RAM Air & Hellhole Cover

Date:  05-17-2019

Number of Hours:  8

Manual Reference:  no ref

Yes, the last major addition to the aircraft’s air-frame. Making good the bottom rear to match the Melvill cowls and later the fitting of the ram air scoop. Its a three step plan.

1. Make good and glass the bottom.
2. Cut and prepare the hatch as a finished item.
3. Fit the RAM air scoop into the hatch and make this all a removable part for access to the hellhole.

After yesterdays mammoth fill session I found a few more areas to patch up to achieve my desired lines.

While the pour foam is a little rough with minor potholes I have my shape.

This gives an idea of the lines, a not very exciting flat bottom to the firewall. I hope the air molecules appreciate it for their runs along the bottom to the prop.

The line to the cowl is now reasonable. There will be some careful filling and tweaking later. The gear legs after glassing will have an all around gap too. For now it seems simpler to just go to the edges of the gear.

Given the pour foam is pretty rough I’m going for the hard shell method. Above is a coat of micro which I will sand smooth when cured. It may need a few more fills and then another sand. This will give me a great base for the later glass layups.

Date:  05-16-2019

Number of Hours:  32

Manual Reference:  no ref

This was another 5 days work. Well four really, I worked on my flying Long-EZ for one day. There is always a benefit in doing supervised maintenance as I am allowed under the regs. I intend to continue this even when I have fully authority to do everything myself on this new build. There is knowledge in the hangars full of licensed people and a second set of eyes is something I would be foolish to give up.

This ram air mod is in two parts. The scoop itself and getting it fitted in the hell hole while still allowing full access to this area. No small challenge.

I first trimmed the gear fairing, if only to reduce unnecessary weight.  Then I had to confirm that this scoop was going to fit and have an idea of how much I was going to be cutting into the floor of the plane. Much less than I though as it turned out. You might notice that I have cleared the scoop of its blue foam mold. That worked out very well using grey release tape and patience while getting the form out from within.

This gives you an idea of the ‘adjustment’ I had to make in the fuselage floor.

The extrusion straight edges show how much extra floor body needs to be added to get a smooth transition to the firewall from the fuselage bottom.

I could make beautifully crafted inserts on blue foam to do the job, OR I could use pour foam of the same density, 2lb per cubic foot or 32kg per cubic meter. The plane won’t know the difference and it is going to be a non structural cover.

I just stuffed some left over foam into the cavity as a base. I did take quite a few photos and measurements for later. You can see here a LOT of fill is required to make the lines right.  Of course most of it will be removed later.

You might notice that I have covered the plate bolts with micro. I also did this with all the seat belt exterior bolts. The idea is that if I ever have to tighten the nuts I don’t want the bolts to rotate. I suspect I will never have to tighten them. They are torqued to spec and have blue torque seal indicator lacquer on them for later visual checks.

A guy has to have some fun. So I did opt for the excess mess over the carefully fitted parts.

Time with the vibration cutter and the power sander removed the bulk. Next came the sandpaper glued to conduit as I used on the strakes. 40 grit paper still needs a little time to cut the foam.

You can see I am still filling a few cavities. Its almost flat on top (or underneath as we are inverted). There is plenty of work left on the sides to go. Where I find a deficit, I just add more pour foam and an hour or so later it is ‘sandable’.

 

 

Date:  05-08-2019

Number of Hours:  12

Manual Reference:  no ref

This RAM air idea came from James Redmonds excellent build site for his Berkut, a larger version of the Long-EZ. That said I have a slightly different take on it to suit my particular Long-EZ build. This modification I expect to add at least .5 inches of Manifold pressure in all flight situation, for ‘free’. That should be well over 100rpm just by making the engine intake more efficient.

The Mike Melvill designed cowls with armpit scoops leave the bottom of the cowl free for an intake separate from engine cooling. That’s a golden opportunity for an engine opportunist like me.

The rules of fluid dynamics tell up that we need to keep scoops less than 11 degrees total side angles or as they say ‘included’ or 7 degrees if only one side of your duct slopes. If you go past that the air goes from laminar to turbulent, no good for our intake into the engine. We want to gather the air, slow it down with expansion and increase the density, like a supercharger on tranquilizers and without moving parts.

I first worked with a protractor and the scoops looked too big. I went back to school triangle trigonometry (via google of course) and the scoop angles started looking correct.

I used some blue foam left over from the wings and marked 65mm being the likely fuel injection air intake diameter. The other end was just as big as I thought I could manage to still fit into the cowl. The duct worked out around 30″ long.

Here’s where it will go and as you see, its not a fit yet.

To my surprise I made a really good plug with a long sanding stick and a makeshift jig.

It will be fitting here, eventually.

I covered the plug in grey duct tape and used some jigs from when I made the fuel pipes and an improvised work bench. Fortunately I’d had five guys help me pull the wings off and invert the fuselage a few days earlier.

I used UND for the first ply, then two plies of BID. Yes just that part was four hours. Why am I so slow? Who cares, it ‘got done’.

Peel ply went on at the end which again took a while but will be worth it. Unlike others, I want to retain this duct shape for the air inside and treat the air outside the duct with fillets for blending into the fuselage. This slightly more difficult path I hope might get me better than +.5MP (manifold pressure). I guess I will never know because we will not be doing a no scoop/scoop double blind test. ….Sorry.

Today I scooped out the insides of the scoop. Another day or so to cure and I’ll try to get the grey duct tape release out. Piece of cake.