These are encouraging numbers for those of us planning on higher RPM
engines.
By the way, do you happen to have the part numbers for the 5-pin
Switchcraft connectors you bought? I'm about to finish off the trim/elevator
and wanted to get the wiring done before closing the surface. Did you use
grommets/protection as the wire passed through the ribs?
Rob
R786
On 10/21/2008 8:40 PM, rshannon@cruzcom.com wrote to rebel-builders:
-> Oops! That got sent in the middle of editing, before it was fully baked.
-> I've tweaked the version below a little more, though I'm not sure it really
-> adds much to my 1st edition gibberish.
->
->
-> On Tue, Oct 21, 2008 at 9:36 PM, Ron Shannon
<rshannon@cruzcom.com> wrote:
->
-> > I'll probably put my foot in something here but (here goes) this doesn't
-> > surprise me.
-> >
-> > With the std. Bing carb, other things being equal the Jabiru 3300
develops
-> > max HP at around 2800 RPM +/-. As all props "unload" with increased
airspeed
-> > and, if the props being compared are more or less appropriate for the
-> > engine, the more finely pitched prop will be more unloaded at a high
cruise
-> > speed than will a coarse prop. To put it another way, the more coarse
cruise
-> > prop will still be pulling at higher airspeed AND slower RPM, because it's
-> > more loaded AND the latter (2800 RPM) also yields greater HP to cope
with
-> > that load. (Notice the difference in WOT: the cruise prop WOT was 300
RPM
-> > less than the climb prop means it was more fully loaded even at slower
RPM,
-> > when at cruise+ airspeed.) Another way to say it is at cruise+
airspeeds, a
-> > finer pitched prop's thrust-per-RPM will max out at a lower speed.
-> >
-> > Of course, the airspeed vs. RPM vs. prop pitch is not a linear set of
-> > tradeoffs, with each one pivoting around the others in perfect
correlation,
-> > in large part because drag increases with the square of airspeed, but
also
-> > because of the sweet spot where max HP occurs.
-> >
-> > In short, the cruise prop developed more thrust at 2800 RPM (max 120
HP)
-> > than the climb prop developed at 3300 RPM (l~100 HP). Of course, as
we all
-> > know, different results occur in the lower speed ranges and different
loads,
-> > i.e., climb.
-> >
-> > That makes sense to me... I think.
-> >
-> >
-> >
-> > On Tue, Oct 21, 2008 at 8:29 PM, Walter Klatt
<Walter.Klatt@shaw.ca>wrote:
-> >
-> >> Ron, why would the coarser prop at 2900 rpm do 130 mph while the
finer one
-> >> do only 125 mph at 3200 rpm? That engine should be producing more
hp at
-> >> the
-> >> higher rpm, which should translate into more speed, not less. With my
-> >> Rebel,
-> >> I have always got more speed out of it if I could pitch my prop for
-> >> maximum
-> >> rpm at WOT.
-> >>
-> >> Walter
-> >>
-> >> -----Original Message-----
-> >> From: mike.davis@dcsol.com [mailto:mike.davis@dcsol.com] On Behalf
Of Ron
-> >> Shannon
-> >> Sent: October 21, 2008 7:19 PM
-> >> To: rebel-builders@dcsol.com
-> >> Subject: Re: [rebel-builders] Jabiru engines
-> >>
-> >> Alright thrill seekers... although the hubbub has settled down of late
-> >> [Yea!] I can't resist passing on this contribution to The Great Jabiru
-> >> Debate [Ed.: See message archives, this subject line. Thou shalt not
-> >> repeat.
-> >> <g>]
-> >>
-> >> Some months ago I made my first contact with a real Jabiru 3300-
powered
-> >> Rebel in the wild. Dan Dyet has one of the earlier mechanical valve lifter
-> >> models on 730R. He reported at first he had problems with cooling,
which
-> >> he
-> >> acknowledged have been addressed in newer models. (He apparently
did not
-> >> use
-> >> a Jabiru nose bowl.) However, he included the following performance
data:
-> >>
-> >> ---
---
-> >>
-> >> I am using the std Bing carb without the economy tuning kit. Haven't
had
-> >> any
-> >> issues with it at all, good carb.
-> >> Engine runs great and starts like a charm (with preheat during winter).
-> >> ...
-> >> I have one of the original models,mechanical lifters.
-> >> I started out with the GT wood prop then switched over to a Sensenich
-> >> ground
-> >> adjustable carbon fiber.
-> >> GT prop at 64" dia and 51" pitch is too coarse for the Rebel airframe.
-> >> GT prop on climb out at 70 mph gave me 2700 rpm 700 fpm solo, cruise
2750
-> >> rpm at 120 mph, WOT 2900 rpm 130 mph.
-> >> Sensenich prop 64" at a pitch setting of 2.5 gave me 2900 rpm at
70mph
-> >> 1000
-> >> fpm solo climb out, cruise 2750 rpm at 110 mph, WOT 3200 rpm 125
mph. With
-> >> this prop I use up less than 200 ft of runway before I'm in the air and
-> >> flying.
-> >>
-> >> ---[end quote]---
-> >>
-> >> He didn't mention the takeoff gross he was carrying for these results,
but
-> >> IMHO, with either of those props, the numbers are not too shabby for
120
-> >> HP.
-> >>
-> >> The newer hydraulic lifter models have redesigned cylinder cooling fins,
-> >> redesigned baffle ducts, better oil pump, better carb tuning, they
specify
-> >> a
-> >> more efficient Positech cooler and reportedly have a bit more
demonstrated
-> >> HP than the early models. The total width of the 3300 is barely 24"
which,
-> >> with a properly fitted nose bowl/cowl, makes for a pretty small drag
-> >> profile
-> >> up front.
-> >>
-> >>
-> >> Ron
-> >> 254R
-> >> http://n254mr.com
-> >>
-> >>
-> >>
-> >>
-> >> -----------------------------------------------------------------
-> >> List archives located at: https://mail.dcsol.com/login
-> >> username "rebel" password "builder"
-> >> Unsubscribe: rebel-builders-unsubscribe@dcsol.com
-> >> List administrator: mike.davis@dcsol.com
-> >> -----------------------------------------------------------------
-> >>
-> >>
-> >>
-> >>
-> >>
-> >>
-> >> -----------------------------------------------------------------
-> >> List archives located at: https://mail.dcsol.com/login
-> >> username "rebel" password "builder"
-> >> Unsubscribe: rebel-builders-unsubscribe@dcsol.com
-> >> List administrator: mike.davis@dcsol.com
-> >> -----------------------------------------------------------------
-> >>
-> >>
-> >>
-> >>
-> >
->
-----------------------------------------------------------------
List archives located at: https://mail.dcsol.com/login
username "rebel" password "builder"
Unsubscribe: rebel-builders-unsubscribe@dcsol.com
List administrator: mike.davis@dcsol.com
-----------------------------------------------------------------
