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.

Monday, December 7, 2020

A million little things

Wow has it really been since October that I last posted an update?  Well I haven't been completely idle these past several weeks but I will admit to going through one of those "less inspired" periods that I go through about once a year.  Hopefully this one is about over...

Anyway, as the title suggests there has been progress but its in the form of a bunch of little things.  Most of the time has been focused on the cowling and getting it properly fitted.  Here are a few of the things I've done since the last update:

  • I beefed up the "flanges" that I created for both the upper cowl to lower cowl seam and the lower scoop seam.  Originally I used about 4-5 layers of regular 9oz fiberglass layers but the end result was less sturdy than I wanted.  I ended up laying down a layer of carbon fiber with a layer of 9oz glass over the top.  That took a bunch of time because I also had to re-drill the holes for the receptacles.
  • I primed the two lower cowl halves so that I could rivet the receptacles on.
  • I adjusted several fastener hole locations to get them to fit better.
  • I installed the prop and spinner to test the gap and it was good for most of the circumference, but one of the bottom halves still needs work.
  • I fabricated a bracket and installed the four remaining fastener receptacles on the firewall at the bottom where the lower cowling and the scoop seam meets the firewall.  I had purposely held off on that area until the scoop was close enough to completion that I could be assured that the lines would match.
  • Cut the oil door opening and fit the oil door to that opening.  Hinge is drilled but still need to work on the latch.
In other news, I also installed the GNC255 tray into the radio stack and managed to get the backing plate installed.  There isn't a lot of hand space behind the panel in that area so it was a bit of a challenge.  This is pretty big since its the last of the avionics install tasks.

The baffling is primed and mostly installed now.  The only thing left is to tie in the bottom cylinder wraps, install the rubber seals, and install the engine mount covers.  That's actually what I am waiting for...I ordered the engine mount covers from Aerosport about a month ago and they still haven't shipped.  I guess Covid is sticking its nose into my business once again.

I also started working on the firewall forward wiring.  That includes moving the MAP sensors to the aft side of the firewall which required fabricating a mount on the sub panel.  Plenty of room but I do have to run the vacuum hoses through the firewall.  Should be easy enough to do.

Here are a few pictures from the past several weeks.  Much of the work was not photographed so I apologize for the lack...

Baffling installed after priming.

Ignition coils installed.

Oil door opening cut.

Seam flanges beefed up with a layer of carbon fiber and another layer of 9oz glass.

Here you can see where the receptacle holes were covered and had to be re-drilled.

Prop and spinner installed and cowling partially attached for fitting.  Good on the top and the left side but the lower right side needs some work.

Those two fasteners at the top of the photo that straddle the seam were installed after everything was fitted properly.

And finally, the cowl completely installed.  I still have several things to do such as the cowl flaps installation but its getting much closer to being done.


Tuesday, October 20, 2020

Baffling

 Actually I've been working on much more than the baffling but since the cowling and the baffling work together to keep the engine cool its a bit of a mixed bag of tricks.  I'm paying extra attention to the baffling because these tightly cowled RV's run hot and I don't want to spend time chasing cooling leaks after I start flying.


As I mentioned in a previous post I had planned to split the lower cowling in half to ease the installation/removal of this huge hunk of fiberglass.  This picture shows the "jig" I created with multiple strips of aluminum to hold the two halves in the exact position needed after I make the cut.  In this picture the cut has been made and as the picture below shows the 5 layers of glass that will become the flange that the fasters attach to.

This is the inside of the cowling with the glass flange laid up and epoxy curing.

Much of the baffle work began with edge deburring, hole cutting, and as indicated by this picture...modifications.  In this case two specific modifications are evident.  First is the little square "patch" you see in the middle of the picture.  This area of the lycoming cylinder has no fins for cooling.  That means if the baffling is flush against the cylinder no cooling air can pass in this area.  If you look at the cylinder picture below you will see what I mean.  My patch basically creates a small gap that will allow air flow past this area.  The second modification is a little harder to see.  On the far left side of the aluminum plate you will see a bracket with a bolt hole in it.  The baffle kit that comes from Van's is for a wide deck engine, my engine is a narrow deck.  They are similar but have a few differences such as the shape of the block and a few bolt holes.  In this case the inside edge of the baffle needed to be cut and reshaped to fit.  Along with that the bolt hole flange had to be fabricated to fit the new shape.

This is a picture of the inside of the same baffle piece.  Here you can see the small air gap that will allow air flow past the smooth portion of the cylinder wall...see below.

Here is the back side of the #5 cylinder.  You can easily see the small area where there are no cooling fins.

On the front side of the engine case there is another area that needed adjustment.  In this picture you can see the original baffle piece shape (it has the part number in blue ink on it) as well as the shape of the piece that I had to fabricate to match the shape of the engine case.

And here is the final product after cutting the improperly shaped baffle material off and attaching the correct shaped piece.  Much better fit.

I had to add this picture as well.  My good friend Ben has been helping me with a few tasks.  In this case he is back-riveting the stiffeners to the wing root top skin.  

I took this picture to help me fabricate a seal for the prop governor area of the baffles.  This is taken from inside of the ring gear opening looking outboard at the left side air inlet.  I need to fabricate a baffle plate that will seal the sides and top of the governor to the top cowl which can be seen at the top portion of the picture.

In this picture you can see the paper clips I am using to slowly trim the baffles down to fit within 3/8"-1/2" of the inside of the top cowling.  It took many iterations of install clips, install top cowling,  remove top cowling, measure, mark, and trim the baffling.

This little area took a LOT of time.  On the sides of the air inlet you will see some curved baffle pieces.  These have to be hand fabricated using paper templates and then aluminum bent to fit.  It took several tries before I was happy with the final product.  I also put one of these curved pieces on the inboard edge even though Van's plans do not call for it.  I may change that in the future but it seems like it prevented yet another possible air leak.

Finally, this is the left side air inlet with the prop governor issue I mentioned earlier.


Wednesday, September 30, 2020

Cowling Part 2

Lots of work on the lower cowling this past week or so.  The scoop has been cut and drilled for quarter turns, the flanges have been completed for the top cowl interface, and yet there is still a ton of work left on the cowling.  I did find that I will be cutting the lower cowl in half.  Removing the scoop also removes the only easy place to hold the cowling up when installing it so I pretty much have to cut it in half if I want the installation and removal process to be relatively pain free.

The cowling isn't the only part of the airplane being worked on.  You can only do so much fiberglass before you either need to wait for some epoxy to set up or just need a shower to get the itchy stuff off of you!  My friend Ben has been coming up and helping work on the baffles.  So far is just lots of off engine fabrication, deburring, and sizing.

I've also started installing some of the accessories (starter, alternator) and the oil cooler.  I want to have as much of this stuff installed as possible (minus the exhaust) so I can finish the wiring and to make sure I have clearances with the cowling.

Holes drilled for the quarter turn fasteners.
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Lower cowling installed without the scoop.

Lower cowl mounted and the scoop cleco'd in place to check clearances.
 
Backup alternator installed but not yet wired up.

Starter installed but not yet wired up.

Oil cooler installed and hoses attached.

What the heck is this?!?  Well, this is my engine dehydrator.  Since its going to be at least several months until the engine will run I filled it with about 5 gallons of oil, and then put together this dehydrator to constantly pump dry air into the oil filler location.  The exit air comes out of the breather hose fitting.  There is a small fish tank air pump wrapped in a breathable bag (sock) that sucks air in from the top of the Tupperware container, through the blue desiccant and then discharges it through the rubber hose into the block.  This should help prevent any sort of corrosion inside the engine.


Cowl flap openings marked and corners drilled.

Cowl flap openings cut.  I'm using the AntiSplat Aero cowl flaps in these locations.  These cowl flaps are servo actuated so that they can be closed in normal cruise.

 

 

Thursday, September 24, 2020

Cowling part 1

I never do things the easy way....

I started the cowling a week or so ago.  As is my standard I feel I need to "improve" things a little.  In the case of the cowling I am using quarter turn fasteners (I did this on the 9 as well and was glad I did) and I'm doing some cosmetic alterations as well.  This cowling is much larger than the one on the 9 and there were times when it was difficult to get the lower cowling on and off.  For the 10 I decided to cut the snorkel section out to make it easier to work with while installing and removing.  That requires lots of work and a bunch more quarter turn fasteners.  You will see what I mean below.  Once that is complete there is a strong possibility that I will split the lower cowling in half so that I can install/remove one side at a time.  more fiberglass work and more quarter turn fasteners.  I'll make that call once I have the scoop complete.

The top cowling half gets fitted first.  You can see the overlap with the skin.  If you look closely you can see the blue line I drew 3" back from the firewall edge.  This line helps me measure forward to determine the precise cut line.  Actually it wasn't one single cut...it was one big cut and a bunch of iterations of sand, install, measure, remove, sand, install....you get the picture.

There are actually many steps in the process before we get to this point but in this picture you can see I am using my laser level to set the horizontal line.  You can also see the wood disc that I made to simulate the back side of the prop spinner.  This helps me set the gap between the prop spinner and the forward edge of the cowl.

Both cowl halves fitted to the airframe.  You can see the line on the upper cowl where I measured forward 3" from the blue line for a cut line.  The bottom cowl will get cut once I have fitted the top cowl.

This picture shows the method I used to locate the quarter turn fastener holes.  I taped those aluminum scrap pieces to the fuselage skin in such a way that I could fold them back once the holes were aligned with the receptacle location.  This worked quite well but I still have to go back and adjust hole positions.

Here both the top and bottom cowl halves have been fitted to the firewall.  I still have some work on the horizontal line but its getting close!

Using these aluminum scrap pieces I positioned them such that I could hold the scoop in a precise position.  Then I used my dremel and a hacksaw blade to cut along the blue line.

Skip ahead several hours and this is what it looks like.  The scoop has been cut out and the flange has been glassed in under it.  (See picture below)

This is the inside of the lower cowl where you can see the fiberglass flange being worked on.  I still have two layers of glass and lots of sanding/filling/etc to do before this is done.