|
I think there are a few things that need
clarification.
The lower RPM runs were not WOT! I just recorded
those on the way up to WOT, all at the same prop pitch. Meaning the only
significant data point is at 6000RPM, which I consider about static. For that
reason, the power level at those lower RPM are more reflecting the prop power
demand than anything else.
As to the RPM difference, It may have been 100 or
150 RPM higher on the long runner than on the short one(tach reading a bit
iffy). There is some thing else I ran into. All previous tests I ran with the
prop showed some intermittent prop noise, seemingly influenced by the wind
condition at testing time. This noise is very stady with the long runner. It is
acoustically so strong you think it is going to blow your brains out. I could
barely stand it until the fuel flow meter stabilized.
I have observed that phenomenon with the same type
or prop on the SOOB at static runups. It seems that the increased power produced
with the long runner is consumed by a sudden drag increase in the prop. This
prop may just not be suitable for that kind of tests.
I will do further tests with different prop
pitch, where the noise issue is one thing I want to find out
more.
I may have to look for another prop.
The MP is measured at the same location in both
cases, about 1" from the rotor housing. The pressure is picked up through a .035
hole. I guess I should have said "MP" and not "MAP", sorry for
that.
Generally I am not very inclined to do a lot more
basic performance tests since the engine is already producing way more power
than my test bed needs for flying.
But that may change as I get further down the road.
Richard Sohn
N2071U
----- Original Message -----
Sent: Wednesday, November 05, 2008 9:09
AM
Subject: [FlyRotary] Re: single rotor
performance
Sounds good Richard. But what about RPM delta at full throttle
between the two different runner lengths? That is the acid test for HP
increase (with a prop load). You are in the best possible position to
test different runner lengths with that single runner manifold. I give a
lot to see a performance curve plot of different runner lengths in increments
of 1" between 8 and 24".
I'm surprised you saw a significant difference in
MP. Where did you have the tap? If it is in the runner I suspect
you may be seeing velocity effects. I know you are aware of the
importance of dynamic and static pressure in this situation so I was wondering
how you arrived at the total pressure.
Also surprised that the long
runner did not cause any idle problems when using a carb. With the
evaporative cooling in the runner, they sometimes freeze up and condensation
of the mixture happens which can cause rough idle. The 2000 rpm idle
helps there I guess.
Tracy
On Wed, Nov 5, 2008 at 9:40 AM, Richard Sohn <res12@fairpoint.net>
wrote:
Another step in the right
direction.
In deciding which way to go with the intake for
the single rotor, I ran two tests. The first one with a short 8" long intake
runner, and a second one with a 24" runner.
The results are certainly not surprising,
however, I had to check the possible impact on idle characteristic.
Except for a different idle mixture setting, I
was not able to detect a difference in idle characteristics at 2000RPM.
There is no need for lower idle with a 3.33 : 1 gear ratio. If for any
reason I want to go lower with idle, I would have to increase the fly wheel
inertia. With no load on the engine it idles down to 1300RPM with the 8"
runner.
The long runner also resulted in a 1" higher
MAP over the short runner.
The 24" runner as shown in the picture will in
the final configuration be at least 3" longer, because the carb has to com
lower than it is now.
The engine config is 12A rotor and housing
using 1 1/2" p-port.
The HP calculation is based on a bsfc of .5 .
This is probably conservative with EGT at 1700F and mixture ratio at 14.6
.
Richard
Sohn
N2071U
--
Homepage:
http://www.flyrotary.com/
Archive and UnSub: http://mail.lancaironline.net:81/lists/flyrotary/List.html
No virus found in this incoming message.
Checked by AVG -
http://www.avg.com
Version: 8.0.175 / Virus Database: 270.8.6/1769 -
Release Date: 11/5/2008 7:17 AM
|