the geometry of being not far off a straight line. I also had to use a
much shorter stop bolt but I have very little over centering in order to
keep the retracted wheel as high as I could. I would have liked to put a
overcenter spring in there in case of pressure loss. I have no
confidence that I have enough over center to keep the gear down if
bouncing down a runway without hydraulic pressure. Didn't see an easy
way to do that though. Nor did I think that more centering would ease my
concern. Any amount of overcentering will at least keep the gear from
folding when parked. Hopefully my pressure relief valve will prevent any
blown hydraulic lines.
Ducky is on her floats as of yesterday. Two sections of scaffolding 10'
high and 11' apart (so floats could slide between them) supported a beam
(two spruce 2x12"s) to lift her by the rear engine mount points. Strut
lengths as per the manual gave 3.5* throat (to fuselage bottom which is
same as the top of the door frame). However I shortened the rear strut
streamlined tube 7/8" and used the second from shortest holes in the top
and bottom adjustable end fittings. Still 3.5* but that gave me one hole
at the top for increasing throat and one hole at the bottom so that the
cross brace tang does not hit the bottom of the strut. With 3/8" hole
spacing in the fittings, that gives about 0.4* change per hole. 3.5* was
my desired throat so that worked out rather well. Note that I have the
old float mounts which are a bit different than the new ones.
As has been mentioned in the past, don't drill more than one hole for
the top forward strut fitting ahead of time because the machined fitting
angle is for 0* throat and you will want to rotate the fitting in the
strut the same amount as your desired throat angle.
A $40. two foot long digital level saved many hours of futzing around.
Removed landing gear weight was 62 lb for JDM wheels, die spring struts,
and fairings. Significant wear was found in the drag link at the lower
bolt hole and also in the bolt holes of the aluminum gussets where the
bottom of die spring strut bolts on. In both cases I attribute the wear
to the axles twisting the main strut (the toe vibrating back and forth).
I was surprised at how little force it takes to twist the main strut
back and forth. Initial touch down and brake application took their toll
after 600 landings. Wayne's die springs and Mohr's bushings were a good
investment.
Ken
119R
Wayne G. O'Shea wrote:
Remember when building your floats fellas, that the main gear retract/extend
mechanism is supposed to be pushed "over centre" just before it hits that
stop bolt to lock "gear down". The manual calls out an AN -12A bolt or
something along that line for the stop bolt and the actual bolt length that
is needed is generally a -5 or -6 to get the throw set properly. You need
to play with the assembly while unhooked from the cylinder clevis and get
the stop bolt set so that the mechanism is definitely going over centre. It
doesn't need to go any great distance over centre.. just enough to guarantee
that on landing that the weight tries to push it even more over centre
against the stop bolt. If you aren't over centre then the weight is going to
retract the hydraulic cylinder.
I am currently, trying to install, a set of floats that where dropped off
here for install. Unfortuately, I'm not actually installing them at this
point, as I am spending hours correcting building errors that this
unfortuate customer shouldn't be paying for twice... as the builder claims
to have done 5 sets of these floats. Maybe I now know why people have had
problems with their hydraulic lines blowing apart... they aren't setting up
the main gear to go over centre and lock, so when they land the entire
landing force is then transmitted into the hydraulic system and that shock
pressure is probably into the thousands of psi!
Wayne
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