Mystery model

[Jmk89]

I did some more work on the latest build today while waiting for the balsa to turn up, which it has now done, so this was an efficient use of time.

Today's task was to make the prop blank.  Here's a photo.


The wood is paulownia.  Since I had a block 300mm long to hand, I made the 400mm length by splicing 2 pieces 300mm x 38mm x 32mm together with about a 87mm long splice.  Then I remembered to wait for the glue to dry and to then drill the hole in the post drill before shaping the blank.  On my calculations this should give a 400mm pitch (i.e. P/D of 1.0).

[Jmk89]

Here's a start on the fuselage.  It's a bit different in that all sides are 0.8mm sheet and the "spacers" or "bulkheads" are glued to the sides first.

Here are a couple of pictures:



To hold them down while the glue sets (I like using aliphatic) without putting holes in the spacers or the sides, I made some little plastic holders with the 3D printer which are held in place by pins and which just push down enough on the spacers to make a good contact with the balsa side.

Here's a photo of a couple of those little gizmos:

[Jmk89]

Some more progress - wings and fins built and ready for sanding

[Jmk89]

I attach a picture of the Mystery model's tailplane plan.  I can't work out what the plan means.  Is it:
1.    sheet on bottom with a little triangle of balsa on top?
2.    sheet on top with extra triangle on top?
3.    sheets on bottom and top and extra triangle on top?
4.    something else?

[Jmk89]

5.   little triangle let into the top sheeting (change of grain direction)?

[dputt7]

Sorry Jeremy, sat here for half an hour trying to make sense of it.  The plan definitely shows sheeting on the top and I think the extra piece is laid over the top, Is that the L.E. could it be to reinforce the L.E. Joint.

[pb_guy]

Is it held on by rubber bands? If so, it might be for strength.

[TheLurker]

The plan definitely shows sheeting on the top and I think the extra piece is laid over the top...

Yup.

All I can think of is that it's to provide a 1/16" thick panel for not much extra tail weight to give a rigid/robust mounting point for the fin. Perhaps also allowing the fitting of the fin with the LE offset to port or starboard.

[Jmk89]

Thanks for the replies, chaps.

The tailplane is held on by rubber bands, according to the article.  But I'm not going to use bands but will use a wire and tube hinge to hold the TP on and for the DT.

I think that the first time I saw this was a picture in a 1950's AeroModeller showing a fitting made by Jim Fullarton - I couldn't find it in the excel index, but it's a bit like Dave Hipperson's hinge for Senator but the tail tips rather than the fuselage.

The sheeting can't be a fin thing - it has twin fins stuck on the TP tips!

[Jmk89]

Today I carved the prop for this model. 

Here are some of the tools I used - Sloyd carving knife, staight carving knife, razor saw and Liogier (French woodworking rasps).


The carving knives are from woodcarving times and are good and rigid in the blade and hold an edge much better than "hobby" knives. 

The French rasps are hand-stitched (the process of making the teeth is called stitching) and are much more effective than the machine stitched rasps that are usually available.  The main reason is that they are slightly out of perfect line and size so that they don't create tracks in the wood which is what happens when each tooth goes along the same line.  So the finish strangely is much better.


I have two of them - a bigger and a finer each in tapered half-round shape.

The other tool that I find very useful when making the saw cuts is a carver's vice - the jaws swivel to hold the workpiece which makes it much easier to hold the prop still while sawing it.



The eagle-eyes will notice that the prop is balsa not paulownia.  When I was carving the paulownia blank shown earlier in this thread, I wasn't using my woodcarving knoves and  trying to hold it still using a "hobby" knife, I snapped that blank and did it so comprehensively that the prop couldn't even be rescued by gluing it back together.