Hi Sam (in Western Aus.) and others.
With the F3B WC just a week or two away I thought it might be topical
to comment on the fridge motor idea based on some personal
experiences.
The model I flew at the 1993 F3B WC in Israel (the Proto) had a vacuum
moulded wing and stabs. The vacuum pump I used then was a standard
fridge compressor with a modified car vacuum advance unit as the
vacuum switch. I currently have a total of three vacuum pumps in my
workshop but possibly out of a resistance to change or nostalgia I
still use the fridge compressor :-)
The Sangoma is a South African all CNC moulded glider designed (using
a vortex lattice code and some other aeronautical software I have
lying around) for the 1999 WC. I have used the same fridge pump to
vacuum the one piece wing skins without any problems. The wing is
manufactured as a single unit of 3.1 m span. (One of the benefits of
having the WC in your own country is that transporting such a wing is
no problem ;-)
The vacuum the fridge compressor can pull depends on your altitude
above sea level but I am getting about 0.8 bar vacuum which is
adequate for most applications. Pretoria is approximately 5000 feet
above sea level.
Some oil slowly leaves the unit as a fine mist and the odd drops from
the outlet. Someone has previously posted that if you place a long
tube leading upwards from the outlet the oil will condense onto the
sides of the tube and run back again. I haven't tried that but it
certainly sounds like it should work well.
We have also used aquarium pumps as vacuum pumps very successfully and
cheaply. With the smaller units you have to make even more certain
that you have no leaks in the vacuum bag.
Hope that helps.
John Monk
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