Prima Ballerina

[kc]

Elsewhere several people mentioned needing a fuselage jig. This is a photo of mine made mostly from scrap.

construction is pretty obvious. Base is Contiplas offcut 3feet by 14 inches. Uprights are Contiplas offcut but MDF might be better.

Slotted bits are fretted out but much better way is to get two lengths of timber - maybe 20mm by 10mm - and laminate them with bits of 1/4 ply (6.5mm not 6mm ) in one long length. Drill for screws and cut them up into sections when glue is dry. Much easier when in one long length. When fixing to uprights put some glue on and one screw and adjust for true vertical - it does not matter then if they were not cut accurately. When glue is dry put in second screw.

My board has 2 BA blind nuts and steel 2BA bolts ( wingbolts are useless they stretch ) but M6 roofing bolts are cheaper and M6 inserts like these from Screwfix are better. Fix them from underneath with an allen key. Or you can buy M6 captive ( blind ) nuts from Toolstation 10 for 90 pence. If the roofing bolts are long you could also put a wingnut on them and use them like studs.

[kc]

That size board does most 40 size models as anyway you do the front end first and when glue has dried slide it along to pull in the tail end.

You will see that my uprights are handed - that means you can turn some around and change the spacing without having extra captive nuts. But the Screwfix inserts come in 50 pack so you could put more in.

The melamine surface means pencil lines for each former can be drawn on and erased later for the next model. Centreline the same although it's handy to scribe a tiny groove for permanent use and pencil that for clarity

[john stones 1 - Moderator]

That looks simple enough K.C, you made the uprights taller on yours ?

Just had a look on Slec site, only £18...I think i'll buy one it'll be quicker.

John

[Martyn K]

The problem with the SLEC uprights is that they are a bit flexible. I manage with them but I usually end up banding opposite uprights together to keep them vertical

Still a very useful tool though.

Martyn

[kc]

Uprights are 7 and 8 inches tall using scrap material. Cut diagonly to save material!

There is another method of making uprights - 2 pieces of rectangular ply or MDF with spacers sandwiched so a threaded rod goes up the middle, then a washer on top and a wing bolt on the long threaded rod. Threaded rod is very cheap - usual trick most people know - when cutting bolts put a nut on before cutting then when you unwind the nut over the cut end it cleans the thread up.

Whatever the uprights are mad from. In use the uprights are pushed into the fuselage until it lines up with centreline then tightened and fine adjustment made without any glue. Then remove all uprights on one side - fuselage can then be removed and glue applied. The uprights are then pushed towards the fuselage & fixed uprights.getting exactly back to alignment. Simple!

[Biggles' Elder Brother - Moderator]

That looks good kc!

And as Martyn says the uprights will be a lot more rigid than the SLEC plastic ones - which can be a bit flexibe if you really push, but it works OK. I tend to go for a light but definite contact, then apply any pressure needed via a clamp whilst checking everything is still in contact with the jig uprights.

BEB

[McG 6969]

Great info & engineering, kc

Always looks 'simples' when somebody built it before.

Thanks

Chris

BRU -BE / CTR Jig Control

[kc]

It's just rather crude woodwork but it has worked well for nearly 30 years.

The front pair in my photo are arranged like that just for the photo.  The photo shows how swopping them from side to side gives an offset ( moves the upright further along the board)  But of course they are normally used opposite each other like the others back in the photo.  Saves on blind nuts!

The slotted pieces are 18mm square by 100mm long with 65mm slots. Those shown were drilled 1/4 at each end and fretsawed out. Not the neatest or the best way. Laminate them in one long piece is better. I may not have explained properly that making them in one piece halves the number of spacers needed because they are twice as long to make the front of one and the tail of the other. You cut right though the middle of the spacer when glue has dried. Less fiddly = quicker.

Drilling 1/4 inch ( or 6.5mm ) or using 1/4 spacers gives clearance for 6mm bolts.

Baseboard has holes 100mm either side of centre line ( 200 from hole to hole ) and about 90mm spacing along the board. Less than 90mm would be better but uses more blind nuts.

Those Screwfix M6 inserts are super - save a few for your workbench and put several in at strategic places to easily clamp anything - gadgets or workpiece - down to the bench. B&Q sell them too but they are much dearer.

Edited By kc on 14/01/2016 18:34:24

Edited By kc on 14/01/2016 18:36:25

[kc]

After BEB published his calculations of where the lipo would probably go I was almost persuaded that putting the lipo in front of normal F1 was not desirable. Almost but not quite persuaded!

I was quite near to chopping the front off my fuselage and rebuilding as per the plan. But my experience electrifying another model told me otherwise. Previously on a different model that had already been flown with an OS46AX i had done a straight swop for a 4S3000 and Turnigy 3536/9. That model had proved that the prop driver needed to be 4 inches further forward and the lipo tight behind the motor to keep CG.

To prove that my instinct was right for the Ballerina as well I made a crude experiment. I made a simple balnce - really a 'seesaw' - just a plank of wood that would allow a glow motor & tank etc to go one end at the CG to prop driver distance and an electric motor and Lipo the same distance on the other side. So a plank balanced on two screws on centreline projecting underneath to make a pivot. Then the glow motor went one end and was balanced by moving the lipo & motor along the other until they balanced. This suggested that the Lipo needed to go right behind the motor. As my motor was slightly lighter than BEB's. I re tried it simulating the heavier motor. That allowed a slightly rearward lipo but not very much.

Then someone pointed out that BEB's calculations did not allow for the weight of the Rx Nicad on the glow model! So putting a normal 600mah NIMH pack on the glow side literally swung the balance towards putting the lipo as far forward as possible i.e with F1 moved right up front immediately behind the motor. Whilst the weight of an electric motor and lipo may be very similar to a glow the significant factor is where the weight comes in a glow engine. Most of the weight is in the steel crankshaft and bearings right at the very front of a glow engine. The electric motor has an alloy prop adaptor and small diameter shaft at the front. Big difference.

So I am now convinced I was on the right track by moving the bulkhead forward. Time will tell and every model will be different because of variations especially at the tail end. So work on the fusealge continues.

[McG 6969]

Hi kc,

First, thanks again for showing us your fuse jig. It is already on my to-do list.

Secondly, I've been following BEB's and your calculations/simulations since the beginning. I should be tempted to follow yours, specially since my tail is going to be Depron & CF only.

I've been drawing mine with the battery box going through F1 and ended by F0 (the new motor mount).

But then, who am I since I never built any RC-model ever... Time will tell...

Cheers

Chris

BRU - BE / CTR CG Control

[kc]

Of course it all depends on how the tail end is built and covered. It will be easy to move the battery back a bit but impossible to move it forward!

 

Nobody so far has mentioned fitting the covering around the cockpit area. I thought it desirable to pre curve the 3/32 balsa by dampening the balsa on the outside only with a little water. Then I fixed it around a handy piece of plastic pipe of about the right diameter and left it to dry.

 

 

Edited By kc on 20/01/2016 19:33:53

[kc]

So after drying for 8 hours two nicely curved pieces of balsa. No hazardous chemicals just water.

I should have used wider rubber bands to avoid marking the balsa, but again a few drops of water in the crushed part will expand the balsa like magic.

[Geoff S]

Posted by Martyn K on 13/01/2016 20:34:32:

The problem with the SLEC uprights is that they are a bit flexible. I manage with them but I usually end up banding opposite uprights together to keep them vertical

Still a very useful tool though.

Martyn

The plastic clamps that SLEC sell fit the Fuselage jig uprights so perfectly I think they must have intended them to be used to help the uprights stay vertical.

Geoff

[kc]

Geoff, I think that the large plastic ( rubber band ) clamps that SLEC used to sell are no longer available. Not listed anyway.

I bought the last pack at a show 2 years ago and they told me they didn't expect to make any more because of some problem with the moulds or dies.

[kc]

This illustrates one of the problems and at the same time the advantages of balsa........it is a very variable material. We all know that some sheets are lightweight and others very heavy. We select a suitable piece for each particular job. With anything that needs to be bent it is necessary to find a sheet that seems able to bend - some will, some won't.

I chose a bendy type of sheet and cut out both parts from the same sheet but when the parts had been dampened then dried wrapped around the pipe I discovered that one fitted the model easily and one did not. If you look at my photo you can see that the right hand one has a different curvature to the left. I gave it another session of wetting and then drying around the pipe but it still didn't fit nearly as well as the opposite side. The one that didn't want to conform to the fuselage shape could perhaps have been forced to fit but that is often just creating a problem later. Especially for lightweight structures like wings but even on fuselages it can eventually be the part that bursts apart with a slight bit of mishandling. So nothing for it but to make a replacement part.

But why did one piece curve nicely and the other not? Well it's a known fact that balsa can be different one end of a sheet to the other. In this case the balsa is much harder to bend on one side of a 4 inch sheet to the other! It's just a fact of life - balsa is that variable. We just have to make use of this variability and select balsa carefully. The piece that will make good strip wood won't be any use for a leading edge and vice versa.

[Peter Miller]

I just form them over teh fuselage as described, that way they fit.

[kc]

I decided to instal the hatch catch before fixing the sheeting. The hatch catch is to the design shown before and is just piano wire with a spring and a washer soldered on. Spring came from an old ballpoint pen.

The whole thing was easy to make - the most difficult part was getting the holes to line up.

There is an additional part to create a length stop. A ferrule from a servo was soldered on to limit projection to about 5/16 inch. Before the spring retaining washer was soldered on a temporary piece of balsa was used to compress the spring a little. This ensures the catch is never loose but always slightly sprung.

Very simple - I suppose it will work..........

[john stones 1 - Moderator]

Looks right to me KC, i'll borrow a pen and do something similar

John

[kc]

I forgot to mention that I thought it necessary to reinforce F3 by putting a liteply doubler inside to take the compression of the spring.

[john stones 1 - Moderator]

O.K will do K.C

[kc]

F3 is just perched on top of the floor so the liteply contacts the end of the floor and goes down onto the side ply doublers by about 6mm. This seems quite strong..

The guide block is necessary to avoid the piano wire dropping out of the former at maximum retraction.  Also the spring must be able to compress enough to allow complete retraction.

Edited By kc on 28/01/2016 18:55:39

[AndyD]

havnt got as far as to do hatches but i suppose i better start,might be copying that as well.

[kc]

My view on hatches is that it's easier to fit the dowel and catch before shaping the hatch. In other words leave the hatch oversize then insert the catch and dowel, then sand to shape. The hatch is a complex shape as the nose has been pulled in and forms a curve rather than a straight taper whilst the top also tapers downwards. So it seem unlikely a rolled sheet hatch could be formed to shape. Planked might be possible but fiddly. Hatch is probably best made from layers of 1/4 balsa to make it hollow and eventually shaped to match fuselage.

My view is also biased because of the possibility of a hatch coming loose in flight and becoming lost in the long grass. I once spent an hour looking for a hatch then went home without finding it ....... it only took half an hour to make another one. Next time it happened I didn't spend much time looking for the old one! So simple construction seems best.

[john stones 1 - Moderator]

You still building or finished yours K.C ?

John