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Growing a
Grumman - Part 12
2010-07-19
With very cold
winter weather for the past 4 weeks working in the hangar at the
cold and windy airfield has not been 'top of mind" - in addition
there has been little activity at the field as a result of the flight
restrictions imposed for the FIFA World Cup - essentially all aircraft
were grounded unless a special flight clearance was obtained! -
utter nonsense but what can you do?
However the
wings are now fully installed after some complications (of course!)
with electrical wiring and fuel piping. I was surprised to find
that the wing tanks are free of any leaks, since it has been at
least 6 years since I sealed the tank end baffles with new O-rings
and PRC sealant - but everything remains dry, not a sign of any
weeping of fuel.That's the good news!
However the
bad news is that those original 'cube' Facet pumps seem to have
failed completely - having now tested all four of them off the aircraft,
not one is pumping worth a damn - cannot fathom what can have happened
to them!
It is amazing
the things that complicate one's life when building a true 'experimental'
aircraft - using parts that Grumman never dreamed off! For instance
with the new fuel pump it was found that the engine would die after
a few seconds running - at first I thought, even though there are
now two inline filters in the fuel line, plus a finger-strainer
in each tank outlet, that the carb jets had been blocked by dirt
sucked through from the wing tanks, so took the carbs off again
and checked those - no blockages! Put them back on and eventually
dicovered that the carbs were flooding. Off come the carbs (yet
again!) to find
that the setting of the float level was incorrect. Since this is
set by bending a tab on the float, it is obvious that the setting
previously adopted to get the motor to run right was dependent on
the inadequate fuel flows being provided by the defective previous
fuel pumps. After readjusting this tab, all appears fine again!
Now that all
wiring to the nav lights and landing lights is complete, I carried
out a (hopefully) final tidy up of the wiring spaghetti behind the
instrument panel - still to do is to replace the windshield and
the panel cover.
With all the
work I have had to do, groping around inside the wings, I removed
the aux tanks completely as they were in the way. Those I can leave
out for a good while since they will not be needed until proving
flights (40 hrs around the airfield!) are completed. Also I have
some new ideas for the piping for these tanks to make for a cleaner,
tidier and lighter installation.
Now I need to
make landing light covers and nav light covers from perspex - this
can be obtained locally and it seems they can be moulded simply
around a wooden former under mild heat - worth a try anyhow! Need
to go shopping for blocks of soft timber first and take up wood-carving.
Now that the
wings are on and the aircraft looks like it is complete, all I hear
around the field is "When's it gonna fly, then?" - Geez,
give a guy a break, after 16 years on this aircraft, you think I
am going to rush the last bit?
2010-08-09
After several
weeks of standing in the hangar the right hand brake has slowly
leaked it's fluid and the pedal goes right to the floor - that brake
is one which had been 'reworked' so many times that it is in fact
no longer worth trying to repair, the major problem being that the
cylinder is worn-out so that it is waider at the top than the bottom!
- luckily a friend found that he had a serviceable Cleveland brake
caliper and this I have now fitted, appears to work just fine! Hopefully
another problem solved!
After obtaining
a Warp-Drive protractor (mine was lost somehow!) from a guy who
had two and kindly gave me his spare one (thanks, Nico!) , I have
started playing with settings on the prop. It seems that I had set
my prop blades at 10 degrees pitch (blade angle), which gave 4800
static engine rpm. At that setting the motor has tons of power and
the prop performs smoothly it seems - but I do not want to run the
motor at that high speed since the best power/torque is found at
4400 rpm.
I had been using,
in the absence of the correct tool a dial indicator gauge (see pic
below). As it turns out that tool is quite accurate, when checked
against the Warp-Drive protractor.
Today I decided
to set the blade-angle at 19 degress - a very coarse setting - just
to see what happens. This I did and then ran the motor up to max
static ropm, which turned out to be 3850 rpm. At this speed and
pitch-setting the prop makes a god-awful noise like it is seriously
hacking at the air!
Did not try
the aircraft out on the strip to see what the acceleration is like
- but I now at least have two parameters - 10 degrees = 4800 rpm
and 19 degrees = 3850 rpm. We can work from there and a chart I
have made up to extrapolate between the two tells me that probably
a setting of about 14 degrees may do the trick. Next time at the
airfield we can now play some more to find the optimum setting.
Warp Drive instructions are to set the prop blades to achieve the
static rpm you want to see, which in turn is the rpms you will achieve
at max throttle in flight.
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