Scale Soaring UK

It was Peter Balcombe's build thread that introduced me to the Algebra while looking for a glider as a follow-on to the the Phase 6 I fly and which would continue to hone my 'crash-landing' skills. The built-up wing should also be repairable in the event of an accident (when, not if) or worse case I might need to sweet-talk Cliff into producing just a replacement wing kit. As a further plus, it seems a good price. So for all the above reasons, I now have a Algebra short kit and it seemed a good idea to do a build thread as a follow-on to Peters prototype builds.

So what do you get in the kit? Well the short answer is 'quite a lot'.

For each wing there is a full set of laser cut wing ribs (24 in total) plus full depth plywood spar webbing, false leading edge and trailing edge, 2 wing servo frames and a wing tip. There is also a set of 4 jigging wing beds to help maintain washout when sheeting. In addition Cliff also supplies laser cut tail-plane halves, rudder post, rudder, AMT bell-crank and fuselage servo plate. Along with all this lovely wood comes a fiberglass fuselage, wing plan and finally, to finish it all off, some decals. The laser cut ribs not only slot into the main spar webbing but they also push into both leading and trailing edges so the resulting wing structure should be fast to build and accurate.

Having worked out what balsa I need to complete the build I am now waiting on my order from Balsa Cabin plus a few other bits and pieces to arrive before I begin my build.

This build should be a test of how well the kit and plan work for an average builder and having looked at the plan in more detail over the past few days I have had several queries which I must thank Peter for helping resolve via his build thread. Hopefully there will not be that many more queries as the build progresses.

Given that this is a larger wingspan than other kits I have built, I now think that my building board may be a bit short so before building commences I now need to go and check if a bit of re-jigging is required!

With the wood, wire, tubes and glue finally all arriving, building has commenced and very quickly one wing frame is now ready for sheeting the upper surface. The laser cut parts fit together well, creating an accurate, square structure. The slowest part was fitting the balsa TE strengthening bits between each rib at the TE and then carefully sanding both the false LE and the TE to match the rib contours. The rib 'legs' ensure the correct washout is built in to the wing but they are easy to break off, as I found out when putting pressure on them sanding back the TE. Putting a length of balsa under the TE keeping the legs off the ground resolved the problem.

I built over the plan just to make sure the ribs were correctly aligned when gluing to the webbing. It soon became apparent that the wing is slightly longer than the plan but the second wing should be exactly the same size as the first so no problem.

8 servo frames are supplied, 4 for Corona servos and 4 for what I think are Hobby King. These two sets proved to be exactly the same size and shape so I glued them in pairs to provide a thicker frame into which I plan to screw my smaller KST servos.

Next step is to sheet the top and bottom surfaces and complete the first wing.

Andy,
Yes, I think the reason for the plan being slightly shorter than the parts is probably down to me rather than the printer!
I think that the DevWing output I used must be the one which takes the dihedral angle into account, so gives a “projected” panel length rather than the “real” length.
However, as you will have found, the interlocking parts means that everything goes together exactly the same on each wing.
I will double check & correct if necessary.

P.S. Don’t forget to add your servo wires & any servo hatch surrounds before fitting the lower skins!
Peter

Sheeting the top of the wing was quite simple as I used 4” x 48” sheets from Balsa Cabin to avoid a join to get the length required. I also used 48” balsa stick and spruce spars for the same reason.

Once the top was sheeted, as Peter has mentioned there are a few things that need to be done before sheeting the bottom, some of which are easily forgotten – fit the aileron servo frame, stick balsa across front and back of servo frames to support the wing sheet when the holes are cut for the servos, servo extension leads for flap and aileron servos, corner gussets if not already in place and the ply end caps for wing joiner and ballast tubes. With all of these bits done, it is simply a case of breaking off the rib legs and then sanding down both the false LE and the TE to match the ribs.
Finally, I could sit the wing in the 4 wing beds ready for fitting the bottom balsa skin.

And this is where is all started to go a bit wrong! On laying the wing in the wing beds it became apparent that the wing was warped. These are longer, slimmer wings than I am used to sheeting and I think my wing skinning technique must be a bit lacking. Anyway, I dampened the top skin, protected the balsa wing beds from the damp wood, laid the wing in the beds and put weights on the spar. Left to dry overnight, the wing was now straight so I carefully sheeted the bottom of the wing, put some weights on top of it and left it to dry. When I removed the weights, it too was warped, so this time I dampened both sides, weighed it down on the wing beds and again left it to dry. This resolved the problem so I could then add the balsa leading edge and shape it followed by the spruce leading edge and then shape it.

The laser cut wing tips are 3/8th balsa so need to be glued to ¼” sheet to give the required thickness before being glued in place and shaped.
That just leaves the wing root end plate to be shaped from PCB material, or in my case from ply sheet. I will make these for both wings while building the second wing.

I have been a bit slow building these past few weeks but now both wings are practically complete and they do look very slim and elegant. Although they were relatively straight to build, shaping the leading edges, trailing edges and wing tips did take more time than I expected, especially shaping the spruce leading edge which I am sure has blunted my sanding block!

If, like me, you are not familiar with building from a plan which shows just one wing then Cliff does sell plans showing both wings and this will be of help. I didn’t realise this alternate plan was an option when I bought the kit so used the plan I had showing the one wing. Why I say this is because the first three root ribs need to be very carefully and correctly positioned relative to the spar web as they are key to the shape of the wing. If you do not get these correct, then one wing will be more swept back than the other. I thought my second wing was fine and it was only by luck that I checked the second wing against the first before the glue was set that I could see they were different and was able to correct my error which resulted from working with an upside down plan.

With that out of the way, even though I took more care with the sheeting on this second wing, just like the first wing it ended-up warped and had to be dampened, laid in the wing beds, weighed down and left to dry to get the correct washout.

Finally I had to shape the ailerons/flaps from trailing edge stock plus balsa strip to get the correct depth and then cut to size and cut and fit thin ply end caps to aileron and flap. Then ply root caps could be shaped and fitted but as you can see there is a gap between the root caps and the flaps. I decided to reduce the width of the flaps slightly and will glue this bit of trailing edge to the wing to better support the end of the root cap which otherwise is likely to get knocked and damaged.

Now they need to be fibre-glassed around the wing roots as per plan and then covered. I will do this alongside work on the fuselage.

Like the wings, the fuselage build is relatively easy but still takes time.

First thing I did was to add some piano wire canopy fixings as per the photo before moving on to the tail-plane.

For the tail-plane, as per Peter’s suggestion, I glued the joiner tubes into the tail-plane halves before shaping them as it is easier to align them with flat surfaces on the tail-plane halves. Having made the two holes in each tail-plane half, I joined them with one piece of tube for the front and one for the back to enable me to make sure the tubes were correctly aligned left/right and up/down as shown in the photo. Once the epoxy had set I then cut the two halves free and shaped then to a symmetrical section. I used aluminium tube which was a good fit over the 14swg wire. Before gluing into the balsa, I nipped together the ends of the tubes to keep glue out.

Looking good Andy

Next comes the wing joiner rods.

These were made from 6 swg piano wire, each rod 240mm long. Both rods were bent so that when laid flat, the bottom of the bent end was 10mm above the surface. According to Peter, this should give the correct dihedral.

There are dimples in the fuselage where the wing joiner rods appear to go but these should be ignored. Instead, the front joiner hole centre should be 415mm from the nose and 24mm up from the bottom of the fuselage. The rear joiner hole is another 96mm back, centred 21mm up from the bottom. Having measured, measured again and then carefully drilled the holes, when test fitted both rods were well out of where they should have been! Just a few millimetres out with the holes and the effect on the rods is significant.

It took a bit of pondering but eventually I enlarged some of the holes to allow the rods more movement and then made plywood plates drilled to fit tightly over the rods. To get the rods in the correct position I put the wings on and then, with the aid of a book under each wing for support, I adjusted both wings to be equidistant from the tail fin i.e. equally swept back, and the same height off the work surface with the tail-fin at 90 degrees i.e. equal dihedral. The plywood plates were then epoxied to the inside of the fuselage to hold the rods in the correct position. The front plates were epoxied into place first and once the glue had set the clamps were removed to allow access to the back plates which are much more fiddly due to lack of access space. I made the front ply plates longer so they would also provide strength for the Multiplex wing locks when added.

Finally I added some epoxy putty around the rods to keep them from twisting. Probably not necessary and a bit 'belt and braces'.

Andy, I agree with adding something to try to stop the rods twisting, especially the front one which is easiest to get at.
I had simple ply plates epoxied to each side of my front one, forming a simple box.
This worked well for a while, but then the epoxy failed & it needs replacing as the rods now move & make rigging more awkward as you have to get the rods centralised & parallel for the wings to slide on!

Peter, given what you say, and with the AMT control rod in place, I have now been able to extend the epoxy putty so that it covers all of the front rod. Given my less than controlled arrivals, I am not sure this will do the trick but only time will tell.

With the wing joining rods in position, the AMT and its control rod could now be added.

Looking at the size of the tail-plane, I positioned the bell-crank 65mm up from the bottom of the fin, where the tail-plane seemed a good fit, and drilled holes on each side to take the tube on which the bell-crank pivots. The bell-crank is supplied with the kit but I found the shoulder to be too wide to fit inside the fin so sanded it back and also drilled it out to take the pivot tube. As soon as the pivot tube was fitted through the holes and lined-up with the wing it was apparent that it was not level so I widened the hole on one side to allow adjustment and then added a couple of nylon washers on either side of the pivot tube on the inside of the fin. I could then adjust until parallel with the main wing and epoxy the washers to hold the tube in its correct position. Easy to do but a bit fiddly. When the glue had dried, I had been so careful with the glue making sure the bell-crank was free to pivot that the tube was still able to slide sideways. I subsequently glued a couple of small washers over the tube on the outside of the fin to correct this before cutting off the excess tube.

With the AMT bell-crank now in position I followed Peter’s build and used a 75cm long 5mm carbon tube for the control rod. This is a bit shorter than required so at the front I used a short 3mm diameter carbon rod that fitted snugly inside the carbon tube and then glued this to a threaded extender and clevis. At the back I glued a short length of 3mm carbon tube into the larger tube, into which I then glued a 2mm threaded control rod and clevis. I had hoped to get a straight run from servo to AMT bell-crank but I found that my servo was too high so I had to put a kink in the rod at the back to give free movement to the AMT. The last step is to glue the fin post into the tail fin but before doing this, check that the bell-crank has sufficient movement. I decided to carve some balsa out of the inside of the fin post to allow more ‘up’ elevator movement although what I now have is probably too much.

Well done Andy, soon have it flying at this rate
I started off with a 1m long tube for the pushrod & reduced the length as necessary once I had measured the total length required, taking account of clevises etc.
I epoxied short 2mm threaded rods into each end & always use metal clevises.
I’m pretty sure that I ended up cranking my pushrod run a little bit as well - the rear fuselage is quite narrow.

It’s always better to have bit more AMT movement than too little as you never quite know how it’s going to go with the first launch of an AMT equipped model.

I’m sure you I’ll love it when you get it in the air.
Peter

Thanks for the encouragement Peter.

Finally the rudder control can be installed. Peter used a wire operated closed-loop in his build and I have used the same method on several of my gliders but I don’t particularly like this method as the wires tend to clutter-up the space inside the fuselage. Luckily, as I was looking for carbon tubes on the Hyperflight site, I came across their pushrod sets comprising a thin carbon rod running in a low friction plastic tube. This looked both flexible and strong so I bought the 1.5mm rod in a 3mm outside tube, which turned-out to be a good size.

First step was to temporarily hinge the rudder to help decide where the control horn should go. I then inset and glued into the rudder a small square of 3mm ply sheet so that I could screw the control horn on to the rudder ( I will also do this for ailerons and flaps). Lining-up the control rod along the outside of the fuselage from rudder to rudder servo let me work out where the control rod outer should exit the rear fuselage. A quick drill hole was then filed to a slot and with the fuselage held upside down the outer tube was pushed through allowing it to snake its way down the fuselage, over the wing rods, and exit at the canopy hatch next to the servo tray. Holding the fuselage upside down as you do this ensures the rod passes over the top of the wing rods.Epoxy putty was used to hold the control rod tube in place at both ends and threaded couplers epoxied onto each end of the rod. The end result is a very light, smooth operation and I will probably bear this method in mind for other builds. Threaded couplers are easily epoxied onto each end.

As yet I am unsure where to position the receiver in the fuselage. Initially I put a receiver tray low down behind the servo tray but then found that when the aileron and flap servo leads are in the fuselage, space gets a bit tight. Now, I think I will pop the receiver behind the battery at the front after adding lead to get the required CoG.

With no more bits left lying around the build appears complete so Oracover has now been ordered to cover the tail-plane and wings.

Prior to covering the wings I first strengthened the wing roots with epoxy and fibreglass cloth as per plan. I used 78g/sq m cloth for this but found the finish to be uneven so after a bit of sanding back I added a further covering of 24g/sq m cloth and Poly-C over the top to provide a much smoother finish. While doing this I also applied this lightweight cloth/Poly-C to a few inches of each wing at the wing tip to strengthen against inevitable knocks. Finally, I covered both tailplane halves with the same 24g/sq m cloth and Poly-C.

With that out of the way, the wings, tailplane halves and rudder were covered in Oracover. Peter tells me that he fibre-glassed his wings and then spray painted them. I tend to add too much weight when I spray so I am much happier to go with the iron-on covering which, incidentally, went on very smoothly. Given how light the covered wings feel I probably could have covered the whole wing in 24g/sq m cloth and Poly-C before the Oracover covering to help against knocks and hanger rash, and the wings would still be light. However, Poly-C is a water-based varnish and can warp thin balsa so maybe this is not such a good idea unless you first seal the balsa, which obviously adds more weight! I am hopeful that my grassy landing zones will not result in damage to the wings, although only time will tell.

With the wings covered, the aileron and flap servo hatches could then be cut out, the servos held in place, and the aileron and flaps marked where the control horns should go. Then I cut small pieces of 3mm plywood sheet and glued these into each aileron and flap so the control horns could be screwed into position after covering. With that, the ailerons and flaps were covered in Oracover.

Both ailerons and flaps were hinged to the wing trailing edge using tape and a strip of Oracover. The flaps are bottom hinged so tape on the top of the hinge line and oracover on the bottom. The ailerons are top hinged so tape on the bottom and Oracover on the top. I find that this combination of tape and Oracover gives strong, flexible hinges with a neat finish.

The servos were then screwed into the servo holders and soldered on to the servo leads installed in the wing earlier. The servos are connected to the control horns using a couple of clevices and a short length of threaded studding. I use metal clevices on the ailerons but have one nylon clevice on each flap as a weak link. Experience shows that when landing using full flap I forget to raise the flaps just before touching the ground and in a poor landing there is a high the risk of damage, hence the weak link.

So the end is now in sight with just a few things to complete. I need to sort out/programme all the control movements, which I have already started, and look for servo covers for aileron and flap before finishing the bottom covering with some coloured trim. Finally I need to add the Multiplex wing retaining system to both wings and then sort out the nose weight to get the correct CoG, starting at approx. 75mm behind the wing LE at the root, as per Peter’s suggestion.

Well done Andy, she looks very nice indeed.
I’m sure you will love flying her.

Fitting the Multiplex wing retaining system to both wings was very easy and the wings now lock into place with a satisfying ‘click’. Getting them off again is a different matter as the two wing retaining rods do now allow much wing movement, so if you forget the little wedge which Multiplex supply to remove the wings you might find getting the Algebra home a bit of a problem.

With such a long nose, relatively little lead is required to arrive at the CoG. I used liquid lead shot mixed with epoxy glue and pushed this right to the front but in doing so I added a bit too much so now have to move the battery back slightly to get the correct CoG at 75 cm from the wing leading edge, which Peter suggests as a good starting point. This will be tuned via dive tests to determine the best position. I am also moving the receiver back to behind the servos as this is a better place for it.

The all-up weight comes out at just over 1.5Kg and to me this feels a light glider for its size. I now need to find some brass rod to fit inside the ballast tubes as I suspect a bit of ballast will come in useful.

I am still looking for servo covers to fit over the servo horns as all the ones I have found are not deep enough.
Programming of the control surfaces is also complete with crow, coupled aileron/rudder and speed, normal and thermal flight modes all set up. Speed raises the flaps by a couple of mm and thermal drops them by the same amount. I suspect most of my flying will be using normal where the flaps are lined-up to the ailerons.

A flying colleague was so impressed with the look of the Algebra that he, too, has order the short kit. I am pleased to say that the kit now comes with both wings shown on the plan and the rib positions on the plan do now line up exactly with the web spar and false LE/TE. This will make building much easier/accurate and it is great to see a supplier taking note of comments and making changes.

Now the wait is on for the right weather conditions and the right slope and looking at the weather forecast, that might some time away.

Over the past few days the forecast for today had been looking promising for the Algebra maiden flight and today turned-out exactly as forecast - sunny with a good 13mph wind coming from the NW/NNW - so off we went to Uffington White Horse in Oxfordshire, my nearest slope for this wind direction.

First flights with my smaller 1.5m mouldie showed loads of lift, albeit conditions were not as smooth as might be hoped. Encouraged by my flying friends, who assured me that conditions were fine, and with an extra 15grm stuck on the outside of the nose of the Algebra just to be sure it was nose heavy, it was time to give it a go.

Since this is the biggest wingspan glider I have built and flown I was nervously on the sticks expecting the unexpected as my friend launched the Algebra, but from the word go it was a total non-event and things went very smoothly indeed. From launch the Algebra happily climbed away with no trimming required. Coupled aileron/rudder as suggested by Peter are another first for me and I was expecting turns to be slow, but far from it. Initial hesitation in turns just meant I had to use a bit more aileron than I was familiar with and as the flight continued I became more and more confident flying this agile, elegant glider. A couple of loops were executed, but it was too early for me to try rolls, and in the slightly turbulent conditions I had to pay attention in the turns as the wings were sometimes kicked into a tighter turn than planned, but a bit more air time to build experience and confidence and I am sure this will become a firm favorite.

It was very easy to gain height in preparation for the dive test and I was glad I had added a bit of extra weight to the nose as once in the 45 degree dive the Algebra stayed put, which shows my CoG to be spot on!

A test of the crow braking while flying showed no change in attitude as the crow braking was introduced, which was reassuring, so now was time for the dreaded landing. I am pleased to say that the landing went well and following a nice, smooth turn on to the landing approach and the wings nicely level, I gently applied crow braking. The Algebra slowed up nicely so I began to push the nose down but the landing place was less than ideal as the ground sloped away so more down was required which lead to a faster than planned landing. However no damage was done and I was both relieved and delighted with how successful this first flight had been.

I now need to see if I can get a bit more flap and aileron movement to improve crow braking without spoiling the set-up, but other than that my plan to use the Algebra as an advanced trainer has been entirely successful so thank you to Peter and Cliff for producing this lovely kit.

I think that a few more flights will give me a chance to finalise the trim of the Algebra after which I will post all the various control surface movements and CoG so anyone contemplating building an Algebra will have my settings and those that Peter has posted for comparison. I will also look at some brass rod for ballast slugs to see how the Algebra flies with a bit more weight and let you know.

Well done Andy.
Hope all goes just as well in all future flights & will be interested to hear of ballasted operation.

Can anybody tell me if these short kits for the Algebra 8 are still available and if so who sells them?

Kind Regards
Michael Campbell

Mike,
Contact Cliff Evans at Laser Cut Sailplanes.

Thanks Peter.

I first got to meet Sean Bannister in the early '80s as he was a source of information for my final year aeronautical engineering degree project
on optimising the design of F3b models. I saw Sean fly the Algebra in Hillingdon and at a F3b comp in Oxford so seeing this thread has brought back many memories!

Mike,
Note that this thread deals with the new Algebra (cruciform tail) whilst the new Algebra 8 has more swept back wings and a T tail. Both have ailerons & flaps & should be available through Cliff.
Peter

Thanks Peter for the clarification

Kind Regards
Michael

I work at a secondary school and yesterday a colleague brought me some neatly rolled plans he’d found whilst clearing out the design and technology dept cupboards. Yep...plans for a 2.5m Algebra kit from I guess the late 80s. Nobody has the first idea how they got there. Maybe a former pupil built one as a project?

The plans themselves probably aren’t much use to anyone now you can get a shiny modern kit from Cliff, but if you want them just pm me your postal address. They’re about 2ft x 3ft.

Rog