With the 3D aero model now complete its onto a new chapter as mechanical and
ancillaries
come into the fore; and fruit has arrived straight off the get go.
After reading and hearing about so many issues regarding the mono retract the
first
thing that has been focused upon is the undercarriage. Having the model
available
now provides the ability to try things out and get answers almost instantly.
So that's exactly what happened as soon as the remaining components of
the assembly were drafted and imported into the picture today.
The first goto was undercarriage action; why does it jam closed on some
aircraft?
Why is it so difficult to retract when throwing that final bit of the lever
forward? It was interesting what showed up! An initial earlier solution drafted
last year was quickly thrown in the bin but it was this study that revealed
where the issue actually now resided.
Having the 3D CAD components assembled allowed a study of the geometry of the
retractable
assembly, and sure enough it was so very possible to jam the undercarriage
in the retracted position; and was remarkably easy to affect; literally
just a mm or two beyond the gate stop on the console did it and the wheel was
stuck fast in the tunnel void.
It was instantly apparent that the only way this could geometrically be possible
is if one of the mechanical arms has moved passed a point to rest within a 90deg
quadrant. So that's where the focus went to and thats what was quickly flushed
out... the rubber block assembly had crossed over and was resting at 80deg
to the swing of its upstream link. And there it was, with the only thing
preventing
jamming in situ now being the weight of the main wheel overcoming the
tension of the bungee spring... Its the very same reason causing that last bit
of retract throw on the cockpit lever being difficult; and perhaps the very
same reason some owners simply tighten up the bungee spring to get things to
park
up. (The attached geometry image shows the factory positioning at the blue
circles, the magenta line being the 90deg quadrant marker relative to pin LG04's
position, the blue line represents the rubber block assembly).
So gee what to do? ?? Well what if things get realigned to their respective
90deg
quadrant? worth a go; what's required? Rotate a single pivot point 10deg and
revision of LG02A... So that's what got drafted out and presto, problem
instantly
gone away to the graveyard of great ideas... Amazing!!! Took all of five
minutes to solve on the 2D and another 10 to draft up a new 3D functional
component
and check for clashing and binding.
With pin LG04's position at LG02A now rotated 10deg on the spring blocks arc it
is now geometrically impossible to jam the undercarriage; even if the main wheel
somehow finds its way up through the tunnel ceiling to the instrument panel
facia; which it now can do if the lever is moved beyond its gated travel.
So that's it, MOD-XX... Done!
Fitting of LG02A-XX and reboring of LG02 for LG04's amended position, being
150mm
horizontal and 7mm vertical from the datum centre bore of LG03.
The other attached images show the difference between LG02A and LG02A-XX; the
position
of the bungee pin on LG02-XX has also been raised a few mm for better
operational clearance.
So can somebody please explain what the bungee spring actually does??? I cannot
find or identify a practical mechanical reason for it at all other than to
overcome
the existing geometry error; unless this perceived error is intentional?
Thanks for reading everything; well done!
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=509435#509435
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