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Avoid Building a Banana!!!


cymaz
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Hi cymaz, i'd make a jig from mdf. cut around 6 accurate rectangles, say 150X100 mm. Cut them across the diagonal, and you have the basis of a decent jig. you need a flat building board, and a method of fixing them, but it's not rocket science. I made mine about ten years ago, and am using it as I write this

ernie

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The Stampe fus is too long for the building jig. I checked the superstructure and it is square on the diagonals. I will add the sides and glue only to the superstructure. Then clamp the tail end together. If I put a plumb line in the middle of the rear former and mark the middle of the rear post and stretch cotton between the two.

This will give me a striaght line from the front. I mark the fuselage sides down to the rear at equal intervals. If the fuselage is straight the measurement should be the same each side all the way down........

am I correct................would this workquestion

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I would avoid doing it that way, if I understand you correctly. If the two sides bend differently (almost certainly will) then your plumb line will not be where you want. However forcing the sides in to be centred on your line should work. If thats what you in fact meant?

I would start by positioning over the centre line, bringing the sides together using the marked line and the line in the middle of the bulkheads/cross members that Peter mentions. As you get further back towards the tail, you may need more pressure on one side than the other. I don't clamp them together at the tail until the very end. If you have done it right they will meet perfectly...... thumbs up

Cheers

Danny

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I found that with the Stampe, if the forward formers are true and square you can simply dry clamp the tail post together and it will be spot on, provinding both sides are identical, if they are not, when you centre the tail post the ends will not meet up exactly, i then checked the straightness of the sides with a 1 metre rulemounted onto 3 blocks, purely to check for straight lines, not squareness or central position, try it all dry first and if its all good, get the glupey glue out cheeky

My double check method was to get a 12" rule, tape this to the front former with 7" exactly sticking out, and measure from that point to the centre of the tail post, do the same for the other side and both measurements should be the same if it is in the correct position

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Many years ago (1961/2) I made a Southern Junior Models 'Southern Dragon'. Whoever designed this kit obviously thought about the 'banana issue' . A balsa 'crutch' was built first around the centre line of the fuselage looking on the plan view. Once the crutch was finished the bulkheads were added to the crutch and then the stringers etc to the bulkheads. A similar arrangement was designed for the polyhedral wing spar which was constructed first. I always thought that if I designed my own plane i would use the crutch method as it ensured there was no distortion. The Southern Dragon was only 42 inches span and was a free flight model. There was the usual warning about putting your name and address on the model which I ignored and hence lost it on it's first flight. The plane /plan is still available through Ben Buckle.

MJE

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There is always good old Pythagoras and his right angle therum, (that's not a vintage builddisgust). I will do both methods..bringing the tail together over a straight builing line then double check by measuring. The ruler never lies!!!

I have checked my string method and the measurements either side of this all the way down the fus were identicle each side.

I have one chance to get this right. Its more nerve wrecking than a maiden flight.

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  • 3 weeks later...

I Jig

I thought some newbie’s to balsa bashing and born again types like me might be interested in my world patented anti banana jig wot I knocked up, sorry made this morning.

Using the old centre line method it’s an old IKEA shelf I’ve been saving for sometime and some wooden blocks faced with balsa which has been stuck on with double sided tape. The blocks themselves are also stuck in place with double sided tape – it didn’t need anything fancier in the way fixings than that. Just position the fuz over the centre line, position the blocks either side and stick down.

You might just be able to see that the nose is raised so that the tail can sit flat, square as well as centered on the line. Yes, it’s not pretty but it worked a treat

I don't think SLEC will loose any sleep.

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I would start by positioning over the centre line, bringing the sides together using the marked line and the line in the middle of the bulkheads/cross members that Peter mentions. As you get further back towards the tail, you may need more pressure on one side than the other. I don't clamp them together at the tail until the very end. If you have done it right they will meet perfectly...... thumbs up

I follow DF and PM's advice and use this method on all my builds. I've found one of the those cheapo DIY laser levels perfect for this, as they project a red striaght line beam down the centreline of the model (over your original drawn line) and this helps when bringing the tailpost together.

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  • 3 months later...

'Crutch' building is my preferred open structure method, Either do the sides or top and bottom halves first. Pin down the centre line longerons for top and bottom or upper and lower spines for the sides. Glue on the half formers then the stringers, when dry remove from the board and join the halves together.

Ruprect

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