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<< Lancair Builders' Mail List >>
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Following up on the recent discussion about the pin-locked doors used on
the ES and early LIVs, I ran an experiment yesterday with a couple of
other Lancair enthusiasts, John Forker and Peter Frost. My door has
been extensively reinforced with unidirectional carbon to improve
stiffness, but I heard reports that the bottom of the door in particular
was pushed out into the air stream when the door seal was pressurized.
So here is the experiment which requires a bit of mental visualization.
It consisted of two steps.
1) We oriented the door so the lower door edge was parallel to the floor
meaning the hinged end was held up in the air by John.
2) Wooden blocks were placed under the forward and aft ends of the door
directly under the door frame horizontal cross member that runs parallel
to the bottom edge of the door.
3) I stood on the middle of the door frame cross member (200 pounds).
This put the lower edge of the door frame in simple bending, center
loaded and end supported.
4) Peter measured deflection before and after, and it was about 0.030
inches (remember, reinforced with lots of uni-carbon).
5) Then we repeated the test with the blocks under the location of the
plastic blocks in the door that guide the pins, and I stood on the door
again. This time the deflection at the bottom center of the door edge
is the sum of the bending deflection measured above (0.030") plus the
cantilever bending of the lower portion of the door as it is pushed
("bent") in the "outward" direction by the inclined force of the door
seal acting against the angled door sill. Said another way, in this
second test, we added bending to the lower vertical portions of the door
frame in the region of the pins. Deflection measured: about 0.200" This
is non-negligible. Incidentally, the door seal is about 1/2 inch wide,
30 inches long along the bottom of the door and pressurized to 20 psi
with the electric pump and pressure switch. Resulting load is 300 psi
at an angle perpendicular to the surface of the door sill (mostly
upward, but with an outward component) so that my 200 load test is not
far wrong.
What this suggests is that the frame is greatly weakened with regard to
bending outward in the vicinity of the door pins, and this is no
surprise since the access panels above the pin blocks effectively remove
the top section of the box beam greatly reducing the stiffness of the
door frame in this region. (We tested with access panels off.)
Peter asked the key question: why have the access panel? In the
pressurized aircraft, the panels are needed to inspect and service the
latching mechanism. In the non-P and ES aircraft, there is little to
inspect (plastic blocks) and they can be inspected by enlarging the hole
on the interior of the door frame through which the pin traverses.
So it seems that the fix is to sand the access door and its seating
surface, bond in with Hysol, and then come over the top with a length
(8-10 inches?) of Unicarbon full width along the top of the frame. I
would think about 6 layers of UNI would do the job. I will do so
shortly (after John and I finish building his long range tank box) and
report on the results.
Fred
LML website: http://www.olsusa.com/Users/Mkaye/maillist.html
LML Builders' Bookstore: http://www.buildersbooks.com/lancair
Please send your photos and drawings to marvkaye@olsusa.com.
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