Ben Buckle Junior 60 build

[Andy Hat]

I'm building a Ben Buckle Junior 60 and I'm not clear on the wing joining.

When it comes to joining the two wing halves, there's no plan (other than the instructions and drawings to build a two part wing). Looking at the roughly cut dihedral brace and/or doubling up the width of the half-joiners, implies that the width of the flat centre section is -greater- than the width of the fuselage. i.e. the two outer ribs are further out than the edges of the fuse. This feels wrong since I'd normally assume that the pressures of the wing bands would go through the ribs, down directly on the top edges of the fuse. I've looked at many pictures online but can't quite determine what's correct.

Also, any ideas on where I can get some nice 4-inch small-hubbed vintage balloon wheels like the Flair Smooth Hub Wheels shown on **LINK** ?

[Mike Etheridge 1]

I am probably repeating myself here but I do have a Ben Buckle Junior 60 fuselage (1946 version) I acquired at the Nationals plus a Keil Kraft 'New Junior 60' (1955) I built in 1962 / 3. They both share the Keil Kraft wing but as the Ben Buckle plane's fuselage is not as wide as the Keil Kraft fuselage (Same as the Flair Junior 60) there is a slight overlap of the centre section which seems to make little difference. I do not have the Ben Buckle plan but I have got the Flair plan which matches the 1955 Keil Kraft plan plus a centre section detail from Keil Kraft. I hope you can make sense of the above ?

[Cuban8]

A word or warning based on what I've seen others suffer. If you keep the original wing structure and then fit an engine or electric motor that's more powerful than what was fitted in the original, you really do risk total wing failure, especially if the model is flown in a manner that is anything more than R/C assist.

I've lost count of the times I've seen these and similar retro designs 'auger in' when over-powered and then looped or flown in windy conditions that would have grounded the originals.

Lovely models, just need to be operated appropriately with modern tech.

[Mike Etheridge 1]

I have to agree with Cuban 8, the wings do need beefing up at the joints. I am sure my wings have ply reinforcements on the joints which are not shown in the detail above. Additional reinforcements would also be advisable. I did feature the electrification of a Mercury Matador on this website a few years ago. The plane which belonged to my nephew Nigel got caught in a thermal at Croydon airport. My nephew put the plane into a spin to escape the thermal but the wings folded and the plane was scrapped and finished up in a dustbin from where I recovered it. I re-built the wings with spruce strip reinforcements on the wing spars.

To date my Junior 60 wings have survived but have only looped the loop twice once with the Ben Buckle fuselage attached and once with a Super 60 fuselage attached.

[Colin Leighfield]

Interesting to read some of the experiences here. When flying my Ben Buckle Mercury Matador (PAW 149 diesel), I got carried away and looped it. The wing folded! I keep kidding myself that it is repairable and I will get around to it. Story of my life!

[Andy Hat]

Thanks. I think I'll make the centre section as wide as the fuselage (so the outer ribs sit on the longerons) and build in a new 1/8 ply dihedral brace.

[PatMc]

Andy, Keil Kraft made 2 versions of the Junior 60.
The original appeared in 1949 and was intended purely for free flight.
The second version came out in 1955 it was also intended for F/F but with the option of single channel RC. A number of design changes were made to the new version, main ones being a wider fuselage in order to fit the receivers & batteries required at the time also the wing design had to a better spar arrangement.
The wing centre section of both versions were the same width as the respective fuselage. If yours has a wider centre section it could be the later design on an old version fuselage.

You can identify which version you have by downloading pdf files of each plan from Outerzone, open the files in Acrobat Reader & comparing them. Here's a link to the 1949 version & here's the 1955 one.

I have a Flair kit Jnr 60 that was based on the 1955 version, I built it around 1986 then refurbed & converted it to electric about 6 years ago.
The wings were never strengthened in any way but if you take a look at the refurb link you'll see they are retained by peg & screw instead of rubber bands. This model has has regularly been looped, rolled, spun down from altitude & flown inverted without any problem, it's also been flown as a floatplane.
In short, it's not the wing and it's joiner strength (at least not the 1955 design wing) that's the problem, it's the method of fixing. The position of the wing band dowels was fine for free flight but allows too much flexibility of the wing position during RC controlled manoeuvres, particularly the leading edge being able to rise off it's seat.

[Andy Hat]

The Flair and KK designs of the wing joiner/centre looks stronger than the Ben Buckle version. I've now joined the wing with a 1/8 ply brace. It was too late to change the wing fixing method but I don't intend to fly it in anything other than a vintage way. I think I might double up the uprights under the wing though.

Does anyone have an estimate of how much Solartex is needed to cover a Junior 60?

Edited By Andy Hat on 31/05/2019 18:39:11

[Dwain Dibley.]

I think I used about five metres on mine.

Have you got some squirrelled away, cos it's Oratex otherwise Andy.

D.D.

[Andy Hat]

Thanks Dwain. 5m? blimey. I have quite a few rolls of Solartex but probably not 5m of the same colour.

I usually use the Hobbyking film, which is excellent, and cheap. Shame they don't do a "solartex" equivalent since I really want to give this a vintage (non-shiny) material look. Oratex is pricey. Tissue wouldn't survive my handling and I've not had much luck covering in nylon. Covering this thing looks like it could easily cost as much as the kit cost to buy. I may have to work out colour-scheme which uses the Solartex that I have in stock...

[Dwain Dibley.]

Sorry...............

I'm being silly mate, its more like 3 meters, 2 on the wings and another on the fuz. You should get one wing panel out of a meter of 26 " wide solartex. I have just been trying to find a photo for you but failed.

D.D.

Edited By Dwain Dibley. on 31/05/2019 23:04:53

[Andy Hat]

It's nearly finished. Just a few more things to do, primarily the decoration. I've ordered some matt black vinyl for that.

I can confirm that less than 3m of Solartex was enough to cover it. Luckily I had this much in cream.

Edited By Andy Hat on 16/06/2019 15:17:06

[Former Member]

[This posting has been removed]

[Dwain Dibley.]

Chortle......................

I did a refurb of a J60 I bought from a swap meet a few years ago, but all the pics have been lost. It was a bare bones buy, built but not covered and it would have helped immensely with the J60 build Q's we have had lately.

D.D.

[Andy Hat]

It's finished!

I had to add 220g of lead to the front to get it anywhere near balancing.

Looking forward to flying it soon. Slightly worried about it climbing too fast and needing permanent downtrim. Also worried about the small rudder - will it be enough to control it?

[PatMc]

Posted by Andy Hat on 20/06/2019 20:56:22:

It's finished!

I had to add 220g of lead to the front to get it anywhere near balancing.

Looking forward to flying it soon. Slightly worried about it climbing too fast and needing permanent downtrim. Also worried about the small rudder - will it be enough to control it?

Looks great, Andy

Once you've flown it a few times & are happy with the trim you could try removing the lead incrementally, adjusting the elevator trim as you do. My Junior has the cg 1.3 inches rearwards to that shown on the plan & has been flying without problems since 1986. The rearward cg improves the glide & widens the speed range.

Control the rate of climb with the throttle & the speed with elevator trim. Don't worry if you end up with some permanent down elevator when you've established a comfortable cruise setting, it will have no ill effect. With the tx trim at neutral mine has 1/4" permanent down elevator which gives a nice cruise setting at about 1/4 - 1/3 throttle.

The Junior is quite responsive to rudder & even though the BB version rudder is much smaller than the Flair the rudder control should be more than adequate.

[Dwain Dibley.]

Very Nice !!!

D.D.

[David Davis]

220 grammes that's nothing!

The Junior 60 was my first successful r/c model and in its first manifestation powered by an Irvine 20 I had to put 680 grammes (1.5 lbs) of lead under the engine to achieve the balance point shown on the plan. It still flew well.

[Andy Hat]

It flies!

Well, the first flight was very scary. under power, and without power, it was ballooning/wallowing/dolphin-ing and there was limited control. I managed to get it down intact (those wheels are great at absorbing a heavy landing!).

So, I put two halves of a lolly stick (4mm) under the leading edge of the tail, added two washers to the top of the motor mount, added another 75g of weight to the front and moved the clevises in by two holes on both the elevator and rudder.

The next flight was much better and followed by 3 more batteries-worth of flights. It flies around nice and slowly. Most enjoyable! (I did learn that trying to take a photo whilst flying is probably not a good idea...)

The extra weight may not have been needed so I'll try taking it out as Pat suggests. Both the rudder and elevator now move ~40 degrees. The Flair tail, with larger moving surfaces) looks much better but these are OK for now. Raising the tail LE 4mm meant that it flew well with zero elevator trim.

Any suggestions on how to permanently build-in the raised tail LE? I'm not sure I'd be able to accurately sand a piece of balsa sloping from 4mm to zero, or cut a slope into the existing rear end.

Edited By Andy Hat on 21/06/2019 20:24:20

[cymaz]

You could raise the wing TE

[Andy Hat]

I think that be a harder permanent change and it might spoil the nice look. it's looking like sanding off the rear (4mm at the back, sloping to zero at the front of the tailplane) may be the best thing to do. Difficult to do accurately but worth a try.

[Andy Hat]

This thread has some interesting stuff about J60 trim/incidence:

**LINK**

Looking at the model, I think I'd rather attempt to make a very slim wedge to go under the tail, rather than hack away at the current fuselage.

Next one I build will have the top longerons continued without a break, until the end of the fuse - like someone on that thread did...

[PatMc]

Cymaz, raising the wing LE would raise the motor thrustline by the same angle exacerbating any pitching up with power tendency.

Andy, to cut the 0 - 4mm wedge shape - cut a piece of balsa (1/4" ?) the desired length by about 8cm - 10cm. Split down the length near the centre angled at the 0 - 4mm. Now cut straight down the grain of each piece to give 2 of the desired wedges. Best done using a small table saw or bandsaw.

Sounds like your first flight antics could have been caused overcontrol due to too much control movement being available, especially the elevator throw.

For comparison I've measured the elevator chord & rudder bottom chord on my Jnr 60 also the control throws & permanent down trim setting of the elevators.

Elevator chord = 35mm, permanent downtrim = 5mm [8⁰] , full up from perm trim = 10mm [17⁰] , full down from perm trim = 7mm [11.5⁰]

Rudder chord = 98mm, throws EW = 43mm [26⁰] .

The rudder is more powerful than necessary because I like to do a few uncharacteristic Jnr 60 aerobatics when I get bored with the normal sedate pattern. Elevator is less powerful but still enough for loops & to hold inverted.
Halving the rudder throws would be more than adequate for normal flying.

Edited By PatMc on 21/06/2019 23:29:55

[David Davis]

"...Next one I build will have the top longerons continued without a break, until the end of the fuse - like someone on that thread did..."

I have built three Junior 60 fuselages and that's exactly what I did with the second and third fuselages. I still needed to use down trim but I'm not surprised, the original model was free-flight, designed to climb under power and to glide once the engine stops.

[Andy Hat]

Pat - Yes the first flight was hairy! If yours is the Flair tail then those measurements make sense. My Ben Buckle has much smaller moving surfaces so need more throw. The throws on the first flight were no where near enough but it was wallowing so much, I don't think anything different would have helped. I can live with what I have for now but if I built one again, I'd go with the Flair tail.

I don't have a table saw so I stuck some balsa to a board and sanded it into a wedge. Then stuck it onto the tail plane seat with double-sided tape. Should be flight testing later...