Time to bite the bullet and make that hole where the 750mm long RAM air tube meets the firewall.

Yes I am still firewall planning too. Those bits of cardboard keep moving around.

You might see a problem here in in the hell hole. The full diameter of the chute opening looses about a third of its width as it make the transition. I was well aware of this when positioning the RAM duct as a greater angle than I wanted was needed to get to the firewall. The other way would have been to make the whole cowl lower or have a middle lump.

My thinking was that once I had expanded the air from opening to firewall I needed to expand it and slow it further with a plenum. Yet here I was doing the opposite, contracting the duct before opening it again at the plenum air filter stage. Well I decided that the small losses here were worth the overall gain of a longer pipe and not increasing the profile of the cowl and hence more airframe drag. We will never know if my choices here were good or not.

Here’s my ugly hole in the wall. I wanted a better transition than what I might do with a file.

Out came the micro to improve this area.

I used the RAM air duct to help line it up and make a match. Of yes I have been working on the transition forward of this entry hole.

I grabbed a bit of foam I will probably never use again. You can see that nice big exit needs a ramp.

Once my block was in place for the ramp all it needed was some 5mt epoxy. There is no need for anything stronger than the foam here or waiting for an overnight cure.

You can see this looks like a smooth transition for the air to go to the firewall.

I have since glassed the end with a flox corner.

I have to say this went on and on.  It has had two fills to make the transition as smooth as I can. It still needs more refining a couple of weeks later. I did another little fill between the plenum and the duct too.

I’ll need even more fiddling after I finalise the plenum angle as I need to move that about 3mm. I didn’t even bother with photos. This is typical of the sort of thing that takes far too long because I want to get it right.  Not perfect, I think I know where that line is now, just right. I am thinking about happy molecules of air, not show plane awards.