Thursday, March 5, 2009

A how to make a vacumn bagged wing

Hi Guys,
Making vacumn bagged foam wings has been around for a long time , but unless someone shows you the steps , many builders are not keen to tackle this method which can produce a light strong wing in a short time, like all things it's easy when you know how.

I have been asked by some of the gliding guys to explain, but might add that this type of construction is even more suited to power planes with thicker airfoils and shorter spans.

This build thread then will detail all the steps and show my latest build , but there are variations to bagging techniques , anybody who has any questions are welcome to ask in the comments section, Or drop me an E-mail.
As always wear gloves when working with epoxies, and work in a well ventilated area
, make sure your work surface is flat and even.

I am not going to cover the template making and foam cutter but needless to say you need a set of cut foam cores and I prefer extruded polystyrene foam , in this case Dow blue foam but local ISO-Board available from the cornice moulding shops also works well, and can be ordered in longish sheets for a few hundred Rand, generally you can only hotwire cut panels accurately to about 800mm in length.

Phase 1.
The preparation of the cores.
The cores are cut in segments and in this case glued together end to end with a thin layer of 5 minute epoxy (Alcolin the type in the syringes)its a tapered wing , so I used the outer shells to hold it accurately while the epoxy glue set (10 mins).
Polyurethane glue also works but seems to be off the store shelves.

The spars are marked out and then masked with tape, this wing has a tapered spar.

I made a simple sander and sand out a groove between the tape , about 3mm deep and with a square edge. I sand the top and bottom grooves and blow the dust off with compressed air.

The carbon tows are wet out on a piece of mylar this wing has 2 x 60k tows to the tip
and then the wing is divided into equal sections and 2 x tows cut and layed up to about 75% then 2 x shorter ones to 50% and then 4 x short ones to 25%
This now means 10 x in total out to 25% which is where the greatest load is.
On a power plane I normally make a constant spar groove and carry the carbon spar throughout.
The next step is to sand the leading edge, a small con-cave block can be used to get an even profile, but this wing is tapered so I sand by hand and eyeball the shape. I then cut some strips about 5cm wide and about 30cm long out of some straight weave
104gr glass cloth, enough for the full length of the wing, I use LR20 epoxy resin and SLC 30 harderner (available from AMT) I have now sanded a nice round leading edge and wet this with a thin line of resin , to this I adhere a single 12k carbon tow , I wet this out with a small brush then add 2 x more tows , one above and one below the leading edge centre line, these are also wet out.
Then I pre wet out the glass strips on some mylar sheet and lay them over/around the leading edge carbon strip. I leave the wings upright while this cures overnight.

These cores now with top carbon spars and carbon/glass re-inforced leading edge are left to cure.
Next steps include the joiner tubes ,Shear webs , end rib and bottom spars.
Time spent so far 1 x weekend.

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