A classic wing break at the edge of the glass

[Alan Cantwell]

i stated a while ago, that you should not glass outside the fuselage boundarys, unless you use the multi layer glass tissue method, nothing shows the damage a central bandage can do to a thin wing,

apart from that, the sellers avin a larf

**LINK**

[Gary Binnie]

It's a Chris Foss Phase 6, built per the instructions.

Looks like it has suffered a mighty whack that no structural design could cater for.

£25 might be on the steep side for this, considering that the servos and receiver were probably involved in the same incident and the airframe is scrap!

GB

[jay cube]

May be its a law by the government not bounde more glasses outside the boundries.

[kc]

Alan, convince me your idea of only 1 inch glass fibre bandage is safe! Give me some facts such as 'this aerobatic plane flew for x years' and specify weight, wingspan etc How many others have used such minimal reinforcement? I would really like to use such a tiny bit of glassfibre but you have not ( yet ) convinced me.

Also I think the wing bolts and wing dowel positions need some reinforcement anyway.

Are you saying its just needed to join the veneer? That is if the veneer were continuous ( as it could be on a constant chord wing with no dihedral ) it would not need fibreglass at all?

[Alan Cantwell]

doesnt need to be so narrow, as long as it sit inside the fuzz, what i do is to glass inside the fuzz, and create a wide seat for the fuzz to sit on, usually, its 4mm, or so, i double this, and use wing seat tape, the glass inside the wing bit is particulary desireable on a thin glider type wing, with these, if its going to get some stick, i use glass tissue, cut rugby ball shaped, about 8inch long, this goes on with thinned out glassing epoxy, the next one is 6inch, then down to the inside of the fuzz width, this shoves the strsses along the wing, where they dissapate, any shock to a wing will seek the easiest brek, thats the edge of the glass, think of a ply fuzz doubler, they run from the front bulkhead, generally to the rear of the wing seat, then it tapers off at about 30 degrees, every wonder what this is for? exactly the same, it dissipates the shock from a hard landing, shear points are what shear points are, and the edge of a glassed wing is a good one,

another point, glass outside the fuzz has to be sanded, unless you cover the egdes with 2inch masking tape, there is a real chance of thinning the veneer out, glassing inside the fuzz, and using thick doublers, and wing tape, negates any sanding at all,

now then, roll on the doubters,

as for uses, all my old style aerobatic models, all 60 size, all where done this way, none have failed, BUT, not built owt for many a year, but the method does not change,

[kc]

In case anybody wondered why I mentioned a 1 inch wide bandage this is a quote of Alan's comments in another thread

" please, do NOT use a 4 inch wide bandage, unless it falls inside the fuselage width, the bandage is to re-inforce the centre join, NOT the wing, i have never used wider than 1 inch, some take some convincing,"

Alan said in the quote above he never used wider than 1 inch but his comment today seems to be a bit wider! A " rugby ball shape about 8 inch long " suggests something a little wider than 1 inch. Please clarify this Alan. Is 1 inch a misprint?

[Alan Cantwell]

no, i said you dont need anything wider than 1inch, but if it makes you happy,

The procedure with the rugby ball shape, is for extreme foam wing re-inforcement, mainly for pylon race, and high speed gliders with thin wings, i had a Phase 6 done like this, no amount of high speed hard turns would snap the wing, mine where usually resin bonded veneer onto foam, i had 3 Phase 5 wings made like this,

[Martin Harris - Moderator]

It makes sense to me, Alan. The veneer takes all the bending loads for the entire span - creating a sharp edged shear point coinciding with a sharp edged support point (the edge of the fuselage) doesn't seem a particularly good idea...

[Alan Cantwell]

my work here is done

[Richard Wood]

The rugby ball shape makes good sense on a thin glider wing - analogous

to a tapered dihedral brace in a built up wing spreading the load.

Veneered foam wings (thin glider wings possibly excepted) are generally

pretty tough & surely any flight load wouldn't really tax the strength of the

wing at the g/f bandage edges - whether inside or outside the fuse, provided

the veneer hasn't been weakened by excessive sanding.

I've always glassed beyond the wing seat & also never had a failure.

Apart from aesthetics, the only real advantage of keeping the glass inside

the fuse would seem to be that sanding isn't necessary, avoiding the possibility

of veneer damage at the bandage boundary.

[Erfolg]

I do see the argument that a 1" strip would re-enforce the joint, where oam is but jointed.

I can also see the point of having a much wider bandage where the purpose of the bandage is to graduate the strength of the wing, due to bending stresses. A simple foam veneer wing, does little to facilitate this.

I can also see the potential benefit for an angled bandage across the wing or the suggested rugby ball contour.

At a practical level, there will always be a concentration of stresses where a transition takes place. I am not keen on the sanding method, as it is to easy to introduce, yet another stress concentration.

In the distant past, large gliders with foam wings, often had stub full depth spars of ply to help distribute the stresses. Not using the glass bandage at all. Then again, George Stringwell, suggested that on tip panels, just epoxying the joint, could be a solution. accepting there will always be a weak point. Why not a nice neat position such as the joint. Where overstressing would result in a nice easy to repair junction.

[Alan Cantwell]

another stress point on a foam wing is to use spars, 1 on the D box, one 3/4s back from the leading edge, and make them the same length, the rear one needs to be 2/3rds the length of the front spar, its all about spreading the load

[Erfolg]

George Stringwell in his book Thermal Soaring, gives a number of examples of alternative methods of graduating stresses. The point is though, it is a partial solution, in that the stress levels will not be equal along the span of a wing, just kept within bands of stress in various zones. There remains higher concentrations somewhere.

Having said all of that, the methods outlined work within reason, seldom seeing a foam wing fail, even at 144" span, under tow line full towline grunt launches. Again there are limitations and moulded wings are stronger still, at lower weight.