Growing a Grumman
- Part 3
Well here we are at
the end of another year - 2004 just flew by, while I put in as many hours
on the Grumman as I could find.
Most of the work,
but not all, has dealt with the engine installation - but also have completed
a lot of work on the airframe and interior that was "sorta"
done - but not completely completed - if you know what I mean!
First though it was
time to get a suitable radiator made up - searched high and low for someone
able to make up a rad to my spec in aluminium and finally after many weeks,
found a company who claimed to be able to do this - always sceptical,
I gave the job to them and kept my fingers crossed!
After a number of
delays, I finally got my radiator - it even looks good, with nice welds.
Effectively it consists of a BMW 540 car radiator, split horizontally
and placed back-to-back. A similar set up is used by many of the tow-truck
cowboys in those hot V8 powered pick-ups we see prowling the roads for
wrecks. Since the original engines in these vehicles was not a V8 but
probably a puny 1600cc 4 cylinder lump, they also need extra cooling.
I think my rad will work, with enough cooling air reaching it.
The radiator is mounted
high up on the firewall and air is ducted directly to it from the cowl
inlets - I simply bracketed the rad to the firewall using rubber exhaust
spools to avoid vibration possibly cracking any welds.
With the engine and
radiator finally mounted to the airframe, all ancillaries in place, and
with oil in the engine, the time had arrived to fire-up the entire catastrophe.
No problem - fired
up right away - and after timing adjustment and rough carb adjustment,
it was sitting there idling tolerably well.
However it proved
quite tricky to get the twin SU carbs set up to run cleanly from idle
to higher rpm. With this set up, not designed for the Chev engine, and
a manifold which had been heavily modified it's a real shot in the dark
- is it the carb jetting that's the problem, or the inlet tract - or even
the carbs themselves being too small? However perseverance pays - and
with the help of a friend, Trevor who has wide experience in serious race
car tuning and set-up, we now have a sweet running motor. A combination
of carb and timing adjustment made simultaneously solved our problem -
but as he pointed out, the stock Chev distributor has no provision for
mechanical advance (all previously electronically controlled) and at high
revs >4500 there is a slight misfire, which Trev puts down to insufficient
spark advance. May need a different distributor to correct this.On the
other hand maybe not, since with the PSRU gearing we will use the motor
should never run more than 4400 rpm.
Two major crises cropped
up during this phase - firstly, apparent low oil pressure, traced to a
sticky gauge needle and secondly, a serious vibration through the entire
aircraft when turning the engine between 1200 - 2000 rpm. At anything
over 2000 rpm or so, the vibration was less - but only because it's frequency
had increased and therefore made it less harsh!
I wondered what could
be the cause, suspecting everything from the mount rubbers to my home-brewed
tubular engine mount. Surely a V6 motor MUST run smoothly in an aircraft,
more or less as in a car, even with the lower relative mass of the structure
to which it is mounted?
To cut a week's investigations
down to a short story - the culprit was the lack of an external balance
weight on the flywheel. It seems that GM do not really balance their crankshafts,
other than by welding a metal weight on to the flex-plate (which I had
replaced with a Nissan 3.0 flywheel).
By installing the
(fully neutrally balanced) Nissan flywheel I had effectively removed the
balance weight essential for smooth running. The solution was simple -
remove the balance weight from the discarded flex-plate and add it to
the Nissan flywheel in the same relative position! And it worked - immediately
the engine ran dramatically smoother! What a relief!
Obviously this solution
is perhaps not the ideal - although if it works for Chev, why not for
me? It would be nice to get the entire bottom-end of the motor (harmonic
damper,crankshaft,flywheel) dynamically balanced as a unit, for perfect
smoothness - but since that requires a strip down of the motor that will
have to wait.
I have a theory -
which has been proven time and time again with aircraft projects. It goes
like this - on starting any major aircraft project, there are so many
items to attend to and work through that you can look at any part of the
aircraft and it's sub-assemblies and find plenty that needs doing. This
situation carries on for a long time with a super-abundance of tasks -
so many in fact, some large, some small that it is almost pointless to
try and make any kind of detailed job-list, other than on a 'things to
do today' basis!
on brings one to the point where, looking around the aircraft, more things
are done than not done - you have to start thinking harder to identify
what remains to be done, and a comprehensive and detailed list of the
remaining items for attention can be tackled - it's at this time that
one knows, with certainty that the end is nigh - if all else remains equal!
The terms I use are relative of course - "the end being nigh"
probably means that we can start thinking in mere years rather than decades
at that stage!
Many major life-skills
can be learned from the building/rebuilding of an aircraft.. Amongst these
4. How to live in
5. and very importantly
- how to scrounge stuff!
view of Motor- Bare
Chev 262 motor on trial mount made of mild steel tube and
welded by yours truly - this mount will NEVER fly!
view of Motor and mounting points which use Nissan 3.0 litre
LDV rear spring shackles as isolators
PSRU backplate and Nissan flywheel and driver sprocket.
This plate is 12mm alloy and bolted to the six threaded
pick up points normally used for connecting the gearbox
to the engine in a car. Alloy radiator at bottom left of
pic awaiting installation on firewall.
view - SU carb setup, may change to Holley or similar for lower
height - but these work okay.