G'morning Chuck.
Sorry I'm telling you what I'm sure you know but
I'm writing this for everyone. Please don't be offended
if it seems too obvious.
The firewall diameter is;
On the plug - 1.4375 " ( 1-7/16")
On the plane - 1.625 " ( 1-5/8" )
A radial engine design with a circular firewall
is not required for a molded balsa fuselage but
it does make things easier.
BTW .... Miles M20 / Blackburn Firebrand / Ryan fireball.
I don't think you need to worry too much
about releasing the balsa shells from the plug.
I rub the raw wood with a paraffin candle, then
melt it in with a hot air gun.
I haven't had any problems.
I put the half shells together on the plug ,
overlapping the raw edges, then cut through both.
It gives a tight seam that I tack together with CyA.
This way it stays straight.
I don't have fancy shop tools. I do have a table saw
and little band saw, drill press and belt sander.
I carve plugs from Home Depot pine or spruce using
a tiny Stanley hobby plane and LOTS of pencil lines.
The Focke-Wulf has 0-0-0 incidence angles set to
a datum line that I establish when I'm carving a plug.
Fun Fact; the seam running down the side of a real
Spitfire is the datum line.
FLAPS! ? Lots of opinions about whether a 1/2A
Stunter needs flaps. They add a huge amount of
work to a build.
I used flaps since my intention was to design a
full blown 1/2A precision aerobatics plane.
I'm glad I did but that's just my opinion.
The outer flap has 17% more area for all the reasons
that full size CLPA does. Mostly it's to counteract
yawing and hinging caused by line pull.
Seriously, the landing gear drag probably affects
the plane more than the flaps. Outside turns are
naturally tighter than inside turns.
Cheers! K.
Adventures in balsa molding.
https://stunthanger.com/smf/12-a-building/cox-spitfire-replica-build-flight-video/msg380034/#msg380034https://stunthanger.com/smf/12-a-building/top-flight-form-flight-thunderbolt-18'/