The inlets are all done now. The job went fairly well except I shouldn't have bothered with painting and waxing the foam plugs as they didn't release. If I did this again I would just apply the light coat of micro slurry, sand and then put duct tape on it as a release.
I ended up having to Dremel out the foam - same as I did on the oil cooler ducts.
I used a bead of RTV all round to make the edges air tight and nut plates to attach the inlet to the baffles. It all fits good and makes the baffles a lot more rigid than before.
I bought some 1mm thick rubber sheet and cut out some strips which are the connectors to the inlet rings. Using big hose clamps to connect the two. The end result is an air tight connection which is also flexible - about 2mm movement in any direction. This is necessary as the inlet rings will be bonded into the cowling and the carbon inlets are connected to the engine so some movement and vibration will occur between the two. Also you need to be able to remove the cowling completely so the hose clamp makes this easy to do.
Onto the plenum.
After much masking and protecting with thick plastic sheet it was time to mix up the 2 part PUR foam. This stuff is super messy to work with and goes everywhere so it's worth protecting anything in the vicinity. I should have put some plastic sheet on the floor too as there was a bit of overspill. Anyway Acetone gets the foam off so that's good to know.
Once mixed you have 30 seconds to pour it in place until it starts to kick off and expand. It also has an exothermic reaction and puts out a bit of heat too.
I wasn't thinking too much here and didn't realise the foam would spill out as much as it did - I ended up having to use my hands (in gloves of course) on the back sides to stop the foam spilling out too much.
The foam expands to 25 times it's original size so you don't need much.
After a 1 hour break for lunch I came back and it was set rock hard.
Time to get out the rasp and do a rough shaping job. This was followed by a sanding bar (hunk of wood with 80 grit sandpaper glued to it) to finish the shape.
When I was totally happy with the shape I used some micro slurry to fill in all the pin holes in the foam and then create a layer on top which I will sand to final shape and this will give a smooth surface for a layup. I'm just going to put duct tape on this as a release. Then it will be ready for a carbon layup - probably going to go for 5 layers of carbon on this job as it's got to be rigid with all that air pressure going on under there.
More about all this next week.
|Plugs all waxed - 9 coats - all ready for layup. I needn't have bothered with waxing as it turns out.|
|4 layers of carbon on main areas and 6 layers on areas where nut plates and hose clamps will go.|
|After trimming and removing the foam plugs. They are plenty strong enough.|
|Loads of RTV to seal the edges and make it air tight.|
|Inside view from the back.|
|With inlet rings in place.|
|2 part expanding foam - messy stuff!|
|All masked up and ready to go.|
|Told ya it was messy!|
|After sanding one side.|
|As you can see I had one tiny leak of foam - easy enough to peel off a shiny surface - which it doesn't stick to - and clean the rest with Acetone.|
|Both sides sanded. Ready to micro now.|
|Loads of pin holes to fill. That's where the micro slurry comes in.|
|Just needs sanding now.|