Another cracking mod from T&J
Modification to Europa
Undercarriage. T&J Ref: M15/1
This mod arises from operational
difficulties found with the ‘Europa’ standard undercarriage lever. Pilots report
that a large amount of force is required to retract the undercarriage and its locking
mechanism seems rather rudimentary. We also realised that in any G manoeuvres, as the
weight of the wheel increased, the mechanical advantage back through the lever meant that
the undercarriage lever and the three bolts attaching it to the operating mechanism were
being put under unacceptable strain. Our modifications seek to:-
- make the lever unobtrusive when not in operation
and recover the recess in the instrument panel for other instruments.
- require a force that can be supplied by a single
finger for operation
- hold up the retracted undercarriage in a way that
did not require the strain to be taken directly by the operating mechanism
- incorporate a mudguard to keep the undercarriage
bay clean.
- make it obvious that the undercarriage was up,
even to idiots like us.
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Lever mechanism as it looked on
return from the certified welder. Notice the double sided anchorage to strengthen the rose
joint connection as recommended by Francis Donaldson. The lever is attached by eight
rivets to the mounting plate. Tufnol blocks at each end provide the bearings |
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This shows our version of the
standard strengthening arm modification from ‘Europa’ along with our own
operating arm which is adjustable in length. The push rod is also adjustable in length
(lock nuts not in place) allowing the mechanism to be finally tuned to achieve the maximum
over the centre position in both directions |
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Looking from the
front of the aeroplane through the engine mounting this shows the undercarriage lever in
the fully down position. The Permagrit sander in the background is not relevant (no wonder
we couldn’t find it!). The almost over centre position of the actuating arm means
there is no tendency for the lever to jump when it is unlatched and provides huge
mechanical advantage to lock the undercarriage down. |
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This shows the actuating arm
approaching the centre of the arc and beginning to raise the undercarriage. The lever is
easy to lift as it is in almost neutral balance with the rubber bungy at this point. |
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This shows the undercarriage half
up. At this point the lever requires its greatest force to operate but the lever is in the
most advantageous position to do that. i.e. straight up. Notice the hook on top of
the mudguard appearing in the bottom of the picture. |
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This shows the lever three quarters
of the way up. The geometry of the mechanism is arranged so that the hook on top of the
mudguard is coming up to exactly mesh with the bar which will finally hold it. At this
point the lever is becoming easier to press as the mechanical advantage on the lever is
greater at this point as it approaches the over centre position. |
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Shows the undercarriage fully
retracted but the lever still has a centimeter to go. Mechanical advantage is highest at
this point as it goes over centre making the lever very easy to push home. |
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Shows the undercarriage fully
retracted. By now the lever is over the centre. The bar is well hooked on to the mudguard
and the whole weight of the wheel is taken by this bar attached to the latched lever and
connected directly to the undercarriage fork via two mudguard struts positioned directly
in line of the tension force taken. Notice the lever adjustment mechanism in the right
foreground. This mechanism, along with the adjustable length push rod, allows minute
adjustment to ensure that the ‘over the center’ mechanism works exactly for both
fully up and fully down positions. Once adjustments are complete it is locked off
permanently. |
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This shows the Hook from underneath
looking up into the U/C bay. Note the alignment of the 'spokes' so that they are in
tension when the wheel becomes heavier in G situations. Using the standard kit system this
force is sent back through the leaver mechanism giving rise to huge forces at the leaver. |
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Shows the undercarriage operating
lever in the cockpit embedded into the side of the tunnel. When the lever is approaching
the either fully up or fully down positions a cam latch tab pops up and only falls back
when the lever is fully flush with the tunnel. It only requires a small finger push to
rotate the cam latch flush with the tunnel and thereby lock the operating lever. It is
easy to feel if either the operating lever or the cam latch is not flush with the tunnel
and confirm that it is locked properly. Notice the indentations for a finger to lift the
locking tab to release it before operation of the lever. |
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This picture shows a close up of
the plywood prototype that we made to demonstrate the action of the locking cam latch. It
is showing the lever approaching the locking position. |
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This picture shows it half way
through the latching motion with both the lever and the latch sticking up above the
surface of the tunnel. Note how the lever kicks up the latch making it impossible to leave
it "almost" locked.
|
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This picture shows the lever in the
final positively latched position. Note how both the top surface of the lever and the
latch are flush with the surface of the tunnel thereby providing an easy way to feel if
the lever is locked properly. Note how the cam of the latch positively engages in the pin
on the lever making it impossible for the lever to be raised. The top pin provides the
identical locking action when the lever is swung over to an identical, mirror image, cam
latch at the other end of its travel. In the actual version the open ends of the two pins
are joined with a plate to stop the lever being pulled out sideways. |
Along with the repositioning of the brake lever
and throttle lever, this will allow the top of the tunnel to be used as a map table. Of
course it will look a whole lot better when it is embedded in grey carpet. Yes that’s
real mahogany on the handle. Whehey!
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MI5-1-0901-T&J
