The Murphy Builders Site

Hello all,

I have to replace my rooftap plate after all.
The problem with the protection plastic can't be solved without serious
damage on the plate. It seems the plastic had to much UV-radiation in all
these years.

Does anybody know if it is usefull to make this topplate thicker then original?
Original the topplate is 0.020". A 0.025"or even a 0.032" plate does make the
top stiffer ecspecially when placing windows. (or do the windows make the
topplate stiffer?).

Any thoughts?

Kind regards,

Marc van Hulzen
PH-REB



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Marc,

From my study of the plans, the strength of the upper cabin really only
comes together after installation of the wings. Think about it: once the very
rigid wings (and their spars) are connected to the front and back carry-
throughs (in the cabin), and the wing struts are attached, the whole unit is
really 'locked' into place laterally and longitudinally. The rest of the aircraft
simply hangs off this structure.

This is why the already flimsy roof skin can accept so many large windows to
begin with. Thicker roof skins will only add unneccessary weight, not
strength. (That said, if you add the full complement of windows, a lot of that
extra weight will end up being cut out in the end!)

There's a bit of rigidity/strength that comes from the overhead channel, but
that is mostly there to keep the shape of the roof and to support the loads
from the flap mechanism (cable).

My 2 cents. Curious if others agree/disagree.

Rob

Rebel 786



On 6/11/2011 5:25 AM, Marc van Hulzen wrote to Marc van Hulzen:

-> Hello all,
->
-> I have to replace my rooftap plate after all.
-> The problem with the protection plastic can't be solved without serious
-> damage on the plate. It seems the plastic had to much UV-radiation in all
-> these years.
->
-> Does anybody know if it is usefull to make this topplate thicker then
original?
-> Original the topplate is 0.020". A 0.025"or even a 0.032" plate does make
the
-> top stiffer ecspecially when placing windows. (or do the windows make the
-> topplate stiffer?).
->
-> Any thoughts?
->
-> Kind regards,
->
-> Marc van Hulzen
-> PH-REB




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Have you tried this for removal of the UV effected protection plastic:
For a big flat piece like the roof skin, lay it on the floor -- cold concrete is
best as it will reduce evaporation. Paint it with Goof-Off and then cover with
aluminum foil. Maybe throw a piece of old plywood on top to keep it all
sandwiched down. After soaking it that way for 3-4 hours the plastic should
either slide or scrape off easily. I use a piece of 032 aluminum sheet with
rounded corners to help scrape some areas.

Not much of a point but I thought I'd throw in that lexan window material is
quite a bit heavier than .020 or 032 aluminum. (Adding windows is worth it,
but it is a weight gain.)

-Ben

On 6/12/2011 2:09 AM, schaumr wrote to Marc van Hulzen:

Marc,

From my study of the plans, the strength of the upper cabin really only
comes together after installation of the wings. Think about it: once the

very

rigid wings (and their spars) are connected to the front and back carry-
throughs (in the cabin), and the wing struts are attached, the whole unit is
really 'locked' into place laterally and longitudinally. The rest of the

aircraft

simply hangs off this structure.

This is why the already flimsy roof skin can accept so many large windows

to

begin with. Thicker roof skins will only add unneccessary weight, not
strength. (That said, if you add the full complement of windows, a lot of

that

extra weight will end up being cut out in the end!)

There's a bit of rigidity/strength that comes from the overhead channel,

but

that is mostly there to keep the shape of the roof and to support the loads
from the flap mechanism (cable).

My 2 cents. Curious if others agree/disagree.

Rob

Rebel 786



On 6/11/2011 5:25 AM, Marc van Hulzen wrote to Marc van Hulzen:

-> Hello all,
->
-> I have to replace my rooftap plate after all.
-> The problem with the protection plastic can't be solved without serious
-> damage on the plate. It seems the plastic had to much UV-radiation in

all

-> these years.
->
-> Does anybody know if it is usefull to make this topplate thicker then
original?
-> Original the topplate is 0.020". A 0.025"or even a 0.032" plate does

make

the
-> top stiffer ecspecially when placing windows. (or do the windows make

the

-> topplate stiffer?).
->
-> Any thoughts?
->
-> Kind regards,
->
-> Marc van Hulzen
-> PH-REB

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