Algebra 3m Mk II

Kit Review by Trevor Hewson

(Originally written in 1994 for 'Sloping Off', the Newsletter of the Christchurch and District Model Flying Club)

Decisions
I bought the Algebra at Sandown after long deliberation over what to build next. The truth is I have more than enough slope soarers already (Anyone want to buy a Wik Salto?!) and didn't fancy taking out a mortgage for one of the new all moulded rockets.

When it comes to flat field soaring though, I have for many years relied solely on the faithful Osprey 100 and so the idea of the Algebra was to have something to cope with windier flat field conditions which would also serve as an alternative to a pure floater in light conditions at the slope.

As with many 'cottage industry' produced kits, the Algebra is packed in a plain brown cardboard box. This one though shows clearly the many years experience that Dick Edmunds has had in supplying kits mail order. Not only is the box itself very sturdy, but bits of foam block are fixed inside and lots of Sellotape is used in order to make sure that nothing can move around in transit. This has a downside when buying over the counter at Sandown - it is just not practicable to remove the components to examine them.

Talking to Dick did though help me to finalise my decision on which model to go for and the fact that he only had white fuselages left went a long way to convincing me that I didn't really want a red one! The only other decision needed was the wing section. Here I opted for the SD 7037, for no other reason than that it is the newer one and he wouldn't have gone to the trouble introducing it if it wasn't better, would he?

Inspection
Back home, I set about extracting the parts from the box. The polyester/glass fus is very neatly made, with a well fitting canopy. The four wing panels are obeche veneered white foam and the inner panels are cut to take a full depth, full length ply main spar and a second, shorter full depth rear spar. The wing joiner rods are beefy but alarmingly short. However, on examining the plan, it is clear that lots of thought has gone into progressively transferring the stress from joiner tubes to ply/hardwood blocks, to spars, and thence to the wing. I made a mental note to make sure all these joints were well made!

There are quite a lot of wooden parts and a parts list would have been helpful to check that they were all there. However, they are all numbered and so identification is no problem. The instructions are best described as adequate, but bitty and confusing would be equally fair. Everything you need to know is there - somewhere!

The fragmented nature of the instructions and diagrams was compounded in my case by my having a separate sheet showing how to build the model with ailerons, the kit being basically a rudder/elevator version. I noticed recently that the MkIII Algebra is now available, in either aileron or R/E form, so maybe a new set of integrated instructions has been produced.

More Decisions
At the time of purchase I had intended to build a Rudder-Elevator-Brakes Algebra. However, most of the way back from Sandown, clubmate Peter was nagging away at me to fit ailerons. A few weeks later I was lucky enough to have a go on a R/E version and one equipped with ailerons and brakes. There was no way I could make a reasonable performance comparison, but I had to agree that it was more fun with ailerons. I did though stick with conventional brakes and resisted the lure of flaps and crow braking.

The Wing
There is a deceptive amount of work in this foam wing! Furthermore it is work that requires considerable thought and care. Attaching front and rear sections to a full depth spar so that the surfaces line up when the spar is sanded down is just one of several challenges. Others include inserting an 18" ballast tube from the wing root without it emerging through the top or bottom veneer, and guessing just where that tube is, when making the incision to insert the brakes!

Whilst the components are of a reasonably high standard, for such a long established kit, there are a few surprising errors. The wing root ribs are too short, the hardwood leading edges not quite deep enough, and the wing joining blocks also just slightly less deep than the wing. Whether these are manufacturing errors or whether they are a result of the change to the SD 7037 wing section, I don't know. They are easily coped with, but irritating nonetheless.

The Fus
If the wing has more work than you think, the fuselage is relatively straightforward. Care is though needed since the fuselage cross section is small and if everything is to go in smoothly, the first few pieces of wood do have to be accurately positioned. I made things harder for myself by deciding to fit a bellcrank in the fus to operate the airbrakes, rather than the 'pull-open and spring-closed' method shown on the diagram. Fitting the bellcrank was real 'ship in the bottle' stuff and even when it was in there, there were several anxious weeks before the wings reached the point where I could find out if it was actually possible to connect the airbrake pushrods to the bellcrank when putting the wings on!

The moment when all these linkage and assembly problems are solved and control surfaces move for the first time is for me always the highlight of the building process. As is often the case when space is tight, the final installation looks quite neat, but with a closed loop to the rudder, a wooden pushrod to the all moving tail, the airbrake bellcrank assembly, two servo leads joining onto extension leads, two joiner rods and a spring to hold the wings together, I have to admit it is a bit of a fiddle to rig.

Colour Coding?
My daughters have always complained that colour-wise my aeroplanes are boring, being mainly various combinations of black, white, red and yellow. So I made the fatal mistake of saying "well, you design a colour scheme then". The result involved all seven colours of the rainbow - and that was just the fin and rudder! Some 80 pieces of film later, (and countless cardboard templates) I have to admit the result cannot be described as boring!

The Best Bit
The maiden flight of the Algebra took place on a blustery autumn Saturday at the North East slope of Win Green, the day before the scheduled (but in the event, postponed) thermal comp. As you may have gathered, were it not for the impending thermal comp. I would have waited for more suitable conditions, but Mike and Brian assured me the conditions weren't as bad as they looked - honest.

Provided a model is built reasonably true, the only real sources of anxiety on maiden flights should be the cg and the pitch trim. The cg was set at the forward limit of the recommended range, but with an all moving tail there is always an element of doubt about the trim. Those of you who know this slope will be familiar with the fight through the turbulence to get out past the trees. Once out there, I eased off the stick and discovered that full down trim was just enough to stop the model from stalling but not sufficient for it to fly forwards! Nevertheless, the flight was enjoyable and I was able to establish that the stall was innocuous (no doubt due to the forward cg position), loops were smooth and rolls take an awful lot of sky - still, this is supposed to be a thermal soarer!

Next on the test schedule were the brakes. These are double bladed Graupner brakes and proved very effective but produced a marked pitch down effect. Given my shortage of down trim and the blustery conditions this was not altogether a bad thing and after a couple of dummy runs, the Algebra came in for a fast, but flat and safe landing, the right hand wing neatly slicing the top off a very wet cow pat on the way! At that point I decided enough was enough, and went home to fit a towhook, adjust the elevator trim and mix in some 'up' with the airbrakes.

A second outing in lighter conditions at the South East slope was a little more infomative. With the right amount of elevator mixed with the airbrakes, a little more aileron movement and the cg eased back towards the centre of the recommended range, the model felt quite at home thermal hunting off the slope. So far, so good.

Conclusion
I still have had no opportunity to fly the Algebra from the flat, so it is too soon to say whether it will meet the original need of providing a competitive thermal soarer in a bit of a blow. However, the initial forays from the slope have demonstrated its capability to handle a range of wind speeds without ballast - it just remains to put its efficiency to the test.