Growing a Grumman - Part 11


After several weeks of cold and rain (not usual in these parts) I managed to get to the airfield for the first time in a while! - no fun working in a dank, cold hangar and not a soul on the airfield!

Finished the riveting of the nose scoop for the underbelly rad housing and mounted this up. It is detachable with a dozen screws for any future maintenance.

Test running the motor now revealed a new problem - the thing would not run cleanly for more than a few minutes. Much pondering and checking left me no option but to remove the carbs and strip them down - to find one carb jet clogged with muck! Cleaned this out, then tried another test run - seemed okay so jumped in and set off for the runway for a high speed run to run a final check of cooling and brakes. Once again the motor sputtered to a halt before even reaching the holding point.

This time there was no sign of clogged jets nor was there any dirt in the tank - but I noticed that my two Facet pumps were only supplying a low volume of fuel to the carb inlet. After much messing about without any success in getting the pumps to actually pump adequately I gave up for the day and resolved to buy a new pump as I have not been happy with the cube Facets of late - just a nagging feeling but I think that feeling was right.

Some days later I picked up a new-design Facet - this one, model 60106 has a rounded composite body and is supposed to definitely deliver 120 litres per hour - better yet it needs no head of fuel to the inlet, as it has the ability to suck! Much better!

Then of course I found that I needed some fittings etc to link it up, so final installation, albeit in a temporary position, had to wait - but eventually, yesterday 2010-05-16 all was hooked up and testing showed that it was capable of delivering 120 litres per hour - success. And after a thorough test the engine keeps on running strong!

One thing though - apart from the fact that the cube Facet pumps had apparently packed up, perhaps blocked up by the muck which I found at the carbs, and evidenced by a definite change in the sound they make when pumping and the lack of volume pumped, some of the piping connecting those pumps to the carb was of 6 mm diameter - and the inlet pipes to the carb float bowl are 6mm as well. Changing those delivery pipes, but not the inlet pipes which are part of the carburettor has been part of the success I think - testing shows that the pump which will deliver 120 lph through a 8mm pipe, will only deliver 60 lph though a 6 mm pipe - so a 2mm (33.333%) increase in pipe diameter results in a doubling of the flow - hmmm!

So for our next trick we need to remove the cube Facets from the firewall - a two man job unfortunately as someone has to be each side of the firewall! - and mount our new Facet (pictured right) in place, along with the second backup Facet I still need to buy. hopefully we can get that done sometime this week, work and weather permitting!

I am thinking that the last pump shown here - almost identical to the Bendix pumps fitted as original equipment on many light aircraft will be the way to go however.

However, we now can say that our engine, cooling and sytems testing phase is complete! I reckon I have identified and hopefully rectified all the 'problem' areas - and it has been quite a lengthy task - better to do all this on the ground though, no matter how long it takes!

Next we will take the wing, still hanging in the rafters of my garage at home, to the airport, to join it's mate already at the hangar - that could happen as early as this week too, and while I have a helper we better get both those wings mounted on to the carry through spar stubs.

Hey! - a new note has appeared on my list of things to do - "Take wing to airfield" - proof that we have made progress!


Over the past weekend we got the wing to the airfield and fitted both wings - still some connecting of piping and wiing to do and we will complete that next weekend with any luck - but I did manage to get the left wing fuel piping connected up - so could pour some fuel into that wing as a test of the tank seals, which are now several years old - I guess at least 6 years has gone by since I installed new seals and the worry was that these would be no good by now having been dry for those years! It seems though that all may be well, as after 1 hour with fuel in the tank nothing appeared to be leaking out!


I disassembled the Facet pumps - there was muck inside them! After cleaning they appear to work okay, at least to judge by the fact that they make plenty noise once again. Once I have tested them for fuel flow rate I expect I will reinstall them, along with the new Facet - thus giving me three pumps - sufficient redundancy I think. This time however we will be adding at least two upstream fuel filters!


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 12


Et Voila! Wings are installed! Almost.
How the wings slide on to the carry-through spar - a tube within a tube - plus the aux tank tube arangement.
Facet Cube Pump stripped
Facet Cube Pump stripped
Facet Cube
Had a visit by the SAAF Silver Falcons with their Pilatus PC7s - nice airshow!
Silver Falcons practicing for their later display at Rand FAGM