Cessna 120 tail fin fairings

[Tim Kearsley]

I'm building the Sarik short kit of the Brian Taylor Cessna 120.  It's progressing well now and moving into the final stages of construction before priming and painting.  I'm struggling a bit though with forming the tail fin fairings.  The plan suggests using balsa block.  The problem is that both the tailplane and fin have airfoil sections, so a block of balsa needs sculpting on both inner surfaces to mate properly with the curved surfaces and then needs carving to match the profile of the rear of the fuselage. 

Are there any other viable techniques to form these fairings.  I did wonder whether they could be formed from thin sheet over a couple of formers? 

[Don Fry]

Some filler, lightened with micro balloons works. Small models, a wetted finger does, clean up when dry.

Bigger stuff, make a concave tool to apply the filler. A a bendy soft cylinder also does the job. Ann Summers can supply such things, or caste your own off a suitable mold.

Once you have the shape, sand/repair, as necessary, some soft aluminum tape can be applied, stretch it as it goes down, with a tool like the back of a spoon, then you can mark panels and lines in. 
not Class 1 scale, but looks Ok.

[Tim Kearsley]

Thanks Don.  I think that's the first time I've heard of a "device" from that particular retailer used in aeromodelling!!

[Don Fry]

At the risk of upsetting moderators, they are expensive. Mould your own. Size as needed.

Another technique, more work, is to build the junction of the joint between fin and horizontal stabilizer in heavier material than the flying machine, and harden the joint with resin. Just the joint. Then apply the filler, harder this time. Sand and repair.

Then tap out litho plate outers, support as necessary, on the model. Foam glues work.. Lot of work. 
Refer to standard sources re keeping litho plate soft. 
 

[john stones 1 - Moderator]

I'm saying nowt, not getting me in bother. 😉

[David Ovenden]

I made these for my Curtiss Condor model from thin litho plate (aluminium) Mostly formed freehand by stretching and moulding over a variety of objects around the workshop.They were glued in place with some shaped blue foam underneath to help keep the shape.

[Tim Kearsley]

Thanks David. Alas, I don't think my skill is quite up to that yet!  They do look very nice indeed.  I think I've solved my own problem now.  I've built up the fairings from a few layers of sheet balsa.  It took a bit of time but with judicious use of sandpaper and a little filler here and there the result is not too bad.  Thanks to all who offered help.

[Dwain Dibley.]

A bit late to the party, but here's mine.

 

D.D.

[Tim Kearsley]

I've made a huge use of your excellent build log Dwain at all stages of the build.  In the end, I made the fairings by building up from layers of 3mm balsa sheet and then carving and sending to shape.  It's worked out OK.  I'm building the wing struts at the moment and have followed the same route as you,  i.e. piano wire with clevis ends.  The only difference is that rather than add balsa profile to the wire I've used some of the K & S streamline aluminium tube.  Construction of the model is almost done now, with priming and painting left to do as I glassed the fuselage rather than covered.