UNICORN By Norman McFarland (1975) another nostagia build

[Alec Turnbull]

Back in the Seventies when I had just started this hobby and I wanted to progress from my Ripmax trainer to a low winger I was drawn to this model, the Unicorn by Norman McFarland, mainly because it was billed as a fast build, I can remember that I built two of these but I dont remember crashing one, although I do remember an aileron coming adrift on the first one but it landed, almost OK, upside down! My fault as I had not pinned the hinges as I read somehere in a magazine it was Ok to just epoxy them in, well...I didn't make that mistake again.

Perhaps I gave one away.

Anway I have decided to scratch that itch once more and do another.

 

Here is the article from Radio Modeller I found online, not the prettiest of models but I do remember how well it flew plus it must have been an easy build for clumsy me.

 

It would have been fitted with the Merco 61 that I had in the old Ripmax Trainer, long gone now of course so before I get going I need to find a suitable retro engine, searched on E Bay for 61 size glow motor fully expecting to find a Merco but this one cought my eye, it was advertised as a PDP Engine, well I have never heard of one of those, when I expanded the picture I recognised the brand logo on the side of the engine.

It was quite clearly an HB 61, made in West Germany and I think from the seventies/eighties so just the job. PDP refers to the porting . I could see from the pics that the needle valve had broken off and it was obvious that someone had used a screwdiver to get the prop driver off at some point, however the seller ( a model shop!) stated the condition was good, well I could see that it was not that good but it was cheap! Half the price of a good Saturday night takeaway, if it turned out to be rubbish I could always return it.

 

As soon as it arrived I could see that it had not been run for a very long time although it did have a brand new glow plug in it, no spare parts listed online so I soldered a bit of brass tube to remaining stub of needle valve and then soldered a bit of piano wire to the tube to give a Heath Robinson needle valve, which, as it turns out, works well.

 

It also came to my attention that the crankshaft had been crudely shortened, so this poor old engine must have been involved in some incedent or other, crankshaft is not bent but there is insufficient length to put a spinner on, but thats OK as I dont intend fitting one on the Unicorn, I had soldered on the needle valve so wasn't going to send it back now.

I pulled off the front part of the crankcase to have a look at the bearings, can only see the rear one as it happens,

 

Dirty in there but the bearing track and the balls are not rusty, they spin over very smoothly and the crank pin is unworn so I dont think this motor has had a great deal of use, so that will do for now.

 

I gave it all a good oiling with some 2 stroke oil and put it back together and on to a test stand, I cant see why it would not run.

Gave it a prime, wizzed it over with the starter connected the glow plug and blow me down it went as soon as the starter touched it

 

 

Once the needle valve was adusted it throttled up lovely, no nasty noises bangs or clonks so this bargain E Bay find will do just well for this project, not perfect by any means, if I wanted perfect I could but a new one one but there is no nostalgia in that ( plus I am a cheapskate!)

 

So now I have to rummage though my stock of stuff to find all I need to start building, I have cut out all the templates.. so on we go.

 

 

Edited November 14, 2023 by Alec Turnbull
Spelling mistake

[jeff2wings]

PDP Perry directional porting so the carb should be a Perry, the carb you have is a Kavan a common replacement back in the day,if  you (or anyone else) is after a merco I have a number of fully rebuilt ones available ,will be watching this thread with interest!

[Alec Turnbull]

Thats interesting Jeff, now I know its a Kavan carb I may be able to find a spare needle valve if I need one, I wonder why it was changed?

[kc]

I would have expected PDP to be the owners initials- it used to be commen to stamp initials on your motor.

[jeff2wings]

Except it doesn't apply here you are getting confused with lasers' lol !

[Nigel R]

Unicorn on outerzone

 

Looks like a really nice basic sport aerobat with minimal build time / effort.

 

I'm sure I have a spare 60 or two somewhere around here...

Edited November 14, 2023 by Nigel R

[Alec Turnbull]

I have now had a good rummage through my stock of stuff, and found almost all that I need apart from some 1/4 square spruce and a snake for the throttle, they are on order and should be here in a day or two, nearest i could get to 1/4 square is 6.5mm.

So while I am waiting I have made up a kit of parts, normally I make up the parts as I need them so a break from my normal haphazard way of building!

 

The first two Unicorns that I built back in the seventies had foam wings as suggested in the build article, but these days I much prefer a built up wing, so starting with wing ribs, 28 of them in 1/8th balsa. Initially had I intended to use the sandwich method, which I have done before but this time once the ribs were bolted together with some 100mm roofing bolts the whole package became like a lump of solid oak and became very difficult to carve, if I possesed a belt sander it may have worked Ok. but I don't.

 

(I had made the template ribs from some left over basswood), so I gave up on that plan and decided to spend a very theraputic couple of hours cutting out each rib by hand.

This also had the advantage of me being able to this in the house rather than the cold garage as I could now control the mess.

 

All done, but my wife came back from work early as she has a cold and cought me in the act, she didn't say a dicky bird! I will probably be reminded of it some time in the near future.....

 

I have cut out all the rest of the parts needed, I did note that the plan calls for the ply fuselage formers to be cut out of 3/16 ply, but the drawing is clearly 1/4, so I have used 1/4, in any case I haven't got any 3/16! Or 1/4 for that matter so I made up my own by laminating some 1/8th of which I have loads, the same was done for the dihedral brace the extra strength will be handy here as the undercarriage is mounted on the brace

 

 

 

I even manage to find a suitable engine mount and a used fuel tank that will do just nicely

 

Now, where is that fuselage jig....blimey in the cold garage....if I sneak it the house I am bound to get caught out again.

[Nigel R]

crikey, you're working fast!

[jeff2wings]

If he had the foam wings it would be ready for covering by  now🤣🤣! 

[Alec Turnbull]

13 hours ago, Nigel R said:

crikey, you're working fast!

One of the only benefits of being old...retirement!

 

While I am on here a shout out to the chaps at SLEC, I ordered some stuff on Monday the 20th and was surprised when it turned up yesterday Tuesday the 21st less than 24 hours after placing the order can't get any better than that!

 

Will be pressing on today, no hurry though, far too soggy at the patch so may have to wait untill the spring.......

[Alec Turnbull]

Started the assembly of the Unicorn with the fuselage, which is my normal approach. The plan calls for the first two bays to be glassed after it is all together, thats too messy for me plus I would think it complicates any repairs (not that I will need any of that!). So ply doublers (1/32) were used instead, sticking to the fuselage sides with aerosol contact adhesive, I use carpet adhesive from the pound shop.

I also thought that it would be a good idea to add a piece of balsa to each side to act as a wing seat, otherwise there was only the 1/8th balsa and a sliver of ply, to my mind not sufficient, nothing shown on the plan, although I have built two of these before I really do not remember what I did last time (but it was nearly fifty years ago).

I took the oppertunity to add some supports for the servo tray and the wing attachment before the fuselage sides are joined together as it is so much easier now.

1/2 inch triangular section runs down the length of the fuselage

Next step, into the jig this morning.

Even though it is a simple box fuselage there is still quite a bit of fiddling around to get the whole thing square, it does taper towards the engine mounting bulkhead and of course rearwards  towards the fin. the drawing does not show a plan view of the fuselage so no mention of how wide the very back end is, I will figure that out later.

So this is far as can go today, carry on on Monday

[Nightflyer]

When I first took up rc flying in 76 a couple of Hastings club members had built Unicorns iirc one was HP61 powered the other Webra 61. Both models flew beautifully and looked nice in the air. I have plans and will build one sometime as an electric conversion. Will follow this build with interest.

[Alec Turnbull]

In my last post I mentioned that there is no plan view of the fuselage, the note on the drawing is saying ''chamfer the inner faces of the 1/2inch triangular before joining''. Of couse I didn't do that. I really cannot remember how I over came this hurdle last time, any way, this is what I did.

I did consider leaving it wide as shown in the last photo, but no that won't do, I put myself in the designers shoes and tried to think what he would have done, I figured that the total width at the rear most part of the fuselage should be the width of the fin (1/4 inch) + the two fuselage sides (1/8 each) so a total of 1/2 inch which would give a nice narrow rear end. so I chamfered the 1/2 triangular (after joining the sides!)

 

Kept going untill I had achieved a nice feathered edge and trial fitted the fin

 

 

There we are, that will do nicely

loosely placed here ready to finally join, which I have to do before I can sheet the top of the fuselage and then fit the top spine

here we are ready for glueing. I removed the fin and replaced it with a piece of scrap 1/4 balsa, once dried I sheeted the sides and fitted and glued the spine, left overnight to dry

 

this morning I had an enjoyable 1/2 hour whittling it down to a nice section

 

All this took place in the dining room as it is warmer in the fridge today than the workshop (garage)!

Next step is to sheet the underside, but before I do that I like to place the servo tray and make a start on the control runs, so much easier when you can see what you are doing.

 

 

Glued and screwed so it not going anywhere. That will do for today, my wife will be home soon so I must tidy up!

 

 

[Alec Turnbull]

Nearly there with the fuselage, I have been putting off starting the wing as I will have to go into the garage to use the workbench so finishing off the fuselage instead for now, I need to mount the engine, I found a suitable engine mount in my stash of stuff but it needed modifying a little bit, first it was a bit too long so chopped a bit off, I am not sure what brand this mount is, made off some sort of hard plastic but it cut on the band saw really easily, there is a gusset between the bulkhead mount and the engine bearers which, I thought made the engine sit a bit too far forward, the Unicorn already has a long nose enough already so I thought it best to remove some of the gusset to enable the motor to sit a bit further back.

 

When i have drilled motor mounts in the past i always seem to get at least one hole just a little bit out, most frustrating trying to get the last screw in, so this time I took a bit more time to accurately measure and double check that the mounting holes line up, no info online about mounting hole spacing but my digital calipers said 25mm between centres and 52mm in the width. I used some masking tape to aid my marks.

 

 

looks a bit wonky but that is because the engine bearer arms are not quite parallel

 

 

Engine fits a treat, a first for me!

 

So to finish the fuselage off I needed to make a hatch to access the fuel tank, The plan says to use rubber bands to attach but I don't want to do that

 

 

 

Much better with some captive nuts and a few button head screws, I had to substitute the tank that I had originally intended to fit as it was just a little bit too big to squeeze in and it pinched the throttle snake, so I have fitted a slightly smaller one, 270cc I hope that is enough.

 

Radio gear installed, temporarily just to see that it all goes together and elevator pushrod made up, rudder will be closed loop.

 

 

And a final mock up, looks quite good if I say so myself......

 

 

 

No more excuses, I have to get on with the wing in the freezing garage, 1/2 hour at a time is all I can stand at the mo, I hope it warms up a bit next week.

[Alec Turnbull]

I am going to make a kit of parts for the wing, most of which I can do in the house, the first part I am going to make is the dihedral brace that also is the mount for the undercarriage, on my original model I had foam wings made up, these had undercarriage mounts built into them so it was easy, the built up version has the undercarriage wires sewn onto the plywood brace with strong thread, a bit more tricky and time consuming, first bent the wires on my wire bender then cut out a piece of 1/4 ply (the drawing calls for 3/16 but I only have 1/4 in stock so it will have to do.

 

I have marked the ply for the position of the wires and drilled some holes to take the thread, I have used strong linen button thread for this

 

 

The wires are canted forward slightly so I decided to relieve the bottom edge of the brace

 

Here it is all sewn up, took about an hour to do that, tricky at first but once you get going and the wires fall into the correct place it gets easier.

 

 

 

Surprisingly rigid, I am going to spread some epoxy on the treads tp stop them unravelling

 

 

 

Absolutely solid now, I also put some epoxy on the backside as well. Making up the rest of the kit of parts will be easy now this is out of the way

 

 

[jeff2wings]

Now that's old school ! I think if I was building this I would have modified it by glueing a set of u/c mounting blocks, the same as you would use for a foam wing to the dihedral brace but well done for sticking with the plan👍

[Alec Turnbull]

1 hour ago, jeff2wings said:

Now that's old school ! I think if I was building this I would have modified it by glueing a set of u/c mounting blocks, the same as you would use for a foam wing to the dihedral brace but well done for sticking with the plan👍

I did consider that and thought about other methods that could have worked but in the end as you say stick to the plan!

[kc]

Old school and used when models didn't last long.      Reliable radio now means models can last a long time so u/c often needs re-bending to proper position.  So the advantage of using u/c blocks with u/c clamps  like foam wings would be that the piano wire could be removed and straightened.

 

( of course rebending is due to softer piano wire nowadays and it's not a comment on your piloting skill!)

[Alec Turnbull]

Suddenly the weather has turned a little warmer up here in the North West, 9C in the garage at the mo compared with -5C a few days ago so taking the advantage of that I am pressing on with the wings for the Unicorn, simple assembly as I made up a kit in the house earlier.

First laid down the spruce lower spar, as the ribs are symetrical I drew a centre line on each one to establish that they are are in the right place using some packing on the trailing edge to keep everything in alignment, I read some time ago in one of Chris Williams excellent build articles on his giant slope soarers that he had used some 5 minute PVA glues to good effect, so I bought some. I haven't used it up to now as I had plenty of aliphatic but I wondered if it would go off quickly in the cold temperatures in the garage, the answer to that is No! I gave it 1/2 hour then a couple of hours still no good so left it overnight, it was OK in the morning.....so I will hang on the that stuff for summer use.

 

Leading edge and top sheeting added, I decided to try my Gorrilla Wood Glue to see if that would do off in the cold, The bottle I have was given to me, part used, a couple of years ago, it is dated 2015 so quite old and had gone a bit lumpy also the applicator on the bottle is unsuitable for squirting out small amounts, so experimenting I decanted an amount into a small ramikin dish and gave it a stir which quickly got rid of the lumps, then applying the glue with a small paint brush, it worked a treat with the Gorilla Glue going off within an hour or so, very acceptable to me at this time of year. I covered the dish with a little bit of cling film after use and kept in the kitchen on a shelf above a radiator, next day the lumps had not reappeared and it was still in perfect condition to carry on using.

 

Before adding the lower sheeting I decided to add a little balsa infil towards the centre section as the drawing shows the wing mounting bolt being inserted here, but it would be hollow, so I think someting a bit more solid would be better.

 

 

Lower side completed just got to carve and sand the leading edge to section and then do it all again for the other side.

 

 

 

 

 

[Alec Turnbull]

The other half of the wing for my Unicorn is now done,finally! Started out by wiping a little vegetable oil on the backside of the plan so I can see what I am doing

 

The other half was quickly put together as in the previous photos

 

 

All I have to do know is work out how to insert the dihedral brace with the undercarriage legs sticking out, and join the two halves together

 

 

Will entail a bit of cutting with the razor saw, then hang the ailerons and I am all done, will try to get it all done before Christmas as the family will not let me spend hours in the workshop (being antisocial)

 

 

 

[Nigel R]

Very neat work 👍

[Alec Turnbull]

On 20/12/2023 at 09:35, Nigel R said:

Very neat work 👍

Thank you Nigel, but the camera does flatter the workmanship a bit!

 

Anyway I have been keen to get this dihedral brace finally fitted into place, complicated of course by the undercarriage wires getting in the way, I am sure were are plenty of better ways of doing this but I decided, for better or worse, to follow the plan, so to start I took a big breath anf hacked away with my pull saw and made a slot in the underside (where a few mistakes wont show when finished!)

 

 

First cut done, no turning back now!  It took a bit more trimming to get the brace to fit perfectly and then on to the other side, that went just the same, so time for glue, I used epoxy on the brace and Gorilla Glue on the faces of the end ribs, clamped them up after some careful checking of alighnment and left it overnight.

In the morning I had this

 

Perfect, but I was a bit ham fisted with the centre sheeting

 

The build article does mention that the centre sheeting should be added after fitting the dihedral brace but in true man fashion I didn't read that bit until after......so I will have to sort that out

 

 

that will do

 

 

The dihedral bace looks quite happy there, I am quite please how it went, I also glued some squares of 1/16 balsa to the ribs and glued them to the plywood brace where I had cut away just a little too much, so nice and rigid again now

 

 

I made up some traiangular gussets where the undercarriage wires poke through so that the covering material with have someting to stick to

 

 

 

hardwood blocks for the wing servo to fit to are glued in, and ailerons sanded to section and hinged

 

Thats me done until the new year as the whole family will be home for the Christmas break, even glancing in the direction of the garage will be frowned upon......

 

A merry Christmas and a happy new year to all the forum meembers who bother to read my ramblings

 

Alec

[Alec Turnbull]

Here is the Unicorn all construction finished and ready for covering, although the wing needs glassfibre bandage on the centre section first, I am waiting for some materials to arrive.

 

 

 

 

 

 

 

 

 

All I have to do know is choose a colour scheme.

 

Since I started this build I hace discovered that Norman McFarland, the designer of the Unicorn, was a member of the club I now fly with, the Rossendale and Hyndburn Club in Lancashire, what a coincedence, sadly he passed away about 30 years ago.

[Alec Turnbull]

I have now covered the fuselage, in fact back in January, but pushed in to one side in frustration. I attempted to attach a clear acetate canopy as shown on the plan and exactly as I did for my first model all those years ago. I had some acetate sheet left over from my Centurion build so used what I had, but it seemed just a bit on the thick side and I had difficaulty in moulding it to the correct shape even with a little bit of heat, so ordered some thinner sheet from SLEC but had similar difficaulty, tried a couple of times using ZAP canopy glue and clamping overnight but when removing the clamps it all sprung apart. This is the glue I used

 

 

Either the glue is useless or I am! On the instructions it does mention to not freeze, it has been in the garage on the shelf over the winter (while I bought all the other adhesives indoors) so maybe I have ruined it. So I gave up and pondered what to do next

 

My next build was a glider, the plan called for a solid balsa canopy, suddenly the penny dropped, no reason why I could not use the same method on my Unicorn, quickly knocked up a shape out some scrap balsa block I had kicking about.

 

 

That was a few weeks ago, I had to start covering my Rex glider so whilst I had the covering iron out and some black film in use I took the opportunity to cover and then attach my new canopy.

 

 

I did cut away the film where the canopy sits so wood is glued to wood

So glad to finally get that little problem solved, now I think it looks better than clear plastic anyway!

 

[Alec Turnbull]

Whilst I have been meddling with my Rex glider I forgot to take some pictures of the finally completed Unicorn.

I had some flourescent covering film (Profilm I think) that came to me in a job lot, seemed ideal for this model and should make the Unicorn plenty visible to these tired old eyes, so here they are....

 

 

Weighs 6lbs 1oz, so here is another model waiting for the weather to improve........ while I get on with yet another!