This week I flew my RV-4/13BREW from Everett Wa. to Medford Ore. and
back.
Headwinds on the way down were brisk- 30 kts at 8500 feet on the way down,
but 35 kt
tailwind on the way back. The engine ran flawlessly but the plane is slow-
true
airspeed was 110 kts at 19.5 manifold pressure,5600 rpm oil temp 161 and
coolant 170,
fuel flow around 8 gpm. My prop is a three blade Catto, 72 dia x 88 pitch.
For one, the plane is over propped. I'm going to have Craig Catto 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, I don't have any pictures of your intake air scoop. What does it
look like?
Paul Lamar
Brian, Sounds like the air isn't getting to the engine. Providing the
throttle plate isn't really undersized it must be seeing a low pressure at
the inlet. If the exhaust augmenter is lowering the cowl pressure and the
intake is not sealed to an outside air source that could lower MP. I would
expect ram air to boost MP above atmospheric at the 8500 ft density
altitude. It might be interesting to know what MP is at a lower altitude
and how MP correlates with the altimeter in the panel. Did you have any MP
problems when you did your static ground tests and I assume the static RPM
was lower than the 5600 of this flight.
( (5600/2.85) X 88/12) X60/5280 is about 147MPH at 90% efficiency.
Could be the design speed of the prop is off somewhat and the diameter a
couple inches to large. Borrowing a prop to test with might be an option
before cutting into the one you have.
george grimes
Should be able to achieve 19.5in at 11,500'.. About 22.5in at 8500'. If you can get
these numbers you're probably about right for intake system (in another thread Brian
said he was at 11,500' - just going for clarification).
Matt-
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