Bob Fairall wrote:
> I have heard of and seen a number of roof entry fresh air systems
> which I gather are very effective, but I recall reading somewhere
> that cutting the roof can compromise the strength of the cockpit
> module.
Well, I guess we all know how to compensate for the loss of strength
caused by cutting a small hole in 3mm foam with about one layer of bid
on each side. ;-) The middle of the "bar" isn't anything more than that,
so if it is structural at all, it is easy to compensate.
I made a roof vent, besides ultimate ventilators on the fuselage sides,
and I can tell you that on the ground at idle these roof vents already
really blow. With anything more than idle I had to close them, as they
produced so much air that it wasn't comfortable anymore.
The advantage over a tail solution is that it is lighter in weight, the
"duct" is considerably shorter so there is less friction hence more air,
and, last but not least, it is not likely that anything from the exhaust
makes it to the roof top (while I wouldn't guarantee that the tail won't
receive some of the exhaust fumes).
My roof vent consists of a small retractable scoop, just 5 cm wide, and
opens up about 1,5 cm. It feeds two eyeball vents in the roof panel.
I followed the procedure explained in the manual for various other
openings: Make a splash mold of the intended roof area, cut the opening,
take away some of the skin on the inside, take out some of the foam
core, and connect the inner skin to the outer skin with flox and bid,
creating a flange at the same time. I made the flange somewhat lower, so
that there was room to make a waterproof seal.
The construction by itself is stronger than the piece taken away.
Frans
|