12.3.6 Nose Oil Cooler

This entry is part 33 of 48 in the series 12 - Engine / Propeller

Time to make an engineering change. The oil is cooled with two oil coolers. The primary oil cooler is in the back with the engine. There’s a secondary oil cooler in the nose that’s used to cool engine oil and provide cabin heat. A factory supplied NACA duct is installed in the side of the nose, the oil cooler is mounted and another duct exits the bottom. Two 1 1/2″ tubes are inserted into the exit duct that supply warm(er) air to the cabin area. A small flap/diverter is installed in after the tubes that would block the air from exiting outside and instead directs it to the cabin. Here’s the problem: At cruise speed, the air is forced through the oil cooler at an incredible rate. And in the winter, the air at cruise altitude can 20 – 30 below zero. Given that, I think the oil cooler would increase the temperature of the outside air maybe 50 degrees. Which means that the cabin would be “heated” with 30 – 40 degree air.

So here’s the plan: I’ll put an additional flap between the NACA duct and the oil cooler to block the outside air. Then run a return line from the cabin to the oil cooler. That way I’ll be heating inside air that already warm.

This plan requires fabricating almost all the parts.

Here’s the plan view. On paper.

I’ll make a form out of foam and cover it with fiberglass. I used a spreadsheet based the formula for the NACA design developed by the NASA predecessor in the 1950’s.

Here’s the form made from glued blocks of foam.

This is the result. Needs a little cleanup but not bad.

This is the duct for the air after it goes through the oil cooler and then out the bottom of the fuselage. I had to make a flange where the oil cooler mounts to it. Because the geometry of the design is different, I had to make a slight modification to the opening so it would cover the entire oil cooler.

Duct cleaned up with the flap that blocks outside air.


Flap open. You can see the inside return air port.

The flap mounts to the bolt that is filed down, drilled and tapped.

Now it’s time cut the opening for the NACA duct. This part always drives me nuts! I’m cutting a hole in the airplane! What if I cut it wrong? Oh well.

Here’s the mark for the opening


Inside view where the duct will go.


After the cut. Hope it’s in the right place.


Duct installed.


Inside view of the installed duct.


The whole assembly installed with oil cooler.

View from the outside with the door open and closed. You can see the oil cooler inside on the left picture.

Partially disassembled. This is the lower portion of the whole assembly (where the heated air exits the bottom of the fuselage. With this lower door closed, the heated air will be diverted into the cabin through two two tubes which will have flexible tubing that supply warm air to the pilot and co-pilot side of the cabin.


Same view with the flap open that blocks the cabin supply lines and exhausts the air outside.

Later, I’ll attach control arms to the pivots for the two doors. Then cables can be attached which will allow opening and closing the doors from inside the cabin

12.3.6 Nose Mounted Oil Cooler

This entry is part 43 of 48 in the series 12 - Engine / Propeller

Time to make an engineering change. The oil is cooled with two oil coolers. The primary oil cooler is in the back with the engine. There’s a secondary oil cooler in the nose that’s used to cool engine oil and provide cabin heat. A NACA duct is installed in the side of the nose, the oil cooler is mounted and another duct exits the bottom. Two 1 1/2″ tubes are inserted into the exit duct that supply warm(er) air to the cabin area. A small flap/diverter is installed in after the tubes that would block the air from exiting outside and instead directs it to the cabin. Here’s the problem: At cruise speed, the air is forced through the oil cooler at an incredible rate. And in the winter, the air at cruise altitude can 20 – 30 below zero. Given that, I think the oil cooler would increase the temperature of the outside air maybe 50 degrees. Which means that the cabin would be “heated” with 30 – 40 degree air.

So here’s the plan: I’ll put an additional flap between the NACA duct and the oil cooler to block the outside air. Then run a return line from the cabin to the oil cooler. That way I’ll be heating inside air that already warm.

This plan requires fabricating almost all the parts. Here’s the plan view. On paper.

 2008-05-15 IMG_6912

I’ll make a form out of foam and cover it with fiberglass. I used a spreadsheet based the formula for the NACA design developed by the NASA predecessor in the 1950’s.

Here’s the form made from glued blocks of foam.

 2008-05-15 IMG_6913

This is the result. Needs a little cleanup but not bad.

 2008-05-18 0907 IMG_7106

Test fit to see if it’s going to work.

2008-06-02 1249 IMG_7125

This is the duct for the air after it goes through the oil cooler. It directs the air out the bottom of the fuselage. I had to make a flange where the oil cooler mounts to it. Because the geometry of the design is different, I had to make a slight modification to the opening so it would cover the entire oil cooler.

 2008-05-18 0908 IMG_7108

Duct cleaned up with the flap that blocks outside air.

 2008-06-08 1301 IMG_7143

Flap open. You can see the inside return air port.

 2008-06-08 1301 IMG_7145

To make the pivot that the flap mounts to, I took a bolt and created a flat on the shank with a file. Then drilled and tapped the holes.

 2008-06-08 1303 IMG_7148

Here’s the mark for the opening

 2008-06-02 0826 IMG_7120

Inside view where the duct will go.

 2008-06-02 0826 IMG_7121

Now it’s time cut the opening for the NACA duct. This part always drives me nuts! I’m cutting a hole in the airplane! What if I cut it wrong? Oh well.

After the cut. Hope it’s in the right place.

 2008-06-02 1248 IMG_7122

Duct installed.

 2008-06-08 1509 IMG_7154

Inside view of the installed duct.

 2008-06-08 1509 IMG_7155

The whole assembly installed with oil cooler.

 2008-06-14 1051 IMG_7166

View from the outside. You can see the oil cooler inside.

 2008-06-14 1051 IMG_7169

Same view with the door closed block outside air from the cooler.

 2008-06-14 1051 IMG_7170

This is the lower air exit.  I’ve installed the two 1-1/2″ tubes that will have flexible tubing connected to them which will go to the left and right side of the cabin.   Here the flap is closed that will force warm air into the cabin.

 2008-06-14 1052 IMG_7173

Same view with the flap open that blocks the cabin supply lines and exhausts the air outside.

2008-06-14 1053 IMG_7174

12.1 Engine arrival

This entry is part 1 of 48 in the series 12 - Engine / Propeller

The engine showed up on February 25th.

A Continental IO550-N. 2,000 hours total time and 0 SMOH (Since Major Over Haul) just out of the shop. Balanced, blueprinted, ported, polished with overhauled cylinders and a fresh coat of paint.

Ain’t it purty?

12.1 Engine Installation Prep

This entry is part 2 of 48 in the series 12 - Engine / Propeller

Now that the fuselage finishing is done, it’s time to mount the engine.

The first task is to remove the wings.

Look Ma! No wings!

Then we rotated the plane and got it in about the right location under the chain hoist. We then rolled the engine under the hoist and hooked it up.

Here’s the engine hanging.

Because the engine will need to be leveled, I picked up a leveling beam at Harbor Freight. I had to violate my personal rule on tool purchases. Which is, always buy the best. This comes from an article I read in the woodworking magazine that offered the saying “When you buy the best, you only cry once.”  A proper engine leveling beam costs hundreds of dollars. This one was $39.95!  But I will only need it one time, right? :-)

Before the engine can be mounted to the firewall, proactive fire protection is needed. In some countries (not ours), a metal barrier must exist between the engine compartment and the cabin. This is a good idea. So Velocity provides a sheet of stainless steel with their engine installation kit. But I didn’t get the stainless steel.

Instead, I picked up a sheet of titanium. Same thickness but half the weight and higher temperature range. :-)

First I took a large piece of cardboard and made a template.

Then transferred it to the titanium and cut it out.

12.1 Engine Installation Prep

This entry is part 3 of 48 in the series 12 - Engine / Propeller

Yesterday, I cut the titanium firewall shield. But some trimming is still required. At Oshkosh, Malcolm had me pickup some grinding stones that supposedly work great on titanium… And they do. I only destroyed two doing the entire firewall. It took about half a day. Put the titanium in place, mark where it’s too big, grind it down and repeat about two-dozen times. You can always take off more but you can’t add any if you take off too much, right?

Next it’s time to attach the engine to the motor mount. But there’s a problem. :-(

The bolts that were supplied are AN7-36A’s. The manual says to use AN7-34A bolts. Sadly, I need the shorter 34A bolts. So now I have to wait until tomorrow for a delivery from Aircraft Spruce & Speciality.

 

12.1.2 Engine Mounts

This entry is part 4 of 48 in the series 12 - Engine / Propeller

Before the engine can be mounted to the airframe, it must first be mounted to the engine mount. The engine mount is what’s known as a “dynafocal” mount. The four bolts all point to the same place which is the center of gravity of the engine.

Here’s the engine mount with the four motor mounts in place.

The trick here is that the bolts can only be screwed in easily when the motor mounts are compressed be tightening the bolts. Which you can’t get in until the motor mounts are compressed by tightening the bolts…  How’s that for a catch-22?

At first, we got the two rear bolts in place but the front bolts were a mile from being in the right position. I called my buddy Albert Khasky. He said that starting the bolts in opposite corners works best. So we started with the left rear. But couldn’t get the front right in position. We tried to move the frame but had no luck. We tried a couple of ways to get the holes to line up. Then I had the idea to use a clamp from one corner of the frame to the opposite corner of the engine. But I couldn’t get the clamp to hold on the engine. So I took a piece of wood and shaped it as a pad.

While I was trying to get the clamp on it, Malcolm said “Hey Don. I think that I can get a small prybar or something between the engine and the mount and pry it into position”.

After that, we had all four bolts in place within about 20 minutes.

Tools of the trade.

Then we moved the plane into the approximate position.

Then we leveled the plane, raised the engine out of the way and attached the cowling.

12.1.2 Engine Installation

This entry is part 5 of 48 in the series 12 - Engine / Propeller

Now that the engine cowling is on, the location of the engine has to be determined. The reference point will be the center of the opening in the cowl for the propeller.

With the cowling in place, a plumb line is run from the center of the opening to the floor where I put a mark. Then a measurement is made from the mark on the floor to the center of the opening.

Then the upper cowling is removed and the engine is lowered into position. The engine is then leveled side to side by laying some weight on the left or right cylinders. The plumb line is then dropped down over the end of the crankshaft and the engine to moved side-to-side until the plumb bob is over the mark on the floor. Then a measurement is made from the mark on the floor to the center of the crankshaft.

Once all the dimensions are correct, holes are drilled through the engine frame into the firewall.

Robbie from next door was drafted to help hold the engine in place while I drilled the first hole. After that he got a picture of me drilling the second hole while Malcolm held the engine.

Once all four holes where drilled, temporary bolts are used to hold the engine in position.

Then we put the top cowling back on to check the fit. Unfortunately, it didn’t fit as well as we hoped. The intake tubes on the rear cylinders prevent the top cowling from fitting.

I’m looking into having the intake tubes modified to lower them. If that doesn’t pan out, I’ll have to create some… “bulges” in the upper cowling. :-(

Next the engine is removed to prepare the firewall for the fiberfrax and titanium. Fiberfrax is a heat resistant ceramic fabric that is applied to the between the firewall and the titanium. Fiberfrax is good up to over 2,000 degree Fahrenheit.

Here’s the firewall with the fiberfrax in place.

The titanium is put over the fiberfrax and screwed in place.

Then the engine is lowered and bolted in place.

The green tape is used to indicate where the center spar caps are located on the other side of the firewall so it’s easy to know where NOT to drill.

12.2.1 Aluminun Oil Lines

This entry is part 6 of 48 in the series 12 - Engine / Propeller

The engine has an oil cooler located just forward of the number 2 cylinder. But an optional second oil cooler is mounted in the nose of the aircraft. This adds oil cooling capacity and can also be used as a cabin heater.

The air intake, ducting and mounting for the nose oil cooler was done a while back. Now it’s time to run the tubing that will carry the oil to and from the oil cooler.

First the two lines are straightened out (they come in a coil) and then each tube is covered with a layer of heat shrink. The manual says to then insert the two tubes in the pilot side duct. Malcolm says if you do that, the two lines could come into contact and transfer heat between them. Sounds reasonable although I don’t think that you’d get that much heat transfer. Malcolm uses a pair a adel clamps that are then pinned together as spacers. I don’t have 8 adel clamps and that seemed like it would take up space in the duct. So I fabricated my own.

I put two additional layer of heat shrink at four locations along the tubing. Then I cut small strips of aluminum to act as a spacer. Rivet the tabs down and there you go:

Before the oil lines are inserted into the duct, a hole is drilled in the duct just aft of the canard bulkhead (for engine controls, antennas and brakes lines):

Another forward of the landing gear bulkhead (for antennas):

And another forward of the firewall (for brake lines). If the holes aren’t drilled first, drilling holes in the duct could damage the oil lines.

 

12.2.1 Aluminum Oil Lines

This entry is part 7 of 48 in the series 12 - Engine / Propeller

Prior to inserting the oil lines in the duct, Malcolm likes to lay in some old nylaflow tubing. This will be used to pull antenna cables and engine controls through the duct later.

Then the oil lines (and nylaflo) and inserted into the pilot side duct. As they emerge from at the nose, they are bent up to the connectors at the oil cooler. Then the tubing is cut and flared and connected to the oil cooler.

Next, a bracket is placed on the firewall and those ends and flared and connected to a pair of bulkhead adapters.

 

12.2.1 Cabin Heat

This entry is part 8 of 48 in the series 12 - Engine / Propeller

The cabin heat ducts below the oil cooler were installed when the nose oil cooler ducting was fabricated. Now, holes will be cut into the canard bulkhead and 1.5″ aluminum tubing will be installed.

The hole on the pilot side will be determined by the location of the tube in the nose oil cooler tube. The two are so close that there’s no room for any turns in the flexible scat tubing.

Here’s the co-pilot side tube in the canard bulkhead.

And the pilot side.

And a view of the flexible scat between the outlet duct and the canard bulkhead.