Yes We Have No Bananas

[Greyhead]

One fault that really makes a model look odd is the “banana” fuselage when the sides have not been pulled in equally at the rear; this is all too easily done, especially if the sides are not of the same density so if “scratch building” try your hardest to get matching wood.

To quote from a kit instructions: “….clamp together (at rear) and then thoroughly check alignment of fuselage visually from front and rear to ensure it is straight and twist free.” Easier said than done!

Whether with age my “eye” for these things has got worse or I’ve got more critical of my build quality I don’t know, then again it may well be these new fangled Varifocal glasses! In any case I don’t feel it is wise to leave this crucial point to luck (look!!).

There are several ways to alleviate the problem.

The best, so I’m told, is to use a commercially made fuselage jig. Unfortunately this is quite an expensive piece of equipment and also bulky to store, so I’ve never invested in one. I devised the method I use a few years ago after reading an article about how the Romans constructed their straight roads, so it has definitely stood the test of time!

Having previously attached the sides securely to at least 2 formers, mark the exact centreline on the formers and the rear post; push pins in vertically at these points. When viewed from rear move the sides until all 3 pins are inline and you’ve got a perfectly straight fuselage; remember to check at the same time that the tail plane mount is square.

It’s a bit difficult to see the effect clearly on the rear view photo, presumably a shortcoming of the camera lens as it is fairly easy to see in practice even with my eyes!

You can also see that I’ve drawn parallel lines on my building board that come in useful on many occasions.

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[Phoenix]

nice tip will keep it in mind when i can fly and will be building lots of p[lanes :D

edit: it would be a idea to check the pins for square :picknose:

 

[Greyhead]

Phoenix

You're dead right, the pins do have to be at the same angle (not necessarily square) and the easiest way is to make them square to the former. If the formers have a rounded base, mark centre between top and bottom longerons, draw a line and align the pins with this.

Grahame

 

[wonwinglo]

What a brilliant tip Greyhead ! Will be using this one in the future,the Romans really were clever people for sure.

 

[Greyhead]

Barry

Yes the Romans certainly found ways to do some very clever things and all without the aid of a computer. I really can’t take the credit for this one; they definitely got there first!!

Grahame

 

[wonwinglo]

BarryYes the Romans certainly found ways to do some very clever things and all without the aid of a computer. I really can’t take the credit for this one; they definitely got there first!!

Grahame

***What I would term a 'Belt & braces' approach to a particular problem,no computers but just good old Mk.1 eyeball ! :computer:

 

[George]

Is this the same Romans who built straight roads to prevent ethnyic type from opening shops on the corners

 

[wonwinglo]

Is this the same Romans who built straight roads to prevent ethnyic type from opening shops on the corners

*** Duncan,somebody once told me that the reason that their roads were so straight is that the chariots had great difficulty in turning corners due to inadequate steering controls ! :poster_oo

 

[duncan]

Hey ! Yiv bin at the sherry-wine ? It wisnae me mister. . must hae bin anither Jock:angel:

 

[wonwinglo]

Dont know my George from my Duncan's !! post Christmas brain not engaging properly.

 

[duncan]

`atsawritethenthenoojimmy!:hehe:

 

[Glider Guider]

The question to be asked is what to do when the pins don’t line up?

In a perfect world a part built fuselage with two identical length sides, where the formers are glued at right angles to the sides should result in a perfectly true fuselage when drawn together at the tail post. Unfortunately due to variations in the balsa wood used to produce the kit, or purchased from your local model shop, all the care in the world can still result in an unsymmetrical fuselage.

One solution is to use a fuselage jig. These can be purchased as a custom made item but they are not cheap or a simple one can be made very easily.

I was given my jig by a fellow modeller giving up the hobby after many years. It comprises a 48” x 12” blockboard base which has been ruled with a 1” grid, to this base are screwed a number of L shaped metal brackets. In use the brackets are positioned a short distance from the sides of the fuselage and wooden wedges are used between the fuselage and the brackets until the fuselage is in the position you want.

With a traditional fuselage which is parallel from the TE forward I construct it normally and only put it into the jig, if needed, to pull the rear ends together, however in more complicated fuselages where all the formers are of different widths and there is no flat area on the sides the jig really comes into its own.

Unfortunately I have no fuselage to show in the jig at present and my wedges have been put away so safe I can’t find them so you’ll have to use a bit of imagination I’m afraid.

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[wonwinglo]

Great tool Dave,you can use shelf brackets screwed through an old self healing board,these have conveniently marked squares as well.

It is a fairly easy job to drive in a few screws at intervals to suit any particular fuselage,fairly crude in comparison with the commercial fuselage jigs but the idea works well.

 

[George]

Barry,

George is the one you met at warwick, so that you can tell us aooart. Other than that I am the good looking young one

 

[Greyhead]

That’s a neat DIY fuselage jig you’ve got there Dave, it could even utilise the underside of a building board. When something like this crops up I always think “why didn’t I think of that?”!!!

As to your question “what to do when the pins don’t line up?” the answer is simple; to produce a straight fuselage the pins have to line up , you can’t alter the laws of mathematics, so adjust the rear post until they do and then worry about tidying things up later. In practice I can’t remember building a model where everything lined up perfectly, no matter how good a modeller you are discrepancies will occur, I suppose there is a possibility that the sum of the discrepancies will cancel each other out but then again I might win the lottery tonight!

If the error at the rear of the fuselage is too great then it’s worth checking it out, the chances are that it’ll be too late to do anything constructive about it but it will be a lesson learnt.

So what can go wrong?

Firstly the fuselage sides can be different lengths but we can reduce the chances of this happening. If the sides are “built up” make one side on the plan, cover it with cling film and then build the next side on top using the first side as a template, any discrepancies will be duplicated. If the sides are from sheet balsa (don’t assume they are equal just because it’s kit) pin them together at a known “square” point, for example the wing trailing edge, then check the front and rear edges and adjust as necessary.

The formers may not be at 90º to the sides. Before fitting the formers ensure that the fuselage side is flat on the building board. On my present model I started the process with a balsa “shaving” trapped under the side, luckily I noticed that something was amiss before it was too late! Having applied the glue, set the former at 90º using a setsquare not your eye, arrange some “scaffolding” to hold it in place then re-check the angle. Leave time for the glue to thoroughly set before continuing.

The above assumes that you have a “standard” fuselage with a parallel sided front section, if it’s a more complex shape or one with the “firewall” at an angle for built in side thrust then things are a bit more difficult, but that’s a different story.

The most awkward problem to deal with is fuselage sides from differing wood qualities. Really the only way to deal with this one is to dampen the outside of the stiffest side to induce the correct amount of bend to match the other side, a very hit or miss process. The moral being to ensure the sides are as near equal as possible before building starts, even if this means making new sides for a kit.

 

[wonwinglo]

The thing to remember is that small variables can build up into big ones,the old adage 'Check twice,glue once' certainly applies here,once the sides are pulled into shape have plenty of clamps ready to stop the wood from curling around,if necessary pre-prepare home made wooden clamp-wedges (this is how they build real homebuilts) to slip over the sheet and formers,allow a good 24 hours drying/curing time before even thinking about releasing anything,all of these tips combined with your jigs and ideas will ensure banana free fuselages and models that fly straight.

 

[wonwinglo]

Barry,George is the one you met at warwick, so that you can tell us aooart. Other than that I am the good looking young one

*** Remember now George,the one with those beautifully made warships in the corner,what a show that was,look forward to the next one at the exhibition centre. :smile2: