Quote Originally Posted by ChristoT View Post
Hi Jazz,

Looking again, I reckon I might be able to make the fuselage and fin moulds in house, meaning only the 4 1m long wing moulds need outsourcing.

That would probably make more sense, as my current project plan is looking at a fortnight for the pattern manufacture, and another week for mould manufacture. If someone can machine each wing moulds in one hit, that's three weeks for the 4.

Charlie, I am very familiar with the technique you describe, as that is how e-Go Aeroplanes (where I was on placement) lay up their wings. They use controlled polystyrene cores, with large sectional cutouts. They have to wet layup, though, which isn't ideal due to weight considerations. Whilst you can cure pre-preg outside an autoclave, the stuff we're going for will need autoclave treatment due to the resin/fibres ratio. Obviously, polystyrene can't take autoclave temperatures! We are looking at a wing loading of about 3.57kg/m2 - which is nothing. Makes more sense to get the weight down early, especially as the electric motor we're provided with is, well, pathetic.

During the design phase, we'll be running a simulator alongside the design, tweaking as required. Another reason why we need the moulds to be spot on - as the BwB has no horizontal stabiliser, it is nigh-on impossible to trim. Unless the centre of gravity and centre of lift line up, you have an unstable aircraft. So you have to add ballast weight to trim, and your advantage of a high-lift, low weight aircraft start slipping away...

We are trying to scrape every single gram off - the contest is highly competitive. Last year, the teams were using the more powerful glow ignition engines (about 2x as powerful), and the winning entry weighed under 1kg - nearly half the weight of my University's design. If we want to win, we need to be one of, if not the, lightest plane on the flight line.
if you are carefully doing a wet layup on a layup table and then vacuum bagging with all various extras and not just mylar a long with then removing a majority of it through pocketing you can achieve results incredibly close to a moulded or autoclaved product at a fraction of the cost and you can still post cure with xps or eps to get every last bit of strength.

For what you are doing carbon for the entire build will not only be expensive but also over built and heavy for the purpose. we used to do builds comps using micro cars for all the components which were like doing small scale payload challenge as the were heavy brushed motors and copper coil actuators, the size you can cut everything down to get the strength to fly if you relay try is crazy we were using something like .5 mm carbon caps on wing ribs were still ott a lot of the time

While moulding is great and you can get some fantastic results if you have a large budget and a proven design if you are doing a one off or prototyping it is a expensive way of doing it to get the same result as perhaps a little more time but significantly cheaper and faster method that allows you to be flexible with your design.