Growing a Grumman - Part 7


Hoo Boy! - does time fly when you are having fun? Here we are many months after moving the aircraft to the airfield, and we are still not flying - BUT we have taxied the machine at speed and found a number of reasons to stop doing that!

Reason 1. Such as brake calipers which are shot - just too old, corroded etc to bother repairing, so looking for a new set - have you seen the price of these lately? I thought about resleeving the calipers, but am not so keen on that, as the Grumman with no steerable nosewheel really relies on brakes for all maneouvring at taxi speeds and at any speed up to about 30 mph - a brake going out can leave you helpless to steer or stop safely, so this could be a disaster looking for a place to occur!

Have investigated motorbike calipers, which in terms of quality of manufacture leave Cleveland calipers looking like what they are - ancient design and bad quality rubbish! Motorbike calipers will hopefully do the trick at a fraction of the cost - but again there will be some modification and adaptation to do! But these will give me reliable braking at least.

Reason 2. The expected problems with engine cooling - we now know after many tests, that the Jess Myers(BAP) solution whereby the rad is placed transversely behind the motor and in front of the firewall will not work on the Grumman as there is simply insufficient space to allow for adequate smooth airflow through the rad fins -this showed up as a problem immediately we started taxiing and could not acheive stable engine temps - after 2 taxi runs the Chev was boiling every time! The airflow was blocked by the lack of adequate space between rad and firewall!

So the next task was to mount the rad under the belly as there is no other place within the cowling where it can fit. After crudely mounting it to the belly and enclosing it in cardboard to simulate a scoop we embarked on many ground runs (static) in order to see whether the motor could be adequately cooled without any forward motion, relying on propwash only.

Eventually after a bit of tweaking to the "scoop" I managed to make repeated runs of 25 minutes at idle rpm (1000rpm) then at 1500 rpm and finally at 2500 rpm. In each case the motor maintained a gauge indicated temp of approx 80 - 90 deg C - and since previous tests showed that the gauge over-reads by 20 deg C, that is very good!

The rad itself is all wrong for this mounting position however as it was designed for elsewhere! So that has to be modified again for under-belly mounting - the top tank and filler, the inlet/outlet pipes and the mounting flanges will need changing.

Currently I am working on building a sturdy but light aluminium frame to hold the rad in the correct attitude under the belly. Once the rad is so mounted then I will need to "clothe" the assembly in a proper scoop with the necessary intake and outlet ducts, for which I will probably use fibreglass lay-up.


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 8


No need for wings just yet! We are far from ready to defy gravity!
In these pictures above, the radiator is mounted in it's original location behind the motor with the aluminium sheet ducting still in place - nice try but no cigar!
Head on view.
The battery is now located behind the transverse beam (the one with the holes in it) and hanging from that beam in it's own carrier.
Basic panel - much more to come!

After discovering that the original positioning of the rad was not going to work, here is an early test of rad cooling flow with rad just hanging out in the breeze under the belly - worked reasonably well!