Friday, January 1, 2021

Its all about cooling

One of my biggest concerns about flying this airplane for the first time is the engine cylinder head temperatures. Traditionally the first hours of an engines life are hot as the rings seat themselves. On the 9A I had piston oil squirters that helped keep the cylinder head temps down, but this engine does not have this option. My only option is to make sure I am making the best of the cooling that is available. That brings me to my last several weeks of work. Cooling mods. I used the baffle kit that comes from Van's and its a huge help, but its designed for a slightly different engine, and even the inter-cylinder baffles that come with the engine fit very poorly. Below are some of the steps I have taken to try to keep the air moving through the cooling fins on the cylinders and keep the cooling drag to a minimum.

The plans call for a series of slots cut into the lower scoop section of the cowling to aid in cooling air flow through the engine. This added air flow is necessary for time when heat load is high such as takeoff and climb phases of flight. They are not needed when in cruise and because these slots are always passing air they create a bit of drag. I decided to install these cowl flaps to eliminate the cooling drag when its not needed. The AntiSplat Aero cowl flaps I purchased are designed to be installed in the bottom of a cowl that has a honey comb core but the scoop area on the 10 cowl does not have honey comb in this area so I had to build up a mounting platform so that the installed flaps are flush on the outside. You will see a picture of the outside down below. To make this mounting platform I used my 3D printer to print up those two white forms you see sitting above the openings. One side was slid into the opening from the outside and the other was fit on the inside so that I would have a smooth flat surface mount.
Up close view of the mounting platform as I was testing fit.

Both flaps installed (no bolts) inside view.

Both flaps installed outside view (looking up at the bottom of the scoop where it overhangs my workbench.

I also formed the fiberglass duct around the top cowl inlet where the prop governor sits.  Still some cleanup work to be done here.

Oil door with hinge and latch cutouts complete.  I did have to fill those two miss-drilled holes on the hinge location and then re-drill the hole.  It took quite a bit of time to get this door to fit the opening properly.
This is the door after I got it all put together.  I did add a bit of carbon fiber plate to keep the door rigid.  This is simply a plate of carbon fiber that was left over from the instrument panel cut out adhered to the door with flox.  It really stiffened up the door.  I had originally used the honeycomb method that vans suggests but the latch I am using does not work well with that type of support.  I used carbon fiber on the 9A and it worked very well.

An outside view of the door after I had faired in the opening a bit.  I am going to have to to a little more sanding as there isn't enough edge distance to allow for paint.

Here you can see the wraps that I put on all cylinders.  The wrap is simply 9oz fiberglass impregnated with ultra black RTV.  These areas are locations where the baffles tend to leak a lot of air and any air not going through the cooling fins is just wasted cooling drag air.

Same as above but a view looking up at the bottom of the cylinders.  The Inter-cylinder baffles are not installed in this picture.

Really hard to see but this is the gap between the cylinders near the injector holes.  There is about a 1/4" gap between the cylinders so I filled it with RTV after putting a barrier of glass/RTV on the surface of the head fins to prevent the RTV from filling the cooling channels.

Aft side of #5 cylinder. 

These are the engine mount covers that I fabricated to prevent any cooling air flow from exiting via the holes in the rear baffles where the engine mounts protrude.  I had originally ordered these from Aerosport but after about 6 weeks I had to cancel that order (poor guys are just swamped) and make my own.  They are not as pretty as the Aerosport version but they will do the trick nicely.