SECTION 11:
ENGINE AND PROPELLER INSTALLATION
RV AIRCRAFT
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sect 11r8 06/24/11
operation where engine cooling is marginal because of limited ram air flow through the engine compartment,
and because fuel flow volume is low. With a high air temperature and low fuel flow, the fuel has more time to
heat up and possibly vaporize before entering the carb or fuel injector. This situation is further complicated
by the use of auto fuel which normally has a lower vaporization temperature than Avgas. One product often
used for thermal protection of fuel lines is Aeroquip Firesleeve, which, as the name implies, is a hose-like
cover installed over the fuel line and clamped at both ends. As the name also implies, this material is
designed to protect the fuel lines (or oil and hydraulic lines) from the direct flames of an engine compartment
fire. Assembled fuel and oil lines are available from Vans in lengths suitable for most RV installations.
NOTE:
Automotive type hose and hose fittings are not acceptable for use in aircraft engine or fuel line
installations. Never use the type of fittings that require the hose (without flared nut end fittings) to slip over a
male fitting and be secured with a hose clamp. Even for low pressure or suction lines, ‘‘tube fitting’’ hose
assemblies should be used, not hose fittings (clamps). NEVER use an aluminum, copper or other rigid fuel
line to connect the fuel system from the fuselage to the engine. It is almost certain to fail, with serious
consequences. This applies to fuel pressure lines and oil pressure lines also. When fabricating fuel line
assemblies, check for line blockage after installing the end fittings. Sometimes the tip of the inner fitting can
gouge out bits of the soft rubber from the inside of the hose, and these can flip up like a butterfly valve and
block the line.
OIL PRESSURE GAUGE LINE
A braided Aeroquip hose similar to fuel lines, is recommended between the oil port on the engine and the
fuselage. 1/4” diameter or smaller is adequate because it is just a pressure line with no volume flow
requirement. Generally a bulkhead fitting is used in the firewall, with an aluminum or copper line running
back to the oil pressure gauge in the panel. Use of an electrical oil pressure sensor would eliminate the need
for these lines and routing.
A restrictor fitting should be used in the engine oil port to limit oil loss in the event of line failure. If not readily
available, a restrictor fitting can be made by taking a standard AN fitting, tapping the inside of the pipe thread
port for a bolt thread, screwing the bolt in tight, cutting it off flush with the end of the fitting, and then drilling
the smallest possible hole through the plug. Welding could also be used to form the plug.
Sensors should not be mounted directly on the engine case or rigid mountings, like pipe nipples, mounted to
the case. The vibration will eventually cause the fitting to break, letting the engine pump pressurized oil
overboard. The sensor is mounted on the firewall and connected to the engine with a flexible hose.
FUEL PRESSURE GAUGE LINE
This should be a hose tapped into the fuel line somewhere between the fuel pump and the carb, and should
be routed to a bulkhead fitting on the firewall, and then to the fuel pressure gauge. If an electric gauge is
used, the sensor may be mounted on the firewall and connected to the fitting with a flexible line.
A Tee fitting on the ‘‘out’’ port of the fuel pump is a good source for the fuel pressure line. A restrictor fitting,
like that described for the oil pressure line, should be used at the source end of the fuel pressure line.
MANIFOLD PRESSURE LINE
A good source for this is the primer port of the left rear cylinder (#4). The line may be 1/8” copper tubing with
compression fittings and a “vibration loop”. Route it through a fitting on the firewall similar to other lines.
Even though there is no flow through the manifold pressure line, a restrictor with a small orifice is still a good
idea. Sonic waves can cause fuel vapors to move through the line and condense in the instrument. Also, the
rapidly varying pressure caused by the valves opening and closing can cause the gauge to flutter wildly and
become unreadable.
PRIMER SYSTEM
The Lycoming 0-320 and 0-360 carbureted engines can be primed for cold starting by cycling the accelerator
pump with the throttle (O-235 engines do not have an accelerator pump). This can be effective for
temperatures down to freezing or slightly below, but will depend on the idle mixture adjustment and jetting of
the specific carb. If starting is routinely required at sub-freezing temperatures, installation of a conventional
hand operated primer system will probably be necessary. Priming three cylinders will be sufficient (one
cylinder’s primer port has probably been used for a manifold pressure source).
Plunger type primers, as used on many light aircraft, work well, but require a separate system. On
carbureted engines, you may also prime the cylinders using pressure supplied by the boost pump. Primer
lines are routed from a port on the gascolator to the cylinders and flow is controlled by a small solenoid-
controlled valve installed between the gascolator and the cylinders. When the pump is on, the lines are
pressurized, the solenoid is activated by a momentary switch in the cockpit and fuel flows to the cylinders.
The only known disadvantage is that the primer system is dependent on the battery for operation. If the
battery were dead, the engine could not be primed manually.
RV
AIRCRAFT
SECTION 11:
ENGINE AND PROPELLER INSTALLATION
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sect 11r8 06/24/11
INDUCTION AIR INTAKE
Most RVs are fitted with the filtered airboxes available in Van’s Accessories Catalog. Different airboxes are
necessary for different sizes of engines and types of induction devices, so be sure you order and install the
airbox appropriate to your airplane.
All of the optional air intake systems are designed to offer a minimum frontal area and flow resistance to the
incoming air. The intake systems also provide excellent manifold pressure from the ram air effect with little
complexity or weight.
FUEL BOOST PUMP
Because of the low (below carb level) location of the wing fuel tanks, an RV must be equipped with a fuel
boost pump as back up for the engine driven pump. Usually the boost pump is a small electric pump, an
example of which (p/n ES 40108 in Van’s Accessories Catalog) is shown in the fuselage plans. Other pumps
and installation locations may be used. However, some pumps are not self-priming and must be located at or
below tank level. Check the pump manufacture’s specifications about this.
When using a fuel injection system or a pressure carb, a high-pressure boost pump and a high-pressure
engine driven pump (quite different than those used on carbureted engines) are required. These pumps are
also available from Van’s.
ENGINE BAFFLING
Section 12 includes a basic explanation of cooling theory and baffling. Prefabricated baffle kits are available
as an option through Van’s Accessories Catalog and should save the builder a lot of time. These kits include
pre-formed aluminum baffling, cowl seal material, and all the hardware and instructions needed. Drawing
and patterns are also available for those masochists who wish to make their own baffles.
Inter-cylinder baffles are normally supplied as a part of the engine. They are essential to proper cooling, and
the exact shape, size, and fit should be maintained if these baffles are being fabricated rather than using the
Lycoming parts. Intercylinder baffles are not included in Van’s baffle kits.
ENGINE BREATHER LINE
An engine crankcase breather line is needed to run from the breather port on the upper rear engine case, to
an overboard dump point. Because there are often droplets of oil included in the blow-by air exiting the
engine crankcase, breather tubes are a major cause of dirty fuselage bottoms. This can be partially avoided
by positioning the breather line outlet so that its contents are blown directly onto the exhaust pipes and
burned. The breather line itself can be 5/8’’ I.D. radiator hose except for the end closest to the exhaust pipe
which should be aluminum or steel tubing.
A relief hole should be drilled in the line several inches above the exit. If the breather line plugs or freezes
shut, the pressure build-up inside the crankcase can blow the front crankshaft seal out of the engine, causing
the rapid loss of oil and engine failure.
Breather separators are available. Usually mounted on the firewall, these units receive the direct line from
the breather outlet and use a screen and sump to separate the oil from the gasses. A vent line is run
overboard for the gasses, and the separator must be drained and cleaned periodically. It’s a messy job, but
many builders prefer it to constantly cleaning the bottom of their airplanes.
CARB AND CABIN HEAT MUFFS
The carb air intake box previously described uses air from the hot air side of the engine cooling system for
alternate air and/or carb heat. While this has proven adequate on the prototype RVs, each builder will have
to evaluate his own installation based the likelihood of carb ice in his intended operating environment. The
air intake box could be altered so that a completely sealed carb heat system could be used, or one could run
a 2’’ air hose from a heat muff and position it to feed into the alternate air inlet of the carb air box without
being attached and closed. At least exhaust heated air would be available for carb heat rather than just
engine heated air.
The heat muff is fabricated to fit around a straight portion of an exhaust pipe. A muff 6-12 inches in length
should be enough to supply heat for the carb and the cabin. Note that the clean air intake is located on the
forward cowl baffle, from which air is routed into the heat muff. The object of this is to assure that un-
contaminated air is heated and routed to the cabin. Other homebuilts have used a much simpler system,
taking warm air directly from the engine compartment, through a simple door on the firewall, and using it for
the cockpit heat. This is a potentially very hazardous practice, as engine compartment air can contain
exhaust from gasket leaks, smoke from burned oil, etc. If a heat muff were being made strictly for carb heat
air, it could intake engine compartment air without risk of problems.
OIL COOLER
Any of the oil coolers typically used in production airplane installations should work well in an RV. The cooler
may be installed on the rear vertical baffle behind cylinder #4, with air admitted through a hole through the
