Hi all Just thought I'd pipe in with my results on my rv7 renises. I'm currently running a prince p tip prop at 68" and it has proven to work extremely well with take of rpm around the 6400 rpm, I've compared it to a 72" whirlwind ground adjustable and the prince was superior in all ways on my install, I find if I could get more rpm and increase my torque it would even be better with my prop, as we need revs to get torque out of our machines I found that I had slightly less take off ability at 3000 ft agl strip and still get better top end with the p tip than the whirlwind. I max out at 175 k tas at strait and level at 8000 ft, hope this helps. Spinning just 7400 rpm.
Cheers Christian
Sent from my iPad
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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