HPA

Looks like another fun day in Leicestershire.

Part 2

The next step is fitting the bent rib.  The photos show that in the tip bay which is a bit extreme, but you will get the idea.


Sand off any excess from the nose of the diagonal rib so it a good fit in the front part of the wing bay. 


Then sand the tail of the diagonal rib until it fits neatly.  Then glue in place.

When gluing, put a smear of glue on both sides of the rib at the mid-point crack.  That way the outside of the bend will stick to the straight rib and the valley of the crack will be re-inforced by a glue bead. Be very stingy with the glue for the valley. 


And here's where I left off.  The next step will be setting the 3 dihedral joints.

Thanks MEETOO.

I was lucky and got some more time today (public holiday in NSW), so I made some good progress on the wing.

First, once the wing ribs had dried out, I glued in the 1/32" straight ribs - the 1/16"straight ribs will be glued in when the dihedral is being set. 


After  the glue had dried, I started fitting the diagonal ribs.  Although it looks like you fit them with lap joints and each rib being straight, I crack each one so one diagonal rib occupies one rib bay.  To measure where the crack needs to go, I hold the diagonal rib with its front end in the intersection between the LE and the rib on the other side of the wing bay and the rib going back along the diagonal.  Where the diagonal rib intersects the straight rib I mark the diagonal rib - that's where the rib has to be cracked.  If you are going to err here, err on the side of making the nose section a smidgeon longer, but don't get carried away (this is why you make wing ribs a good 3mm longer than the actual length ).

Next, bend the diagonal rib so you can check that the front part follows the correct line from the LE intersection with the "other"  to the mid-point of the current rib.
To make the crack, I position my scalpel blade on the rib where I want the crack and lift one end until I feel the rib weaken.  Then stop.  You don't want to break the rib in half, just make it bend.

To make the crack, I position my scalpel blade on the rib where I want the crack and lift one end until I feel the rib weaken.  Then stop.  You don't want to break the rib in half, just make it bend.


 

Results from Mike Smith :-)

There's now a short video on Youtube of the days flying

Quote from: RolandD6 on Oct 04, 2026, 11:16 AMNo

That was going to be next on the list. I have some blond shellac flakes and industrial methylated spirits. Normal hardware shop metho can contain about 5% water as well as 5% methanol.

I should also add many plastics like acrylic ink and paint have a specific gravity around 1.1 so about 1.1gm/cc. That is ignoring any pigment. Titanium oxide (white) has a specific gravity of about 4.25

I think there are a number of tricks with chemicals for getting more of the water out, if that's what you want. Easily found on the net.

I think you mean titanium dioxide. It comes in different crystal forms, at least one of which is less dense than 4.25. 

If memory serves, the Baby Biplane is based on its designers memory of the Comet C-1 Pursuit. You can find the original here: https://outerzone.co.uk/plan_details.asp?ID=10832

Paul,

Thanks for the photo. It is a shame that the model did not fly as well as it looked. But, it is good to see how well the tissue turned out.

A few years ago I competed in the Legal Eagle class in the Uk indoor duration nationals. The rules specify Japanese tissue and we tend to use uncoated Esaki or the slightly lighter, and more porous, Gampi. I wonder if it is possible to get a lighter tissue sealed for less weight? Initial experiments, in my other thread, suggest not.

https://hpa.aeromodelling.gr/index.php?topic=419.0

It is really helpful to post examples when they are unsucessful. In this vain, I rolled Pledge onto CKS 6gsm without the earlier sponge application of thinned Zapon.


The action of the roller tore the tissue. I don't know if using a sponge for the initial coat if Pledge would help. I suspect not, as subsequent rolled coats would likely soften the first and tearing would still occur. Presumeably, the Zapon is not softened by acyrilic varnishes.

I have ordered some Durofol, as mentioned by Mr Alfrey, to use as a base. Further experiments will continue when it arrives.

Here is another experiment I tried. The result was satisfactory for a very light indoor model for flying purposes but it is very water sensitive; ie. damp fingers may make hole in the finish.

The tissue was 6 gsm Tengujo.

The sealing mixture was 10% Matisse M8 Spreader Medium and 90% water with a few drops of acrylic ink for colour. When dry, the sealant is virtually 100% spreader medium.

Only one model was covered, a Baby Biplane from the old HPA plans page. The design has been altered and reduced in size to fit into a 21cm square box.

It flys but not very well because the incidence of the lower wings do not match. The miss-match is small but enough to cause some very weird 'manoeuvres'.

Looks like you made great progress today. Will follow the build  with interest.

The Knights lost 19-18!!!

But the ribs came out of the alcohol in good condition this morning and are now drying on some workshop hand towel.

First the straight ribs


And now the diagonals