Roger's Algebra Build Log


Hello all, I'm Roger Harris - new to the club and to slope soaring. I did a fair bit of power flying around 15 years ago but found it a bit 'samey' after a while. I needed something with a challenge and a goal - soaring seems the ideal thing!

I started with a Multiplex Cularis - good fun but a bit fragile to fly off the slope (especially when one's landings are less than optimal...). Then Rob S. kindly sold me the Stargazer - much better but still breakable! Finally along came the Spectre. Somewhat tatty but almost indestructible. So I've got a nice stable of models for the slope.

On the thermal side, I had nothing other than the Cularis. Paul H., however, had a couple of big boxes hanging around which he wanted to move on, so I bought them from him. They comprised of a full kit for an Algebra 3m thermal soarer, a glass fuse of unknown provenance and another set of wings and tail, various other oddments.
Exciting prospects indeed!

Finally I got a chance to sort it all out and indeed there's a full Algebra kit. The glass fuse is something called a Diamond, from Clive Hall Models. 

I plan to build the Algebra first, as standard, then the Diamond with straight wings, single dihedral and a mid- or T- tail.

After this morning's great meet-up at Ditchling Beacon, I came home enthused - a 3m Algebra would've gone beautifully in today's conditions. Of course, once I get it built we'll be into Winter and constant 50kt winds... ;-)

The first thing to sort out was a building board. My workbench, being made out of recycled pallets, is not level in either direction so I built a board, which I lay on top of the workbench, with tapered battens on each edge to bring it level and keep it flat. A flat and level surface on which to build is vital for a straight aeroplane and it's worth the effort to get it right. I actually checked mine with a spirit level!
Here you can see the building board with the first few wing components ready for assembly. The board itself is plasterboard over a 12mm chipboard base, all kept square and straight with 3/4"x2" battens underneath.

On the left of the photo above, you can see a small paint brush and a plastic pot towards the back of the board. I watered down the PVA glue slightly to allow me to apply it more thinly, then painted it on with the brush. A thorough rinse with tap water after use means both the pot and the brush can be re-used.

Note I've laid out the components in handed pairs - less chance of making two left wings that way!

The parts shown are for the wing-joiner boxes. I carefully sanded down the parts to remove any traces of plywood release-agent from the surface, then glued together the first two bits of each wing box:
Next will be the second ply web seen at the top of the photo. After that, I have to cut the slots in the foam wings. Eeek! Not done that before!


I glued-up the wing tube boxes. The cutting of the wood didn't seem all that accurate but I guessed they knew what they were doing. 

Then came the big moment - marking up and cutting the wings.

The thin slots for the long spars were already cut, so I just had to cut the wider slots for the actual boxes.

As I was cutting out the slots, it occurred to me that there was no way of jigging the assemly to get the wings straight and level - good thing I made my building board nice and 'true'.

I found some brass tubing which, with a little shimming, was just the right size to fit into the wing joiner tubes. I then figured that if the wings were held flat on the building board, with the trailing edges straight, the tubes would hold the joiner tubes in line with each other - so the wings would not have different incidences when assembled. Here's what I came up with:

1) Completed wing boxes with temporary joiner tubes

2) Joiner tubes made from brass tubing with aluminium tape to shim them:
3) Test assembly on the bench:
... there's a straight batten keeping the trailing edge in line.

4) Glueing up:

The idea was that, with the wing held flat to the bench and the tempoaray joiner tubes holding the wing sockets in line, the result would be a nice straight and true assembly.

Unfortunately it didn't work - one of the joiner tubes in the wing was much higher than the other, resulting in the 'twist' between the two wings. Hmm.

See next installment for the cure! 
The rest of the wing was allowed to hang over the edge of the building board - thus not needing to flatten out the undercamber and allowing the two wings to align nicely.

Then I glued up the wing box again and inserted it in the wing, with light clamps holding the two wings together in the centre. I was careful to make sure the clamps only touched the wing profile, thus allowing the wing box to line up with its opposite number.
Glad to say this time it worked. Both wing joiner tubes are in line, no twist between the two wings! Hooray!

Next job, leading and trailing edges to be glued on.

Well the leading edges were easy enough but the trailing edges proved more challenging!

The instructions just said to glue them on. Which I did. Then I noticed they did not follow the line of the wings at all. They looked as if the flaps were permanently down.
You can see in the photo of the lower wing that the trailing edge has a definite 'droop'.

It dawned on me that I should have sanded the rear edges of the wings to get the trailing edges to line up with the section. Hm. 

Not having anything with which to sand accurately I decided to use the gap-filling qualities of the glue to do the job for me.

So I decided to try a different way. I cut the trailing edges off and tried again.

I laid the wing on its back, weighting it down and pinning the trailing edge to the board.
I knew those old scuba diving weights would come in handy one day...
The idea was to keep a continuous line between the rear part of the wing and the top of the trailing edge.

Rather surprisingly it worked!

Before I did the main wing sections I fitted the ballast tubes and spoilers. 

The spoilers were straightorward - just cut big holes in the wings! The spolier casing will provide strength so I didn't make boxes.

The ballast tubes required making a jig to keep them straight.

This worked reasonably well - the second one went a bit close to the bottom of the wing but it was acceptable.

So, leading and trailing edges, ballast tubes, spoilers all fitted. Next job, wing tips and sanding to section.

Well lots of sanding, planning and carving this time. Not much to report other than lots of dust!

Having got the LE and TE stuck onto the foam cores correctly, it's time to get everything as smooth as possible. It's amazing how, while visually nice, things are very lumpy and bumpy when you get a sanding block to them.

If you remember from a previous post, I have a piece of 2" square Ali tube which I'd been using to help weight down  the wings while glueing. I cut a section of this off to give me a nice flat and square sanding block. A bit of 2" double-sided tape and a piece of sandpaper glued to it, it looks like this:

It's essential to have a square and flat sanding block - equally as important as a square and flat building board!

When it comes to sanding the ends of the wing panels for joining, the appropraite angle to allow for dihedral will be achieved by blocking up the wingtip to the correct height, then using this sanding block on the other end. Because it's square, it'll create a perfect right-angle with the building board. 

That's it for this episode. "Dust, anyone? Dust?"

Just a couple of shots of the wingtips:

Cannot believe how much dust.

All flying tail plane (AFT) now - it's built in two halves. Each half starts off as a block of balsa, glued together from two pieces
It has to be tapered in thickness from the root to the tip:
I used a razor plane, seen to the right of the pictures, to do the main work, then finished off with my trusy Ali-Tube sanding block with 120 grit paper.

After tapering, an aerofoil section has to be sanded into the AFT.

You begin by marking a centre line around the edge of the piece. This is essential as it's really easy to get lost as to where you are.
After getting a rough aerofoil section, the tips are rounded and a new centreline drawn on them
Then these are shaped and final sanding done
The two halves will join either side of the vertical fin, using piano wire joiners which are located in tubes glued into either half of the AFT

It'a really important to get these straight. I lined up the trailing edge of the AFT with a straight line on the building board, then made all my measurements from that.
Slots were cut into the AFT and the barss tubes glued in. The joiner wires are longer than the tubes to allow for the thickness of the fin. I had no wire of equal diameter, so I cut the slots in the AFT over length to allow me to use the joiner wires as jigs to keep the tubes in line.

In the photo below you can see the original end marks for the slots and that I've extended the slots to allow for the extra length of wire.
That's the AFT done. It'll need the slots to be filled with scrap hardwood. I have to build the fuse before that so I can see how much hardwood I have as scrap!

So that's the wings and horizontal stabiliser prepared as far as I can. Final finishing and jigging for these parts will be accomplished when the fuse is built, when I'll be able to do my first test-rig of the aircraft.

Fuselage next, then!

After interminable sanding, creating the wings and tail plane, it was a relief to get to some actual building again!

After checking the fuselage sides, made from 1mm ply, were  identical (not checked thoroughly enough - will cause me trouble later!), the doublers were glued in place.
Those old SCUBA diving weights coming in handy again!

Longerons were glued in place, then once again sides checked for accuracy and conformity (once again i didn't check properly, wrongly assuming they'd be accurately cut at the factory). They were clamped together and sanded down to give an identical shape.

Phew! Avoided the mistake of making two left sides!

The plans call for drawing paralell lines on the drawing board to help lining up the fuselage sides for joining. I also made up some temporary formers to hold everything nice and square. I temporarily glued these to the board.

In order to see how things would fit, I offered up the radio gear, it became clear I'd need a nose-block if the fuselage sides were not to be tortured into a tight curve at the front.

I then spent a very tedious few hours making and glueing cross-pieces out of 1/8" square to join the two sides. No guidance was given on how to do this and, unable to figure out how to invert the fuselage to do the bottom without losing the squareness, I did a lot of faffing around with tweezers glueing in the bottom pieces. Unfortunately, I don't have a picture of that, but this shot taken later shows the cross pieces at the top of the fuse - you can see how narrow it is at the back - trying to get the bottom pieces in was an exercise in patience and tenacity! There were hundreds of the buggers! Well, thirty-odd anyway...
After the sides were joined, i glued the fuselage bottom on - good job I like peanut butter...
Note that I have supported the fuselage underneath to help counteract the weights on top. 

This dry, I then started with sorting out the internals - pushrod for the elevator, elevator control horn etc., doing a loose fit to see how things would go.

Next installment, fitting the wing joiner dowels... fiddly! 

So, having built the fuselage it's time to start fitting the wings.

When I built the fuse sides,  part of the process was to drill small, 1/16", pilot holes for the wing joiner dowels. These dowels are very thick piano wire, bent to the required dihedral angle (seen here already installed in the covered fuse)
Once the fuse has been assembled, these holes must be opened out to accept the dowels. I first drilled out to a slightly smaller diameter than the dowels, then used a small file to gradually adjust them to suit.
Inevitably, there were some inaccuracies and the incidence of the two wings did not quite match up. So I marked the required adjustments and filed accordingly
Eventually I was satisfied and of course I absolutely _had_ to do a test rig...
Cor... big innit!?

So, the main parts of the aircraft are finished, and the test rig has gone well - now for covering. More soon :-)

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