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fly boy311/12/2018 14:07:20
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3520 forum posts
18 photos

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

Levanter11/12/2018 14:50:16
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881 forum posts
436 photos

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

Cuban811/12/2018 15:04:46
2727 forum posts
13 photos

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 Sleath11/12/2018 15:39:32
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3374 forum posts
272 photos

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

kc11/12/2018 15:55:03
6032 forum posts
168 photos

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.11/12/2018 16:38:14
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8439 forum posts
772 photos

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 boy311/12/2018 18:22:41
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3520 forum posts
18 photos

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

kc11/12/2018 18:36:20
6032 forum posts
168 photos

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

flyingace10003.jpg

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

kc11/12/2018 18:41:01
6032 forum posts
168 photos

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 boy311/12/2018 18:55:47
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3520 forum posts
18 photos

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

kc11/12/2018 19:22:27
6032 forum posts
168 photos

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 boy311/12/2018 20:12:58
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3520 forum posts
18 photos

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 boy311/12/2018 21:36:46
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3520 forum posts
18 photos

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

kc12/12/2018 11:10:39
6032 forum posts
168 photos

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

kc12/12/2018 11:25:44
6032 forum posts
168 photos

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 boy312/12/2018 12:13:24
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3520 forum posts
18 photos

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 Jones12/12/2018 12:19:53
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3218 forum posts
1397 photos

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.

img_20181212_120038[1].jpg

No sheeting on the underside:

img_20181212_120109[1].jpg

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

fly boy312/12/2018 14:04:37
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3520 forum posts
18 photos

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

fly boy312/12/2018 16:09:40
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3520 forum posts
18 photos

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

kc12/12/2018 17:08:49
6032 forum posts
168 photos

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.

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