just might push me over the edge...
Charlie
On
9/17/2015 11:17 PM, Neil Unger wrote:
Charlie, As usual anything is possible. The 2.85 ratio is
easier to alter the gear set , but by the time the “little” mods are done the
cost climbs yet again. May look at the possibility as all the drawings
are done and alterations are now much simpler. Will get the bugs out of
this one first. Most prop makers that I went to just do not want to hear
“rotary”. The revs are there but the torque is not compared to a
lyc. Much to learn in this area. Regards, neil.
Sent: Friday, September 18, 2015 12:44 AM
Subject: [FlyRotary] Re: New psru
Hi Neil,
Congrats on your progress; it looks nice. I like the idea of being
able to source some of the parts locally, given that international shipping
can cost more than a lot of parts.
The damper issue is a real bummer. IIRC, Tracy's been running a later
version of his 2.85 directly coupled to an aluminum racing flywheel. One or
two others have used light weight steel flywheels, but I think they were still
using Tracy's damper mechanism, which doesn't look too complicated to build
with precision machine tools that you obviously have access to.
I know you'll hate to hear this question, but....are there provisions to
use the 2.85 ratio in your design? The reason I ask is that many of us have no
desire to turn the engine beyond 7500 rpm, and that wide ratio means cruise
rpm at the prop of well below 2000 rpm. Most of us are flying planes that
can't swing the 7-8 foot diameter prop needed to maintain efficiency at those
low prop rpms. It also complicates getting a prop made that will perform
correctly, since it's outside the area where most prop makers have worked.
It's confused some reputable prop makers here in the USA, even with the 2.85
ratio.
Again, congrats on the new design,
Charlie
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