SECTION 11:
ENGINE AND PROPELLER INSTALLATION
RV AIRCRAFT
11-1
sect 11r8 06/24/11
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 are not very specific at times.
This is intentional. The wide variation of possible engine/propeller combinations 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 engine. The same ‘‘quality control’’ rules and practices which apply to factory aircraft apply to
homebuilts as well.
To help simplify the process, Vans has developed Firewall Forward Installation kits for the Lycoming engines
that we sell. We will briefly consider a number of common points in this section, but for detailed drawings and
instructions you will need to buy the Firewall Forward documentation, which is available separately from the
Firewall Forward kits.
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 standard 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, WI.
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: RV-6A/7A/8A/9A 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. An
offset is built into the mount to help compensate for “P” factor, so the engine is not aligned with the airplane
centerline.
The rough position of the mount is shown by the pre-punched tooling holes in the firewall. Do NOT simply drill
the tooling holes to 3/8. Offer the mount to the firewall, and use some long 3/16 bolts to attach it. The holes in
the weldment will likely not align perfectly as the weldments vary slightly. It may be necessary to pull the part
into alignment, and/or file the 3/16 tooling holes to shift them slightly. If the mount is not exactly centered on
the firewall, that is OK. 3/8” either side to side or up and down will make no difference.
With the mount thus attached to the firewall, drill the holes out to 3/8 using the mount as a guide, and insert
3/8 bolts as you proceed. Any gap between the firewall and mount will usually disappear when the fasteners
are tightened. If the gap is still there when the nuts are appropriately torqued, AN9790 washers may be used
to eliminate it.
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.
DYNAFOCAL ENGINE MOUNT INSTALLATION
Study the construction drawings 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.
Because the mounting bolt kits must supply all the washers for builders installing used isolation mounts, if
you buy both new isolation mounts and a new bolt kit, you will probably end up with some duplication and
some extra large washers if you order new isolation mounts. Throw them in your spare hardware box. Use
only the number and type of washers shown on the drawing.)
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 and
SECTION 11. ENGINE AND PROPELLER
SELECTION AND INSTALLATION
RV
AIRCRAFT
SECTION 11:
ENGINE AND PROPELLER INSTALLATION
11-2
sect 11r8 06/24/11
there are several other brands) 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. The bolt simply “bottoms out” on the steel tube insert that passes through
the center of the isolators.
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. Beautifully made stainless steel exhaust
systems for all RVs are available through Van’s Accessories Catalog.
If you prefer to do your own exhaust system fabrication, you can save some money. Unless you are a very
talented welder, you will want to use mild steel automotive exhaust pipe instead of stainless. 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 pipes can be cut into sections for the various
curves needed. By splicing together a number of these bends, a satisfactory system can be made
inexpensively, but it will weigh more than the stainless 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.
THROTTLE CONTROL
The standard throttle differs between the side-by-side and tandem airplanes. In the side-by-side RVs it is a
locking push/pull control in the center. 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
Many builders may prefer more traditional vernier or quadrant controls and 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.
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 ordered from various homebuilt aircraft supply shops. Routing should
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
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 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
