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,
If it is inside the cowl, drag is insignificant.You forgot to consider
the "UGLY FACTOR".Maybe you could put fins on it and tell everyone
it is a torpedo.;-)Personally, I don't want an 8' pipe hanging on
the belly of my a/c.As I recall, the perfect exhaust system is 105"
in length. But I don't see anyone flying with that type of system either.
IMHO, the best muffler is a turbo.
Mark
Agreed on the turbo.
It looks better on flat bottom RV's.:)
Paul Lamar
It is also easy to say as you have a 48" wide cowl :)
Paul Lamar
Yes, I had my reasons for choosing the Lancair ES kit.A 4' wide firewall
was one of them.
Mark
It's around 24 inches on a RV4 as I recall.
Paul Lamar
Paul,
The stock RV-4 cowl has bulges on both sides.Seems those could be
put to some good use.Maybe an RX-7 oil cooler would fit in one side
and the intake plenum in the other.
Mark
Both Mike and Brian shaved them off since the engine is only 12 inches
wide not
counting the plugs. Makes a slick looking cowl.
Paul Lamar
Brian,
On Mazda cars the Racing Beat straight-through muffler works
well.If you used it in conjunction with and external muffler.... a
wrapped perforated augmenter tube it probably would be the quietest compromise.
My dad used augmenter tubes on a Grumman Wigeon engine conversion.
Many parts were taken from a Cessna 310. Barry Bordes
Paul,
I had an idea of how I might be able to salvage my tangential muffer.
First I cut off the down pipe so that I could gain access to the innards.
Then I took a hammer and punch and opened up the each of the perforations
by 3 - 4 times the original size (see picture). There are 8 rows of
approx. 15 perforations per row. So I enlarged approx. 120 perforations.
Finally, I welded the down pipe back in place. I took it to the airport
and installed it and did a test run. It is much, much quieter than
the DNA muffler I have been running. So much so that I didn't even
need to close the cabin door or use the Zulu ANR headset while
running it. Unfortunately, it is set up for different style EGT
probes than what I was running on the DNA setup, so I'll have to
wait for the new probes to arrive to see how this mod affects the
EGTs. Power seems better than before, so that's a good sign.
Mark
One other thing to do on an experimental exhaust that I can envision is to put
a three or four bolt flange on the outlet to be able to remove the down pipe
for inspection without having to cut and then weld up again. Flanges for
headers would work and the gaskets are readily available. Safety wire
required. Minor weight penalty for big saving in inspection difficulty. Once
the design has been well proven, the flanges could be left off further builds.
Dale Davies
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