This week I flew my RV-4/13BREW from Everett Wa. to MedfordOre.
and back. Headwinds on the way down were brisk- 30 kts at 8500
feet onthe way down, but 35 kt tailwind on the way back. The
engine ran flawlessly but theplane is slow- true airspeed was
110 kts at 19.5 manifold pressure,5600 rpm oiltemp 161 and
coolant 170, fuel flow around 8 gpm.
My prop is a three blade Catto, 72 diax 88 pitch. For one, the
plane is over propped. I'm going to have CraigCatto cut it down
a little during the winter maintenance. The other thing is
that the cooling scoop is effective, but way too draggy, so I'm
going to re-do it this winter.
Another issue is my left brake line- I"ve melted it twice. It's
plastic, and although it is shielded from the exhaust pipes and
insulated with fiberfrax, I think that heated air from the
exhaust pipes is being forced out the opening in the cowl where
the brake line goes to the gear leg. That's where I have found
the line melted.
I want to put a reverse scoop near the exhaust
pipes to get the heated air out of the cowl, and to replace the
brake line with stainless steel. Everything inside the cowl
except for the brake line looks OK- I wrapped and shielded
everything - wires, coolant, fuel,and oil lines. There are
three NACA ducts bringing air into the cowl to cool the
alternator, the coils and exhaust pipes, and an exhaust eductor
to suck air through the cowl and over the muffler.
Comments?
Brian Trubee
Couple of questions.
EGT?
Size of throttle body?
Is the engine ported?
The manifold pressure is very low.
Is the air filter plugged? :)
Are you getting cold air?
8 GPH is 50 pounds per hour at 6.25 pounds per gallon. At a BSFC of .47
leaned that
is only 106 HP. At a fuel burn of .5 that is only 100 HP. If it is really
rich and
the BSFC is .55 and that is only 90 HP.
You need a p-port Brian :)
Paul Lamar
Brian,
As some of you know my Wheeler will be a blend of certified parts and
experimental parts. I noticed the issues with the nylon brake lines long
ago. I went to NAPA and bought (8) 12" standard brake lines that go on
trucks from the hard line to the wheels. I also bought a 25 foot roll of
3/32 brake tubing, 24 double flare fittings, and a double flare tool. Total
for all of this was $170.00. After I got back to my plane, within 2 hours I
had the brake lines made up from the master cylinders to the wheels. Galv
steel line inside the cockpit, 12 inch flex at the master cylinders, at the
turn into the wings (mine are removable) one more at the flex point of the
gear leg, and the last one at the wheel. I don't anticipate melting my
brake lines. This is the way my Viking was done, and I had no issues with
my 1968 Viking until I blew the Continental up.
My fuel and oil system will be similar. The materials are inexpensive, and
the labor is minimal. Cheap insurance.
Kevin Alderman
brian,
This is the blind leading the blind as I have yet to depart
the earth, but tied to a tree I get MP of 22 at 5000 rpm and from memory 24
at 5600 rpm. Where are you reading it from? Neil.
It's been a while since I did any static runs on the ground. I"d just be
guessing at
this point to give some numbers for static running.
Brian Trubee
Brian,
You stated "...my EGT temps- they show up to 2000 at times- and above
1800 most of the time in cruise." I too experienced very high EGT's
in excess of 1800* when I was using a muffler that was too
restrictive. Also, power was way down, but it was quiet. ;-) The
high temps ended up damaging the o-rings and I had to rebuild the
engine. Since replacing the muffler the egt's have dropped down to
1600 - 1650* range and power is much improved. I suggest you examine
and modify or replace your current muffler.
Mark
The best muffler for a rotary is 3 to 8 feet long about 4 to 5
inches in diameter. That gives the lowest aero drag for a given
silencing. Lowest frontal area. Mufflers work by the exhaust
gases rubbing on the metal surface losing kinetic energy to skin
friction and losing heat to the metal surfaces. The cooler the
gases in a pipe the lower the gas speed. When high speed gas
exits a pipe there is a sudden expansion that causes the noise.
The idea here is to cool the gases before they get to the end of
the inner pipe.
The inner tube is best done in .045 Inconnel but there is a
trade off with thickness. If you make the inner tube 2 inches
in diameter and use 321 SS make it .065 thick with a bunch of
holes drilled in it. The outer tube can be .030" thick 321 SS
as it will always run cooler. Also make the front of the
muffler look like this.
Don't drill any holes for the first 8 to 10 inches. The slip
stream will blow cooling air down between the coaxial tubes. At
the back end make the inner tube 6 inches shorter than the outer
tube. That will act as an ejector to draw cooling air between
the two tubes. Patent applied for:)
A 2 inch diameter SS tube .065 thick 72 inches long will weigh
about 8.8 pounds.
A 4 inch diameter SS tube .030 thick 72 inches long will weigh
about 7.50 pounds.
Here is a dwg.
A 2.5 inch inner tube and a 5 and 1/2 inch outer tube may give a little less
back pressure for a weight trade off.
Paul Lamar
Paul,
In this co-axial design, do you propose that the inner tube remain fully open or
could anything be gained by slightly crimping (fish tailing) the inner tube
outlet end to tweak the back pressure and encourage more exhaust gas energy to
exit via the drilled holes?
Thanks,
Jack
At the expense of back pressure. Any fish tail should be a constant area.
Also the rotary is excellent at destroying fish tails so they need to be beefed
up.
You will also get a bit more aero drag with a constant area fish tail.
Paul Lamar
Paul,
I wasn't advocating any extreme fishtailing, only wondering whether a (very)
mild crimping (elongating) of the exit end on the internal tube might increase
exhaust gas back pressure a little bit and thereby encourage additional energy
to exit through the drilled holes. The (very minor) crimping wouldn't reduce the
inner tube's cross section area but might alter the flow a little bit and cause
some component of gas volume to escape out the side holes.
Your photos of Ed Anderson's experiments certainly demonstrate the potential for
problems.
Thanks,
Jack
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