Growing a Grumman - Part 12


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?


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.


More pics! Click the image for larger (1024x768) view - I have provided the large size images as I know you guys want to see DETAILS!

>>> Next - Part 13


General view of the (almost) complete airplane.
General view of the (almost) complete airplane.
General view of the (almost) complete airplane.
General view of the (almost) complete airplane with Trevor, who has been my engine 'guru' and general consultant on this project
General view of the (almost) complete airplane
Wingtip Lights - working - only now do I discover that regulations require separate switches for each side! WTF?
The official Warp-Drive protractor - claims to measure blade angle to 0.25 of a degree!
Close up.
My cheapo dial gauge - turns out that this is quite accurate for setting blade-angle! Just levelling the blade in this shot.