=EF=BB
=EF=BBFwiw, 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, causi
ng 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 pivo
t tube. Bent due to having been side loaded when the gear was in the down po
sition, an angle where that tube is totally unbraced/supported. I suspect ma
ny 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). W
hen 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 tes
t. I find that with this tension my gear takes minimal effort over its entir
e swing range in flight.
Cheers,
PeteZ
> On Dec 3, 2022, at 9:55 AM, Area-51 <goldsteinindustrial@gmail.com> wrote:
>
@gmail.com>
>
> With the 3D aero model now complete its onto a new chapter as mechanical a
nd ancillaries come into the fore; and fruit has arrived straight off the ge
t go.
>
> After reading and hearing about so many issues regarding the mono retract t
he first thing that has been focused upon is the undercarriage. Having the m
odel available now provides the ability to try things out and get answers al
most instantly. So that's exactly what happened as soon as the remaining com
ponents of the assembly were drafted and imported into the picture today.
>
> The first goto was undercarriage action; why does it jam closed on some ai
rcraft? Why is it so difficult to retract when throwing that final bit of th
e lever forward? It was interesting what showed up! An initial earlier solut
ion drafted last year was quickly thrown in the bin but it was this study th
at revealed where the issue actually now resided.
>
> Having the 3D CAD components assembled allowed a study of the geometry of t
he retractable assembly, and sure enough it was so very possible to jam the u
ndercarriage in the retracted position; and was remarkably easy to affect; l
iterally 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 po
ssible is if one of the mechanical arms has moved passed a point to rest wit
hin a 90deg quadrant. So that's where the focus went to and thats what was q
uickly flushed out... the rubber block assembly had crossed over and was res
ting at 80deg to the swing of its upstream link. And there it was, with the o
nly thing preventing jamming in situ now being the weight of the main wheel o
vercoming the tension of the bungee spring... Its the very same reason causi
ng that last bit of retract throw on the cockpit lever being difficult; and p
erhaps the very same reason some owners simply tighten up the bungee spring t
o get things to park up. (The attached geometry image shows the factory posi
tioning at the blue circles, the magenta line being the 90deg quadrant marke
r 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 respectiv
e 90deg quadrant? worth a go; what's required? Rotate a single pivot point 1
0deg and revision of LG02A... So that's what got drafted out and presto, pro
blem instantly gone away to the graveyard of great ideas... Amazing!!! Took a
ll of five minutes to solve on the 2D and another 10 to draft up a new 3D fu
nctional component and check for clashing and binding.
>
> With pin LG04's position at LG02A now rotated 10deg on the spring blocks a
rc it is now geometrically impossible to jam the undercarriage; even if the m
ain wheel somehow finds its way up through the tunnel ceiling to the instrum
ent panel facia; which it now can do if the lever is moved beyond its gated t
ravel.
>
> So that's it, MOD-XX... Done!
>
> Fitting of LG02A-XX and reboring of LG02 for LG04's amended position, bein
g 150mm horizontal and 7mm vertical from the datum centre bore of LG03.
>
> The other attached images show the difference between LG02A and LG02A-XX; t
he position of the bungee pin on LG02-XX has also been raised a few mm for b
etter operational clearance.
>
> So can somebody please explain what the bungee spring actually does??? I c
annot find or identify a practical mechanical reason for it at all other tha
n to overcome the existing geometry error; unless this perceived error is in
tentional?
>
> 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_43
7.jpeg
> http://forums.matronics.com//files/5c1a69af_790e_4a51_a3bd_8506e15c35f6_34
3.jpeg
> http://forums.matronics.com//files/e8371182_c043_4319_a5aa_c216cd42e8bb_15
7.jpeg
> http://forums.matronics.com//files/f6e8ca6f_6a3a_43da_8d31_fb5ae6e8e277_18
9.jpeg
> http://forums.matronics.com//files/0ef69eca_b797_45ac_828c_7cdc5f70dafb_18
9.jpeg
>
>
>
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