Engine Installation Is One of the Most Time Consuming and Most Important Phases of Construction

Section11 : Engine and Propeller Instration

Engine installation is one of the most time consuming and most important phases of construction.

Although it is extremely important that everything be done correctly, these instructions will intentionally not be very specific at times, because the wide variation in possible engines means there may be more than one "right way". In most respects, the engine installation in an RV is just like that of any other airplane using the same type engine. Thus the same "quality control" rules and practices which apply to factory aircraft apply to homebuilts as well. We will cover a number of these items, plus some detailed fabrication and Installation instructions where applicable.

RECOMMENDED ENGINE INSTALLATION MANUAL

One of the books recommended in Section 1, Firewall Forward by Tony Bingelis, is an excellent reference manual for engine installations, and contains much more detailed information than we are able to include in this manual. This is particularly true if you choose to vary from stock procedures.

We recommend acquiring and thoroughly studying this book before beginning your engine installation.

Firewall Forward is available from the Experimental Aircraft Association, (EAA) Oshkosh, Wl.

INSTALLING THE ENGINE MOUNT TO THE FUSELAGE

The typical RV engine mount is unique because it combines mounting structure for both the engine and the main landing gear legs. (There are a couple of exceptions: the RV-6A/8A engine mounts includes the mount for a nose gear leg, and the landing gear in the RV-8 is mounted in the fuselage.) Because of the gear leg mount feature and forward cockpit design, six attach points are used rather than the usual four. Any irregularities in the firewall alignment will be reflected in the engine and landing gear alignment. Errors such as this can be corrected (within limits) by placing spacers under one or more of the engine mount attach points to re-align the engine mount. This will not be obvious until after the engine is attached.

CONICAL ENGINE MOUNT INSTALLATION

The conical engine mount supplied with the kit has the correct alignments built in. It simply bolts to the firewall.

Attaching a conical mount engine is relatively easy because all four bolts through the engine case are parallel. The conical rubber mounts that give the mounting style its name are set into the recesses in the engine case, the engine is mated to the mount and the bolts installed. Tightening all bolts evenly will position the engine correctly.

Van's does not stock the rubber isolation mounts for conical engines, but recommends that the builder buy mounts listed for production types using the same engine: Piper Tri-Pacers, for instance, used O320 conical mount engines, and RV builders have used these isolation mounts successfully.

DYNAFOCAL ENGINE MOUNT INSTALLATION

Study Fig. 11-1 until you understand the correct placement of the isolation mounts and washers.

(Isolation mounts and mounting bolt kits are available through Van's Accessories Catalog.)

Mounting a dynafocal engine is a bit more difficult because of the converging lines of the mount bolts.

The rubber isolation mounts (commonly known as " Lord" mounts, although Lord is a specific brand name) are designed so they align when tightened and compressed. The bolt holes through the four mounts will not coincide with the holes in the engine case at repose (no compression load). When installing the engine, it is necessary to have it suspended from a hoist. When the engine is suspended, it can be moved into position on the engine mount and the two upper isolation mounts and bolts installed and partially tightened. Then, by lifting the engine with the hoist, and actually lifting part of the airframe weight too, the upper isolation mounts are flexed upward enough that the lower mounts are brought (almost) into position. Basically, the technique is to get one or more bolts started, and then force the engine in the opposite direction so that remaining bolt holes can be aligned. We have found that the best place to start is the top.

Once in place, tightening is easy because the mount rubbers have a steel insert which bottoms out when the correct amount of compression is reached.

EXHAUST SYSTEM

Probably the first thing that should be installed on the engine, once it is mounted on the airframe, is the exhaust system. This is the big, hot, unmovable item which cables and fuel lines must be routed around.

Several suppliers have made systems available specifically for RVs. Be sure to specify your aircraft type and engine model when you discuss requirements with your supplier. Exhaust systems for all RVs are available through Van's Accessories Catalog.

If the builder prefers to do his own exhaust system fabrication, he can do so at considerably less cost.

Unless he is a very talented welder, he will want to use mild steel automotive exhaust pipe. A good place to start is to purchase the required exhaust flange, some 1-3/4" exhaust pipe of the thinnest wall thickness available, and several 6" radius "U" bends of 1-3/4" dia. These 180° pipes can be cut into sections for the various curves and switchbacks needed. By splicing together a number of these bends, a satisfactory system can be made inexpensively, with little weight increase over a custom built stainless steel system. However, there is a lot of labor involved, and we have found that nearly all builders prefer to purchase a ready made exhaust system.

Design of the exhaust system can affect the power output of an engine somewhat. One of the more efficient type systems is commonly called the "crossover exhaust," and it connects the rear two cylinders into one exhaust outlet, and the forward two cylinders into another. This assists in scavenging the exhaust, reduced backpressure on the engine, and results in slightly increased power as well as quieter arid smoother running.

THROTTLE CONTROL

The standard throttle differs between the side-by-side and tandem airplanes. In the RV-6/6A it is a locking vernier push/pull control in the center console. Installation is straightforward; through the firewall and to the control arm on the carb. The tandem airplanes use a throttle quadrant, mounted on the left sidewall of the cockpit. Cables are available through Van's Accessories Catalog.

MIXTURE CONTROL

Although they are not used on production aircraft, a medium duty "choke cable" type control is sufficient for this. A cable with a core wire diameter of 0.062 to 0.070" works well and routing is easy because of the flexibility of this 3/16 O.D. cable. The cable must be must be anchored at some point near the mixture control handle on the carb to insure positive control.

Many builders may prefer more traditional vernier or quadrant cables. These are usually fitted with rodend bearings that connect to the mixture arm on the carburetor. Fittings, special washers, and hardware for anchoring and connecting the engine end of throttle and mixture cables are offered in Van's Accessories Catalog. See Fig. 1 1-1 1.

TACHOMETER DRIVE

The Lycoming engine is equipped with a mechanical tachometer drive. A cable, turned by this drive, is connected directly to a mechanical tachometer on the instrument panel. The cable can be made to order by any automotive speedometer shop, or can be ordered from various homebuilt aircraft supply shops. Routing should be planned to maximize the bend radius of the tach drive line to prevent excess friction, wear, and premature breakage.

Electronic tachometers are also widely available and should be installed using the manufacturer's instructions.

FUEL LINES

Fig. 1 1-2 shows a proposed layout for fuel lines and filter for use on a carbureted engine. Fuel lines up to fuel filter (gascolator) can be 3/8" soft aluminum tubes, just like the remainder of the system back to the tanks. However, since there is relative motion between the engine and the airframe, flexible lines must be used for routing the fuel from the fuselage to the engine mounted fuel pump.

One good hose for this purpose is Aeroquip 701 , a medium pressure hose with a stainless steel wire braid shield on the outside. It is available for use with reusable fittings and hose assemblies can easily be fabricated by the homebuilder Wherever possible, hoses should be routed so there is "slack" or "bows" in the line to permit easy movement and flexing due to engine vibration, and to lessen the load on end fittings. Fuel lines should not be installed straight and tight between the accessories.

Fuel lines should also avoid close proximity to exhaust pipes, or should be thermally insulated if close

routing is unavoidable. Sometimes a heat shield as shown in Fig. 1 1-3 must be installed to shield the fuel lines.

Thermal insulation of all fuel lines within the engine compartment is recommended even if proximity to exhaust pipes is not a factor. During operation, the air temperature within the lower rear portion of the engine compartment (where these fuel lines are located) can rise to a level sufficient to vaporize fuel within the lines and thus cause vapor lock. The engine will run rough or stop. This condition is likely to occur during ground operation where engine cooling is marginal because of limited ram airflow through the engine compartment, and because the low fuel flow requirements for taxi and pre-take off check 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 or 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 also) from the direct flames of an engine compartment fire.

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 on which the hose (without flared nut end fittings) slips over a male fitting and is held on 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 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 type line is recommended for use between the oil port on the engine and the fuselage, similar to that for the fuel system. 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. A typical practice is to mount the sensor on the firewall and connect it to the engine with a flexible hose.

FUEL PRESSURE GAUGE LINE

This should be a small shielded rubber hose taken off the fuel line somewhere between the fuel pump and the carb, and should be routed to a bulkhead fitting in 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). Line used can be 1/8" copper tubing with compression fittings. Because of the small diameter of the line, and the non-critical nature of the manifold vacuum, the copper line can be used if a vibration bend (see Fig. 1 1-2) is made in the line. Route 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 and the rapidly varying pressure caused by the valves opening and closing can cause the gauge to flutter to the point where it is unreadable. PRIMER SYSTEM

The Lycoming 0-320 & 0-360 carbureted series engines can be primed for cold starting by cycling the accelerator pump (pushing the throttle in and out). 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).