Bill,
The attached plots show the results of
climb tests made with the muffler intact when the 68x68 prop was installed at
BBB in Minnesota. Airspeed data was collected continuously but just isn’t
on the upper plot. The painful story of why this was done is in the
archives. The gross weight for these tests is about 200 lb less than the
gross weight when leaving Texas. On the return flight, we were at 10,500
ft to clear the hills between Scottsbluff, NE and home which is Laramie, WY.
I have had the plane to 17500 ft and it was still climbing
but I didn’t want to get over 18000 ft so stopped climbing at that
altitude. Performance has been quite similar despite changes in intake
plenum and runner configuration and cooling exit area. Lynn has given
some reasons why there may be optimum throttle positions other than wide
open. In my case, with fuel injection , long runners, and the injectors
close to the intake ports, I don’t know how much effect the things he
lists would have. I’ve had the throttle body-plenum- runner
assembly on a flow bench and could not see evidence of turbulent flow in the
plenum. The effect of removing the intact muffler and flying with just a
short downturn at the cowling exit has also been minimal (except for the noise).
The data was collected by a data logging
system that I made that records 17 channels of air and engine information every
three seconds.
I also wondered about the effect of density
altitude on the performance of the engine compared to the prop and whether I
was developing sufficient power for flight. Prior to my first flight, I
asked well respected RV resource Bob Breshear at the Land of Enchantment fly-in
in Las Cruces about this. He just smiled, pointed to the sky, and said “Props
are made to work up there”.
I’m still not sure about all the
implications of what he said, but I didn’t question him further.
Steve
-----Original Message-----
From: Rotary motors in aircraft
[mailto:flyrotary@lancaironline.net] On
Behalf Of Bill Bradburry
Sent: Tuesday, June 16, 2009 7:52
AM
To: Rotary motors in aircraft
Subject: [FlyRotary] Re: Not
developing full power.
Steve,
What results has your repaired muffler given
you?
It strikes me that you should be able to get over 6K
static (and take off) RPM with the 2.17 drive. That shouldn’t
change much with altitude I think. You will have less air for the engine
to breathe, but it will be easier for the prop to turn in the thinner
air. You were getting about 5K on your take off and climb from
Texas. Your climb rate was only about 400 fpm also. You lifted off
at close to 1K feet at 6 minutes and reached close to 4K feet at 14
minutes. Lets say 3200 ft in 8 minutes. At higher altitudes I
don’t know if you could climb.?? Do you think all this was caused
by the muffler?
Your prop rpm was right in there with your indicated
airspeed. Both were about 148-149 mph at cruise.
If you still have throttle left after the engine
maxes out, I think that indicates a problem of some kind. I
encourage you to try and discover what causes it. One reason is that I am
having the same situation! :>) My static is around 5400 rpm max
and there is still throttle left. I am still working on my cooling, so I
can not run the engine. But I don’t think I am developing enough
power to try to fly.
Where did you get the data?
Bill B