Marcus Stent and Steve Kepp Original text
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Marcus Stent and Steve Kepp Original text |
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MONGOOSE
WING LAYUP By
Marcus Stent The wings are two-piece with a joiner that
runs through the fuselage. Therefore
there are 4 mould halves. There moulds are CNC machined aluminum The information is an accumulation of my
own experiences and tips and help from many other people. 1.
Wax. We use PLP 10, mould release wax that is 10% synthetic. 2.
Paint. Our best results have been with a two pack acrylic urethane by
‘DeBeer’ I let this dry for 24 Hours.
3.
Put on lots of epoxy. We use Araldite 3600LC by Ciba-Gigi, it is very
thin and we can cook it in an oven at about 60 degrees C. This doubles
the strength and crispness of the resin.
Pouring on the epoxy before the glass helps to stop tiny air
bubbles forming. 4.
25-g/m glass at 90/0 degrees.
5.
More resin
6.
93 g/m Carbon cloth at 45/45degrees.
7.
Work the resin up through the Carbon and then soak up excess epoxy with
paper towel until there are no wet patches. The epoxy left in the cloth
has been measured to be about equal to the weight of the glass and
Carbon. 8.
1mm Balsa with cutouts for the Spar (40mm tapering to 15mm) and servo
wells. The balsa is run through a sanding jig (a Dremel with a sanding
drum, mounted to a board at an angle) to bevel the edges of the balsa to
a very fine point (0.0mm). This is very important to stop fine
‘witness lines’ on the surface of the wing.
We also bevel the L.E. and stop the balsa 2mm from the L.E. of
the mould. We do not need to add any epoxy/micro balloon filler to the
L.E. 9.
100g/m Glass strip (50mm tapering to 25mm) over the Spar cutout in the
Balsa. This is to stop tiny dimples in the surface (they appear only
where the spar is) from the carbon spar. This is wet out on the bench
and placed over the gap in the balsa. 10.
Carbon Spar material. This is currently 48k tow, I wet this out on the
table and placed in the spar cutout in the balsa. I make huge spars
because the launch stiffness is very important. I use 20 tows at the
root tapering to 4 at the tip. 11.
Spread the epoxy for inner layer onto the balsa. 12.
Put down square patches of 6 oz (200GSM) Carbon over the servo well
cutouts 13.
25g/m glass cloth 90/0 degrees and squeegee off any excess epoxy. 14.
Peel ply 15.
Put down lots of Paper Towel. I use 3 layers, overlapping in the middle
to make 6 layers over the spar. 16.
Bag sealing tape, I use the high temperature tape (for autoclaves) and
this works well because I can pull the bag from the tape and then
re-stick it again. 17.
For the vac bag I use Plastic sheet (100 micron), from the hardware
store. 18.
Now pull vacuum to 15”Hg and after 15 minutes I disconnect the vacuum,
lift the plastic sheet and remove the epoxy filled paper towel. I then
put in two layers of fresh paper towel, reconnect the bag and pull
vacuum to 15”Hg (0.5 Bar). The
reason for this is that it makes the removal of the peel ply much easier
because there is less paper towel filled with epoxy. 19.
I then put the mould into my homemade oven ( I use foam sheets made into
a box, placed over the mould, with an electric fan heater and a
thermostat inside) at 60 degrees C for 24 Hours. 20.
When the skins are cured I peel off the peel ply and use a sharp knife
blade at a very shallow angle to trim the edges of the mould. I have
found that a chisel can lift the edges of the skins from the mould. Note: We have recently changed from 26”Hg
to 15”Hg and have found that the weave ‘print through’ of the
Carbon fibre onto the surface finish is almost eliminated. To be continued… I will send through my
internal structure next week Hi
Eric,. My name is Steve Keep, I have been working with Marcus Stent on the structures side with the Mongoose,.. Currently I am producing the tailplanes and was curious about the layup you are using. Looking at the photos on the website www.f3j.dk it looks like there is very little spar material and you rely mainly on the carbon sock shearweb for strength? A big problem we have had on Vtails (not ours so much but alot of others) is after a hard landing when the tail gets slapped on the ground the top spar cap delaminates from the shearweb,.. We have tried various ways to get around this and I am always looking for how others make their Vtails stong enough but not to heavy. Mine have been strong enough but I am looking at getting them lighter... Another question is about the antenna, It looks like in the photo it is one piece of wire either side of the nut and soldered to the nut so effectively you have a split antenna, one going up either side?? Is this correct?? I run an antenna in mine too but go up one side just in front of the spar then down the leading edge to the other side.. Marcus forwarded a email from you about some of the layup details and the fact that you have gone back to using gelcoat instead of the 2 pack paints? I am curious as to why as when have gone the other way, played with the gelcoat and had troubles, lately we have been using the Debeer 2k paints with wonderful results. The surface finish is fantastic and stays as it comes out of the mould where as all the other colour systems we have used have deformed or deteriorated a day or two after we pull the wings from thhe moulds.. Could you expand on the reasons you have moved back to gelcoat?? I hope you can spare the time to respond and I look forward to your reply.. I have a pic of marcus and the "Goose" just after his win at the National Champs in Jan. if you are interested I can email it through.. Cheers Steve Hi
Erik, My layup at the moment is two layers of 0.5oz cloth both at 45 on the outside then 0.5mm balsa then 1 layer of 0.5oz at 90 inside. The paint is sprayed into a warm mould (in an oven @ 40-50 degrees for an hour) and then heat cured at 40 degrees for 1 hour then layup straight onto the paint, no primer or preparation required. When I mix the paint I do not use any reducer or thinner on the last colour coat, this gives a slightly rougher surface (orange peel effect) and the resin adheres fairly well to it. I have some really REALLY sticky tape we used in the Airforce for airframe temporary repairs to get aircraft back to home base for permanent repairs, that has not succeded in pulling paint of the fibreglass yet... One paint system I have used in the past with a lot of success is using just the tinter from epoxy based paints, thin to spraying consistancy and spray in the tinter, when the epoxy is layed up over the tinter for the layup it cross polinates with the paint and chemically cures the paint tinter and havent found any normal household chemicals which effect the cured paint....fairly light system but not total opaque. I will give the antenna system a go in the next tail. One other thing to mention which I have found very useful with very light weight cloth. Get some of the cheapest hairsray you can find and spray a light "dust" coat over the cloth before you cut it out, let it dry for a minute or two then cut out you cloth and you will find it a lot stiffer and easier to handle, when it is wet out with resin it disolves the hairspray after a minute or so just like to ordinary binder agent used in the cloth when manufactured..give it a try and let me know what you think? I had to come up with this method because I was given a 100m roll of 0.5oz cloth that had a sticky roller on the weaving machine when it was made and had a pulled thread about 50mm from one end right the way through the roll and becasue of the fault they didn't put the binder on the cloth. You can sneeze at the other end of my shed and watch the cloth become unuseable at the other end!!! The hairspray holds it in position so you can pick it up and place it on the mould.. I have included a pic of my latest creation for BAE systems (previously British Aerospace).. The Brumby Mk 4. 4 meter span and the last testflight before delivery to the customer last tuesday was at a ballasted weight of 62kg!!!! Big barge to fly.. The next aircraft they want done is on the drawing boards at the moment, looking like 6 meter span and 150kg...... I also am manufacturing a 2.7m electric glider UAV for a group in Canberra (National Capital of Aus) who has a contract for supply to the Australian Army for survelliance work..... I will be at the Avalon Airshow next week, Hope to get lots of pics and put them up on a web site, will let you know whenit is done if you like....
Cheers Steve 13.
januar 2003 Eric, 24.
januar 2003 Hi Erik, 28.
januar 2003 Erik,
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