RCM&E at 60: Kakadu, the first free plan

[Dad_flyer]

The magazine is 60 years old in May, as I discovered on the announcement of the RCM&E 60th anniversary fly-in 2020.

I would like to go to the fly-in, and I quite like vintage models, so I looked up and found what was in that first issue. Unlike today, the model plan is not listed on the cover, and other early issues seem to have no plans. Radio control and Electronics are to the fore, and all types of model, not just aircraft. Anyway, there is Kakadu on page 47:

It is not printed full size as we are treated to now, and was not a new plan. It was redrawn from Modell. Fortunately Outerone have both versions as there are many more details on the German version. That includes all the formers. RCM&E do give the dihedral, which Modell missed off.

[Dad_flyer]

So plan printed out, and wings started.

I am trying to resist changing things. I don't want to spend ages mulling over it. I am giving myself two allowed changes: this will be electric as I have not got IC accessories, and the sheeting at the wing root is rounded to avoid sharp corners.

Despite temptation, I am not going to add LE sheeting as a D box for the wings, or add elevators to make it 3 channel. It feels strange looking for just one servo in the spares box!

I shall need some care in places as most of it is 2mm sheet, which in places is sufficiently different from 1/16" and 3/32".

[Dad_flyer]

Four wings nearing completion. I think I have got two left, two right, two long, and two short in the correct combination.

I have not put the root ribs in yet. I have had gaps in other models when putting the root ribs in at the correct angle using a rib gauge, then aligning the dihedral of the wing. Someone suggested on another thread to leave the root ribs out, then glue them in when joining the wings. Sounds like a good plan, until I think about how to cut the top spars and top root sheeting to the correct size when the root ribs are not there. Any advice?

[Martian]

Nice to see traditional balsa bashing

[Nigel R]

"Any advice?"

I'd cut the root rib from soft 1/8.

Plenty of meat to sand back, to achieve a nice fit, if you need to.

[Frank Skilbeck]

Best way with the wings is to make up the wing joiner plates with the correct dihedral, glue this to the spars with the wings at the correct dihedral and then add the root ribs and then the top sheeting.

[Dad_flyer]

Thank you for the suggestions Nigel and Frank.

There are no wing joiner plates in the structure, but I could of course put in some light balsa to hold the angle while fitting the rest. That might suit well. I had thought of a thicker rib to sand back. That would work well when I get my Permagrit sanding block, otherwise I struggle to sand straight.

[Frank Skilbeck]

Yep the plan doesn't show any dihedral braces, I think I would be tempted to put a 1/16" (1.5mm) light ply front and rear of the spars. Friend had a 2nd hand, never flown, Junior 60, wings folded in gentle flight, on inspection the dihedral braces were made from balsa.

May not be a problem with the small model, but easily added now.

[Piers Bowlan]

Like Nigel, I think I would use 1/8th balsa for the root ribs and just make a little template out of scrap balsa to get the dihedral angle correct. Then, when you glue the finished wing halves together you won't need to do any sanding. As it is a little, lightweight model, I probably wouldn't bother with dihedral braces but, as an alternative, a 1in strip of glass fibre 'bandage' will avoid any breakages here. Impregnate the GF tape with epoxy before wrapping it around the centre section. Wear disposable gloves! Some people use PVA as an alternative.

No, I wouldn't add a leading edge 'D-box' either but the wings will be quite flexible when finished, which prompts me to ask, what will you be covering it with? Litespan from Solarfilm was ideal for this kind of lightweight open structure and is still listed on their website but not in all the colours. I also don't know if the Balsaloc adhesive is still available but I believe PVA can be used as an alternative, but best to phone them to make sure.

[Dad_flyer]

Thank you Piers. I did not get long to look at this yesterday evening and most of that I spent on shaping the LE and TE. I had got as far as thinking about a bandage instead of a brace. The wings are not deep, so a brace would separate the rib into two pieces. Not a problem particularly, but a pain.

I am planning to cover in polyester lining material and dope on the open structure of the wing, and tissue and dope on the solid balsa fuselage and tail. The material is 60gsm, so is a little heavy possibly, but not too much. I have not used it before, but others here have recommended it. It certainly pulls round corners well, and should shrink with heat. As I was not really planning to make this model, it feels like a free testbed, and fabric texture looks nice. A little like nylon, but I think lighter? The German version of the plan says 'Japanpapier 33g/qm' in the materials list. That sounds quite heavy if g/qm in German is gsm.

I flew Mayfly with just varnish for quite a while, then I covered with tissue and dope. The extra strength was remarkable, I have not cracked the wing tip plates since, or mashed the soft balsa sides or wings in the hangar. I am hoping the lining material will be that and more, and an extra piece may even work as the bandage. I am expecting the model to be under 1 1/2 lbs and it is designed to fly on '0.5- 0.8ccm' which is only 75 watts on a good day.

[Piers Bowlan]

Where do you get your polyester lining material from Dad Flyer? I bought some 'Poly Fiber' material whilst I was at the LAA Rally Sywell last year. They did a demonstration, covering a (full sized ) elevator and it went on a treat, I thought I would try it on a model at some stage. The lightweight stuff they do is described as 1.87oz/squ yd. (it's American) so anyone good at sums please let me know what it really weighs for comparison. It's stuck onto an open structure with 'Poly-Tak' but I thought modelling dope would be OK to fill the weave. I bought it from Aircraft Coverings Ltd at Henstridge, Somerset, incase anyone is interested. Just click on Stits Poly Fibre at the top

 

Edited By Piers Bowlan on 06/02/2020 09:42:22

[Simon Chaddock]

Piers

Its 63.4 g/sqm.

Did not the sum myself - there is a converter in Google!

[paul d]

I got my polyester silk from hobby craft, very light and strong and it's only £2.50 a metre (900mm wide) applied it with a warm iron using de-luxe materials "covergrip" shrunk it with a slightly hotter iron then 3 coats of thinned dope.....

[Piers Bowlan]

Thanks Simon, thank goodness for Google, very helpful. Well, hobby craft seem to be doing well as they have stores all over the place. Wish we could say the same for the LMS.

[Nigel R]

"There are no wing joiner plates in the structure"

I feel I would personally be deviating from the plan, if the plan didn't show braces. Relying on a butt joint is asking for trouble.

[Dad_flyer]

Thank you all for the suggestions. Not sure which way to go, probably a mixture.

Piers, the material is off cuts from SWMBO, so just standard sewing stuff. I have not done a test piece yet. (SWMBO asked to be wife_nonflyer at first, until she found out that SWMBO was an option)

[Dad_flyer]

Not quite back on this build yet, but a few notes in case I forget.

Motor: 0.8cc is about 100W (and 75g for a PAW). I was hoping to use a 2830 1000kv that I have spare. On eCalc that needs a 10" prop to get anywhere near power on 2s, and for 3s I only have large batteries.

Balsa: Having got new balsa stock from SLEC, I shall do the 2mm sides as 3/32 soft. The 2mm top and bottom of the fuselage as 1/16 softish. The main 2mm fuselage doublers as 1/16 medium+ and diagonal grain (most of that is in front of the CG). Tail is 3mm, so 1/8 soft.

Dihedral: Joining the wings is the next build step. On the RCM&E plan the dihedral is 5.5 degrees, same on both wings. On the Modell plan it is 6.5 Deg. I think I shall go with 5.5.

[Dad_flyer]

Made up a jig for the dihedral angle. Then joined the upper wing.

And did the top sheeting.

I was pleased with a square and neat job, until I tried to remove it from the board. I had not done enough to stop it sticking to the glass. I did get it off without breaking or twisting, but there is damage to the lower sheeting.

Repairs next, then more protection when doing the lower wing.

[Dad_flyer]

Cut out the worst section and replaced it.

There is still some tearing. My decision on the joining, after the suggestions above, was to put the root ribs in with the wing jigged up, and to use three ribs. I had cut one extra anyway, and my template was another one in 1/8". That gives a bit more glue area and no sanding. It feels ok without any dihedral brace (as the plan) I was also going to put on a bandage of an extra layer of doped or glued on polyester. That will deal with the remaining damage on the lower skin.

The other pair of wings is jigged up with a piece of film to prevent this one sticking to the board.

[Dad_flyer]

Second wing join came out better.

I had to put in some filler pieces where I had not cut the angle correctly. I now have a Permagrit which is brilliant and wood have made this so much better.

Now onto the fuselage.

[Dad_flyer]

I noticed too late, but not too much too late. The fuselage side cut out for the lower wing is totally the wrong shape. I had cut it out from one side, but I still had the piece to glue back in.

The plan is very fuzzy, so I had to try to copy a rib from the built wing to make the correct template.

That seemed to fit when cut out.

The incidences are:

Lower wing and horizontal stabiliser: 0 deg

Top wing +4.5 deg . That seems a lot?

Down thrust 2 deg.

Right thrust is unclear. Depending which line I look at it is 1 degree or 2.5 degrees. Try 1.5 degrees?

[Dad_flyer]

The nose has doublers and triplers.

I did not put slots in the main doublers for the main formers. Too many cuts on both sides. The wing saddle tripler and the lower formers have the tabs, which is useful in putting the cabin insides together.

I cut the formers with the grain the wrong way, so they have 1/6" stiffeners.

I think the battery will be able to slide forward under the motor, so there is an opening in S1 for that.

[Bob Cotsford]

4.5 degrees does sound a lot for the top wing. Are you measuring the incidence from the bottom line of the ribs or by the max chord line through the centre of the leading edge radius? If the latter then the real incidence is even more, and the lower wing -ve. I've only seen a difference of maybe 2 degrees on any bipe I've owned.

[Dad_flyer]

The angles are measured from the flat bottom of the wings. I have just double checked on the RCM&E version of the plan.

This is designed as only single channel, and I am not putting on elevators. Rudder and throttle only. Does this incidence make sense for basically guided free-flight?

[Bob Cotsford]

I guess it does, my Eros certainly had a lot of longitudinal dihedral and needed the wing t/e raising a good 1/4" to get it to penetrate instead of climbing. It still needed lots of down elevator with the throttle open and would have benefited from 1/8" under the tailplane l/e too. I think the message here is "don't overpower it"!