Hints and Tips -Bowed foam blocks
Regular readers might remember I had a problem with my leading edges. The
internal stresses in the foam resulted in a slight bow to the centre and tip L.E
cores - not by much - perhaps 1/8th inch but enough to be noticable when you
look along the L.E.
Come layup time, extra care just needs to be taken to ensure the cores are kept
straight - although I found that the nature of the bi-axial cloth bending over
the L.E tends to naturally straighten the cores anyway. Just keep checking with
a nice long straight edge.
The trailing edges were not too bad - I guess they are that much thicker. On the
port side it all looked straight as it was being put together but now I can
stretch a thread of cotton between the root core/flap T.E and the tip T.E, I
have found that the outrigger rib is actually a little too high (i.e has little
more washout than it should) and that the flap/aileron - as you sight along the
T.E is 'kinked' by about 1/8th inch.
Anybody else willing to own up to this?
I don't know what the tolerance is - and I doubt if it will have any effect on
the flying characteristics - but for the starboard wing I am using a simple
method of ensuring that the trailing edges do remain straight as you progress
through the bottom T.E skin and flap/aileron closeout layups which I would like
to share with you. This hopefully will ensure that all your wings are 100
%straight!
The instructions say that as you bond the T.E cores to the spar that you should
ensure straightness 'by sighting along it'. I think that because the T.E cores
still have their 'funny foam joggles' attached at this stage - and in my case
particularly on the starboard wing they were slightly bowed too - that you
should use a straight edge of some form.
I went to my local lumber strore and got then to cut me some 2.5 inch wide
strips of 1/4 inch hardboard (or better still plywood). These were 6 foot long.
Getting them to cut them on their circular saw ensured a nice straight edge.
In the center of one I drill a 1/16 inch hole down the centerline every 6 to 8
inches, in the other strip the holes were offset from one side by about 1/2
inch.
Using the slot which will become the flap trailing edge as a sight guide, I
fixed the first straight edge using 1.5 inch long finishing nails into the 'foam
joggles' which will eventually get cut off. The tip T.E strip I shortened
slightly, then fixed it to the 'foam joggle' ensuring it was lined up with the
trailing edge too.
You will find that they certainly aid your sighting of the T.E's and help keep
everything straight as you do your layups.
By the time you do your top skin layup the trailing edge will be stiff enough
not to worry anymore - but just keep an eye on the bottom skin aileron close-out
(the one not supported) it is quite easy to bend it out of shape during the
layup process.
Hope this helps anyone who is about to start on their wings. (The leading edge
layups took me just over 6 hours to do - thank goodness for slow setting
hardener - and bi-axial cloth)!
Regards
Martin Tuck
#152
Wichita, Kansas
|