Step 11.1, Canopy jettison mechanism

Imagine you're flying along and suddenly everything has just gone to hell.  You have no choice at all, but to leave the aircraft in midair.  In an airplane with a sliding canopy, one just slides it open and out you go.  Alas, it's not so easy in a tip up canopied airplane when the canopy opens against the prevailing wind.  To overcome this obvious design oversight, Van's has thoughtfully provided a canopy release mechanism. Under dire circumstances the canopy may be released from its hinges via the canopy release handle.  The canopy can then be pushed upward and free of the aircraft.

The utility of the canopy release is a ready topic of discussion on-line.  The two main arguments being, one, that it is unlikely that one would be wearing a parachute in the first place, and two, that the release mechanism may not work as designed, especially since its never been tested in flight.  Either way, I think it's still a nice thing to have.  I look at it as a kind of Jesus handle -- pull the handle under emergency circumstances and you'll be meeting Jesus in a jiffy.

But there is another use for the canopy release mechanism, and that is, if you want to remove the canopy for maintenance.  With out the canopy in the way, the interior of the aircraft is much easier to access.  So for this reason I have decided to install the canopy release hardware.

To begin there are a bunch of UHMW (Ultra High Molecular Weight) blocks of polyethylene plastic.  This is the same or very similar to the kind of plastic used for kitchen cutting boards.  It offers excellent durability and very low friction which makes it ideal for use as hinge pin guides and bell crank bearings.

The basic mechanism is a handle protruding through the instrument panel that pulls on a lever attached to a bell crank.  The bell crank turns the action 90 degrees such that when the handle is activated the bell crank pull inward on connecting rods which in turn pull the pins from the canopy hinges.  In the photo below, the lever and connecting rods are visible -- the bell crank assembly is upside down.

And here is the bell crank installed showing the connecting rods withdrawn.

A wider view looking backward towards the back of the instrument panel.  The canopy hinges on the left and right sans canopy. The lever can be seen at center, left of forward deck central rib.  The release handle, not shown, connects to the lever and continues rearward through the instrument panel.

I'll leave the attachment of the handle until after the instrument panel is complete.  So for now, the canopy jettison mechanism is finished.  And so is this post.