Growing a Grumman - Part 5


Since Christmas 2007, when Part 4 was written, we have experienced all kinds of delays - from the annual holiday shutdown of the entire nation, it seems, to the machinist taking his own sweet time, once he had returned from vacation in January! The upshot of this was that I received the last machined parts, these being the mainshaft, with taper and key way, plus the prop hub and flange only in early March!!! I would recommend anyone tackling such a project to actually own a lathe and a milling machine - that way you control the pace of events!

So, with these final bits in hand the past 10 days have been spent fitting the PSRU components together and mounting to the engine, in the hopes of actually spinning the darn thing - however first I had to get a friend who has a small lathe to machine up some spacers, which fit fore and aft of the front and rear bearings to position the driven sprocket correctly and in line with the driver sprocket. Once this was done - hey presto, it all turns. One thing yet to make is the adjuster mechanism to raise and lower the upper assembly containing the driven sprocket in order to properly tighten the belt. Doing this manually, by simply pulling the upper assembly upwards until the belt will tighten no more, at least allowed for test running - and I am happy to report that at all engine rpm up to 4000 everything seems to run just fine - quiet - true and without any flapping of the belt. Happy, happy, happy!

We are still not done though, as it seems we have a slight miscalculation in the spacer thicknesses so that the belt is running on about 95% of the driven sprocket width - but that is easily rectified with new spacers, which are quick to make.

Haven't run with the prop on - and won't until I can get the aircraft out of the garage - I think it would probably about blow the tiles off the roof - but we will give that a try - outside - soon!

Meanwhile the nosebowl is undergoing modification to fill the gap between the original nosebowl and the newly extended prop flange and spinner position. This involves urethane foam blocks, glue and a great deal of mess - and we haven't even started on the fibreglassing yet!


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 6


Cowlings closed - with original Grumman nosebowl after initial cutting to clear the PSRU.
Radiator catch tank - currently made of (heavy) copper - will be replaced with aluminium tank.
Radiator filler access.
Nosebowl radically chopped - entire front will be rebuilt to new length and shape, using original fasteners only.
Catch tank moved to pax side of aircraft - too much other stuff (fuel pumps and piping) in it's original location on the pilot side. Foam slab sanded roughly to shape for clearance blister.
Urethane foam base glued and bolted in and gaps filled with insulation foam from aerosol can - awful stuff to work with as it sticks to everything in site and takes ages to fully cure!
Forming the blister for the catch tank. Since the tank has to at the same height, or higher than the radiator filler neck, there is no alternative but to make a blister.
Next to be mounted is the Warp Drive 72 in prop - can't wait!
Ready to slap some more foam pieces on - I bought a large slab of foam in 40 mm thickness for about R170 ($20) from a manufacturer near me. The pink on the left of the upper cowl is the release agent drying before getting fibreglass laminations for blister.
Ugly - ugly! and messy!
Foam pieces glued on - I started out using quickset epoxy two-part, but quickly changed to a hot glue gun, as continually mixing small amounts of the epoxy is a pain - and it is vastly expensive stuff!
Finally together - Prop flange is Lycoming SAE2 pattern.
Now we have started sculpting the foam to shape - easy to do with a saw blade and coarse (production 40 grit) sandpaper.
The white stuff filling the gaps is "Polyfilla" - used for patching cracks and holes in your house walls - gypsum powder basically - mix it with water to the consistency you desire and away you go - sands nice and smooth. Takes a while to set though
Starting to get the shape, still lots of filling and patching needed! Seems a pity to have to make holes for cooling!
Starting to get an idea of how it will look.