Rob Schmitt wrote:

>> I used one sheet of aluminum, fairly thin gage as I recall (T6061 0.016 gage 
>> 3’x3’ sheet worked for me). It spans the back and front spar. It does bend 
>> down over the front of the front spar and I used a “bar” of aluminum 
>> probably 1/8” thick by 1” to secure it (Screws) to the front spar. Two bars 
>> in front, one for the pilot, one for the copilot. The sheet is “V - notched” 
>> for the center stick opening so that it is continuous at the back of the 
>> seat but not the front. At the back, the aluminum is also bent down over the 
>> spar and a “bar” of aluminum is used as well screwed to the rear spar.<<

Just to clarify this, I'm sure Rob doesn't mean to simply cut a v-notch
with a pair of tin snips....far better to make the vertex by drilling a
hole, then cutting into the hole tangentially with the snips so there's
not an actual notch or the stress riser that it would create.  Aluminum
is not so great at fatigue, so giving it a head start with a real notch
(which is likely to become the origin of a crack) is not preferable. 
Deburring those critical areas is also recommended.  A deburring tool is
pretty cheap from Aircraft Spruce, and you'll use it many times, once
you see how well it works, and understand the concept of why you should
remove burrs (which comes after the application of a few Band-Aids, or
have seen fatigue failures in critical items).

I have to admit that the canvas seat in N891JF works pretty well, and
it's been in place since 1990.  Whether canvas or aluminum, it's worth
inspecting the thing for tears or other damage every year during the
condition inspection.  Failure at a bad time could ruin your whole

Mark Langford, Huntsville, AL
ML "at"

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