Subject: [FlyRotary]
Re: : Percent Power, Throttle position, & RD-1C performance
Took closer note of throttle
position on todays flight. At 2000 ft the throttle was only about 1/3
open (position of throttle quadrant, but it closely mirrors butterfly position)
at economy cruise setting which was 6.0 GPH. This is about 42%
power, 82 HP according to the EM2 which is fairly close but not perfectly
calibrated yet. The same power setting with the -B drive would bave been
a bit further open.
Thanks for checking this out. My plane
is a bit heavier, but I have 3 rotors, so I’ll set the butterfly spring
to default at about 35% open. But now the bigger issue is:
I did a quick check of MAP at 1000
ft at full throttle and found I was not getting any drop at 150 MPH and had
.5" boost at 220 MPH (ram air recovery I assume). I did not get
around to checking it in slow climb which would more accurately compare to what
you would see on a dyno.
Tracy
What RPM do those speeds correspond to? I
looked again at my plot of MAP vs RPM and wonder if something is amiss –
maybe I can get some insight on this. If you go to http://members.cox.net/alg3/Dynamometer%20test%20report.htm, at the bottom of the page, you’ll see the plot. About 2”
HG drop at 5000 PRM, almost 4” at 6000. The inlet plenum and TB can be
seen on the attached photo.
I really don’t think that my air
intake plenum could be causing this drop as the flow area is larger than the TB
flow area, with smooth transition into the barrels. My TB barrels themselves are
5” long, 44mm dia. The butterfly is near the inside end, and the MAP sensing
port is just downstream from, and directly in line with, the butterfly shaft. Could
there be a significant drop in the barrels? If the measured drop is ‘real’,
then a) I’m surprised that I could get such good power, and b)
eliminating the drop would significantly increase the power.
Tracy, what is the configuration of your TB, and where are you measuring
MAP – at the TB before any runner length?
Al
Thanks,
Tracy. I
was hoping there would be someone out there flying with the same TB diameters.
Like
most things, TB diameter is a tradeoff. My conclusion from the dyno data
is that 44mm per rotor (1 ¾) is a bit small as the MAP is dropping off over
5000 RPM. But if you want to idle at 1500, and have a decent transition
from there to 3000; 1 ¾ is good. For a 2.85 to redrive, I’d want to
increase that flow area by 30% or so – to about 2” dia for each
rotor.
My
data may not be representative because of restricted flow to the TB. The
‘airbox’ size is restricted by the cowl, and may have restricted
the flow a bit. In hindsight, it would have been smart (and easy) to make
a run with the airbox off and see what difference it made.
Al