Build query

[fly boy3]

Hi all, plan calls for the tongue on bottom of the fin which slots into top of the fus to be of vertical grain. The complete balsa part of the tongue is over 4 1/2 inches across. I would need 2peices joined together. Would cross grain be suitable and safe. Thanks

[Levanter]

FB3

I think I know what you mean and you are restricted in the width of the sheet of balsa perhaps?

Is it possible to use vertical grain as much as possible, then the piece you have to join would probably not matter which way it was orientated.

Levanter

[Cuban8]

Vertical grain will be so much stronger and the designer has factored that into the design for a reason. Using fore and aft grain will probably not fail during normal flying, (personally, I'd not chance it) but as sure as 'eggs is eggs' you'll knock the fin during transport and it'll shear straight off. Equally, if the model flips on landing or whatever, it's bound to fail. On a fast model, flutter might be an issue. Keep to what the designer has called for in this case.

Edited By Cuban8 on 11/12/2018 15:07:03

[Geoff S]

I agree with both Levanter and C8. Vertical grain all the way for me. Don't use 4" wide balsa with a 0.5" piece either. Better to have pieces of a similar size.

Geoff

[kc]

Disagree with Geoff - could be the design needs a 1/2 strip of hard balsa for strength at the hinge line glued to a light /soft piece for the rest of the fin. Grain should be vertical as Geoff said. Otherwise join the 1/2 bit to the front of the fin ( might be just a small triangle needed)

Joining bits to make a wider sheet is best done before cutting to final shape. Sometimes you just need to add a small scrap piece not a whole sheet.

If you state what design you are building some of us may have the plan to look at and advise more accurately.

[ken anderson.]

FB3...you gonna have to bite the bullet and spend a little bit dosh and get a suitable bit of wood...better than losing a model through a bit of cross grain''

ken anderson...ne...1...cross grain/dosh dept

[fly boy3]

The model in question has been down loaded from Outerzone and printed for me by a vary kind forum member of whom I am very grateful. The model is Flying Aces Sportster 54inch w/s for 32 four stroke. The tongue itself is only 2.5 inches long, but I'd part of a segment 4.5 inches long. Re Ken,s comment, is balsa available in 5 inch sheets ? Cheers all. ps  I would post a picture but am using an iPad.

Edited By fly boy3 on 11/12/2018 18:24:10

[kc]

I suggest adding a bit to the sheet in the area I marked in pink

Edited By kc on 11/12/2018 18:45:27

[kc]

The other possibility is to put the pattern onto the 4 inch balsa sheet and fit as best you can - if the grain is about 45 degrees it will be strong enough.

[fly boy3]

Hi KC, good ideas, the 4 inch sheet with grain slighly off vertical seems the best solution in this case as we need no joins.Will have to send to Slec for the balsa. The first idea is also good with a small piece joined as shown in pink. Of the 2 which one would be the safest do you think ? They say bones are stronger when repaired after a break, wonder if this applies to wood lol Thanks. ps have you built this model KC ?

Edited By fly boy3 on 11/12/2018 18:58:09

[kc]

No, I have not built this model but just looked up the plan on Outerzone.

Not much difference in strength. Join sheets using the standard method of utilising the machine cut edge (instead of cutting it yourself ) for accuracy. I place the 2 bits tight together, stick masking tap over the join, then place over the edge of the bench and let the joint hinge open to apply PVA. Close the joint and apply a masking tape to the other side. Or leave the joint closed and apply thin cyano from the non masking tape side. Use the same thickness of sheet for both parts preferably the same sheet. Sheets vary and especially 1/4 which sometimes is only 6mm.

I can see why you asked before about laminating. David Mellor's advice was good ( see his postings for much info on laminating) However for simplicity I would make the rudder TE from 2 layers of 1/8 balsa using 2 long scarf joints, then do the second layer with joints staggered and the grain at a different angle to the first layer.

Edited By kc on 11/12/2018 19:23:14

[fly boy3]

Thanks for your help KC, soon I will have to make a former for the wing tips, they are enormous lol. Will have to practice the technique first. Cheers

[fly boy3]

This model has a steep learning curve for me,lots of stringers. The correct size stringers are a loose fit in laser cut rib slots. I am using Aliphatic glue on the rest of the model. Is this glue also a good filler glue or is there a better alternative ? Cheers

[kc]

I don't use aliphatic so I don't know if it fills gaps, but I wouldn't expect it to fill very much without something like micro balloons added to stiffen the mixture. Micro balloons works well with 5 minute epoxy to make a stiff mixture, but it's possibly too heavy if you need to do it on every former. .

Much better to fill the gap with a sliver of balsa after fitting stringers. ( plane a length off balsa with a razor plane if you need a lot ) Better still cut your own stringers from balsa with a balsa stripper to correct size. Or order a few more stringers and hope they fit better. ( check whether the slots or stringers are metric sizes rather than imperial!) The fuselage stringers won't be too critical but the fit of the wing spars would need to be very close to make a strong wing with  unsheeted construction..

Edited By kc on 12/12/2018 11:14:12

[kc]

On checking the small plan on the screen I cannot see whether the wing is fully sheeted on top or just the centre section. Maybe ribs W1 and W2 are thinner than W3 to allow for sheeting only centre section. Difficult to tell without the fullsize plan.

[fly boy3]

Thanks for the info KC, the stringers are not loose enough to allow a sliver of balsa so I will persevere with Aliphatic. Re sheeting the plan calls or sheeting only from root rib w1 to rib w2. Cheers

[Ian Jones]

Just taken a quick snap of my wing, not a good photo by a long way but you can see the sheeting on the top centre section.

No sheeting on the underside:

As for the black patches... make sure you fit decent servos in the first place!

[fly boy3]

Must say Ian superb work and covering, looks like the wing struts are flexible wires. ? Cheers

[fly boy3]

For KC. I have gone and bought a balsa stripper to cut my own stringers lol, should pay for itself in the future. Cheers and thanks

Edited By fly boy3 on 12/12/2018 16:10:28

[kc]

If you have bought a SLEC balsa stripper it is possible to cut non standard sizes by making extra spacers from paper or card or veneer or ply or even a couple of layers of masking tape to cut just a little thicker.

Cutting thicker than 1/8 means making several light cuts rather than one cut to full depth.

[Levanter]

FB3
Aliphatic is not really a gap filling glue and any that are will add unnecessary weight. The strongest glue joints are best made close fitting.

It seem your gap in the stringers is big enough to notice but not as you say enough to fit slivers of balsa which was KC's good suggestion. Your problem is quite a common one and instead of trying to fit thin strips you can easily cut small wedges. There are many ways to do this but even a shaving off the edge if an offcut will generally do.

Fit the stringer in the notch as normal. Put some glue on both sides of the wedge and slip it into place. It is best to leave them like this until the glue has dried when the joint will be stable. The extra can be trimmed off and then lightly sanded back to the correct level. Easily done in a fraction of the time it takes to describe it.

I frequently have to do this whether by accident or design.

Levanter

[Ian Jones]

Those bracing wires are the usual fishing line traces with clevises at the ends, makes for quick assembly at the field.

[fly boy3]

Thanks Ian, what a beauty. Since I only have a plan, this is the first time to see model in the flesh lol. I am well pleased. Cheers

[Ian Jones]

Also to help with quick assembly are the wing spars:

When fully assembled the wire braces prevent the wings from sliding off!