My Hatband replica build

[Jmk89]

I got on with the tail feathers today.

Fin

The fin is made in one piece, even though it looks unlike other fins on John's models. His typical fin is a rhombus on top and another as an under fin, with the whole thing made in one piece and attached through the fuselage.  The one piece construction does make the fin a bit more structurally resilient.

However, the photos of Hatband seem to have a perfectly square upper fin, and a rhombus under fin, with the latter set a bit further back.  However, I decided not to abandon the one piece construction method.  So the TE of the upper fin is the spar for the under fin. and there are solid parts that match the lines of the upper and lower longerons.  I think I will use 1/16" to sheet the area where the fins go through the top and bottom of the fuselage so I get a solid fin attachment.

First I laid out the 1/8" square parts of the structure.  The lower outline and the spars are medium density and the rest is soft.


Then the 1/32' x 1/8" diagonals are fitted in.


Once dry, it will be sanded flat on both sides and the outline will be rounded over.

Tailplane

First step is to shape the LE and TE (including 1/32" deep notches in the TE for the straight ribs) and glue the LE, TE and curved tips together.


Then the straight (3 x 1/16" and 8 x 1/32") ribs and the diagonal ribs, which were sandwiched out last night were removed from the isopropyl alcohol that they soaked in overnight and were laid out to dry.

[Jmk89]

Tailplane (cont)

Last step today was to glue in the straight ribs.


Tomorrow the diagonal ribs will go in.

After that, prop, prop assembly and nose block and pylon to do.  That might not be so speedy - clients are asking me to do legal work for them.  Don't they know I have important model building to do?

Then covering.  I wonder if I should ask whether mylar under tissue is allowed.  It isn't an aerodynamic improvement, but rather a technique to improve the durability of the tissue covering.  Any weight advantage makes no difference for a model in a class that has minimum weight rules.

[Jmk89]

All the airframe has been completed so the last few days' work has been making the noseblock, prop blades and prop assembly. 

For this, I followed the directions in JOD's Better Propellers articles (especially article 2).  Since this can be obtained easily from the Plans Gallery at https://hpa.aeromodelling.gr/plans/details.php?image_id=2204
I( won't clutter up the thread with a repetition of the information you can find there.

Here's a photo of the prop in the pitch jig with the attachment wires being epoxied to the blades. 


The orange thing in the vice at the bottom of the photo is a piece of 125mm PVC pipe with sandpaper attached - although JOD says he doesn't use undercamber on his prop blades, there is about 2% of undercamber in the ARAD 6% airfoil that I like to use and the pipe makes a good sander to achieve that undercamber.  I hold the blade at about 15° to the left and sand  the blade along that angle - it reduces the amount that you have to roll the blade to put the undercamber in the right place ( this is really an adaptation of the method used when making props by moulding them on a tin can or bottle).

The wood is not balsa but paulownia - because I have it and it is nice to carve.