A further demonstration that the monowheel doesn't comply with CS-VLA (in
respect
of side loads on the main under carriage).
Duncan McF.
> On 03 December 2022 at 16:44 Pete <peterz@zutrasoft.com
> mailto:peterz@zutrasoft.com > wrote:
>
>
>
>
>
> Fwiw, my experience:
>
> 1- difficulty in getting the gear into to and out of the up-gate
> (regardless
of bungy tension) was due to the flap rod adjustment being too short, causing
the flaps to top-out, restricting the gear up travel.
>
> 2- general binding of the swing-arm was due to a bent gear/engine frame
> pivot
tube. Bent due to having been side loaded when the gear was in the down
position,
an angle where that tube is totally unbraced/supported. I suspect many
frames in the field are bent. The builder of my bird had actually shimmed the
arm bushing to accommodate and reduce the binding (band aid solution). When
repairing my frame, i added a truss to the frame at the correct angle to support
the tube and prevent any future bending.
>
> 3- the bungee is simply to assist the pilot in raising the gear. I
> tensioned
mine such that it pulls the gear up about 60% when doing the gear swing test.
I find that with this tension my gear takes minimal effort over its entire
swing range in flight.
>
> Cheers,
> PeteZ
>
>
>
>
>
>
> > > On Dec 3, 2022, at 9:55 AM, Area-51
> <goldsteinindustrial@gmail.com mailto:goldsteinindustrial@gmail.com > wrote:
> >
> >
> > 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
> >
> >
> >
> >
> > Attachments:
> >
> >
> > http://forums.matronics.com//files/0c2811c4_5687_479e_8d89_ed360c7f4c9c_437.jpeg
> >
> > http://forums.matronics.com//files/5c1a69af_790e_4a51_a3bd_8506e15c35f6_343.jpeg
> >
> > http://forums.matronics.com//files/e8371182_c043_4319_a5aa_c216cd42e8bb_157.jpeg
> >
> > http://forums.matronics.com//files/f6e8ca6f_6a3a_43da_8d31_fb5ae6e8e277_189.jpeg
> >
> > http://forums.matronics.com//files/0ef69eca_b797_45ac_828c_7cdc5f70dafb_189.jpeg
> >
> > > ===================================
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