Bob's Ballerina

[Bob Cotsford]

Ok, so I'm in.

I opted for the cut parts kit to make life easy. It's not cheap but it does contain a fair old number of cut parts. The cutting is a mix of laser on the balsa and thin ply, and CNC for the thicker ply. Some of the wood grades are not what I would have chosen, for instance the ribs are medium grade tangential cut - the creamy even grained wood that flexes really easily. I'd have gone for quarter cut - the stiffer cut with a prominent almost mottled grain. It's the same with the fuselage sides. I'm guessing that this grade of wood gives a more consistent cleaner cut than firmer quarter cut stock.

I haven't decided which engine I'll use yet, the choices being OPS Sport 40, OS 40 SF, SC 40, MDS 40 () , Evolution 36 or an ASP 52 FS. Or I could whip the OS 40 LA back off the Scallywag fun-fly that doesn't get flown much.

So, first steps:

Me being me I mark the inside of the fuselage sides so that I end up with both a left and a right, then mark the extent of the doublers so I know where to slap glue on:

Add the doublers - I used Wickes own brand solvent based contact glue. It's quite runny so is easy to spread out in an even coat. Once the doublers are in place I use a wallpaper seam roller to press them down tight. Don't try this from the balsa side!

Finally weigh them down with an assortment of toolboxes on top of MDF kickboard offcuts to spread the weight.

Right, that's it for tonight.

[john stones 1 - Moderator]

You've glued those doublers on the outside Bob,

John

[Chris Barlow]

Stop it John! They are up side down though!

Welcome aboard Bob. I can see an educational blog coming here so I'll be following.

[Low pass Pete]

Welcome to the build frenzy Bob. My choice would be the SC52 four-stroke for the donkey.

I also have purchased the CNC and wood packs. Some points that I have noted so far on these:

1. F3 is missing. - Easily remedied however as I used F2 as basic template and cut if f rom the rest of the sheet

2. Undercart plate doublers are too narrow when the slot is set for 8 swg. I have resolved this by gluing so slot is correct width and then I have used cut offs from the fus stringers which are 1/8 square spruce. Then a quick fettle to make the plate look ok.

3. The rear stringers supplied with pack where actually balsa so I made a trip to Inwoods my local shop and replaced these.

Edited By Low pass Pete on 21/01/2016 06:35:17

Edited By Low pass Pete on 21/01/2016 06:49:37

[Craig Thomas]

Did you contact them to complain Pete? I have never bought a cnc wood kit before but would expect it to be right.

[Low pass Pete]

Hi Craig

Ref F3 I did contact Beth but no comeback on that. No offer to supply .

Ref plate, not yet as I found it only a day or so ago.

Ref 1/8 stringers no but maybe I should have. Nothing has been a showstopper really but does relect that perhaps the CNC pack etc was rushed into supply to meet the Jan deadline

Regards

Peter

Edited By Low pass Pete on 21/01/2016 06:52:24

[Bob Cotsford]

Peter, I noticed the U/C plates problem and the large area of spare balsa on the former sheet.

One issue I have found is F1. This is pre-drilled for some particular brand and size of mount set as a side-mounted engine. No use to the majority of builders unless you know exactly which brand and size of mount it's for, you want to go side-mounted and that mount fits your engine. F1 is also drilled for a throttle connection, again only a plus if you have the right engine and mount.

As for the engine - the SC40 voted itself in by virtue of the fact it was still fitted to a mount (I can't remember what it last powered, no doubt a hole in the ground!) and when offered against the plan the overall length is perfect - that's one job saved as I don't have to drill a new mount.

I think I'm going for an inverted installation, it gets the needle and silencer out in the open with out extensions by the look of things. I'll extend the hole in F2 for the tank to suit. This is where it's handy having the wing peg lower than Pete's original position.

Because I only had the cut parts I've not got the stringer issue, they are coming from stock. I'm planning on moving the cockpit back to give it a more racy look. That will just mean cutting down the former at the rear of the cockpit to follow the line of the fuselage front.

More progress tonight with luck.

[McG 6969]

Hello Bob,

Welcome to the MB 2016.

I just added a chair in this room...

Cheers

Chris

BRU - BE / CTR MB Control

[Bob Cotsford]

Make yourself comfy Chris, there's plenty of room. Progress on this build may be a little intermittent as enthusiasm waxes and wanes and other projects interrupt the flow. I started the Ballerina as covering the Chunderbird (Ian Maher's Thunderbird kit build) had drained my mojo and I needed something different - a change is as good as a rest, so they say. If the change is from a 90" to a 50" model it's definitely a walk in the park!

[Former Member]

[This posting has been removed]

[Bob Cotsford]

I think there's plenty of meat under the locating hole on F2 Brian. It's not as though it's a 60 powered aerobat. I'm more concerned about the light grade of balsa used for the fuselage sides which don't appear to be reinforced with stringers on the lower edge, it just 3/32 sheet sides. I'm sure it will be strong enough really

[john stones 1 - Moderator]

Funny you should say that Bob, I'm just starting the fuzz and have cut 1/8 stringers for the lower edge.

John

[Bob Cotsford]

sounds like a smart move John, especially if you fly from rabbit infested fields.  It'll also give more meat to glue the bottom sheeting to.

Edited By Bob Cotsford on 21/01/2016 15:19:09

[Bob Cotsford]

Posted by Low pass Pete on 21/01/2016 06:32:59:

2. Undercart plate doublers are too narrow when the slot is set for 8 swg. I have resolved this by gluing so slot is correct width and then I have used cut offs from the fus stringers which are 1/8 square spruce. Then a quick fettle to make the plate look ok.

I can see why these appear wrongly cut, in fact they are cut as per the plan which specifies a 1 1/8" main plate with 7/16" wide additional strips - err that makes 7/8" total leaving a 1/4" gap! See the plan shot below.

Not much progress, I stacked the ribs in two packs aligned with stubs of 1/4" sq and tied with masking tape. Then I popped a 16mm spade bit through them - pillar drills are essential once you've had one a while. The masking tape helps to reduce splintering on the rib surfaces, and the high speed of the pillar drill allows the spade bit to cut cleanly. I did notice that the rib slots were a tight fit for 1/4" and looked as though they would even be shallow for 6mm stock. Other than that I've stripped my wing spars from a firm, straight grained sheet of 1/4" and found most of the needed hardware from recycled parts. The only thing I'm short of is the tank, my smallest being 10 oz which would be a bit of a tight fit lengthways. I've ordered an 8 oz slant front tank off ebay.

Here's the U/C mount dimensions in the background:

[Bob Cotsford]

A little more done, but not much. I'm moving the cockpit back, just a personal preference thing, so I extended the front deck line back to get the new height for F5 and trimmed it using F3 as a pattern. I've also marked the former and snake exit positions on the fuselage and it highlighted another couple of minor issues with the cut parts kit. I'm putting in 1.5 degrees of right sidethrust (sorry Peter but old habits die hard). That's why the F1 lines appear out of place on the LH side.

First issue, which is actually a benefit, is that the sides extend to include the 3mm underside sheet in front of the wing, which is echoed on F2's length. This gives an extra 3mm of meat below the wing dowel. Probably why it looked fine to me when I looked only at the former and not the plan.

Second issue - I'll be using standard ex-ARTF horns which give a height of 7/8", if I cut the elevator snake exit to suit the snake hole in F10 is 6mm too high. The way it directs the snake you would need a control horn of about 3/8", an invitation for slop in my opinion.

[Chris Barlow]

I think it'll look quite racy with the cockpit moved further back, nice idea Bob.

Have you adjusted the tailplane seat up to F10?

[Bob Cotsford]

Chris, I was thinking that I'd just extend the seat forward by 5mm so that the joiner clears the rudder, saves having to fit an infill to tidy it up. I have this vague idea of making it a mini-Thunderbird within the limits of the cut parts (I'm loath to throw away the wingtips and fin just to copy the T'bird style - read tight fisted). I did think about going for a radial cowl but decided to make it the T'bird's in-line little sister. I've got plenty of orange and black HK film left over to dress the Ballerina in matching rags.

I couldn't bring myself to condemn the model to carrying a massive exhaust can so it's getting the 52 4-stroke after all, mounted inverted.

[john stones 1 - Moderator]

Choice made in heaven Bob

John

[Bob Cotsford]

First the fuselage sides ready to start joining bits, with 1/8*1/4" soft strips to locate a tank bay floor, servo bearers and as longerons on the rear lower fuselage, this last is so that I will be able to radius the lower edges without losing contact area for the bottom sheet. I've glued F1-F6 to one side, if F1 looks a bit sqiffy it's because I'm putting in 1 1/2 degrees sidethrust. I didn't really glue F4 in upside down and back to front and then have to drill the throttle cable hole afterwards, honest. I did however use the scrap from the centre of F2 to add a reinforcing plate round the wing dowel hole in F2, and I had to extend F1 and F2 by 3mm each to match the sides.

Next a dry fit in the jig to check everything will line up and especially that the tailplane seat will come out level. The grid printed on the Slec jig is a great help here.

Now I'm happy everything fits and lines up, the fuselage comes out of the jig, glue is slapped on the former edges and it goes back into the jig where the alignment is checked again. I've used 30 minute Z-poxy epoxy, it's needed for the engine bulkhead so while I've got some mixed I used it for the other formers. White glue would be just as good for F2-F6 but as I'd got enough mixed, in it went. Checking the tailplane is level again:

After reading some of the comments on other threads with regard to the width of formers F7-F10 I was expecting problems, but a dry fit gave a nice curvy profile. You might notice the 1/8" sq strip under the tailplane seat - it's there to make it easier to set the infill flush with the seat cut in the sides. It is just a strip of very light balsa cut from the CNC kit part surrounds. In fact all the strip so far has come from this 'scrap'.

[Former Member]

[This posting has been removed]

[Bob Cotsford]

It must go to the back of the queue

It must go to the back of the queue

It must go to the back of the queue

It must go to the back of the queue

It must go to the back of the queue

It must go to the back of the queue

It must go to the back of the queue

ok, but only after I've opened the box and had a good paw at it.

[Bob Cotsford]

I tried Peter's method on the forward sheet, glue it to the side then dampen it - I let it soak with a piece of wet kitchen towel laid on it for twenty minutes or so. After this it pulls down onto the formers easily. Pin it to the 1/4sq spine then dry it out with the heat gun. For the second side I tucked the top edge under the sheet I'd already formed then cut through both along the centreline. A light sand to tailor the fit, white glue where the formers can still be reached then bind it up tight while the glue dries. I clamped/taped a ruler along the seam to keep the join flat.

I don't think it looks bad with all the rear formers left as per the drawing, if anything it just makes it a bit more curvy.

[Bob Cotsford]

Onto the wings and another error in the CNC kit - the undercarriage beams are too short - I had to pack doubler R1A out with a piece of 6mm to reach the U/C beam. I opened the end of my paper servo lead tube to form a scoop so that sliding a lead in should be easier - Danger, Wet Glue!:

Servo mount - 3mm liteply with a 3mm birch ply backer to take the servo screws:

And finally, if you must drop a wing, try not to drop it onto a CA glue bottle -- my wing skin is patched before it's even completed!

[Martyn K]

You would be amazed how many balsa patches I have on the Aurora. Nasty flake lightweight wood. Light - yes - brittle - far too brittle..

Nice build Bob

M

[Bob Cotsford]

Martyn, I think that's why I'm tending towards bigger models - 3/32 sheeting is so much more resilient which pays dividends when you keep dropping sections of model.