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Ben Buckle Junior 60 Build Print
Written by Dilbert Grumpyman   
Saturday, 18 October 2008 09:21

Ben Buckle Junior 60

by Trevor Barton

 

Well, having survived the challenge of the Orion-E build, I decided it was time to try something a little more adventurous. I'd heard a lot about Ben Buckle kits, they are supposed to have a reputation for quality, and seemed like a good compromise between building something from scratch and building from a fully cut kit. So, I took my £70-odd to our friendly local model shop and got myself one of these...


A Ben Buckle Electric Junior 60. Well, the first Junior 60 was built long before I was born, 14 years to be precise. That makes me a young'un in comparison. The original was free flight, I believe. Ah, those were the days. Spend ages building a model with loving care and attention, cover it with tissue or silk and dope, mount an expensive motor on the front, fire it up and chuck it in the air in the vague hope that it'll fly, not fly too far, and land in a fairly controlled manner when the engine finally cuts. Men were men, and models were nervous.

Oh, by the way, if you click on any of the pictures, they should open up in full technicolor glory in a new window.

I'd decided to be as original as possible - well nearly anyway. The only concessions I made over the original were the addition of a miniature transistorised millimetre-wave multi-channel spread-spectrum proportional radio control system with proportional servo-mechanisms, a three-phase three-quarter horsepower brushless electric motor and associated microcontroller-based speed controller and a lithium-polymer secondary cell with a capacity that would have rivalled that of the largest primary-cells of the era. In 1946, the transistor was yet to be invented, 2.4GHz was probably just about or maybe above the limits of anything at the time (you'd have to ask my father - or his), spread-spectrum was a thing of the future, the microcontroller in the speed controller is more powerful than any single computer and probably all computers on the planet put together, and lithium was something that was fun to put in water in school science experiments.

Well anyway, for all its age it looked like a nice kit - a box full of balsa, die-cut but all the ribs were at least the same shape. Much of the work is done with square section - most of the tail, all of the fuselage is made from 1/4" square or 1/4x3/16 strip. I started off with the tail because that looked the easiest bit to get my eye in.

Here's where I made one change to the original. By all accounts the original rudder isn't big enough. So much so that there is a Junior 60 in our club that has some transparent acrylic sheet taped on the back of the rudder to make it larger. So I decided to pre-empt that and made the rudder bigger right from the start. Not a lot, maybe about 1cm wider, but as it turns out it made all the difference. I also made a built-up rudder rather than the 1/4" sheet one on the original - might as well save a bit of weight on the tail, and I already suspected I was going to have trouble balancing it with the short nose that was so common on kits of that era.



Next came the fuselage. Both sides are built on top of each other, and after the first side was built I cam up with the brilliant (for me) idea of using small bits of sellotape on each of the glue joints to stop the top side sticking to the bottom side. That worked well, so remember it if you need to do something similar.

Just about everything on the model was glued with aliphatic resin unless strength called for epoxy. If you don't know, and I didn't before I built this, aliphatic resin is a PVA-like glue that cures hard, and unlike PVA, which cures to a rubbery consistency, it can be easily sanded.



Next the fuselage sides were glued together, using the trusty Farnell and RS catalogues as weights. ...



And then the tail end was glued, making sure it was straight, and the fuselage cross members fitted and glued.



Next came the undercarriage. That was a work of art, even if I do say so myself. It's stitched on to the first former with thread. OK, not cotton thread as in the original but I used some nylon kite string I had lying around. Here I used the only cyano on the entire model - first on the end of the string to harden and stick the individual strands together so it could be easily pushed through the holes like a needle, and secondly after it had been fitted to secure the string tightly into the former. After that I flooded the whole thing with epoxy to secure everything and to stop the string vibrating around and fraying. I borrowed our big soldering iron from work to solder the undercarriage legs together after wrapping them in tinned copper wire.

I also built the battery box at this point, you can see it nestled between the undercarriage legs.


Next was the nose The top bit's a hatch cover, and I had fun getting all the internal triangular corner pieces to align correctly where the three of them met, and I'm quite proud of the result - it all fitted nicely without any gaps.


After that came quite a bit of sanding to smooth it all off into that lovely Junior 60 rounded nose.


The motor mount I had to design myself, because the Ben Buckle plan called for a 600 size brushed motor but of course I was installing a brushless. The mount is deliberately a loose fit because I wanted to be able to vary the amount of side thrust if I needed to, and in the final setup I ended up cutting slots in the mount plates that rest against the bearers to allow the mount to twist a bit, and there's a tad of right thrust. I'm not sure I need have bothered, really, but I did and it works fine.

The motor is a Scorpion 3014-18, 1064 RPM/volt, and delivers about 400W on a 12x6 prop. Plenty for this plane, and way more than it would have had in its heyday. It flies level on less than half throttle and I can get 25 minutes easily from my 5300 mAh 3s LiPos


Then came the wing. That was pretty straightforward as wings go. Unfortunately wood that was supplied with the kit to make the spars was badly warped - not only did one end sit up about 3" if they were laid flat on the workbench, and a 3/16" bow if they were laid vertically as they go into the wing, and there was about a 30 degree twist in one of them. So I had to go and buy my own.

Actually, that brings me to my main disappointment with the kit - the quality and quantity of the stock wood was poor. The 1/4" square and 1/4x3/16" stock was of varying consistency, and to cap it all there wasn't enough, by quite a long shot - at least two or three 3 foot lengths of each. There was a bit of 1/2" sheet missing for the nose area, and the pre-cut trailing edge webbing pieces were about 1/4" too short for the gaps between the ribs so I had to cut my own.

Not a lot, in terms of cost - perhaps three or four quid's worth at hobby shop prices, and probably nothing like that at wholesale prices, but disappointing for a £70 kit. Another club member found the same when he built a Ben Buckle Super 60, and it's not really a good advertisement for the brand, especially considering the good reputation it has had in the past.

My other beef was with the quality of the plan itself - when I came to lay the second wing I discovered that the wings as drawn on the plan were about 1/4" different in length. Not only that, but the position of the ribs on each wing was different - the whole thing was asymmetrical. OK, I realise that the plan was drawn a long time before CAD, but if I'd made errors that large in my undergraduate drawing classes I'd have been pulled up for it. It might be that the original has suffered over the years in reproduction, I don't know, but it was a bit sad. Never mind, though, a quick application of vegetable oil to the plan meant I could lay out the second wing on the back of the first.


Another minor alteration to the original plan was to build a self-contained centre section box. The original had only a single rib in the middle of the centre flat section of the wing, and the outsides were comprised of the inner ribs of the dihedral part of the wing. I scrapped that in the pursuit of a wing that wouldn't clap if I pulled a loop (and I have seen a Junior 60 clap doing just that) and built a stand-alone box that allowed me to have a much stronger centre join.

And here the wings are going together. I do like that packet of 18 clips from Homebase. Look at the way the light shines through the sheeting, I just love building in wood!  There's  a lot of dihedral.

And finally, an aircraft ready to cover. You can see another concession to modern construction techniques - plastic snakes for the control rods rather than the balsa strip pushrods on the plan. Well, I couldn't be bothered, and I've used balsa pushrods in the past and that plane kept crashing!

Then came the covering - Vintage Solartex. It went on easy as pi (whatever that means), with just an application of Balsaloc on the under chambered ribs to ensure it stuck when I tautened it.  I'm not sure if that was really needed, but it did the job.  See the little holes drilled in each rib?  They're to let the hot air inside the wings equalise to the outside as it expands when the covering's being tautened.  Otherwise the internal air pressure tends to pull the covering off the ribs as it balloons out.  Not my idea, but a good one.

And finally the painting. I was originally going to paint the traditional scalloped wing leading edge like on the picture on the box, but in the end I couldn't be bothered with the faff. So, straight edges it was, and even then I couldn't be bothered to do anything with the rudder, justifying my laziness with not wanting to add any tail weight.

And the flying? It flies brilliantly and look at it, doesn't it look beautiful in the air?

All in all a thoroughly enjoyable experience building it, even with my quibbles with the quality of the kit, and it's a joy to fly. After full function aerobatic models it can be a bit of a challenge to fly, in the sense that you have to anticipate more the model's behaviour because you can't correct as easily as you can with ailerons and a flat wing, but it's a forgiving fly. I particularly enjoy cross wind landings and touch-and-gos (what is the plural of touch-and-go, it's not touch and goes!) - with no ailerons or tail wheel steering they can be fun. Whatever I do with it, though, it's a fun fly, and well worth the build.  What's nore, the wings don't clap when it loops!