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Author Topic: Algebra 2.5m MK II Build....  (Read 10134 times)
jiberjaber
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« on: March 23, 2010, 11:39:27 AM »

So I managed to pick up a Algebra 2.5 Mk2 kit at the recent Old Warden swap meet for what I thought might be a bargin price.  I noticed it and circled it a few times before going for it... I was sure that there was a build thread on here or RCG but I seem to have drawn a blank on that...

What I have discovered is that there are quite a few version of this glider, both in wing span and fus.

This one is the 2.5m version and seeing as it was sold as a complete kit and no glass fus was in there, I assume it is the ply fus version - certainly looks that way from the instructions I have.

The instructions make reference to Edmonds Model and look ike they are based around making it RE only.  I guess this makes it the EMP version?

The wings appear to be some sort of ply covering over what looks like polystyrene core, not taken them out of the packing yet to inspect them but did notice some of the ply is lifting a little.

So there are a few decisions I need to make for when I start to build it.  There is an optional air brake which can be fitted... and some thought on what to do about the wings, I have attached a scan of the diherdal options... not sure which one to go with... with this being quite an old model, I am sure there have been a few built and owned so please feel free to provide your opinion on which version is the better and why Smiley

I am thinking about trying this on a bungee first but then some sort of electric conversion... though I might just convert it to electric first of all...

So go on.. post your memories and thoughts please... more the merrier Smiley

* algebradihedraloptions.pdf (98.45 KB - downloaded 315 times.)
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Jason
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« Reply #1 on: March 23, 2010, 12:35:28 PM »

Hello Jason i also have this kit but mine is the 3mtr version with the glass fus.

Looks a very nice kit  Grin

Looking forward to your build thread  Cool
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boffin
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« Reply #2 on: March 23, 2010, 08:47:38 PM »

Jason,

I was active in BARCS Open in the 80’s in the heyday of EMP Algebra products and can offer the following dimly remembered data, having built many of Dick Edmonds models and flown them in competition with great success.

History: EMP

Algebra 2M : These were available in RE thermal and aerobatic layout with Eppler airfoils (thermal) and semi symmetrical (slope) wing sections. The slope versions, for their day, were indecently quick and I remember trying to keep up with Sean Bannister flying a 2M aerobatic at Horcum on a Primrose Valley 1984 modelling holiday with a lead sled Apache and failing miserably.

Algebra 2.5m or 100S : Plans were available for built up or foam wings with Eppler 193 and 205 sections. Fuselage options were 1/32” built up ply or glass , introduced circa 1985. Production of these elegant, value for money fuselages stopped soon after the demise of the ‘before its time’ 4m Calculus.

Algebra 3m : A very popular entry level BARCS Open competition model built usually as RES and very capable of slot winning performance. I recall E193 and E205 as the sections of the day and wing loadings of 10-12 oz/Ft^2 were the norm………way heavier than current F3j typical practice.

History: Sean Bannister

Sean Bannister was the original Algebra designer and his Algebra 8 and Glass Elephant designs were REAS and formidably competitive  in the hands of Maidstones Rod Potts , still active in 200Watt/kg. Algebra 8 derivatives live on in the hands of FQ’s meadowhay and are still my most pretty large thermal soarer. There are some similarities between Chris Foss’  Hi Phase and Algebra 8. Who knows which came first.

You need to check what airfoil you have on your kit. The section should be flat bottomed, the cores should be polystyrene with obechi covering attached with contact adhesive , not ply and I am concerned that time has allowed the ingress of moisture into the cores and deteriorated the glue bond.

You need to be very careful with time expired obechi/foam wings unless they have been LE/TE capped and stabilised with glass/epoxy or tissue/dope.

Regards Ian


« Last Edit: March 23, 2010, 08:49:11 PM by boffin » Logged
jiberjaber
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« Reply #3 on: March 23, 2010, 10:17:15 PM »

Thanks for the info there Ian,  I met Rod a few times last year at Brian's comps and had a nice cuppa in his shed

This is certainly the EMP 100s version I think from the instructions.  The wings are as you describe, wood veneered polystyrene however no idea of the section, there in reference in the instructions but they are down in the shed at the moment.  As far as I know it's "wood" but light in colour, no idea what obechi looks like  Embarrassed

There is a strong theme of keeping the wings in sealed bags through the instructions, unfortunately these seem to have been stored with the rest of the kit in the open.  The kit looks like it has been taken out of a box at some time and all held together with masking tape.  The wings are still in their core beds but none of the ends are finished off, so the polystyrene is exposed at all ends.  The have two slots in the root end which I assume is for the wing joiners to be fitted in to.  I did think they were ailerons until I undid the masking tape!

I am a little worried that the wings might by u/s now from what your saying.  I was thinking of glassing them when complete. 

I might take some pics tomorrow depending on how much I get done of the other things I need to do.
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Jason
jiberjaber
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« Reply #4 on: March 23, 2010, 10:36:36 PM »

It turned out I hadnt put the instructions down the shed yet, they were in the stagin post (Kitchen) before the last leg of the journey...

The instructions mentioned SD7037 as the section for the wing.  No idea what that looks like... I'll see what google throws up.

The non-RE version has RG15 according to the instructions. 

*EDIT*
Heres a good article google dredged up...

http://www.ae.illinois.edu/m-selig/uiuc_lsat/lsat_5bulletin.html
http://www.gliders.dk/sd_7037_and_sd_7032.htm

« Last Edit: March 23, 2010, 10:41:02 PM by jiberjaber » Logged

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Jason
boffin
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« Reply #5 on: March 24, 2010, 06:15:29 PM »

Jason,

Foam wings stored badly in an unheated shed or attic suffer hot/cold and dry/wet cyclical changes which often deteriorates glue joints badly and allows the obechi veneer to lift. I have brought panels back to life using a hypodermic and well thinned (meths) skinning epoxy. Weigh the panel down with bags of sand until set……..about 50lbs on a half panel to get the epoxy  to penetrate. Weight, inevitably, increases.

There would be no point in glassing the wing until you are sure that the veneer is attached to the foam……….but then there will be no point as you will have a mega stiff junction under the veneer.

Regards Ian
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jiberjaber
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« Reply #6 on: March 25, 2010, 12:40:08 PM »

Thanks Ian, are there any symptoms to look for on the wings?  I have had a good poke around and I can not lift the veneer without it pulling the foam out (which I stopped before it started doing that).

Is this a major issue to putting it on a bungee or winch and less of an issue if I convert to electric?
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Jason
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« Reply #7 on: March 25, 2010, 01:03:08 PM »

Jason any pictures of it  Cool
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boffin
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« Reply #8 on: March 25, 2010, 06:33:31 PM »

Jason,

I have the greatest respect for EMP products but they are now outclassed by moulded RTF’s. Your only reasons for building it would be nostalgia or curiousity to see how much better the 21st century product had become.

My recommendations would be to use the hypo/epoxy method of damage repair, clad it in heat shrink and use it on the bungee only. I would not glass it and would not convert to electric as the Algebra 2.5m with foam wings is already heavy enough. You get no warning of foam wing failure. Pull too much EL and its all over.

If by strange chance you are really taken with the handling then build a set of 3.5m wings for it ……..the fuselage will take this quite well. Then you might consider electric or winch.

FWIW, If you are into vintage builds, I would have a gander at the Charles Rivers site and look for Bubble Dancer, a Drela design, and much respected in the US. The European AVA is a licensed composite Bubble Dancer.……….If this takes your fancy, then the guy who makes the XP kits this at some cost.

I guess that I am suggesting not to expect too much from the Algebra . Build it, bungee it and move on to something better.

Regards Ian
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jiberjaber
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« Reply #9 on: March 26, 2010, 10:45:55 AM »

Given I only paid 17 quid for the kit, I dont mind building it and giving it a go, I certainly am not expecting it to be a modern performer - its made of wood for a start Smiley It will only be the 2nd or 3rd build I have done, so if nothing, the build experiance will be good for me.

I might just use it on the slope...but my mind isnt made up yet.  As long as I dont have to spend a fortune on covering it or similar, then I dont mind building it up, I certainly wont be wasting a receiver on it as a permanent fixture but I can afford to blow 15 quid or so on a couple of servos for it....  heck if I dont like it I am sure the brother in law would find a use for it Smiley

I'll take some snaps today down the shed, subject to if I feel the need to go flying by the time I get down there Smiley
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Jason
jiberjaber
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« Reply #10 on: March 26, 2010, 12:48:35 PM »

Some pics of the unstarted kit.








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Jason
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« Reply #11 on: March 26, 2010, 12:52:18 PM »

Looking good Jason  Cool
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PDR
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« Reply #12 on: March 31, 2010, 01:58:00 PM »

I built one of these back in the mid 80s and they're a super machine - in fact I bought two kits at the time and only sold the other (unstarted) kit last year (for £70 - you got a bargain!) and still think I may regret not building it. BTW - The parts are bundled together with masking tape ass supplied - this was a common packaging method at the time.

These kits were very complete. You should find not only towhook and wing-joiner hardware, but also the tail belcrank and the rudder closed-loop linkage and even the outer tube for the optional ballast tube in the kit. The instructions should be on 2 sheets - a large sheet of drawings, a smaller sheet showing some details for the FG fuselage option plus an A4 sheet of typed instructions that add to the general notes on the large plan.

The wing has three full-depth 1/16" ply spars, at least one of which goes out to about the half-span position - they're pretty strong for anything but seriously aggressive power winch launches (I cross-country'd mine with 2lbs of ballast and would dive it from 800 feet at 45 degrees to get past the sink!). The kit is "flexible" in that it can be built as standard with straight or polyhederal and rudder/elevator (and optional spoiler) control for basic thermal and 100S use (obviously without the spoilers). The plans then show lots of options for ailerons, different dihederal angles, kunchle-jointed ailerons, brakes and the ballast tube. The age of the design is shown by the way it uses central servos for spoilers etc rather than individual ones (servos were large and expensive in 1985!). You can improve on this now by using small servos mounted in the wings. I would glass the wings if you have had enough experience to do it without adding excessive weight - it makes them a bit stiffer and much more durable. If you haven't much experience doing lightweight glassing then dope/tissue or film would be better.

The fuselage is a wrapped ply structure that looks tricky but is actually quite straight-forward to build provided you follow the instructions. IIRC you tack two srips of wood to the bench, soack the ply and then wrap it over the formers and trap it between the strips, leaving it for 48 hours to dry. The result is very stiff and reasonably strong.

It sounds like you have the Selig-section on yours - this was offered as a later option. My original had Eppler 193 wings and was very nice, but I built a pair of selig wings and they were just as floaty but had a better speed range. If you're going to do the aileron option then use flat wings, but if you want to do the rudder-elevator version then the suggested polyhederal layout gives much better handling.

Boffin's right that it won't offer the raw performance of today's mouldies, but it's a very nice model and will put up a pretty respectable performance nonetheless.

So go on, built it! Or I'll give you £20 for it if you change your mind...

:0)

PDR
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Personally, I have nothing against work, particularly when performed quietly and unobtrusively, by someone else. I just don't happen to think it's an appropriate subject for an 'ethic'.
richard
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« Reply #13 on: March 31, 2010, 03:50:19 PM »

I had a few algebras too. The 2.5M was by far the best handling, I made my first ever fly-off in using this model
The 3m was also good, but the 4M was a real pig!

My models used the selig 3021 section. I had two with the box fuzelage and the last one I built was with the "new" rolled ply fuzelage.

For the dihedral, I would recommend the 8 & 8 degree option Smiley
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jiberjaber
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« Reply #14 on: April 01, 2010, 10:42:01 PM »

Cheers guys.  One of the guys at the field suggested a pva/water mix over tissue which he reckoned would soak through the obeachi and in to the foam / wood join.   

No experience myself to know any difference.  I think I might see about making the fus first whist thinking about the rest.
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Jason
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