pat teakle vega

[terry white]

Hi guys, just to butt in here Epoxy and Polyester should not be mixed. Keep to one or the other. Roo must have been lucky in the past. If mixed the bond will appear to have taken(like the polyester to wood situation that Jack spoke about) however a little later down the road when both are cured thoroughly it will de-bond on the first hard landing.
Many of us model fliers will remember the olden days finding either fuselage former's or servo bearers etc rattling around in the bottom of the fus after such a landing.
Many of us modern glass ship flyers have taken to bonding in the fuselage former's with silicone as devised by the Germans some years ago. The idea behind it is that this more flexible joint allows the fuselage to distort throughout its total length when required to do so without breaking a more solid bond.Most former's are used as a shape keeper or servo mount anyway and silicone adhesive is ideal for this. Also in engineering terms it is not a great idea to hold a flexible item with a non flexible bond. This works well for either epoxy or polyester. Can be obtained in clear or white, small or large amounts.

[jack]

Good points terry,to be honest l havent heard of useing silicon to fit out a glass fuz,always used resin and cloth,though l do take your points...something that is done on glass boat hulls is to space the bulkheads away from the hull to avoid "hard" points forming which then show on the outside,the bulkheads are attached with fillets of glass cloth....maybe this method could cross over to glass models?,has anyone tried using grp sheet for formers???,not too much weight difference..jack

[jack]

terry,just wondering if there is a preffered grade/type/brand of silicon to bond in formers to polyester fuselages???...jack.

[Cliff Evans]

Jack, I would use Sikaflex 512. Like **** to a blanket!!

[John Vella]

Jack, I use Henkel Unibond. Regards John.

[terry white]

Hi Jack, It appears that others are using the the same system that I mentioned earlier, in as much that we have steered away from the hard bond associated with epoxy or polyester resin when it comes to fitting out the former's and servo trays in the fus. I am sure any good flexible bonding material doing the same job would suffice.
One must not think that a flexible bond is weak because it is not. (fish tanks come to mind)
My technique is to scuff the area well, make the former etc a little undersized say 2-3 mm all round so as to make sure there is thickness and flexibility in the joint,load the former with the silicone and fit to position holding it in place with a couple of small balsa wedges. Finally running a whetted/soaped finger around to finish.

There are a number of associated advantages with this system.
1) the former shape and size need not to be an exact fit which is often difficult to achieve inside a fus.
2) The former need not be made as one but in a number of parts if preferred.
3) The former/joint is somewhat easier to remove and clean away if need be for repairs.

Having said all that I would still glass/cloth fit the wing joining former in the top of the fus with the same resin the fus is made of for the obvious reason. hope that helps. Terry

[jack]

thanks terry,and also to everyone else,its good to know that help and info is there for the asking....l will be doing a build type blog when l start on the vega,as l mentioned,this is going to be a sport vega,so hopefully the build will be of interest to other vega builders/owners