I like F3A Pattern ships. They go exactly
where you tell them, so if any manoeuvre doesn't work its you
the pilot - you cant blame the plane! I think that they make
excellent skill improvers as they respond so directly to the
controls, no funny wobbly business. I am however a very
average pilot and I like practical planes that I can bung in
the car, fly and then chuck back in the garage.
I have no aspirations toward competition, and have a
mortgage, so one of the big fancy French moulded jobs for
£4000 from Probuild was just a laugh. I also have a huge
liking for those bullet proof Laser engines, and equally
bullet proof Fleet Radio, so with a budget of £1000 and a
target of a 2 metre, high powered F3A Pattern plane I set
off.
There are very very few big pattern ship kits on the market
it would seem. Marvic models, and Newman Precision Products
have long gone, leaving only Dave Smith Models. I had a DSM
Excelsior 188 a few years back with a Laser 150. Very nice it
was too, but the power wasn't quite enough and with the tank
right behind the engine in-flight variations of CG caused a
few trim problems. DSM now make an Excelsior 2000, at 2 Metre
span its the biggest of the range, going for £200, sold to
me, thank you Mr Smith. Now I needed an engine, and some
means of mounting the tank on the CG to eliminate trim
variations.
Among the range of Laser Engines is a 240 vee twin,
specifically designed for aerobatics and dishing out stonks
of power on straight fuel. Unlike the YS aerobatic engines,
Lasers have no fuel pump, so still determined to mount the
tank on the CG I looked at possible ways around this. The
incredibly helpful Neil Tidey of Laser Engines suggested I
look at fuel regulators and bladder tanks.
I found a regulator on the web called the 'Cline Proportional
Control Fuel System' which is basically a 20 gram marvel that
sits between a pressurized tank and the carburettor. By
controlling the pressured feed from the tank it feeds the
carb with a constant pressure of fuel, regardless of tank
position, or model attitude. Their website explains it MUCH
better though. I would however need two of these regulators -
one for each cylinder of the Vee twin !
There is apparently only one make of big bladder tank in the
world - Tettra. A bladder tank is basically a big condom
inside a baby bottle. The condom is filled with fuel, and
when the tank is pressurized the condom is compressed and
pushes fuel out of the top! The advantage of this is that
there is no clunk, and no air in the tank, so no burpy half
tank misfires, and the tank can be run absolutely dry.
So now I had my shopping list: Excelsior 2000, Laser 240V,
pair of Cline regulators and a Tettra bladder tank. The
engine was the easy bit and before I knew it I had in my hand
an exquisitely finished piece of British engineering. The
Excelsior however got lost in the post for six weeks, and
damned if I could find anyone in the UK that had any Cline
regulators or Tettra tanks. Time to hit that webby thing.
The Cline homepage offers international delivery at $50 a
throw, so an email to Ohio had two of these in the post and
sure enough the smallest parcel I have ever received plonked
on the doormat a few days later. The regulators seemed very
solidly made, the theory looked fine and all other bits were
supplied, including one-way valves, tee joints and tube
plugs.
The only supplier of Tettra bladder tanks in the UK is
Probuild, and the 500cc job at £25 a shot was never in
stock! I read in a magazine that Chip Hyde the USA F3A
Champion is a keen user, so I tracked down his site and he
punts them out for $20 a piece. An email to Albuquerque had
one on its way. Two days later it arrived in this country and
then it took Parcelfarce two weeks to loose it and charge me
£11 to find it again, then after that I had to travel 30
miles to collect it from Milton sodding Keynes.
Now I had all the bits I could start to work out how the hell
to fit this lot together and came up with he following
schema. Please forgive the crap artwork - I hate Microsoft
Word:
When looking at the probable installation for the first time
I thought shit I'm going to need 10 metres of fuel tube and a
plumber! but its actually much simpler and more logical than
it looks. The picture below shows the installation from the
underneath. The regulators are mounted back to back, and lie
between the cylinders and the one way pressure valves
actually fit inside the exhaust pressure tube.
On the left hand side of the fuselage (top of picture) there
are three tubes, from front to back they are, fuel filler,
fuel overflow and exhaust pressure. All are blocked in
flight, and all opened to fuel up.
Picture 1
Another decision I made was to mount the engine using thick
aluminium columns. The engine mounting bolts go from the
inside of the firewall, through the columns and then through
the engine backplate. This is different from the usual
approach of mounting Laser Vee engines onto a thick plank of
wood, and frees up the area behind the engine to pass tubes,
glow plug wires and wotnot.
The construction of the airframe was quite trying. The
Excelsior is not the worst of kits, but it aint the best
either. Even though the fuselage is pre-built, there is a lot
of work involved in building it into an accurate plane. After
I had already completed quite a bit of the fuselage I noticed
it was twisted, and had to split the rear end to re-set it.
The wing can fit into the fuselage cutout with about 20mm of
fore and aft movement altering the incidence as you go. There
is also no distinct datum line to work on either, so quite
what the wing incidence is involves some guesswork. The
instructions are normal British cottage industry style, you
know, fit the tail into the fuselage, install the radio gear
and good luck to you old chap.
Talking of the wing, I measured the total span and it was
1840mm, over 6 inches shorter than the 2 metre wingspan
advertised by DSM. I contacted DSM on this point and a super
chap called Sandy told me that it was a '2 Metre' model as it
fitted within the FAI regulation 2 Metre box. I'm sure this
is great news for Christophe Peasant Le Roux, as that means
he can enter my old Wot 4 in next years championships as that
too fits inside the FAI 2 Meter box.
The wing seemed acceptably well made and has two full-span
carbon fibre spars top and bottom, you could probably balance
a Rhino on the finished item. I replaced quite a bit of the
balsa strip as the supplied stuff was bent, and used much
thinner stuff for the rear fuselage stringers and bottom
cover. As the thing is designed for a YS 140, quite a bit of
modification is required for a Laser 240V. I shortened the
nose by 25mm and as there is no underwing exhaust, I extended
F1 & F2 to but up to the cowling. Also the underbelly
thing that goes under the wing has to be scratch built and
looks like a toy boat.
As you can see, its a big old thing,
and that's a super king size bed its on as well.
The radio gear was the best Fleet had to offer, PCM Receiver,
and metal gear servos all round. The rudder servo was a high
torque job, knocking out 7Kg. Each elevator has a micro servo
embedded into each tailplane half, giving very short direct
control. The 1500ma NMH battery is under an access hatch as
far back as it will go. Also, being a lazy sod I fitted a
remote charge lead and remote glow setup.
Firing up the engine for the first time was always going to
be interesting, would all that plumbing work ? Could the
pressure system take both exhausts? and nobody I knew had
used one regulator before, let alone two. As per normal with
running in a new engine, I put my car on the drive, and with
the plane in the garage tethered it to the car.
A twelve volt battery and hi-torque starter struggles to turn
the engine over but on the fourth attempt off it went. After
allowing it to warm up and gently get through a tankfull, I
let it cool and ran it up again. I gradually increased the
gas up to full power and noticed that the plane was
remarkably vibration free. This was in contrast to the brick
garage which looked like it was going through a major
earthquake. I also noticed that the plane was moving forwards
at a slow but increasing speed - the thing was pulling my
bloody car along the driveway. It was definitely time to go
flying.
The plane has now had four outings, and about a dozen
flights. Its smooth, responsive, does exactly what you tell
it, and its very very fast. Vertical performance is
positively scary, from a tail slide it will accelerate
vertically out of sight in a few seconds. Half throttle is
all that is needed for most of the flight. I'm still
tinkering with all sorts of trimming settings, and haven't
even begun to come anywhere near its limits yet, and quite
probably never will.
And what about all that plumbing? It works perfectly! Any
throttle position, any speed any attitude, straight up or
straight down you get a constant bubble-free supply of fuel
right down to the last cc in the tank.
