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TIARA ENGINE: I was initially reluctant to go with the Tiara. The engine hasn't been manufactured for thirty years. When Continental stopped production on it they unfortunately dropped support as well. The remaining stock was sold off and finding the parts is now a bit of a treasure hunt. However as I spoke with folks who fly Aircars with the Tiara in them, I consistently heard praise for the engine. Common words were "Smooth" , "Powerful" , "Lots of torque", "Quiet", "Fuel Efficient". I started wondering what the heck is going on here? A little research showed that the Tiara started off on the wrong foot with pilots and never really recovered from it. The earliest Tiaras (late 1960s "A" engines) Suffered from a couple crank failures. Continental beefed up the crank in the "B" and "C" engines but by that time the damage had been done. It didn't help that the only production aircraft that the engines were put into were the Piper Pawnee Ag Plane. Crank failures are bad, especially for an aircraft that lives at 500' or less AGL. Continental stuck with the engine until about 1978 when they dropped the program. Its a shame as the engine was, in many ways, ahead of its time. But the nature of the marketplace at the time largely prevented manufacturers from adopting the Tiara into any new airframes.
MODIFICATIONS/NOTES ON PLANS: I am sticking to the plans the best that I can. That said the plans are about as slim as they can get regarding details of the engine installation. I suspect that Spence and Andy had a lot more information "in the day" but I did not receive much in terms of the engine install with my plans set. I have been given some additional diagrams by Bruce Lowerre that have been helpful. Other information has been found in the scribbling on the edges of the plans, photographs, and the Piper Pawnee and Tiara manuals.
NOTES ON ASSEMBLY:
ENGINE MOUNT In spite
of the lack of information much of this becomes somewhat intuitive as to
where to put things. My main concern was to get the engine mount
in the right place and build it strong. There are no specs as far
as I could find for specifics to the engine mount. I started by cannibalizing
an existing Pawnee PA-36-285 engine mount. The engine bushings for
the Tiara on this mount cost $500 each so I was grateful that the bushings
off of the mount I had were in good shape. If they were not I would
have considered fabricating a new mount using IO-520 bushings ($75.00 ea.).
The existing Pawnee mount is cut back to the basic square bed frame that
holds the rubber mounts, and three stubs of the former support trusses
that are picked up at the prop end for the Aircar mount. Basically
the mount is positioned on the car frame so as to not allow the exhaust
to interfere with the left rear wing spar, and allow the Aileron cables
to duck under the forward thrust tubes. There were no notes on any
plans as to exact positioning with the exception of the thrust line which
is 1 degree downward. My final position placed the bolts at the front
end of the "engine frame" about three inches above the bolt holes on the
car frame. This allowed the aileron cables to sneak over the forward
thrust tubes. It also maintained a close to stock angle for the lower
diagonal support tubes.
FIREWALL: The firewall is
yet another item on the list of aircar parts that takes at least twice
as long as a conventional aircraft due to the complexity of the
part. Instead of a simple flanged pan, the Airier firewall is a three
dimensional "stairway" shaped shield that also has to go around and protect
the rear wing spars. It seems like it would have been easier to modify
the car-frame and rear wing attach points to accommodate the tight
fit of the Tiara, but that can be for somebody with a greater understanding
of engineering tubular structures. The firewall material is .020
304 stainless. I initially thought of welding the seams but in the
end opted for stainless cherry pop rivets and firewall sealant. Elegant
no, but effective. One area that proved to be especially tricky was
routing the stainless around the rear wing spars. The wing rear mount
bolt needs to be accessible, to accomplish this I drilled a 1" hole in
the stainless firewall to allow the bolt to go through: and found some
1" SS Sink hole plugs to cover the hole/bolt once the wing is installed.
EXHAUST: The exhaust was
made largely using parts salvaged from the Tiaras Pawnee system.
All of the Tiara parts are some unknown alloy of stainless. I say
unknown because it is stainless, but while welding, it seemed to be a bit
more porous and of a lesser quality than the 321 stainless I was used to.
All used pieces were abrasive cleaned down to bare metal before welding.
The parts were TIG welded using argon and back gassing the weld.
For the design of
the system, I had a few photos from some other Tiara Aircars exhaust installations
but decided to depart from their methods on the pilots side of the engine.
I didn't like the "example" system because it did not maintain slip joints
on the pilot side of the engine. The original Tiara system had slip
joints throughout. Basically the exhaust is stock Tiara on the passengers
side. But on the pilots side I modified the #3 and #5 cylinders header
pipes by cutting them at the apex of the curve and spinning them 180 degrees
to direct the flow towards the rear of the aircraft. For the #1 cylinder,
I cut a stub off of a spare piece for the mount to the head, and cut the
slip joint off of an extra #2 header. I then took those two
pieces and joined them with a tight-radius store bought 2" Stainless steel
elbow. The tight radius was required to keep adequate clearance between
the exhaust and firewall section over the pilot side rear wing spar.
The muffler was next.
The stock muffler slipped nicely onto the passenger side headers.
I then welded several curves together ending in a slip joint for the pilots
side. The muffler "can" had to be modified for cabin heat.
I purchased two stand-off rings and welded them to the existing can.
Next an aluminum sheet was rolled around the can with an inlet and outlet
tube welded onto it and Wha-la, cabin heat! The muffler assembly
is held to the two side exhaust using two store-bought 3/16" pin clamps,
and the weight is supported by hangers which are bolted to the engine block
at the oil pan.
ELECTRICAL: I converted
the engine to a 12 Volt system. This included an new alternator and
having the starter rebuilt with a new 12 volt armature. The primer
valve seems to work just fine with 12 volts so I did not pursue a
12 volt unit
PLUMBING: A tiara installation
requires the following plumbing: Fuel in, fuel return and fuel pump to
throttle control. A hose from the MAP to the fuel pump aneroid.
Four oil lines: two each to and from the oil cooler and oil filter.
An oil pressure line, fuel pressure line, and manifold pressure line, a
fuel pump seal drain, manifold drain, injection spider drain, cylinder
head fuel drains - one for each side of the engine. Hoses for the
Air/Oil Seperator (3), If your counting that's 19 different
hoses, and I probably forgot at least one!
IGNITION: I spent a lot
of time deliberating over the ignition system. The initial reports
on the stock D2000 magneto were that it was not reliable and some were
unfortunately refering to it as the "suicide mag" It was apparently
one of those brilliant 1970s ideas to get the parts count down. Unfortunately,
both sides of the magneto share the same drive gear and if the drive gear
fails you are left with no spark. I did some research speaking with
a couple magneto shops and found that the failures were largely the result
of over tightening the four inner cover screws. This would warp the
magneto case and cause a mis-alignment of the drive gear with the two rotor
gears. Bendix fixed this issue in the D-3000 Magnetos by eliminating
the inner attach screws and using only the outer four screws.
The overhauled D2000 system I acquired also eliminated the inner screws.
A second issue that I ran up against with the D2000 dual is that I needed
a starting vibrator that matched the magneto. I was able to find
a few used 24 volt units, but extensive searching did not yield a single
12 volt unit (My system is 12 volts) I was also unable to find a
impulse coupling that would work with the mag. Apparently this magneto
is the ONLY system that turns at 3/4 crankshaft speed. All of the
other six cylinder systems out there turn at 1 1/2 X the crankshaft speed.
I needed to come up with a way to retard the ignition to start the engine.
I then started looking
into some of the aftermarket electronic systems. Many of these systems
offer benefits that are not possible with a standard magneto. These
mostly include variable timing and a longer duration, hotter spark.
The 3/4 magneto drive speed eliminated the lasar system from the running.
The Lightspeed Engineering system uses small magnets mounted in the back
side of the flywheel or prop hub, and the Electroair system uses a toothed
timing wheel mounted to the crankshaft. The Electroair system won
out as it was the most easily adapted to the Tiara engine. It also
automatically retards the timing for engine start up.
The most difficult
part of the ElectroAir system was mounting and aligning the timing wheel
to the crankshaft pulley. I needed it to stand off enough to not
interfere with the alternator belt, but keep it close enough to make it
possible to mount a Hartzell reversible prop with its reversing ring:
that is if I'm actually able to find one. Another challenge with
the mounting of the timing wheel is that the pulley is attached to the
crank with a large nut that is a friction fit. I therefore needed
to come up with a way to get the timing wheel in the right position AFTER
the nut is tightened down. Then to make it more difficult I wanted
to have a balanced assembly. So I mounted the timing wheel to the
pulley with four spacers. I then turned the assembly on the lathe
to cut the inner hole in the timing wheel (for the socket to tighten the
crank bolt), and cut the timing teeth to make them true to the pulley.
I then drilled four extra holes in the timing wheel that would later be
used to hold the wheel in the correct position when tightening the pulley/timing
wheel assembly onto the crankshaft. This whole assembly was sent
off to be precision balanced and two Benjamin's later the assembly came
back. To mount the assembly to the crank I made a rig that would
hold the crank at 15 degrees BTDC, and a second plate that held the pulley
at the 15 BTDC position while I would tighten the nut down to the specified
245 Ft/Lbs (that's tight!)
The rest of the system
is a matter of finding a good place for the coils and controller and hooking
up all of the wires. I'll give a report of how well the system works
once the engine is up and running
QUADRENT/CONTROLS: I
decided when I did my cabin that I would end up putting the engine quadrant
and switches on the overhead console. I did this primarily to simplify
the routing of the control cables. It allows a straight shot from
the engine to the cockpit and a simple connection to my home brewed
quadrant.
MONITERING: A
few years back I bought a Rocky Mountain Instrument MicroMoniter, see http://www.rkymtn.com/
It monitors all engine parameters and includes a timer and fuel totalizer,
as well as a few other bells and whistles. The monitor was installed
along with a six way switch to allow me to monitor all six of the Tiaras
cylinders CHT and EGT. The monitor allows the user to set custom
alarm points to alert the pilot when one of the parameters is out of range.
It also has a RS232 serial output to GPS or to a laptop to
review the engine data post flight.
THINGS I WOULD DO DIFFERENTLY NEXT TIME:
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